FEMA 259/January 1995 

EngineeringPrinciples 
andPractices 

for Retrofitting Flood Prone 
Residential Buildings 

January 1995 

Federal Emergency Management Agency 
Mitigation Directorate 


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Table of Contents

Table of Contents ...............................
List of Figures .................................
List of Tables .................................
List of Formulas ................................
Nomenclature..................................
Foreword ....................................
Acknowledgement.

Metrification

..................................

Lii Chapter 1: Introduction to Retrofitting ................

How to Use This Manual ..........................
Methods of Retrofitting ............................
General Retrofitting Cautions ........................
Retrofitting Process ..............................

Chapter II: Regulatory Framework ..................

National Flood Insurance Program (NFIP) ................
Community Regulations and the Permitting Process ...........
Model Building Codes ............................
Code Compatibility with the NFIP .....................

Chapter III: Parameters of Retrofitting ............ .... 

Examination of Owner Preferences ........... ...... 
Community Regulations and Permitting ........ ... .... 
Technical Parameters ................... .......... 

Page 

... i
. .. 

v

.. xv
. xvii
. xxi
.xxxi
xxxiii
xxxv

*. I-1 

. . I-1
.. 1-4
. I-27
.1-29

. II-1 

. 11-2 

II-19 

II-21 

11-23 

III-1 

.. III-2 

III-16 

III-18 

Page i 


* Table of Contents 

Page 

Chapter IV: Determination of Hazards ................ . IV-1

Analysis of Flood Related Hazards ..................... . IV-2
Analysis of Non-Flood Related Hazards .................. IV-48
Geotechnical Considerations ......................... IV-55

Chapter V: Benefit/Cost Analysis and

.. V-1 

Benefit/Cost Analysis Process ............... . V-1
Evaluate Hazards .............................. . V-6
Estimate Potential Damages ......................... . V-9
Identify Costs Associated with Alternatives ................ V-13
Estimate Benefits ............................... V-14
Compute Benefit/Cost Ratio and Net Present Value ........... V-1l9
Select a Method ................................ V-25

AlternativeSelection................ .

Chapter VI: General Design Practices .. .V I-1 

Elevation..... .. ... ... ....... .. .. ..... VI-E. 1 
Relocation..... .. ...... ... .. .... ... .... VI-R.1 
Dry Floodproofing . . ..... ..... .... .. ..... VI-D. 1 
Wet Floodproofing . ...... ... .. .... .. ..... VI-W.1 
Floodwalls .... . .... .. ...... .... .. ..... VI-F.1 
Levees....... . ...... . ..... .... .. ..... VI-L.1 

Page ii 


* Table of Contents 
Page 

_ Chapter VII: Case Studies .VII-1 

Case Study #1: Elevating Houses on Masonry Walls,
Masonry Piers and Wood Posts
Tug Fork Valley, West Virginia .VII-3

Case Study #2: Elevating Homes on Crawl Space
Dry Creek, Goodlettsville, Tennessee .VII-18

Case Study #3: Relocating a Slab-On-Grade House
Tampa, Florida .VII-30

Case Study #4: Floodwalls, Levees, and Perimeter Drains
Bailey Creek, Madison, Connecticut .VII-54

Case Study #5: Perimeter Floodwall, Henson Creek
Prince George's County, Maryland .VII-64

Case Study #6: Wet Floodproofimg a House on a Crawl Space 
Henson Creek, Prince George's County, Maryland .VII-78 

Case Study #7: Dry Floodproofmg a House with a Walk-out 
Basement, Henson Creek, Prince George's County, Maryland ... VII-90 

Case Study #8: Veneer Wall, Dry Floodproofmg
Tug Fork Valley, West Virginia .VII-105

Appendices 

Appendix A: The National Flood Insurance Program .A-1 
Appendix B: Glossary of Terms .B-1 
Appendix C: Glossary of Resources .C-1 
Appendix D: Alluvial Fan Flooding .D-1 
Appendix E: Benefit/Cost Analysis of Hazard Mitigation Projects 

User's Guide .E-1 

Page iii 


* Table of Contents 

LIST OF FIGURES PAGE

v-1 Flooding Along Major Rivers Can Create Widespread Damage 

I-1 Elevation on Solid Perimeter Foundation Walls .... ............ 
1-2 Elevation of Existing Residence on Extended Foundation Walls ....... 

. xxxi 

1-7 
1-8 

I-9

I-10
I-10

1-3 Elevation on Piers .......... 

1-4 Elevation on Posts ......... 

1-5 Structure Elevated on Posts .1........ 

1-6 Elevationon Piles .............. 

1-7 Structure Elevated on Piles .1......... 

........................ 
........................ 
.. ... .... .... ... 

.. ... .. ... .. .. ... 

.. 

. I-il 

1-12

.. .... ... .. ... .... 

1-8 Structure Placed on a Wheeled Vehicle for Relocation to a New Site . . 1-14
1-9 Structure to be Relocated ............................. I-15
I-10 Dry Floodproofed Structure ........................... 1-18
I-l1 Wet Floodproofed Structure ........................... I-20
1-12 Structure Protected by Levee and Floodwall ................. 1-22
1-13 House Protected by a Floodwall ......................... 1-23
1-14 House Protected by a Levee ........................... 1-24
1-15 Primary Steps in the Retrofitting Process ................... I-30

11-1 Typical Floodplain Cross Section . .1.1..................... .II-5
II-2 Typical Flood Profile for Riverine Floodplains . .1.1..............II-7
11-3 Typical Wave Height Transect . 1........................

.. II-9 
11-4 Typical FIRM for Riverine Flooding ..1.1.................. .II-10 
11-5 Typical FIRM for Coastal Flooding . .1.1.................. .I-10 

111-1 Preliminary Floodproofing/Retrofitting Preference Matrix ........ III-4 
III-2 Low Point of Floodwater Entry Survey for a Typical Residential 

Structure.................................

III-8

III-3 Retrofitting Screening Matrix ......................... III-19 
III-4 Instructions for Retrofitting Screening Matrix ............... III-20 
III-5 Photographs Showing Mud Lines on Homes are a Source of Historical 

Information ................................ III-22 
III-6 Hydrostatic Forces ................................ III-22 
III-7 Fast-moving Floodwaters Caused Scour Around the Foundation and 

Damage to the Foundation Wall ................... III-24
III-8 Lateral Forces Resulting From Saturated Soil ............... III-27
III-9 Buoyancy Forces Resulting From Saturated Soil .............. III-27
III-10 Preliminary Building Condition Evaluation Worksheet .......... III-34

IV-1 Flood-Related Hazards . ............................. IV-2
IV-2 House Location on the FIRM ...... .................... IV-3
IV-3 Stream Location on the FIRM ...... .................... IV-4
IV-4 House Location on Flood Profile for Flat Rock Brook ... ........ IV-5

Page v 


D Table of Contents 

. 

. 

. 

.V-8 

LIST OF FIGURES (continued) 

IV-5 Coastal FIRM. 

IV-6 Summary of Stillwater Elevations. 

IV-7 Illustration of Flood Depth and Design Depth .. 

IV-8 Hydrostatic Forces. 

IV-9 Hydrostatic Force. 

IV-10 Saturated Soil Hydrostatic Forces. 

IV-11 Combination Soil/Water Hydrostatic and Buoyancy Forces . 

IV-12 Hydrostatic Force Computation Worksheet .................

IV-13 Example Hydrostatic Force Computation . 

IV-14 Hydrodynamic and Impact Forces . 

IV-15 Equivalent Hydrostatic Force Computation Worksheet.
IV-16 Example Equivalent Hydrostatic Force Computation.
IV-17 Hydrodynamic Force (High Velocity) Computation Worksheet 
IV-18 Example Hydrodynamic Force (High Velocity) Computation 

IV-19 Impact Force Computation Worksheet ....................
IV-20 Example Impact Force Computation .
IV-21 Rectangular Area Enclosed by a Floodwall or Levee .
IV-22 Rectangular Area Partially Enclosed by a Floodwall or Levee 

PAGE 

. IV-6 

. IV-7 

. IV-9 
IV-10 
IV-11 
IV-13 
IV-16 
IV-18 
IV-19 
IV-20 
IV-23 
IV-24 
IV-27 
IV-28 
IV-33 
IV-34 
IV-36 
IV-37 
IV-40 
IV-48 
IV-49 
IV-49 
IV-51 
IV-52 
IV-57 
IV-61 
IV-61 
IV-63 
IV-64 
IV-66 
IV-67 

V-2 

IV-23 Telluride, Colorado, Alluvial Fan . 
IV-24 Non-Flood-Related Natural Hazards. 
IV-25 Wind Design Process . 
IV-26 Wind Design Process Illustration . 
IV-27 Seismic Design Process ................. 
IV-28 Seismic Design Process Illustration . 
IV-29 Geotechnical Considerations Decision Matrix. 
IV-30 Local Scour at Piers, Piles, and Posts . 
IV-31 Scour Action on a Ground-Level Building. 
IV-32 Process for Estimating Potential Scour Depth. 
IV-33 Flow Angle of Attack . 
IV-34 Terminating Strata . 
IV-35 Additional Embedment. 
V-1 Benefit/Cost Analysis Process ........................... 
V-2 Critical Steps in Evaluating Flood Hazards .V-6 
V-3 Discharge Versus Elevation (Rating Curve) .V-6 
V-4 Critical Steps in Evaluating Flood Hazards 
V-5 FIA Depth-Damage Data Table .V-10 
V-6 Types of Benefits Evaluated .V-14 
V-7 Critical Steps in Benefit/Cost Ratio Analysis .V-20 
V-8 Factors Weighing on Alternative Selection .V-25 
V-9 Preference Ranking Worksheet .V-27 
V-10 Floodproofing Measure Component Takeoff Guide 
V-li Detailed Cost Estimating Worksheet .V-32 
Page vi 

.V-29


* Table of Contents 

LIST OF FIGURES (continued) PAGE 

VI-1 Design Process ........... ............... ....... VI-2
VI-2 Topographic and Site Survey . ....... VI-6

VI-3 Mechanical, Electrical, Plumbing, and Related Building 

SystemsData Sheet ................ . . ...... VI-11
VI-4 Structural Reconnaissance Worksheet. ....... VI-19

....... VI-20

Loading ... ..VI-5FoundationSystem..... 

VI-6 
VI-7 
VI-8 

VI-El 
VI-E2 
VI-E3 

VI-E4 
VI-E5 

VI-E6 
VI-E7 
VI-E8 
VI-E9 
VI-E10 

VI-Ell 

VI-E12 
VI-E13 
VI-E14 
VI-E15 

VI-E16 
VI-E17 
VI-E18 

VI-E19 

VI-E20 
VI-E21 

VI-E22 
VI-E23 
VI-E24 
VI-E25 

Building Weight Estimating Worksheet ............. ...>... VI-29
Column Tributary Area ........ ....... VI-32
Wall/Girder Tributary Area. ....... VI-32

Existing Wood-Frame Residence With Crawl Space . 
Install Network of Steel "I" Beams . 
Lift Residence and Extend Foundation Walls; Relocate 
Utility and Mechanical Equipment Above Flood Level . 
Raising a Wood-Frame-Over-Crawl-Space Structure. 
Set Residence on Extended Foundation and 
Remove "I" Beams . 
Install Network of Steel "I" Beams . 
Raising a Wood-Frame-Over-Crawl-Space Structure on Piers . 
Set Residence on Reinforced Piers ..................... 
Relocate Utility and Mechanical Equipment Above Flood Level . 
Creation of a New Masonry Enclosed Area on Top of an 
Abandoned Basement ................... ...... 
Creation of a New Masonry Open Area on Top of an 
Abandoned Basement (Piers) .............. ...... 
Set Residence on Reinforced Piers ............... ........ 
Existing Slab-on-Grade Wood-Frame Residence ....... ...... 
Install Steel "I" Beam Network and Prepare to Lift Walls . ...... 
Lift Residence and Extend Masonry Foundation Wall; Relocate 
Utility and Mechanical Equipment Above Flood Level ..... 
Raising a Slab-on-Grade Wood Frame Structure Without the Slab 
Set Residence on New Foundation and Remove "I" Beams ...... 
Lift Residence and Extend Masonry Foundation; Relocate 
Utility and Mechanical Equipment Above Flood Level ..... 
Raising a Slab-on-Grade Wood-Frame Structure Without 
the Slab Intact ............................. 
Set Residence on New Foundation and Remove ,I, Beams ...... 
Excavate Under Existing Slab and Install Network of Steel 
"I" Beams ............................... 
Raising a Slab-on-Grade Wood-Frame Structure With the Slab .... 
Set Residence on New Foundation and Remove "I" Beams ...... 
Design Process for an Elevated Structure ................. 
Elevation Field Investigation Worksheet .................. 

VI-E.3 

VI-E.4 

VI-E.5 

VI-E.6 

VI-E.7
VI-E.8
VI-E.9
VI-E. 10
VI-E.12

VI-E.13 

VI-E. 14 
VI-E. 15 
VI-E. 18 
VI-E. 19 

VI-E.20 
VI-E.21 
VI-E.22 

VI-E.23 

VI-E.24
VI-E.25

VI-E.26 
VI-E.27 
VI-E.28 
.VI-E. 30 
VI-E.33 

Page vii 


* Table of Contents 
LIST OF FIGURES (continued) PAGE 

VI-R1 

VI-R2 

VI-R3 

VI-R4 

VI-R5 

VI-R6 

VI-R7 

VI-R8 
VI-R9 
VI-R10 
VI-Rl1 
VI-R12 
VI-R13 

VI-R14 
VI-R15 
VI-R16 
VI-R17 
VI-R18 
VI-R19 
VI-R20 

VI-R21 

VI-D1 
VI-D2 

VI-D3 
VI-D4 
VI-D5 
VI-D6 
VI-D7 
VI-D8 

House Relocation ................................. VI-R. 1 
Relocation Process .VI-R.2 
Relocation/Elevation Contractor Selection Checklist .VI-R.5 
When a house is too large to be relocated in one piece, 
careful planning is necessary to cut the structure and 
move the pieces separately .VI-R.9 
Clearing Pathways Beneath the Structure for Lifting Supports .. . .. VI-R. 11 
Pathways for Lifting Beams .VI-R. 14 
Beams Supported by Cribbing are Placed at Critical 
Lift Points .VI-R. 15 
Structure is Separated From Foundation .VI-R. 16 
Excavation of Temporary Roadway .VI-R. 17 
Trailer Wheel Sets are Placed Beneath the Lifting Beams .VI-R. 18 
House is Lowered onto Trailer Wheel Sets .VI-R. 19 
Tractor is Used to Pull House to Street .VI-R. 19 
As house is pulled to street level, wheels are continually blocked 

to prevent sudden movement .................
House is Stabilized and Connected to Trailer ............
Journey to New Site Begins ......................
Foundation Preparation at New Site .................
Support Cribbing is Placed .......................
Materials for New Foundation are Readied .............
New Foundation Wall Construction Begins .............
Once foundation walls are completed, house is lowered

ntidrcnnecteri tn fniinribtirn 

-1w1WiIIM_;WtUXl>LlJl......................

A 

... VI-R.20 
... VI-R.20 
... VI-R.21 
.... VI-R.22 
... VI-R.23 
... VI-R.23 
... VI-R.24 

Final Preparations for Backfilling and Landscaping ...........

Process of Selection and Design ....................... 
The best way to seal an existing brick-faced wall is to add 
an additional layer of brick with a seal in between. 
Just sealing the existing brick is also an option ......... 

A wrapped house sealing system can be used to protect 
against low level flooding ...................... 

A shield hinged at its bottom could prevent low level 
flooding from entering a garage or driveway ........... 

A door opening may be closed using a variety of materials 
for shields ............................... 

A shield can help prevent low level flooding from entering 
through a doorway .......................... 

VI-R.25
VI-R.25

VI-D.2

VI-D.6 
VI-D.7 
VI-D.8 
VI-D.8 
VI-D.9 

Where a window is exposed to a flood, bricking up the opening could 

eliminate the hazard ............. 
Dry floodproofed homes should have an effective drainage 

system around footings and slabs to reduce water pressure 

on foundation walls and basements ..... ....... .I. .. .VI-D. 10

Page viii 


m-Table of Contents 

LIST OF FIGURES (continued) PAGE 

VI-D9 
VI-D10 
VI-D11 
VI-D12 
VI-D13 
VI-D14 
VI-D15 
VI-D16 
VI-D17 
VI-D18 
VI-D19 

VI-D20 

VI-D21 

VI-D22 

VI-D23 
VI-D24 
VI-D25 
VI-D26 
VI-D27 
VI-D28 
VI-D29 
VI-D30 
VI-D31 
VI-D32 

VI-Wi 
VI-W2 

VI-W3 
VI-W4 

VI-W5 

VI-F1 
VI-F2 

Drain System Around a Slab-on-Grade House.
Existing Building Structural Evaluations.
Typical Design Strip ........ ...
Typical Slab Uplift Failure. 
Selection of Sealants/Coatings.
Selection and Design of Wrapped Sealant Systems.
Plain View of Wall Section .........................
Selection/Design of a Brick Veneer Sealant System.
Selection/Design of Plate Shields ......................
Typical Residential Masonry Block Wall Construction.
Common Faults Contributing to Seepage Into Basements 
Typical French Drain System .
Typical Exterior Underdrain System with Sump Pump Showing

Two Alternative Configurations in the Side View . 

Details of a Combination Underdrain and Foundation 
Waterproofing System. 
Typical Interior Drain Systems. 
Types of Sump Pumps . 
Sump Pump Field Investigation Worksheet. 
Sump Pump Design Process . 
Typical Sump Detail ........................... 
BackwaterValve..... I ......... 
. .. 
Floor Design With Ball Float Check Valve ............. . .. 
Backwater Valve Selection ....................... . .. 
Backwater Valve Field Investigation Worksheet ... . . . . . 
. .. 
Emergency Power Design Process ........... . . . . . 
. .. 

Typical Opening for Solid Foundation Wall ...... ... .. 
NFIP-Compliant Residential Building Built on Solid 

Foundation Walls with Attached Garage ... ..... 
Elevated Air Conditioning Compressor ........ .. ..... 
Flood Enclosure Protects Basement Utilities from 

Shallow Flooding ................. .... 
Wet Floodproofing Field Investigation Worksheet .. ......... 

Typical Residential Floodwall .............. . . . . . . . . .
Typical Residential Floodwall .............. . . . . . . . . .

VI-D.11 
VI-D.15 
VI-D.17 
VI-D.19 
VI-D.24 
VI-D.25 
VI-D.27 
VI-D.29 
VI-D. 33 
VI-D.50 
VI-D.51 
VI-D.52 

VI-D.54 

VI-D.55 
VI-D.57 
VI-D.58 
VI-D.61 
VI-D.63 
VI-D.65 
VI-D.73 
VI-D.73 
VI-D.74 
VI-D.75 
VI-D. 82 

V I-W .4 

V I-W .5
V I-W .9

V I-W .10 

VI-W.12

. VI-F.2 
. VI-F.2 

Page ix 


* Tableof Contents 
LIST OF FIGURES (continued) PAGE 

VI-F3 
VI-F4 
VI-F5 
VI-F6 
VI-F7 
VI-F8 
VI-F9 
VI-Flo 
VI-Fi 1 
VI-F12 

VI-F13
VI-F14
VI-F15
VI-F16
VI-F17
VI-F18
VI-F19
VI-F20
VI-F21
VI-F22
VI-F23
VI-F24
VI-F25
VI-F26
VI-F27
VI-F28
VI-F29
VI-F30
VI-F31
VI-F32
VI-F33
VI-F34
VI-F35
VI-F36

VI-L1 
VI-L2 
VI-L3 
VI-L4 
VI-L5 
VI-L6 

Gravity and Cantilever Floodwalls .
Buttress and Counterfort Floodwalls .
Stability of Gravity Ploodwalls...
Concrete Cantilever Floodwall Reinforcement.
Stability of Cantilever Floodwalls.
Typical Reinforced Concrete Floodwall.
Typical Section of a Brick-Paced Concrete Floodwall.
Typical Brick-Faced Concrete Floodwall.
Seepage Underneath a Floodwall .

.... .... VI-F.3 
. ... .... VI-F.3 
. ... .... V I-F.4 
.... ....VI-F.5 
........VI-P.6 
........V I-F.7 
........VI-F.8 
... .. VI-F.9 
....VI-F.12 

Reducing Phreatic Surface Influence by Increasing Distance 

from Foundation to Ploodwall 
Floodwall Design Process ....... 
Failure by Sliding ............. 
Failure by Overturning .......... 
Failure Due to Excessive Pressure ... 
Forces Acting on a Floodwall ...... 
Typical Reinforcing Steel Configuration 
Typical Floodwall Closures ....... 
Closure Variables ............. 
Sample Patio Drainage to an Outlet ... 
Sample Patio Drainage to a Sump .... 
Typical Gravity Floor Drain ....... 
Typical Patio Sump Pump Installation . 
Typical Patio Gravity Floor Drain Installation 
Typical Floodwall With Check Valve ..... 

Waterstop..............

Floodwall to House Connection . 
Typical Cosmetic Facings .... 
Floodwall Supporting Columns 
Floodwall Supporting Columns 
Typical Step Detail ........ 
Typical Floodwall Steps ..... 
Typical Floodwall Steps ..... 
Typical Floodwall Landscaping 
Floodwall Inspection Worksheet . 

Typical Residential Levee ............. 
Drainage Toe Details 

... ... ... .. . 

.............. 

.. ... ... ... ... 

.. . 
... ... .. ... 

... ... .. ... 
... ... . 
... ... .. ... 

... ... ... .. 

.... .. ... .. 
... ... .. .. 
... ... ... . 

. .... .. ... ... .

.. .. ....... ... .

.. ... ... . 
... .. ... . 

.. ... ... ...... . 

.. ... ... ....... 

.. .... .. .V I-F.63..... 

... ... ... V I-F.64 ..... 
... ... ... V I-F.65 ..... 

...... .. .VI-F.65 ..... 

... ... ... ... V I-F.66 
.. ... ... ... ... 

... ... . 

V I-F.13

VI-F.315

......... 

VI-F. 16 

V I-F.16
V I-F.19 ... 
V I-F.35 ... 
V I-F.44 ... 
V I-F.45 ... 
V I-F.53 ... 

VI-F.54 ... 
VI-F.54 .... 
VI-F.55 .... 

VI-F.57 ..... 
V I-F.60 ..... 
VI-F.61
V I-F.63

.................... . .. ... .
Drain Pipe Extending through Levee ........... . .. 
... V I-L.10 ... 
Interior Storage Area .................... .. VI-L.ll .... 
Compacted Lifts ....................... .. V I-L .15 .... 
Access over the Levee ................... .. VI-L.16 ....

0 

Page x 


P Table of Contents 

LIST OF FIGURES (continued) PAGE 

VII-1.1 
VII-1.2 
VII-1.3 
VII-1.4 
VII-1.5 
VII-1.6 
VII-1.7 
VII-1.8 
VII-1.9 

VII-2. 1 
VII-2.2 
VII-2.3 
VII-2.4 

VII-2.5 

VII-2.6 

VII-2.7 

VII-3.1 
VII-3.2 
VII-3.3 
VII-3.4 
VII-3.5 
VII-3.6 
VII-3.7 
VII-3.8 
VII-3.9 
VII-3. 10 
VII-3. 11 
VII-3.12 
VII-3.13 
VII-3.14 
VII-3.15 
VII-3.16 
VII-3.17 
VII-3.18 
VII-3.19 
VII-3.20 
VII-3.21 

Tug Fork Valley ..............
Typical Wall Detail Section .......
Interior Column Detail ..........
Flood Louver Detail ............
Masonry Pier Plan .............
Masonry Pier Detail Section .......
Insulated Utility Pipe Chase Detail
Pipe Chase Detail Section ........
Wood Post/Beam Detail Section .....

Dry Creek Project .......................... 
Typical Home Raised About Two Feet 
Typical Home Raised About Five Feet 

. ..... 

.. .... 
...... .... .. 
...... .... .. 
...... 

.... .. 

..... . .... .. 
..... . .... .. 
... ... 

.... .. 

... ... 

.... .. 

... . .. 

...... VII-4 

..... .VII-10

VII-11 

..... .

..... .VII-11

VII-12 

..... .
.. V II-14 
V II-15 
V II-15 
V II-16 

VII-19

...... 
.............. ...... VII-27 
.............. ...... VII-27 

Example of a Home Raised With the Brick Veneer in Place During 
Construction .................... ...... VII-28 
Example of a Home Raised With the Brick Veneer in Place Completion 
.......................... ...... VII-28 
Provisions for equalization of hydrostatic head was 
accomplished with foundation vents and/or flexible flaps on crawl-
space access door. . ......... . .VII-29 
Example of a Home Raised With Air Conditioner Compressor Unit 

VII-29 

VII-31 
VII-32 
VII-33 
VII-34 
VII-34 
VII-35 
VII-36 
VII-36 
VII-37 
VII-37 
VII-38 
... VII-40 
... . VII-40 
.... VVII-41

VII-42 
... . VII-43 
.... VVII-43 
.... VVII-44 
.... VII-42 
VII-45 
VII-45 

... 

Page xi 

on Elevated Platform ............. 

Temporary Supports for the Slab ........
Fireplaces Require Special Attention ......
Timber Cribbing ..................
Piers Cut Away Using Air Saw .........
Piers From Original Foundation .........
Cutting Reinforcing Steel .............
Garage Floor Slab Removed ...........
Holes in Garage Wall to Insert Steel Beams
Excavation Below Slab to Allow Access ....
Excavation and Tunneling Completed .....
Slab Cut With a Street Saw ...........
Long Nosed Shovel Attachment .........
Perimeter Grade Beam Being Removed ....
Snoot Being Used to Tunnel Under Slab ....
Shims Used on Underside of Slab ........
Wedges Used on Underside of Slab ......
Relocated Concrete Block Home ........
Concrete Block Counterbalance .........
New Piers and Wood Cribbing .........
Exterior Concrete Masonry Block Wall ....
Breakaway Exterior Walls ............

.. ...... .. 
... .. ... . 
.. ...... . 
.. ..... .. 
.. ..... . . 
.. ..... .. 
.. ..... .. 
.. ... .. .. 
. ...... .. 
. . ..... .. 
..... . ... 
...... .. . 
...... ... 
..... ... . 

..... .... 
..... ... . 
... .. .... 


*- Table of Contents 

LIST OF FIGURES (continued) PAGE 

VII-3.22 Interior

Shoring. 

VII-47 

VII-3.23 Plastic Sheeting for Weather Protection . VII-47 
VII-3.24 One Section of the House has been Raised Preparatory to 
Insertion of Dollies .................... . . 

VII-48 

VII-4. 1 Surface Water Problem (Before) 

VII-56 

VII-4.2 Surface Water Problem (After) . . . . . . . . . .. . . . . . VII-56 
VII-4.3 Site Plan ................ . . . . . . . . . .. . VII-58 
VII-4.4 Typical Detail Section Floodwall . . . . . . . . . .. . . . . VII-59 .. 
VII-4.5 Typical Detail Section of Backfilled LFloodwall . . . . . . VII-59 
VII-4.6 Patio Area Sump Pump Detail ... . . . . . . . . . 
.. . 
. . . VII-60 
VII-4.7 Footing Drain Detail ........ . . . . . . . . . 
.. . 
. . . VII-60 
VII-4.8 Completed Patio Floodwalls .... I . . . . . . .. 
.. . 
VII-61 .. 
VII-4.9 Site Plan: House on Opposite Side Of Bailey Creek-and . . . 
Engineering Solutions ... .. . . . . . . . . .. . 
. . . 
VII-62 
VII-4. 10 Typical Drain Detail ......... . . . . . . . . . .. . . . . VII-63 
VII-4. 11 Sump Pump and Sump Detail ... . . . . . . . . . .. . VII-63 

VII-5. 1 Location Plan ........................ ... .. VIL-68

VII-5.2 Preexisting Slab-on-Grade Construction Detail .... VII-69 

VII-5.3 Site Plan ........................... VII-72

VII-5.4 Typical Floodwall Detail Section ............ . VII-73

VII-5.5 Footer Detail ........................ VII-74

VI1-5.6 Wall-to-House Connection Detail ............ I .. .. I 
VII-74

VII-5.7 Drain Detail ......................... ..... ... VII-75

VII-5.8 Sump Detail .............. . . . . . .
..... ... VII-75

VII-5.9 Floodwall Steps and Landscaping Timber ....... . . . . . . VII-76 
VII-5. 10 Sump Pump Outlet and Raised Air Conditioner Unit . .. . . .... ... VII-76 
VII-5. 11 Completed Project ..................... . . . . . . VII-77 

VII-6. 1 Location Plan .................. ... ... .. ... .. V II-79 .... 
VII-6.2 Preexisting Foundation Wall Section Detail ... ... .. ... .. V II-80 .... 
VII-6.3 Dry Floodproofing Calculations ....... ... ... ... .. .. V II-81 .... 
VII-6.4 Wet Floodproofing Calculations ....... .. .I .... .. .. V II-83 ..... 
VII-6.5 Site Plan ..................... ... .. ... ... . V II-87 ..... 
VII-6.6 Block Vent Detail ............... ... ... .. ... . V II-88 ..... 
VII-6.7 Access Door Detail .............. .. ... ... .. . V II-88 ...... 
VII-6.8 Anchorage Detail for Sheds ......... ... .. ... ... .. . V II-89 ... 

VII-7. 1 Location Plans ................. ... ... .. ... ... V II-91 ... 
VII-7.2 Dry Floodproofing Calculations ....... . ... .. ... ... ... .. 
VII-7.3 Preexisting Walk-out Basement Foundation' Wall Detail Section .... . VII-95
VII-7.4 Site Plan ..................... ... .. ... ... .. V II-96 .... 

Page xii 


* Table of Contents 
LIST OF FIGURES (continued) PAGE 

VII-7.5 

VII-7.6 
VII-7.7 
VII-7.8 
VII-7.9 

VII-7. 10 
VII-7. 11 
VII-7.12 
VII-7.13 
VII-7.14 
VII-7.15 
VII-7.16 
VII-7.17 

VII-8.1 
VII-8.2 
VII-8.3 
VII-8.4 

D-1 
D-2 
D-3 
D-4 
D-5 
D-6 
D-7 
D-8 
D-9 

D-10 

D-11 

D-12 

Concrete Patio, Replacement Floodwall, and New 

Access for Basement Detail ................... VII-97 
Step and Wall Detail Elevations ...... . . . . .. ..... VII-98 
Concrete Floodwall Detail ......... . . . . .I ..... .VII-99 
Downspout Connection to Drain Detail . . . . .. ..... VII-99 
Floodwall Connection to House Detail . . . . . . .. .... VII-100 

Floodwall Supporting Columns Detail ........... .VII-100
Step Detail ................ ........... .VII-101
Step Detail ................ ........... .VII-101
Sump Pump Detail ............ ........... VII-102
Stair Section ............... ........... .VII-102
Air Conditioning Pad and Sump Pump ........... VII-103
Floodwall and Supporting Columns . . ........... VII-103
Stairs and Supporting Columns .... ........... .VII-104

o

Veneer Wall Detail Section ......... . . . . . . .. . . ... VII-106 
Veneer Wall Metal Anchor Detail Section . . . . . . . . . ... VII-106 
Aluminum Flashing Detail Section .... . . . . . . . . . ... VII-107 
Watertight Closure Section ......... . . . . . . . . . .. . VII-108 

Telluride, Colorado Fan .... I........ D-2 
Alluvial Fan Flooding Damage, Telluride, Colorado . D-2 
Rancho Mirage, California Fan Damage (1979) . D-3 
Oblique View of an Alluvial Fan . D-3 
Reinforced Upfan Walls . D-22 
Reinforced Upfan Walls . D-22 
Floodwall Protecting Residence in Colorado . D-23 
Debris Flow Levee . D-24 
Diversion Levee in Colorado . D-25 
Typical Subdivision Plot Plan . D-26 
Typical Rural Plot Plan . D-27 
Typical Dispersion Design . D-28 

Page xiii 


Table of Contents 

T 

LIST OF TABLES 

I-1 Advantages 
1-2 Advantages 
1-3 Advantages 
I-4 Advantages 
I-5 Advantages 

and Disadvantages 
and Disadvantages 
and Disadvantages 
and Disadvantages 
and Disadvantages 

of Elevation .................. 
of Relocation .............. 
of Dry Floodproofing ............ 
of Wet Floodproofing ............ 
of Floodwalls and Levees ...

II-1 Typical Summary of Discharges Table ....................
II-2 Typical Summary of Coastal Stillwater Elevations .............
II-3 Model Code Groups ...............................
II-4 Model Codes/NFIP Requirements: Items to be Reconciled .......

III-1 Elevation and Relocation Cost Guide .....................

PAGE 

1-13 
1-16 
I-19 
1-21 
1.....

1-25 

* . 11-6
. . II-8
. 11-22
. II-24

III-10 

III-2 Floodwalls and Levees Cost Guide ...................... III-1 1
III-3 Dry Floodproofing Cost Guide ........................ III-12
III-4 Flood Shields Cost Guide ............................ III-12
III-5 Preliminary Cost Estimating Worksheet ................... III-13
III-6 Flood Risk .................................... III-14

IV-1 Flood Data Summary .............................. . IV-6
IV-2 Effective Equivalent Fluid Weight of Soil(s) ................ IV-13
IV-3 Soil Type Definitions Based on USDA Unified Soil Classification IV-14
IV-4 Drag Coefficients ................................ IV-21
IV-5 Freeboard and Factor of Safety Recommendations ............. IV-45
IV-6 Typical Bearing Pressure by Soil Type (from Table IV-3) ........ IV-59
IV-7 Scour Factor for Flow Angle of Attack, K ................. IV-65
IV-8 Typical Values of Coefficient of Permeability k for Soils ........ IV-71

VI-1 Approximate Bearing Capacity for Masonry Materials .... ...... VI-24 
VI-2 Wall Lateral Support Requirements ...... ................ VI-24 
VI-3 Weights of Construction Types ....... ................. VI-28 

VI-D1 Essential Equipment/Appliances to Operate From 
Emergency Power Source .. ... ... . .... . ... .. .. .VI-D.79 
VI-D2 Typical Electrical Appliance Loads .... ................. VI-D.82 
VI-D3 Example of Maximum Generator Sizing Procedure ... ........ VI-D.83 
VI-D4 Example Step Sequence Manual Start Minimum Generator Size . . . VI-D.84 
VI-D5 Minimum Panel Bus Sizes .......................... VI-D.89 

VI-F1 Soil Factors for Floodwall Design ..................... VI-F. 17 
VI-F2 Assumed Soil Factors for Simplified Floodwall Design ......... VI-F.40 
VI-F3 Typical Floodwall Dimensions for Clean, Dense, Sand 
and Gravel (Soil Types GW, GP, SW, SP) ........... VI-F.41 

Page xv 


i Table of Contents 

LIST OF TABLES (continued) PAGE 

VI-F4 Typical Floodwall Dimensions for Dirty Sand and Gravel of 
Restricted Permeability Soil Types: (GM, GM-GP, SM, 
SM-SP) . VI-F.42 
VI-F5 Moment (j) and Deflection (a) Coefficients . VI-F.48 

VI-L1 Stone Protection Layer Guidance ...................... . VI-L.9 
VI-L2 Cost Estimate Example . VI-L. 12 
VI-L3 Levee Cost Estimating Worksheet . VI-L. 13 

VII-1.1 

RetrofittingforStructureElevation........... .. ... .. . .VII-7

Cost 

VII-2. 

1 DryCreekFloodproofingProject ................ 

Summary . VII-21 
VII-2.2 Cost Analysis Table .............................. VII-24 
VII-2.3 Post-ProjectQuestionnaire ... .. .. . VII-26

Results ............. .

VII-3. 1 Detailed Cost Estimate Elevation of a 36x36 (1296 sf) One-Story 

Home 2 Feet Above Ground ..................... VII-52 
VII-3.2 Detailed Cost Estimate Elevation of a 36x36 (1296 sf) One-Story 

Home 10 Feet Above Ground ..................... VII-53

VII-8. 1 Floodproofing Cost for a Veneer Wall ................. . . VII-109

Page xvi 


T

Table of Contents 

LIST OF FORMULAS

IV-1

IV-2 
IV-3 
IV-4 

IV-5

IV-6 
IV-7 
IV-8 
IV-9 

IV-10

IV-li 
IV-12 
IV-13 
IV-14 
IV-15 
IV-16 
IV-17 

IV-18 
IV-19 
IV-20 
IV-21 
IV-22 
IV-23 
IV-24 
IV-25 
IV-26 

V-1

V-2 
V-3 
V-4 

V-5

V-6 
V-7 
V-8 
V-9 

V-10

V-11 
V-12 
V-13 
V-14 

Flood Depth....................................
Flood Protection Elevation .. ... ..............
Floodproofing Design Depth .........................
Lateral Hydrostatic Forces ...........................
Saturated Soil Hydrostatic Forces .......................
Combined Water and Soil Forces .......................
Cumulative Lateral Hydrostatic Force ....................
Buoyancy Force .................................
Conversion of Low Velocity Flow to Equivalent Head ..........
Conversion of Equivalent Head to Equivalent
Hydrostatic Force ............................
Total Lateral Hydrostatic Force ........................
High Velocity Hydrodynamic Pressure ....................
Total Hydrodynamic Force ...........................
Normal Impact Force ..............................
Special Impact Forces..............................
Runoff Quantity in an Enclosed Area ....................
Runoff Quantity from Higher Ground Into a Partially
Enclosed Area ..............................
Seepage Flow Rate Through a Levee or Floodwall ............
Minimum Discharge for Sump Pump Installation .............
Bulking Factor .....

Bulin ................................

Fcto 

Specific Weight of Water-Sediment Mixture ................
Recommended Freeboard ............................
Allowable Bearing Capacity ..........................
Maximum Potential Scour at Embankment Toe ...............
Maximum Potential Scour at Structure ....................
Volume of Seepage ...............................

Scenario Damages ................ . . . . . . . . . . . . .
Building Damages ................ . . . . . . . . . . . . .
Contents Damages ................ . . . . . . . . . . . . .
Displacement Costs ............... . . . . . . . . . . . . .
Rental Income Losses .............. . . . . . . . . . . . . .
Expected Annual Damages ........... . . . . . . . . . . . . .
Expected Avoided Damages .......... . . . . . . . . . . . . .
Expected Annual Benefits ........... . . . . . . . . . . . . .
Present Worth Factor .............. . . . . . . . . . . . . .
Present Value of Estimated Annual Benefits . . . . . . . . . . . . .
Present Value of Estimated Annual Costs .. . ..... ..... ..
Benefit/CostRatio ....... ...... . . . . . . . . . . . . .
Net Present Value ................ . . . . . . . . . . . . .
Adjusting Unit Cost for Local Communities . . . . . . . . . . . . .

PAGE 

. IV-8 
. IV-8 
. IV-9 
IV-1l 
IV-12 
IV-15 
IV-16 
IV-17 
IV-21 

IV-22 
IV-22 
IV-25 
IV-25 
IV-30 
IV-31 
IV-37 

IV-38 
IV-38 
IV-39 
IV-42 
IV-43 
IV-44 
IV-58 
IV-63 
IV-64 
IV-69 

V-14 

. V-15

V-15 
V-16 
V-16 
V-17 
V-17 
.V-18 
.V-19 
V-20 
.V-20 
.V-21 
V-21 
V-30 

Page xvii 


: i Table of Contents 

LIST OF FORMULAS (continued) PAGE 

VI-1 Determining Footing Size. VI-21 
VI-2 Maximum Loading of Existing Footing. VI-21 
VI-3 Bearing Capacity of an Existing Concrete Masonry 
Foundation Wall ............................. VI-22 
VI-4 Slenderness Ratio . VI-23 
VI-5 Calculation of Live Load . VI-30 
VI-6 Calculation of Tributary Area for Load-bearing Walls .......... VI-31 
VI-7 Calculation of Tributary Area for Center Girder . VI-32 
VI-8 Calculation of Tributary Area for Columns . VI-32 
VI-9 Calculation of Wall/Column Loads. VI-33 
VI-10 Calculation of Self Weight of Wall/Column. VI-34 
VI-i1 Calculation of Total Load Carried by the Wall or 
Column to the Footing or Foundation ................ VI-34 

VI-D1 Total Discharge Head ............................. NrI-D.66

VI-D2 Head Loss Due to Pipe Fittings ....................... N1-D.67

VI-W1 Buoyancy Force on a Tank ............. VI-W.36

VI-W2 Concrete Volume Required to Offset Buoyancy VI-W.37 

VI-F1 Buoyancy on a Floodwall .......... ... ... .. .. VI-F.20 ..... 
VI-F2 Floodwall Weight .............. I. ... ... ... ... . V I-F.21 
VI-F3 Footing Weight ................ .. ... ... ... . V I-F.21 ... 
VI-F4 Weight of Soil Over Floodwall Toe ... ... ... .. ... . V I-F.22 ... 
VI-F5 Weight of Soil Over Floodwall Heel ... .al ... ... ... ... V I-F.22 ... 
VI-F6 Weight of Water Above Floodwall Heel ... ... ... ... V I-F.23 ... 
VI-F7 Total Gravity Forces Per Linear Foot of's .............. VI-F.23 
VI-F8 Net Vertical Force ...... ........ ... ... ... .. V I-F.23 .... 
VI-F9 Sliding Forces ................ .... .. ... .. V I-F.24 .... 
VI-FlO Frictional Force ............... ... .. ... .. V I-F.25 ..... 
VI-Fll Cohesion Force ................ ... ... ... . VI-F.26 ..... 
VI-F12 Saturated Soil Force Over Floodwall Toe .I ... ... ... . V I-F.27 ..... 
VI-F13 Sum of Resisting Forces to Sliding .... .. ... ... ... . V I-F.27 ... 
VI-F14 Factor of Safety Against Sliding ...... ... ... .. ... . V I-F.28 ... 
VI-F15 Sum of Overturning Moments ....... ... ... ... .. . V I-F.29 ... 
VI-F16 Sum of Resisting Moments ......... ... ... ... ... V I-F.30 ... 
VI-F17 Factor of Safety Against Overturning . . ... ... ... ... V I-F.31 ... 
VI-F18 Eccentricity ... ... ....

.................. ... .. VI-F.32

Pressure ... VI-F.33 ....VI-F19 Soil ........ . . ... .. ... 
VI-F20 Cross-Sectional Area of Steel ....... ... ... ... .. VI-F.34 .... 
VI-F21 Plate Thickness due to Bending Stresses . . ... ... ... .. V I-F.47 .... 
VI-F22 Plate Thickness due to Deflection Stresses ... ... ... .. V I-F.47 .... 
VI-F23 Bending Moment ................ .. ... ... .. V I-F.49 ..... 
VI-F24 Bending Stress ................. .. ... ... ... ... . 

Page xviii 


i Tableof Contents 

LIST OF FORMULAS (continued) PAGE 
VI-F25 Shear Force ................. .. V I-F.50 

VI-F26 ... V I-F.50 

Shear...... . .. 

Stress 

VI-F27 Plate Deflection for a One-Way Span V I-F.51
VI-F28 Allowable Deflection ........... V I-F.51

VII-1. 1 Dry Creek House Raising Costs ..... ..... V II-23 

Page xix 


* Table of Contents 
NOMENCLATURE 

a Deflection coefficient 
Moment coefficient 

ly Specific weight of water 
IyS Specific weight of the water/sediment mixture 
'Ysol Unit weight of soil 
or Allowable stress for closure plate material 
Ab Computed deflection 

Aba Allowable deflection 
p Mass density of water 
a Diameter of post 
A Area 
a,b Span lengths between the walls and center girder 
AB Expected Annual Benefits 
Aasbc Specific Area enclosed by a floodwall/levee 
A,, Column tributary Area 
AD Expected Annual Damages 

Ag Center girder tributary Area 
Ah Width of footing heel 
As Cross-sectional Area of reinforcing steel required per foot width of wall 

At Column tributary Area 
AVD Expected Avoided Damages 
AW Wall tributary Area 

Page xxi 


* Table of Contents 
NOMENCLATURE (continued) 
b Width of object (structure) perpendicular to flow 
B Width of footing 
BCR Benefit/Cost Ratio 
BD Scenario Building Damages 
BF Bulking Factor 
BFE Base Flood Elevation 
BRV Building Replacement Value 
c Residential terrain runoff coefficient 
C Width of footing toe 
Cd Drag Coefficient 
CD Scenario Contents Damages 
Cf Coefficient of friction 
CF Cubic Foot 
CFR Code of Federal Regulations 
cfs Cubic feet per second 
CR Building Contents Replacement value 
Crs Rolling shear Constant 
Cs Allowable soil Cohesion value 
C:, Concentration of sediment in the fluid mixture by percent of volume 
d Depth of flooding 
D Depth of saturated soil over which hydrostatic forces are considered 
Page xxii 


* Table of Contents 
NOMENCLATURE (continued) 
dl. 5Q design Depth of flooding from a discharge 50% greater than the design 
discharge 
Da Height of vertical foundation member above grade 
Db Depth of burial of vertical foundation member 
DD Displacement Days 
df Distance between reinforcing steel and floodwall face opposite retained 
material 
dh Equivalent head due to low velocity flood flow 
Dh Depth of soil above the floodwall heel 
DIS Scenario Displacement costs 
DL Dead Load 
dQ design Depth of flooding from the design discharge 
DRR Daily Rental Rate 
Ds Difference in elevation between the bottom of the sump and the point 
of discharge 
Dt Depth of soil above the floodwall toe 
e Eccentricity 
E Modulus of Elasticity 
EABpv Present value of Estimated Annual Benefits 
EAE Expected annual number of floods of a given depth 
EACpV Present value of Estimated Annual Costs 
ECCpV Present value of Engineering and Construction Costs associated with a 
retrofitting measure 
Page xxiii 


* Table of Contents 
NOMENCLATURE (continued) 

ECD Expected Contents Damage 
EFF Effectiveness of mitigation measure in reducing expected damages from 

a flood of a given depth 

FA Floor Area of building in square feet 
f Freeboard (factor of safety) 

fb Bending stress 

Fb Vertical hydrostatic Force (buoyancy) 

FBFM Flood Boundary and Floodway Map 

Fb1 Buoyancy Force acting on a floodwall heel 

FbZ Buoyancy Force acting on a floodwall toe 

fo Bearing capacity of masonry 

Fc Cohesion Force between the footing and the soil 

Fd Hydrodynamic Force 

Fdh Equivalent hydrostatic Force due to low velocity flood flow 

Fdif Differential soil/water Force 
FE Flood Elevation for a specific flood frequency 
FEMA Federal Emergency Management Agency 
Ff, Frictional Force between the bottom of the footing and the soil 
Fh Lateral hydrostatic Force from standing water 
FH Cumulative lateral Hydrostatic Force 
FIA Federal Insurance Administration 
FIRM Flood Insurance Rate Map 

Page xxiv 


* Table of Contents 
NOMENCLATURE (continued) 
FIS Flood Insurance Study 
Normal impact load 
Fp Saturated soil Force over the toe of the footing 
FPE Flood Protection Elevation 
FPL Flood Protection Level 
fps Feet per second 
FR Sum of Resisting Forces to sliding 
fr. Shear stress 
F., Special impact load 
FSS Maximum Shear Stress 
FS Factor of Safety 
Fsat Lateral hydrostatic Force from saturated soil 
FS(07) Factor of Safety against Overturning 
FS(SL) Factor of Safety against Sliding 
Fv Net Vertical Force 
g Acceleration of gravity 
gpm Gallons per minute 
GS Lowest Ground Surface elevation (grade) or other reference feature 
(slab or footing) adjacent to structure 
h Distance from bottom of structure to water level 
H The floodproofing design depth over which flood forces are considered 
h. Height of closure 
Page xxv 


i Tableof Contents 

NOMENCLATURE (continued) 
if fittings Head loss through the pipe fitting(s) 
lifpipe Head loss due to pipe friction 
H, Height of unbraced foundation wall 
i Interest rate 
I Effective moment of Inertia 
ir Rainfall intensity 
ihg Hydraulic gradient between two points 
IPD Post-Disaster Inflation 
k Coefficient of permeability for soils 
K Scour factor based upon flow angle of attack 
kp Passive soil pressure coefficient 
Kp Resistance coefficient of the pipe fitting(s) 
KS Effective section modulus 
I Length 
lbs Pounds 
lbs/ft3 Pounds per cubic foot 
LF Linear Feet 
LL Live Load 
L. Minimum uniformly distributed live Load 
M Mass of object 

max Maximum flood depth considered above zero flood depth 
Mb Bending Moment 

Page xxvi 


T

Table of Contents 

NOMENCLATURE (continued) 
MDDF Expected damage by flood depth 
min Minimum damaging flood considered above zero flood depth 
MO Sum of Overturning Moments 
MR Sum of Resisting Moments 
MSL Mean Sea Level 
n Assumed life of a structure 
NAVD North American Vertical Datum 
NFIP National Flood Insurance Program 
NGVD National Geodetic Vertical Datum 
NOAA National Oceanic and Atmospheric Administration 
NPV Net Present Value or benefit of a mitigation measure 
NRCS Natural Resources Conservation Service 
NWS National Weather Service 
P Load 
Pd Hydrodynamic Pressure due to high velocity flow flood 
PD Lateral hydrostatic Pressure from saturated soil 
Pdh Hydrostatic Pressure due to low velocity flood flows 
Ph Hydrostatic Pressure from standing water 
psi Pounds per square inch 
PWF Present Worth Factor 
q Soil pressure 
Q Discharge in a given unit of time 
Page xxvii 


o Table of Contents 
NOMENCLATURE (continued) 

Qa,bc Runoff Quantity (discharge) from a defined area 

QBC Allowable Bearing Capacity 

QSP Minimum discharge for sump pump installation 

QU Ultimate bearing capacity 

RENT Scenario rental income losses 

Rr Resistance due to foundation friction 

RF Flood depth considered above zero flood depth 

s Slenderness ratio 

Sa Allowable Soil bearing pressure (capacity) 

SA Section Area of component 

Sbc Soil bearing capacity 

SC Effective (unit) weight of concrete 

SCD Total Scenario Damages (per event) 

Sd Potential scour depth 

SF Square Foot (feet) 

SFHA Special Flood Hazard Area 

S2 Unit weight of wall material 

SL Snow Load 
Smax Maximum potential depth of scour hole 

SP Specific gravity of sediment 

Sq. Mi. Square Mile 

sr Seepage rate 

Page xxviii 


* Table of Contents 
NOMENCLATURE (continued) 
SW Self Weight of component 
t Time of impact 
TA Total Area occupied (SF) 
TDC Displacement Costs per day (per SF) 
tftg Footing thickness 
TH Total Head 
TL Total Load 
TLdjI Total Load due to dead, live, and snow loads 
TVA Tennessee Valley Authority 
LI Foundation wall thickness 
twall Floodwall thickness 
UCFEMA FEMA Unit Cost at specific location 
UC1IW Unit Cost for a locality 
USACE U.S. Army Corps of Engineers 
USGS United States Geological Survey 
V Velocity of floodwater 
VI Volume of concrete required to offset tank buoyancy 
V8 Shear force 
V, Volume of tank 
w Span lengths between walls or wall and girder 
Wa Total gravity forces 
WC Width of closure shield 
Page xxix 


Table of Contents 

Wftg 
Wg 

Wn 

Wi 
WPIFEMA 

WPIiocai 

ws 

Wsh 

Wst 

Wt 

Wu 

Wwh 

y 

NOMENCLATURE (continued) 

Weight of the footing 
Total gravity forces per linear foot of wall 
Weight of object for normal impact loads 
Weight 
FEMA Wholesale Price Index for a locality 
Wholesale Price Index for a locality 
Weight of object for special impact loads 
Weight of soil over floodwall heel 
Weight of soil over floodwall toe 

Weight of tank 

Unit weight of component 

Weight of floodwall 

Weight of water above floodwall heel 

Support width factor 

Page xxx 


FOREWORD 

The riverine and coastal floodplains of the United States are among the most highly desirable 
areas in the nation for habitation and construction. Unfortunately, many of these areas are very 
susceptible to flooding, which is the single most expensive and persistent natural disaster the 
country experiences. Flooding causes millions of dollars in property damage each year, despite 
concentrated efforts of government and the private sector to mitigate flood hazards. 

The National Flood Insurance Program (NFIP) was created in 1968 by the Congress not only to 
provide federally-backed flood insurance to those who generally were not able to obtain it from 
private-sector companies, but also to promote sound floodplain management practices in flood-
prone areas. The floodplain management aspects of the program are administered by the Mitigation 
Directorate and the insurance aspects are administered by the Federal Insurance Administration 
(FIA), both parts of the Federal Emergency Management Agency (FEMA), under the authority 
of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 
1973, U.S.C. 4001-4128, as amended. 

Figure v-: Flooding along major rivers can createwidespreaddamage. 

One NFIP mission is to work with communities to reduce future flood losses by establishing 
guidelines for protecting existing and new development in flood-prone areas. The program 
makes flood insurance coverage available for structures in those communities that adopt and 
enforce floodplain management ordinances and regulations that meet or exceed the minimum 
NFIP requirements as provided for in Section 44 of the Code of Federal Regulations (44 CFR). 
Coverage is available for walled and roofed structures that are principally above ground and not 
entirely over water, including manufactured homes that are anchored to permanent foundations. 
Flood insurance is available for all structures in a participating community, whether the structures 
are located inside or outside the floodplain identified by FEMA. 

Owners who have experienced flooding know that complete recovery is often impossible. In 
addition to the time and money spent repairing or replacing damaged items, they must also deal 

Xxxi 


with cleaning property, alleviating health risks and safety hazards, losing time from work, find

ing alternative housing, and the emotional toll of the experience. Responding to flood events 

also depletes resources at every level of government. Human resources and capital must be 

diverted to providing emergency services, rebuilding public facilities, financing individual 

assistance for uninsured victims, and to other efforts. In the Great Midwest Flood of 1993, for 

example, FEMA estimated damage costs exceeded $10 billion. 

Many of the flood insurance claims received by the NFIP are for structures that have previously 
incurred flood damage. Structures for which two or more claims of more than $1,000 each have 
been paid during the previous ten-year period are considered to be repetitive loss structures 
according to the NFIP. Most repetitive loss claims are for small amounts and involve structures 
built before NFIP-compliant floodplain management regulations were adopted by the community. 
However, owners have the option of taking steps to reduce the likelihood of serious future 
flood damage. Retrofitting individual flood-prone structures is a proven technology that has 
been in use for many years. 

If a flood-prone structure is substantially damaged, certain criteria established by the NFIP must 
be met prior to the initiation of any repair activity. Specifically, NFIP regulation 44 CFR 
60.3(c)(2) requires communities to ensure that substantially damaged or improved residential 
structures be elevated so that the lowest floor is at or above the Base Flood Elevation, (BFE), 
also known as the 100-yearflood level. "Substantially damaged" is defined as damage of any 
origin sustained by a structure whereby the cost of restoring the structure to its before-damaged 
condition would equal or exceed 50% of the value of the structure before the damage occurred. 

Given the potential cost of recovering from a serious flood event and meeting the NFIP's criteria 
for restoring substantially damaged property, the owner of a flood-prone home has an incentive 
to undertake retrofitting measures to limit future flood damages. FEMA and the other contributing 
agencies and organizations have developed this manual to provide engineering and related 
economic guidance to professional designers and local officials about what constitutes technically 
feasible and cost-effective retrofitting techniques. 

However, the guidance provided in this manual should be considered generic in nature, subject to 
final refinement in accordance with local regulations and specific site and structural conditions. 
It is not intended to be used as a code or specification, nor as a replacement for the engineer's or 
architect's standard of performance. Through the information and analyses presented in this 
manual, local officials, and design professionals will gain a better understanding of the advantages 
of retrofitting and may choose to take steps that could ultimately save the nation millions of 
dollars each year. 

Richard T. Moore 
Associate Director for Mitigation 
Federal Emergency Management Agency 


O ACKNOWLEDGEMENT 

FEMA acknowledges the following agencies and organizations for their contributions to 
this manual: 

OF AGRICULTURE| 

4 U.S. DEPARTMENT 

e A _ | w ~~~~~~~~~~~~~~~~~~SOLtl

CONSERVATION SERVICE 

8 0 DEttV

me~~~ r 

* Brudis & Associates, Inc.
e Dewberry & Davis
* Flo Engineering, Inc. 
* French & Associates, Ltd. 
* National Association of Home Builders, (NAHB), Research Center 
* National Institute of Building Sciences (NIBS) 
* Soza & Company, Ltd. 
xxxiii 


. METRIFICATION

FEMA is committed to the federal government's transition to metric. However, English 
units remain the standard of practice for residential construction. Therefore this manual 
has been prepared using English units. 

However, it is foreseeable that the metric system will be the standard of measurement in 
this country within the next few years. With this in mind, soft metric conversion's have 
been provided to promote familiarity with the metric system. 

A critical component of unit conversion is rounding. Designers should check to ensure 
that rounding does not exceed allowable tolerances for design or fabrication. 

Metric Conversion Factors
Quantity From English Units To Metric Units Multiply By:

Length foot (m) 0.3048
inch (mm) 25.4

Area square foot m2 0.092
acre m2 4047

Volume gallon L 3.7714
cubic foot m3 .0283

Pressure psf Pa 47.8803
psi kPa 6.8947

Power horsepower kW .746
W 746

Weight pounds kg .4535 

Flow cfs Ips 28.3 

Velocity fps mps 0.3048 


CHAPTER I

Featuring: 

How to Use This Manual 
Methods of Retrofitting 
General Retrofitting Cautions 
Retrofitting Process 

E-1 X 

INTRODUCTION 
TO RETROFITTING 


-INTRODUCTIONTO RETROFITTING

L 

HOW TO USE THIS MANUAL METHODS OF GENERALRETROFITrING

I N 
I 
_ 

RETROFITTING t CAUTIONS 
IGRETROFITTINGPROCESS 

Goals and Intended Users Elevation Homeowner Motivation 
Organization of 

Relocation Parameters of Retrofitting 

the Manual 
Dry Floodproofing Determination of Hazards 

Wet Floodproofing Benefit/Cost Analysis 

Floodwalls & Levees Design 

[ Construction 

IOperation and Maintenance 

20/ 


Chapter I: Introduction to Retrofitting 

Table of Contents 

How to Use This Manual ........................................ I -1

Goals and Intended Users ......................................... ! .I -1

Organization of the Manual .I -2 

-

Methods of Retrofitting .I 4 
Elevation .I -6 
Elevation on Solid Perimeter Foundation Walls.I -7 
Elevation on Open Foundation Systems.I -9 
Relocation.................................................................................................................... I-14 
Dry Floodproofing. I-17 
Wet Floodproofing.I -20 
Floodwalls and Levees.I -22 

General Retrofitting Cautions.I -26 

Retrofitting Process.I -28 
Homeowner Motivation .I -28 
Parameters of Retrofitting .I -28 
Determination of Hazards .I -28 
Benefit/CostAnalysis.I -29 
Design.I -29 
Construction................................................................................................................. I -29 
Operation and Maintenance .I -29 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -i 
January 1995 


How to Use This Manual 

HOW TO USE THIS MANUAL

Other flood-related technical 

resources are available through 
federal agencies such as FEMA, 
the U.S. Army Corps of Engineers, 

and the Natural Resources 

ConservationService,aswellas 
state,regional,andlocalagencies. 
See Appendix C, Glossary of 
Resources. 

Thismanualwillprovidevaluable 

assistanceto the design profes-

sional. It is not intendedto be 

usedas a code or specification, 

engineer's orarchitect'sstandard 

of performance. 

GOALS AND INTENDEDUSERS 

This manual has been prepared by the Federal Emergency 
Management Agency with assistance from other agencies and 
organizations involved in the nationwide effort to assist local 
governments, engineers, architects, and property owners 
involved in retrofitting flood-prone residential structures. Its 
objective is to provide engineering design and economic guidance 
to engineers, architects, and local code officials about 

what constitutes technically feasible and cost-effective retrofit

ting measures for flood-prone residential structures. 

The focus ofthis manual is the retrofitting of one-to four-family 
residences subject to flooding situations without wave action. 

The manual presents various retrofitting measures that provide 
both active and passive efforts and employ both wet and dry 
floodproofing measures. These include elevation ofthe struc

ture in place, relocation ofthe structure, construction of barriers 

(levees and floodwalls), dry floodproofing (sealants, closures, 

sump pumps, and backflow valves), and wet floodproofing 

(flood-resistant materials and protection of utilities and con

tents). 

The goal of this manual is to capture state-of-the-art information 
and present it in an organized manner. To the maximum extent 
possible, existing data and modem research have been utilized 
as the cornerstone of this document. Detailed sections covering 
the evaluation, planning, and design of retrofitting measures are 

included along with case studies of completed retrofitting 

efforts. Methods for performing economic analyses of the 

various alternatives are presented. 

Pnninpprinn Prinvinles and Practices of Retrofitting Flood-Prone Residential Structures 1-1 
January 1995 


ChapterI: Introduction to Retrofitting 

The architect, engineer, or code official must recognize that 

retrofitting a residential structure influences how that structure 
reacts to hazards other than those associated with floodwaters. 
Flood-related hazards such as water-borne ice and debris 

6 impact forces, erosion forces, and mudslide impacts, as well as 
non-flood-related hazards such as earthquake and wind forces, 
Coastal situations subject to wave shouldbeconsideredintheretrofittingprocess. Retrofittinga 
action are not addressed in this structure to withstand only floodwater-generated forces may 
manual. For information on that impair the structure's ability to withstand the multiple hazards 
area the reader is referred to mentioned above. Thus, it is important to approach the retro

oS. Corps 
of Engineers (USACE) Shore perspective. 
ProtectionManual. 

Manual, and the U Atry fitting method selection and design process with a multi-hazard 

ORGANIZATION OF THE MANUAL 

This manual has seven chapters and five appendixes. 

Chapters 1, 11, and III 

* Introduction to Retrofitting 
* Regulatory Framework 
* Parameters of Retrofitting 
Chapters IV and V 

* Determination offHazards 
* Benefit/Cost Analysis and Alternative Selection 
These chapters give detailed guidance on how to focus on the 
specific retrofitting solution that is most applicable forthe 
residential structure being evaluated. 

I -2 Enqineerinq Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


How to Use This Manual 

The balance of the design manual encompasses the following: 

ChapterVI 

* Design Practices 
This chapterprovides step-by-stepdesignprocessesfor each 
retrofitting measure. (Note: Each retrofitting measure has its 
own tab and is organized as a subchapter.) 

ChapterVII 

* Case Studies 
This chapter is a collection of information on the actual retrofit-
ting of specific residential structures.
Throughout this manual, the following icons are used, indicating:

Special Note: 

I0 

IccC 

I ccD 

Formula: 

Bomb: 

Significantorinterestinginformation 

Use of a mathematical formula 

I Special cautions need to be exercised 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I-3 
January 1995 


Chapter I: Introductionto Retrofitting 

~~~~~~L,

METHODS OF RETROFITTING 

Retrofitting involves a combination of adjustments or additions 
to features of existing structures that are intended to 
eliminate or reduce the possibility of flood damage. Retrofitting 
measures includes the following: 

Elevation: 

Relocation: 

Dry Floodproofing: 

Wet Floodproofing: 

Floodwalls/Levees: 

The elevation ofthe existing structure 
on fill or foundation elements such as 
solid perimeter walls, piers, posts, 
columns, or pilings. 

Relocating the existing structure 
outside the identified floodplain. 

Strengthening of existing foundations, 
floors, and walls to withstand flood 
forces while making the structure 
watertight. 

Making utilities, structurecomponents, 
and contents flood-and water-
resistant during periods of flooding 
within the structure. 

The placement of floodwalls or 
levees around the structure. 

I -4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


See page I-26 for general cautions 
to consider in the implementation 
of a retrofitting measure. 

Methods of Retrofitting 

Retrofitting measures can be passive or active in terms of 
necessaryhuman intervention. Active or emergency retrofitting 
measures are effective only if there is sufficient warning 
time to mobilize labor and equipment necessary to 
implement the measures. Therefore, every effort should be 
made to design retrofitting measures that are passive and do 
not require humanintervention. 

Fnninrigrmnn Prinrinie anndPracticae nf Retrnfiftinn Flood-Prone Residential Structures I -5 
January 1 995 


Chapter I: 

6 

Cost is an important factor to 
consider in elevating structures. 
As an example, lighter wood-frame 

structures are easier and often 
cheaper to raise than masonry 
structures. Masonry structures 
are not only more expensive to 
raise, but are also susceptible to 
cracks. 

'olv 

Base Flood is defined as the flood 
having a 1% chance of being 
equaled or exceeded in any given 
year. The Base Flood Elevation 
(BFE) is the elevation to which 
floodwaters rise during a Base 
Flood. 

Introduction to Retrofitting 

ELEVATION 

Elevating a structure to prevent floodwaters from reaching 

damageable portions is an effective retrofitting technique. 

The structure is raised so that the lowest floor is at or above 

a designated flood protection elevation (FPE). Heavy-duty 

jacks are used to lift the existing structure. Cribbing sup

ports the structure while a new or extended foundation is 

constructed below. In lieu of building new support walls, 
open foundations such as piers, columns, posts, and piles are 
often used. Elevating a structure on fill is also an option in 
some situations. 

While elevation may provide increased protection of a 
structure from floodwaters, other hazards must be considered 
before implementing this strategy. Elevated structures 

may encounter additional wind forces on wall and roof systems, 

and the existing footings may experience additional loading. 

Extended and open foundations (piers, piles, posts, and col

umns) are also subject to undermining, movement, and impact 

fahilures caused by seismic activity, erosion, ice or debris flow, 

mudslide, and alluvial fan forces, among others. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 
Elevation on Solid Perimeter 
Foundation Walls 
Flood Protection Elevation (FPE), 
also referred to as the Flood 
Protection Level (FPL), is the 
elevation (height) to which a 
retrofittingmeasureis designed.
Typically, the FPE is a function of 
the expected flood elevation 
(normally the BFE) plus a minimum 
freeboard value of 1.0 foot. 
Elevation on solid perimeter foundation walls is normally used in 
areas of low to moderate water depth and velocity. After the 
structure is raised from its current foundation, the support walls 
can often be extended vertically using materials such as masonry 
block or cast-in-place concrete. The structure is then set 
down on the extended walls. While this may seem to be the 
easiest solution to the problem of flooding, there are several 
imotncnsdrin. 
important considerations. 
Depending on the structure and potential environmental 
loads (such as flood, wind, seismic, and snow), new, larger 
footings may have to be constructed. It may be necessary to 
reinforce both the footings and the walls using steel reinforcing 
bars to provide needed structural stability. 
Deep floodwaters can generate loads great enough to collapse 
the structure regardless of the materials used. Constructing 
solid foundation walls with openings or vents will 
help alleviate the danger by allowing hydrostatic forces to 
be equalized on both sides. For new and substantially damaged 
or improved buildings, openings are required under the NFIP. 
Elevation 
Utilities and electrical 
circuits moved above 
flood level 
Lightweight or mobile items; 
ca be strender the 
house and moved prior to 
flooding 
1R 
' 
e1_ 
:.... Openings on each wall ensure entry of 
a."" : :,.water to equalize hydrostatic pressures 

Figure I-1: Elevation on Solid Perimeter Foundation Walls 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -7 
January 1995 


Chapter I: Introduction to Retrofitting 

Fgr1-:M7ioofEitn

eiconEtneFonainWl 

Figure 1-2: Elevation of Existing Residence on Extended Foundation Walls 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Figure 1-3: Elevation on Piers 

Methods of Retrofitting 

Elevation on Open Foundation 
Systems 

Open foundation systems are vertical structural members that 
support the structure at key points without the support of a 
continuous foundation wall. Open foundation systems 
include piers, posts, columns, and piles. 

ELEVATION ON PIERS 

The most common example of an open foundation is piers, 

which are vertical structural members that are supported entirely 
by reinforced concrete footings. Despite their popularity in 
construction, piers are often the elevation technique least suited 
for withstanding significant horizontal flood forces. In conventional 
use, piers are designed primarily for vertical loading; when 
exposed to flooding, they may also experience horizontal loads 
due to moving floodwater or debris impact forces. Other 
environmental loads, such as seismic loads, can also create 
significant horizontal force. For this reason, piers used in 
retrofitting must not only be substantial enough to support the 
vertical load ofthe structure, but also must be sufficient to resist 
a range of horizontal forces that may occur. 

Piers are generally used in shallow depth flooding conditions 
with low-velocity ice, debris, and water flow potential, and are 
normally constructed of either masonry block or cast-in-place 
concrete. In either case, steel reinforcing should be used for 
both the pier and its support footing. The reinforced elements 
should be tied together to prevent separation. There must also 
be suitable connections between the superstructure and piers to 
resist seismic, wind, and buoyancy forces. 

Engineering Principles and Practices of F RetrofittingFlood-Prone Residential Structures I -9 
January 1995 


Chapter I: Introduction to Retrofitting 

ELEVATION ON POSTS OR COLUMNS 

Elevation on posts or columns is frequently used when flood 

-E H1-

conditions involve moderate depths and velocities. Made of 

wood, steel, or precast reinforced concrete, posts are generally 

square-shaped to permit easy attachment to the house structure. 

However, round posts may also be used. Set in pre-dug holes, 

posts are usually anchored or embedded in concrete pads to 

handle substantial loading requirements. Concrete, earth, gravel, 

a Poet or crushed stone is usually backfllled into the hole and around
the base of the post.

Reinfonce 

Concrete FootingrWhile piers are designed to act as individual support units, posts 
Figure 1-4: Elevation on Posts nomnally must be braced. There are a variety ofbracing techniques 
such as wood knee and cross bracing, steel rods, and 
guy wires. Cost, local flood conditions, loads, the availability of 
building materials, and local construction practices fiequently 
influence which technique is used. 

Columns differ from posts in the
size of their application. Posts are
small columns.

..~~~~~~~

Figure 1-5: Structure Elevated on Posts 

I- 10 Enaineerina Princioles and Practices of Retrofittina Flood-Prona Raeidantial Struicrean 

-I -vo r h.._ ..__Jnr9I 

January 1 995 


Figure 1-6: Elevation on Piles 

Methods of Retrofitting 

ELEVATION ON PILES 

Piles differ from posts in that they are generally driven, orjetted, 
deeper into the ground. As such, they are less susceptible to 
the effects of high-velocity floodwaters, scouring, and debris 
impact. Piles must either rest on a support layer, such as 
bedrock, or be driven deep enough to create enough friction to 
transfer anticipated loads to the surrounding soil. Piles are often 
made of wood, although steel and reinforced precast or prestressed 
concrete are also common in some areas. Similar to 
posts, they may also require bracing. 

Because driving piles generally requires bulky, heavy construction 
machinery, an existing house must normally be moved aside 
and set on cribbing until the operation is complete. The additional 
cost and space needs often preclude the use of piles in 
areas where alternative elevation methods for retrofitting are 
technically feasible. 

Several innovative methods have been developed for setting 
piles. These include jetting exteriorpiles in at an angle using 
high-pressure water flow, and trenching, or auguring, holes for 
interior pile placement. Augured piles utilize a concrete footing 
for anchoring instead of friction forces. This measure requires 
that the existing home be raised several feet above its final 
elevation to allow room for workers to install the piles. 

Fnnineerinn Princinles and Practice s of Retrofittino Flood-Prone Residential Structures I -11 
January 1995 


Chapter I: Introduction to Retrofitting 

LL.5,~~~~~ 

MD..A

3.,A. 

P 

jdli.. .1.._ 

Figure 1-7: Structure Elevated on Piles 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

Tablel-I Advantages and Disadvantages of Elevation 

Advantage. I 

* Ifelevated to the BFE, allows 
for a substantially damaged or 
Improved structure to be brought 
Into complIance with the NFIP 
* Reduces flood risk to the structure 
and its contents 
* Eliminates the need to relocate 
vulnerable items above the flood 
level in the house during conditions 
of flooding 
* Often reduces flood insurance 
premiums 
* Techniques are well-known and 
qualified contractors are often 
readilyavailable 
* Reduces the physical, financial, and 
emotional strain that accompanies 
flood events 
* Does not require the additional land 
that may be needed for floodwalls or 
levees 

Dlsadvantages 

* Cost may be prohibitive 
* The appearance of the structure may 
be adversely affected 
* The structure should not be occupied 
during a flood 
* Access to the structure may be 
adversely affected 
* Not appropriate in areas with high-
velocity water flow, fast-moving ice or 
debris flow, or erosion unless special 
measures are taken 
* Additional costs may be incurred to 
bring the structure up to current 
building codes for plumbing, electrical, 
and energy systems 
* Forces due to wind and seismic 
hazards must be considered 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I-13 
January 1995 


Chapter I: Introduction to Retrofitting 

RELOCATION 

Another retrofitting method is to move the structure to a location 
that is less prone to flooding and flood-related hazards such 
as erosion. This method is commonly referred to in retrofitting 
literature as relocation. The structure may be relocated to 
another portion of the current site or to a different site. The 
surest way to eliminate flood damage to a structure is to remove 
it from the floodplain and relocate it to a flood-free location. 
The procedure normally involves placing the structure on a 
wheeled vehicle. The structure is then transported to a new 
location and set on a new foundation. 

Relocation is an appropriate measure in high hazard areas 
where continued occupancy is unsafe and/or owners want to be 
free from flood worries. It is also a viable option in communities 
that are considering using the resulting open space for more 
appropriate floodplain activities. Relocation may offer an 
alternative to elevation for substantially damaged structures that 
are required under local regulations to meet NFIP requirements. 

.I---1. __ -. 

-I . 

Figure 1-8: Structure Placed on a Wheeled Vehicle for Relocation to a New Site 

1-14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

While similar to elevation, relocation of a structure requires 
additional steps that normally increase the cost ofthis retrofitting 
method. These additional costs include moving the structure, 
purchase and preparation of a new site to receive thestructure 
(with utilities), construction ofanew foundation, and restoration 
ofthe old site. 

Mosttypes and sizes of structures can be relocated either as a 
unit or in segments. One-story wood-frame houses are usually 
the easiest to move, particularly if they are located over a crawl 
space or basement that provides easy access to floor joists. 
Smaller, lighter wood-frame structures may also be lifted with 
ordinary house-moving equipment and often can be moved 
without partitioning. Houses constructed of brick, concrete, or 
masonry are also movable, but usually with more difficulty and 
increased costs. 

Structural relocation professionals should help owners to 
consider many factors in the decision to relocate. The structural 
soundness should be thoroughly checked and arrangements 
should be made for temporary housing and storage of belongings. 
Many states and communities have requirements governing 
the movement of structures in public rights-of-way. 

Figure I-9: Structure to be Relocated 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I-15 
January 1995 


Chapter I: Introduction to Retrofitting 

I 

Table 1-2 Advantages and Disadvantages of Relocation 

Advantages Disadvantages 

* Allows for substantially damaged * Cost may be prohibitive 
or Improved structure to be 
brought Into compliance with the 
NFIP * A new site must be located 
* Significantly reduces flood risk to the * Dispositionof the flood-prone lot 
structure and its contents must be addressed 
* Relocationtechniques are well-known * Additional costs may be incurred to 
and qualified contractors are often bring the structure up to current 
readilyavailable building codes for plumbing, electri

cal, and energy systems 

* Can eliminate the need to purchase 
flood insurance or reduce the
premium

* Reduces the physical, financial, and 
emotional strain that accompanies 
flood events 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

DRYFLOODPROOFING 

Anotherapproachto retrofittingis to seal thatportion of a 
structure below the flood protection level, making that area 
watertight. The objective of this approach is to make the walls 
and other exterior components impermeable to the passage of 
floodwaters. Creating an impervious membrane, such sealant 
systems can include wall coatings, waterproofing compounds, 
impermeable sheeting, or supplemental impermeable wall 
systems, such as cast-in-place concrete. Doors, windows, 
sewer and water lines, and vents are closed with permanent or 
removable shields or valves. 

The expected duration of flooding is extremely critical when 
using sealing systems because seepage can increase overtime, 
Dry floodproofing is not allowed rendering the floodproofing ineffective. Waterproofing comunder 
the NFIP for new and pounds, sheeting, or sheathing may fail or deteriorate if exposed 
substantially damaged or improved 
residential structures to floodwaters for extended periods. Sealant systems are also 
located in a Special Flood Hazard subject to damage (puncture) in areas that experience water 
Area. Additional information on flow ofsignificant velocity, or ice or debris flow. 
dry floodproofing can be obtained 
from FEMA Technical Bulletin 3-Dry floodproofing is usually appropriate only where floodwaters 
93, entitled Non-Residential 

Floodproofing Requirements and are less than three feet deep, since most walls and floors in 
Certification for Buildings residential structures may collapse or buckle under higher water 
Located in Special Flood Hazard levels. Research in this area has been conducted by the U.S. 

Areas in Accordance with the

.N-snathq Army Corps of Engineers and is available in a document entitled 

are also applicable in residential Floodproofing Tests, August 1988. 
situations. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -17 
January 1995 


Chapter I: Introduction to Retrofitting 

~~~~~~~~~~~~~~~~~~~~~~~~Ls 

Backflowvalve i 

Account for sewer and drain backup 
Figure I-10: Dry Floodproofed Structure 

Dry floodproofing is also not recommended for structures with 
a basement. Thesetypes of structurescan be susceptible to 
significant lateral and uplit, or buoyancy, forces. When dry 
Even brick or concrete block walls 
should not be floodproofed above 
a height of three feet (without an 
extensive engineering analysis) 
floodproofing awood-frame superstructure, only buildings 
constructedof concrete block or faced with brick veneer 
should be considered. Weaker construction materials, such as 
wood-frame superstructure with siding, will often fail at much 
due to the danger of structural lower water depths from hydrostatic forces. 
failure from excessive hydrostatic 
and other flood-related forces. 

The designer should consider 
incorporating freeboard into the 
three-foot height constraint as a 
factor of safety against structural 
failure. Other factors of safety 
might include additional pumping 
capacity and stiffened walls. 

I-18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

TableI-3 Advantages and Disadvantages of Dry Floodproofing 

Advantages 

* Reduces the flood risk to the 
structure and contents if the design 
flood level is not exceeded 
* May be less costly than other retrofitting 
measures 
* Does not require the extra land that 
may be needed for floodwalls or 
levees 
* Reduces the physical, financial, and 
emotional strain that accompanies 
flood events 
* Retains the structure in its present 
environment and may avoid significant 
changes in appearance 
Disadvantages 

* Does not satisfy the NFIP requirement 
for bringing substantially 
damaged or Improved residential 
structures Into compliance 
* Requiresongoing maintenance 
* Flood insurance premiums are not 
reducedfor residential structures 
* Usually requireshuman intervention 
and adequate warning time for 
installation of protective measures 
* Measures can fail or be exceeded 
by large floods, in which case the 
effect will be as if there were no 
protection at all 
* If design loads are exceeded, 
walls may collapse, floors may 
buckle, and the structure may even 
float, potentially resulting in more 
damage than just letting the 
house flood 
* The structure should not be occupied 
during a flood 
* Shields are not always aesthetically 
pleasing 
* The damage to the exterior of the 
structure and other property may not 
be reduced 
* May be subject to leakage, which 
could cause damage to the structure 
and its contents 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -19 
January 1995 


n-c 

\Chapter I: Introduction to Retrofitting

L A 

WETFLOODPROOFING 

Another approach to retrofitting involves moding a structure 

to allowfloodwatersto enter itin away thatwillminimize 

damagetothe structureand itscontents. This typeof protec

tion is classified as wet floodproofing. 

Wet floodproofing is often used when all other techniques are 
not technically feasible or are too costly. It is generally appropriate 
if a structure has available space in which to relocate and 

temporarily store damageable items. Utilities and firnaces may 
also needto be relocatedor protectedalongwith othernon-
movable items by using flood-resistant building materials. Wet 

floodproofing may also be appropriate for structures with 
basementsand crawlspacesthat cannotbe protectedtechni-
Wetfloodprooflngisnotallowed cally or cost-effectively by other retrofitting measures. 

under the NFIP for new and 

substantiallydamagedor im- Compared with the more extensive flood protection measures 
provedstructureslocatedin a described in this manual, wet floodproofing is generally the least 
SpecialFlood Hazard Area. Refer . The majorcosts ofthis measure involve the rear-
to FEMA's Technical Bulletin #7

93, entitled Wet Floodproofing rangement ofutility systems, installation of flood-resistant 

Requirements for Structures materials, acquisition of labor and equipment to move items, 
Located in Special Flood Hazard and organization of cleanup when floodwaters recede. Major 
Areas in Accordance with the disruptions to structure occupancy often result during conditions 

.~l? of flooding. 

Wet Floodproofing 

Openingsprovided Lowestfloor 
to~letwaterin =o 

Furnaceandutilities ' I

relocated

are _. s 

Largeappliancesaremoved 
orwrappedinwaterproofbags 

Figure I- 1: Wet Floodproofed Structure 

I-20 Enoineerino Princioles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

Table i-4 Advantages and Disadvantages of Wet Floodproofing 

Advantages 

* No matter how small the effort, wet 
floodproofing can, in many instances, 
reduce flood damageto a building and 
its contents 
* Compared to a dry floodproofing 
measure, loads placed on the walls 
and floors of a building may be 
greatly reduced due to equalized 
hydrostatic pressure 
* Costs for relocating or storing contents 
(except basement contents) 
after a flood warning is issued are 
covered by flood insurance under 
certain conditions 
* Wet floodproofing measuresare often 
less costly than other measures 
* Does not require extra land, which 
may be needed for floodwalls or 
levees 
* Reduces the physical, financial, and 
emotional strain that accompanies 
flood events 
Disadvantages 

* Does not satisfy the NFIP requirement 
for bringing substantially 
damaged or Improved structures 
Into compliance 
* Flood warning is usually needed to 
prepare the building and contents for 
flooding 

* The evacuation of contents from the 
flood-prone area is dependent on 
human intervention 
* The structure will get wet inside, and 
possibly be contaminated by sewage, 
chemicals, and other materials borne 
by floodwaters. Extensive 
cleanup may be necessary 
* The structure should not be occupied 
during a flood 
* The structure may be uninhabitable for 
a time after flooding 
* There may be a need to limit the uses 
of the floodable area of the building 
* There may be some ongoing maintenance 
requirements 
* Additional costs may be incurred to 
bring the structure up to current 
building codes for plumbing, electrical, 
and energy systems 
* To avoid foundation wall collapse, care 
must be taken when pumping out 
basements 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -21 
January 1995 


Chapter I: Introduction to Retrofitting 

FLOODWALLS AND LEVEES 

Another retrofitting approach is the construction of localized 
barriers between the structure and the source offlooding. 
There are two basic types of barriers: levees and floodwalls. 
They can be built to any height but are usually limited to four 
feet for floodwalls and six feet for levees due to cost, aesthetics, 
access, water pressure, and space. Local zoning and building 
codes may also restrict use, size, and location. 

A levee is typically a compacted earthen structure thatblocks 

floodwaters from coming into contact with the structure. To be 

effective over time, levees must be constructed of suitable 

materials (i.e., impervious soils) and with correct side slopes for 

stability. Levees may completely surround the structure or tie to 

high ground at each end. Levees are generally limited to homes 

where floodwaters are less than five feet deep. Otherwise, the 

0

cost and the land area required for such barriers usually make 

46 them impractical for the average owner.
Floodwalls and levees are not
allowed under the NFIP for new Floodwalls are engineered barriers designed to keep floodwa-
and substantially damaged or ters from coming into contact with the structure. Floodwalls
improved structures located in a

SpecialFlood Hazard Area. can be constructed in a wide variety of shapes and sizes but are
typically built of reinforced concrete and/or masonry materials.

Floodwalls and Levees 

r Floodwall is reinforced 

Levee is compacted andanchoredto withstand

fill with 2:1 or 3:1 slope_ __ _ 

hydrostatic

E i,] load 

E_ _ _ f _ 

forsewer 
I and drain backupSumpand pump handleseepage 

. | ~~~Account 

and internaldrainage Bowvalve 

FigureI-12: StructureProtectedbyLevee and Floodwall 

I-22 Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

Figure 1-13: House Protected by a Floodwall 

Generally, residential floodwalls 
are only cost-beneficial at providing 
protection up to four feet and 
levees up to six feet, including one 
foot of freeboard. 

A floodwall can surround an entire structure or, depending 
on the flood levels, site topography, and design preferences, 
it can protect isolated structure openings such as doors, 
windows, or basement entrances. Floodwalls can be designed 
as attractive features to a residence, utilizing decorative 
bricks or blocks, landscaping, and garden areas, or they 
can be designed for utility at a considerable savings in cost. 

Because their cost is usually greater than that of levees, 
floodwalls would normally be considered only on sites that 
are too small to have room for levees or where flood velocities 
may erode earthen levees. Some owners may believe 
that floodwalls are more aesthetically pleasing and allow 
preservation of site features, such as trees. Special design 
considerations must be taken into account when floodwalls 
or levees are used to protect homes with basements because 
they are susceptible to seepage that can result in hydrostatic 
and saturated soil pressure on foundation elements. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -23 
January 1995 


Chapter I: Introduction to Retrofitting 

i k 
The costs of floodwalls and levees can vary greatly, depending 
on height, length, availability of construction materials, labor, 
access closures, and the interior drainage system. A levee 
Provisions for closing access 
openings must be included as part 
could be constructed at a lower cost if the proper fill material is 
available nearby. 
of the floodwall or levee design. 

Figure 1-14: House Protected by a Levee 

I -24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Methods of Retrofitting 

Table I-5 Advantages and Disadvantages of Floodwalls and Levees 

Advantages [ Disadvantages 

* The area around the structure will 
be protected from inundation 
without significant changes to 
the structure 
* There is no pressure from floodwater 
to cause structural damage to the 
home or other structures in the 
protected area 
* These barriers are usually less 
expensive to build than elevating 
or relocating the structure would be 
* Occupants do not have to leave 
the structure during construction 
* Reduces flood risk to the structure 
and its contents 
* Reduces the physical, financial, and 
emotional strain that accompanies 
flood events 
* Does not satisfy the NFIP requirements 
for bringing substantially 
damaged or Improved structures 
Into compliance 
* Levees and floodwalis can fail or be 
overtopped by large floods or floods 
of long duration, in which case the 
effect will be as if there were no 
protection at all 
* May be expensive 
* Both floodwalis and levees need 
periodicmaintenance 
* Interior drainage must be provided 
* Local drainage can be affected, 
possibly resulting in water problems 
for others 
* No reduction in flood insurance rates 
* May restrict access to structure 
* Levees require considerable land 
area 
* Floodwalls and levees do not 
eliminate the need to evacuate 
during floods 
* May require warning time and human 
intervention for closures 
* Floodplain management requirements 
may make floodwalls and 
levees violations of applicable codes 
and/or regulations 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -25 
January 1995 


ChapterI: Introductionto Retrofitting 

GENERAL RETROFITTING CAUTIONS 

Appropriately applied retrofitting measures have several advan

tages over other damage reduction methods. Individual owners 

can undertake retrofitting projects without waiting for govern

ment action to construct flood control projects. Retrofitting 

may also provide protection in areas where large structural 

projects, such as dams or major waterway improvements, are 

not feasible, warranted, or appropriate. Some general cautions 

should always be considered in implementing a retrofitting 

strategy. These include: 

* Substantial damage or improvement requirements under the 
NFIP, local building codes, and floodplain management 
ordinances render some retrofitting measures illegal. 
* Codes, ordinances, and regulations for other restrictions, 
such as setbacks and wetlands, should be observed. 
* Retrofitted structures should not be used nor occupied 
during conditions of flooding. 
* Most retrofitting measures should be designed and constructed 
by experienced professionals (engineers, architects, 
or contractors) to ensure proper consideration of all factors 
influencing effectiveness. 
* Most retrofitting measures cannot be installed and forgotten. 
Maintenance must be performed on a scheduled basis to 
ensure that the retrofitting measures adequately protect the 
structure over time. 
* Floods may exceed the level of protection provided in 
retrofitting measures. In additionto implementing these 
protective measures, owners should consider continuing-
and may be required-to purchase flood insurance. In 
some cases, owners may be required by lending institutions 
to continue flood insurance coverage. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


General Retrofitting Cautions 

* When human intervention is most often needed for successful 
flood protection, a plan of action must be in place and an 
awareness of flood conditions is required. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter I: Introduction to Retrofitting 

RETROFITTING PROCESS 

A good retrofitting project should follow a careful pat of 
exploration, fact finding, analysis, detailed design, and construction 
steps. The successful completion of a retrofitting project 
will require a series of homeowner coordination and design 
input meetings. Ultimately, the homeowner will be living with the 
retrofitting measure, so every effort should be made to incorporate 
the homeowner's concerns and preferences into the final 
product. The primary steps in the overall process are shown in 
Figure I-15 and include: 

HOMEOWNER MOTIVATION 

The decision to consider retrofitting options usually stems from 

having experienced or witnessed a flooding event in or near the 

structure in question; having experienced substantial damage 

from a flood or an event other than a flood; or embarking on a 

substantial improvement, whichrequires adherence to local 

floodplain regulations. The homeowner may contact other 

homeowners, community officials, contractors, or design 

professionals to obtain information on retrofitting techniques, 

available technical and financial assistance, and other possible 

options. 

PARAMETERS OF RETROFITTING 

The goal ofthis step is to conduct the necessary field investiga

tions, regulatory reviews, and preliminary technical evaluations 

to select applicable and technically feasible retrofitting tech

niques that warrant further analysis. 

DETERMINATIONOF HAZARDS 

This step involves the detailed analysis of flood, flood-related, 

and non-flood-related hazards and the evaluation of specific 

sites and structures to be retrofitted. 

I-28 EngineeringPrinciplesand Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Within each of these steps, 
homeowners are involved in 
providing input into the evaluations, 
analyses, decisions, and 
design concepts to ensure that the 
final product meets their requirements. 
Finally, maintenance of the 
constructed retrofitting measure is 
the responsibility of the 
homeowner. 

Retrofitting Process 

BENEFIT/COST ANALYSIS 

This step is critical in the overall ranking of technically feasible 
retrofitting techniques, and it combines an objective economic 
analysis of each retrofitting measure considered with any 
subjective decision factors introduced by the homeowner or 
others. 

DESIGN 

During this phase, specific retrofitting measures are designed, 
construction details developed, cost estimates prepared, and 
construction permits obtained. 

CONSTRUCTION 

Upon final design approvals, a contractor is selected and the 
retrofitting measure is constructed. 

OPERATION AND MAINTENANCE 

The development of a well-conceived operation and maintenance 
plan is critical to the overall success of the project. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -29 
January 1995 


Chapter I: Introduction to Retrofitting

I I 

--Homeowner Motivation 

0~~ Hoeone Coordination

-' 

Parameters of Retrofitting 

; tf 

Determination of Hazards 

{i| 

Benefit Cost Analysis 

7 

NL=W 

Design 

jjl-Construction

.I 

7 -, '----N: -i 

-.U:e-v '" ... :-.:c 

I 

Figure I-15: Primary Steps in the Retrofitting Process 

I -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


* C HAPTERII
i} Alan ',N -"

I I 

REGULATORYFRAMEWORK

Featuring: 

National FloodInsurance Program (NFIP) 
CommunityRegulationsand the Permitting Process 
Model Building Codes 
Code Compatibility with the NFIP 


(000" k 

II 

NATIONAL FLOOD 
INSURANCE PROGRAM 
(NFIP) I 
COMMUNITY REGULATIONS 
AND THE 
PERMITTING PROCESS 
MODEL BUILDING CODES 
I 
CODE COMPATIBILITY 
WITH THE NFIP 
Flood Hazard Information * Building Officials and Code 
Administrators (BOCA) 
Floodplain Management 
Regulations 
* Southern Building Code 
Congress Intemational 
Insurance Program 
(SBCCI) 
* International Council of 
NFIP Flood-Prone Building Code Officials (ICBO) 
Building Performance 
Standards * Council of American Building 
Officials (CABO) 
* National Fire Protection 
Association (NFPA) 

IK

-_WS , mu , _ 

= 

)1 


Chapter II: Regulatory Framework 

Table of Contents 

National Flood Insurance Program (NFIP) .......................................... II -2
Flood Hazard Information .......................................... II -4
RiverineFloodplains.......................................... II -4
Coastal Floodplains ........................................... II -8
ZoneDefinitions.......................................... II-11

........ L 3....................

FloodplainManagementRegulations II-13 

Insurance Program ........................................... II --16
Pre-FIRM Versus Post-FIRM (Insurance Purposes) ........................................... II -17
NFIP Flood-Prone Building Performance Standards ..................................... , IL-18

* Community Regulations and the Permitting Process ..................................... II -19

Model Building Codes ..................................... II -21

CodeCompatibilitywiththeNFIP ..................................... II -23

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures 11.
Inni mrvs 1Qq!r! 


I 

REGULATORY FRAMEWORK 

Most retrofitting projects are regulated by local floodplain, zoning, and building code ordinances. 

In addition to governing the extent and type of activities allowable in the regulatory floodplain, 
these codes set construction standardsthat must be met both by newconstructionand by 
substantial improvement and repair of damaged buildings. The portions of these ordinances 
dealing with retrofitting are generally derived from guidance issued by FEMA under the NFIP 
and the U.S. Army CorpsofEngineers (USACE). 

This chapter discusses thetypical community floodplain management and building code 

environment, including: 

* the role of local officials in a retrofitting project, 
* the various tenets of theNFIP, and 
* the compatibility of items covered in model building codes withtheNFIP. 
Each jurisdiction may adopt standards that are more restrictive than the minimum NFIP requirements, 
but this sectionwill examine only the minimum federal regulations governing construction 
in a Special Flood Hazard Area. Local building codes and construction standards vary widely 
across the country. 

L 

In individual communities, local 

regulations are the mechanism by 

which NFIP requirements are 

enforced. The reader is encour

aged to contact local floodplain 

management and building code
officialsto determine ifmore

restrictive requirements are in 

place. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ,~~~~~I 1-1 
January 1995 


Chapter II: Regulatory Framework 

NATIONAL FLOOD INSURANCE PROGRAM (NFIP) 

The creation ofthe National Flood Insurance Program was a 
major step in the evolution of floodplain management. During 
the 1 960s, Congress became concerned with problems 
relatedto the traditional methods of dealing with flood 
damage. It concluded: 

* Flood protection structures are expensive and cannot 
protect everyone. 
* People are still building in floodplains and therefore are 
risking disaster. 
* Disaster relief is inadequate and expensive. 
* The private insurance industry cannot sell affordable flood 
insurance because only those at significant risk will buy it. 
* Federal flood control programs are funded by all taxpayers, 
but they primarily help only those who live in the floodplains. 
In 1968,Congresspassed theNational Flood Insurance Act to 

correct some ofthe shortcomings ofthe traditional flood control 

and flood reliefprograms. The Act created the National Flood 

Insurance Program (NFIP) to: 

* Guide future development away from flood hazard areas; 
* Require that new and substantially improved buildings be 
constructed to resist flood damage; 
* Provide floodplain residents and owners with financial 
assistance after floods, especially after smaller floods that 
donot warrant federaldisasteraid; and 
* Transfer some of the costs of flood losses from the taxpayers 
to floodplain property owners through flood insurance 
premiums. 

Enainearina Princinlas and Practices of RPstrnfittint, Flodnr-Pronsa PRsiantial Stritire-
January 1995 


National Flood Insurance Program (NFIP) 

Congressoriginallycharged the Departmentof Housing and 
Urban Development's (HUD's) Federal Insurance Administration 
(FIA) with responsibility for the program. In 1979, the FIA 
and the NFIP were transferred to the newly created Federal 
Emergency Management Agency (FEMA). 

Currently, the floodplain management aspects ofthe program 
are administered by the Mitigation Directorate and the insurance 
aspects are administered by the Federal Insurance Administration, 
both parts of FEMA. 

=nminagrinn PrinnirIae anrd Prantirp S nf.Rptrnfittinn Flood-Prone Residential Structures HI-3 

_ ,W~fi,.vs

Ja hymnuarv ., .my1995, -, , . -____.............. . .. 

January 1995 


Chapter II: Regulatory Framework 

L w Jg| FLOOD HAZARD INFORMATION 

Communities that participate in the NFIP's Regular Program 
typically have a detailed Flood Insurance Study (FIS), which 
presents flood elevations of varying intensity, including the base 

V, (100-year) flood, areas inundated by the various magnitudes of 
FEMA has developed a home flooding, and floodway boundaries. Thisinformation is pre-
study course on how to use a sented on a Flood Insurance Rate Map (FIRM) and on a 

Flood InsuranceStudy (FIS). Flood Boundaryand FloodwayMap (FBFM). 

Contact your local FEMA regional 

office (telephone numbers listed in 

Appendix C)for furtherinforma-Riverine Floodplains 

tion. 

The FIS report for riverine floodplains describes in detail how 

the flood hazard information-including floodways, discharges, 

velocities, and flood profiles for major riverine areas-was 

developed for each community. 

The area ofthe 100-year riverine floodplain is often divided into 
a floodway and a floodway fringe. The floodway is the channel 
of a watercourse plus any adjacent floodplain areas that must 
be kept free of encroachment so that the cumulative effect of 
the proposed encroachment, when combined with all other 
existing or proposed encroachments, will not increase the 100year 
flood elevation more than one foot at any point within the 
community. 

The area between the floodway and 1 00-year floodplain 

boundaries is termed the floodway fringe. The floodway fringe 

encompasses the portion of the floodplain that could be com

pletely obstructed without increasing the water-surface elevation 

of the 1 00-year flood by more than one foot at any point. 

Many states and communities limit the allowable increase to 

lessthan one foot. 

Enoinesrinn Prinnin~ls and Practicepq nf RPtrnfittinn Flonrd-PrnenPnirantin .QI ttri ti+ra.

--a a s 1 -Ie a m --*1 I I ---I1995 J n a

-<sivl * 

January 1 995 


National Flood Insurance Program (NFIP) 

|!a LIMIT OF FLOODPLAINFOR UNENCROACHED 100-YEARFLOOD 

GROUND SURFACE 

AREA OF ALLOWABLEFLOELAIN 

ENCROACHMENTRAER4G

OROW SURFAdE ECOAWN

WILLSEO

N OTCAUSE A SURCHARGE ON FLOODPLAIN 

THAT EXCEEDS THE
INDICATEDSTANDARDS

LINEA -E15 THE FLOOD, ELEVATIONBEFOREENCROACHMENT
LINE C -D IS THE FLOOD ELEVATION AFTER ENCROACHMENT

SURCHARGENOT TO EXCEED 1. FOOTFEDERAL MANAGEMENT RE UIEMENTI ONLEUR HEIGHT SPECID

EMERGENCY AGENCY r By STATE. 

Figure I1-1: Typical Floodplain Cross Section 

Discharges are determined for various locations and flood 
frequencies along the stream and are presented in a summary 
table in the FIS report, as shown in Table II-1. Flood profiles 
depict various flood frequency and channel bottom elevations 
along each studied stream. Figure 11-2 illustrates a flood profile 
included in a typical FIS. For most streams with significant 
flood hazards, the FIS for riverine floodplains normally contains 
discharges and water-surface elevations for the 10-, 50-, 100-, 
and 500-year floods, which have annual exceedence probabilities 
of 10%, 2%, 1%, and 0.2%, respectively. 

Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures II -5 
January 1995 


Chapter II: Regulatory Framework 

Table1-I Typical Summary of Discharges Table 

Drainage 
Flooding Source and Location Area Peak Discharges(CFS) 
(Sq. Mi.) 10-Yr 50-Yr 100-Yr 500-Yr 

Overpeck Creek 

* Upstream of the confluence 8.1 910 1,310 1,490 1,960 
of Flat Rock Brook 
* Upstream of the confluence 5.7 760 1,090 1,200 1,600 
of Tributary to Overpeck Creek 
* Upstream of the confluence of 3.0 530 750 830 1,100 
MetzlersCreek 
Tributary to OverpeckCreek 

* At its confluence with Overpeck 1.0 275 445 545 810 
Creek 
Metzlers Creek 

* At its confluence with Overpeck 2.4 453 625 704 995 
Creek 
FlatRock Brook 

* At its confluence with Overpeck 2.5 665 1,075 1,315 1,980 
Creek 
11-6 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures 
January 1995 


:3 (a-. 
CD m3 
I~rl 
f' 
(0 CC 
-
0 
-U ~io 
a/) 125 
MD 
0. _. 
CD 00 
CD 
CD 
C)0 
0 
-14 
120 
CDW 
CD 
0 
CD 
W z 
'a 
-n0 
0 
0~ 
0 
0-
a 
(D 
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C 
0 
115 
15a) 
>L 
CD0) 
110 
CL 
CD 
_. 
C 105 
0cC) 
CD 
CD 
7.5 7.6 7.7 7.8 7.9 8.0 
Stream Distance in Thousands of Feet above Confluence with Overpeck Creek 
.1 

z 

5. 
In

0

0 

0. 
5. 
CA 
0) 

SD
O

0 
I0 

Q 

Z1
M

3 

I 


ChapterII: Regulatory Framework 

Coastal Floodplains 

In coastal communities that contain both riverine and coastal 
floodplains, the FIS may contain information on both coastal 
and riverine hazards. These analyses include the determination 
ofthe storm surge stillwater elevations forthe 10-, 50-, 100-. 
and 500- year floods as shown in Table 11-2. 

Tablell-2 Typical Summary of Coastal Stillwater Elevations 

Elevation (feet) Above NGVD
Floodina Source and Location 10-Yr 50-Yr 100-Yr 500-Yr

ATLANTIC OCEAN 

Entire shoreline within Floodport 8.2 8.9 9.2 9.8 

MERRIMACK RIVER
Entire shoreline within Floodport 59 7.2 8.2 8.9

These stillwaterelevationsrepresentthepotential flood eleva

tions from tropical storms (hurricanes and typhoons), extra

tropical storms (northeasters), tsunamis, or a combination of 

any ofthese events. The FIS wave analysis includes an 

estimate of the expected beach and dune erosion during the 

1 00-year flood and the increased flood hazards from wave 

heights and wave runup. 

The increases from wave heights and runup are added to the 
stillwater elevations to yield the regulatory base flood elevation. 

This manual doesnotcover Figure II-3illustrates the typical wave height transect showing 

design issues in CoastalHigh the effects of physical features on thewave heights and corre-

Hazard Areas (V Zones). sponding base flood elevation. 

11-8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


National Flood Insurance Program (NFIP) 

V ZONE _ A ZONE
WAVE HEIGHT GREATERTHAN3IT. iEW lHEIGHTLETo THU 3T.

00tE 0_~ CR 0rra 

II I I I i 
1 g ! ! ! !

v"mm "M-_ 

Figure 11-3: Typical Wave Height Transect 

A FIRM generally shows areas inundated during a 1 00-year 
flood as either A Zones or V Zones. An example of a FIRM 
for riverine flooding is shown in Figure 11-4, while a FIRM for 
coastal flooding is shown in Figure II-5. Retrofitting designers 
may use data from FIS materials to determine floodplain limits, 
flood depth, flood elevation, and flood frequency. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 11-9 
January 1995 


Chapter II: Regulatory Framework 

Figure 11-4:Typical FIRM for Riverine Flooding 

ZONE AE 
(EL 7) 

Figure 11-5: Typical FIRM for Coastal Flooding 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


National Flood Insurance Program (NFIP) 

FEMA is in the process of 
converting from use of the 
National Geodetic Vertical Datum 
(NGVD) to the North American 
Vertical Datum (NAVD). Both 
datum references will be in use 
until the transition is completed. 

Zone Definitions 

A Zones: are the Special Flood Hazard Areas (except 

coastal V Zones) shown on a community's FIRM. 
There are six types of A Zones: 

A SFHA where no base flood elevation is provided. 

A#: (Numbered A Zones; e.g., A7 or A14) SFHA 
where the FIRM shows a base flood elevation in 
relation to National Geodetic Vertical Datum 
(NGVD) or North American Vertical Datum 
(NAVD). 

AE: SFHA where base flood elevations are provided. 
AE Zone delineationsare used on newFIRMs 
instead of A# Zones. 

AO: SFHA with sheet flow, ponding, or shallow flooding. 
Base flood depths (feet above grade) are 
provided. 

AH: Shallow flooding SFHA. Base flood elevations in 
relation to NGVD or NAVD are provided. 

AR Area of special flood hazard that results from the 
decertification of a previously accredited flood 
protection system that is determined to be in the 
process of being restoredto provide a 1 00-year or 
greater level of flood protection. 

B Zones: Areas of moderate flood hazard, usually depicted 
onFIRMs as betweenthe limits of the base 
and 500-yearfloods. B Zones are also used to 
designate base floodplains of little hazard, such as 
those with average depths of less than one foot. 

Pnninaarinn Prinninip and Practircs of Ratrofittina Flood-Prone Residential Structures II -11 
January 1995 


Chapter II: Regulatory Framework 

C Zones: Areas of minimal flood hazard, usually depicted 
on FIRMs as above the 500-year flood level. B 
and C Zones may have flooding that does not 
meet the criteria to be mapped as a Special 
Flood Hazard Area, such as ponding and local 
drainage problems. 

D Zones: Areas of undetermined but possible flood 
hazard. 

V Zones: Special Flood Hazard Areas subject to coastal 
high hazard flooding. There are three types of 
V Zones, which correspond to the A Zone 
designations: 

V: SFHA where no base flood elevation is provided. 
V#: (Numbered V Zones; e.g.,V7 orV14) SFHA
where the FIRM shows a base flood elevation in
relation to NGVD orNAVD.

0 

YE: SFHA where base flood elevations are provided.
VE Zone delineations are now used on new FIRMs
instead of V# Zones.

XZones: appear on newer FIRMs and incorporate areas 
previously shown as B and C Zones. 

11- 12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


National Flood Insurance Program (NFIP) 

FLOODPLAINMANAGEMENT 
REGULATIONS 

The floodplain management aspects of the NFIP are implemented 
by communities. A "community" is a governmental 
body with the statutory authority to enact and enforce development 
regulations. The authority of each unit of government 
varies by state. Eligible communities can include cities, 
villages, towns, townships, counties, parishes, states, and Indian 
tribes. In 1994, more than 18,350 communities participated in 
theNFIP. 

To participate in the NFIP, communities must, at a minimum, 
regulate development in their floodplains in accordance with the 
NFIP criteria and state regulations. To do this, communities 
must require a permit before any development proceeds in the 
regulatory floodplain. Before the permit is issued, the community 
must ensure that two basic criteria are met: 

* All new buildings and substantial improvements to existing 
buildings will be protected from damage by the base flood, 
and 
* New floodplain development will not aggravate existing 
flood problems or increase damage to other properties. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures It -13 
January1995 


Chapter II: 

Regulatory Framework 

Several definitions are needed to guide the designer through 
floodplain management regulations. The NFIP definition of key 
terms is provided below: 

Structure: For floodplain management purposes, a walled and 
roofed building, including a gas or liquid storage 
tank that is principally above ground, as well as 
a manufactured home. 

Basement: Any area ofthe structure having its floor subgrade 
(below ground level) on all sides. 

Lowest Floor: The lowest floor ofthe lowest enclosed area 
(including basement). An unfinished or flood-
resistant enclosure, usable solely for parking, 
building access, or storage in an area other than a 
basement is not considered a building's lowest 
floor, provided that such enclosure is not built so 
as to render the structure in violation of the 
applicable non-elevation design requirement of 44 
Code of Federal Regulations (CFR) Ch. 1 (60.3). 

Enclosed Area Below BFE: An unfinished or flood-resistant 
enclosure, usable solely for parking, building 
access, or storage in an area other than a basement 
that has an elevation below the BFE. 

Substantial Damage: Damage of any origin sustained by a 
structure whereby the cost of restoring the structure 
to its before-damaged condition would equal or 
exceed 50 percent ofthe value of the structure 
before the damage occurred. 

Substantial Improvement: Any reconstruction, rehabilitation, 
addition, or other improvement of a structure, the 
cost of which equals or exceeds 50 percent of the 
value of the structure before the "start of construction" 
ofthe improvement. This term includes 
structures that have incurred "substantial damage," 
regardless of the actual repair work performed. 
The term does not, however, include either: 

II -14 Enaineerina Principles and Practices of Retrofitting Flood-ProneResidential Structures 
January 1995 


adA 

The definitions of pre-FIRM and 
post-FIRM are different for 
insurance and floodplain management 
purposes. 

National Flood Insurance Program (NFIP) 

1. any project to correct existing violations of state 
or local health, sanitary, or safety code specifications 
that have been previously identified by 
the local code enforcement official and that are 
the minimum necessary to assure safe living 
conditions, or 
2. any alteration of a "historic structure," provided 
that the alteration will not preclude the 
structure's continued designation as a"historic 
structure." 
Pre FIRM: A pre-FIRM building (for floodplain management 
purposes) is a building for which the start of construction 
occurred before the effective date of the 
community's NFIP-compliant floodplain manage

mentordinance. 

Post-FIRM:Apost-FIRM building (for floodplain management 
purposes) is a building for which thestart of 
construction post-dates the effective date ofthe 
community's NFIP-compliant floodplain management 
ordinance. 

Under NFIP criteria, all new (post-FIRM) and substantially 
damaged/substantially improved construction of residential 
structureslocatedwithinZones Al -A30, AE, and AH must 
have the lowest floor at or above the BFE. Therefore, elevation 
and relocation are the retrofitting alternatives that enable a post-
FIRM or substantially damaged/substantially improved structure 
to be brought into compliance with the NFIP. 

Utilizing the aforementioned definitions and local codes, the 
designer can begin to determine which retrofitting measures may 
be acceptable for each specific home. 

Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures II -15 
January 1995 


Chapter II: 

Regulatory Framework 

INSURANCE PROGRAM 

Federally-backed flood insurance is made available in 
communities that agree to implement NFIP-compliant floodplain 
management programs that regulate future floodplain development. 
Communities apply to participate in the program in order 
to make flood insurance and certain forms of federal disaster 
assistance available intheir community. 

Everyone in a participating community can purchase flood 
insurance coverage, even for properties not located in mapped 
floodplains. Insurance provides relief for all floods, including 
those that are not big enough to warrant federal disaster aid, 
as long as a general condition of flooding exists. 

The federal government makes flood insurance available 
only in communities that adopt and enforce floodplain 
management regulations that meet or exceed NFIP criteria. 
Because the communities will ensure that future development 
will be resistant to flood damage, the federal government 
is willing to support insurance and help make it affordable. 

The Flood Disaster Protection Act of 1973 expanded the 
program to require flood insurance coverage as a condition of 
federal aid or loans from federally-insured banks and savings 
and loans for buildings located in identified flood hazard areas. 
Most communitiesjoined the NFIP after 1973 in order to make 
this assistance available for their flood-prone properties. 

NFIP flood insurance is available through many private flood 

insurance companies and independent agents, as well as directly 

from the federal government. All companies offer identical 

coverage and rates as prescribed by the NFIP. 

II -16 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


National Flood Insurance Program (NFIP) 

Pre-FIRMVersus Post-FIRM 
(Insurance Purposes) 

For flood insurance rating purposes, residential buildings are 
classified as being either pre-FIRM or post-FIRM. 
Please refer to Appendix A-The 
National Flood Insurance Pre-FIRM construction is defined as construction or substantial 
Program-for generalinformation improvement begun on or before December 31, 1974, or 
and an example of the costs of before the effective date ofthe community's initial FIRM, 
insurance coverage for structures weve is later. 
subject to various flooding whichever is later. 
scenarios. 
Post-FIRM construction includes construction or substantial 
improvementthat began after December31, 1974, or on or 
after the effective date of the community's initial FIRM, whichever 
is later. 
Insurance rates for pre-FIRM buildings are set on a subsidized 
basis; while insurance rates for post-FIRM structures are set 
actuarially on the basis of designated flood hazard zones on the 
community's FIRM and the elevation of the lowest floor of 
the building in relation to the BFE. This rate structure provides 
owners an incentive to elevate buildings in exchange for receiving 
the financial benefits of lower insurance rates. Subsequent 
to substantial improvements, apre-FIRM building may retain its 
pre-FIRMrate or become a post-FIRM building for flood 
insurancerating purposes. Only elevation or relocation techniques 
may result in reduced flood insurance premiums or in 
eliminating the need for flood insurance. 

EnaineerinaPrinciples and Practicesof Retrofittina Flood-ProneResidential Structures II -17 
January 1995 


Chapter II: Regulatory Framework 

sNFIP BUILDING

_9 FLOOD-PRONE 

PERFORMANCE STANDARDS 

The NFIP has established minimum criteria and design perfor-
ea mance standards that communities participating in the NFIP 
10-OV IM must enforce for structures located in Special Flood Hazard 
Areas. These standards specify how a structure should be 
Communities often adopt flood- constructed in order to minimize or eliminate the potential for 
plain regulations that exceed the flood damage. 
NFIP minimum requirements. 

FEMA, the U.S. Army Corps of Engineers (USACE), the 
Tennessee Valley Authority (TVA), the Natural Resources 
Conservation Service (NRCS), and several states and local 
government entities have developed technical guidance manuals 
and information for public distribution to assist in the application 
ofthese requirements by the building community (i.e., building 
code and zoning officials, engineers, architects, builders, developers, 
and the general public). These publications, which are 
listedin Appendix C, GlossaryofResources, contain guidelines 
for the use of certain techniques and materials for design 
and construction that meet the intent ofthe NFIP 's general 
design criteria. These publications also contain information on 
the generally accepted practices for flood-resistant design and 
construction. 

FEMA has also undertaken a multi-year effort to incorporate 
the NFIP flood-damage-resistant design standards into the 
nation's model building codes and standards, which are then 
adopted by either states or communities. This effort has yielded 
the Code Compatibility Report, which examines the compatibility 
ofNFIP regulations, technical standards, and guidance 
with the model building codes/standards. 

II -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Community Regulations and the Permitting Process 

COMMUNITY REGULATIONS AND THE PERMITTING

PROCESS 

Regulation ofthe use of floodplain lands is a responsibility of 
state and local governments and, in limited applications, the 
federal government (wetlands, navigable waterways, federal 
lands, etc.). It can be accomplished by a variety of procedures, 
such as establishment of designated floodways and encroachment 
lines, zoning ordinances, subdivision regulations, special 

The floodway is the channel of a use permits, floodplain ordinances, and building codes. These 

river or other watercourse and the land-use controls are intended to reduce or eliminate flood 

adjacent land areas that must be 

reserved in order to discharge the damage by guiding and regulating floodplaindevelopment. 

base flood without cumulatively 

increasingthe water surface As was explained in ChapterI, flood-prone communities that 

elevation more than a designated participate in the NFIP are required to adopt and enforce, at a 
height. minimum, NFIP-compliant floodplain regulations to qualify for 

many forms of federal disaster assistance and for the availability 
of flood insurance. 

Many states and communities have more restrictive requirements 
than those established by the NFIP. In fact, state and 
community officials, using knowledge of local conditions and in 
the interest of safety, may set higher standards, the most common 
of which are listed below. 

* Freeboard is the elevation difference between the flood 
protection elevation and the anticipated flood elevation. 
Freeboard requirements provide an extra measure of flood 
protection above the design flood elevation to account for 
waves, debris, hydraulic surge, or insufficient flooding data. 
* Restrictive standards prohibit building in certain areas, such 
as the floodplain, conservation zones, and the floodway. 
* The use of building materials and practices that have 
previously proven ineffective during flooding may be 
prohibited. 
Ennineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures II -19 
January 1995 


Chapter II: Regulatory Framework 

Before committing a significant investment oftime and 
money in retrofitting, the design professional should contact 
the local building official for building code and floodplain 
management requirements and information on obtaining necessary 
permits. 

II-20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Model Building Codes 

MODEL BUILDING CODES

Several model codes and standards have been developed over 
a period of years under the auspices of various organizations. 
The most widely accepted model codes are: 

National Building Code: developed by the Building Officials 
and Code Administrators (BOCA), generally 
adopted by eastern and midwestern states; 

Standard Building Code: developed by the Southern Building 
Code Congress International (SBCCI), generally 
adopted by southern states; 

Uniform Building Code: developed by the International 
Council of Building Officials (ICBO), generally 
adopted by western states; 

One- and Two-Family Dwelling Codes: developed by the 
Council of American Building Officials (CABO), 
used for residential structures in various parts ofthe 
country; and 

NFPA Life Safety Codes: developed by the National Fire 
Protection Association (NFPA), used as a standard 
for fire protection in various parts of the country. 

Documents for each of the above codes follow standardized 
formats for content and references. Most model code groups 
also maintain product material evaluation reports, which contain 
specific testing information on a variety of building products. 

EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures H -21 
January 1995 


Chapter II: Regulatory Framework 

Table 1-3 Model Code Groups 

National Codes (BOCA): * BOCA National Building Code 

* BOCA National Fire PreventionCode 
* BOCA National Mechanical Code 
* BOCA National Plumbing Code 
* BOCA Property Maintenance Code 
StandardCodes (SBCCI): * Standard BuildingCode 

* Standard forFloodplainManagement 
* Standard MechanicalCode 
* Standard Gas Code 
* Standard PlumbingCode 
* Standard ExistingBuildingCode 
* Standard HousingCode 
* Standard Fire Prevention Code 
Uniform Codes (ICBO) * Uniform Building Code 

* UniformMechanical Code 
* International Plumbing Code 
* Uniform Fire Code 
* Uniform Housing Code 
NFPAStandards: * NFPA 101 -Life Safety Code 

* NFPA 70 -National Electrical Code 
* NFPA54 -National Fuel Gas Code 
* NFPA 58 -Standard for the Storage and 
Handling of Liquefied Petroleum Gases 
CABO One-and TWo-* CABO One-and Two-Family Dwelling Code 

Family Dwelling Code: 

Most communities have adopted model codes from one of 
these groups. Many of these codes have incorporated provi.
0-140 sions ofthe NFIP floodplain management regulations pertaining 
to building standards. 

States and local governments 

often make their own amend-FEMA is working closely with the model building code groups 

ments to the above codes. to ensurethatNFIP requirementswillbe accessible,credible, 

and easierto use and enforce by the building community. This 
ongoing effort is aimed at placing as many of the NFIP floodplain 
management requirements as possible into the model 
building codes. For more information on the model building 
codes, contact the local building and permitting officials or refer 
to the model code groups. 

I1 -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Code Compatibility with the NFIP 

CODE COMPATIBILITY WITH THE NFIP

Given the variation in Istandards 

between model building codes, it 
is very important that the designer 
contact a local building official to 
ascertain any building code and/ 
or floodplain management 
requirements that would be 
unique to the specific retrofitting 
project or local jurisdiction. 

Designers should consult FEMA's 
Code Compatibility Report to gain 
a thorough understanding of how 
differences in NFIP standards and 
other codes affect the model code 
in use in a given community. The 
designer is responsible for 
determining a feasible resolution 
to these differences; it is recommended 
that designers obtain 
concurrence from local officials. 

Undercontract to FEMA, in 1992 the National Institute of 
Building Sciences (NIBS) consulted on an examination ofthe 
compatibilities between the NFIP regulations and technical 

guidance to the model codes. A report of this study-FEMA's 
CodeCompatibilityReport-provided a basis for coordinating 
NFIP documents with the model codes. It also represents a 
starting point for the preparation of a consensus flood-resistant 
constructionstandard. 

Table II-4 presents the general items that need to be reconciled 
between the model codes and NFIP requirements. Refer to the 
Code Compatibility Report for conflict resolution or the individual 
code documents for additional information. 

FnninAerinnPrinninlpqand Practirca nf Ratrofiftinn Flood-Prona Raeidantial Structuras II -23 
January 1995 


Chapter II: Regulatory Framework 

Table1-4 MODEL CODES/NFIP REQUIREMENTS: Items to be Reconciled 

ITEMS TO BE RECONCILED WITH THE NFIP BOCO SBCCI ICBO NFPA CABO 

Use of Registered Professionals X X 
Wind, Seismic & Snow Loads X X X X 
Footing & Slab Design X X X 
Standards for Use of Wood Materials X X X X 
Geotechnical Reports and Requirements for Open X X X X 
Foundations 
Corrosion Protection X X X 
Hydrostatic and Hydrodynamic Load Considerations 
and Computations X 
Occupancy in Basements Below the BFE X X X 
Consistency of Criteria for Residential and X 
Non-Residential Buildings X 
Anchorage Requirements X 

Exposed Ductwork X 

Utility Clearances X 
Standards for Sealants X 

Standards for Breakaway Walls X 
Design Tables Based on Materials X 

Design Considerations for Floodwalls X 
Protection of Electrical Systems Below the BFE X 
Grounded and Labeled Power Outlets for Pumps and X 
Motors 
Maintenance of Interior Finishes for Different 
Occupancies _ 
Complete Flood Design Criteria X X 
Alternate Forms or Means of Construction X 
Site Preparation Requirements X 

X 
Walls, Floor & Roof Sheathing Design X X X X X 

Vapor Barrier Requirements 

S 

X=ltem that must be reconciled between model codes and NFIR 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


CHAPTERIII

_ _ g 1 0 S o 8 1~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PARAMETERS 
OF RETROFITTING 

Featuring: 

Examination of Owner Preferences 
Community Regulations and Permitting 
Technical Parameters 


DPARAMETERS OF RETROFITTING 

K1~ 

EXAMINATION OF
OWNER PREFERENCES

Initial Homeowner
Meetina

Initial Site Visit

Aesthetic Concerns

Economic Considerations

Risk Considerations 

Accessibility 

COMMUNITY REGULATIONSI AND PERMITTING 

LocalCodes 

Building Systemsl 

Code Upgrades 

Offsite Flooding Impacts 

TECHNICAL
PARAMETERS

Flooding Characteristics 

Site Characteristics 

Building Characteristics 

Historic Preservation 

Multiple Hazards 

0 


Chapter III: Parameters of Retrofitting 

Table of Contents 

Examination of Owner Preferences........................... III -2
The Initial Homeowner Meeting ........................... III -5
The Homeowner Learns: ........................... III -5
The Designer Learns: ........................... III -5
Initial Site Visit ........................... III -7
Aesthetic Concerns........................... III -9
Economic Considerations........................... III -9
Risk Considerations ........................... III -14
Accessibility for the Disabled ........................... III -15

Community Regulations and Permitting ........................... III -16
Local Codes ........................... III -16
Building Systems/CodeUpgrades ........................... III -16
Offsite Flooding Impacts ........................... III -17

TechnicalParameters ........................... III -18
Flooding Characteristics ........................... III -21
Flood Depth ........................... III -21
FloodVelocity ........................... III -24
Onset of Flooding ........................... III -25
Flood Duration ........................... III -25
Site Characteristics ........................... III -26
Site Location ........................... III -26
Soil Type ........................... III -27
Building Characteristics ........................... III -28
Substructure........................... III -28
Superstructure ........................... III -29
Support Services ........................... III -29
Building Construction ........................... III -31
BuildingCondition ........................... III -32

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures HI January 
1995 


Balancing Historic Preservation Interests with Flood Protection .............................. III -35
Multiple Hazards .III -36

Flood-Related....a.a..s.......................................................................................... II-3

Flood-Related Hazards .................. III -37
Non-Flood-Related Hazards .. ....... III -38

: .0

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


PARAMETERS OF RETROFITTING 

In this chapter, the factorsthat influence retrofitting decisions areexamined and compared 

with various methods to determine the viability of specific retrofitting techniques. These 

factors include: 

* homeownerpreferences, 
* community regulations and permitting requirements, and 
* technical parameters. 
Factors such as homeowner preference and technical parameters are key elements in identifying 
appropriate retrofitting measures, while consideration ofthe multiple flood-related and non-
flood-related hazards is critical in designing the retrofitting measure and/or avoiding the selection 
of a poor retrofitting method. 

This selection of alternatives can be streamlined through the use oftwo generic retrofitting 

matrices, which are designed to help the designer narrow the range offloodproofing options: 

PreliminaryFloodproofing/ Retrofitting PreferenceMatrix(FigureIII-1),which focuses 
on factors that influence homeowner preference and those measures allowable under local 
regulations. 

Retrofitting Screening Matrix (Figure III-3), which focuses on the objective physical factors 
that influence the selection of appropriate retrofitting techniques. 

Rninorn I II Drin,.rqi -Sndi DratjtirogQ nf Ratrnfiftinn Flood-Prnne Residential Structures III-1 

Jauy-11VI I. alla .1995 . . 

January 1 995 


Chapter III: Parameters of Retrofitting 

EXAMINATION OF OWNER PREFERENCES

The proper evaluation of retrofitting parameters will require a 
series of homeowner coordination and design input meetings. 
Ultimately the homeowner will have to deal with the flood protection 
environment on a daily basis. Therefore, the functional and 
cosmetic aspects ofthe retrofitting measure, such as access, 
egress, landscaping, appearance, etc., need to be developed by 
including the homeowner's thoughts and ideas. Most retrofitting 
measures are permanent and should be considered similar to a 
major home addition or renovation project. The design should 
incorporate the concepts of those who will be using the retrofitted 
structure. 

Issues that should be addressed include: 

* retrofitting aesthetics, 
* economic considerations, 
* risk considerations, 
* accessibility, 
* local code requirements, 
* building mechanical/electrical/plumbingsystem upgrades, 
and 
* offsite flooding impacts. 

In order to avoid any future 
misunderstandings, designers 

should use their skills and knowledge 
of retrofitting projects to 
address technical implications 
while working with homeowners. 
Many owners have little or no 
technical knowledgeof retrofitting 
and naturally look to the designer 
or local official for guidance and 
expert advice. 

I11-2 Enaineerina Principles and Practices of Retrofittina Flood-Prone ResidAntial Strutinuire 

__- .-i, -J ry1995

January 1995 


Examination of Owner Preferences 

The Preliminary Floodproofing/Retrofitting Preference 
Matrix,(FigureII-1), assiststhe designerin 
documenting the initial consultation with the homeowner. 

The first consideration, measure allowed by community, 
enables the designer to screen alternatives that are not 
permissible and must be eliminated from further consideration. 
Discussion of the considerations for the 
remaining measures should lead to a "no" or "yes" for 
each of the boxes. Examination ofthe responses will 
help the homeowner and designer select retrofitting 
measures for further examination that are both viable 
and preferable to the owner. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 111-3 
January 1995 


Chapter Hi: Parameters of Retrofitting

Owner Name: Prepared By:
Address: Date:
Property Location:,

\Floodproofing riM 2 rfI
Measures

D__ a S

Elevation Elevation Elevation Elevation Elevation Relocatior Dry Flood-Wet Flood-Floodwalls 
on on Fill on Plers on Posts on Piles proofing prooling and 
Foundation and Levees 

Considerations Walls Columns 

MeasureAllowed or 

Owner Requirement 

Aesthetic Concerns 

High Cost Concerns 

Risk Concerns 

Accessibility Concerns 

Code Required 

Upgrade Concerns 

Off-SilteFlooding Concerns 

TotalIRes= 

Instructions: Determine whether or not floodproofing measure is allowed under local regulations or 
homeowner requirement. Put an Yx"in the box for each measure which is not allowed. 
Complete the matrix for only those measures that are allowable (no Y in the first row). For 
those measures allowable or owner required, evaluate the considerations to determine if 
the homeowner has concerns which would impact its implementation. A concern is defined 
as a homeowner issue which if unresolved would makethe retrofitting method(s) infeasible. 

If the homeowner has a concem, place an Y in the box under the appropriate 
measure/consideration. Total the number of '1x's.' The floodproofing measure with the least 
number of "x's" is the most preferred. 

Figure II-1: PreliminaryFloodproofing/RetrofittingPreferenceMatrix 

m-4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Examination of Owner Preferences 

THE INITIAL HOMEOWNER MEETING 

The first step in the homeowner coordination effort is the 
educational process for both the designer and the property 
owner. This step is a very important one. 

The Homeowner Learns: 

* How it was determined that the home is in the floodplain; 
* Possible impacts of an actual flood; 
* Benefits offlood insurance; 
* Physical, economic, and risk considerations, and 
* What to expect during each step in the retrofitting process. 
The Designer Learns: 

* Floodhistoryofthe structure; 
* Homeowner preferences; 
* Financial considerations; 
* Special issues, such as accessibility requirements for the 
disabled, and 
* Informationaboutthe subjectproperty suchas: 
-topographic surveys, 
-site utility information, and 
-critical home dimensions. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter III: Parameters of Retrofitting 

During this initial meeting, the designer and homeowner should 
jointly conduct a preliminary assessment ofthe property to 
determine which portions ofthe structure require flood protection 
and the general condition ofthe structure. This initial 
evaluation will identify the elevation of the lowest floor and the 
elevation of potential openings throughout the structure through 
which floodwaters may enter the residence. 

111-6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


The evaluation of information 
obtained during the initial meeting 
with the homeowner will help the 

designer and owner address the 
flood threat to the entire structure 
and the vulnerability of specific 

openings to floodwater intrusion. 

'000%0 

Sometimes it is necessary for a 

field survey to be conducted by a 

professional land surveyor before 

design documents are developed. 

However, frequently the 

homeowner and designer may be 

able to develop a rough elevation 

relationship between the expected 

flood elevation, the elevation of 

the lowest floor, and the low points 

of entry to the structure sufficient 

for an initial evaluation. 

Examination of Owner Preferences 

INITIAL SITE VISIT 

A Low Point of Entry determination, illustratedin Figure III2, 
determines the elevation of the lowest floor and each of 
the structure's openings, and may include: 

* basement slab elevation; 
* windows, doors, and vents; 
* mechanical/electrical equipmentand vents; 
* the finished floor elevation of the structure; 
* drains and other floor penetrations; 
* water spigots, sump pump discharges, and other wall 
penetrations; 
* other site provisions that may require flood protection, such 
as storage sheds, wellheads, and storage tanks; and 

0 the establishment of an elevation reference mark on or near 
the house. 

Oncethe LowPoint of Entrydeterminationhas beencom

pleted, the designer/owner can determine the flood protection 

elevation andlor identify openings that need to be protected 

(in the case of dry floodproofing). 

PrnninIgmeanrd Practince nf Retrofittinfi Flood-Prone Residential Structures 111-7 
January 1995 

C1nsinmarinn 


Chapter III: Parameters of Retrofitting 

The approximate height of the retrofitting measure can be 
used by the owner and designer as they evaluate each of the 
ok',' parametersof retrofitting discussed in this chapter. In 
addition to determining the Low Point of Entry, this initial

A detailed discussion of how to site visit should be used to assess the general overall condi

evaluate the costs of different ti oft structure.
alternatives and the effect of the tion ofthe structure.
Low Point of Entry may be found
in the chapter on Benefit/Cost

Analysis. 

Low Point of Ent Low Point of EntV Utility Hazards 
Hose Bibrrf Lw rPintdow Entry A/C Unit A. 

SulpPm Electricf(Gas Meter 1 
Dijcharg g I / 

II I. Ij / 
1i

I /-I -/ 

II~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I 

L&--:-.i---owPoint of Entry 
--------1_________a______ u__t Windowor Door Sill 

Low Point of Ent Structural openin Dryer Vent
Top of Window Wells Window or Door Sill
Top of Areaway Stairwell Backflow Hazards

\Lowest Floor Elevation Sanitary Sewers
Top of Basement Slab or
Top of First Floor

Figure 111-2: Low Point of Floodwater Entry Survey for a Typical Residential Structure 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


ONIA 

I001W 

Sometimespropertyownersare 
reluctantto participatein retrofit-
ting measures because they are 
concerned with how the work will 
alter the physical appearance of 
theirproperty.Suchreluctance 

maybe overcomewith avideo 
displayofbeforeandafterscenes 
of a building. This can be accom-

plished with a personal computer 
(PC)anda video camera. ThePC 
canbe loadedwith a video capture 
card, whichwill allowtransferof a 
video image to the PC. The 
camcorder or VCR image is 

captured while in the pause mode 

andprojectedto the PCmonitor. 

Imagescanthenbe editedto 

portraythemin varioussurround-

ings and with structure modifica-
tions. These simulated pictures in 
color or black and white can be 
developed with currently available 
computer software. 

Examination of Owner Preferences 

AESTHETICCONCERNS 

Although physical and economic considerations may help 
determine feasible retrofitting measures forindividual buildings, 
the homeowners may consider other factors equally or more 
important. Aesthetics, for example, is a subjective issue. 

The homeowner may reject a measure that scores high for all 
considerations except aesthetics. On the other hand, what may 
be aesthetically pleasing to the homeowner may not be 
technicalyappropriateforaproject. Here,adesignermustuse 

skill and experience to achieve a common ground. In doing so, 
the homeowner's preference should be considered, while not 
jeopardizing the structural, functional, and overall success ofthe 

proposedproject. 

An aesthetically pleasing solution that also performs well as a 
retrofitting alternative can be achieved through an understanding 

ofthe relationship between the existing and proposed modifica

.' 

aons,dcreativetreatmentand modificationofsurrounding 

landforms, proper landscaping techniques, and preservation of 

essential and scenic views. 

ECONOMIC CONSIDERATIONS 

At this point, the designer should not attempt to conduct a 

detailed cost analysis. Rather, general estimates ofthe cost of 

various retrofitting measures should be presented to the 

homeowner. 

As discussed in Chapter I, the cost of retrofitting will depend on 

avariety of factors including the building's condition, the retro

fitting measure to be employed, the design flood elevation, the 

choice of materials and their local availability, the availability and 

limitations of local labor, and other site-specific issues (i.e., soil 

conditions and flooding levels) and other hazards. 

shiv Sz.. 
ll z*_l Structures 111^9

PininlIR Residential

Ian

Isvw~

llII r Dni~jnn snti Practices of RetrofittinaFlood-Prone 

Elyll:IIlljIIs; 

January 1995 


Chapter III: Parameters of Retrofitting 

The following costs are nationwide 
averages that may need to be 
adjusted for local economic 
conditions. They were derived 
from various sources including 
the USACE document, Flood 
Proofing, How to Evaluate Your 
Options and various post-disaster 
documents prepared by FEMA as 
a result of the Midwest Flood of 
1993, Hurricane Andrew in Florida 
(January 1993), the Northridge 
California earthquake (January 
1994), and flooding in Southeast-
em Texas (November1994). They 
are provided to assist in economic 
analysis and preliminary planning 

purposes. 

Table IlI-I Elevation and Relocation Cost Guide 

Type Elevation Relocation Per 

_______ ______ ______ Cost Cost 

Wood-Frame Building on Open Foundations $18 $28 square foot 
(Piles,Posts or Piers) 

Wood-Frame Building on Solid Foundation 
Walls $13 $23 square foot 

Brick Building $24 $39 square foot 

Slab-on-Grade Building $22 $37 square foot 

Table ll-Assumptions: 

1. Elevation costs include foundation, extending utilities, and miscellaneous items, such as 
sidewalks and driveways. 
2. Elevation unit cost is based on a 2-foot raise. Add $0.75 per square foot for each additional 
foot raise up to eight feet. Above 8 feet, add $1.00 per square feet. 
3. Relocation costs include off-site relocation (less than 5 miles) and new site development for a 
1,000 SF building. Extrapolation of this unit cost to larger buildings may result in artificially 
high estimates because the costs of relocation do not increase proportionally with building size. 

III-10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Examination of Owner Preferences

-At

IWf 

in relocating a structure, the cost 
of preparing the new site and 
cleaning up the old site must be 
considered. 

Table111-2Floodwalls and Levees Cost Guide 

Type Cost Per 
Floodwalls, two feet above ground level $77 linear foot 
Floodwalls, four feet above ground level $113 linear foot 
Floodwalls, six feet above ground level $160 linear foot 
Levees, two feet above ground level $34 linear foot 
Levees, four feet above ground level $63 linear foot 
Levees, six feet above ground level $105 linear foot 

Floodwall costs are based upon typical foundation depth of 30 inches. Levee costs are 
based upon typical foundation depth of one foot, 1 0-foot top width, and 1:3 side slopes. 
Levee costs include seeding and stabilization. Additional costs that may need to be 
estimated for both floodwalls and levees are as follows: 

Interior Drainage $3,800 lump sum 

Closures $66 square foot 

Riprap $28 cubic yard 

Sidewalk (3' wide) $9 linear foot 

Driveway (asphalt) $6 square yard 

Driveway (concrete) $16 square yard 

More detailed cost estimating guidance is provided in Chapters V and VI. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ;111-11 
January 1995 


Chapter III: Parameters of Retrofitting 

TablellI-3 Dry Floodproofing Cost Guide 

Type Cost Per 
Sprayed-on cement (1/8 inch) $3 square foot 
Asphalt (2 coats below grade) $1 square foot 
Periphery drainage $28 linear foot 
Plumbing check valve $600 lump sum 
Sump and pump installation $1,000 lump sum 

Table 111-4 Flood Shields Cost Guide 
Type Cost Per 

Metal $66 square foot
Wood $21 square foot

Additional costs which may be included: 

* temporary living quarters (displacement costs) thatmay be 
necessary during construction (estimate: relocation -3 to 4 
weeks; elevation-2 to 3 weeks) 
* professional or architectural design (10% of thecosts of 
selected retrofitting measures), 
* contractors' profit (1 0% of the estimated costs), and 
* contingency to account for unknown or unusual conditions. 
Table III-5 can serve as a guide for developing the initial 
planning level estimate for each retrofitting alternative being 
considered. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Examination of Owner Preferences 

Table III-5 Preliminary Cost Estimating Worksheet 
Owner Name: Prepared By: 
Address: Date: 
Property Location: 

Cost Component Unit Unit Cost Quantity Total 

Subtotal Retrofitting Measure 
Contractor's Profit (10%) 
Design Fee (10%) (optional) 

Loss of Income (optional) .
Displacement Expenses (optional)
Contingency

Subtotal Other Costs

Total Costs

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


119L 
Chapter III: Parameters of Retrofitting 

RM 

RISK CONSIDERATIONS 

Another element that is included in the evaluation of retrofitting 
measures is the risk associated with a do-nothing approach. 
Risk can also be established among the various measures by 
knowing the exceedence probability offloods and the design 
flood levels for competing measures. Relocation is an example 
of how retrofitting can eliminate the risk of flood damage. On 
the other hand, a levee designed to protect against a 10percent 
chance annual exceedence probability (1 0-year) flood 
would have an 88-percent chance of being overtopped during 
a 20-year period. Such information will assist the homeowner 
in evaluating the pros and cons of each measure. Table III-6 
provides the probabilities associated with one or more occurrences 
of a given flood magnitude occurring within a specific 
number of years. 

Table III-6 Flood Risk 

Frequency-RecurrenceInterval (Year-Event) 

10 25 50 100 500 

1 10% 4% 2% 1% 0.2% 

Length 10 65% 34% 18% 10% 2% 

Period 20 88% 56% 33% 18% 5% 

25 93% 64% 40% 22% 5% 

30 96% 71% 45% 26% 6% 

50 99+% 87% 64% 39% 10% 

100 99.99+% 98% 87% 63% 18% 

The table values representthe probabilities, expressed in percentages, of one or 

more occurrences of a flood of given magnitude or larger within a specified 

number of years. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


W 

Examination of Owner Preferences 

Flood probabilities are also useful in evaluating the homeowner 
inconvenience aspects of retrofitting. Reducing cleanup and 
repairs, lost time from work, and average non-use of a building 
from once in two years to once in ten years could be a powerful 
incentive for retrofitting even though other aspects may be less 
convincing. 

ACCESSIBILITY FOR THE DISABLED 

Accessibility for the disabled is an issue that must be addressed 
primarily on the specific needs ofthe owner. Many retrofitting 
measures can create access problems for a housethat was 
previously fullyaccessible. The Americans with Disabilities Act 
(ADA) of 1990 and the Fair Housing Amendment Act (FHA) 
of 1988 and other accessibility codes and regulations do not 
specifically address private single-family residences, which are 
the focus of this manual. However, the above-mentioned 

regulations contain concepts that may be of assistance to a 

designer representing a disabled property owner. 

It is important for the designer to remember that the term 
disabled does not refer only to someone who uses a wheelchair. 
Other disabilities may include: 

* limited mobility requiring the use of a walker or cane, which 
can inhibit safe evacuation; 
* a person's limited strength to open doors, climb stairs, 
install flood shields, or operate other devices; and 
* partial or total loss of hearing or sight. 
Special considerations such as small elevators may be needed. 

Discussion ofthe above factors with the homeowner and 

utilizationofthe PreliminaryRetrofittingPreference 

Matrix will allow the designer to rank the retrofitting methods 

by homeowner preference. 

Engineerina Principles and Practices of RetrofittingFlood-Prone Residential Structures 111-15 
January 1995 


Chapter III: Parameters of Retrofitting 

COMMUNITY REGULATIONS AND PERMITTING 

LOCAL CODES 

Most local governments regulate building activities by means of 
building codes as well as floodplain and zoning ordinances and 
regulations. With the intent of protecting health and safety, most 
local codes are fashioned around the model building codes 

Atp discussed in Chapter 1I. The designer should be aware that 

modifications may be undertaken to make the model codes 
A designershould become familiar more responsive to the local conditions and concerns in the 
withthe prevailing conditions, area, such as seismic and hurricane activity, extreme cold, or 
codes, and legal restrictions . 
particular to a building's location, 

Determination of which retrofitting measures are allowed under 
local regulations is an important step in compiling the Preliminary 
Floodproofing/Retrofitting Preference Matrix. Retrofitting 
measures not allowed under local regulations will be screened 
and eliminated from further consideration. 

BUILDING SYSTEMS/CODE 

UPGRADES 

Other local code requirements must be met by owners building 
improvements. Most building codes require approval when 
Somecommunities is considered, especially if structural modification and/

reque televation 

Some communities require that 
structures undergoing substantial or alteration and relocation of utilities and support services are 

rehabilitation, either because of involved. 
previous damage or significant 
improvements/additions, be 
broughtinto compliance with cIf more strigent laws have beensadopted since abuilding was 
current building codes. In constructed, local code restrictions can seriously affect the 
additionto floodplainmanage-selection of a retrofitting method because construction may be 

ment requirements, theserequire-expected to comply with new building codes.
ments could include items such as
the addition of fire alarms, removal
of lead water pipes, upgrades in
electrical wiring, etc.

III -16 Enoineerino PrinciDles and Practices of Retrofittina Flood-Prone Residential Strutres 

_ ,_ _ -J ,._ ...... . __..__ ; n..___ . ............. _.__....January. 1995

January 1 995 


Community Regulations and Permitting 

Addressing offsite impacts and 

issues is as much a matter of 
responsible practice and con

science as it is a requirement of 
most building codes and floodplain 
management ordinances. 

NFIP, state, and local regulations 
do not allow construction within a 
floodway or, in some cases, within 
a floodplain that would back up 
and increase flood levels. 

OFFSITE FLOODING IMPACTS 

Where a chosen retrofitting measure requires the modification of 
site elements, a designer shall consider how adj acent properties 
will be affected. 

* Will construction of levees and floodwalls create diversions 
in the natural drainage patterns? 
* Will new runoffs be created that may be detrimental to 
nearby properties? 
* If floodproofing disturbs the existing landscape, will regrading 
and relandscaping undermine adjacent streets and 
structures? 
* Will the measure be unsightly or increase the possibility of 
sliding and subsidence at a later date? 
* If a building is to be relocated to another portion of the 
current site, or if it is to be elevated, will it encroach on 
established easements or rights-of-way? 
* Will the relocated building infringe on wetland areas or 
regulated floodplains? 
These and other questions must be addressed and satisfactorily 
answered by the designer and homeowner in selecting the most 
appropriate retrofitting measure. Both must be aware of the 
liabilities that may be incurred by altering drainage patterns and 
other large-scale site characteristics. The designer should insure 
that any modified runoffs do not cause negative impacts on the 
surrounding properties. The means necessary to collect, 
conduct, and dispose of unwanted flood or surface water 
resulting from retrofitting modifications must be understood and 
clearly resolved. 

Enaineerina Principles and Practices of F letrofittina Flood-Prone Residential Structures III- 17 
January 1995 


Chapter III: Parameters of Retrofitting 

TECHNICAL PARAMETERS 

'Once the designer has resolved preliminary retrofitting prefer

ence issues with the owner, a more intensive evaluation ofthe 

technical parameters is nonnally conducted, including flooding, 

site, and building characteristics. Figure 111-3 provides a 

Retrofitting Screening Matrix (worksheet) that can be used to 

evaluate which measures are appropriate for individual struc

tures. Instructions forusing this matrix are presented in Figure 
111-4. The remainder ofthis chapter provides background 

information on each of the technical parameters, which will be 

useful to the designer in completing the Retrofitting Screening 

Matrix. 

IEI-18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
.lam I1ll I car,

..c.. c y .-rr 

..


Technical Parameters 

Owner Name: Prepared By: 
Address: Date: 
Property Location: 

Measures levation Elevation Elevation Relocation Dr Flood Wet Flood Floodwalls 
.on ; on Fill on Piers, proofing proofing and 
Foundation Piles, Levees 
Walls Posts,and 
-Parameters--: : Columns 

Measure Permitted by Community 
or Preferred by Homeowner : . 

FloodDepth _ ___ 

Shallow (<3 feet) ___ 

I

Moderate (3 to 6 feet) __ WA

. NIA 
Deep (>6 feet) -WN/A N/A N/A 
ti; Flood Velocity 

Slow/Moderate (s5 fps) 

A Fast (>5 fps) 1 1 1 WNA | 1 
im Flash Flooding 
ii Yes (<1 hour) 1 r T 2 1 2 
8 No _ L11 
Ice and Debris Flow _ . 
Yes 
No 
3Site Location 
0 
6 
_ 
4 N/A 11 
j j 
4 
i 
Floodway 
OtherA Zone 1 T T 
5 
T I 
5 | 5 5T 5 5 
Soil Type 
0 Permeable l | 3 | 3 
c5 Impermeable 1 -
0 
Building Foundation 
Slab on Grade i 
Crawl Space _ I _ _ __A 
.-Basement | 6 |6 | | 6 1 r 
E Building Construction (Framing) 
5 Concrete or Masonry _ _ | 
' Wood and Others 
_Building Condition 
Excellent to Good 
Fair to Poor 6 6 6 6 6 
Figure I11-3: Retrofitting Screening Matrix 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III- 19 
January 1995 


Chapter III: Parameters of Retrofitting 

r 
The Retrofitting Screening Matrix (Figure 111-3)is designed to screen and eliminate 

retrofitting techniques that should not be considered for a specific situation. 

Step 1: Screen alternatives which are not permitted nor preferable to the homeowner and are eliminated 
from further consideration, by inserting NIP (not permitted) in the appropriate box(es) on the 
Measures Permitted by Community row. If a N/P is placed in a column representing a retrofitting 
measure, that alternative is eliminated from consideration. 

Step 2: Select the appropriate row for each of the nine characteristics that best reflect the flooding, site, 
and building characteristics. 

Step 3: Circle the N/A (not advisable) boxes that apply in the rows of characteristics selected. Do not 
circle any N/A boxes where there Is a plan to engineer a solution to address the specific 
characteristic. 

Step 4: Examineeach column representing the different retrofitting measures. If one or more NIA boxes 
are circled in a column representing a retrofitting measure, that alternative is eliminated from 

consideration. 

Step 6: The numbers enclosed in the boxes represent special considerations (detailed below) which 
must be accounted for to make the measure applicable. If the consideration cannot be 
addressed, the number should be circled and the measure eliminated from consideration. 

Step 6: Retrofitting measures that remain should be further evaluated for technical, benefit-cost, and 
other considerations. A preferred measure should evolve from the evaluation. 

NIA Not advisable in this situation. 

NIP Not permitted in this situation. 

1 Fast flood velocity is conducive to erosion and special features to resist anticipated erosion may 
be required. 

2 Flash flooding usually does not allow time for human intervention; thus, these measures must 

perform without human intervention. Openings in foundation walls must be large enough to 
equalize water forces and should not have removable covers. Closures and shields must be 
permanently in place, and wet floodproofing cannot include last-minute modifications. 

3 Permeable soils allow seepage under floodwalls and levees; therefore, some type of subsurface 
cutoff feature would be needed beneath structures. Permeable soils become saturated under 
flood conditions, potentially increasing soil pressures against a structure, therefore some type of 
foundation drain system or structure may be needed. 

4 Ice and debris loads should be considered and accounted for in the design of foundations and 
floodwall/evee closures. 

5 Any retrofitting alternative considered for the floodway must meet NFIP, state, local, and 
community floodplain requirements concerning encroachment/obstruction of the floodway 
conveyance area. 

6 Not advisable in this situation, unless a specific engineering solution is developed to address the 
specific characteristic or constraint. 

Figure III-4: Instructions for Retrofitting Screening Matrix 

III -20 Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures 
January 1995 


Technical Parameters 

FLOODING CHARACTERISTICS 

Riverine flooding is usually the result of heavy or prolonged 
rainfall or snowmelt occurring in upstream inland watersheds. 
In some cases, especially in and around urban areas, flooding 
can also be caused by inadequate or improper drainage. In 
coastal areas subject to tidal effects, flooding can result from 
wind-driven and prolonged high tides, poor drainage, storm 
surges with waves, and tsunamis. 

There are several different flood characteristics that must be 
examined to determine which retrofitting measure will be best 
suited for a specific location. These characteristics not only 
indicate the precise nature of flooding for a given area, but can 
also be used to anticipate the performance of different retrofitting 
measures. These factors are outlined below. 

Flood Depth 

Determining the potential depth of flooding for certain flood 
frequencies is a critical step because it is often the primary 
factor in evaluating the potential for flood damage. 

A building is susceptible to floods of various depths. Floods of 
greater depth occur less frequently than those of lesser depths. 
Potential flood elevations from significant flooding sources are 
shown in Flood Insurance Studies (FIS) for most participating 
NFIP communities. For the purpose of assessing the depth of 
flooding a structure is likely to endure, it is convenient to use the 
flood levels shown in the study, historical flood levels, and flood 
information from other sources. The depth of flooding affecting 
a structure can be calculated by determining the height of the 
flood above the ground elevation at the site of the structure. 

Engineering Principles and Practices of R Retrofitting Flood-Prone Residential Structures III -21 

January 1995 


Chapter III: Parameters of Retrofitting 

[1-5: Photographs showing mud lines on homes are a source of 

historical information. 

[Hydrostatic 

fames 

_~~~~~~~~

i_V 

w1101w 711 
Buoyancyor uplift forces 
increasewth lood depth. 

Figure 111-6: Hydrostatic Forces 

For those areas outside the limits of an FIS or state, community, 
or privately prepared local floodplain study, determination of 
flood depth may require a detailed engineering evaluation of 
local drainage conditions to develop the necessary relationship 
between flow (discharge), water-surface elevation, and flood 
frequency. The designer should contact the local municipal 
engineer, building official, or floodplain administrator for guidance 
on computing flood depth in areas outside existing study 
limits. 

Floodwaters can impose hydrostatic forces on buildings. These 
forces result from the static mass of water acting on any point 
where floodwater contacts a structure. They are equal in all 
directions and always act perpendicularly (or normally) to the 
surfaces on which they are applied. Hydrostatic loads can act 
vertically on structural members such as floors and decks 
(buoyancy forces) and laterally (hydrostatic forces) on upright 

Ill -22 EngineeringPrinciples and Practices ofRetrofitting Flood-Prone Residential Structures 
January 1995 


Technical Parameters 

structural members such as walls, piers, and foundations. 
Hydrostatic forces increase linearly as the depth of water 
increases. Figure III-6 illustrates the hydrostatic forces generated 
by water depth. 

If a well-constructed building is subject to flooding depths of 
less than three feet, it is possible that unequalized hydrostatic 
forces may not cause significant damage. Therefore, consideration 
can be given to using barriers, sealants, and closures as 
retrofitting measures. If shallow flooding (less than three feet) 
causes a basement to fill with water, wet floodproofing methods 
can be used to reduce flood damage to basements. 

If a residential building is subject to flooding depths greater than 
three feet, elevation or relocation are often the most effective 
methods of retrofitting. Water depths greater than three feet can 
often create hydrostatic forces with enough load to cause 
structural damage or collapse if the house is not moved or 
elevated. One other potential method (provided the cost is not 
prohibitive) is the use of levees and floodwalls designed to 
withstand flooding depths greater than three feet. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III-23 
January 1995 


Chapter III: Parameters of Retrofitting 

Flood Velocity 

The speed at which floodwaters move (flood flow velocity) is 
normally expressed in terms of feet per second (fps). As 
floodwater velocity increases, hydrodynamic forces imposed by 
moving water are added to the hydrostatic forces from the 
depth of still water, significantly increasing the possibility of 
structural failure. Hydrodynamic forces are caused by water 

The use of existing and historical moving around an object and consist of positive frontal pressure 
data can be very useful in analyz-against the structure, drag forces along the sides, and negative 

ing the flood threat. Through 

interviews with residents, approxi-pressures on the building's downstream face. Greater velocities 
mate dates of flooding may be can quickly erode, or scour, the soil supporting and/or sur-
established, as well as remem-rounding buildings. Thus, the impact drag, and suction from 
bered depths of flooding, types of these fast-moving waters may move a building from its foundavelocity 
(moving or standing tion or otherwise cause structural damage or failure. 

water), duration of flooding, etc. 
Once the dates have been established, 
the designer can check Unfortunately, there is usually no definitive source of information 
other sources such as newspapers to determine potential flood velocities in the vicinity of specific 

and the National Weather Service 

buildings. Hydraulic computer models or hand computations 

for additional information. 

based on existing floodplain studies may provide flood velocities 
in the channel and overbank areas. Where current analysis data 
is not available, historical information from past flood events is 
probably the most reliable source. 

Figure 111-7: Fast-moving floodwaters caused scour around the foundation and damage 
to the foundation wall. 

III-24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Flash flooding will usually 
preclude the use of any retrofitting 
measure that requires human 

intervention. 

Technical Parameters 

Onset of Flooding 

In areas of steep topographyor those areas with a small 
drainage area, floodwaters can rise very quickly with little or no 
warning. This condition is known as flash flooding. High 
velocities usually accompany these floods and may preclude 
certain types of retrofitting, especially those requiring human 
intervention. In a flash flooding situation, damage usually begins 
to occur within one hour after significant rainfall. Ifa building is 
susceptible to flash floods, insufficient warning time can preclude 
the installation of shields on windows, doors and floodwalls, 
as well as the activation of pump systems and backup 
energy sources. Temporarily relocating movable contents to a 
higher level may also be impractical. However, such measures 
may be effective if a building is not subject to flash flooding and 

the area has adequate flood warning systems, such as television 

-vs~~~~~~~ 

A detailed hydrograph can provide 

information on duration of 
flooding. However, such information 
is usually not available, and 
the cost of creating a new study is 
usually prohibitive. One potential 
source of information is to check 
similarly sized drainage basins in 
neighboring areas to see if 
historical data exists. 

and radio alerts. 

Flood Duration 

In areas of long-duration flooding, certain measures such as dry 
floodproofing may be inappropriate due to the increased chance 
of seepage and failure caused by prolonged exposure to 
floodwaters. 

Engineering Principles and Practices of F RetrofittingFlood-ProneResidential Structures III -25 
January 1995 


ChapterIII: Parameters of Retrofitting 

611% SITE CHARACTERISTICS

Site characteristics such as location, underlying soil conditions, 
and erosion vulnerability play a critical role in the determination 
of an applicable retrofitting method. 

Site Location 

The floodplain is usually defined as the area inundated by a 
floodhhaving a 100-year floodfrequency. The riverine floodplain 
is often fbrther divided into a floodway and a floodway 
flinge. 

As defined earlier, the floodway is the portion ofthe floodplain 
that contains the channel and enough ofthe surrounding land to 
enable floodwaters to pass without increasing flood depths 
greater than a predetermined amount. If there are high flood 
depths and/or velocities, this area is the most dangerous portion 
ofthe riverine floodplain. Also, since the floodway carries most 
ofthe flood flow, any obstruction may cause floodwaters to 
back up and increaseflood levels. For these reasons,the NFIP 
and local communities prohibit new construction or substantial 
improvement in identified floodways that would increase flood 

levels. Relocation is the recommended retrofitting option for a 
structure located in a floodway. Community and state regulations 
may prohibit elevation of structures in this area. However, 

elevation on an open foundation will allow for more flow 

conveyance than a structure on a solid foundation. 

The portion ofthe floodplain outside the floodway is called the 
floodway fringe. This area normally experiences shallower 
flood depths and lowervelocities. With proper precautions, it is 
often possible to retrofit structures in this area with an acceptable 
degree of safety. 

III-26 Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures 
January 1995 


Technical Parameters 

/ 

SATURATED 

/ SOIL 

Figure 111-8: Lateral Forces Resulting 
From Saturated Soil 

Figure 111-9: Buoyancy Forces 
Resulting From Saturated Soil 

Contact the local office of the 
Natural Resource Conservation 
Service (NRCS) or a local 
geotechnical engineering firm to 
obtain guidance on the permeability 
or consolidation features of 
soils native to the area. Because 
the site may have been backfilled 
with non-native materials during 
original construction, NRCS data 
should be used carefully. 

Soil Type 

Permeable soils, such as sand and gravel, are those that allow 
groundwater flow. In flooding situations, these soils may allow 
water to pass under floodwalls and levees unless extensive 
seepage control measures are employed as part of the retrofit-) 
ting measures. Also, saturated soil pressure may build up 
against basement walls and floors. These conditions cause 
seepage, disintegration of certain building materials, and structural 
damage. Levees, floodwalls, sealants, shields, and closures 
may not be effective in areas with highly permeable soil 
types. 

Saturated soils subject horizontal surfaces, such as floors, to 
uplift forces, called buoyancy. Like lateral hydrostatic forces, 
buoyancy forces increase in proportion to the depth of water/ 
saturated soil above the horizontal surface. Figures 111-8 and 
III-9 illustrate the combined lateral saturated soil and buoyancy 

forces. 

For example, a typical wood-frame home without a basement 
or proper anchoring may float if floodwaters reach three feet 
above the first floor. A basement without floodwater in it could 
fail when the ground is saturated up to four feet above the floor. 
Uplift forces occur in the presence of saturated soil. Therefore, 
well-designed, high-capacity subsurface drainage systems with 
sump pumps may be an effective solution and may allow the use 
of dry floodproofing measures. 

Other problems with soil saturated by floodwaters need to be 
considered. If a building is located on unconsolidated soil, 
wetting ofthe soil may cause uneven (differential) settlement. 
The building may then be damaged by inadequate support and 
subject to rotational, pulling, or bending forces. Some soils, 
such as clay or silt, may expand when exposed to floodwaters, 
causing massive forces against basement walls and floors. As a 
result, buildings may sustain serious damage even though 
floodwaters do not enter or even make contact with the structure 
itself. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III -27 
January 1995 


Chapter III: Parametersof Retrofitting 

BUILDING CHARACTERISTICS 

Ideally, a building consists of three different components: 
substructure, superstructure, and support services. The 
substructure consists ofthe foundation system; the superstructure 
consists ofthe portion ofthe building envelope above the 
foundation system. The support services are those elements 
that are introduced into a building to make it habitable. 

These components are integrally linked together to help a 
building maintain its habitability and structural integrity. Any 
action that considerably affects one may have a minimal or 
sometimes drastic effect on the others. An understanding of 
building characteristics and types of construction involved is 
therefore an important consideration in deciding upon an 
appropriate retrofitting measure. 

Substructure 

The substructure of a building supports the building envelope. 
It includes components found beneath the earth's surface, as 
B*y well as above-grade foundation elements. This system consists 
of both the vertical foundation elements such as walls, posts, 
A cracked foundation is one 

idcratio fo a weakoundion. piles, and piers, which support the building loads and transmit 

indication of a weak foundation.
The use of floodwalls and levees them to the ground, and the footings that bear directly on the
may be the easiest and most soil.
practical approach to retrofitting a

structure with a poor foundation. At any given time, there are a number of different kinds of 

relocation of the building's super-loads acting onabuilding. Thefoundationsystemtransfers 
structure onto a new foundation. these loads safely into the ground. In addition to dead and live 
loads, retrofitting decisions must take into account the buoyant 
uplift thrust on the foundation, the horizontal pressure of 
floodwater against the building, and any loads imposed by 
multiple hazards such as wind and earthquake events. 

The ability ofa foundation system to successfully withstand 
these and other loads or forces, directly or indirectly, is dependent 
to a large extent on its structural integrity. A designer 
should determine the type and condition ofa building's foundation 
system early in the retrofitting evaluation. 

III -28 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures 
January 1995 


Technical Parameters 

All foundations are classified as either shallow or deep. Shallow 
foundations consist of column and wall footings, slab-ongrade, 
crawl space, and basement substructures; deep foundations 
include piles. Even though each ofthese foundation types 

Retrofittingof structures with may be utilized either individually or in combination with others, 
basements is not covered in this most residential buildings located outside coastal high hazard 
manual. areas are supported on shallow foundations. Each type has its 
own advantages and limitations when retrofitting measures are 
being evaluated. Whichever is used in a building, a designer 
should carefully check for the structural soundness of the 
foundation system. 

Basement walls may be subject to increased hydrostatic and 
buoyancy forces; thus, retrofitting a building with a basement is 
often more involved and costly. 

Superstructure 

The superstructure is the portion of the building envelope above 
the foundation system. It includes walls, floors, roof, ceiling, 
doors, and other openings. A designer should carefully and 
thoroughly analyze the existing conditions and component parts 
ofthe superstructure to determine the best retrofitting options 
available. Flood- and non-flood-related hazard effects should 
also be considered; the uplift, suction, shear, and other pressures 
exerted on building and roof surfaces by wind and other 
environmental hazards may be the only reasons needed to rule 
out elevation as a retrofitting measure. 

Support Services 

These are elements that help maintain a human comfort zone 

and provide needed energy, communications, and disposal of 

water and waste. For a typical residential building, the combina

tion ofthe mechanical, electrical, telephone, cable TV, water 

supply, sanitary, and drainage systems provides these services. 

An understanding ofthe nature and type of services used in a 

building is necessary for a designer to be able to correctly 

predict how they may be affected by retrofitting measures. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III -29 
January 1995 


Chapter III: Parameters of Retrofitting 

I I For example, the introduction of new materials or the alteration 
ofabuilding's existing features may require resizing existing 
services to allow forthe change in requirements. Retrofitting 
may also require some form of relocated ductwork and electrical 
rewiring. Water supply and waste disposal systems may 
have to be modified to prevent future damage. This is particularly 
true when septic tanks and groundwater wells are involved. 
If relocation is being considered, the designer must consider all 
these parameters and weigh the cost of repairs and renovation 
against the cost of total replacement. 

1I -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


For general consideration of 
retrofitting measures, all construction 
should be classified as wood 
material unless all walls and 
foundations are concrete and 
masonry. 

Technical Parameters 

Building Construction 

Modem buildings are constructed with a limitless palette of 
materials integrated into various structural systems. A 
building may be constructed with a combination of various 
materials. Thus, the suitability of applying a specific 
retrofitting measure may be difficult to assess. 

Concrete and masonry construction may be considered for all 
types of retrofitting measures, whereas other materials may not 
be structurally sound or flood-damage resistant and therefore 
not suitable for some measures. When classifying building 
construction as concrete and masonry, it is important that all 

walls and foundations be constructed of this material. Otherwise, 
there may be a weak link in the retrofitting measure, 
raising the potential for failure when floods exert hydrostatic or 
hydrodynamic forces on the structure. 

Masonry-veneer-over-wood-frame construction must be 

identified since wood-frame construction is less resistant to 

lateral loading than a brick-and-block wall section. 

Engineering Principles and Practicesof Retrofitting Flood-ProneResidential Structures Ill -31 
January 1995 


Chapter III: Parameters of Retrofitting 

'now. | Building Condition 
A building's condition may be difficult to evaluate, as many 
structural defects are not readily apparent. However, careful 
inspection ofthe property should provide for a classification of 
"excellent to good" or "fair to poor." This classification is only 
Typically,a designer will begin a for the reconnaissance phase of selecting appropriate retrofitting 
retrofitting project with an initial measures. More in-depth planning and design may alter the 
analysis of the present conditions. initial judgment regarding building condition, thereby eliminating 
Decisions based on early findings 
may be revised after a more some retrofitting measures from consideration at a later time. 
detailed analysis. 
Analysis ofa building's substructure, superstructure, and 
support services may be done in two stages-an initial analysis 
usually based on visual inspection, and a detailed analysis 
(discussed in Chapter VI) which is often more informative, 
involves greater scrutiny, and usually requires detailed 
engineering calculations. 
In the course of an analysis, a designer should visually 
inspect the walls, floors, roof, ceiling, doors, windows, and S 
other superstructure and substructure components. Walls 
should be examined for type of material, structural stability, 
cracks, and signs of distress. A crack on a wall or dampness 
on concrete, plaster, wood siding, or other wall finishes 
may be a sign of concealed problems. Doors, windows, 
skylights, and other openings should be checked for cracks, 
rigidity, structural strength, and weather resistance. 
Metal-clad wood doors or panel doors with moisture-
resistant paint, plastic, or plywood exterior finishes may 
appear fine even though the interior cores may be damaged. 
Aluminum windows may be checked for deterioration due to 
galvanic action or oxidation from contact with floodwater. 
Steel windows may be damage-free if they are well protected 
against corrosion. Wood windows require inspection 
for shrinkage and warping, and for damage from moisture, 
mold, fungi, and insects. 

Flooring in a building can include a vast range of treatments. 
It involves the use of virtually every material that can be walked 

S 

III -32 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures 
January 1995 


Technical Parameters 

upon, from painted concrete slabs to elegant, custom-designed 
wood parquet floors. A designer should investigate the nature 
of both the floor finishes and the underlying subfloor. Vinyl or 
rubberized plastic finishes may appear untouched due to their 
resistance to indentations and water; however, the concrete or 
wood subfloor may have suffered some damage. Likewise, a 
damage-free subfloor may be covered with a scarred finish. 

An initial analysis of the conditions of the roof and ceiling of a 
building can be done by observation during the early decision-
making stage. An understanding of the materials and construction 
methods will be necessary at a later date to evaluate fully 
the extent of possible damage and need to retrofit. The roofs 
over most residential buildings consist of simple to fairly complex 
wood framing that carries the ceilings below and plywood 
roof decks above, over which the roof finishes are placed. 
Finish materials include asphalt, wood, metal, clay and concrete 
tile, asbestos, and plastic and are available in various compositions, 
shapes, and sizes. In some cases, observation may be 
enough to determine the suitability, structural rigidity, and 
continuing durability of a roof system. However, it may be 
necessary to pop up a ceiling tile; remove some shingles, slate, 
or roof tiles; or even bore into a roof to achieve a thorough 

inspection. 

The inspection also determines if the building materials and 

component parts are sound enough for the building easily to 

undergo either elevation, relocation, or wet or dry 

floodproofing. If not, floodwalls or levees around the structure 

may be the best alternative if allowable. 

Figure III- 10 presents a template that a designer can utilize to 
document findings during the initial building condition survey. 

Enaineerina PrinciDles and Practices of IRetrofittina Flood-Prone Residential Structures 111-33 
January 1995 


Chapter III: Parameters of Retrofitting 

Owner Name: Prepared By: 
Address: Date: 
Property Location: 

Preliminary Building Condition Evaluation Worksheet 

Condition 
Building Components Excelleto i Notes and Materials 

Good Fi oPo 

Substructure 
Footings 
Foundation 
Foundation Walls 

Other 

Superstructure 

Floors
Walls
Ceilings

Doors
Windows
Roof

Other 

Support Services 
Heating System 
Plumbing System 
Air Conditioning System 
Water Supply 
Sewage 

Other 

Comments 

Figure 111-10: Preliminary Building Condition Evaluation Worksheet 

III -34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Technical Parameters 

BALANCING HISTORIC 
PRESERVATION INTERESTS WITH 
FLOOD PROTECTION 

Many historic building features were developed, either deliber

ately or intuitively, as responses to natural and environmental 

hazards, and to local climate or topography. Recognizing how 

and why these features were intended to work can help in 

designing a program of'preventive measures that is historically 

appropriate and that minimizes incongruous modifications to 

historic residential properties. 

There are retrofitting steps that will not have a negative or 
even significant impact upon the historic character of a site 
or its particular features. Preventive measures can be 
carried out without harming or detracting from historic 
character, as long as design and installation arepcarefully supervised 
by a professional knowledgeable in historic preservation. 

There may well be instances, however, when~a measure' that 
best protects the site also may result in some loss of historic 
character. In such a case, the designer and the owner will have 
to weigh the costs of compromising character or historic 
authenticity against the benefits of safeguarding the site or a 
particular site feature against damage or total destruction. One 
example of such a choice is the decision whether to elevate a 
historic structure located in a flood hazard area, relocate it out 
of the area, retrofit it with wet or dry floodproofing techniques, 
or leave it in its existing state to face the risks of damage 
or loss. It is difficult to prescribe a formula for such a decision, 
since each situation will be unique, considering location, structural 
or site conditions, the variety of preventive alternatives 
available, cost, and degree of potential loss of historic character. 
Here are some questions the designer may wish to pose in 
deliberating such a decision: 

*What is the risk that the historic feature or the entire site 
could be totally destroyed or substantially damaged if the 

Enaineerina PrinCiolesand Practices of I :IetrofittinaFlood-Prone Residential Structures 1II1-35 
January 1995 


Chapter III: Parameters of Retrofitting 

'g--v |preventive 

measure is not taken? Ifthe measure is taken, to 
what degree will this reduce the risk of damage or total 
destruction? 

Are there preventive alternatives that provide less protec

tion from flood damage but also detract less from historic 

character?What are these, and what is the trade-off 

between protection and loss of character? 

* Is there a design treatment that could be applied to the 
preventive measure to lessen detraction of historic character? 
MULTIPLE HAZARDS 

The selection of a retrofitting method may expose the structure 
to additional non-flood environmental hazards that could 
jeopardize the safety ofthe structure. These multiple hazards 
can be accommodated through careful design ofthe retrofitting 
measures or may necessitate selection ofa different retrofitting 
method. Multiple hazards include both flood-related and 
non-flood-relatedhazards. Information concerning the 
analysis and design for these multiple hazards is contained 
in Chapters IV and VI. 

The significant flood-related hazards to consider include ice 
and debris flow, impact forces, erosion forces, and mudslide 
or alluvial fan impacts. The major non-flood-related hazards 
to consider include earthquake and wind forces. Less 
significant hazards addressed in Chapter IV include land 
subsidence, fire hazards, snow loads, movable bed streams, 
and closed basin lakes. Multihazards may affect a structure 
independently, as with flood and earthquakes, or concurrently, 
as with flood and wind in a coastal area. 

I11-36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


It is importantto consider these 
multiple hazards when screening 
and selecting a retrofitting measure. 
However, the designer should be 
aware that structures can be 
engineered to withstand these 
multiple hazards, and the existence 
of these hazards alone may not 

oustifytheseliiatirdsalonemspedebris

nof

justify the elimination of specific 
homeowner-preferred

retrofitting 
methods. The local buildingcodes 
normallycontain additional 
guidanceconcerningnatural 

hazard-resistant

designand 

construction practices. 

Technical Parameters 

Flood-Related Hazards

IMPACT FORCES -ICE AND DEBRIS FLOW

In colder climates, floodwaters may carry chunks of ice that can 
act as a battering ram on a structure. During a flood, ice can 
also form around the structure. Rising floodwaters can lift a 
structure, resulting in severe damage. Flash and high-velocity 
floodwaters often carry debris such as cars, sheds, boulders, 
rocks, and trees that can destroy most retrofitting measures 
as well as the structure itself. 

Retrofitting measures suitable for areas of ice and debris 
flow may include elevation on fill, relocation, levees, and 
armored floodwalls. 

EROSION FORCES 

If a soil is highly erodible, fast-moving floodwaters can undermine 
foundations and cause building, levee, or floodwall failures. 
The consideration of soil erosion is critical when retrofitting a 
building located in the floodplain. With the exception of deep 
foundation systems such as piles, shallow foundation systems 
generally do not provide sufficient protection against soil erosion 
without some type of protection or armoring measure of below-
grade elements. The local office ofthe Natural Resources 

Conservation Service (NRCS) will generally have information 

concerning the erodibility ofthe soils native to a specific site. 

ALLUVIAL FANS 

Because ofthe potential for high flood velocities, significant 

flow, and varying channel locations, alluvialfans present 

many unique challenges. In the upper portions of the fan, the 
only feasible retrofitting technique may be relocation. However, 
on lower portions ofthe fan where the flood velocities and 
depths are low, several options may be available. The 

hazards associated with alluvial fan flooding are discussed 

in detail in Appendix D of this manual. 

EnaineerinaPrinciDles and Practices of Retrofittina Flood-Prone Residential Structures 

January 1995 


Chapter III: Parameters of Retrofitting 

FEMA is currently involved in an 
interagency task force developing 
earthquake-resistant design 
standards in the wake of recent 
disasters. For additional information 
contact FEMA's Mitigation 
Directorate or the appropriate 
Regional FEMA office. 

If 

At'

Strengthening an existing masonry 

block foundation wall can be 
complicated and normally requires 
the expertise of a designer knowledgeable 
in this type of work. The 
local building codes may contain 
additional guidance concerning 
earthquake-resistant design and 
construction materials. 

Non-Flood-RelatedHazards 

EARTHQUAKE FORCES 

Earthquake protection steps can be divided into two categories: 

steps that deal with the building structure itself, and steps that 

can be taken with other parts of the building and its contents. 

The most important step for the structure is making sure that it is 
properly bolted down onto its foundation so it will not slide off 
in an earthquake. Another important step, especially if the 
foundation is being raised to place the structure above flood 
levels, is to make sure the foundation can withstand an earthquake. 
For masonry block foundations, this usually means 
strengthening key portions ofthe wall by installing reinforcing 
bars in the blocks and then filling them with concrete grout. 

WIND FORCES 

High winds impose forces on a home and the structural elements 
of its foundation. Damage potential is increased when the 
wind forces occur in combination with flood forces. In addition, 
as a structure is elevated to minimize the effects of flood forces, 
the wind loads on the elevated structure may be increased. 

A conventional structure is normally built to resist vertical 
downward loads (its own weight) plus live loads (contents, 
people) on the floor and snow and wind loads on the roof 
Occasionally, structural elements are laid on top of each other 
with minimal fastening. However wind forces can be upwards, 
or from any direction exerting considerable pressure on structural 
components such as walls, roofs, connections, and anchorage. 
Therefore, wind loads should be considered in the design 
process at the same time as hydrostatic, hydrodynamic, and 
impact dead and live loads as prescribed under the applicable 
codes. 

III-38 Engineering Principles and Practices of Retrofitting Flood-Prone ResidentialStructures 
January 1995 


CHAPTER IV

-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" 

DETERMINATION OF HAZARDS

Featuring: 

Analysis of Flood-Related Hazards 
Analysis of Non-Flood-Related Hazards 
Geotechnical Considerations 


DETERMINATIONOF HAARDS 
ANALYSIS OF FLOODRELATED 
HAZARDS 
ANALYSIS OF NON-FLOODRELATED 
HAZARDS I GEOTECHNICAL 
CONSIDERATIONS 
Flood Depth Wind Forces Bearing Capacity 
Hydrostatic Forces 
Seismic Forces Scour Potential l 
Hydrodynamic Forces 
Land Subsidence Frost Zone 
Impact Forces 
Permeability 
Riverine Erosion 
Shrink-Swell Potential 
Interior Drainage 
Alluvial Fans 
Closed Basin Lakes 

K Movable Bed Steams 

I 

2.11 

Chapter IV: Determination of Hazards 

Table of Contents 

Analysis of Flood-Related Hazards ............................................................ IV -2
Flood Depth ............................................................ IV -2
Riverine Areas ............................................................ IV -2
Coastal Areas ............................................................ IV -6
Hydrostatic Forces ............................................................. IV -10
Lateral Hydrostatic Forces................... ......................................... IV -11
Saturated Soil Forces............................................................... IV -12
Combined Water and Saturated Soil Forces ........................................................IV -15
Vertical Hydrostatic Force .............................................................. IV -17
Hydrodynamic Forces ............................................................... IV -20
Low Velocity Hydrodynamic Forces ......................................................... ... IV -21
High Velocity Hydrodynamic Forces ............................................................ IV -25
Impact Loads ............................................................ IV -29
Normal Impact Forces .............................................................. IV -30
Special Impact Forces............................................................... IV -31
Extreme Impact Forces.............................................................. IV -32
Riverine Erosion .............................................................. IV -35
Interior Drainage.............................................................. IV -36
Alluvial Fan Flooding Hazards .................... ......................................... IV -40
Bulking Factor.............................................................. IV -41
Hydrostatic and Hydrodynamic Loads............................................................ IV -42
Freeboard.............................................................. IV -43
Safety Factors .............................................................. IV -44
Closed Basin Lakes ............................................................ IV -46
Movable Bed Streams ............................................................ IV -47

Analysis of Non-Flood-Related Hazards ....................... ..................................... IV -48
Wind Forces.............................................................. IV -48
SeismicForces ............................................................ IV -50
Protection of the Structure ................... ......................................... IV -52
Protection of Non-Structural Building Components and Building Contents .......IV -53
Land Subsidence .............................................................. IV -53

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -
January 1995


Geotechnical Considerations........................ IV -55
Bearing Capacity .. ................. IV -58
Scour Potential ................ IV -60
Frost Zone Considerations ................ IV -68
Permeability ................. IV -68
Shrink-Swell Potential.................. IV -70

IV -ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


DETERMINATION OF HAZARDS 

Chapters I through III introduced retrofitting and guided the designer through the technical 
process of pre-selecting retrofitting techniques for consideration. In this chapter, the 
analyses necessary to determine the flood-and non-flood-related forces and other site-
specific considerations that control the design of a retrofitting measure are presented. This 
informationmay be useful in preparing benefit/cost analyses and determining which retro

fitting alternatives are infeasible. The analysis of hazards contributes to the design criteria 
for retrofitting measures, which are described in Chapter VI. 

Retrofitting measures must be designed, constructed, connected, and anchored to resist 
flotation, collapse, and movement due to all combinations of loads appropriate to the 
situation, including: 

* flood-related hazards, such as hydrostatic and hydrodynamic forces, impact forces, 
interior drainage considerations, and the effects of erosion; 
* site-specific flood-related hazards, such as alluvial fans, closed basin lakes, and 
movable bed streams; 
* non-flood-related environmental loads, such as earthquake and wind forces and land 
subsidence; and 
* site-specific soil or geotechnical considerations, such as soil pressure, bearing capacity, 
scourpotential, shrink-swell potential, and permeability. 
Pnnint-garinn Prinnin~lp and Prantices of Retrofittina Flood-Prone Residential Structures IV -1 
January 1995 


Chapter IV: Determination of Hazards 

ANALYSIS OF FLOOD-RELATED HAZARDS

] The success of any retrofitting measure depends on an accu-
I Flood-Related Hazards rate assessment of the flood-related forces acting upon a

I 

structure. Floodwaters surrounding a building exert a num-
I Flood Depth I ber of forces on the structure, including lateral and vertical 
hydrostatic forces, hydrodynamic forces, impact forces, and 
I Hydrostatic Forces erosion effects. Additionally, interior drainage, closed basin 
lakes, alluvial fans, and movable bed streamspose flood-
Hydrodynamic Forces related hazards that require consideration. 

I Impact Forces Hydrostatic forces (pressures) are caused by water above the

I 

surface of the ground that is either stagnant or moving slowly. 
Erosion Hazards Saturated soils beneath the ground surface also impose 
hydrostatic loads on foundation components. 

I Interior Drainage 

I

I Hydrodynamic forces (pressures)result from the moderate-
Impact loads are imposed on the structure by waterborne 
Closed Basin Lakes objects; their effects become greater as the velocity of flow, 
the weight of the objects, and the duration of the impact 
Movable Bed Streams increase. The basic equations for analyzing and considering 
these flood-related forces are provided below. 

I Alluvial Fans or high-velocity flow of water against or around a structure. 

Figure IV- 1: Flood-Related Haz ards 

FLOOD DEPTH 

Riverine Areas 

The determination of expected flood depth at a site is a 
Additional information concern-critical aspect of the overall determination of flood-related 
ing the determination of flood-hazards. One method of determining the 100-yearwater-
related forces will be available ir surface elevation is to look at the Flood Insurance Rate Mapthe next revision of the Flood 
Design Load Criteria incorpo-(FIRM) panel depicting the location of the structure in 
rated in Section 5 of ASCE 7 question. On most FIRMs, floodplains are delineated for 
Standard, Minimum Design floods of 100-and 500-year frequencies. As an example, 

Loadsfor Buildingsand Other
Structures, expected to be
published in 1995.

IV -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Figure IV-2 shows the portion of a community's FIRM 
where a subject home is located. 

Figure IV-2: House Location on the FIRM 

In this example, the location of the home was determined 
by pacing off the distance from the intersection of Van 
Nostrand Avenue and Jones Street. The house is located 
approximately 50 feet north of the intersection. Converting 
this distance to the map's scale (one inch equals 400 feet), 
the house is 0.125 inches along Jones Street from its intersection 
with Van Nostrand Avenue, and 0.125 inches from 
Jones Street. 

The darker shaded area on the map is the 100-year floodplain. 
The lighter shaded area denotes the 500-year floodplain. 
The house is located in this area between two wavy 
lines numbered 127 and 128. These are the 100-year flood 
elevations at those locations on Flat Rock Brook. Therefore, 
the 100-year flood elevation affecting the home in this 
example is between 127 and 128 feet, based on the National 
Geodetic Vertical Datum (NGVD). 

Flood elevations for the other frequencies are shown on the 
stream's water-surface profile in the FIS report. For the 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -3 
January 1995 


Chapter IV: Determination of Hazards 

above example, the position of the house on Flat Rock 
Brook was determined by drawing a line on its location on 
the FIRM (Figure IV-3) perpendicular to the stream. The 
point where this line crosses the streamline is the location of 
the house along the stream. 

\9>1Att l | l | | | | ~~129

\ 

plied by 400 feet pr ih of m . CESTER 
ZONE X * X

;EoZONE lSTREET/

\\ xt\\ 2l

~~RM/v 1// 

Aeu ONE XFla

n h Nstr an bridge is

a\\Loca thpnon FlnatRc B w w evi

\ 

pointare=126 4 , 25 1 an N

\ \12 //S

\<\ 128 

\ \0--11inhs, \\// tha whe totea

\ 124 a meauemn covre

91 Z~~~~ONEX/

_>\ %/ 1 OZONE X s / 

Figure IV-3: Stream Location on the FIRM 

The distance along the stream (Figure IV-3) is then measured 
from the home to Van Nostrand Avenue, the nearest 
bridge structure across Flat Rock Brook. This distance is 

0.1I1 inches, a measurement that when converted to the map 
scale is equal to approximately 45 feet (0.11 inches multiplied 
by 400 feet per inch of map). 
The Van Nostrand Avenue bridge is then located on the Flat 

Rock Brook profile (Figure IV-4) and measured 0.45 inches 
upstream (45 divided by 100 feet per inch, which is the 
horizontal scale of the profile). This location is marked as 
the point on Flat Rock Brook with water-surface elevations 

equivalent to the house. The elevations on the profile at this 
point are 124.5, 125.9, 127.1, and 128.1 feet for the 10-, 
50-, 100-, and 500-year floods, respectively. The bottom of 
the Flat Rock Brook channel shown on the profile is at 

119.5 feet. 
IV -4 EnaineeringPrinciplesand Practices of Ratrofittinn Flooid-Prone Resideantial Structuresa

I -vr_**~%-~--^%---._.._ 1995

.*.~~ .z__-aiav. 

Janluarv 1995 


C3-rM 

CD( 

_

=y -UIIII 

o. T 
CD ci) ~~125 

0 -
0

CD I 

ci) o 120 

0 

J0> 

CD 0 (). -L 

~i' ILL 115 r 

0 -n 
-
0 

0 w~~0 0
CD 0 >0 ------

CD 11 

(D 0~~~~~~~~~~~~~~~~~~~~~~~~ 

Year I

(n 0 ~~~~~~~~~~~~~~ 500Flood 

2D 0~----~ ---~ ~ ~ ~ ~ 1 0 YearFlood 

~~~~~~~~~ 

D)-----0Y a lo

C--
C -------~~~~~~~~Stream C

7.37. . . . Bed .8798081C
Stream Distance in Thousands of Feet above Confluence with Overpeck Creek 

0L 

N 


Chapter IV: Determination of Hazards 

S~~~~~~~~~~~~~~~~

TableTV-i Flood Data 
Summary 

Frequency Elevation 

Channel 119.5 ft.
Bottom

10-yr. 124.5 ft. 

50-yr. 125.9 ft. 

100-yr. 127.1 ft. 

500-yr. 128.1 ft. 

-r 

Flood elevations in coastal A and 
VZones are based on wave height 
and runup added to the stillwater 
elevation. For the 1 00-year 
frequency flood (BFE), refer to the 
FIRM. For other flood frequencies, 
the flood elevation can be 
estimated by multiplying 1.55 
times the difference between the 
stillwater elevation and the 
ground surface elevation. A 
detailed discussion of the methodologies 
involved in computing 
wave heights and runup is beyond 
the scope of this manual. Refer to 
FEMA's Guidelines and Speciflcationsfor 
Wave Elevation 
Determination and VZone 
Mapping, Third Draft, July 1989, 
for more information. 

Once the flood frequency and associated elevation information 
is obtained, a summary table can be created and used to 
calculate the depth of each flood frequencyto be considered. 
Table IV-1 depicts the flood data obtained from the 
FIS for this example 

Coastal Areas 

In coastal areas, the determination of the expected water 
surface elevation for the various recurrence interval floods 
is made by locating the structure and its flooding source on 
the FIRM, identifying the corresponding flooding source/ 
location row on the summary of stillwater elevation table, 
and selecting the appropriate elevation for the recurrence 
interval in question. 

As an example, consider a building located on Georgetown 
Street (as depicted on Figure IV-5). From the FIRM we 
can identify the flooding source as the Atlantic Ocean. 
Review of the entire area map for the FIS would indicate 
the Town of Fenwick Island (and Georgetown Street) is 
located between Bethany Beach and the Delaware-Maryland 
State Line. 

ZME AE 

Figure IV-5: Coastal FIRM 

IV -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 

0

0


Analysis of Flood-Related Hazards 

This flooding source/location is located on the summary of 
stillwater elevations table (Figure IV-6). From this table, 
flood elevations of 6.2, 7.8, 8.6, and 10.2 feet above NGVD 
are identified for the 10-, 50-, 100- and 500-year frequency 
floods, respectively. 

Summary of Stillwater Elevations 

Atantic Ocean 

Coastline from Cape Henlopen
-tojust south-of -DeweyBeach------6.5------8.2------9.2------11.3----

Coastline from just south of
Dewey Beach to just north of
Bethany Beach 6.4 8.0 8.9 10.8

Coastline from just north of
Bethany Beach to Delaware-
Maryland state line 6.2 7.8 8.6 10.2

Chesapeake Bay
Coastline at Chance 4.2 5.4 5.8 6.8

Delaware Bay
Coastline from Kent-Sussex
County line to Cape Henlopen 6.6 8.5 9.3 11.3

Indian River Bay
Entire coastline 4.7 6.4 7.5 10.8

Rehoboth Bay
Entire coastline 3.9 5.9 7.0 10.8

Assawoman Bay
Coastline within Sussex County 3.8 5.4 6.0 10.2

Little Assawoman Bay
Entire Coastline 3.8 5.4 6.0 10.2

National Geodetic Vertical Datum of 1929 

Figure IV-6: Summary of Stillwater Elevations 

Enaineerina Princinles and Practices of Retrofittina Flood-Prone Residential Structures IV -7 
January 1995 


Chapter IV: Determination of Hazards 

I 

When computing flood depth, be. 
sure to utilize the lowest ground 
surface adjacent to the structure 
in question as shown in Figure 
IV-7. 

I 

Flood depth can be computed by subtracting the lowest 
ground surface elevation (grade) adjacent to the structure 
from the flood elevation for each flood frequency, as shown 
in Formula IV-1. 

j j d =FE -GS= _feet 

where: d is the depth of flooding (in feet); 

FE is the flood elevation for a 
specific flood frequency (in feet); 
and 

GS is the lowest ground surface 
elevation (grade) adjacent to a 
structure (in feet). 

Formula IV- 1: Flood Depth 

S

For design purposes, a factor of safety (freeboard) is typically 
added to the flood elevation to develop a retrofitting 
design level as illustrated in Formula IV-2: Flood Protection 
Elevation. 

IC-f DI 

FPE =FE +f = _feet 

U. 
where: FPE is the flood protection elevation
(in feet);

FE is the flood elevation for a 
specific flood frequency (in feet); 
and 

f is the factor of safety (freeboard), 
typically a minimum of 1.0 foot. 

Formula IV-2: Flood Protection Elevation 

The floodproofing design depth (H), which is used to 
calculate flood-related hazard forces, is the difference 
between the FPE and the lowest grade adjacent to the 
structure. This computation is shown in Formula IV-3. 

v -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

II 

H=FPE-GS=_feet 

In some instances involving where: H is the floodproofing design depth

combined soil and water forces, 

over which flood forces are

another reference feature such as 
the top of slab or footing is considered (in feet); 
normally used instead of lowest FPE is the flood protection elevation 
adjacent grade to compute the for a specific flood frequency (in 
floodproofing design depth. feet); and 

GS is the lowest ground surface 
elevation (grade) adjacent to the 
structure (or other reference 
feature such as a slab or footing) 
(in feet). 

Formula IV-3: Floodproofing Design Depth 

._ 

Figure IV-7: Illustration of Flood I)epth and Design Depth 

Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures IV -9 
January 1995 


Chapter IV: Determination of Hazards 

HYDROSTATIC FORCES

Hydrostatic Forces 

Lateral Water Pressures Hydrostatic pressures (loads), at any point of floodwater 
contact with the structure are equal in all directions and 
Saturated Soil Pressures always act in a perpendicular manner to the surface on 
which they are applied. Pressures increase linearly with 
Combined Water and ] depth or "head" of water above the point under consider-
Saturated Soil Pressures ation. The summation of pressures over the surface under 
Equivalent Hydrostaticconsideration represents the load acting on that surface. 
Pressures due to Velocity ] For structural analysis, hydrostatic forces, as shown in 
Figures IV-9 and IV-10, are defined to act: 

Vertical (Buoyancy)
Water Pressures

* vertically downward on structural elements such as flat 
Figure IV-8: Hydrostatic Forces roofs and similar overhead members having a depth of 
water above them; 

* vertically upward (uplift) from the underside of generally 
horizontal members such as slabs, floor diaphragms, 
and footings (also known as buoyancy); 
* laterally, in a horizontal direction on walls, piers, and 
similar vertical surfaces. (For design purposes, this 
lateral pressure is generally assumed to act on the 
receiving structure at a point one-third of the water 
depth above the base of the structure or two-thirds of 
the altitude from the water surface, which correlates to 
the center of gravity for a triangular pressure distribution.) 
Hydrostatic forces include lateral water pressures, saturated 

soil pressures, combined water and soil pressures, equiva

lent hydrostatic pressures due to velocity flows, and vertical 

or buoyancy pressures. The computation of each of these 

pressures is illustrated in the sections that follow. 

For the purpose of this document, it has been assumed that 
hydrostatic conditions prevail for stillwater and water 
moving with a velocity of less than ten feet per second. 

IV -10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

* Flood Protection Elevation 
| Wm T T T T 

ti t t Fb: Vertical Upward 
(Buoyancy)Forces 

Figure IV-9: Hydrostatic Force 

Hydrostatic loads generated by velocities up to 10 feet per 

second may be converted to an equivalent hydrostatic load 

using the conversion formula presented later in this chapter. 

Lateral Hydrostatic Forces 

The basic equation for analyzing the lateral force due to 

hydrostatic pressure from standing water above the surface 

of the ground is illustrated in Formula IV-4: 

Fh =%PhH =2yH2 = lbs/LF 

where: Fh is the lateral hydrostatic force 
from standing water (in pounds 
per linear foot of surface) acting 
at a distance H/3 from the point 
under consideration; 

PhIN is the hydrostatic pressure due to 
standing water at the point under 
consideration (in pounds per 
square foot), (Pl= yH); 

S is the specific weight of water 

(62.4 pounds per cubic foot); and 
H is the floodproofing design depth 
(in feet). 

Formula IV-4: Lateral Hydrostatic Forces 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -11 
January 1995 


Chapter IV: Determination of Hazards 

Saturated Soil Forces 

If any portion of the structure is below grade, saturated soil 

forces must be included in the computation in addition to the 

hydrostatic force. This situation is illustrated in Figure IV

10.The basic equation for analyzing the resultant lateral 
force due to hydrostatic forces from saturated (non-expansive) 
soil is: 
I-I 

Fatm=%SDI=% PDD= lb/LF

I C0 I 

-where: Ft is the lateral force from saturated 
soil acting at a distance D/3 from 
the point under consideration (in 
pounds per linear foot of surface); 

PD is the lateral hydrostatic pressure 
due to saturated soil at the point 

Formula IV-5: Saturated Soil under consideration (in pounds 

Hydrostatic Forces is not suitable per square foot); 

for expansive soils, due to the 

unpredictable nature of these S is the equivalent fluid weight of 

soils. Due to the continual saturated soil (in pounds per cubic 

shrink and swell of expansive foot); and 

soil backfills and the variation of D is the depth of saturated soil (in 

their water content, the stability feet) over which hydrostatic

and elevation of these soils and 

overlaying soil layers may vary forces are considered. 

considerably. The analysis of 

hydrostatic pressure and bearing Formula IV-5: Saturated Soil Hydrostatic Forces 
capacity for expansive soils 
should be conducted by a 
qualified soils engineer. Preferably, 
expansive soils should be 
removed and replaced by stable 
soils. 

IV -12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

W Flood Protection Elevation 

Figure IV-10: Saturated Soil Hydrostatic Forces 

The equivalent fluid pressures for various soil types are 

presented in Tables IV-2 and IV-3. The equivalent fluid 

weight of saturated soil is not the same as the effective 

weight of saturated soil. Rather, the equivalent fluid weight 

of saturated soil is a combination of the unit weight of water 

and the effective saturated weight of soil. 

Table IV-2 Effective Equivalent Fluid Weight of Soil(s) 

Column A Column B 

S. Equivalent 
Equivalent Fluid Weight 
Fluid Weight of 
Soil Type' ofMoist Soil Submerged 
(pounds per Soil and 
cubic foot) Water 
(pounds per 
cubic foot) 

Clean sand and gravel: GW, GP, SW, SP 30 75 

Dirty sand and gravel of restricted permeability: 35 

77 
GM, GM-GP, SM, SM-SP 

Stiff residual silts and clays, silty fine sands, 
clayey sands and gravels: CL, ML, CH, MH, SM, 45 82 
SC, GC 

Very soft to soft clay, silty clay, organic silt and 100 

106 
clay: CL, ML, OL, CH, MH, OH 

Medium to stiff clay deposited in chunks and 120 142 
protected from infiltration: CL, CH 

Note: See Table IV-3 for soil type definitions. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -13 
January 1995 


Chapter IV: Determination of Hazards 

Table IV-3 Soil Type Definitions Based 
on USDAUnified Soil Classification 

Soil Type Group Description

Symbol 

Gravels GW Well-graded gravels and gravel 
mixtures. 

GP Poorly graded gravel-sand-silt 
mixtures. 

GM Silty gravels, gravel-sand-silt 
mixtures. 

GC Clayey gravels, 
gravel-sand-clay mixtures. 

Sands SW Well-graded sands and gravelly 
sands. 

SP Poorly graded sands and 
gravelly sands. 

SM Silty sands, poorly graded 
sand-silt mixtures. 

SC Clayey sands, poorly graded 
sand-clay mixtures. 

Fine Grain Silt ML Inorganic silts and clayey silts. 
and Clays 
CL Inorganic clays of low to 
medium plasticity. 

OL Organic silts and organic silty 
clays of low plasticity. 

MH Inorganic silts, micaceous or 
fine sands or silts, elastic silts. 

CH Inorganic clays of high plasticity, 
fine clays. 

OH Organic clays of medium to high 
plasticity. 

IV -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Combined Water and Saturated Soil 
Forces 

When a structure is subject to hydrostatic forces from both 
saturated soil and standing water (illustrated in Figure IV

11), the resultant cumulative lateral force, FH'is the sum of 
the lateral water hydrostatic force, Fh, and the differential 
between the water and soil pressures, F dir The basic equation 
for computing Fdifis: 

=D 
. 5 
'foo ' 
Fdif = 12 (S-y)D2 
= _lbsALF 
where: Fdif is the differential soil/water force 
acting at a distance D/3 from the 
point under consideration (in 
pounds per linear foot of 
surface); 
S is the equivalent fluid weight of 
submerged soil and water (in 
pounds per cubic foot); 
D is the depth of saturated soil 
(in feet); and 
Y is the specific weight of water 

(62.4 pounds per cubic foot). 
Formula IV-6: Combined Water and Soil Forces 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -15 
January 1995 


ChapterIV: Determination of Hazards 

6 FH Fh + FdIf=_ IbsfLF 
Note that while Fh and Fd1!do not 
act at the same point, we can where: FH is the cumulative lateral hydro-
assume for structural analysis static force acting at a distance 
purposes that FH acts at a H/3 from the point under considdistance 
H/3 above the point 
under consideration. eration (in pounds per linear foot 
of surface); 

Fh is the lateral hydrostatic force 
from standing water (from 
Formula IV-4); and 

Fdif is the differential soil/water force 
(from Formula IV-6). 

Formula IV-7: Cumulative Lateral Hydrostatic Force 

V Flood Protection Elevation 

F~~~~~~~~~~~~F

H13

D

F~ ~ ~ ~ 7A-Area of 
F. ~ ~ ~ ~ ~ ~ ~ ~ ~ ,~ H orizontal 
D~~~~~ F ~~~Surf ace 

T t FbT t t

t 

Figure IV-I 1: Combination Soil/Water Hydrostatic and Buoyancy Forces 

IV -16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Vertical Hydrostatic Force 

The basic equation for analyzing the vertical hydrostatic 
force (buoyancy) due to standing water (illustrated by 
Figure IV-l 1.) is: 

F=~~~~~b yAH= lbs 
where: Fb is the force due to buoyancy (in 
pounds); 
Y is the specific weight of water 
(62.4 pounds per cubic foot); 
A is the area of horizontal surface 
(floor or slab) being acted upon 
(in square feet); and 
H is the floodproofing design depth 
(in feet). 

Formula IV-8: Buoyancy Force 

The computation of hydrostatic forces is vital to the successful 
design of floodwalls, sealants, closures, shields, 
foundation walls, and a variety of other retrofitting measures. 
The following Hydrostatic Force Computation 
Worksheet (Figure IV- 12) can be utilized to conduct hydrostatic 
calculations. Figure IV- 13, Example Hydrostatic 
Force Computation, illustrates the use of the worksheet. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Iv -17 
January 1995 


HYDROSTATIC FORCE COMPUTATIONWORKSHEET 

Owner Name: Prepared By:
Address: Date:_
Property Location:

Variables: Summary ofForces
H (Floodproofing Design Depth)= Fh=
D (Depth of Saturated Soil) = Fsat=
y (Specific Weight of Water) = 62.4 lbs/cubic foot Fdif=
S (Equivalent Fluid Weight of Saturated Soil) = FH=
A (Area) = Fb=

Formula IV-4: Lateral Hydrostatic Force From Freestanding Water 

Fh =%PhH = %yH2= 

Formula IV-5: Lateral Hydrostatic Force From Saturated Soil 

Fsat = S D2or %PDD= 

Formula IV- 6: Lateral Hydrostatic Force
From Standing Water and Saturated Soil

Fdif= I/ (S-y) D2 

Formula IV-7: Total Lateral Hydrostatic Force From
Standing Water and Saturated Soil

FH= Fh+ Fddf 

Formula IV-8: Vertical Hydrostatic Force (Buoyancy) 

Fb= yA = 

Note: Formulas IV-4-6 do not account for equivalent hydrostatic loads due to 
velocity floodwaters (less than 10 fps.). If velocity floodwaters exist, recompute FH 
using Formula IV- 11. 

Figure IV- 12: Hydrostatic Force Computation Worksheet 

IV- 18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

i HYDROSTATIC FORCE COMPUTATION WORKSHEET 

I 

Owner Name: 5t WMt Prepared By: -=V
Address: m 1S Date: 3i

lZy mier 1e l'et 

PropertyLocation: 7M 3I 9S lcnots 4. L-arrLA 

Variables: Summary of Forces 
H (Floodproofing Design Depth)= *Fh= LA9"1 bI LP 
D (Depth of Saturated Soil) = Z F, t= tio > kipsIL 
y (Specific Weight of Water) = 62.4 lbs/cubicfoot Fdi = l  \ \t 1LF 
S (Equivalent Fluid Weight of Saturated Soil) = AFH= 6C> 1\s ILP 
A(Area)= Mentor*-lucO-:5 4 F, Z9c,5ZCD %U5 

Formula IV-4: Lateral Hydrostatic Force From Freestanding Water 

Fh=VZPH = Vr/W =/*Xi4(i.4 Q) k99 ls Lp 

Formula IV-5: Lateral Hydrostatic Force From Saturated Soil 

F= I/D ( V)L -as

2 SD= Lo/4)(z t\'O I/LF 

Formula IV-6: Lateral Hydrostatic Force
From Standing Water and Saturated Soil

Fdif= 1 (S-)D = YL&4SE;-ZI'i 1h44Q(L (L 4)
-\ O \ t5 /L5 

Formula IV-7: Total Lateral Hydrostatic Force From
Standing Water and Saturated Soil

FH= Fh+ Fd;= 4991 16LrF * jot I/L 

H ~~ ~ ~ ~ F. ~ ~ i.~ ~ .. ... 
I 

Formula IV-8: Vertical Hydrostatic Force (Buoyancy) 

I 

Fb=yAH= (4-Li 4as)(20O0OeX'4 &) 

-z2,sqo 1IS

8s 

Note: Formulas IV-4-6 do not account for equivalent hydrostatic loads due to 
velocity floodwaters (less than 10 fps.). If velocity floodwaters exist, recompute F. 
using Formula IV-1 1.

I 

J 

Figure IV-13: Example Hydrostatic Force Computation Worksheet 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV-19 
January 1995 


Chapter IV: Determination of Hazards 

HYDRODYNAMIC FORCES 

When floodwaters flow around a structure at moderate to 
high velocities, they impose additional loads on the structure, 
as shown in Figure IV- 14. These loads consist of 
frontal impact by the mass of moving water against the 
projected width and height of the obstruction represented by 
the structure, drag effect along the sides of the structure, 
and eddies or negative pressures on the downstream side of 
the structure. 

Low velocity hydrodynamic forces are defined as situations 

where floodwater velocities do not exceed 10 feet per 

second, while high velocity hydrodynamic forces involve 

floodwater velocities in excess of 10 feet per second. 

Negative Pressure 

(Suction) on 
DownstreamSide w 0 

Drag Effect 
on Sides 

Figure IV-14: Hydrodynamic and Impact Forces 

IV -20 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Sources of data for determining 
flood flow velocity include 
hydraulic calculations, historical 
measurements, and rules of 
thumb. Floodwaters one foot 

deep moving in excess of five 
feet per second can knock an 

adult over and cause erosion of 
stream banks. Overbank velocities 
are usually less than stream 

channel velocities. If no data for 
flood flow velocity exists for a 

site, the reader should contact an 
experienced hydrologist or 
hydraulic engineer for estimates. 

Table IV-4 Drag 
Coefficients 

Width to height Drag Coefficient 
Ratio b/h Cd 
From 1 to 12 1.25 

13 to 20 1.3 
21 to 32 1.4 
33 to 40 1.5 
41 to 80 1.75 

81 to 120 1.8 
160 or more 2.0 

Low Velocity Hydrodynamic Forces 

In cases where velocities do not exceed 10 feet per second, 
the hydrodynamic effects of moving water can be converted 
to an equivalent hydrostatic forceby increasing the depth of 
the water (head) above the flood level by an amount dh, 
which is: 

dh-CdV2 =_feet

2g 
where: dh is the equivalent head due to low 
velocity flood flows (in feet); 
Cd is the drag coefficient (from Table 
IV-4); 
V is the velocity of floodwaters (in 
ft/sec); and 
g is the acceleration of gravity 
(equal to 32.2 ft/sec2). 

Formula IV-9: Conversion of Low Velocity Flow to 
Equivalent Head 

The drag coefficient Cddepends on the proportions of the 
shape of the object around which the water flows. The 
value of Cd,unless otherwise evaluated, shall not be less than 

1.25 and can be determined from the width-to-height ratio, 
b/h, of the structure in question. The width (b) is the side 
perpendicular to the flow and the height (h) is the distance 
from the bottom of the structure to the water level. Table 
IV-4 gives Cdvalues for different width-to-heightratios. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -21 
January 1995 


Chapter IV: Determination of Hazards 

The value dh is then converted to an equivalent hydrostatic 

pressure through use of the basic equation for lateral 
hydrostatic forces introduced earlier in this chapter and 
modified as shown below: 

I-II 

IDco li 

Fdh= y (dh)H = PdhH = lbs/LF 

where: Fdh is the equivalent hydrostatic 
force due to low velocity 
flood flows (in pounds per linear 
foot of surface); 

Y is the specific weight of water 

(62.4 pounds); 
H is the floodproofing design depth 
in feet; 
dh is the equivalent head due to low 
velocity flood flows in feet; and 
Pdh is the hydrostatic pressure due to 
low velocity flood flows (in 
pounds per square foot) 

(Pdh = y (dh)). 

Formula IV-10: Conversion of Equivalent Head to Equivalent 
Hydrostatic Force 

The resultant lateral hydrostatic force due to low velocity 
hydrodynamic pressures is then added to the lateral hydrostatic 
pressures due to standing water and saturated soil to 
obtain the total lateral hydrostatic force shown below and 

A-' 

While Fdh acts at a point H/2, it 
is normally a small percentage of 
FH,therefore, we can assume that 
Fdh acts at the same point H13 as 

FH. 

illustrated in the Equivalent Hydrostatic Force Computation 
Worksheet, Figures IV-15 and IV-16. 

DCD D 

FH Fh +F. +Fd lbsILF 

H h dif dh 

where: variables were defined previously in 
Formulas IV-4, IV-6, IV-7, and IV-lO. 

Formula IV- 11: Total Lateral Hydrostatic Force 

IV -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related: Hazards 

EQUIVALENT HYDROSTATIC FORCE
COMPUTATION WORKSHEET

Owner Name: -Prepared By:
Address: _ Date:
Property Location:

Variables: Summary of Forces 
b (width of structure perpendicular to flow) = Fdh= 
=

H (floodproofing design depth) = Fh 
h (height of water above structure bottom) = Fdif=
V (velocity of flood water, 10 feet per second or less) = F =
y (specific weight of water) = 62.4 lbs/cubic foot
g (acceleration of gravity) = 32.2 feet per second squared

Formula IV-9: Conversion of Low Velocity Flood Flow to Equivalent Head 

dh== Cd'V2
2g

Develop Cd: 
b/h = 
From Table IV-4; Cd= 

Formula IV-10: Conversion of dh to Equivalent Hydrostatic Force 

Fdh= Y(dh)H= 

Formula IV-l 1: Total Lateral Hydrostatic Force 

FH = Fh+Fdif +Fdh= 

Figure IV-15: Equivalent Hydrostatic Force Computation Worksheet 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -23 

January 1995 


ChapterIV: Determination of Hazards 

EQUIVALENTHYDROSTATICFORCE
COMPUTATIONWORKSHEET

OwnerName: vA . Prepared By: --f
Address: v. W^r 5-rM*r Date: to1l idl
PropertyLocation:-rM 3 , LcT LA

So nom 6 

Variables: Summary of Forces 
b (width of structure perpendicular to flow)= 3 Fdb = i I LF 
H(floodproofingdesigndepth)=4' Fh= '499 1bfLF 
h(heightofwaterabovestructurebottom)= F.,= 1I s/L

3 lto t 
V (velocity of flood water, 10 feet per second or less) = = -415 ls ILF 
y (specific weight of water) = 62.4 lbs/cubic foot 
g (acceleration of gravity) = 32.2 feet per second squared 

Formula IV-9: Conversion of Low Velocity Flood Flow to Equivalent Head 

CdV2 

dh = 2 = 

2g 

/NS \Develop Cd: 

_____)____ b/h= 10 

z C3ZZ iSec) FromTab1elV-4;Cd=1.Z5 

OA-Q+ --ze 

Formula IV-10: Conversion of dh to Equivalent Hydrostatic Force 

Fdh y(dh)H= C(z1 &A * 

.- 45 16s/ur 

Formula IV-l 1: Total Lateral Hydrostatic Force 

FH= Fh+ Fdir+ Fdh= L499 +41014+ 5 jlos/LF 

: Hyrti Fc C/LF 

Figure IV-16: Example Equivalent Hydrostatic Force Computation 

IV -24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

HIGH VELOCITY HYDRODYNAMIC 
FORCES 

For special structures and conditions, and for velocities 

greater than 10 feet per second, a more detailed analysis 
and evaluation should be made utilizing basic concepts of 
fluid mechanics and/or hydraulic models. The basic equation 
for hydrodynamic pressure is: 

v 2 

: -lbs/SF

CdP

=d 

where: Pd is the hydrodynamic pressure (in 
pounds per square foot); 
p is the mass density of water (1.94 
slugs/ft3 ); 
V is velocity of floodwater (in feet 
per second); and 
Cd is the drag coefficient (taken 
from Table IV-4). 

Formula IV-12: High Velocity Hydrodynamic Pressure 

After determination of the hydrodynamic pressure (Pd)' the 
total force (Fd)against the structure (see Figure IV-14) can 
be computed as the pressure times the area over which the 

water is impacting: 

F =P A-lbs 

ails ~~~~dd 

where: Fd is the total force against the 
structure (in pounds); 
Pd is the hydrodynamic pressure (in 
pounds per square foot); and 

A is the submerged area of the 
upstream face of the structure in 
question (in square feet). 

Formula IV-13: Total Hydrodynamic Force 

ln,.mn~pinjn Drineidnle and Practices of Retrofittinn Flood-ProneResidentialStructures IV-25 

Januarv 1995 


Chapter IV: Determination of Hazards 

Figure IV- 17,Hydrodynamic Force (High Velocity) Computation 
Worksheet, can be used in the computation of 
high velocity hydrodynamic forces, while Figure IV-18 
illustrates the computations. 

IV -26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

HYDRODYNAMIC FORCE (HIGH VELOCITY)
COMPUTATIONWORKSHEET

Owner Name: Prepared By: 
Address: Date:_ 
Property Location: 

Variables: Summary of Forces 

p (mass density of water) = 1.94 slugs/ft3 Pd =
V (velocity of floodwater, > 10 feet per second) Fd=
Cd(drag coefficient) =
A (submerged area of upstream face of structure) =

Formula IV-12: High Velocity Hydrodynamic Pressure (Force) 

Pd =Cdp (VI/ 2) 
Develop Cd. 
b/h = 
From Table IV-4; Cd= 

Formula IV-13: Total Force Against the Structure 

Fd = Pd A= 

M 

Figure IV-17: Hydrodynamic Force (High Velocity) Computation Worksheet 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IVIV-27 
January 1995 


Chapter IV: Determination of Hazards 

HYDRODYNAMICFORCE (HIGH VELOCITY)
COMPUTATION WORKSHEET

OwnerName: 5 *AI vA Prepared By: Address: 
v12 UJAr-'R dSeT Date: Loe:I 19'4 

PropertyLocation::TrN 313, 5cro% N (a. LOT 4 

Variables: Summary ofForces 
p (mass density of water) = 1.94 slugs/ft3 Pd= I5 9 1H 

V (velocity of floodwater, >10 feet per second) = 12.' 5 Fd= 2 I, C UP5 
Cd(drag coefficient) =I, Z 5 
A (submerged area of upstream face of sttucture) = l 

_ I2 O ___ 

a 

Formula IV-12: High Velocity Hydrodynamic Pressure (Force) 

Pd=Cdp (W 2)= 

1.94 Sft ~~Z Develop Cd: 
a1.5( 1yg-b/h = 
iJ" 5u 7 A From Table IV-4; Cd= l.ZY 

sh

-~ ~ ~~Z lb same 

Fonnula IV-13: Total Force Against the Structure 

Fd= d A= (V \+frr")C a 4 ) 

Fu& L 00 \1 E 

Figure IV-I 8: Example Hydrodynamic Force (High Velocity) Computation 

IV -28 Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

IMPACT LOADS 

Impact loads are imposed on the structure by objects carried 
by the moving water. These loads are the most difficult to 
predict and define, yet reasonable allowances must be made 
for these loads in the design of retrofitting measures for 
potentially affected buildings. To arrive at a realistic allowance, 
considerablejudgment must be used, along with the 
designer's knowledge of debris problems at the site and 
consideration of the degree of exposure of the structure. 
Impact loads are classified as either: 

* no impact (for areas of little or no velocity or potential 
source of debris); 
* normal impact; 
* special impact; or 
* extremeimpact. 
Engineerina Principles and Practices ol Retrofitting Flood-Prone Residential Structures IV -29 
January 1995 


Chapter IV: Determination of Hazards 

Normal Impact Forces 

Normal impact forces relate to isolated occurrences of 
typically sized ice blocks, logs, or floating objects striking 
the structure (see Figure IV-14). For design purposes, this 
can be considered a concentrated load acting horizontally at 
the flood elevation, or any point below it, equal to the 
impact force created by a 1,000-pound mass traveling at the 
velocity of the floodwater acting on a one-square-foot 
surface of the submerged structure area perpendicular to 
the flow. The calculationof normal impact forces is shown 
in Formula IV-14. 

Li = MV =W~V -F lbs
F _= gt

where: Fn is the normal impact force (in 
pounds); 
wn is weight of object (1,000 lbs for 
normal impact loads); 
g is acceleration of gravity (32.2 ft/ 
sec 2); 
t is time of impact (generally 1 sec 
or less); 
V is velocity of flow (in feet per 
second); and 
M is the mass of the object computed 
as w.Ig. 

Formula IV-14: Normal Impact Force 

IV -30 Enqineerina Principles and Practices of Retrofittino Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Special Impact Forces 

Special impact forces occur when large objects or conglom

erates of floating objects, such as ice floes or accumulations 
of floating debris, strike a structure. In an area where 
special impact forces may occur, the load considered for 
design purposes is the impact created by a 1 00-pound load 
times the width of building, acting horizontally over a one-
foot-wide horizontal strip at the flood elevation or at any 
level below it. Where stable natural or artificial barriers 
exist that would effectively prevent these special impact 
forces from occurring, these forces may not need to be 
considered in the design. 

E MV wV 1OObV
u lullFS= t gt 32. 2t 

where: F. is the special impact force (in 
pounds); 
Ws is weight of object (in pounds) 
(100 lbs/ft x width of structure 

(b) normal to flow); b is shown in 
Figure IV-14; 
b is the width of structure normal 
to flow (in feet);
g is acceleration of gravity

(32.2 ftlsec2); 
t is time of impact (generally 1 sec 
or less); 
V is velocity of flow (in feet per 
second); and 
M is the mass of the object 
computed as w/g 

I 

Formula IV-15: Special Impact Forces 

IV -31 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ; ~~IV-31 

January 1995 


/iI--

Chapter IV: Determination of Hazards 

Whether impact loads should be allowed for depends on data 
that can be obtained from a number of sources: 

* historic records and the FIS; 
* interviewswith local residents and floodplain management 
officials; 
* floodway versus floodplain location; 
* upstream debris potential; and 
* climatologic information. 
Impact forces are critical design considerations that must be 
thoroughly evaluated. The following Impact Force Computation 
Worksheet, Figure IV-19, can be used to conduct 
those calculations, while Figure IV-20 illustrates those calcu

lations. 

Extreme Impact Forces 

Extreme impact forces occur when large, floating objects and

Where extreme impact loads are a 
threat, the preferred retrofitting masses, such as runaway barges or collapsed buildings andalternativeis relocation. structures, strike the structure (or a component of the structure). 
These forces generally occur within the floodway or 
areas of the floodplain that experience the highest velocity 
flows. It is impractical to design residential buildings to have 
adequate strength to resist extreme impact forces. 

IV -32 EnaineerinoPrinrinlss andiPractices nf Pctrnfittiret Flnnnrl-Dr-nc -;A.-s.-.+;:IC0+,.

I>ttLICu --4, 

-->--a ,r--. . IILII.IlJ_41 a -{icazl~iyEvuc-iul 'JLIUL.LUrIe 

January 1995 


Analysis of Flood-Related Hazards 

IMPACT FORCE COMPUTATION WORKSHEET 

Owner Name: Prepared By:
Address: Date:
Property Location:

Normal Impact Loads 

Variables: Summary of Forces 

w. (weight of object) = typically, 1,000 pounds
g (acceleration of gravity) = 32.2 ft/sec2 F =
t (time of impact) = typically, 1sec. F,=
V (velocity of floodwater)=
M (mass of the object computed as wjIg)
Formula IV-14: Normal Impact Force 

F MV wV
n t = gt

Special Impact Loads 

Variables: 

b (width of structure normal to flow) =
w, (weight of object) = 100 (b) =
g (acceleration of gravity) = 32.2 ft/sec2
t (time of impact) = typically, 1 sec. or less
V (velocity of floodwater)=
M (mass of the object computed as wIg) =

Formula IV- 15: Special Impact Forces 

MV w5V 100bV
F =-=-t gt 32.2t = -lbI=s

Figure IV-19: Impact Force Computation Worksheet 

Engineering Principles and Practices of Retrofitting Flood-Prone ResidentialStructures IV -33 
January 1995 


Chapter IV: Determination of Hazards 

IMPACT FORCE COMPUTATION WORKSHEET 

Owner Name: 5 M t'r-* Prepared By: TeV
Address: z W4-mr-tSM-rET Date: 10131 IIS
PropertyLocation: , 38 Sec-o'

, 

Normal Impact Loads 

Variables: Summaryof Forces
wn (weight of object) = typically, 1,000 pounds
g (acceleration of gravity) = 32.2 ft/sec2 F = 3-r3 IL5
t (time of impact) = typically, 1 sec. FJ= kleti
V (velocityoffloodwater)= I% l t
M (massof the object computed as wj/g)=3-

Formula IV-14: Normal Impact Force 

FWnV(l$o Z*+fB

s3 \5( 

n. t t CS Z. Z + 4j t t sc 
t~~ 343\ 

Special Impact Loads 

Variables:
b (width of structure normal to flow) = 3
w1 (weightofobject) = = lac (so

I00(b) o 4(30 3000+
g (acceleration of gravity) = 32.2 ft/sec2
t (time of impact) = typically, 1 sec. or less
V (velocityof floodwater) = t1 -BD
M (mass of the object computed as wig)-=  '/iz.Z -E4/1 J

Formula IV-15: Special Impact Forces 

M w,V =lObV _(lo it(4)(0 &1)CLJ.I~sa*) 

5igure Example m32.2t Fc Czmp at I -sc) 

;eisure IV-20: Example Impact Force Computation 

IV -34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

RIVERINE EROSION 

The analysis of erosion that impacts stream banks and 
nearby overbank structures is a detailed effort that is usually 
accompanied by detailed geotechnical investigations. Some 
of the variables that impact the stability (or erodibility) of 
the stream banks include the following: 

* critical height of the slope; 
* inclination of the slope; 
* cohesive strength of the soil in the slope; 
* distance of the structure in question from the shoulder of 
the stream bank; 
* degree of stabilization of the surface of the slope; 
* level and variation of groundwater within the slope; 
* level and variation in level of water on the toe of the 
slope; 
* tractive shear stress of the soil; and 
* frequency of rise and fall of the surface of the stream. 
Both FEMA and the USACE have researched the stability 
of stream banks in an effort to quantify stream bank erosion. 
However, concerns over the universal applicability of the 
research results preclude their inclusion in this manual. It is 
suggested that when dealing with streambanks susceptible to 
severe erosion, the designer contact a qualified geotechnical 
engineer or a hydraulic engineer experienced in channel 
stability. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -35 
January 1995 


S Chapter IV: Determination of Hazards 

i 

Rainfall intensities f or the 

eastern half of the United States 

are available from H'YDRO-35,a 

publication of the N; ational 

Weather Service (NAVS),while 

rainfall intensities fe 

ir aet

western half of the L 
can be obtained fromi NOAA 
ATLAS 2, also publis shed by the 
NWS. Rainfall interisitiesare 
available for a range of storm 

frequencies including ;the 2-, 
10-, 25-, 50-, and 100-year 60minute 
events. The:2- or 10-
year intensity rainfalI is consid- 

ered a minimum desi 
for pumping rates wiienflood-
waters prevent gravity discharge 
from floodwalls and levees.The 
100-year intensity rainfall 
should be the maximum design 
value for sizing gravit' flowpipes and/or closures 

The rational formula (Q=cirA) is 
used to compute the amount of 
precipitation runoff from small 
areas. It is generally not applicable 
to drainage areas greater 
than 10 acres in size. 

INTERIOR DRAINAGE 

The drainage system for the area enclosed by a levee or 

floodwall must accommodate the precipitation runoff from 

this interior area (and any contributing areas such as roofs 

and higher ground parcels) and the anticipated seepage 

through or under the floodwall or levee during flooding 

conditions. 

There are two general methods for removing interior drainage. 
The first is a gravity flow system, which provides a 
means for interior drainage of the protected area when there 

is no floodwater against the floodwall or levee. This is 

accomplished by placing a pipe(s) through the floodwall or 

levee with a flap gate attachment. The flap gate prevents 

flow from entering the interior area through the drainpipe 
when floodwaters rise above the elevation of the drain. 

The second method, a pump system, removes accumulation 
of water when the elevation of the floodwater exceeds the 

elevation of the gravity drain system. A collection systemcomposed of pervious trenches, underground tiles, or sloped 
surface areas transports the accumulating water to a sump 
area. In the levee application, these drains should be incorporated 
into the collection system. The anticipated seepage 

from under and through levees and floodwalls must also be 
taken into consideration by combining it with flow from 
precipitation (see Figure IV-2 1). 

Floodwallor Levee 

House 

J~s Enclosed
Y 1 C Area

An=(x)(y) 

I~~~~~~~~Ix .1 

RectangularArea

FigureIV-2 1: 

Figure IV-2 !: Rectangular Area Enclosed by a Floodwall or 
Levee 

IV -36 Engineering Principles and Practices of Retrofittino Flood-Prone ResideontialStruiicture 
Januarv 1995 


Analysis of Flood-Related Hazards 

6 

The residential terrain runoff 
coefficient, c, is used to model the 
runoff characteristics of different 
land uses. Use the value for the 
predominant land use within a 
specific area or develop a 
weighted average for areas with 
multiple land uses. The most 
common coefficients are 0.70 for 
residential area, 0.90, for commercial 
area, and 0.40 for 
undeveloped land. 

Figure IV-22: Rectangular Area Partiall: y 
Enclosed by a Floodwall or Levw 

To determine the amount of precipitation that can collect in 
the contained area, the rainfall intensity, given in inches per 
hour, must be determined for a particular location (see 
note). This value is multiplied by the enclosed area, Aa, in 
square feet, a residential terrain runoff coefficient (c) of 0.7, 
and a conversion factor of 0.01. The answer is given in 
gallons per minute. 

mmU

U 

Qa= 0U01 cir Aa= gpm 

where: Q. is the runoff from the enclosed 
area (in gal/min (gpm)); 
Aa is the area enclosed by the floodwall 
or levee (in square feet); 
c is a residential terrain runoff 
coefficient of 0.7; 
0.01 is a factor converting the answer 
to gallons per minute; and 
ir is the intensity of rainfall (in 
inches per hour). 

Formula IV-16: Runoff Quantity in an Enclosed Area 

In some cases, a levee or floodwall may extend only partially 
around the property and tie into higher ground (see 
Figure IV-22). For such cases, the amount of precipitation 
that can flow downhill as runoff into the protected area, A., 
must be included. To calculate this value, the additional 
area of land, Abl that can discharge water into the enclosure 
should be estimated. This value is then multiplied by the 
previously determined rainfall intensity, ir,by the most 
suitable terrain coefficient, and by 0.01. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -37 
January 1995 


Chapter IV: Determination of Hazards 

When determining the minimum 
discharge size for sump pumps 
within enclosed areas, the 
designer should consider the 
impacts of lag time between 
storms that control the gravity 
flow mechanism (i.e., inside and 
outside the enclosed area) and the 
storage capacity within the 
enclosed area after the gravity 
discharge system closes. If the 
designer is not familiar with 
storm lag time and the computation 
of storage within an enclosed 
area, an experienced hydrologist 
or hydraulic engineer should be 
consulted. 

_ojI 

Inc D w er 

Qb =001 CirAb = gpm 

where: Q1b is the runoff from additional 
contributing area (in gal/min 
(gpm)); 

Ab is the area discharging to the area 
partially enclosedby the floodwall 
or levee (in square feet); 

c is the most suitable terrain runoff 
coefficient; 

0.01 is a factor converting the answer 
to gallons per minute; and 
ir is the intensity of rainfall (in 
inches per hour). 
Formula TV-17: Runoff Quantity from Higher Ground into a 
Partially Enclosed Area 

Seepage flow rates from the levee or floodwall, Q, must also 
be estimated. In general, unless this seepage rate is calculated 
by a qualified soils engineer, a value of two gallonsper 
minute for every 300 feet of levee or one gallon per minute 
for every 300 feet of floodwall should be assumed during 
base 100-year-floodconditions. 

I wr 

QC= sr(l) 

where: QC is the seepage rate through the 
levee/floodwall (in gallonsper 
minute); 

sr is the seepage rate (in gallons per 
minute) per foot of levee/floodwall; 
and 

I is the length of the levee/floodwall 
(in feet). 

Formula IV-18: Seepage Flow Rate through a Levee or Floodwall 

IV -38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

The values for inflow within the enclosed area, runoff from 
uphill areas draining into the enclosure, and seepage 
through the levee/floodwall should be added together to 
obtain the minimum discharge size, Q5,Pin gallons per 
minute (gpm) for the sump pump. 

I_ 
imgwr Qp= Q +Qb+ Q 
where: QSp is the minimum discharge for 
sump pump installation (in gpm); 
Q. is discharge from an enclosed 
area (from Formula IV-16) 
(gpm); 
Qb is the discharge from higher 
ground to a partially enclosed 
area (from Formula IV- 17) (in 
gpm); and 
Q, is the discharge from seepage 
through a floodwall or levee 
(from Formula IV- 18) (in gpm). 

Formula IV-19: Minimum Discharge for Sump Pump Installation 

Important considerations in determining the minimum 
discharge size of a sump pump include storage available 
within the enclosed area and the lag time between storms 
that impact the enclosed area and the area to which the 
enclosed area drains. Sump pumps will continue to operate 
during flooding events (assuming power is constant or 
backup power is available), but gravity drains will close 

once the floodwater elevation outside of the enclosed area 
exceeds the elevation of the drain pipe/flap gate. Therefore, 
the critical design issue is to determine runoff and seepage 
that occurs once the flap gate closes. Typical design solutions 
incorporate a freeboard of several inches or more to 
control the 10-year flood event safely. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -39 
January 1995 


Chapter IV: Determination of Hazards 

ALLUVIAL FAN FLOODING HAZARDS 
Alluvial fan floods are natural hazards in the western 
A detailed discussion of alluvial United States. Alluvial fan flooding is characterized by 
fan flooding and techniques for sudden unpredictable, high-velocity flow that transports 
retrofittingunder those conditions dangerous debris down steep mountain drainages to the 
is presented in Appendix D: valley floor below. The type of detailed information avail-
I AlluvialFan Flooding. able for other flood-prone areas is not yet available for 
alluvial fan situations, but a profile of this type of flooding 
and general measures to mitigate its impacts are beginning 
to emerge. 
Alluvial fans are landforms evolved from a history of flood 
events debouching from steep-sloped watersheds onto 
valley floors or piedmonts. Across the western United 
.00* States alluvial fans are appealing to residential developers 
for their vistas, and the pressure to construct on fans is 
Alluvial Fans: Hazards and increasing as the valley floors become populated. On most 
Management (1989) is a FEMA fans, there is evidence of past floods, but the history of 
publication that provides an 
overview of alluvial fans and development is relatively short and the consequences of a 
related management issues, and 1 00-year return period flood may not have been fully 
briefly discusses retrofitting of addressed. 
residential structures. Another 
FEMA publication entitled 
Reducing Losses in High Risk 
Flood Hazard Areas: A Guidebookfor 
Local Officials specifically 
addresses alluvial fan 
flooding as a regulatory problem 
and provides outlines for the 
development of regulations and 
master plans for communities. 
This guidebook also summarizes 
the Dawdy Method for flood 
frequency estimates on alluvial 
fans and presents the Colorado 
Statute HB-1041 as a model 
geologic hazard ordinance that 
includes alluvial fan flooding . 
hazards. 
Figure IV-23: Telluride, Colorado, Alluvial Fan 

IV -40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Flood hazards on alluvial fans are compounded by high 
velocities, hyper-concentrated sediment flows, severe 
erosion, and massive sediment deposition. 

Retrofitting designs are typically dependent on the assessment 
of flood hazards (specifically flow depth and velocity), 
but for alluvial fans this information may not be available. 
FIRMs may provide general information such as the delineation 
of flood hazard zones and 1 00-year maximum flow 
depths. Local ordinances may recommend methods for 
determining design criteria. Additional available information 
may include the apex peak discharge and potential 
sediment concentrations. Retaining a qualified engineer 
may be necessary to determine design flow conditions at the 
property location. 

Some aspects of alluvial fan flood loads are comparable to 
riverine flooding. Flow analyses including hydraulic loading 
and buoyancy are similar in principle to riverine flooding, 
but several key elements are different. Alluvial fan analyses 
should consider the severe velocity gradients, the combined 
effects of water and sediment mixtures, boulder impact 
pressure, and hydraulic loading on the upstream side of a 

structure. 

Formulas for the computation of sediment-water mixtures, 
hydrodynamic forces, freeboard, and factor of safety recommendations 
are provided below. 

Bulking Factor 

The design flood conditions must be evaluated considering 
the increased flood discharge related to sediment bulking. 
The bulking factor, BF, is given by Formula IV-20. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -41 
January 1995 


Chapter IV: Determination of Hazards 

[ 11l1 1_ 

JE 

l BF ~~~~~~~~~~~~~~~~~~1. 

Concentration of Sediment (C,) 
values are estimated by engi- 

neers experienced with this type 
of analysis and typically range 
from 0-50% (decimal equiva-
lent). 

1_________________________ 

In hyperconcentrated sediment 
flows,. where the sediment 
concentrations range from 20 to 
45 percent sediment by volume, 
the hydrostatic pressurescan be 
30 to 75 percent greater than 
from clear water. 

1.0 

BF = 

0- C, 

is a dimensionless factor applied 
to riverine discharge values (Q) 

to account for sediment bulking; 
and 
is the concentration of sediment 
of the fluid mixture by percent 
(decimal equivalent) of volume. 

where: BF 

Cv 

Formula IV-20: Bulking Factor 

For semi-arid alluvial fans, typical bulking factors range 
from 1.1 to 1.2 for sediment concentrations of 0.10 to 0.15 
by volume. Bulking factors for mud flows can be as high as 

2.0 (C = 0.50). 
Hydrostatic and Hydrodynamic 

Loads 

Hydrostatic loading is the force of the weight of standing 
water acting in a perpendicular manner on a submerged 
surface Sediment suspended in floodwater will increase 

the specific weight of the fluid as a function of sediment 
concentration by volume C,. Water with a high sediment 
concentration will impose greater hydrostatic pressures than 

clear water. 

Likewise, hydrodynamic loading is related to the density of 
the fluid, which will increase with sediment loading. The 
greater mass the fluid has, the more momentum it will 
transfer when it impinges on an obstacle. 

To include the effects of sediment loading in hydrostatic and 
hydrodynamic calculations, the specific weight of water is 
replaced with the specific weight of the water-sediment 
mixture (Formula IV-21). 

IV -42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

-It' 

In alluvial fan situations, 
hydrostatic and hydrodynamic 
forces developed using Formulas 
IV-4 through IV- 13 should be 
recomputed replacing the 
specific weight of water (y ) with 
the specific weight of the water-
sediment mixture (y,). 

ffi!1 Ys= (1-C)y + cSSP y= __lbs/ft3 

where: ys is the specific weight of the 

water-sediment mixture, in lbs/ft3 ; 

C, is the sediment concentration by 

volume expressed as a percent 

(decimal equivalent); 

y is the specific weight of water, 

62.4 lbs/ft3 ; and 
SP is the specific gravity of sediment 
(dimensionless). 

Formula IV-21: Specific Weight of Water-Sediment Mixture 

The additional live load attributed to sediment should be 
considered in all calculations of hydrostatic loading with 
volumetric concentration of five percent or greater. This 
additional hydrostatic load will be most significant near the 
fan apex where sediment concentrations are higher and will 
decrease in the downfan direction. The loading factor 
related to sediment will be negligible in the sheet flow zone. 

Freeboard 

Prediction of alluvial fan flooding parameters is not an exact 
science, so safety factors should be considered in retrofitting 
design. Freeboard is the additional design height of walls, 
levees, and foundations above the base flood level to account 
for velocity head, waves, splashes, and surges. The 
conditions of superelevation and flow runup can be severe 
for mud, debris, and high velocity flows and should be 
evaluated separately. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -43 
January 1995 


Chapter IV: Determination of Hazards 

The U.S. Army Corps of 

Engineers recommends that the 

freeboard () be greater than or 

equal to 2.0 feet in alluvial fan 

situations. 

Hydrostatic, hydrodynamic, and 
impact loading design should fall 
within constraints imposed by 
local ordinances or building codes. 
Where local guidelines are not 
available, factors of safety pre

sented in Table IV-5 should be 
applied to design loads for 
structure design. 

The U.S. Army Corps of Engineers (draft report, undated) 
recommends that the amount of freeboard be based on the 
velocity head plus the increase in depth caused by a 50% 
increase in flow rate, with a minimum value of 0.5 feet, 
expressed by the equation shown in Formula IV-22: 

MEE,.3 5f = |disQdesign-dQdesign)+ V2/2g= ft 
where: 
f 
V 
g 
is the recommended freeboard in 
feet; 
is the velocity of flow in feet per 
second; 
is the acceleration of gravity 

(32.2 ftlsec2 ); 
d SQdesignis the depth of flooding from a 
discharge 50% greater than the 
design discharge, in feet; and 
dQdifgnis the depth of flooding from the 
design discharge (typically the 
1 00-year event), in feet. 

Formula IV-22: Recommended Freeboard 

Safety Factors 

A safety factor greater than one is an additional measure of 
safety to account for unanticipated or unquantifiable factors. 
In the case of retrofitting on alluvial fans, additional safety 
should be built into the design, depending on the engineer's 
perception of the sensitivity of the flow conditions to change. 
The engineer must also weigh the cost of obsolescence if a 
retrofitting technique becomes inadequate with continued 
development. Safety factors are always a compromise between 
the desire for added protection and the additional costs 
associated with retrofitting design and construction. 

IV -44 Engineering Principlesand Practicesof Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

Table IV-5 Freeboard and Factor of 
Safety Recommendations 
Type of Flooding 
Type of Flooding 
Shallow Water Flooding, < 1 ft. (FIRM Zones A andB) Wtr____<3f.12 
Freeboard 
~~(ft.) 
1 
Factor of 
Safety 
1.10 
Moderate Water Flooding, < 3 ft. 1 1.20 
Moderate Water Flooding, < 3 ft. with potential 
debris, rocks < 1 ft. diameter and sediment 
for 1 1.20 
Mud Floods, Debris Flooding < 3 ft., minor surging 
and deposition, < 1 ft. boulders 
2 1.25 
Mud Flows, Debris Flows < 3 ft., surging, mud 
levees, > 1 ft. boulders, minor waves, deposition 
2 1.40 
Mud and Debris Flows > 3 ft., surging, waves, 
boulders > 3 ft., major deposition 
3 1.50 
Source: 1986 Colorado Floodproofing manual 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -45 
January 1995 


/ 49mlbi' 

Chapter IV: Determination of Hazards 

CLOSED BASIN LAKES 

Two types of lakes pose special hazards to adjacent devel-

More information on closed basin opment: lakes with no outlets, such as the Great Salt Lake 

lakes, alluvial fan, and movable and the Salton Sea (California); and lakes with inadequate, 

bed stream hazards can be 
obtainedfromthe Community or elevated outlets, such as the Great Lakes and many 
Rating System (CRS)Commen-glacial lakes. These two types are referred to as "closed 
tarySupplementfor Special basin lakes." Closed basin lakes are subject to very large 
Hazards Credit, dated July 1994. fluctuations in elevation and can retain persistent high water 
This document is available 1v1 
through Flood Publications, evels. 
NFIP/CRS, P.O. Box 501016, 
Indianapolis,Indiana46250-Closed basin lakes occur in almost every part of the United 

10 16. Telephone (317) 845-2898. States for a variety of reasons: lakes in the northern tier of 

states and Alaska were scoured out by glaciers; lakes with 
no outlets (playas) formed in the west due to tectonic 
action; oxbow lakes along the Mississippi and other large 
rivers formed as a result of channel migration; and sinkhole 
lakes form in areas with large limestone deposits at or near 
the surface where there is adequate surface water and 
rainfall to dissolve the limestone (Karst topography). 

Determination of the flood elevations for closed basin lakes 
follows generally accepted hydrological methods, which 
incorporate statistical data, historical high water mark 
determinations, stage-frequency analysis, topographical 
analysis, water balance analysis, and combinations of these 
methods. While NFIP regulations do not specifically address 
closed basin lakes, communities that develop mapping 
and regulatory standards addressing these hazards may 
receive flood insurance premium credits through the NFIP 
Community Rating System. The designer should determine 
if a local community has mapped or enacted an ordinance 
covering this special hazard. 

IV -46 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Flood-Related Hazards 

MOVABLE BED STREAMS 

Erosion and sedimentation are factors in the delineation and 
regulation of almost all riverine floodplains. In many rivers 
and streams, these processes are relatively predictable and 
steady. In other streams, sedimentation and erosion are 
continual processes, often having a larger impact on the 
extent of flooding and flood damages than the peak flow. 

Extreme cases of sedimentation and erosion are a result of 
both natural and engineered processes. They frequently 
occur in the arid west, where relatively recent tectonic 
activity has left steep slopes, where rainfall and streamrflow 
are infrequent, and where recent and rapid development has 
disturbed the natural processes of sediment production and 
transport. 

Movable bed streams include streams where erosion (degradation 
of the streambed), sedimentation (aggradation of 
the streambed), or channel migration cause a change in the 
topography of the stream sufficient to change the flood 
elevation or the delineation of the floodplain or floodway. 

Analysis of movable bed streams generally includes a study 
of the sources of sediment, changes in those sources, and 
the impact of sediment transport through the floodplain. 
While NFIP regulations do not specifically address movable 
bed streams, communities that develop mapping and regulatory 
standards that address these hazards may receive flood 
insurancepremium credits through the Community Rating 
System. The designer should determine if a local community 
has mapped or enacted an ordinance covering this 
special hazard. 

Engineering Principles EndPractices of Retrofitting Flood-Prone Residential Structures IV -47 
January 1995 


Chapter IV: Determination of Hazards 

ANALYSIS OF NON-FLOOD-RELATED HAZARDS

Non-Flood-Related
Hazards

Wind Forces 

Seismic Forces 

Land Subsidence 

Figure IV-24: Non-Flood-Related 
Natural Hazards 

The designer must be aware that 
retrofitting actions may trigger a 
threat from multiple natural 
hazards and be prepared to 
address these issues. 

While floods continue to be a major hazard to homes 
nationwide, they are not the only natural hazard that causes 
damage to residential buildings. Parts of the United States 
are subject to high winds that can accompany thunderstorns, 
hurricanes, tornadoes, and frontal passages. In 
addition, many regions are threatened by earthquake fault 
areas, land subsidence, and fire and snow hazards (Figure 
IV-24). 

Retrofitting measures can be designed to modify structures 
to reduce the chance of damage from wind and other non-
flood-related hazards. Fortunately, strengthening a home to 
resist earthquake damage can also increase its ability to 
withstand wind damage and flood-related impact and 
velocity forces. 

WIND FORCES 

High winds impose significant forces on a home and the 
structural elements of its foundation. Damage potential is 
increased when the wind forces occur in combination with 
flood forces, as often occurs in coastal areas. In addition, 
as a structure is elevated to minimize the effects of flood 
forces, the wind loads on the elevated structure may be 
increased, depending on the amount of elevation and the 
structure's exposure to wind forces. 

Wind forces exert pressure on structural components such 
as walls, roofs, connections, and foundations. Therefore, 
wind loads should be considered in the design process at 
the same time as hydrostatic, hydrodynamic, impact, and 
building dead and live loads, and loads from other natural 
hazards such as earthquakes. 

IV -48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Non-Flood-Related Hazards 

Wind Design Process 

Determine base wind speed 

I 

Translate wind speed 
pressures using building code I 

Apply pressures to 
entire structure 

Transfer the lateral sum of these I 
lateral pressures into the primary 
resisting frame or shearwalls 

[Determine wind design pressures 
for primary resisting frame 

Check foundation for increased
loading due to overturning
from lateral loads

Design secondary framing
members

Figure IV-25: Wind Design Process 

The concept of wind producing significant forces on a 
structure is based on the velocity difference of a medium 
(air) striking an obstruction (the structure). Wind speeds 
vary depending on the location within the United States and 
the frequency with which these loads occur. Model building 
codes have adopted isolines showing the wind velocity for 
an exceedence frequency of 50 years as recommended by 
the American Society of Civil Engineers (ASCE). The 
design velocity for a particular site can be determined from 
these isoline charts. If no local code is in force, the designer 
should refer to the ASCE 7 Standard, Minimum Design 
Loads for Buildings and Other Structures. 

Whatever the governing code or wind load standard in 
force, the application of the wind loads is primarily the 
same, and is shown in Figure IV-25 and illustrated in Figure 

IV-26. 

Wind 

Buildingcode Sum of pressures 
interpretation transferred

to and 
(secondary by shear 

framing resisted 
members wallsor primary 

designed 
for this uniform resisting

frame 
loading) 

CLL 

E 

0 

Effecton 
foundation

due to 
momentcreated 
by overtuming 

Figure IV-26: Wind Design Process Illustration 

FEMA recently completed two building performance 
assessments following Hurricanes Andrew (August 24, 
1992) and Iniki (September 11, 1992). FEMA assessed the 
structural performance of residential building systems 
damaged by hurricane winds; provided findings and recommendations 
for enhancing building performance under 
hurricane wind conditions; and addressed building materials, 
code compliance, plan review, construction techniques, 
quality of construction, and construction inspection issues. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -49 
January 1995 


Chapter IV: Determination of Hazards 

Copies of these documents can 
be obtained from FEMA: 

FEMA (FIA-22), Building
Performance: Hurricane
Andrew in Florida; Observa-
tions, Recommendations and
Technical Guidance, February
1993.

FEM4 (FIA-23), Building 
Performance: Hurricane Iniki 
in Hawaii; Observations, 
Recommendations and Technical 
Guidance, March 1993. 

If no local code is in force, the 
designer should refer to the 

ASCE 7 Standard, Minimum 
DesignLoadsfor Buildings and 
Other Structures. 

These reports present detailed engineering discussions of 
building failure modes along with successful building 
performance guidance supplemented with design sketches. 
Please refer to these documents for specific engineering 
recommendations. 

SEISMIC FORCES 

Seismic forces on a home and the structural elements of a 
foundation can be significant. Seismic forces may also 
trigger additional hazards such as landslides and soil liquefaction, 
which can increase the damage potential on a 
home. Seismic forces act on structural components such as 
walls, roofs, connections, and foundations. Similar to wind 
forces, seismic forces should be considered in the design 
process at the same time as hydrostatic, hydrodynamic, 
impact, and building dead and live loads, and loads from 
other natural hazards such as hurricanes. Design assumptions 
for seismic loadings are normally based upon local 
building codes. 

Figures IV-27 and IV-28 illustrate the process for estimating 
seismic hazards and determining the ability of existing 
structural components to withstand these forces. 

IV -50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Non-Flood-Related Hazards 

Seismic Design Process 

Determine seismic region 

Determine lateral loads 
using building code 

I 

Apply loads to the structure in

accordance with building code

Transfer the lateral load into the
primary resisting frame or shear walls

Check foundations for increased loading due to
overturning from lateral loads

Check for lateral forces on elements
of structural and non-structural components

Design secondary framing members

Figure IV-27: Seismic Design Process 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -51 
January 1995 


Chapter IV: Determination of Hazards 

Groundmovement 
Design assumptions 
based on building 
code. Lateral forces 
transferred to and 
I-
Effect on 
0 
due to earthquake resisted by designed foundation due to 
wallsor primary moment created 
resisting frame by overturning 
Figure IV-28: Seismic Design Process Illustration 

Additional information concerning 
the determination of flood- 
related forces will be available in 
the next revision of the Flood 

DesignLoad Criteria incorpo-
rated in Section 5 of ASCE 7 
Standard, MinimumDesign 

Loadsfor Buildings and Other 
Structures, expected to be 
publishedin 1995. 

When making repairs to a flood-damaged home or considering 
retrofitting structures to minimize the impact of future 
flooding events, there are certain practical steps that can be 
taken at the same time to reduce the chance of damage from 
other hazards. Earthquake protection steps can be divided 
into two categories: steps that deal with the building struc- 
ture itself, and steps that can be taken with other parts of the 
building and its contents. 

Protection of the Structure 

For the building structure, the most important step is making 
sure the home is properly bolted onto its foundation so that it 

will not slide off in an earthquake. Another important step, if 
raising the foundation to place the house above flood levels, 
is to make sure the foundation can withstand an earthquake. 

Key portions of masonry block foundations usually require 
strengthening by installing reinforcing bars in the blocks and 
then filling them with concrete grout. FEMA has developed 
a sample plan for strengthening a masonry block foundation 
wall. This type of work can be complicated and normally 
requires the expertise of a professional engineer, architect, or 

contractor. 

IV -52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Non-Flood-Related Hazards 

FEMA's Technical Information on Elevating Substantially 
Damaged Residential Buildings in the Midwest (August 24, 
1993)provides procedures for determining seismic forces 

and recommendations for seismic retrofitting of a wood-

frame structure. For more information on protecting a 

structure from seismic hazards, contact the appropriate 

FEMA Regional Office's MitigationDivision. 

Protection of Non-Structural Building 
Components and Building Contents 

The additional cost for seismic 

strengthening was estimated by For non-structural building components and contents, 

FEMA (during the Midwest earthquake protection usually involves simpler activities that 
Flood of 1993) to range from homeowners can undertake themselves. These include 
17-23% of the base repair cost anchoring and bracing of fixtures, appliances,chimneys,

for elevating a 1,000-SF wood-

tanks, cabinets, and shelves.

frame structure on masonry
foundation walls. FEMA has
prepared some simple one-page

LAND SUBSIDENCE

descriptions (details) and costs 

associated with these steps that 

are available in a publication Subsidence of the land surface affects flooding and flood 

entitled Protecting Your Home 

from EarthquakeDamage damages. It occurs in at least 38 states. Although there are 

(1993). no national figures for increased flood damage due to 
subsidence, it can increase flood damage to entire communities 
that are subject to coastal flooding, and it threatens 
larger or smaller areas elsewhere. Because the causes of 
subsidencevary, selected mitigation techniques are required 
in different situations. 

More information on land Subsidence may result in sudden, catastrophic collapses of 
subsidence hazards can be the land surface or in a slow lowering of the land surface. In 

obtained from the CRS Commen

tarySupplementfor Special either case, it can cause increased hazards to structures and 
Hazards Credit, dated August infrastructure. In some cases, the causes of subsidence can 
1992. This document is available be controlled. 

through Flood Publications, 

NFIP/CRS, P.O. Box 501016, 

Indianapolis, Indiana 46250-Subsidenceis typically a function of withdrawal of fluids or 
1016. Telephone (317) 845-gases, the existence of organic soils, or other geotechnical 
2898. factors; it requires an extensive engineering/geotechnical 

Fnnineerinn Prinrinlas and Practices c)f Retrofittinc Flood-Prone Residential Structures IV -53 
January 1995 


Chapter IV: Determination of Hazards 

analysis. While NFIP regulations do not specifically address 
land subsidence, communities that develop mapping and 
regulatory standards addressing these hazards may receive 
flood insurance premium credits through the NFIP Community 
Rating System. The designer should determine if a local 
community has mapped or enacted an ordinance covering 
this special hazard. 

IV -54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Geotechnical Considerations 

GEOTECHNICAL CONSIDERATIONS 

Soil properties during conditions of flooding are important 
factors in the design of any surface intended to resist flood 
loads. These properties include: 

Information on land subsidence, * saturated soil pressures (covered previously in Chapter 
which is sometimes caused by IV under Hydrostatic Forces); 
flooding conditions, can be found 

in the Analysis of Non-Flood-
Related Hazards Section of * allowablebearing capacity;
Chapter IV.

* potential for scour; 
* frost zone location; 
* permeability;and 
* shrink-swellpotential. 
The computation of lateral soil forces and determination of 

soil bearing capacity are critical in the design of foundations. 
These forces plus the frost zone location and potential 
scour play an important role in determining the type of 
foundation to use. Likewise, the permeability and 
compactibility of soils are key factors in selecting borrow 

materials for backfill or levee construction. 

If unsure of local soil conditions, obtain a copy of the U. S. 
Department of Agriculture, Natural Resource Conservation 
Service Soil Survey of the general area. This survey provides 

valuable information needed to conduct a preliminary evalua

tion of the soil properties, including: 

* type, location, and description of soil types; 
* use and management of the soil types; and 
r nninQ II OrinnP inrninoonAn,Prortices of RatrnfiftinnFlnnd-ProneResidentialStructures IV -55 

U-111JIanuIary kl I III -_ . ---.9 .5 

January 1995 


Chapter IV: Determination of Hazards 

The physical properties of soil 
are critical to the design, 
suitability,and overall stability 
offloodproofingmeasures. 
Therefore,thedesignershould 
consult a geotechnical engineer 
if the soil properties at a site do 

notsupport the useof the chosen 
retrofittingmethod.A 
geotechnicalengineer should 
also be consulted for any 

information that cannot be 

obtainedfromtheSoilSurveyor 
the local office of the Natural 
ResourcesConservationService. 

* engineeringand physical properties including plasticity 
indexes,permeability,shrink/swellpotential, erosion 
factors, potential for frost action, and other information. 
This information canbe compiled using Figure IV-29 
(Geotechnical Considerations Decision Matrix) to enable 
the designer to determine the suitability of the specific soil 

type to support the various retrofitting methods. It is 
important to note that while the soil properties may not be 
optimum for specific retrofitting methods, facilities can 
often be designed to overcome soil deficiencies. 

The following sections begin a discussion of the various soil 
properties, providing the information necessary to fill out 
the decision matrix (Figure IV-29) and to understand the 

relationship between these soil properties and retrofitting 
measures. 

IV -56 Enaineerina Prinninlas and Practinsa nf Rstrofittinn FRnnd-Prnne Resirdential gtriirtiimr 

_---------1, r-~---a-- -*w N---.. . . -. .Jna 1995 
January 1995 


GeotechnicalConsiderations 

Geotechnical Considerations Decision Matrix 

-

Owner Name: Prepared By: 

Address: Date:
Property Location:

\Retrof itting
Measures

Elevation Flood-
on on Fill on Piers on Posts on Piles proofing proofing and 
Foundation and I Levees 
Walls Columns 

TElevation

EleatonElvaionElvaio | Relocation Dr We lo Fodals 

Soil ProDeries i 

High = 

Lateral Soil Moderate
Pressure

High
Bearing Moderate
Capacity

Low 

High__ _ _ __ 

Potential for Moderate
Scour 
Low =

H igh__ _ _ __ _ _ _ __ _ 

Moderate_

Shrink/Swell 

Potential
Low 

H ig h_ _ _ _ _ _ _ _ __ 

Potential Moderate
Front Action
Low_ 

_

H igh _ _ _ _ _ _ __ 

Moderate_____

Permeability 

ILow 

Instructions: 

This matrix is designed to help the designer identify situations where soil conditions are unsuitable when applied to 
certain retrofitting measures, therefore eliminating Infeasible measures. It is not intended to select the most suitable 
alternative. Instructions for use of this matrix follow: 

1. Circle the appropriate description for each of the soil properties. 
2. Use the NRCS survey, information from this and other reference books, and engineering judgment to determine 
which methods are Suitable (S)/Not Suitable (NS) for each soil property. Enter S or NS in each box. 
3. Review the completed matrix and eliminate any retrofitting measures that are clearly unsuitable for the existing soil 
conditions. 
Figure IV-29: Geotechnical Considerations Decision Matrix 

. _ _ 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -57 

Januarv 1995 


Chapter IV: Determination of Hazards 

BEARING CAPACITY 

et *t-Anothert, important consideration is the allowable bearing 

An approach developed by capacity of the soil. The weight of the structure, along with 

FEMA during the elevation of the weight of backfilled soil (if present), creates a vertical 

substantially damaged homes in 

Florida and the Midwest is to pressure under the footing that must be resisted by the soil. 
reuse the existing footings, if The term "allowable bearing pressure" refers to the maxi-
allowed by code. mum unit load that can be placed on a soil deposit without 

causing excessive deformation, shear failure, or consolidation 
of the underlying soil. The allowable bearing capacity is 
the ultimate bearing capacity divided by an appropriate 
factor of safety, typically 2 to 3. 

QBC = QJFS = lbs/SF 

where: QBC is the allowable bearing capacity 
(in pounds per square foot); 

Q. is the ultimate bearing capacity (in 
pounds per square foot); 
FS is a factor of safety, typically 2 or 
3 (as prescribed by code.) 

Formula IV-23: Allowable Bering Capacity 

Table IV-6 presents estimated bearing capacities for various 

soil types to be used for preliminary sizing of footings only. 

The actual allowable soil bearing capacity should be deter

mined by a soils engineer. Most local building codes specify 

an allowable bearing capacity to be utilized in design if the 

soil properties have not been specifically determined. 

Once the allowable bearing capacity is determined by the 
soils engineer or a conservative estimate prescribed by code 
is made, the designer can determine the capacity of the 
existing foundation to support the expected loads. Depending 
on the outcome of that evaluation, the designer may 
need to supplement the existing footing to support the 
expected loading condition (i.e., keep the actual bearing 

IV -58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Geotechnical Considerations 

Table IV-6 

Typical Bearing Pressure
by Soil Type (from Table IV-3)

SoilType(Symol) Bearing Capacity

Soil Type (Symbol) (lb.If.) 

Clay, Soft (CL, CH) 600 to 1,200 

Clay, Firm (CL,CH) 1,500to 2,500 

Clay,Stiff (CL, CH) 3,000to 4,500 

Loose Sand, Wet (SP, 800 to 1,600 

SW, SM) 

FirmSand, Wet (SP, 1,600to 3,500 
SW, sm.SM,SC) 2,700to3,00 

Gravel(GW, GP, GM, 2,700 to 3,000 

IGC) I _ _ _ __ _ _ 

Certain types of soil-loose sands 
and soft clays (SP, SW, SM, SC, 
CL, CH)-exhibit very poor 
bearing capacities when saturated; 
therefore, foundation, 
levee, and floodwall applications 
in those conditions would not be 
feasible without special treatment. 

pressure below the allowable bearing pressure of the soil) as 
a result of the retrofitting project. 

The ability of soils to bear loads, usually expressed as 
shearing resistance, is a function of many complex factors, 
including some that are site-specific. A very significant 
factor affecting shearing resistance is the presence and 
movement of water within the soil. Under conditions of 
submergence, some shearing resistance may decrease due to 
the buoyancy effect of the interstitial water or, in the case of 
cohesive soils, to physical or chemical changes brought 
about in clay minerals. 

While there are many possible site-specific effects of saturation 
on soil types, some classes of soil can be identified that 
have generally low shearingresistances under most condi

tions of saturation. These include: 

* fine silty sands of low density, which in some localities 
may suddenly compact when loaded or shaken, resulting 
in a phenomenon known as liquefaction; 
* sand or fine gravel, in which the hydraulic pressure of 
upward-moving water within the soil equals the weight 
of the soil, causing the soil to lose its shear strength and 
become "quicksand," which will not support loads at the 
surface; and 
* soils below the water table, which have lower bearing
capacity than the same soils above the water table.
Other types of saturated soils may also have low shearing 

resistances under loads, depending on numerous site-specific 

factors such as slope, hydraulic head, gradient stratigraphic 

relationships, internal structures, and density. Generally, the 

soils noted above should not be considered suitable for 

structural support or backfill for retrofitting, and when they 

Iv 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ; ~IV-59 
January 1995 


Chapter IV: Determination of Hazards 

are known to be present, a soils engineer should be con

sulted for site-specific solutions. 

Mechanicalproperties of all soils are complex. Attempts to 
construct water- or saturated soil-retaining/resisting structures 
without a thorough understanding of soil mechanics 
and analysis of on-site soils can result in expensive mistakes 
and project failure. 

SCOUR POTENTIAL 

Erosion of fill embankments, levees, or berms depends on 
the velocity, flow direction, and duration of exposure. 
Scour is localized erosion caused by the entrainment of soil 
or sediment around flow obstructions, often resulting from 
flow acceleration and changing flow patterns due to flow 
constriction. Where flow impinging on a structure is 
affected by diversion and constriction due to nearby structures 
or other obstructions, flow conditions estimated for 
the calculation of depths of scour should be evaluated by a 
qualified engineer. 

Scour under building foundations and around supporting 
walls and posts and the erosion of elevating fill can render 
structural retrofitting and resistive designs ineffective, 
possibly resulting in failure. Figures IV-30 and IV-31 
illustrate scour at open foundation systems and ground 
level buildings. 

Maximum potential scour is critical in designing an el

evated foundation system to ensure that failure during and 
after flooding does not occur due to any loss in bearing 
capacity or anchoring resistance around the posts, piles, or 
piers. 

IV -60 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Geotechnical Considerations 

a 

Figure IV-30: Local Scour at Piers, Piles and Posts 

Depth of

Flooding

=d 

Drection of Flow 

Aa of Greatest 
Scour Depth at 
Both Upstream Corners 

Figure IV-3 1: Scour Action on a Ground-Level Building 

Engineering Principles and Practices of Retrofitting Flood-Prone ResidentialStructures IV -61 
January 1995 


Chapter IV: Determination of Hazards 

J*1 

Resistance to scouring increases 
with clay content and/or the 
introductionofbondingagents, 
whichhelpbondthe internal 

particlesof a soil together. 

1*'

DScour 

The factor "a" in Formula IV24 
is the diameter of an open 
foundation member or half of 
the width of the solid foundation 
perpendicular to flood flow. 

The potential for foundation scour is a complex problem. 
Granular and other consolidated soils in which the individual 
particles are not cemented to one another are subject to 
scour erosion and transport by the force of moving water. 
The greater the velocity or turbulence of the moving water, 

the greater the scour potential. Soils that contain sufficient 
proportions of clay to be described as compact are more 
resistant to scour than the same grain sizes without clay as 

an intergranular bond. Likewise, soils with angular particle 
shapes tend to lock in place and resist scour forces. 

Shallow foundations in areas subject to flood velocity flow 
may be subject to scour, and appropriate safeguards should 
be undertaken. These safeguards may include the use of 
different, more erosion-resistant soils, deeper foundations, 
surface armoring of the foundation and adjacent areas, and 
the use of piles. 

The calculation for estimating maximum potential scour 
depth at an elevated or ground-level foundation member 
(Formula IV-24) is based upon the foundation (or foundation 
member) shape and width, as well as the water velocity 
and depth, and type of soil. 

Where elevation on fill is the primary retrofitting measure, 
embankments must be protected against scour and erosion. 
at the embankment toe may be calculated as shown in 
Formula IV-24. 

IV -62 Enqineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Geotechnical Considerations 

Estimate Maximum 
Allowable Scour 

Investigate presence of 
underlying strata which would 
terminate scour action 

Estimate anticipated 
scour depth 

Estimate required 
depth of foundation members 

I 

Interpret results 

Figure IV-32: Process for Estimating 
Potential Scour Depth 

The scour information presented 
is the best available; 
however, there is not a general 
consensus within the scientific 
community that these scour 
formulas are valid. Research 
continues into this area. 

05 ) 33 1 =

= d[1.1(a/d)0 4 (V/(gdr)feet 

Where:siai is the maximum potential depth 
of scour hole (in feet); 
d is thedepth of flow upstreamof 
structure (in feet); 
a is the diameter of post, pier, or 
pile or half the frontal length of 
the blockage (in feet); 
V is the velocity of flow approaching 
the structure (in feet per second); 
and 
g is the acceleration of gravity (32.2 
feet per second.) 

Formula IV-24: Maximum Potential Scour at Embankment Toe 

The maximum potential scour depth predicted by the 
following equation represents a maximum depth that could 
be achieved if the soil material were of a nature that could 
be displaced by the water's action. However, in many 
cases, a stronger underlying strata will terminate the scour 
at a more shallow elevation. Figure IV-32 illustrates the 
process of determining the potential scour depth affecting a 
foundation system. 

Iv 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures TXIVF -63on 
January 1995 


C Chapter IV: Determination of Hazards 

Step 1: Compute Maximum Allowable Scour. The scour 
depth at square and circular pier, post, and pile 
foundation members and/or a ground-level building 
can be calculated as follows: 

macall ~~~~~.65.4 
a ~~~~S., (

= (d)(K) [ 2-2-. 

where: variables are the same as in 
Formula IV-24. For additional 
information, refer to the 
document, "Highways in the 
River Environment" (U.S. Dept. 
of Transportation, 1987). 

K is the scour factor for flow angle 
of attack. K = 1 for buildings 
perpendicular to flow; additional 
values of K are shown in Table 
IV-7. See Figure IV-33. 

Formula IV-25: Maximum Potential Scour at Structure 

The above scour equation applies to average soil conditions 
(2,000 -3,000 psf bearing capacity). Average soil conditions 
would include gravels (GW, GP, GM and GC), sands 
(SW, SP, SM, and SC), and silts and clays (ML, CL, MH, 
CH). For loose sand and hard clay, the maximum scour 
values may be increased and decreased, respectively, to 
reflect their lower and higher bearing capacities. However, 
the assistance of a soils engineer should always be sought 
when making this adjustment, computing scour depths, and! 
or designing foundations subject to scour effects. 

Figure IV-33: Flow Angle of Attack 

If a wall or foundation member is oriented at an angle to the 
direction of flow, a multiplying factor, K, can be applied to 
the scour depth to account for the resulting increase in 
scour as presented in the following table. 

IV -64 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Geotechnical Considerations 

Table IV-7 

Scour Factor for Flow 
Angle of Attack, K 

Length to Width Ratio of Structural 

Angle of Member In Flow 
Attack 
4 8 12 16 

0 1 1 1 1 

15 1.15 2 2.5 -3 
30 2 2.5 3.5 4.5 

45 2.5 3.5 4.5 5 
60 2.5 3.5 4.5 6 
Numerous scour equations can be 

utilized to estimate scour depths. 

The U.S. Department of Trans-Step 2: Investigate Underlying Soil Strata. Once the 

portation recommends a factor of maximum potential scour depth has been estab

safety of 1.5 for predicting lished, the designer should investigate the underly

building scour depth. ing soil strata at the site to determine if the underlying 
soil is of sufficient strength to terminate scour 
activities. Information from the NRCS Soil Survey 
may be used to make this assessment. 

Figure IV-34 illustrates a scour terminating strata. If an 
underlying terminating strata does not exist at the site, the 
maximum potential scour estimate will become the anticipated 
scour depth. However, if an underlying terminating 
strata exists, the maximum potential scour depth will be 
modified to reflect this condition, as shown in Step 3. 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures IV -65 
January 1995 


Chapter IV: Determination of Hazards 

Foundation 
Member

Flood Protection Elevation w
W
Erosion Avoided by

d Direction of Flow 

Terminating Strata 

I i i.. I--,--,---;-_

.-: :. -i1 -.oiI 

.. i -i ik ----i 

-_ 1-i '-.: 

/ 

Figure IV-34: Tenninating Strata 

Step 3: Determine the Anticipated Scour Depth. Based on 
the results of Step 2, the designer will determine 
the anticipated scour depth to be used in determining 
the depth to which the foundation element 
must be placed to resist scour effects. If a terminating 
strata exists, the expected scour would stop 
at the depth at' which this strata starts, and the 
distance from this point to the surface is considered 
to be the potential scour depth, (Sd),Figure 
IV-34. If no terminating strata exists, the maximum 
potential scour (smax) computed earlier 
becomes the potential scour depth (Sd). 

IV -66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Geotechnical Considerations 

Step 4: Determine Required Depth of Foundation Members. 
Scour will increase the height above grade 
of the vertical member, since the grade level 
would be lowered due to scour and erosion (see 
Figure IV-35). As this occurs, the depth of burial 
(Db)of the vertical foundation member also 
decreases an identical distance. This can result in 
a foundation failure because the loss of supporting 
soils would change the assumed conditions under 
which the elevated foundation system was designed. 
To account for this, the vertical foundation 
member depth used for the purpose of determining 
an acceptable design must be increased by 
the amount of potential scour depth, (Sd). 

a 

D, 

Additional Depth of 
Sd Embedment Required 

Figure IV-35: Additional Embedment 

Step 5: Interpret Results. Foundations, footings, and any 
supporting members should be protected at least 
to the anticipated scour depth. If the structural 
member cannot be buried deeper than the anticipated 
scour depth, the member should be protected 
from scour by placing rip-rap (or other 
erosion-resistant material) around the member, or 
by diverting flow around the foundation member 

with grading modification or construction of an 
independent barrier (floodwall or levee). For 

Pnninoerinn Prinrinlps and Prartircs of Retrofittino Flood-Prone Residential Structures IV -67 

Januay 15_ A , ... .-__r-

January 1 995 


Chapter IV: Determination of Hazards 

situations in which the anticipated scour depth is 
minimal,the designer should use engineering 

judgment to determine the required protective 
measures. Whenever the designer is unsure of the 
appropriate action, a qualified geotechnical engineer 
should be consulted. 

FROST ZONE CONSIDERATIONS 

Because certain soils under specific conditions expand upon 
freezing, the retrofitting designer must consider the frost 
heave impactin the design of shallow foundations. When 
frost-susceptible soils are in contact with moisture and 
subjected to freezing temperatures, they can imbibe water 
and undergo very large expansions (both horizontally and

At vertically). Such heave or expansion exerts forces strong 
enough to move and/or crack adjacent structures (founda-
Localbuildingcodes generally tions, footings, etc.). The thawing of frozen soil usually 
specifythe depthof the zone proceeds from the top downward. The melted water cannot 
of maximum frost penetration. drain into the frozen subsoil, and thus becomes trapped, 
In the absenceof guidance in possibly weakening the soil. Normally, footing movements 

the local building code, refer 
to the NationalWeather caused by frost action can be avoided by placing part of a 
Serviceorthe NRCS Soil foundation below the zone of maximum frost penetration. 

Survey. 

PERMEABILITY 

Of principal concern for the construction of retrofitting 

measures such as levees and floodwalls arethe properties of 

the proposed fill material and/or underlying soils. These 

properties will have an impact on stability and will deter

mine the need for seepage and other drainage control 

measures. 

IV -68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


While impervious cutoffs such as 
compacted impervious core, 
sheet pile metal curtains, or 
cementitious grout curtains can 
be designed to reduce or eliminate 
seepage, their costs are 
beyond the financial capabilities 
of most homeowners. However, 
several lower-cost measures to 
control seepage include pervious 
trenches, pressure relief 
wells, drainage blankets, and 
drainage toes. 

It is very important that the 
designer keep the units in this 
formula consistent. The results 
of Formula IV-26 depend on the 
homogeneity of the foundation 
and the accuracy of the coefficient 
of permeability. The results 
should be considered as an 
indication only of the order of 
magnitude of seepage through a 
foundation. 

GeotechnicalConsiderations 

Since most retrofitting projects are constructed using locally 
available materials, it is possible that homogenous and 
impermeable materials will not be available to construct 
embankments and/or backfill floodwalls and foundations. 
Therefore, it is essential that the designer determine the 
physical properties of the underlying and borrowed soils. 

Where compacted soils are highly permeable (i.e., sandy soils), 
significant seepage through an embankment and under a 
floodwall foundation can occur. Various soil types and their 
permeabilities are provided in Table IV-8. 

The coefficient of permeability provides an estimate of 
ability of a specific soil to transmit seepage. It can be used 
(Formula IV-26) to make a rough approximation of the 
amount of foundation underseepage. Formula IV-26 may 
be used in lieu of Formula IV- 17 for large levee/floodwall 
applications when the coefficient of permeability for the 
specific site soil is known. 

Q=ki hg A 
where: Q is the discharge in a given unit of 
time; 
k is the coefficient of permeability 
for the soil foundation (in feet per 
unit of time); 
ihg is the hydraulic gradient (h/L) 
which is the difference in head 
between two points divided by 
the length of path between two 
points (dimensionless); and 
A is the gross area of the foundation 
through which flow takes 

place (in square feet). 
Formula IV-26: Volume of Seepage 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -69 
January 1995 


Chapter IV: Determination of Hazards 

SHRINK-SWELL POTENTIAL 

As mentioned earlier in this chapter, due to the continual 
shrink and swell of expansive soil backfills and the variation 
of their water content, the stability and elevation of these 

Soilthat exhibit severe shrink-soils and overlaying soil layers may vary considerably. 

Soils that exhibit severe shrink-
swell characteristics includeclays These characteristics make the use of these soils in engiand 
clay mixtures such as soil neering/construction applications imprudent. The NRCS 
types CH, CL, ML-CL, SC, and Soil Survey for a specific area offers guidance on the shrink-
MH. swell potential of each soil group in the area as well as 
guidance on the suitability of their use in a variety of applications 
including engineering, construction, and water 
retention activities. If the designer is unsure of the type or 
nature of soil at the specific site, a qualified soils engineer 
should be contacted for assistance. 

The physical soil parameters at the retrofitting and potential 

borrow sites are an important design consideration. 

Homeowners and designers should clearly understand that 

the advice of a professional soils engineer is vital when 

planning retrofitting measures that are not ideal for the 

physical soil parameters at a given site. 

IV -70 Enaineerino PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Geotechnical Considerations 

TableIV-8 Typical Values of Coefficient of Permeability kfor Soils

I 

Soil Type 
and Description 

Well-graded clean gravels,
gravel-sand mixtures 

Poorly graded clean 

gravels, gravel-sand-silt 

Silty gravels, poorly 

graded gravel-sand-silt 

Clayey gravels, poorly 
graded gravel-sand-clay 

Well-graded clean sands, 
gravelly sands 

Poorly graded clean 
sands, sand-gravel mix 

Silty sands, poorly 
graded sand-silt mix 

Sand-silt clay mix with 
slightly plastic fines 

Clayey sands, poorly 
graded sand-clay mix 

Inorganic silts and clayey

silts 

Mixture of inorganic silt 
and clay 

Inorganicclays of low to 
medium plasticity 

Organic silts and silt-clays,
low plasticity 

Inorganic clayey silts, 
elastic silts 

Inorganic clays of high 
plasticity 

Organic clays and silty 
clays 

Typical Coefficient of 
Symbol I Permeability, Ft/Day 

GW 

GP 

GM 

GC 

SW 

SP 

SM 
SM-SC 

SC 

ML 
ML-CL 

CL 
OL 

MH 
CH 
OH 

75 

180 

1.5 x 10-3 
1.5 x 10-4 
4.0 

4.0 

2 x 10.2 

3.0x 10-3 

7.5 x 10-4 
1.5 x 10-3 
3.0 x 10-4 
1.5 x 10-4 
Quite variable 
1.5 x 10-4 
1.5 x 10-2 
Quite variable 
1 1. 
1 cm/sec= 2,840 ft/day = 
2 ft/min 

1 ft/year = 1 x 10-6cm/sec 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -71 
January 1995 


CHAPTERV

.. I 

BENEFIT/COST ANALYSISAND 
ALTERNATIVE SELECTION 

Featuring: 

Evaluate Hazards 
Estimate Potential Damages (No Action Alternative) 
Identify CostsAssociatedwith Alternatives 

Estimate Benefits 
Compute Benefit/Cost Ratio and Net Present Value 
Select a Method 


/001ii

II

I BENEFIT/COST ANALYSIS AND
ALTERNATIVE SELECTION

I 
IF 

200 

.


Chapter V: Benefit/Cost Analysis and Alternative Selection 

Table of Contents 

The Benefit/Cost Analysis Process ................................................ V -1

Evaluate Hazards ............................................... V -3

Estimate the Potential Damages (No Action Alternative) .......................................... V -3

Costs Associated with Alternatives ............
Estimate Benefits ................................................
Compute Benefit/Cost Ratio and Net Present Value ................................................
Evaluate Results ...............................................
Select a Method ...............................................

Evaluate Hazards ...............................................

V.3...................................V -4 
V -4 
V -4 
V -5 

V -6 

Determine Flood Frequency, Discharge, and Elevation .............................................. V -7
Compile DischargeVersus Exceedence Probability Curve .........................................V -7

Estimate Potential Damages ............................................... V -9

Identify Costs Associated with Alternatives ............................................... V -13

Estimate Benefits ........... V-14

Compute Benefit/Cost Ratio and Net Present Value . .. V -19 
Convert Estimated Annual Benefits to a Present Value . .. V -20 
Convert Estimated Costs of Retrofitting to a Present Value .. V -21 
Compute the Benefit/Cost Ratio and/or Net Benefit .. V -22 

Select a Method .. V-25 

Detailed Cost Estimating ... V -28 

Sources for Unit Costs ... V -30 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V -i 
January 1995 


BENEFIT/COST ANALYSIS

AND ALTERNATIVE SELECTION

Benefit/cost analysis is a powerful tool to help determine whether the benefits of a prospective 
hazard mitigation project are sufficient to justify the costs ofthe project. This analysis can also 
be used to assist in ranking different retrofitting alternatives. 

A user's guide and computer disks for a computer model, Benefit/Cost Analysis of Hazard 
Mitigation Proj ects, developed by FEMA is included as Appendix E to this manual. The 
benefits calculated by the model are expected future benefits estimated over the useful lifetime of 
the retrofit project. To account for the time value of money, a net present value is calculated 
automatically by the model. 

THE BENEFIT/COST ANALYSIS PROCESS 

Benefit/cost analysis provides estimates of the benefits and 

-I,' costs of aproposedproject. The term "benefit/cost analysis" is 
used to denote economic analyses that apply either the maximum 
present value criterion or the benefit/cost ratio criterion to 

Benefit/Costvs. Cost-Effective evaluate prospective actions. Both costs and benefits are 
Analysis. Benefit/cost analysis 
differs from cost-effectiveness discounted to their present values The maximum present value 
analysis in one major way-it criterion subtracts costs from benefits to determine if benefits 
considers a project's merits (or exceed costs. Benefit/cost ratios provide an alternative evaluabenefits). 
Analysis of cost- tion: prospective actions in which benefits exceed costs have 
effectiveness simply identifies the benefit/cost ratios above 1.0. 
least expensive way to achieve an 
objective. Benefit/cost analysis 
also takes into account the usually 
different benefits of various 

I retrofitting measures. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter V: BenefitlCost Analysis and Alternative Selection 

__W 

The "benefits" considered in a 
retrofitting measure are the future 
damages and losses that are 
expected to be avoided as a result 
of the measure. 

Evaluate Hazards 

i 

Estimate
Potential Damages

I 

Identify Costs for 
Each Alternative 
I 

Identify Benefits for
Each Alternative

i 

Compute B/C Ratio 
and Net Present Value 
for Each Alternative I 

4 

Evaluate Results 

. 

Select a Method 

The logic of benefit/cost analysis implies that the alternative with 
the highest maximum present value or highest benefit/cost ratio 
is the desired alternative. 

The benefits of retrofitting projects are avoided future damages. 
Benefits are not the damages incurred in an event already 
experienced, even if such damages would have been avoided 
by the retrofit project. Rather, benefits are the present value of 
the sum of expected avoided future damages for all levels of 
intensity offuture floods. 

To estimate future damages (and the benefits of avoiding them), 
the probabilities of future events must be considered. The 
probabilities of future events profoundly affect whether or not a 
proposed retrofitting measure is cost effective. The benefits of 
avoiding flood damage for a building in the 10-year floodplain 
will be enormously greater than the benefits of avoiding flood 
damage for an identical building situated at the 1,000-year flood 

0 

level. 

Each proposed retrofitting project must be evaluated on its own 
merits, comparing the benefits and costs of a specific project 
and/or alternatives. In particular, the benefits of a project may 
vary markedly depending on the vulnerability of the existing 
home to damages and losses, the probabilities of future damages, 
and the effectiveness of the mitigation measure in avoiding 

future damages. 

Figure V-1 presents the basic steps in performing any benefit/ 

cost analysis. These steps are summarized below. 

Figure V-I: Benefit/Cost Analysis 
Process 

S 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


The Benefit/Cost Analysis Process 

EVALUATE HAZARDS 

Conducting a benefit/cost analysis of flood hazard mitigation 
projects requires estimating the expected frequency and severity 
of flooding in the area under consideration. Detailed flood 
information is given in Flood Insurance Studies (FISs) and on 
Flood Insurance Rate Maps (FIRMs) where such studies are 
available. In some cases, estimates of expected flood frequency 
and severity may have to be made. State, local, and 
privately prepared studies may exist as well. 

Chapter IV-Determination of Hazards-provides guidance on 
the development of the flood hazard information required for 
conducting a benefit/cost analysis. 

ESTIMATE THE POTENTIAL 
DAMAGES (NO ACTION 
ALTERNATIVE) 

Estimating the benefits of prospective flood hazard mitigation 
projects requires site-specific data to establish expected 
damages as a function of flood depth (and other flood hazards 
such as high velocity, ice/debris flows, or soil failure, where 
appropriate). The expected flood hazard relationships developed 
in the previous step are used in conjunction with actuarial 
flood damage data developed from FIA flood insurance claim 
data and compiled in tables and graphs of damage versus depth 
of flooding. The flood hazard mitigation benefit/cost computer 
model presented in Appendix E considers property damage and 
certain other economic losses. 

COSTS ASSOCIATED WITH 
ALTERNATIVES 

The costs of a flood hazard mitigation project vary according to 
the retrofitting measure and generally include direct construction 
costs, engineering or architectural design fees, permit fees, 
contractor's fees, the cost of temporary living quarters, and loss 
of income due to design/construction activities. Guidance on 
estimating these costs is provided in Chapter III. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter V: Benefit/Cost Analysisand Alternative Selection 

INA 

of.*,%T 

FEMA has developed a computer 

program,Benefit/Cost Analysis of 
Hazard Mitigation Projects (see 
Appendix E), which can be used to 

evaluate the benefiticost ratio of 
the flood hazard mitigation 
measures presented in this manual. 
The program requires an IBM-
compatible computer with 15 Mb of 
availablehard disk storage, 4 Mb 
of available RAM, and a color 
monitor, and the QuattroTM Pro for 
Windowsspreadsheet. 

ESTIMATE BENEFITS 

The benefits of a flood hazard mitigation project are the avoided 
future damages. Benefits cannot be determined exactly because 
the times and severity of future flooding events are not known 
exactly. Rather, benefits are estimated by probability, based on 
experienced or hypothetical floods of various severity. 

COMPUTE BENEFIT/COST RATIO AND 
NET PRESENT VALUE 

The computation of benefit/cost values involves discounting 
projected benefits and their associated costs to their present 
values and computing either a benefit/cost ratio or a maximum 

present value. Benefit/cost ratios of 1.0 or greater and positive 
net present values indicate a cost-beneficial project. 

EVALUATE RESULTS 

The results of a benefit/cost analysis include the present value of 

damages and losses avoided, costs of the specific retrofitting 
measure, and calculation of either the net present value or 
benefit/cost ratio. As previously stated, alternatives with a 
positive net present value or a benefit/cost ratio greater than 1.0 
indicate a cost-beneficial project. 

Where more than one alternative is being considered, the 
aforementioned results should be tabulated and compared for 
each alternative. Ranking ofthe alternatives from the highest to 
lowest net present value or benefit/cost ratio will indicate the 
desirability (from a benefit/cost standpoint) of each alternative 
with respect to other alternatives. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


The BenefitlCost Analysis Process 

For guidance on performing 

benefit/cost analysis using manual 

methods, please refer to "How to 

Evaluate Your Options" prepared 

by the U.S. Army Corps of 

Engineers National Flood Proofing 

Committee. A complete reference 

for this document is provided in 

Appendix C. 

SELECT A METHOD 

The existence of a favorable benefit/cost ratio is not the sole 
factor for the selection of a retrofitting measure. Other economic, 
technical, and subjective factors can influence the 
homeowner's selection of a retrofitting measure. 

Conducting a benefit/cost analysis for a flood hazard mitigation 
project requires various data and judgments to estimate the 
expected frequencies and intensities of damage-producing flood 
events. Further estimates are made of both the benefits and 
costs associated with the different retrofitting measures. The 
calculations involved with establishing these estimates can be 
fairly complicated. FEMA's computer program (see Appendix 
E) addresses many of these complexities. 

Engineering Principles and Practices of F RetrofittingFlood-Prone Residential Structures 
January 1995 


Chapter V: BenefitlCost Analysis and Alternative Selection 

EVALUATE HAZARDS

Determine Flood 
Frequency, Discharge 
and Elevation 

Compile Discharge 
vs. Exceedence 
Probability Curve 

Figure V-2: Critical Steps in 
Evaluating Flood Hazards 

A Flood Insurance Study (FIS) 
consists of an FIS report, Flood 
Insurance Rate Map (FIRM), and 
(in non-coastal floodplains) a 
Flood Boundary and Floodway 
Map (FBFM). The FIS report 
describes how the flood hazard 
information was developed for the 
community. The FIRM shows 
areas inundated during a 100-year 
flood event. The FBFM delineates 
the regulatory floodway adopted 
within the community. 

To perform a benefit/cost analysis, the flood hazard to the 
structure in question must be determined in terms of the frequency 
and intensity of expected floods. The hazard analysis 
must include the expected frequency of flood hazards (e.g., a 
50-year flood), depth offlooding, and in the case of'riverine 
flooding, the corresponding intensity or severity of the flood 
[e.g., discharge of 1,500 cubic feet per second (cfs)]. 

To perform an economic analysis inriverine flooding situations, 
the relationship between discharge and water-surface elevation 
(often referred to as the rating curve, depicted in Figure V-3) 
and the relationship between discharge and exceedence probability 
must be known. This section describes how to develop 
this data (the process is illustrated in Figure V-2). In coastal A 
Zones, FISs provide a table of the flood frequency versus flood 
elevation relationship. 

129 

126 

127 

0 126 

z 

t 125 

z

0 

F 124 

4 

LU 

W 123

0

0 

-J 122 

LL 

121 

120 

119 L 

0 400 800 1,200 1,600 2,000 2,401 

DISCHARGE (CFS) 

Figure V-3: Discharge Versus Elevation (Rating Curve) 

v-6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1 995 


To obtain a copy of the FIS for the 
community in question, contact 
FEMA at 1-800-358-9616. 

The various agencies that maintain 
flood informationare listed in 
Appendix C. 

Evaluate Hazards 

DETERMINE FLOOD FREQUENCY, 
DISCHARGE, AND ELEVATION 

Several tools exist that can be utilized to obtain information on 
the flood hazards affecting the structure in question. A Flood 
Insurance Study (FIS) is available for most flood-prone communities 
throughout the United States. 

In some cases, an FIS may not be available for a community, or 
it may have insufficient data for the flooding source affecting the 
building. In these cases, the designer can turn to the U.S. Army 
Corps of Engineers (USACE) and Natural Resources Conservation 
Service (NRCS), which provide flood hazard information 
reports for many flooding sources. The U.S. Geological Survey 
(USGS) and the Tennessee Valley Authority (TVA) also publish 
stream gaging data and have flood information reports for 
various flooding sources. 

State or local floodplain studies may also be available for the 

community. For more infonnation concerning available data, 

contact the floodplain management services office of the 

USACE or the local offices ofthe USGS, TVA, NRCS, or 

your municipal engineer, floodplain administrator, flood control 

district, or water control boards. 

COMPILE DISCHARGE VERSUS 
EXCEEDENCE PROBABILITY CURVE 

For riverine A Zone scenarios, FEMA' s benefit/cost computer 

program takes the data for flood frequency, discharge, and 

elevation and automatically compiles the discharge versus 

elevation and discharge versus exceedence probability curves. 

This information is critical for the development of the depth-

damage relationships presented in the next step. 

Coastal A Zone flood models are based on storm surge models 
or tide gage analyses, which predict flood elevations. The FIS 
gives flood elevations relative to a benchmark elevation, generally 
the National Geodetic Vertical Datum of 1929 (NGVD). 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter V: Benefit/CostAnalysis and Alternative Selection 

Unlike riverine FIS data, flood data given in the FIS for coastal 
A Zones includes a table of exceedence probability (flood 
frequency) versus flood elevation. FEMA's benefit/cost computer 
model analyzes these data and creates a smooth curve 
relating exceedence probability and flood depth. This regression 
fit gives the annual exceedence probability for all floods in 
one-foot increments of depth. 

From the annual exceedence probabilities, calculated as de

scribed above, the expected annual number of floods in a given 

one-foot increment is calculated by difference. For example, 

the expected annual number ofa two-foot flood (i.e., all floods 

between 1.5 and 2.5 feet) is calculated as the exceedence 

probability for a 1.5-foot flood minus the exceedence probabil-

Determine Flood ity for a 2.5-foot flood. 
Frequency, Discharge 
and Elevation 
For a given coastal area covered by an FIS and a FIRM, the 
elevations of the 10-, 50-, 100-, and 500-year floods are 

Compile Discharge 

vs. Exceedence constantover the entire area. However, the probability of a 
Probability Curve given flood depth occurring at a specific site depends very 
_MMMNMMMMMM strongly on the elevation of the particular site. Thus, the Zero 

Figure V-4: Critical Steps in 

Evaluating Flood Flood Depth Elevation ofthe facility under evaluation has a 
Hazards profound impact on the degree of flood risk experienced at the 
site. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Estimate Potential Damages 

ESTIMATE POTENTIAL DAMAGES 

Estimating the potential damages to a structure for the no-action 
(before mitigation) alternative is a critical step in the overall 
development of expected benefits from retrofitting measures. 
The potential damages (flooding depth and loss of function) 
from the no-action alternative serve as the baseline from which 
future avoided damages can be computed for various retrofitting 
alternatives. 

Data regarding depth-damage relationships from FIA data 
tables (Figure V-5), which express damage to a building as a 
percentage ofthe building replacement value, or the analyst's 
data can be input to FEMA's benefit/cost analysis computer 
program, which will then prepare flood depth-versus-damage 

and probability-versus-damage relationships. 

The estimated damages and losses for the existing building at 

each flood depth depend on the depth-damage functions for 

items such as building and contents, displacement, and rental 

losses. The expected damages and losses also depend very 

strongly onthe degree of flood risk at the site under evaluation. 

Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures V -9 
January 1995 


Chapter V: BenefitlCost Analysis and Alternative Selection

Flood Insurance Administration (FIA) Depth-Building Damage Data 

Building Damage Percent by Building Type (based upon replacement value) 
1 Story 2 Story Split Level 1 or 2 Split Level 
Flood without without without Story with with Mobile 
Depth Basement Basement Basement Basement Basement Home 
-2 0 0 0 4 3 0 
-1 0 0 0 8 5 0 
0 9 5 3 11 6 8 
1 14 9 9 15 16 44 
2 22 13 13 20 19 63 
3 27 18 25 23 22 73 
4 29 20 27 28 27 78 
5 30 22 28 33 32 80 
6 40 24 33 38 35 81 
7 43 26 34 44 36 82 
8 44 29 41 49 44 82 
9 45 33 43 51 48 82 
10 46 38 45 53 50 82 
11 47 38 46 55 52 82 
12 48 38 47 57 54 82 
13 49 38 47 59 56 82 
14 50 38 47 60 58 82 
1 5 50 38 47 60 58 82 
16 50 38 47 60 58 82 
17 50 38 47 60 58 82 
18 50 38 47 60 58 82 

Figure V-5: FIA Depth-Damage Data Table 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Estimate Potential Damages 

Scenario damages are based on 
depth of flooding, not on flood 
hazard risk. Two identical buildings 
at different locations will have 
identical scenario damages, given 
the same depth of flooding. 

__v.' 

Even for buildings with high 
expected annual damages, mitigation 
projects are not necessarily 
cost-beneficial. Whether or not a 
project is cost-beneficial depends 
on the cost of the mitigation 
project and on the effectiveness of 
the mitigation project in avoiding 
damages, as well as on the 
expected annual damages. 

FEMA's benefitlcost ratio model characterizes losses expected 
both before and after mitigation as follows: 

Scenario Damages: Scenario damages indicate the estimated 
damages that would result from a single flood of a particular 
depth at the building under evaluation. For example, the scenario 
damages for a three-foot flood are the expected damages 
and losseseach time a three-foot flood occurs at a particular 
site. Scenariodamagesdo NOT depend on the probabilityof 
floods at that location. The model tabulates scenario damages 
for each flood depth from -2 to 18 feet for building damages, 
contents damages, displacement costs, and rental income losses 
(as well as other categories not applicable to residences). The 
total damages and losses are shown for each flood depth. This 
information shows the total vulnerability ofthe existing building 

to flood damage, how these damages are distributed among 

different categories of damages, and how these damages vary 

with flood depth. 

Expected Annual Damages: Expected annual damages take 
into account the annual probabilities of floods of each depth. 
Expected annual damages are the average damages per year 
expected over a long time period. "Expected annual" does not 
mean that these damages will occur every year. For each flood 
depth, expected annual damages are calculated by multiplying 
the scenario damages times the expected annual number (probability) 
of floods of each depth. 

The expected annual damages are tabulated in the same way as 
scenario damages. Expected annual damages will generally be 
much smaller than scenario damages because the expected 
annual number or annual probability of a flood of a given depth 
is usually much less than one. 

Enaineering Principles and Practices of I RetrofittingFlood-Prone Residential Structures 
January 1995 


Chapter V: 

Scenario damages and expected 

annual damages provide different 

information. Scenario damages 
describe how bad flood damages will 

be each time a flood occurs. How- 
ever, because scenario damages do 
not consider flood probabilities, 
theydo not providesufficient 
information for decision making. 
Scenariodamages for a given flood 
depth may be high, but if the flood 
probability is very low, no mitigation 
actionmay be warranted.If a five- 

foot flood causes$50,000in dam- 
ages but such a flood is expected to 
occur only once in 1,000 years, then 
simply repairing the very infrequent 
flood damage may be the most 
sensiblestrategy. 

Benefit/Cost Analysis and Alternative Selection 

The scenario damages before mitigation and the expected 
annual damages before mitigation provide, in combination, a 
complete picture ofthe vulnerability ofthe building to flood 

damage before undertaking a mitigation project. 

Expected annual damages consider flood probabilities. A 
building with high expected annual damages means that not only 
are scenario damages high, but also that flood probabilities are 

relatvely high. If expected annual damages arehigh, thenthere 
will be high potential benefits in avoiding such damages. 

Damages after mitigation depend on the damage before mitigation 
and damage befoe 

on the mitigat 
tionandonthe effectiveness ofthemitigationmeasurein 
avoiding damages. The expected annual damages and losses 

after mitigation also depend very strongly on the degree of flood 
risk at the site under evaluation. For some mitigation projects, 
such as relocation or buyout, the scenario damages and ex

ected annual losses after mitigation will be zero. For other 
p 
mitigation projects, such as elevation or flood barriers, scenario 
damages and expected annual losses after mitigation will be 
lower than before mitigation but not zero. FEMA's benefitlcost 
ratio model tabulates after-mitigation losses in the same way as 
before-mitigation losses. 

V-12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Estimate Benefits 

IDENTIFY COSTS ASSOCIATED WITH ALTERNATIVES

Once a detailed review ofthe flood hazard and associated 
losses has been performed, the costs associated with each of 
the technically feasible alternative retrofitting measures must be 
determined. Developing detailed construction cost estimates is 
crucial to ensuring that the homeowner can afford to complete 
the project. In Chapter III, a methodology for developing 
preliminary estimates of the cost of various retrofitting measures 
was presented. The methodology for developing detailed 
construction costs is similar, but requires more detail and 
definition ofproject component quantities and unit costs and 
often occurs after the preliminary economic analysis. Gener

ally, the designer's/homeowner's approach to examining 
retrofit alternatives and selecting the one that is most appropri

ate is an iterative cycle including these steps: 

e examine technical feasibility of alternatives; 

* develop preliminary cost estimates of each alternative 
being considered; 
* model benefit/cost ratios of considered alternatives; 
* rank alternatives based on benefit/cost ratios; 
* develop more detailed design study(ies) of highly ranked 
alternative(s) and detailed cost estimate(s); and 
* refine benefit/cost model(s) if previous step yields cost 
figure(s) significantly different from previous estimate(s), 
and re-rank alternatives as indicated based on new ratios 
and homeowner preference. 
Detailed cost estimating is discussed later in this chapter. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V -13 
January 1995 


Chapter V: Benefit(CostAnalysis and Alternative Selection 

ESTIMATE BENEFITS

Expected 

Annual Damages I 
ONOWNEOMMME 

Expected Annual 

Avoided Damages 

I 

Figure V-6: Types of Benefits 
Evaluated 

The benefits of a flood hazard mitigation project are the reduction 
in damages that would otherwise be expected. Expected annual 
benefits are defined as the sum of expected avoided damages. 
The computer program presented in Appendix E automatically 
computes values for the types of damages illustrated in Figure V-6 
and explained below. 

Scenario Damages: The expecteddamages per flood 
event of a given flood depth at the residence. Scenario 
damages (SCD) are the sum of building damages (BD), 
contents damages (CD), displacement costs (DIS), and rental 
income losses (RENT) for floods of each depth per scenario. 

FornulaV-i: Scenario Damages 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995 


Estimate Benefits 

* Building Damages: (BD) are defined as the product of 
floor area ofthe building (FA), replacement value of the 
building per square foot (BRV), and the modified/depth 
damage function (MDDF), which is the expected damage 
by flood depth expressed as a percentage of building 
replacement value. 
-. 13 

BD = (FA) (BRV) (MDDF)

M 

where: BD is the total amount of building 
damage per scenario in dollars; 
FA is the floor area ofthe building (in 
square feet); 

BRV isthe replacement value of the 
building (dollars per square foot); 
and 

MDDF is the expected damage by flood 
depth,expressed as a percentage 
of building value. 

Formula V-2: Building Damages 

* Contents Damages: (CD) are estimated as the product 
of the expected contents damage (ECD) and the total 
building contents replacement value (CRV) for each 
flood depth. Building and contents damages can also be 
taken from the depth-damage curves developed by FIA. 
I OI 

CD = (ECD) (CRV)

*Im 

where: CD is the total contents damage in 
dollars; 

ECD is the expected contents damage by 
flood depth,expressed as a 
percentage of contents replacement 
value; and 

CRV is the total building contents 
replacement value in dollars. 

FormulaV-3: Contents Damages 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V-15 

January 1995 


Chapter V: BenefitiCostAnalysis and Alternative Selection 

* Displacement Costs: (DIS) are defined as the product of 
displacement days necessary (DD), the total costs of 
displacement per day per SF (TDC), and the total area 
occupied (TA). 
DIS = (DD) (TDC) (TA) 

where: DIS is therelocation cost in dollars; 
DD is the estimated number of displacement 
days necessary for floods of 
flood depth; 
TDC is the estimated displacement costs 
per day per SF; and 
TA is the total area occupied in SF. 

Formula V-4: Displacement Costs 

* Rental Income: Losses are also included if all or part of 
the residence is rented. Rental income losses (RENT) are 
the product of displacement days (DD) and the daily rental 
rate (DRR). 
Formula V-5: Rental Income Losses 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
Januarv 1995 


Estimate Benefits 

* Expected Annual Damages: Expected annual damages 
(AD) are the product of scenario damages (SCD) and the 
expected annual number of floods of a given depth 
EAE): 

AD = (SCD) (EAE) 

where: AD is the expected annual damages in 
dollars; 
SCD is the scenario damages (as defined 
previously) in dollars; and 
EAE is the expected annual number of 
floods of a given depth. 

Fornula V-6: Expected Annual Damages 

* Expected Avoided Damages: Expected avoided damages 
(AVD) are the product of scenario damages (SCD), 
the expected annual number of floods (EAE), and the 
effectiveness ofthe mitigation measure (EFF): 
I. 
AVD= (SCD) (EAE) (EFF) 

where: AVD is the expected avoided damages in 
dollars; 

SCD are scenario damages for each 
damaging flood of a given depth (in 
dollars); 

EAE is the expected annual number of 
floods of a given depth; and 

EFF is the effectiveness ofthe mitigation 
measure in reducing expected 
damages from a flood of a given 
depth (percent of expected damages 
expressed as a decimal 
equivalent). 

Formula V-7: Expected Avoided Damages 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter V: BenefitlCost Analysis and Alternative Selection 

a Expected Annual Benefits: The expected annual 
benefits (AB) ofa hazard mitigation project are the sum 
of expected avoided damages (AVD) over the range of 
flood depths considered. FEMA's benefit/cost model (see 
Appendix E) includes a range of from -2 feet to 18 feet. 

.lol 
L @R'a 
AB= 
max 
X AVD 
RF=min 

where: AB is the expected annual benefits in 
dollars; 

RF is the flood depth considered above 
the zero flood depth elevation (in 
feet); 

mi isthe minimum damaging flood 
considered above the zero flood 
depth elevation (in feet); 

max is the maximum flood depth considered 
above the zero flood depth 
elevation (in feet); and 

AVD is the expected annual avoided 
damages frorn each flood depth 
above the zero flood depth elevation 
considered (in dollars). 

Formula V-8: Expected Annual Benefits 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Compute Benefit/Cost Ratio and Net Present Value 

COMPUTE BENEFIT/COST RATIO AND NET PRESENT 
VALUE 

One important aspect of benefit/cost analysis is accounting for 
the time value of money. The value of money changes over time 
due to economic, political, and other factors. Interest rate 
changes may impact the estimation of costs and benefits expected 
to occur in the future. 

For that reason, benefit/cost analysis requires a common basis 

for comparing estimates ofproject costs and benefits. This is 

usually accomplished by converting present, future, and annual 

project costs and benefitsto a common basis suchas present 

value, future value, or average annual values. 

The assumed interest rate, or discount rate, is the factor that 
controls the conversion of future values to present values. 

Increasing the discount rate lowers the present value of future 

benefits/costs and, conversely, lowering the discount rate raises 

the present value of future benefits/costs. 

As previously mentioned, either the benefit/cost ratio or maxi-

Formulashereareautomatedin mum present value (net benefit) criterion can be used to evalu-
FEMA'sbenefitlcostprogram ate each prospective retrofitting action. Earlier sections of this 
(AppendixE). chapter have built the foundation for completion of the analyses 

_______________________ discussedbelow. 

0nninrin Drinpinle canr4 Prar-tig-a of RatrnfiffinnFloord-ProneRAsidentialStructures V -19 

JlllCVl1Wau I995--. . 

ary1 vg 

January 1995 


ChapterV: 

Convert
Estimated Benefits
to Present Value

Convert 

Estimated Costs 

to Present Value 

Compute
BenefitfCost
Ratio

Figure V-7: Critical Steps 
in Benefit/Cost Ratio 
Analysis 

Benefit/Cost Analysis and Alternative Selection 

CONVERT ESTIMATED ANNUAL 
BENEFITS TO A PRESENT VALUE 

After determining the average annual damage to be prevented 
by the retrofitting measure, the present worth of damages 
prevented over the expected life of the structure can be 
determined. To make this determination, one must first assume 
the building's life expectancy; this will normally be the useful 
life of the structure. However, analysts can use the period the 
homeowner plans to occupy the home, or the length of the 
mortgage. Secondly, an interest rate for borrowing money to 
retrofit must be assumed. This rate may be obtained from any 
bank. The analyst can then use the following formula to 
computea present worth factor for the assumed life of the 
structure and the assumed interest rate: 

(1 + i)n 
where: PWI is the present worth factor; 
n is the assumed life of the structure 
(years); and 
i is the assumed interest rate for 
borrowing money (decimal 
equivalent of percent per year). 

Formula V-9: Present Worth Factor 

S

Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures 
January 1995 


Compute Benefit/Cost Ratio and Net Present Value 

Multiply the average annual damage prevented by retrofitting by 
the present worth factor to determine the present-day value of 
these expected flood damages avoided. 

*fi EABpV = (PWF) (AB) 

where: EABpvis the present value of estimated 

annual benefits in dollars; 
PWF is the present worth factor; and 
AB is the expected annual benefits of a 

mitigation project in dollars.
FormulaV-10: PresentValue of Estimated Annual Benefits

CONVERT ESTIMATEDCOSTS OF
RETROFITTING TO A PRESENT
VALUE

The primary cost of a retrofitting measure will be the engineering 
and construction costs, which already represent present-day 
values. Should the retrofitting measure require annual operation 
and maintenance costs (including replacements), these estimated 
periodic costs should be converted to a present-day value, 
using the same methodology previously employed to convert 
annual benefits to a present value worth. 

EACPV= (PWF) (AC) + ECCPV 

where: EACpvis the present value of estimated 

annual costs in dollars; 
PWF is the present worthfactor; 
AC is the expected annual cost (in 

dollars) for operation and maintenance 
of a specific retrofitting measure; 
and 

ECCpvis the present value of the engineering 
and construction costs associated 
with a specific retrofitting 
measure, in dollars. 

Formula V- I 1: Present Valueof Estimated Annual Costs 

Retrofittina Flood-Prone Residential Structures V -21 

Ennineerinn Prinrnin~l and Practices of 
January 1995 


Chapter V: Benefit/Cost Analysis and Alternative Selection 

COMPUTE THE BENEFIT/COST 
RATIO AND/OR NET BENEFIT 

Once the present value of the benefits and costs associated 
with a retrofitting measure is computed, dividing the present 
value ofthe benefits by the present value ofthe costs will 
enable the designer to fairly evaluate a number of retrofitting 
alternatives. 

BCR = EABPV / EACPV 

-
where: BCR is the benefit/cost ratio; 
EACPV is the present value of 
estimated annual costs in 
dollars; and 
EABPV is the present value of 
estimated annual benefit in 
dollars. 

Formula V- 12: Benefit/Cost Ratio 

An alternative evaluation measure is to subtract the present 
value of the costs from the present value of the benefits. 

no 

NPV =EAB -EACPV 

where: NPV is the net present value or 
benefit ofthe mitigation 
measure; 

EACPV is the present value of 
estimated annual costs in 
dollars; and 

EABPV isthe present value of 
estimated annual benefits 
in dollars. 

Formula V-13: Net Present Value 

Engineering Principlesand Practicesof Retrofitting Flood-Prone Residential Structures 
January 1 995 


Compute Benefit/Cost Ratio and Net Present Value 

A benefitlcost ratio of 1.0 or greater indicates that the benefits 
of the retrofitting alternative exceed the costs. The alternative 
with the highest benefit/cost ratio or net benefit would be the 
preferred alternative from an economic perspective, if the same 
level of protection (design flood) is being evaluated. 

It should be pointed out that the entire procedure of generating 

a benefit/cost ratio is not an exact science but instead a subjective 
process. The creation of a benefit/cost ratio is intended to 
give an idea of the cost effectiveness of a specific retrofitting 
technique in comparison to the other options available. As long 
as the same procedures are utilized in all scenarios, the ratio 
should provide the designer with an idea ofthe relative cost 
effectiveness of all options. 

Benefit/costmodelscanbe usedto optimizethe selectionofa 

retrofitting measure by analyzing incremental improvements to a 
selected alternative. This is accomplished by maximizing 
(avoided damages) benefits while minimizing project costs. It is 
an iterative process whereby an original retrofitting solution is 

modified by adding or deleting design features and/or designated 
protection levels. Each modification will have an impact 
on the project benefits and costs and subsequently the benefit/ 
cost ratio. This technique will assess the relationship between 
increased (decreased) cost and increased (decreased) effectiveness 
for the range of modifications with a particular retrofitting 
measure analyzed. 

The following example illustrates this optimizationtechnique. 

Pnnineerinm Prinninipe and Practices of IRetrofittinoFlood-Prone Residential Structures V -23

January 1995 8&A ----

January 1995 


Chapter V: Benefit/Cost Analysis and Alternative Selection 

Benefit/Cost Analysis Optimization Example 

Given: A one-story, 2,500 SF slab-on-grade building with a first floor elevation 
of 6.0 NGVD is subject to coastal A Zone flooding (1 -yr = 2.0', 1 0-yr = 
5.0', 50-yr = 7.0', 100-yr = 9.0', and 500-yr = 10.0'). 

Building replacement is estimated at $50/SF; contents replacement at $8/SF, 

and rental cost (displacement) at $ 1/SF. 

Alternative 1: Construct a 3-foot-high floodwall (9.0' NGVD) around the 
building. The floodwall has a 30-year useful life and project costs are estimated 
at $10,000 with an annual maintenance cost of $250. 

Floodwalls are considered effective to one foot belowtheir flood protection 
elevation. In this case, seepage and leakage concerns reduce the project 
effectiveness to 90% for floods reaching 6.0' NGVD; 85% at 7.0,' NGVD; 
80%NGVD, and 0% at 9.0' NGVD and above (since the water elevation is 
the same both inside and outside the floodwall due to overtopping). 

Alternative 1 Results: Benefit/cost ratio of 1.03 indicates this project is 
beneficial to pursue. 

However, the homeowner is concerned that seepage and leakage will damage 
flooring and building contents (and result in a potentially expensive temporary 
relocation) and is therefore considering adding an interior drainage system 
(periphery drainpipe and sump pump system) to Alternative 1. Economic 
optimization can be used to indicate whether or not this design change would 
be cost-beneficial. 

Alternative 2: Construct an interior drainage system with the 3' floodwalI 
proposed in Alternative 1. New project costs are estimated at $15,000 with 
annual maintenance of $350. The drainage system improves project effectiveness 
to 100% at all flood depths up to and including 8.0' NVD. 

Alternative 2 Results: Benefit/cost ratio of 0.81 indicates the addition of an 
interior drainage system would not be a beneficial modification to Alternative 

1. 
This results from the fact that the increased benefits (damages avoided) are 
not sufficient to support the additional construction cost and annual maintenance 
expenditures. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Select a Method 

SELECT A METHOD 

While benefit/cost analysis provides an indication as to whether 
or not a retrofitting alternative is cost-beneficial, it is not the sole 
parameter upon which retrofitting measures are selected. 
Occasionally, there will be more than one favorable alternative, 
or the designer will customize the retrofitting measure, either by 
combining several methods or varying the level of protection. 

Owner preference can also have an impact on sound economic 
analysis and make a less cost-beneficial alternative a more 
preferable choice. The cost of the retrofitting measure may be 
the pivotal factor in a homeowner-financed retrofitting project. 
Conversely, local code requirements may limit the use of a 
method preferred by the homeowner. In the final analysis, it is 
the owner who must be satisfied with the retrofitting alternative. 
Each of these factors (aesthetics, local code requirements, and 
hazards such as wind, earthquake, erosion, impact, and other 
forces) may affect the applicability of a specific retrofitting 
measure. The designer is advisedto considerthese factors 
along with the cost and benefit/cost ratio ofthe various alternatives 
(see Figure V-8). 

Factors Weighing on * PresentWorth of Benefits: This indicates the present 
Alternative Selection worth of annual damages avoided by the retrofitting alterna

* Present Worth of tive. The designer should review this value in terms ofhis/ 
Benefits her expected benefit (threshold for damages to be avoided). 
* Total Project Cost 
* Benefit/Cost Ratio * TotalProject Cost: This represents costs requiredto 
* Technical Feasibility construct the retrofitting alternative. The designer 
* Need for Human shouldreviewthis value in terms of how the project 
Intervention suits the homeowner's budget. 
* Need for Annual 
Maintenance * Benefit/Cost Ratio: As discussed previously, this 
Figure V-8: Factors Weighing on value indicates whether analternative is cost-beneficial. 
Alternative Selection The higher the value, the more cost-beneficial the alternative. 
The designer should review the benefit/cost 
ratios for the retrofitting alternatives being considered. 

Fnnineprinn Princinles and Practices of Retrofittina Flood-Prone Residential Structures V -25 

January 1995 


Chapter V: 

Benefit/Cost Analysis and Alternative Selection 

o Technical Feasibility: The designermustjudge the 
technical solution(s) that best address the project objectives. 
* Aesthetics: This value reflects the owner's view on the 
way the retrofitting alternative fits in with the appearance of 
his/herhouse. 
* Human Intervention Requirements: This reflects the 
need for human intervention to operate the retrofit measure 
and the warning time required to conduct the required 
activity. 
* Annual Maintenance: This reflects the intensity of 
annual maintenance required by each retrofitting alternative. 
A preference scale or order of preference ranking can be 
utilized with the table presented in Figure V-9 to arrive at a 
subjective decision on the retrofitting method to be selected. 
The preference scale assigns numbers 0 to 10 to each alternative 
by factor, with 0 indicating not liked and 10 meaning liked a 
lot. The values assigned to the various factors for each alternative 
are totalled, and the alternatives with the highest total 
should be the optimal choices. 

The preference scale process can also be modified by weighting 
the decision factors to reflect the increased importance of any 
specific factor. For example, if total project cost were the 
predominant factor, the value (0-10) could be multiplied by a 
factor, for example, 2, which would double its contribution to 
the overall score, thereby reflecting its importance. 

Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Select a Method 

OwnerName: PreparedBy:
Address: Date:
PropertyLocation:

Decision Factors 

Other
PW Technical Human Annual Total
Alternative Benefits Cost B/CRatio Difficulty Aesthetics InterventionMaintenance Score

Prlevnreact-on  A6 * '-3 i 

Impotnce "' 1.0 .~ ____ 0
WeightedScore' 8 5 6 8 = 45

Prefren e,

1. _ _ _ _ _ _ _ _ _ 
Preference_-----------------------------

-----7-7_

Importance 

WeightedScore 

2. 
Preference
Importance
WeightedScore

3.
Preference
Importance
WeightedScore
4.
Preference
Importance
WeightedScore
5. _ _ _ _ _ _ _ 
Preference
Importance
WeightedScore

6. 
Preference
Importance _ ------------------------------------
WeightedScore

Instructions:
This matrix may be filled out by the designer in consultation with the homeowner. The objective of this matrix is to
select an alternative for design from competing alternatives which had previously passed screening for technical
feasibility and homeowner preference.

For each alternative, enter the alternative name (i.e. 1A, 1B, 1C) and unweighted preference score (0-10) on the first
row. A score of 0 indicates the measure is the least preferred in terms of the decision factor, while a score of 10
indicates the measure is the most preferred. A blank column is provided for any additional decision factor(s) which
are being considered by the designer or homeowner.

Based upon the relative importance of each decision factor to the designer and homeowner, develop and enter an
importance factor (weighting amount) for each decision factor on the second row. Multiply the unweighted preference
score by the importance factor (weighting amount) and enter the result on the third line. Total the first and third lines
on the right hand column (Total Score). The preferred alternative is the one with the highest weighted score.

Figure V-9: Preference Ranking Worksheet 

Engineering Principles and Practices of Retrofitting Flood-15roneResidential Structures V-27 
January 1995 


Chapter V: 

Benefit/Cost Analysis and Alternative Selection 

DETAILED COST ESTIMATING 

Previously, in Chapter III, we were able to utilize a unit cost 
(per square foot) for a specific retrofitting measure, such as 
elevating a wood-frame building on an open foundation and 
adding ancillary items for fill and landscaping, to arrive at a 
preliminary construction cost estimate. When and ifthe cost 
estimate is refined after the retrofit measure alternatives are 

further defined from a design standpoint, the costs of each may 

be found to differ from earlier estimates that were used to rank 

the retrofit alternatives. Ifthis difference in estimated cost is 

significant for a given alternative, the benefit/costratio for that 

alternative could be affected. Therefore, the designer/analyst 

may re-run the benefit/cost model for any alternatives affected 

in this way, which could result in a different ranking of potential 

retrofitalternatives. 

When the retrofitting measure is designed (as discussed in 

Chapter VI), the cost estimate can be refined by identifing and 

pricing all ofthe components ofthe retrofitting measure. For 

example, site preparation, building preparation, permitting, 

excavation and earthwork, foundation, concrete, reinforcing, 

framing, elevation, utility extension, connections, code upgrades, 

backfill, site stabilization, access/egress, landscaping, and 

interest costs can be estimated and then aggregated. 

Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures 
January 1995 


Select a Method 

Cost estimate accuracy can be directly related to the level of 

detail in a quantity breakdown. Quantities or components not 

identified usually do not get estimated and may not be covered 

by any allowed-for contingency, resulting in less accurate 

estimates. Figure V-10, the Floodproofing Measure Compo

nent Takeoff Guide, was developed to identify cost items 

typically found in the various retrofitting measures. However, 

every retrofitting application is unique and may include more of 

or fewer than the components listed. 

Floodproofing Measure Component Takeoff Guide 

Elevation Techniques 

* Site Preparation 
* Building Preparation 
* Elevation of Structure 
* Foundation Construction 
* Connection of Structure to New Foundation 
* Extension of Utility Systems 
* Required Code Upgrades 
* Exterior Finish Work 
* Interior Finish Work 
* Access and Egress 
* Site Grading and Stabilization 
* Landscaping 
Relocation Techniques 

* Preparation of Existing Site 
* Preparation of Existing Building 
 Preparation of the Route 
* Elevation of Structure 
* Transfer of Building to Transportable Frame 
* Moving Building 
* Preparation of New Site (Including Utilities) 
* New Foundation Construction 
* Transfer of Building to New Foundation 
* Connection of Utility Systems 
* Exterior Finish Work 
* Interior Finish Work 
* Access and Egress 
* Site Grading and Stabilization 
* Landscaping 
* Demolition of Old Foundation 
* Grading and Stabilization of Old Site 
* Route Modification Reversals 
Floodwalls 

* Site Preparation 
* Excavation 
* Construction of Floodwall 
* Closure Installation 
* Access and Egress 
* Drainage System Installation 
* Site Grading and Stabilization 
* Interior Area Finishing 
* Utility System Adjustment 
* Landscaping 
Levees 

* Site and Borrow Area Preparation 
* Earthwork 
* Drainage System Installation 
* Access and Egress 
* Site Grading and Stabilization 
Shields 

* Building Preparation 
* Shield Installation 
* Interior Drainage System 
* Utility System Modification 
Sealants 

* Building Excavation and Preparation 
* Sealant Application 
* Interior Drainage System 
* Utility System Modification 
Figure V-10: Floodproofing Measure ComponentTakeoffGuide 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter V: 

Benefit/Cost Analysis and Alternative Selection 

SOURCES FOR UNIT COSTS 

Once a detailed quantity takeoff has been completed, unit-cost 
information can be obtained for individual items from a variety 
of sources. These sources include: 

* local construction industry data collected from published 
indexes or solicited from several construction companies; 
i average nationwide construction cost data, available 
from various publications, that contain factors for 
adjusting the average nationwide costs to specific locations 
and present-day values; and 

* data collected by the FEMA Mitigation Directorate for 
areas ofthe United States that have recently experienced 
major flooddarnage. These unit costsmay haveto be 
adjusted to a specific geographical area by multiplying 
the FEMA unit costby a factor of the Bureau of Labor 
Wholesale Price Index (or other published cost index) for 
the subject community and the community for which FEMA 
has data. 
FEMA has observed post-disaster inflation due to material and 
labor shortages that has significantly impacted the costs of 
restoring flood-damaged houses. For example, the cost of 
materials and labor was 10% higher after the 1993 Midwest 
flooding than before the storm. In the extreme case (catastrophic 
disaster) such as Dade County, Florida, after Hurricane 
Andrew, the increase was 25%. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Select a Method 

Unit costs are adjusted for local conditions with the following 
computation: 

local FEMA (WPI loaIWPIFEMA) (OPD) 

where: UC local is the unit cost of a specific 
retrofitting measure componentat 
the location in 
question; 

UC FENMA is the FEMA unit cost for a 
specific retrofitting measure 
at a specific location; 

WPIFEMA is the wholesale price index 
or other published cost 
index forthe locality at 
which FEMA has unit price 
data; 

WPIlocal is the wholesale price index 
or other published cost 
index at the locality for 
which a unit cost is needed; 
and 

IPD is post-disaster inflation due 
to a shortage of skilled 
labor and limited availability 
of materials. It ranges from 
100 percent to 125 perent, 
but is normally 11 0 percent. 

Formula V-14: Adjusting Unit Costs for Local Communities 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Chapter V: BenefitlCostAnalysis and Alternative Selection 

Once appropriate unit-cost information has been collected, the 
Floodproofing Measure Component TakeoffGuide (Figure V10) 
and the Detailed Cost Estimating Worksheet (Figure V- I 1) 
can be used to develop the detailed cost estimate. It is important 
to include the contractor's profit and a contingency item to 
cover unexpected costs. 

Owner Name:_ Prepared By: 
Address: Date: 
Property Location: 

Floodproofing Measure: (Describe Project Specifics) 

Estimating Item Quantity Unit Unit Cost ItemCost 

Subtotal 

Design Fee 

Contractor's Profit 

Subtotal 

Contingency 

Total 

FigureV-l 1: Detailed Cost Estimating Worksheet 

V-32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Select a Method 

At the completion of this chapter, the designer has determined 
flood and non-flood-related hazards; developed and evaluated 
retrofitting alternatives; and, in concert with the homeowner, 
selected a retrofitting measure that addresses the flooding 
problem. The next step, covered in Chapter VI, is to develop a 
detailed design of the selected retrofitting measure and produce 
construction documents. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V -33 
January 1 995 


CHAPTER VI

*7< ; s1 4;,; I , : ,0',9 0 I 
GENERAL DESIGN PRACTICES

Featuring: 

Field Investigation 
Analysis of Existing Structure 
Design 

Construction 


I 
MM 
FIELD INVESTIGATION I 
ANALYSIS OF EXISTING 
STRUCTURE I 
DESIGN AND 
CONSTRUCTION 
Local Building 
Requirements 
Hazard Determination 
Documentation of 
[Existing Building Systems_ 
Homeowner Preferences 
| 
Structural 
Reconnaissance 
Footings and Foundation 1 
Systems l 
Lateral Loads 
Vertical Loads 
| 
Relocation 
Dry Floodproofing 
Wet Floodproofing 
Elevation 
] 
J 
Capacity vs. Loading Floodwalls 
Levees 


Chapter VI: General Design Practices 

Table of Contents 

Field Investigation .......................................... VI -3
Local Building Requirements .......................................... VI -3
Surveys .......................................... VI -3
Structure Survey .......................................... VI -4
Topographic Survey .......................................... VI -5
Site Utilities Survey .......................................... VI -7
HazardDeterminations ........................................... VI -9
Documentation offExistingBuilding Systems ............. ............................. VI -9
Homeowner Preferences .......................................... VI -14
HomeownerCoordination.......................................... VI -14
Maintenance Programs and Emergency Action Plans .......................................... VI -15

Analysis of Existing Structure ........................................... VI -16
Structural Reconnaissance .......................................... VI -16
Footings and Foundation Systems .......................................... VI -19
Footings .......................................... VI -20
Bearing Capacity .......................................... VI -21
Lateral Loads ........................................... VI -24
Vertical Loads .......................................... VI -25
Dead Loads .......................................... VI -26
Live Loads .......................................... VI -29
Roof Snow Loads ........................................... VI -29
Calculation of Vertical Dead, Live, and Snow Loads .......................................... VI -29
Capacity Versus Loading .......................................... VI -34
Load Combination Scenarios .......................................... VI -34

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -i 
January 1995 


Elevation 

Types of Residential Structures That Can Be Elevated ................... ..................... VI -E. 1
Houses over a Crawlspace ........................................ VI -E.2
Houses over Basements ........... VI- E. 11
Houses on Piles, Piers, or Columns ........................................ : VI -E. 16
Slab-on-Grade Houses ........................................ VI -E.16
Elevating a Slab-on-Grade Wood-Frame House ........................................ VI -E.17
Elevating a Slab-on-Grade Masonry Structure .. ...................................... VI -E.29
Heavy Building Materials/Complex Design ............. ........................... VI -E.29

Field Investigation Concerns ........................................ VI -E.31

Property Inspection and Existing Data Review ............. ........................... VI -E.3 1

Code Search ........................................ VI -E.31

Design........................................ VI-E.3 4a

Elevation Sample Calculation ........................................ VI -E.31

Construction Considerations ........................................ VI -E.92
PriortoLifing anyHouse ......................................... VI -E.92
Slab-on-Grade House, Not Raising Slab With House ........................................ VI -E.92
Slab-on-Grade House, Raising Slab ........................................ VI -E.93
House over Crawlspace/Basement ........................................ VI -E.94
House on Piles, Columns, or Piers ........................................ VI -E.95

Relocation 

Step 1 -Selection of a House Moving Contractor .............. .......................... VI -R.3
Experience ........................................ VI -R.3
Financial Capability ........................................ VI -R.3
Professionalism and Reputation. .................................................... ........................... VI -R.3
Cost of Services ................... VI -R.4

VI -ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Step 2 -Analysis of Existing Site and Structure ..................................... VI -R.6
LiftingBeamPlacement ..................................... VI -R.7

Step 3 -Selection, Analysis, and Design of the New Site ..................................... VI -R.10
SiteAccess ..................................... VI -R.10
Penmits..................................... VI -R.10

Existing,Site ..................................... 

Step 4 -Preparation of the VI -R.11 

Step 5 -Analysis and Preparation ofthe Moving Route .............. ....................... VI -R.12
Identify Route Hazards ..................................... VI -R.12
ObtainApprovals ..................................... VI -R.13
Coordinate Route Preparation ..................................... VI -R.13

Step 6 -Preparation of the Structure ..................................... VI -R. 14
DisconnectUtilities..................................... VI -R.14
Cut Holes in Foundation Wall for Beams ..................................... VI -R.14
Install Beams ..................................... VI -R.15
Install Jacks ..................................... VI -R.15
Install Bracing as Required ..................................... VI -R.16
Separate Structure from Foundation ..................................... VI -R.16

Step 7 -Moving the Structure..................................... VI -R.17
Excavate/Grade Temporary Roadway ..................................... VI -R. 17
Attach Structure to Trailer ..................................... -VI -R.18
Transport Structure to New Site ..................................... VI -R.21

Step 8 -Preparation of the New Site ..................................... VI -R.22
DesignFoundation................................................................................................... VI -R.22
DesignUtilities ..................................... VI -R.22
Excavation and Preparation of New Foundation ... .................................. VI -R.22
Constructionof Support Cribbing.. ...................................... VI -R.23
Construction of Foundation Walls ..................................... VI -R.24
Lower Structure onto Foundation ..................................... VI -R.24
Landscaping..................................... VI -R.25

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -iii 
January 1995 


Step 9 -Restoration of Old Site ..................................... VI -R.26
Demolish and Remove Foundation and Pavement ................................ ...................VI -R.26
Disconnect and Remove All Utilities ................................ VI -R.26
Grading and Site Stabilization ................................ VI -R.27

Dry Floodproofing 

Dry Floodproofing ..................................... VI -D. 1
Emergency Operations Plan ..................................... VI -D.3
Inspection and Maintenance Plan ..................................... VI -D.4
Sealants and Shields ..................................... VI -D.5
Field Investigation ........................... ........................................................ "I " VI -D.12

....................... 

Design ........... VI -D.14
Confirm Ability of Structure to Accommodate Dry Floodproofing Measures ............. VI -D. 14

Selection and Design of Sealant Systems ....................................................... VI -D.23
Coatings....................................................... VI -D.23
WrappedSystems ....................................................... VI -D.24
Brick Veneer Systems ....................................................... VI -D.28

Selection and Design of Shield Systems ....................................................... VI -D.32
Plate Shields ....................................................... VI -D.32

Construction Considerations for Sealants and Shields .................................. VI -D.49

Drainage Collection Systems .................................. VI -D.50
FrenchDrains .......................................................................................................... VI -D.52
Exterior Underdrain Systems ................. VI -D.53
InteriorDrain System ................. VI -D.56

VI -iv Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sump Pumps . VI -D.58
.................................... 
Types of Sump Pumps ..................................... VI -D.58
Ifiltration vs. Inundation ..................................... VI -D.59
Coordination with Other Floodproofing Methods ................. .................... VI -D. 59
Field Investigation ................................................................................................V I -D .60

.... 
Design ............... VI -D.63

BackwaterValves ......................................... ....................................................................... VI -D.72 
FieldInvestigation. VI -D.74 
Design.VI -D.74 

EmergencyPower.VI -D.79 
Field Investigation.................................................................................................... VI -D.81 
Design .VI -D.82 
Construction .VI -D.91 

Wet Floodproofing 

Protection ofthe Structure .VI -W.2 
Foundations .VI -W.2 
Cavity Walls .................................................................................. ......................... VI -W.2 
SolidWalls .VI -W.3 

Design of Openings in Foundation Walls for Intentional Flooding of Enclosed Areas 
Below the FPE .VI -W.4 

Use of Flood-Resistant Materials .VI -W.6 

Building Operation and Maintenance Procedures and Emergency Preparedness Plans . VI -W.7 
Flood Warning System .VI -W.7 
Inspection and Maintenance Plan .VI -W.7 
Flood Emergency Operation Plan .VI -W.8 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -V 
January 1995 


Protection of Service Equipment .................................. VI -W.9
Relocation .................................. VI -W.9
Elevation .................................. VI -W.9
In-PlaceProtection.................................. VI -W.10

Field Investigation .................................. VI -W. 11

DesignOverview .................................. VI -W.14
Mechanical Systems .................................. VI -W. 15
Piping Systems .................................. VI -W. 16
Tanks .................................. VI -W. 16
Homeowner Coordination .................................. VI -W. 17
For ShieldingMeasures .................................. VI- W. 17
For Relocation Measures .................................. VI -W.17
Developing Design Details and Specifications .......... ........................ VI -W. 18
Verify Design with Homeowner .................................. VI -W. 18
Prepare Construction Documents .................................. VI -W. 18
Electrical Systems .................................. VI -W. 19
Central Heating System Alternatives .......................... VI -W.22
Gravity Furnaces ........................ VI -W.23
Forced Warm Air Furnaces ........................ VI -W.24
Hot Water Heating Boilers ........................ VI -W.25
Heat Pump Compressors ........................ VI -W.26
Central Cooling System ........................ . VI -W.26
Indoor Units ........................ VI -W.26
OutdoorUnits ........................ VI -W.27
Ductwork......................... VI-W.27
UnitaryA/C Systems ........................ VI -W.27
Ductwork Systems ........................ VI -W.27
Piping Systems ........................ VI -W.29
Fuel Supply/Storage Applications ........................ VI -W.30

In-Space Heating Equipment ........................ VI -W.3 1
Room Heaters and Wall Furnaces ........................ VI -W.3 1
Oil/Kerosene Heaters ........................ VI-W.31
Electric Heaters ........................ VI -W.32

Water Systems ........................ VI -W.32
Drinking Water Wells ........................ VI -W.32
On-Site Portion of Water Systems ........................ VI -W.33

VI -vi Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sewer Systems........................................................................................................ VI-W.34
On-Site Portion of Sewer Systems ................................ VI -W.34
SepticTanks............................................................................................................ VI-W.35
Telephone Systems ................................ VI -W.37
Cable TV Systems ................................ VI -W.38

Construction.......................................................................................................................VI-W .39
Electrical................................ VI -W.39
Mechanical..............................................................................................................VI-W.40

Floodwalls 

Types of Floodwalls ................................ VI -F.2
Gravity Floodwall ................................ VI -F.3
CantileverFloodwall ................................ VI -F.5
CounterfortFloodwall................................ VI -F.9
ButtressedFloodwall................................ VI -F.10

Field Investigation ................................ VI-F.11

Design ................................ VI -F.14
Floodwall Design (Selection and Sizing) ................................ VI -F.14
Sliding................................ VI -F.16
Overturning................................ VI -F.16
Pressure ................................ VI -F.16
Floodwall Design -Simplified Approach .............................................................

.VI -F.42
Floodwall Appurtenances .......................... VI -F.46
Floodwall Closures .......................... VI -F.46
Drainage Systems .......................... VI -F.55
Seepageand Leakage .......................... VI -F.60
Seepage Through the Floodwall .......................... VI -F.60
Seepage Under the Floodwall .......................... VI -F.61
Leakage Between the Floodwall and Residence ............... ................... VI -F.62
Architectural Details .................................. VI -F.63

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -vii 

January 1995 


Maintenance Considerations ........................................... VI -F.70
Construction ........................................... VI -F.73

Levees 

Field Investigation........................................... VI -L. 1

Design........................................... VI -L.4
Standard Criteria ........................................... VI -L.4
Maximurn Settled Height of Six Feet .............. ............................. VI -LA
Minimum Crest Width ofFive Feet ........................................... VI -L.5
Floodwater Side Slope of 1 Vertical on 2.5 Horizontal ........................................ 4 -L.5
Land Side Slope ........................................... VI -L.5
One Foot of Freeboard ........................................... VI -L.5
InitialPhases............................................. V. -L.6
Locate Utility Lines That Cross Under the Levee ............................................ V. -L.6
Provide"Cut-Off' forLevee Foundation Seepage........................................... VI -L.7
Identify Foundation Soil Type .............................................................................-

VI L.7 
Clay Foundation .......................... VI -L.7 
Sandy Foundation .......................... VI -L.7 

SeepageConcerns.......................... VI -L.8
Scouring/Slope Protection .......................... VI -L.9
InteriorDrainage .......................... VI -L.10
Maintenance.......................... VI -L.l I
Cost .......................... VI -L. 12

Construction .......................... VI -L.14
Soil Suitability .......................... VI -L.14
CompactionRequirements.......................... VI-L.14
SettlementAllowance ............... VI -L.15
Borrow Area Restrictions ............... VI -L.15
Access Across Levee ............... VI -L. 15

VI -viii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


GENERAL DESIGN PRACTICES

Chapter IV introduced the analyses necessary to quantify the flood-and non-flood-related 
hazards that control the design of a specific retrofitting measure. The objective of Chapter 
VI is to apply the anticipated loads developed in Chapter IV to the existing site/structure 
and design an appropriate retrofitting measure. 

This chapter covers the process of designing each retrofitting measure and developing 
construction details and specifications, providing the designer with tools to tailor each 
retrofitting measure to local requirements and homeowner preferences. Separate sections 
for elevation, relocation, dry floodproofing, wet floodproofing, floodwalls, and levees are 

I presented. 

The design of these retrofitting measures is a straightforward but technically intensive 
approach that will result in the generation of construction plans that may receive a building 
permit and mitigate potential flood and other natural hazards. This design process is 
illustrated in Figure VI- 1. 

Many elements of the design process (field investigation, homeowner coordination, maintenance 
considerations, and analysis of existing structure) are common to many of the 
retrofitting measures, warranting a general discussion of these elements. 

EngineeringPrinciples and Practices of Retrofitting Flood-Prone ResidentialStructures VI-1 
Januarv 1995 


Chapter VI: GeneralDesign Practices 

Field Investigation 

* Low Point of Entry Survey 
* Site Topography 
* Utility Locations 
* Local Building Regulations 
Homeowner * Hazard and Risk Determinations 
* Homeowner Preferences 
* Individual Preferences 
* Community Requirements 
Conceptual Design 

* Calculations and Analysis
_~~~~~~~~~~~~~~~~~~~~~ 

* Type, Size and Location 
* Preliminary Cost Estimates 
I Revision * Construction Access 
Homeowner Coordination * Maintenance Considerations 

* Conceptual Design 
* Access Requirements 
* Emergency Operations Plan 
Final Design 

I * Calculations and Design 
I Agreement a Details and Specifications 
* Cost Estimates 
I Revision * Permits/Access
Homeowner Coordination * Maintenance Considerations

* Final Design 
* Access Requirements 
* Easements/Waivers 
Construction 

I Agreement * Contractor Selection 
a Construction Inspection 

* As-Built Documentation 
Homeowner Coordination 

I 

* Maintenance Program I 
* Emergency Operations Plan 
Figure VI-1: Design Process 

VI -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

FIELD INVESTIGATION 

Detailed information must be obtained about the site and 
existing structure to make decisions and calculations concerning 
the design of a retrofitting measure. The designer 
should obtain the following information prior to developing 
retrofitting measure concepts for the owner's consideration: 

* local building requirements; 
* surveys; 
* final hazard determinations; 
* documentation of existing structural, mechanical, electrical, 
and plumbing systems; and 
* homeowner preferences. 
LOCAL BUILDING REQUIREMENTS 

Close coordination with the local building code official is 
critical to obtaining approval of a retrofitting measure 
design. The designer should review the selected retrofitting 
measure concept with the local building official to identify 
local design standards or practices that must be integrated 
into the design. This discussion may also identify, and 
provide an opportunity to resolve, issues where construction 
of the retrofitting measure may conflict with local 
building regulations. 

SURVEYS 

A detailed survey of the site should be completed to supplement 
the information gathered during the Low Point of Entry 
Determination (discussed in Chapter III) and to identify and 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -3 
January 1995 


ChapterVI: General Design Practices 

locate structure, site, and utility features that will be needed for 
the design ofthe retrofitting measure. 

Structure Survey 

The structure survey is a vertical elevation assessment at 
potential openings throughout the structure, whereby floodwaters 
may enter the residence. It may include: 

* basement slab elevation; 
* windows, doors, and vents; 
* mechanical/electricalequipmentand meters; 
* finished floor elevation of the structure; 
* drains and other floor penetrations; 
* water spigots, sump pump discharges, and other wall 
penetrations; 
* other site provisions that potentially may require 
flood protection such as storage tanks and outbuildings; 
and 

* the establishment of an elevation reference mark on or 
near the house. 
VI -4 Engineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Field Investigation 

Topographic Survey 

A detailed retrofitting design should not be developed 

without a site plan or map of the area. A state registered 

Professional Land or Property Line Surveyor can prepare a 

site plan of the area, incorporating the Low Point of Entry 

Determination information, as well as general topographic 

___________________________ and physical features. The entire site and/or building lot 
should be mapped for design purposes. A typical topo-
WI' graphic and site survey is shown in Figure VI-2. General 
surveying practices should be observed, but as a minimum 
Field surveys for design purposes the site plan should include: 
should be performed by a state 
registered Professional Land or 

Property Line Surveyor. * spot elevations within potential work areas; 

* one-foot or two-foot contours, depending on degree 
of topographic relief; 

* property lines, easements, and/or lines of division; 
* perimeter of house and ancilliary structures (sheds, 
storage tanks); 
DA-inpprinn Drnr:i of RPtrrnfittinn Flnoo-Prne Rsidential Structures VI -5

lti-R 

January 1995 


Chapter VI: General Design Practices 
j Sample Topographic Survey 
I 
I 
I 
I 
I 
I 
I I North 
I'll0 
I 
f 
R1 ai 
f|a 
I 
I 
I 
I 
I 
I 
/1I 
,I 
I 
~ ~ ~ ~/-_ DrnensOputI I 

--, -~t, ~ t _ca Grd. 29.70 
st1 S.o 

--~~~~~3 D111
, -K , / Mr s1 5X hm 28'x 43

Edge ofRoad Avenue Ex 84' StormDrain Easement 

-------- , 

Ex 1O'Sanitary Sewer 
_ -_ __ 

1I_ 

I _-Ex 15'Storm Drain 

II 

I I 

Plan View 

Mltt srald 

FFigure VI-2: Topographic and Site Survey 

VI -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

* driveways, sidewalks, patios, mailbox, fences, light 
poles, etc.; 
* exposedutility service(meters,valves, manholes, etc).; 
* road or streets; 
* downspout locations; 
* trees, shrubs, and other site landscaping features; 
* building overhangs and chimney; 
* window, door, and entrance dimensions; 
* mechanical units such as A/C and heat pumps; and 
* otherappropriateflood data. 

Additionally, the site plan should extend at least 50 to 100 feet 

beyondthe estimatedconstructionwork area.The purpose of 

extending the site map beyond the estimated work limits is to 

insure that potential drainage and/or grading problems can be 

resolved. Construction site access for materials and equipment 

as well as sediment and erosion control measures may also have 

an effect on the adjacent work area. Local building code 

mapping issues should also be addressed. 

Site Utilities Survey 

As part ofthe field investigation, above-and below-ground site 

utilities should be identified. Above-ground utilities, such as 
Contact local utility companies power lines, manhole covers, electric meters, etc., can be 
regarding the location of under-
located both horizontally and vertically on the topographic map.

ground utilities before construction 
begins. Underground utilities, such as sanitary and storm drain lines, 
wells and septic tanks, and electric or gas service, will require 

DnPrnirino :nrl Drnxr.tinraof IRotrnfiftinnFonnd-PronenResidential Structures._..__._._ VI -7 

I yIII IIII .. _ I .__.__

=fylt : III y ;:a1I wl r I-. I._.._. i~v~i -. -.-.-.._ 

January 1995 


Chapter VI: General Design Practices 

.. .~~~~ ~ ~~ ~ ~ ~ ~ ~ ~ ~~~ 

an investigationthroughthe appropriateutilityagency. Local 
utility companies and county, municipal, and building code 
officials will be able to assist in the identification ofthe underground 
utilities. Sometimes a copy of the topographic map and 
area can be submitted to the utility agency, who will prepare a 
sketch oftheir underground service. A checklist of underground 
services includes: 

* water main and sanitary sewer pipes; 
* water and sanitary service pipes; 
* cable television; 
* gaslines; 
e storm drain pipes; 
* water wells; 
* electric service; 
* telephone cables; and 
* other local utility services. 

In some instances, exact horizontal and vertical locations ofthe 
utility service may be required. A smallhole, more commonly 
referred to as a test pit, can be dug to unearth the utility service 
in question. Typically this service is perforned by alicensed 
contractor or the utility provider. 

VI -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

By identifying the utility services and units, provisions can be 

developed during the detailed design that will protect these 

utilities and keep them operational during a flood. Design 

provisions forutility relocation, encasement, elevation, anchor

ing, and, in some instances, new service, can be prepared. 

HAZARD DETERMINATIONS 

The designer (with the homeowners) should review the risk 
determinations previously conducted in Chapter III and confirm 

If the design flood elevation is the flood protection design level and required height ofthe 

less than the 100-year flood retrofitting measure selected. Not merely a function of ex-

elevation, the retrofitting measure pected flood elevation, freeboard, and low point of entry, this 

may violate FEMA standards. analysis should consider the protection of all components below 
Check with the local building 
official or the FEMA Regional the design elevation (i.e.below-grade basement walls and 
Office for clarification. associatedappurtenances). 

The analysis of flood-and non-flood-related hazards was 
presented in detail in Chapter IV. The designer should utilize 
the calculation templates presented there to finalize expected 
design forces. 

DOCUMENTATION OF EXISTING 
BUILDING SYSTEMS 

Documentation ofthe condition ofthe existing structure is an 
important aspect ofthe design of elevation, relocation, and dry 
and wet floodproofing measures. This topic was introduced in 

Chapter III as reconnaissance designed to provide preliminary 
information on the condition of an existing structure and its 
suitability forthe various retrofitting methods. 

Pnninaarinn Prinninipeand Prantircs ofRatrofittina Flood-Prone Residential Structures VI -9 
January 1995 


Chapter VI: General Design Practices

As the design of a specific elevation, relocation, or dry and wet 
floodproofing measure is begun, the designer should conduct a 

49 

detailed evaluation of the type, size, location, and condition of 

Since the data sheets providedin theexisting mechanical, electrical, and plumbing systems. The 
this book are generalized for enclosed Mechanical, Electrical,Plumbing,and related Building 
residential housing applications Systems Data Sheet (Figure VI-3) can be used to document the 
and ask for information that may resultsofthis examination. 
not be applicable to a specific 
retrofitting measure, the designer 
should exercise judgment in 
collecting the information cited 
on the checklists. 

VI -10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

(Note: Collect only the data necessary for your project) 

Owner Name: Prepared By:
Address: Date:
Property Location:

A. EXTERIOR UTILITIES AND APPURTENANCES 
Water
O On-site well or spring
O Public water system

Water Purveyor's Name: 

Sanitary
O On-site septic and drain field
O Public sewerage

Storm 

o On-site
O Public sewerage
Incoming Electrical Service
O Overhead a Underground
O Voltage E 120/240 volt 10 0 120/208 volt 10
O Direct Burial Size:
O Service Entrance Cable Amps:
O PVC Conduit

o RGS Conduit
Transformer #:
E Power Co:
Power Meter #:
Contact:
Estimated Transformer Rating:
Fault Current Rating:

Telephone Service
Cl Company:
a Overhead E Underground
El Cable Pair
El Pedestal E Grounded
E Direct Burial

Cable TV 

 Company:
E Overhead E Underground# of channels:
E PVC CATV #:
E Direct Burial E RGS: Contact:
Page 1 of 3 

Figure VI-3: Mechanical, Electrical, Plumbing and Related Building Systems Data Sheet 

Practicesof Retrofittina Flood-Prone Residential Structures

FnninpprinnPrinrin1P an1nd VI -11 

January 1995 


Chapter VI:General Design Practices

Other Utilities 
Ol Natural Gas 
Utility Company Name: 
Location of service entr ance: 
Meter Location: 
O LPG 
Utility Company Name: 
Location of gas bottle: 
How is tank secured? 
n Oil 
Oil Supplier: 
n Above ground tank O Underground tank 
Size gallons 
Location 
Vent terminal 
Elevation:_ feet or elevation above grade? feet 
Fill cap type: 
B. DOMESTIC PLUMBING 
Water 
El Location of service entrance 
Main service valve? E Yes Cl No 
Backflow preventer? VI Yes 0 No 
Type of water pipe El Copper Cl Iron E Plastic 
D Domestic water heater 
al Gas BTU/HR 
E Oil GAUHR 
E Other Specify units 
Size: gallons 
Location: 
E Sanitary Drainage 
Floor served? 
Fixtures below BFE El Yes El No 
Backwater valve installed in fixtures below BFE? E Yes 3 No 
Backwater valves needed (if none exist) E3 Yes C] No 
El Storm Drainage 
Basement floor drains connected? El Yes E3 No 
Is storm combined w/sanitary? El Yes E No 
C. HEATING SYSTEM 
Type E Central System El Space heaters 
Central System 
E Warm air El Hot water E Steam 
Warm Air Furnace 
Location: El Basement El 1st Floor 0a __floor El Attic Page 2 of 3 0 
Figure VI-3: Mechanical, Electrical, Plumbing and Related Building Systems Data Sheet (continued) 

VI -12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
.Iani iarv I 9.R 


Field Investigation 

Type: O Upflow Cl Downflow 0 Horizontal El Low Boy 
Fuel: C] Natural Gas E LPG O Electric E Coal E Wood 
Burner: E Atmospheric O Fan assisted 
Condensing: O Yes Cl No 
Venting: E Natural draft 0 Forced draft E Direct vent 
Air Distribution: O Gravity 13 Ducted 

E Sheet metal ductwork 
Cl Flexible, non-metallic runouts 
O Fiberglass ductboard 
O Location 

Air Outlets: a Floor E Low sidewall O High sidewall El Ceiling E 2nd floor 
Hot Water/Steam: 
Boiler: 0 Hot Water E Steam 
Location: 0 Basement E 1st Floor E __floor o Attic 
Fuel: 0 Natural Gas 0 LPG O Electric O Coal E Wood 
Terminal Units: 0 Baseboard 0 Radiators 0 Other 

In-Space Heating Equipment 

Gas E Room heater E Vented 0 Unvented 
E Wall Furnace E Conventional E Direct vent 
E Floor Furnace 

Oil/Kerosene: E Vaporizing oil pot heater E Powered atomizing heater 

E Portable kerosene heater 
Electric Heaters: E Wall E Floor O Toe space E Baseboard 
Radiant Heat: E Panels E Embedded fireplace E Portable cord and plug 
Solid Fuel Heaters: E Simple fireplace E Factory built E Radiant 

E Circulating E Freestanding 
Stoves: E Conventional E Advanced design E Fireplace insert 
El Pellet stove 

D. COOLING SYSTEM 
Type E Central E In-space Conditioners 
Central Systems E Split system A/C E Unitary A/C E A-Coil add-on 
E Split system heat pump 

Split Systems: 
Indoor unit locat ion: E Basement E 1st Floor E _floor E Attic 
Type: E Upfic)w 0 Downflow O Horizontal 
Air distribution: O Sheet metal ductwork 

O Fiberglass ductboard 
O Flexible non-metallic runouts 
Air outlets: E Floor 0 Low sidewall 
O High sidewall E Ceiling 

Outdoor unit location: 

In-space Air Conditioners: El Window air conditioners Page 3 of 3 
El Ductless split systems 

Figure VI-3: Mechanical, Electrical, Plumbing and Related Building Systems Data Sheet (continued) 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -13 
January 1995 


Chapter VI: General Design Practices

HOMEOWNER PREFERENCES 

A detailed discussion of homeowner preferences was presented 
in Chapter III. The designer should confirm the 
homeowner's preferences regarding: 

* retrofitting measure type, size, and location(s); 
* project design desires/preferences; 
o limitations on construction area; 
* estimated construction budget; and 
* potential future site improvements. 
Once the designer has collected the above-mentioned information, 
a conceptual design of the proposed retrofitting measure 
can be discussed with the homeowner. 

At this time the designer should also review and confirm 
coordination and future maintenance requirements with the 
homeowner to ensure thattthe selected retrofitting measure is 
indeed suitable. 

Homeowner Coordination 

Homeowner coordination is similar for each of the retrofitting 
methods and involves reviewing design options, costs, specific 
local requirements, access and easement requirements, maintenance 
requirements, construction documents, and other information 
with the homeowner and regulatory officials to present 
the alternatives, resolve critical issues, and obtain necessary 
approvals. 

VI -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

Maintenance Programs and 
Emergency Action Plans 

Development of appropriate maintenance programs for retrofitting 
measures is critical to the continued success of retrofitting 
efforts. Refer to FEMA Technical Bulletin 3-93 Non-ResidentialFloodproofing-
Requirementsand Certificationfor 
BuildingsLocatedin Special FloodHazardAreasin Accordance 
with the NFIP for additional guidance concerning 
minimum recommendations for Emergency Operations Plans 

and Inspection and Maintenance Plans. While this bulletinwas 
prepared for non-residential structures, it contains sound advice 
for the development of inspection, maintenance, and emergency 
operation plans. 

Design information presented in this chapter relates to field 
investigation, design calculations and construction details, and 
construction issues. Since many ofthe key elements in the field 
investigation phase were discussed above, only those issues that 
are critical to the design and successful construction of the 
particular retrofitting measure are included here. 

Engineering Principles and Practices of F letrofittingFlood-ProneResidential Structures VI -15 
January 1995 


Chapter VI: General Design Practices 

ANALYSIS OF EXISTING STRUCTURE 

The ability of an existing structure to withstand the addi

tional loads created as a result of retrofitting is an important 

design consideration. Accurate reconnaissance of the 

foundation and estimates of the capacity of various struc

tural systems are the first steps in the design of retrofitting 

measures. The objective of this analysis is to identify the 
extent to which structural systems must be modified or 
redesigned to accommodate a retrofitting measure such as 
elevation, relocation, dry and wet floodproofing, levees, or 
floodwalls. The steps involved in this analysisinclude: 

* structural reconnaissance; 
* determination of the capacity of the existing footing and a 
foundation system; V 
* analysis ofthe loads imposedby the retrofitting measure; 
and 
* comparison of the capacity of the existing structure to 
resist the additional loads imposedby the retrofitting 
measure. 

STRUCTURAL RECONNAISSANCE 

In order to determine whether a structure is suited to the 
various retrofitting measures being considered, the type and 

condition of the existing structure must be surveyed. Some 
structural systems are more adaptable to modifications than 
others. Some retrofitting methods are more suited for, or 
specifically designed for, various construction types. Ofthe 

retrofitting methods discussed, elevation, dry floodproofing, 
and relocation most directly affect a home's structure. 
Floodwalls and levees are designed to prevent water from 

reaching the house and thus should not have an impact on 

VI -16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures
January 1995


Analysis of ExistingStructure 

the structure. Wet floodproofing techniques have a lesser 
impact on the structure due to equalization of pressures, and 
also require analysis of the existing structure. 

Several sources of information concerning the details of 

construction that were used in a structure include: 

* construction drawings from the architect, engineer, or 
builder. These are usually the best and most reliable resource 
for determining the structural systems and the size of 
the members; 
* information available from the building permits office; 
* plans of any renovations or room additions and a recent 
record of existing conditions; 
* contractors who have performed recent work on the 
house, such as plumbing, mechanical, electrical, or other 
kinds; 

* a home inspection report, if the home has been recently 
purchased. While these reports are not highly detailed, 
they may give a good review of the condition of the 
house and point out major deficiencies. 
If the aforementioned information is not available, the 
designer (with the permission of the owner) should determine 
the type and size of the critical structural elements. 
The structural reconnaissance worksheet provided at Figure VI4 
can be used to document this information. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures .VI -17 
January 1995 


Chapter VI: General Design Practices 

-

Owner Name: -Prepared By: 

-

Address: Date: 
Prooertv Location: 
StructuralReconnaissance Worksheet 
Sketch and Description of Existing Structure: 

Condition
Item Material Size (Excellent, Notes

Fair,Noe

Good, 

Unacceptable) l
Footing Concrete
Concrete
Foundation Concrete
Wall Masonry
Brick
Masonry
Wood Frame
Walls Masonry
Metal Frame
Wood Joist

Floor System Beam 

Wood Truss 

Truss
Roof System
Rafter
Wood Siding
Exterior Brick Veneer

Stucco 
Drywall 
Interior Plaster 
Finishes 
Wood .. 

Figure VI-4: Structural Reconnaissance Worksheet 
VI -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Existing Structure 

FOOTINGS AND FOUNDATION 
SYSTEMS 

Elevating a house exposes it to The foundation system of ahouse (footings and foundation 
greater vertical loads from 
increasedwindloadingsand walls) serves several purposes. It supports the house by

additionalweight,and horizontal transmitting the building loads to the ground, and it serves as an 
andshearloadsfrom increased anchor against uplift and against forces caused by wind, seismic,
windforces. Figure VI-5illus-flooding, and other loads. Foundation walls (below grade)

tratesthe variousloadsthat affect restrain horizontal pressures from adjacent soil pressures. The 
a foundation system. foundation system anchors the house against horizontal, vertical, 

and shear loads from water, soil, debris, seismic, snow, and 
wind hazards. Retrofitting measures such as elevation change 
the dynamics ofthe forces acting on a house. 

Snow 

Wind Forces 4 Loads 
Dead Loads Seismic Forces 

-ni

/\BuoyancyLive Loads Impact Forces _i + ii Forces _ Soil Forces _ 
Flood Forces 
o 0 
1 t t t t t $D 2IE[~ 
I--O.oL 
o 
20. 
0 
Figure VI-5: Foundation System Loading 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -19 
January 1995 


Chapter VI: General Design Practices 

M_ 

For linear foundation walls, the 
width of the footing is normally 
two times the thickness of the 
foundation wall. The depth of the 
footing is normally equal to the 
thickness of the foundation wall. 

Perimeter drainage systems may 
be used if the bearing soil is 
adversely affected by saturation. 
Often soils under bearing pressure 
will not become saturated due to 
low permeability. Each situation 
should be evaluated separately. 

4. 
When older foundation systems 
(such as stone) are encountered, 
the designer should consult the 
local code on what procedures/ 
applications are allowable. The 
compressive strength of stone 
walls is so variable that professional 
testing and specialized 
expertise is usually required. 

Footings 

Footings are designed to transmit building loads to the ground 
and should be placed completely below the maximum frost 
penetrationdepth. Thesize of thefootingcan be determined 
by the formula below: 

A = P/Sb= ft2 
where: A 
P 
Sbc 
is thebearingarea ofthe 
footing in square feet; 
isthe loadin pounds;and 
is the allowable soil bearing capacityin 
poundsper squarefoot. 

Formula VI-1: Determining Footing Size 

An existing footing should be checked to determine its maximum 
loading condition. Rearranging the above formula will 
provide the maximum load for the existing footing. 

xP=AS= lbs 

where: Pmax istheloadinpounds; 
A is the bearing area ofthe footing 
(in square feet); and 
S isthe soilbearing capacityin 
poundsper square foot. 

FormulaVI-2: Maximum Loadingof ExistingFooting 

VI -20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Existing Structure 

In conducting this computation, it is important to confirm the 

size and depth of the footing and bearing capacity ofthe soil to 

assure that the existing conditions meet current codes. In the 

absence of reliable information, excavation may be required to 

confirm the depth, size, and condition ofthe existing footing. 

The designer should also check the existing footing to ensure 
that it has a perimeter drainage system to prevent saturation of 
the soil at the footing. If one does not exist, the designer should 
consider including this feature in the design ofthe retrofit. 

Bearing Capacity 

The bearing capacity of an existing concrete masonry foundation 
wall can be estimated if the designer knows the size and 
grade ofthe block, using the following formula. 

. 

We=FcsA= lbs 
-w 
where: W. is the total weight per linear foot 
the wall will support; 
Fc is the bearing capacity ofthe 
masonry from Table VI-1; 
s is the slenderness ratio, which is 
computed from the height or 
length to thickness ratio ofthe 
member in question; and 
A is the cross sectional area per 
linear foot of wall. 

Formula VI-3: Bearing Capacity of an Existing Concrete 
Masonry Foundation Wall 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -21 
January 1995 


Chapter VI: General Design Practices 

At 

To limit the effects of slenderness 
on masonry walls, American 
ConcreteInstitute (ACI)530 

provides maximum height or 
length to thickness ratios. Height 
or length is based on the location 

of the lateral support elements 
that brace the masonry and permit 
the transfer of loads to the 
resisting elements. Nominal wall 
thickness may be used for t . 

Table VL-2: Wall Lateral Support 
Requirements, provides maximum 
slenderness ratio values for 
bearing and non-bearing walls. 

The slenderness ratio, s, (which is less than 1.0) can be computed 
as follows: 

aCa0 

s = 1.2 -H /37t = 

where: s is the slenderness ratio, a dimensionlessvalue; 
H1 
t 
istheheightofthe unbraced 
foundation wall in inches; and 
isthethicknessofthe wallin 
inches. 

Formula VI-4: Slenderness Ratio 

By changingthevalueofthe bearingcapacityaccordingto the 

conditions identified on the site, the designer can determine the 

approximate weight that the foundation wall will support. If the 
type of block and mortar is unknown, the most conservative 
values should be used. Intrusive methods of investigation must 
be employed to determine footing depth, thickness, reinforce

ment, condition, or drainage. Technology exists for investiga

tion of walls using x-ray, ultrasound, and other methods; 

however, these methods may be too costly for residential 

retrofitting projects. 

VI -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1 995 


Analysisof Existing Structure 

The approximate bearing capacity 
of concrete and reinforced 
concrete materials may be quite 
variable due to regional differences 
in concrete mix, aggregate, 
reinforcing practices, and other 
factors. In general, the approximate 
bearing capacity of concrete/ 
reinforced concrete is substantially 
greater than masonry block: a 
conservative estimate ranges from 
500 to 1,000 pounds per square 

inch. Additional information on 
the capacity and strength of 

concrete mixtures can be obtained 

from the American Concrete 
Institute (ACI) 318. 

Approximate Bearing Capacity 
Table VI-I for Masonry Materials 

Type of Stress and Masonry Type of Mortar 
Unit or Condition N S M 
Allowable stress, lb/in2 

Compression, f., lb/in2 
Brick, SW 300 350 400 
Brick, MW 275 310 350 
Brick, NW 215 235 290 
Concrete block, grade A walls 85 90 100 
Concrete block, grade B walls 70 75 85 
Concrete block, grouted piers 90 95 105 
Cut granite 640 720 800 
Cut limestone, marble 400 450 500 
Cut sandstone, cast stone 320 360 400 
Rubble, rough, random 100 120 140 
Glass block, min. 3 in. thick 

Exterior walls: Unsupported surface area < 144 ft2
Unsupported length < 25 ft
Unsupported height <20 ft

Interiorwalls: Unsupported surface area < 250 ft2 
Unsupported length and unsupported 
height < 25 ft 

Table VI-2 Wall Lateral Support 
Requirements 

Maximum 
Construction 
SlendernessRatio (Iftwor 
h/tw) 
Solid or Solid 20 
Bearing Grouted 
Walls 
All Other 18 
Non-Bearing Exterior 18 
Walls Interior 36 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -23January 1995 


Chapter VI: General Design Practices 

LATERALLOADS 

The ability ofexterior foundation walls and interior structural 
walls to withstand flood-related and non-flood-related forces is 
dependent upon the wall size, type, and material. Interior and 

For additional informationconcexterior walls are checked for failure from overturning, bending,

For additional iformation concern-and shear (horizontal, vertical, and diagonal). If the stress 
ing the performance of various 
structuralsystems, refer to the U.S. caused by the expected loading is less than the code-allowable 
Army Corps of Engineers research stress for the expected failure mode, the wall design is accept-

study entitled Flood Proofing able. Conversely, if the stresses caused by the expected 

Tests,August,1988. loadings are greater than the code-allowable stresses for the 

expected failure mode, the design is unacceptable and reinforc

ing is required. 

Due to the large number of wall types and situations that can be 
encountered that would make a comprehensive examination of 
this subject unwieldy for this manual, only procedural and 
reference information for lateral load resistance is provided. 
The process of analyzing foundation and interior walls is outlinedbelow: 

Step 1: Determine the type, size, material, and location ofthe 
walls to be analyzed. 

Step 2: Using ACI 530 (Building Code Requirements for 
Masonry Structures) as a reference for masonry 
construction, determine the code-allowable overturning, 
bending, and shear stresses for the wall in question. 
ACI 530 has tables of allowable stress information 
for masonry structures based on physical testing. 

The American Plywood Association offers information 
on allowable loads in plywood shear walls. 
Watch for increased soil pressures due to overturning 

VI -24 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 

-Iw--~--------o----J-- anuary____

----------- 1995

January 1995 


A'E* 

For additional information on 
loadingconditions for exterior and 
shear walls, refer to ASCE 7. 

i 

Analysis of Existing Structure 

in the wall. ACI 318 should be used for reinforced 

concrete walls, and ACI 318.1 for non-reinforced 

concrete walls. 

Lateral loads are distributed to the shear walls via the 
diaphragms of the floor or roof. Distribution is based 
upon relative stiffnesses ofthe walls. Use extreme 
care in the design of diaphragm-to-wall connections. 
Most codes require that an additional eccentricity 
(factor of safety) be considered in the location of the 
resultant ofthe lateral loads. 

Step 3: Compare the stresses caused by the expected 
loadings versus code-allowable stresses (capacities) 
for each wall being analyzed. If the stresses caused 
by the expectedloadingsare less than the code-
allowable stresses, the design is acceptable; if not, 
reinforcement is required or another method should 
be considered. 

VERTICAL LOADS 

In addition to the loads imposed by floodwaters,othertypes of 
loads must be considered in the design of a structural system, 
such as building dead loads, live loads, snow loads, wind 
loads, and seismic loads (if applicable). Flood, wind, and 
seismic loads were discussed earlier in Chapters III and IV. 
This section deals with the computation of dead loads, live 
loads, and snow loads. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -25 
January 1995 


Chapter VI: General Design Practices 

Dead Loads 

Dead loads are the weight of all permanent structural and 
nonstructural components of a building, such as walls, floors, 
roofs, ceilings, stairways, and fixed service equipment. The sum 
ofthe dead loads should equal the unoccupied weight ofthe 
building. The weight of a house can be determined by quantifying 
the wall and surface areas and multiplying by the weights of 
the materials or assemblies. A list ofthe weights of some 
construction types is provided in Table VI-3. In additionto the 
weight ofthe structure, any furnishings and equipment located in 
the house must be added to the total. The worksheet provided 
at Figure VI-6 can be used to make a preliminary estimate of 
the weight of a structure. To use Figure VI-6, the designer 
should: 

Step 1: Determine the construction ofthe various components 
ofthe building, quantify them, and enter this information 
in the second column; 

Step 2: Look up the weight of these assemblies and enter that 
figure into the third column; 

Step 3: Multiply the quantities by the unit weights to obtain 
the construction component weights, and enter the 
result in the fourth column; 

Step 4: Add these component weights in column four to 
obtain an estimate ofthe total weight ofthe structure. 
Entertheresult in the box at the bottom of column 
four. 

VI -26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of ExistingStructure 

Table VI-3 Weights of Construction Types 

Weight, lb/ft2 

Construction surfacearea 

Wood stud wall, 2x4, interior, '/-in drywall 2S 8 
Interior, wood or metal 2x4s, plaster2S 19 
Exterior, drywall; 4-in batt insul.; wood siding 11 
Exterior, drywall; 4-in batt insul.; 4-in brick (MW) 47 
Exterior,drywall; 4-in batt insul.; 8-in concrete block 60-65 

Metal stud wall, 2x4, interior, %-indrywall 2S 7 
Exterior, drywall; 4-in batt insul.; 1-in stucco 23 

Metal stud wall, exterior, drywall; 4-in batt insul.; 2-in drywall 18 
Exterior, drywall; 4-in batt insul.; 3-in granite or 4-in brick 55 

Plaster, per face, wall, or ceiling, on masonry or framing 8 

Ceramic tile veneer, per face 10 

Masonry wall, 4-in brick, MW, per wythe 39 
4-in conc. block, heavy aggregate, per wythe 30 
8-in conc. block, heavy aggregate, per wythe 55 

Glass block wall, 4-in thick 18 

Glass curtain wall 10-15 

Floor or ceiling, 2x10 wood deck, outdoors 8-10 
Wood frame, 2x1 0, interior, unfinished floor; drywall 8-10 
ceiling 

Concrete flat slab, unfinished floor; susp. ceiling 80-90 
Concrete pan joist (25 in o.c., 12-in pan depth, 3-in 90-100 
slab), unfinished floor; susp. ceiling 

Concrete on metal deck on steel frame, unfinished floor; 65-70 
susp. ceiling 

Finished floors, add to above: 
Hardwood 3 
Floortile 10 
1/2-in terrazzo 25 
Wall-to-wall carpet 2 

Roof,sloping rafters or timbers, sheathing; 10-in batt insul.; 12-15 
%/2-in

drywall 
Built-up5-ply roofing, add to above 6 
Metal roofing, add to above 3-4 
Asphalt shingle roofing, add to above 4 
Slate ortile roofing, '/4-in thick, add to above 12 
Wood shingle roofing, add to above 3-5 

1

Insulation, batt, per 4-in thickness 

0.17
Insulation, rigid foam boards or fill, per inch thickness 

Stairways: 
Concrete 80-95 
Steel 40-50 
Wood 15-25 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -27 

January 1995 


Chapter VI: General Design Practices 

Owner Name: Prepared By: 
Address: Date: 
Property Location: 

BuildingWeight Estimating Worksheet 

Construction Type Surface Weight (Ibslsf) of Weight 

(1) Area (2) Surface Area (3) Component (4) 
Walls 

Exterior 

Interior 

Floors 

First
Second

Attic 

Roof 

Special
Items
Fireplace*

Chimney* 

StructureWeight 

Furnishings 

Total Weight 

Figure VI-6: Building Weight Estimating Worksheet
*Do not include if chimney/fireplace has a separate foundation.

VI -28 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of Existing Structure 

Live Loads 

Live loads are produced by the occupancy of the building, not 

Check local codes for guidance on including environmental loads such as wind loads, flood loads, 
acceptable live loads. In the snow loads, earthquake loads, or dead loads. For residential 
absence of code information use one- and two-family dwellings, a typical floor live load is a 

ASCE 7. 

uniformly distributed load of 40 pounds per square foot. 

LL=ALo lbs 

where: LL is the live load in pounds; 
A is the area of each floor of the 
residence in square feet; and 

Lo istherminimumuniformlydistributed 
live load in pounds per 
square foot. 

Formula VI-5: Calculation of Live Load 

Roof Snow Loads 

The roof snow load varies according to the geography, roof 
slope, and thermal, exposure, and importance factors. Local 
building codes should be consulted to find the snow load and 
how to apply it to the structure. Take particular care to account 
for drift and unbalanced snow loads. If no local code is available, 
the designer should refer to ASCE 7 for this information. 
In areas of little snowfall, codes may require a minimum roof 
snow load. 

Calculation of Vertical Dead, Live, and 
Snow Loads 

Dead, live, and snow loads act vertically downward and are 
carried by the load-bearing walls or the columns to the foundation 
system. The load-bearing walls support any vertical load in 
addition to their own weight. The amount ofthe dead load 

Engineering Principles and Practices olf Retrofitting Flood-Prone Residential Structures VIA 29 
January 1995 


Chapter VI:General Design Practices 

carried by a wall or column is calculated based on the partial 
area ofthe roof and floor system (tributary areas) that are 
supported by that wall or column plus its own weight (self 
weight). The tributary areas are illustrated in Figures VI-7 and 
VJ-8 and determined as follows: 

For the load-bearing walls, a one-foot-widestrip of floor or 
roofperpendicularto the floorjoists orrooftrusses multiplied 
by halfthe span lengthofthejoist ortruss. Strip width 
is the same dimension as the joist or truss spacing. 

I-I I
Is= o A = 1w/2= ft2

where: A. is thewall tributary areain square 
feet; 
I is the length of the wall in feet; 
and 

w is the span length between walls 
or the wall and center girder in 
feet. 

Fornula VI-6: Calculationof Tributary Area for 
Load-bearing Walls 

VI -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of ExistingStructure 

b o-ExteriorWallTributaryArea 

TrbutaryArea 

_________ ii~~~~~~~~~~ 

Figure VI-7: Column Tributary Area Figure VI-8: Wall/Girder Tributary Area 

A = I(a+b)/2 = ft2 

g 

,where:Ag isthecentergirdertributaryarea 
in square feet; 
1 is the length ofthe wall in feet; 
and 
a+b is the span length between the 
center girder and walls in feet. 

FormulaVI-7: Calculationof Tributary Area for Center 
Girder 

* For columns the tributary area is the area bounded by 
imaginary linesdrawn halfway between the column and the 
adjacent load-bearing wall or column in each direction. 
At = (w/2)(112) = -ft2 

where: At is the columntributary area in 
square feet; 
I is the length ofthe wall surrounding 
the column in feet; and 
w is the span length between walls 
surrounding the column in feet. 
I 

Formula VI-8: Calculationof Tributary Area for Columns 

-31

VI -31

Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures ; ~~VI 
January 1995 


Chapter VI:General Design Practices

To calculate the loads, follow the steps below: 

Step 1: Inspect the roofand the floor construction to identify 

load-bearing walls. Mark the direction, the span 
length, and the supportingwalls or columns forthe roof 
trussesand floorjoists. 

Step 2: Calculate the roof and the floor tributary areas for
each load-bearing wall and column.

Step 3: For each load-bearing wall and column, multiply the 
tributary areas by the dead, live, and snow loads to 
find the total loads. 

coociI=c.II

U 

TLdis= (DL + LL + SL) At=, lbs 

where: TLdis is the total dead, live, and snow 
loads acting on a specific wall or 
column in pounds; 
DL is the dead load in pounds per 
square foot (from Figure VI-6); 
LL is the live load in pounds per 
square foot (from Formula VI-5); 
SL is the snowloadin poundsper 
square foot (from code); and 

At is the tributary area ofthe wall or 
column in square feet (from 
Formulas VI-6 and VI-8). (When 
analyzing walls use Awinstead of 
At.) 

Fonnula VI-9: Calculation of Wall/Column Loads 

VI -32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


. Analysis of ExistingStructure 

Step 4: Calculate the selfweight of the wall or column. Add 
any overbearing soil and foundation weight to the 
total. This information can be taken from the calculation 
template shown in Figure VI-6. 

E-I13

_ ,,01 SW=SAWU= Ibs 

where: SW is the self weight ofthe component 
in pounds; 
SA is the section area of the component 
in square feet; and 

Wu is the unit weight of the componentin 
pounds per squarefoot of 
surface. 

FormulaVI-10: Calculationof the SelfWeight of the Wall! 
Column 

Step 5: Add all the above calculated loads to find the load 
carried by the wall or column to the foundation or 
footing. 

-1 

100a 

1001

F-I TL=SW+TLdis = lbs 

where: TL is the total load carried by the 
wall or column to the footing or 
foundation in pounds; 

SW is the self weight ofthe component 
in pounds; and 

TLdis is the total dead, live, and snow 
loads acting on a specific wall or 
column in pounds. 

Formula VI-11: Calculation of Total Load Carried by the 
Wall or Column to the Footing or Foundation 

VI -33

V-33

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ;~~ V 
January 1995 


Chapter VI: General Design Practices 

CAPACITY VERSUS LOADING 

The next step is to examine the capacity ofthe existing founda

tion component or system versus the expected loading from a 
combination of dead, live, flood, wind, snow, and seismic loads. 
This analysis willprovide an initial estimate ofthe magnitude of 
foundation modifications necessary to accomplish an elevation 
or relocation project. 

Model building codes (BOCA, ICBO, SBCCI, CABO) 

require the analysis of a variety of loading conditions and then 
base the capacity determination on the loading condition that 
presents the most unfavorable effects on the foundation or 

structural member concerned. 

It is the purpose of the load combinations to identify critical 
stresses in structural members (or nonstructural members) and w 
critical conditions used to design the support system. Since 

Designers should refer to ASCE 7-every conceivable situation cannot be covered by standard load
95 when conducting load combina-cases, soundengineeringjudgmentmust be used.
tion analysis.

Load Combination Scenarios 

ASCE 7-95 prescribes how to analyze flood loads in concert 
with other loading conditions. This guidance involves the use of 
two methods-allowable stress design and strength design. In 
the case of allowable stress design, design specifications define 

allowablestressesthat maynot be exceededby loadeffects 

due to unfactored loads, that is, allowable stresses contain a 

factor of safety. 

In strength design, design specifications provide load factors, 
and, in some instances, resistant factors. 

The analysis of loading conditions may be checked using either 
method provided that method is used exclusively for proportioning 
elements of tat construction material. The designer 

VI -34 Enaineerina Princinles and Practices of Petrofittinm FInnr.Prmna Radv4antial QStnrtmn~a 

January 1995 


Analysis of ExistingStructure 

should consultASCE 7-95 for guidance in analyzing the multi-
hazard loading conditions described below: 

The following symbols are used in defining the various load 
combinations. 

D Dead Load 

E Earthquake Load 

F Load due to fluids with well defined pressures and 
maximumbeights 

F FloodLoad 

H Load due to weight and lateral pressure of soil and 
water in soil 

L Live Load 

Lf Roof LiveLoad 

.~~~~~~~~~~~ 

R RainLoad 

S SnowLoad 

T Self-Straining Force 

W WindLoad 

Thesesymbolsare based upon informationfromASCE 7-95 
but do not match exactlyas several symbolshadto be revised 
to accommodate symbols already used in this manual. Refer to 
ASCE 7-95 for clarification and additional information. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -35 
January 1995 


Chapter VI: General Design Practices 

STRENGTH DESIGN METHOD 

When combining loads using the strength design methodology, 
structures, components, and foundations should be designed so 
that their strength equals or exceeds the effects ofthe factored 
loads inthe followingcombinations: 

1. lAD 
2. 1.2(D+F+T) +1 .6(L+H) + 0.5(L or S or R) 
3. 1.2D+ 1.6(LrorSorR)+(0.5Lor0.8W) 
4. 1.2D+ 1.3W+0.5L +0.5(L orS orR) 
5. l.2D+ .OE+0.5L+0.2S 
6. 0.9D+ (1.3W or 1.OE) 
Exception: The load factor on L in combinations (3), (4), and 

(5) shall equal 1.0 for garages, areas occupied as places of 
public assembly, and all areas where the live load is greater than 
100 lb/ft2 (pounds force per square foot). 
Each relevant strength limit state shall be investigated. Effects of 

one or more loads not acting should be investigated. The most 
unfavorable affects from both wind and earthquake loads 
should be investigated, where appropriate, but they need not be 
considered to act simultaneously. The structural effects of 
Flood (F.) should be investigated in design using the same load 
factors as used for L (live load) in the basic combinations of 2 

and 4. The structural effects of Fmshould also be included 
when investigating the overturning and sliding in the basic 
combination 6 using a load factor of 0.5 when wind also occurs 
and 1.6when acting alone. 

VI -36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Analysis of ExistingStructure 

ALLOWABLE STRESS METHOD 

When combining loads using the allowable stress method, the 
loads should be considered to act in the following combinations, 
whichever produces the most unfavorable effect on the building, 
foundation; or structural member being considered. 

1. D 
2. D+L+F+T+(LrorSorR) 
3. D+(WorE) 
4. D+L+(LrorSorR)+(WorE) 
The most unfavorable effects from both wind and earthquake 

loads should be considered, where appropriate, but they need 
not be assumed to act simultaneously. Buildings and other 
structures should be designed sothat the overturning moment 
due to lateral forces (wind or flood) acting singly or in combina

tion does not exceed two-thirds ofthe dead load stabilizing 
moment unless the building or structure is anchored to resist the 
excess moment. The base shear due to lateral forces should not 

exceed two-thirds of the total resisting force due to friction and 
adhesion unless the building or structure is anchored to resist 
the excess sliding force. Stress reversals should be accounted 
for where the effects of design loads counteract one another in a 
structural member orjoint. 

Analyzing the existing structure's capacity to resist the expected 

loads is sometimes a long and tedious process, but it must be 
done to ensure that the structure will be able to withstand the 
additional loadings associated with various retrofitting measures. 
The objective ofthis analysis is to verify that: 

* the existing structure is able to withstand the anticipated 
loadings due to the retrofitting measure being considered;
n...4,

:..I..

.....

--- --, oo,-,#;*tinr^ Clnr-Prnn PReirdentiai Structires VI -37 

Engineeringyrlncip1UbanU r19A9U5O ul "UMAULMU I -I J 

January 1 995 


ChapterVI:General Design Practices

 the existing structure is unable to withstand the anticipated 
loadings due to the retrofitting measure being considered 
and requires reinforcement or other structural modification; 
and/or 
e 

the retrofitting measure should be eliminated from consideration. 

Using the information presented herethe designer should be 
able to conduct the analyses to implement the stated objective 
and identify the measures/modifications that must be designed. 

VI -38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation 

Table of Contents 

Types of Residential Structures That Can Be Elevated .................. ...................... VI -E. 1
Houses over a Crawlspace ........................................ VI -E.2
Houses over Basements ........................................ VI -E. 11
Houses on Piles, Piers, or Columns ........................................ VI -E. 16
Slab-on-GradeHouses ........................................ VI -E. 16
Elevating a Slab-on-Grade Wood-Frame House ........................................ VI -E. 17
Elevatinga Slab-on-GradeMasonryStructure......................... ............... VI -E.29
Heavy Building Materials/Complex Design ............. ........................... VI -E.29

FieldInvestigationConcerns........................................ VI -E.31
Property Inspection and Existing Data Review ................ ........................ VI -E.3 1

Code Search ........................................ VI -E.31

Design........................................ VI -E.34
Elevation Sample Calculation ........................................ VI -E.48

Construction Considerations ................................................................................................ VI -E.92
PriortoLifing anyHouse ................................... VI -E.92
Slab-on-Grade House, Not Raising Slab With House .................... .............. VI -E.92
Slab-on-Grade House, Raising Slab .................................. VI -E.93
Houseover Crawlspace/Basement.................................. VI -E.94
House on Piles, Columns, or Piers................................... VI -E.95

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -E.i 
January 1995 


ELEVATION 

One of the most common of all retrofitting techniques is to raise an entire existing super

structure above the desired flood protection elevation. When properly done, the elevation 

of a house places the living area above all but the most severe floods. 

In general, the steps required for elevating a building are essentially the same in all cases. 

A cradle of steel beams is inserted under (or through) the structure; jacks are used to raise 

both the beams and structure to the desired height; a new, elevated foundation for the 

house is constructed; utility systems are extended and modified; and the structure is
lowered back onto the new foundation and reconnected.

While the samebasic elevationtechniques are used in all situations, the final siting and 
appearance of the house will depend on the final elevation and type of foundation used. 
However, the actual elevation process is only a small part of the whole operation in terms 

of planning, time, and expense. The most critical steps involve the preparation of the
house for elevation and the construction of a new, adequately elevated foundation. The
elevation process becomes even more complex with added weight, height, or complex

design or shape of the house. Brick or stucco veneers may require removal prior to 
elevation. Building additions may need to be elevated independently from the main structure. 

TYPES OF RESIDENTIAL STRUCTURES THAT CAN BE 
ELEVATED 

The elevation of houses over a crawlspace; houses with 
basements; houses on piles, piers, or columns; and houses 
-I,' on a slab-on-grade are examined here. In each of these 
situations, the designer must account for multiple (non-
Figures VItEh throughVo-E5 flood-related) hazards, such as wind and seismic forces. The 

onextendedsolidfoundation various methods utilized to elevate different home types are 

walls.Subsequentfiguresfor illustrated in the pages that follow, providing the designer with 
variouselevationtechniqueswill an introduction to the design of these measures. 
include only those illustrations 

unique to that technique. 

Enaineerina Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.1 
January 1995 


Chapter VI: General Design Practices 
Elevation 

' F -I 

Information on the design of 
foundation wall openings and 
adjustment of existing utility 
systems can be found in the Wet 
Floodproofing section of Chapter 

VI. 
HOUSES OVER A CRAWLSPACE 

These are generally the easiest and least expensive houses to 
elevate. They are usually one-or two-story houses built on 
a masonry crawlspace wall. This allows for access in 
placing the steel beams under the house for lifting. The 
added benefit is that since most crawlspaces have low 

clearance, most utilities (heat pumps, water heaters, air 
conditioners, etc.) are not placed under the home; thus the 
need to relocate utilities may be limited. Houses over a 
crawlspace can be: 

* elevated on extended solid foundation walls (see Figures 
VI-El through VI-E5); or 
* elevated on an open foundation such as masonry 
piers (see Figures VI-E6 through VI-E8). 
VI-E.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

Figure VI-El: Existing Wood-Frame Residence with Crawlspace 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.3 
January 1995 


Chapter VI: General Design Practices 
Elevation 

1. Ltting Beam 
2. Existing Masonry Foundation 
3. HydraulIc Jack 
4. Lateral Support Beams 
Figure VI-E2: Install Network of Steel "I" Beams 

Vi -E.4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

1. Excavated Area 
2. Existing Crawlspace 
3. Existing Concrete Footing 
4. Extending Masonry Foundation Wall 
5. Openings for Floodwater 
Figure VI-E3: Lift Residence and Extend Foundation Walls; Relocate Utility and 
Mechanical Equipment Above Flood Level 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.5 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Figure VI-E4: Raising a Wood-Frame-Over-Crawlspace Structure 

VI -E.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

1. Existing Wood Floor System 
2. Heightened Crawispace 
3. Openings for Floodwater 
Figure VI-E5: Set Residence on Extended Foundation and Remove "I" Beams 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.7 
January 1995 


Chapter VI: General Design Practices 
Elevation 

1. Existing Foundation to Remain 
2. New Reinforced Masonry Piers 
3. New House Support Beams 
Figure VI-E6: Install Network of Steel "I" Beamns 

VI -E.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Typesof Residential Structures That Can Be Elevated 

Figure VI-E7: Raising a Wood-Frame-Over-Crawlspace Structure on Piers 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.9 
January 1995 


Chapter VI: General Design Practices 

0 

Elevatlon 

1. NowReinforced Masonry Piers 
2. ExistingFoundation 
3. New Ieoated Reinforced Masonry Pier 
and Fooling 
Figure VI-ES: Set Residence on Reinforced Piers 

VI -E.10 Enaineedna Princioles and Practices of Ratrofittinn F~nnr1-PmnnaRaqirlantical *n wriinaga

_I,,_ __..____..._..,"_J 1995

,,,......

_.....

January 1995 


Typesof Residential Structures That Can Be Elevated 

FEMA's post- and pre-FIRM 
requirements do not allow 

basements below the Base Flood 
Elevation (BFE) for substantially 
damaged/improved and post-
FIRM applications. For more 
information on what retrofitting 
measures are allowable under 
FEMA guidelines, refer to 
Chapter II, Regulatory Framework. 

HOUSES OVER BASEMENTS 

These houses are slightly more difficult to elevate because 
their utilities are usually in the basement. In addition, 
basement walls may have been extended to the point where 
they cannot structurally withstand flood forces. Houses 
over basements can be: 

* elevated on solid foundation walls by creating a new 
masonry-enclosed area on top of an abandoned and 
filled-in basement (see Figures VI-E9 through VI-E 10); 
or 
* elevated on an open foundation, such as masonry piers, 
by filling in the old basement (see Figures VI-El I and 
VI-E12). 
Engineering Principles and Practices of IRetrofitting Flood-Prone Residential Structures VI -E.1I 
January 1995 


Chapter VI: General Design Practices 
Elevation 

1. Existing Wood Floor and Joists 
2. Existing Woodframe 
3. Now Windows 
4. Now Masonry Enclosed Area 
5. Openings for Floodwater 
Figure VI-E9: Relocate Utility and Mechanical Equipment Above Flood Level 

VI-E.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

Existing floor system 

1V 

I 

This area maybe used for bilding

access, parking, and storage only 

New reinforced concrete slab 

se existin cntinuous concrete footing.

i codeiss tisTied. Al 

100-year lood 

level 

First floor 

-Sole plate 

New 8" 

masonryblock wall 

_MEM" Required 

I ,:' "moroo at 

I 

| 

Figure VT-E IO: Creation of a New Masonry Enclosed Area on Top of an Abandoned Basement 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.13 
January 1995 


Chapter VI: General Design Practices 
Elevation 

w~I ExistingFor sM IOraor Rood 
I 
FirstNow 
t-Sd6 Pkf 
I 
A 
~~-
b 
Ne~wMKPW 
bem 
-NoW hwe 
beam po 
It-1E New I fod Now 
Minhrod masonry 
pierandfooing 
remnfVrc 
masonrypiw 
_ ii:~~~rw 
I I I 
Us"xisingcontinuousconcrobfooting, I 
ifcodeis slatife 4v I I 

Figure VT-EI1: Creation of a New Masonry Enclosed Area on Top of an Abandoned Basement 
(Piers) 

VI -E.14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

Figure VI-E12: Set Residence on Reinforced Piers 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.15 
January 1995 


Chapter VI: General Design Practices 

Elevation 

HOUSES ON PILES, PIERS, OR 
COLUMNS 

The process of elevating a house on piles, piers, or columns 
is slightly more complex in that temporary relocation of the 
house may be part of the elevation process. With the use of 
this type of foundation, the house may need to be lifted off 
the existing foundation and temporarily relocated on-site. 
The existing foundation is then removed and/or reconstructed, 
and the house is reset on the new foundation. 
However, raising the home above the working area may 
provide sufficient room to auger pier and column foundations 
and to jet pile foundations. 

SLAB-ON-GRADE HOUSES 

These houses are the most difficult to raise in that if the slab 
is to be raised with the house, a trench must normally be 
dug under the house to provide a space for inserting lifting 
beams. However, intrusive techniques that place beams 
through the structural walls have proved to be successful in 
elevating slab-on-gradehomes, as well. If the existing slab is 
to remain in place, then the house must be detached from 
the slab, the structure raised separately from the slab, and a 
new floor system built, along with an elevated foundation. 

While slab-on-grade houses may be the most difficult to 

raise, a number of elevation options exist with regard to 

raising the structure with or without the slab and using a 

first floor composed of wood or concrete. The various 

alternatives include: 

VI -E.16 Enaineenna Principles and Practices of Retrofittinn Floond-PrnnaRaeidential Structures 

v-Iw ___. .__ -W w_ Ju 19 5 

_.......w al w %--

January 1995 


Types of Residential Structures That Can Be Elevated 

Many of the techniques that 
require interior home modifications 
are applicable only to 
structures that have suffered 
extensive interior damage. For 
additional information, refer to 
FEMA publications entitled 

Technical Information on Elevating 
Substantially Damaged 
Residential Structures in the 
Midwest, August 24, 1993, and 

Technical Information on Elevating 
Substantially Damaged 
Residential Buildings in Dade 
County, Florida, January 29, 

1993. 

Elevating a Slab-on-Grade Wood-
Frame House 

* Elevating a slab-on-grade wood-frame house without 
the slab, using a new first floor constructed of wood 
trusses (see Figures VI-E13 through VI-E17); 
* Elevating a slab-on-grade wood frame house without 
the slab, using a new first floor constructed of a concrete 
slab on top of fill (see Figures VI-E1 8 through VIE20); 
* Elevating a slab-on-grade wood frame house with the 
slab intact (see Figures VI-E2 1 through VI-E23); 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.17 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Figure VI-E13: Existing Slab-on-Grade Wood-Frame Residence 

VI -E.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

1. Lateral Support Beam 
2. Concrete Slab 
3. Hydraulic Jack 
4. Lifting Beam 
I 

Figure VI-E14: Install Steel "I" Beam Network and Prepare to Lift Walls 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.19 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Figure VI-E15: Lift Residence and Extend Masonry Foundation Wall; Relocate Utility and 
Mechanical Equipment above Flood Level 

VI -E.20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

N wS"wall asb-lor 

* -

Ne tn jobt -100yFir

floodr 

> __ ~~~~~~~~~~~~~~ ~~Forfloodwtr 

ENotwi8"tmasonry 1

blook wall 

g~~~~~~~~~~~~~~~~Eitn Sle

Existingslab concrete~ ~ ~ ~ ~ lat

ground 

Use existing continuous concretefooting, 
if codeis satisfied. 

Figure VI-E16: Raising a Slab-on-Grade Wood-Frame Structure Without the Slab 

Enaineerina PrinCiplesand Practices of Retrofittina Flood-Prone Residential Structures VI -E.21 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Figure VI-E 17: Set Residence on New Foundation and Remove "I" Beams 

VI -E.22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

Figure VI-E 18: Lift Residence and Extend Masonry Foundation Wall; Relocate Utility and 
Mechanical Equipment Above Flood Level 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.23 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Figure VI-E19: Raising a Slab-on-Grade Wood-Frarne Structure Without the Slab Intact 

VI -E.24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

1. New Concrete Slab 
2. Extended Masonry Walls 
3. Existing Slab 
Figure VT-E20: Set Residence on New Foundation and Remove "I" Beams 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.25 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Figure VI-E2 1: Excavate Under Existing Slab and Install Network of Steel "I" Bearns 

VI -E.26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

Figure VI-E22: Raising a Slab-on-Grade Wood-Frame Structure With the Slab 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi-E.27 
January 1995 


Chapter VI: General Design Practices 
Elevation 

|, Existing Slab Elevated 
|2. Openings for Floodwater 

Figure VI-E23: Set Residence on New Foundation and Remove "I" Beams 

Vi -E.28 Engineering Principle is and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Residential Structures That Can Be Elevated 

Elevating a Slab-on-Grade Masonry 
Structure 

* Elevating a slab-on-grade masonry structure with the 
slab intact; 
* Elevating a slab-on-grade masonry structure without the 
slab using a first floor constructed of a concrete slab on 
top of fill; 
* Elevating a slab-on-grade masonry structure without the 
slab using a first floor constructed of wood framing; 
* Installation of an elevated concrete slab within an 
existing masonry structure; 
* Installation of an elevated wood-frame floor system 
within an existing masonry structure; 
* Creation of a new masonry livable area on top of an 
existing one-story masonry structure; and, 
* Creation of a new wood-frame livable area on top of an 
existing one-story masonry structure. 
HEAVY BUILDING MATERIALS/ 

COMPLEX DESIGN 

The elevation process becomes even more complex with 
added weight, height, or complex design of the house. 
Brick or stucco veneers may require removal prior to 
elevation. Combination foundations (i.e., slab-on-grade and 
basement) should be evaluated jointly and separately and the 
worst case scenario utilized for design purposes. Building 
additions may need to be elevated independently from the 
main structure. Due to the extreme variability of structural 
conditions, a structural engineer should evaluate the suitability 
of lifting this type of house. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.29 
January 1995 


Chapter VI: General Design Practices 

Elevation 

The entire elevation design process is discussed here and 
then illustrated with a detailed example of the design for a 
crawlspace home (Figure VI-E24). 

Elevation Design Process 

Field Investigationand 
CodeSearch 

CalculateGravityLoads 
(Dead, Live, Snow, andVerticalFlood Loads) 

CalculateLateralLoads 

I

(Wind,Seismic,and Flood-Related) 

'I, 

Check ExistingStructurefor Loading 
Truss to Wall Connection 
PlywoodRoof Diaphragm 
Upper LevelWalls 
FloorDiaphragm 

I 

+TDesign Strengthening 0NotOK Not OK
40__R

OK 

CuheckExisting I 
Foundationfor Leadinis 

HDesign Strengthening Not OK Not OK Select Another Measure 

. ... .. .. 

Design NewFoundationWalls 

Design NewTop of FoundationWall Connection 

DesignSill Plate Connections 

DesignNew Access k 

Design Utility Extensions 

SpecifyAdditionalInsulation 

Figure VI-E24: Design Process for an Elevated Structure 

VI -E.30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation Concerns 

FIELD INVESTIGATION CONCERNS 

PROPERTY INSPECTION AND 
EXISTING DATA REVIEW 

During the field investigation, the designer should inspect 
the property and review existing data to confirm the applicability 
of the selected alternative and to confirm specific 
design guidance such as the height of elevation and type of 
foundation to be utilized. The designer should utilize the 
guidance presented in the beginning of this chapter where 
detailed information and checklists for the collection of 
information on the Structural, Mechanical, Plumbing, and 
Electrical Systems was presented. Much of the data has 
been discussed previously in Chapters III and IV. At a 

minimum, the designer should collect information on the 

following checklist (Figure VI-E25). 

CODE SEARCH 

During the field investigation the designer should also 
conduct a search of local floodplain ordinances, building 
codes, restrictions to deeds, restrictions in subdivisions, 
zoning regulations, and state building codes. Included with 
this search, a visitwith the local building official should be 
planned to determine any special requirements for the 
locality. During the code search,the following should be 

determined: 

* floodplainordinance; 
* building code in effect; 
* design wind speed; 
* design seismic zone; 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.31 
-January 1995 


Chapter VI: General Design Practices 
Elevation 

* ground snow loads; 
* frost depths; 
* restrictions on height (overall building, portions of 
building relative to materials in use, allowable height/ 
thicknessratios); and 

* restrictions on foundations. 
VI -E.32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation Concerns 

Owner Name: Prepared By: 

Address: Date:
Property Location:

Elevation Field Investigation Worksheet 

U Does site topography data cover required area U Yes U No
Additional data required
IJ Any construction access issues?

U Site and building utilities identified? IOYes U No
Potential utility conflicts identified? U Yes U No
Describe conflicts:

U Review homeowner preferences:
Can aesthetics reconcile with site and building constraints? L Yes U No
How?

U Confirm type and condition of existing framing:
U member sizes_ spans
L connections U supports
Q Confirm type and condition of foundation:
U type U depth
U size
I3 Confirm types and condition of existing construction materials:
U roof _ floor
U walls U foundation

!J Confirm soil information:
U type U depth of rock
Q bearing capacity U susceptibility to scour and erosion

U Confirm characteristics of flood-related hazards:
LI BFE U velocity

U frequency Q duration
U potential for debris flow_

O Confirm characteristics of non-flood-related hazards: 

 wind Useismic 
U snow U other:
U Review accessibility considerations:

 access/egress
U special resources for elderly, disabled, children
Architectural constraints noted:
Is clearance available to install lifting beams andjacking equipment? U Yes U No
U Check local codes/covenants for height or appearance restrictions:
U deed/subdivision rules U local building codes
Restrictions:

Figure VI-E.25: Elevation Field Investigation Worksheet 

Structures VI -E.33

atrAfittinm Fiono.Prnne Resideantial

*..M ,Q

January195l l u Gu rIauwwo WI Is% .... to . IV-I-e o 
January 1995 


ChapterVI: General Design Practices 

* Elevation 
DESIGN 

To illustrate the design process, a 
worked example is shown following 
the instructionsfor Steps1-7. 

in the Chapter VI section on Wet 
Floodproofing. The designer 
should refer to local codes for 
guidance on Steps 8 and 10. 

If building and flood guidance is 

not covered by the local building 

code, refer to ASCE 7. 

The design process for an elevated structure shown in 

Figure VI-E24 consists of the following steps: 

Step 1: Calculate gravity loads. 

The computation of gravity (vertical) loads such as building 

dead and live loads and buoyancy forces was presented in 
Chapter IV. 

Snow Loads: There are no "typical" formulas for houses, 

since the calculation of snow loads depends upon the 

building code in use, the geographic area in which the house 
is located, and the size and shape of the house and roof. 
The governing building codewill clearly spell out the 
correct procedure to follow. Most procedures are simple 

and straightforward. Some houses will be more complex 
due to their shape or quantity of snow that must be allowed 
for. However, the general procedure is as follows: 

* To determine the ground snow load, consult snow maps 
within the building code, and/or local requirements with 
the local building official. 

* Determine importance factors. 
* To determine the exposure factors, analyzethe surrounding 
terrain, trends in snow patterns, and slope of 
roof. 

* Determine the snow load. 
o Determineconsiderations for drifting snow by examining 
any adjacent house or structure, a mountain above 
the house, or higher roofs. 

VI -E.34 EnoineerinaPrinciplesand Practices ofa,1RPtrnfittinn FInnr.Prnna DaoLanflnr O+rIL 
January 1995 


Design 

* Determine considerations for sliding snow by examining 
steep slope on roof or higher roofs. 
Step 2: Calculation of lateral loads. 

The calculation of building lateral loads includes wind, 
seismic, and flood-related loads. One objective of the wind 

If the local building code does not and seismic analysisis to determine which loading condition 

cover wind, snow, or seismic
issues, refer to ASCE 7. controls the design of specific structural components.

Wind Analysis: There are no "typical" formulas for 
houses, sincethe calculation of wind loads depends upon 
the building code in use and the size and shape of the house. 
The governing building code will clearly spell out the 
correct procedure to follow. Most procedures are simple 
and straightforward. Some houses will be more complex 
due to their shape. However, the general procedure, as 
illustrated in Chapter IV, is presented below. 

* Determine wind speed and pressure by consulting wind 
maps within the building code, and checking local 
requirementswith the local building official. 
* Determine the importance factors and the exposure 
category. 
* Determine wind gust and exposure factors and analyze 
the building height and shape, whether the wind is 
parallel or perpendicular to the roof ridge, and whether 
it is windward or leeward of roofs/walls. 
* Determine the wind load. 
* Distribute the load to resisting elements based upon the 
stiffness of shear walls, bracing, and frames. 
Pnnineerinn Print-inipq and Practices of Retrofittina Flood-Prone Residential Structures VI-E.35 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Seismic Analysis: There areno "typical" formulas for 
houses since the calculation of seismic loads depends upon 
the building code in use and the size and shape of the house. 
The governing building code will clearly spell out the 
correct procedure to follow. Some houses will be more 
complex due to their shape. However, the general procedure, 
as illustrated in Chapter IV, is presented below. 

* Calculate dead loads by floor. These include permanent 
dead loads (roof, floor, walls, and building materials) 
and permanent fixtures (cabinets, mechanical/electrical 
fixtures, stairs, new locations for utilities, etc.). 

* Determine if the snow loadmust be included in the dead 
load analysis. Most building codes require the snow load 
to be included for heavy snow regions. The building 
code will list these requirements. 
 Determine the seismic zone and importance factors. 
* Determine the fimdamental period of vibration (height 
of structure materials used in building). 
* Determine total seismic lateral force by analyzing site 
considerations, building weights, and the type of resisting 
system. 
 Distribute the loads vertically per the building code, 
keeping in mind additional force at the top of the building. 

* Distribute the loads horizontally according to the building 
code and the stiffness of resisting elements. The 
code-prescribedminimum torsion ofthe building (center 
of mass vs. center of rigidity), shear walls, bracing, and 
framesmust be considered. 
VI -E.36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Flood-Related Forces: The computation of flood-related 
forces was presented in Chapter IV, and includes the following: 

* Determine Flood Protection Elevation (FPE). 
* Determine type of force (hydrostatic or hydrodynamic). 
* Determinethe susceptibility to impacts from debris (ice, 
rocks, trees, etc.). 
* Determine susceptibility to scour. 
* Determineapplicability of and susceptibilityto alluvial 
fans. 
* Determine design forces. 
* Distribute forces to resisting elements based upon 
stiffness. 
Step 3: Check ability of existing structure to withstand 
additional loading. 

Chapter IV presented general information on determining 

the ability of the existing structure to withstand the addi

tional loadings imposed by retrofitting methods. The 

process detailed below is similar for each of the building 

types we expect to encounter. First, the expected loadings 

are tabulated and compared against allowable amounts 

determined from soil conditions, local code standards, or 

building material standards. The following list of existing 

building components and connections should be checked. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.37 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Roofs: The plywood roof diaphragm, trusses, connections, 
and uplift on roof sheathing should be capable of resisting 
the increased wind and seismic loads. The American Plywood 
Association has published several references that are useful 
in this calculation. These include: 

* Roof Sheathing Fastening Schedules for Wind Uplift; 
* Diaphragms;and 
* Residential and Commercial 
These reference materials or the local building codes will 

give the designer the necessary plywood thicknesses and 

connection specifications to resist the expected loadings, 

and/or will provide loading ratings for specific material 

types and sizes. 

If the roof diaphragm and sheathing are not sufficient to 
resist the increased loading, the design can strengthen these 
components through the following: 

e 

increase the thickness of the materials, and/or 

* strengthen the connections with additional plates and 
additional fasteners. 
Roof Truss to Wall Connections: The roof trusses and 

truss connections to walls should be checked to ensure that 

they will resist the increased wind loads. Of critical impor

tance are the gable ends, where many wind failures occur. 

The American Plywood Association has published several 

references that are useful in this calculation. These include: 

* Panel Handbook and Grade Glossary, and 
* Residential and Commercial. 
VI -E.38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


For additional information on the 
performance of various building 
system products, refer to product 
evaluation reports prepared by the 
model code groups. 

Design 

These reference materials or the local building codes will 
give the designer the necessary truss size, configuration, and 
connection specifications to resist the expected loadings, 
and/or will provide loading ratings for specific truss and 
connection types and sizes. 

If the roof trusses and wall connections are not sufficient to 
resist the increased loading, the design can strengthen these 
components through the following: 

* increase the amount of bracing between the trusses; and/ 
or 
* strengthen the connections with additional plates and 
additional fasteners. 
Upper Level Walls: The upper level walls are subject to 
increased wind pressure and increased shear due to increased 
roof loads. Both the short and long walls should be 
checked against the shear, torsion, tension, and deflection, 
utilizing the governing loading condition (wind or seismic). 

The American Plywood Associationhas published several 
references that are useful in this calculation. These include: 

* PanelHandbookand Grade Glossary; 
* Residential and Commercial; and 
 Diaphragms. 
These reference materials or the local building codes will 

give the designer the necessary wall size and configuration 

and connection specifications to resist the expected load

ings, and/or will provide loading ratings for specific wall 
types, sizes, and connection schemes. 

Fnnineprinn Princinles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.39 
January 1995 


Chapter VI: General Design Practices 

Elevation 

If the upper-level walls are determined to be unable to 

withstand the increased loadings, the designer is faced with 

the difficult task of strengthening what amounts to the entire 

house. In some situations this may be cost prohibitive, and 

the homeowner should look for another retrofitting method, 

such as relocation. Measures the designer could utilize to 

strengthen the upper-level walls include: 

* adding steel strapping (cross bracing) to interior or 
exterior wall faces; 
* adding a new wall adjacent to the exterior or interior of 
the existing wall; 
* bolstering the interior walls in a similar fashion; and/or 
* increasing the number and sizes of connections. 
Floor Diaphragm: The floor diaphragm and connections 

are subject to increased loading due to flood, wind, and 

seismic forces. The existing floor diaphragm and connec

tions should be checked to ensure that they can withstand 

the increased forces that might result from the elevation. 

The American Plywood Association has published several 
references that are useful in this calculation. These include: 

* Residential and Commercial and 
* Diaphragms. 
These reference materials or the local building codes will 

give the designer the necessary floor size and configuration 

and connection specifications to resist the expected load

ings, and/or will provide loading ratings for specific floor 

types, sizes, and connection schemes. 

VI -E.40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

If the floor diaphragm or connections are determined to be 
unable to withstand the increased loadings, the designer 
could strengthen these components by: 

* adding a new plywood layer on the bottom of the 
existing floor diaphragm; 
* increasing the number and size of bracing within the 
floor diaphragm; and 
* increasing the number and size of connections. 
Step 4: Analyzeexisting foundation. 

The existing foundation should be checked to determine its 
ability to withstand the increased gravity loads from the 
elevation, the increased lateral loads due to soil pressures 
from potential backfilling, and the increased overturning 
pressures due to seismic and wind loadings. The designer 
should tabulate all of the gravity loads (dead and live loads) 
plus the weight of the new foundation walls to determine a 
bearing pressure, which is then compared with the allowable 
bearing pressure of the soil at the site. Not including 
expected buoyancy forces in this computation will yield a 
conservative answer. 

If the existing footing is insufficient to withstand the additional 
loadings created by the elevated structure, the design 
of foundation supplementation should be undertaken. The 
foundation supplementation may be as straightforward as 
increasing the size of the footing and/or more substantial 
reinforcement. The designer may refer to the ACI manual 
for footing design, recent texts for walls and footing design, 
and applicable codes and standards. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.41 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Step 5: Design the new foundation walls. 

-itl 

The design of a new foundation, whether it be a solid or 

For wet floodproofing ap plica- open foundation, is usually governed by the local building 

tions, where openings in founda- codes. These codes will have minimum requirements for 

tion walls are necessary, ]refer to foundation wall sizes and reinforcing schemes, including 

the section on Wet Floodj proofing seismic zone considerations. The designer should consult 

in this chapter. the appropriate code document tables for minimum requirements 
for vertical wall or open foundation reinforcement. 

For new slab applications where the lower level is allowed 
to flood and the slab is not subject to buoyancy pressures, 
the designer can utilize the Portland Cement Association 
documentConcrete Floors on Ground as a source of 
information to select appropriate thicknesses and reinforcing 
schemes based upon expected loadings. The slab 
loadings will vary based upon the overall foundation design 
and the use of the lower floor. 

Step 6: Design top-of-wall connections. 

Top-of-wall connections are critical to avoid pullout of the 

sole plate, floor diaphragm, and/or sill plate from the ma

sonry foundation. A preliminary size and spacing of anchor 

bolts is assumed, and uplift, shear, and tension forces are 

computed and compared against the allowable loads for the 

selected bolts. Where necessary, adjustments are made to 

the size and spacing of the anchor bolts to keep the calcu

lated forces below the allowable forces. It is usual to 

include a factor of safety of 1.3 to respond to flood, wind, 
and seismic forces. 

VI -E.42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Step 7: Design sill/sole plate connections. 

The existing sill/sole plate connections will be subject to 

increased lateral loads and increased uplift forces due to 

increased wind and buoyancy loading conditions. The sill/ 

sole plate is designed to span between the anchor bolts and 

resist bending and horizontal shear forces. The designer 

should refer to the appropriate wood design manual that 

provides recommended compression, bending, shear, and 

elasticity values for various sill/sole plate materials. Using 

these values, the designer checks the connection against the 

expected forces to ensure that the actual forces are less than 

the allowable stresses. If the sill/sole plate connection is 

insufficient to withstand expected loadings, the size of the 

sill/sole plate can be increased (or doubled), and/or the 

spacing of the anchor bolts can be reduced. 

Step 8: Design new access. 

The selection and design of new access to an elevated 
structure is done in accordance with local regulations 
governing these features. Special homeowner requirements-
for aesthetics, handicapped accessibility, and/or 
special requirements for children and the elderly-can be 
incorporated using references previously discussed in 
Chapter III. 

Connection of the new access to the house should be 
designed in accordance with the local codes. The foundation 
for the access measure will either stand alone and be 
subject to its own lateral stability requirements or it will be 
an integral part of the new elevated structure. In either 
case, analysis of the structure to ensure adequate foundation 
strength and lateral stability should be completed in accordance 
with local codes. 

It should be noted that any access below the BFE should 
incorporate the use of flood-resistant materials. The designer 
should refer to FEMA Technical Bulletin 2-93, 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.43 
January 1995 


Chapter VI: General Design Practices 
Elevation 

entitledFlood Resistant Materials Requirements for BuildingsLocated 
in Special Flood Hazard Areas in Accordance 
with the National Flood Insurance Program. 

Step 9: Design utilities extensions. 

The field investigation will reveal the specific utility systems 
that will require relocation, extension, or modification. 
Where possible, utility systems should be relocated above 
the flood protection level. Local utility companies should 
be contacted about their specific requirements governing the 
extension of their utility service. In many instances, the 
local utility company will construct the extension for the 
homeowner. Critical issues in this extension process include: 

* handling of utilities encased in the existing slab or walls; 
* coordination of disconnection and reconnection; 
* any local codes that require upgrades to the utility 
systems as part of new construction or substantial repair 
or improvement; 
* introduction of flexible connections on gas, water, 
sewer, and oil lines to minimize potential for seismic 
damage; 
* potential for relocation or elevation of electrical system 
components from existing crawl space and/or basement 
areas; and 
* design of separate GFI-type electrical circuits and use of 
flood-resistant materials in areas below the BFE. 
VI -E.44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Step 10: Specify increased insulation requirements. 

Elevated floors and extended utility system components 
may increase the potential for heat loss through increased 
exposure and airflow and necessitate additional insulation. 
The designer should evaluate the energy efficiency of each 
aspect of the project, compare existing insulation (R-values) 
against the local building code, and specify additional 
insulation (greater R-value) where required. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.45 
January 1995 


d -V Chapter VI:General Design Practices 
Elevation 

Elevation Sample Calculation 

GIVEN OR OBTAINED FROM THE FIELD INVESTIGATION: 

The owner ofa single-story crawlspace home intends to elevate the structure to eliminate a 
repetitive flooding hazard. Her desire is to raise the structure one full story (8 feet) and use the 
lower level for storage and parking. She contracted with a local engineer to perform the design. 
The engineer's investigation revealed the following information about the existing structure: 

* crawlspace home with four (4) block courses (no reinforcement); 
* the first-floor elevation is two (2) feet above the surrounding grade (which is level); 
* the property is located in a FEMA-designated floodplain (Zone A4) and is subject to a 
100-year flood four (4) feet in depth above ground level; 
* floodwater velocities in the area of the house average six (6) feet per second; 
* floodwater debris hazard exists and is characterized as normal; and 
* the structure is classified as apre-FIRM structure. 
FIRSTFLOORt*e-eOI LO 

EXISTING FRONT ELEVATION 

1 of 44 

VI -E.46 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures 
January 1995 


Elevation Sample Calculation 

Elevation Sample Calculation 

Additional Information on Existing Home 

* Wood-Framed House 30 ft. x 60 ft. 
* Gable Roof 4:12 slope 
* Per the 1991 Uniform Building Code 
-80mph WindZone 
-SeismicZone2B 
-Ground SnowLoad of 40 psf 
* Flat open terrain surrounding house 
-IIIrII_ T 

. . T-I 1. 

. . . . .r. . . .nr'l|TI 

...... _;_-VENT 

r, r Fb . .T1....rPROPOSED SIDEELEVATION

pf~r?~-c

~~~~ 0 ~~~~~~~~~8 16 

~

' ... . ' A .' .............. :.: A ~.. ~~~!... .........

Extended foundation walls are proposed to be constructed of 8-inch-thick concrete masonry 

units. The existing footing is 2 feet wide by 1 foot thick concrete reinforced with 3-#4 rebars 

continuous and#4 dowels extending up into masonry 24 inches. Slab on grade will be 3-1/2 to 

4 inches thick. 

Interior walls ofthe living area (elevated) are composed of 4-inch studs at 16 inches o.c. with 
plaster on each side. Exterior walls have 4-inch studs at 16 inches o.c., plaster on the inside, 
and sheathing and wood siding on the exterior-walls are insulated with fiberglass insulation. 

2 of 44 

Ennineerinn Print-inhs and Practicesqof Retrnfittinn Flood-Prone ResidentialStructures VI -E.47

J-ay--._ WI _1_

_.M995_- __ 

January 1995 


Chapter VI: General Design Practices
Elevation _

Elevation Sample Calculation 

First-floor fiaming consists of2xl 2's at 16 inches on center supported by the exterior long walls 
and a center support. Floorcoverings are hardwood (oak) with a 3/4-inch plywood subfloor. 
There is 10 inches of insulation betweenthejoists. A gypsum ceilinginthe proposed lower area 
is planned. 

,:e,:::'.:,: ~ ~ ~ :.'.N~ 

~ ~ ~ 

.. .... .:. 

N .,:' -F N 

Roof fiwning consists of pre-engineered wood trusses at 16 -iches on center. Thetop chord 

consists of 2x6's and the web andbottom chordconsist of 2x4's. The roof is fiberglass shingles 
withfelt on 1/2-inch plywood. Theceiling is 1/2-inch plasterwith 1/2-inchplywood backup. 
There are 16 inches of fiberglass insulation above the ceiling. 

: : : L 11.1:,::;:.:: LIA L : -U..., T,

: :I 

II II~~~ ~~IfI ~~ r~

I Ifiit1

A: 
WA i, r1VI>1:l5. 11 111!11t :llI~I1 

.~:....... :: . : 2 ~ ilVC)1lS~ W M96 91 --

............... 14"WRA. AMINS: PLAN:
... .......

3 of 44 

VI -E.48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 1: Calculate Vertical Loads 

fI 

Elevation Sample Calculation 

Calculations: 

Step 1: Calculate vertical flood loads 

The calculation of buoyancy forces and comparison with structure weight is a critical determination 
of this problem. While buoyancy ofthe first floor is not an issue (since it is elevated four 

feet above the BFE), buoyancy ofthe entire structure (slab, foundation walls, and superstructure) 
must be checked if dry floodproofing is being considered for the lower level. If buoyancy 
forces control, dry floodproofing ofthe lower level is not applicable. 

Calculate Buoyancy Forces (from Formula IV-8) 

Fb = yAH = (62.4 lbs/ft3)(30ft x 60 ft)(4 ft) = 449,280 lbs 

Calculate StructureWeight by Level 

Tabulate Dead Loads by Floor 

Roof:
Shingles -Asphalt -1layer 2.0 psf
Felt 0.7 psf
Plywood-32/16 -1/2 inch 1.5 psf
Trusses @ 16 inches o.c. 5.0 psf

2x6 Top Chord
2x4 Web and Bottom

Total 9.2 Vsf (RQof) 

4 of 44 

Ennineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.49 
January 1995 


Chapter VI: General Design Practices 

Elevation 

, E 
Elevation Sample Calculation 
First Floor Ceiling: 
Insulation-16inch of fiberglass 
1/2inchlplywood 
1/2inch plaster and lath 
Misc., heating, electrical, cabinets 
8.0 psf 
1.5 psf 
10.0 psf 
2.0 psf 
Total 21.5 psf (1st Floor Ceiling) 
FirstFloor: 
Oak Floor 
Subfloor-3/4 inch plywood 
Joists (2x12) 
Insulation -10 inch fiberglass 
Misc., piping, electrical 
Gypsum ceiling -1/2 inch 
4.0 psf 
3.0 psf 
4.0 psf 
5.0 psf 
3.0 psf 
2.5 psf 
Total 21.5psf (lst Floor) 
Wails: 
Interior -wood stud, plaster eachside 
Exterior -2x4 @16 inches o.c., plaster 
insulation, wood siding 
Lower Level -8 inch masonry, reinforcement 
at 48 inches on center 
20 psf 
18 psf 
50psf 

5 of 44 

VI -E.50 Enaineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 1: Calculate Vertical Loads 

Elevation Sample Calculation 

Total Weights by Level 

Roof: 
Surface Area = [15.81 ft. + 2 ft. overhang]x[60 ft + 2 ft. overhang]x[2] = 2208 ft2 
Projected Area = [15 + 2 (15/15.81)]x[60 + 2]x[2] = 2095 ft2 

Shingles: 2208 ft2(2 psf) = 4416 lbs
Felt: 2208 ft2 (0.7 psf) = 1546 lbs
Plywood: 2208 ft2(1.5 psf) = 3312 lbs
Truss: 2095 ft2(5 psf) = 10,475 lbs

First Floor Ceiling: 

Area=60x30= 1800 ft2 

Insulation: 1800 ft2(8 psf) = 14,400 lbs
Plywood 1800 ft2(1.5 psf) = 2,700 lbs
Plaster 1800 ft2(10 psf) = 18,000 lbs
Misc. 1800 ft2(2 psf) = 3,600 lbs
Walls

1801fext. (4' trib.)( 8 psf) = 12,960 lbs
157 Ifint. (4' trib.)(20 psf) = 12,560 lbs

Subtotal W2 = 83,970 lbs 

6 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.51 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Elevation Sample Calculation 

First Floor Including Lower Level:
Area = 60 x 30 = 1800 ft2

Oak Floor 1800 ft2(4 psf) = 7,200 lbs
Subfloor 1800 ft2(3 psf) = 5,400 lbs
Joists 1 800 ft2(4 psO = 7,200 lbs
Insulation 1800 ft2(5 psO = 9,000 lbs
Misc 1800 ft2(3 psf) = 5,400 lbs
Ceding 1800 ft2(2.5 psf) = 4,500 lbs

Walls 

180 If ext. (4' trib.)(18psf) = 12,960 lbs
157 Ifit. (4' trib.)(20 psf) = 12,560 lbs
285 If lower level (4' trib.)(50psf) = 57,000 lbs

Subtotal W1 = 121,220 lbs 

Total Weight, W = WI + W2 = 205,190 lbs = 205 kips 

CompareBuoyancyForce Against Structure Weight 

DL=> 1.5 Fb
205,190 lbs <= 1.5 (449,280)
205,190 lbs < 673,920 lbs

Therefore, buoyancy forces control and the building (ifdry floodproofed) will float during flood 
events, unless structural measures, such as floor anchors or additional slab mass, or non-
structural measures such as allowing the lower level to flood, are utilized to offset/equalize the 
buoyancy forces. 

In our example, since buoyancy controls and the magnitude ofthe project represents a substantial 
improvement, the homeowner is required to allow the lower level to flood by incorporating 
vent openings in the foundation wall. While this action will equalize hydrostatic pressures on the 
foundation walls, hydrodynanmic and impact forces will still apply. 

7 of 44 

VI -E.52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads 

Elevation Sample Calculation 

Step 2: Compute lateral loads 

Lateral Flood Loads 

Compute lateral hydrostatic forces due to four (4) feet of water moving at six (6) feet per 
second. 

FromFormulaIV 

Fh 1/2 yH1
= (1/2) (62.4 lbs/ft3 ) (4 ft)2
= 499.2 lbs/lf acting at 1.33'

FromFormulaIV-9 

CdV2 (1.25) (6 ft / sec)2
dh = 2g = 2 (32.2 ft/sec2)

= 0.70 ft 

FromFormulaIV-10 

Fdh = y (dh)H
= (62.4 lbs/ft3 ) (0.70 ft) (4 ft)
= 174.7 lbs/lf acting at 1.33'

FromFormulaIV-11 

F FH+

FH = h +dh 

= 499.2 lbs/lf + 174.7lbs/lf 
= 674 lbs/lf acting at 1.33' 

Because the owner decided to intentionally flood the lower level, the above-calculated lateral 
hydrostatic flood forces are negated and not considered further in this example computation. 
However, if dry floodproofing were being considered, these lateral forces may have exceeded 
the allowable stress on the wall, resulting in a probable wall failure. 

8 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.53 
January 1995 


Chapter VI. General Design Practices 

Elevation 

Elevation Sample Calculation 

Calculate Hydrodynamic Forces on CMU Wall (From Formula IV- 12) 

V2 

= (1.25) (1.94 slugs/fl3 ) [6 ft lseC)2 

= 43.65 lbs/ft2 

bh = 3 ft = 7.5 < 12

4 ft 
Table IV-3 
Cd = 1.25 

Calculate Total Force on Building Face (upstream) (From Formula IV-13) 

Fd PdA
= (43.65 lbs/ft2) (4') (30')
= 5,238 lbs

From geotechnical conditions, a friction factor of 0.3 may be used. 
Dead load of structure = 839 lbs/ft (180 fl) 
= 151,020 lbs 

Calculateresistancedue to foundationfriction 

Rf = 151,020 lbs (0.3)
= 45,306lbs

Since 45,306 lbs> 5,238 lbs., building will not slide. 

9 of 44 

VI -E.54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads 

Elevation SampleCalculation 

Calculate Normal Impact Forces (FromFormulaIV-14) 

F -wV 

n gt 

(1,000 lbs) (6 ft l sec) 186lbs 

(32.2 ft/sec 2 ) (1 sec) 
Since vents are being used to equalize the hydrostatic pressure, the wall will be subject to a net 
load equal to the combined hydrodynamic and impact loads. The ability of the new foundation 
wall to withstand these forces is presented toward the end of Step 5. 

WIND 

Since the house is being elevated, wind pressures will be increased on the home. Depending 

upon the amount of elevation, additional bracing of the roof or walls may be necessary. 

Reference: 1991 Uniform Building Code 

Basic wind speedhasbeendeterminedtobe 80mph. (From Figure 23-1 in 1991 UBC and 

verification with local building official.) 

From Table 23-F, wind stagnation pressure (q) based upon wind speed is:
q5= 16.4 psf

From Table 23-K, Building Category is IV 

From Table 23-L Importance factor for wind, I = 1.0 

From Definitions, Section 2312, House is Exposure C 

From Table 23-G, Combined Height, Exposure and Gust Factor Coefficient (Ce)is 

Height Above Ground Ce
0-15 ft 1.06

20 1.13 
25 1.19 
10 of 44 

ResidentialStructures VI -E.55

nr-aineerinn Prinninles and Practices of Retrofitting Flood-Prone 

January 1995 


Chapter VI: General Design Practices 
Elevation 

Elevation Sample Calculation 

From Section 2316, Equation 16.1 

P CeCqsj 
where, 
P = Design WindPressure 
C = Combined Height, Exposure and Gust Factor 
Ce = Pressure Coefficient for Structure or Portion 
q = Wind StagnationPressure 
I = Importance Factor 

for this house, 

P = (1.06)(Cq)(16.4psf)(1.0) = 17.4(Cq)psf 
(L113) (Cq)(1 6.4 psf)(. .0) = 18.5(Cq)Psf 
(1I.1 9)(C )( 16.4 psf)( 1.0) = 19.5(Cq)Psf 

where Cq is determined from Table 23-H. 

Primary Frames and Systems Using Method 1 outlined in 1991 UBC 

Note: Elements and Components of the Building should be checked. (i.e.,siding, shingles, 
gable ends, windows, etc.) 

11 of 44 

VI -E.56 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads 

Elevation Sample Calculation 

From Table 23-H, pressure coefficients are 

Walls: 
WindwardWall 
LeewardWall 
Cq= 0.8 
Cq = 0.5 
ib 
C 
award 
outward 
Roof: 
Wind perpendicular to ridLeeward Roof 
Windward Roof 
4:12 slope 
ge: 
C = 0.7 
Cq = 0.8 
Cq =0.3 
outward 
outward or 
inward 
Wind parallel to ridge: 
Cq =0.7 outward 

12 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.57 
January 1995 


Chapter VI: General Design Practices 
Elevation 

jI 

Elevation Sample Calculation 

I 

Wind.Perpendicular to Ridge 

Walls: 

Windward: 

(inward) P = 17.4psf (0.8) = 14.0psf (0-15 R) 
P= 18.5psf (0.8) = 14.8psf (20 It) 
Leeward: 
(outward) P = 17.4 psf (0.5) = 8.7psf (0-15 ft) 
P = 18.5psf (0.5) = 9.3psf (20 It) 
Roof: 
Windward: 
(outward) P = 18.5 psf (0.9) = 16.7 psf (20 ft) 
or 
(inward) P = 18.5psf (0.3) = 5.6 psf (20 ft) 0 
Leeward: 
(outward) P = 18.5psf (0.7) = 13.0 psf (20 ft) 
RIME 

13 of 44 

VI -E.58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads 

Elevation Sample Calculation 
Wind Parallel to Ridge 
Walls: 
'imdward: 
(inward) 
Leeward: 
(outward) 
P = 19.5 psf (0.8) 
P = 19.5 psf (0.5) 
= 15.6 psf 
= 9.8 psf 
(25 ft) 
(25 ft) 
Roof: 
P = 18.5 psf (0.7) 
P = 19.5 psf (0.7) 
= 13.0 psf (20ft) 
= 13.7 psf (25 ft) 

Seismic 

Since the house is being elevated, the potential for seismic loading/overturning design loads will 
be increased on the home. Depending upon the amount of elevation, additional bracing of the 
roof or walls may be necessary. 

Reference: 1991 Uniform Building Code 

Seismic Zone 2B has been determined for this home (Figure 23-2 in 1991 UBC and verification 
with local building official). 

14 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.59 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Elevation Sample Calculation 

The seismic load on the house depends upon the dead load. This load must be tabulated on a 
floor-by-floor basis as was presented in Step 1 under Tabulate Dead Loads by Floor. 

Check if Snow Load must be included in Seismic calculations: 

Reference: 1991 Uniform Building Code 

Ground Snow= 40 psf
Roof Slope, a= 18.40

From Table A-23-T, Importance factor, I = 1.0 
From Table A-23-S, Snow Importance factor, CI 0.6 

From Section 2343, Equation 434lA 
Pf = C01P 
where, 

Pf = MinimumRoofSnowLoad
ICe = Snow Exposure Factor
I = Importance Factor
P8 = Basic Ground SnowLoad

9~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

for this house, 
Pf= 0.6 (1.0) (40 psf) =24 psf< 30 psf 

thus, by Section 2334(a)3 snow load is not included (it is recommended that the building official 
be consulted if in doubt) and the total weight of 205 kips as calculated in Step 1 under Tital 
Weighak by Level can be used in this seismic analysis. 

15 of 44 

VI -E.60 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads 

Elevation Sample Calculation 

From Section 2333(h)2D, Table 23-0 and Table 23-J the Static Force Procedure may be 

used.
hi= 10'-0", heightto First Floor
h2 = 10'-0"+ 8'-0"= 18'-0" heighttoFirstFloorCeiling

per UBC Section 2334(b)2A, equation 34-3 

the fundamental period of vibration, in seconds, T
T = C(hn)3/4
where,

T = Fundamental Period of Vibration, in seconds 

Ct Numerical Coefficient 
hn = Height at Level n, in feet 
Leveln UppermostLevel 

for this house,
C, =0.02
h 18'-0"

therefore,
T = 0.02 (18.0)3/4 = 0.175 seconds

From our field investigation (and NRCS soil reports), it was determined that the soil profile was 
dense (S2) to a depth of over 200 feet. Thus per Table 23-J the site coefficient for S2is S = 

1.2 
16 of 44 

Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.61 
January 1995 


Chapter VI: General Design Practices 

Elevation 

f Elevation Sample Calculation 

Per UBC Section 2334(b), Equation 34-2
C = 1.25 S/T213
where:

C = Numerical Coefficient
S = Site Coefficient
T = Period of Structure

for this house, 

1.25 (1.2) 
C=(0.17)23 = 4.79 
> 2.75 maximum by code, therefore use C = 2.75 

From Table 23-I, Seismic Zone Factor, Z = 0.20
From Table 23-L, Importance Factor, I = 1.0
From Table 23-0, Section 2333(0 and Section 2334(c), Numerical Coefficient, Rw = 6

Per UBC Section 2334(b), Equation 34-1, the total seismic design lateral force is,
V = ZICW/Rx
where:

V Total Seismic Lateral Force
I = Importance Factor
C = Numerical Coefficient
R = Numerical Coefficient

w 

W = Total Seismic Weight 

thus for this house,
V = 0.2(1.0)(2.75)(205 kips)/6 = 18.8 kips

Per UBC Section 2334(d) & (e) the total lateral force due to seismic must be distributed
vertical and horizontally.

17 of44 

VI -E.62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads 

Elevation Sample Calculation 

First consider load acting perpendicular to long direction of house. 

.S.. i~....i-. 

,~~~~~~~..=.: -..,'-:, -. .--., ..'..-"'''-' 

LEVELI--

0 . ......
'.''.'"'........., -: .. ...... ..

5i-... ....-...

ii EE -N N.V:i .... 

UE~l 

Per formula 34-7 the "extra" force at the uppermost level is 
Ft = 0-07 TV 
where: 

F. = "Extra"Force 
T = XPeriod 

V = Total Seismic Lateral Force 

for this house T < 0.7 seconds, therefore the building code allows us to set Ft 0.0 

the forces are distributed vertically by formula 34-8, 

(V -Ft)w~hx 

where: 

V = Total Seismic Lateral Force 
F -"Extra" Force at Top 
W -Weight of Level Under Consideration 
hx= Height to Level Under Consideration 

18 of 44 

Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.63 

January 1995 


Chapter VI: General Design Practices 
Elevation 
Elevation Sample Calculation 
for this house, 
LATERAL FORCES PERPENDICULAR TO LONG DISTANCE 
Seismic 
Level 
First Floor 
Ceiling 
1 
Height 
(ft) 
hxWX 
10'-0" 
18'-0" 
Level 
Weight 
(kips) 
83.97 
121.22 
(wx)(h)x 
840 
2182 
Lateral 
Force 
(kips) 
Fx 
5.23 
13.57 
Level 
Shear 
(kips) 
FX 
5.23 
18.8 
3022 18.8 
Wind 
Level 
Wind 
Pressure 
(psf)( V 
Px 
Area 
f 
ax 
Lateral 
Force 
(kips) 
HxIFx 
Level 
Shear 
(kips) 
First Floor 
Ceiling 11.12 11.12 
1 (14.0+8.7) (8')(60') 10.9 22.1 

19 of 44 

VI -E.64 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 2: Compute Lateral Loads

Elevation Sample Calculation 

F. (18.8--O0)w h 0 h,
=o.006221w 

3022 

* Wind Pressure Calculations for First Floor Ceiling (Load = Area x Pressure) 
worst shear is generated by 5.6 psf inward or windward 
Roof: (pressure) (area) (slope) 
(5.6+13.0psf) (15.81ft) (60ft) (5/15.81) =5.58kips 

Wall: (area) (pressure) 
(1 ft) (60 ft) (14.87 + 9.3 psf) = 1.45 kips a 
(3 ft) (60 ft) (14.00 + 8.7 psf) 4.09 kips . 

11.12kips 
LATERAL FORCES PARALLEL TO LONG DIRECTION 

Seismic 

Level Lateral Level 
Height Weight Force Shear 
(ft) (kips) (kips) (kips) 
Level hx -WX (w)(h) Fx IFX 

First Floor 
Ceiling 10'-0" 83.97 840 5.23 5.23 

1 18'-0" 121.22 2182 13.57 18.8 

3022 18.8 

20 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.65 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Eev S 

Elevation Sample CalculationI 

Wind 

Wind Lateral Level 
Pressure Area Force Shear 
(ps) (ft2) (kips) (kips) 

Level PX ax HX Fx 

First Floor 

Ceiling * * 4.57 4.57 

1 (14.0+8.7) (8')(30') 5.45 10.02 

* Wind Pressure Calculation for First Floor Ceiling (Load = Pressure x Area) 
Gable: (area) (pressure)
1/2 (1)(12/(4)( 1')(1 5.6 + 9.8 psf) =0.04kips <*
[l/2(30)(5)-1/2 (1)(12/(4)(1)](14.8 + 9.3 psf) = 1.77 kips v*

Wall: (area) (pressure)
(30 fi) (1 ft) (14.87 + 9.3 psf) =0.72kips*
(30 ft) (1 ft) (14.0 + 8.7 psf) =2.04kips

4.57 kips 
From the previous two tables it is seen that: 

a Wind controls when forces are in the perpendicular to the long direction (both floors). 

* Seismic controls when forces are in the parallel to the long direction (both floors). 
21 of 44 

VI -E.66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 3: Check Existing Structure for New Loads 

Elevation Sample Calculation 

Step 3: Check existing structure for new loads 

For this example analysis, the existing structural components were assumed to be adequate for 

the loading conditions. However, the designer should check the existing truss-to-wall-connec

tions, plywood roof diaphragm, upper level walls, and floor diaphragm for their ability to resist 

increased loadings. 

Step 4: CheckExistingFoundation 

Per UBC Table 23-A, LiveLoad = 40 psf with no concentrated loadrequirementsfor a 1

foot-wide strip through the short distance ofthe house 

Snow: (24 psf) (1') (1 5'+2' overhang) = 408 plf
First Floor LL: (40 psf) (1') (15'/2) = 300plf
Dead Loads:

Roof: 

shingles: (15.81' +2') (2 psf) (')= 35.6plf 
felt: (15.81' + 2') (0.7 psf) (1') = 12.5 plf 
plywood: (15.81' + 2') (1.5 psf) (1') 26.7plf 
truss: (15' + 2'(15/15.81)) (5 psf) (1') = 84.5 plf 

Ceiling: 

insulation: (1 5') (1') (8 psf) = 120 plf 
plywood: (15') (1') (1.5 psf) = 22.5 plf 
plaster: (15') (1') (2Opsf)= 150plf 
misc: (15') (1') (2 psf) = 30 plf 
wall (ext) (4') (1') (18 psf) = 72 plf 
wall(int)' (15'/2) (1') (20 psf) 150plf 

First Floor: 
flooring: (15'/2) (1') (4 psf) = 30plf 
subfloor: (15'/2) (1') (3 psf) = 22.5plf 
joists: (15'/2)(1') (4 psf) = 30 plf 
insulation: (15'/2) (1') (5 psf) = 37.5 plf 
misc: (15'/2) (1') (3 psf) = 22.5 plf 
ce:ing (15'/2) (1') (2.5 psf)= 18.8plf 
wall (ext) (4') (1') (18 psf) = 72plf 

22 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.67 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Elevation Sample Calculation 

wall(int~l (15'12) (1P) (20 psf)= 150plf
new lower level

wanl (lO') (11)(50 psf) = 500Ipf
Total Dead Load 1587 plf

' Note that a 20 psfpartition load is applied here; this approach is conservative due to the 
amount of interior walls in this building. 

From our field investigation it was determined that an allowable bearing pressure of 2000 psf 
was acceptable. 

Total gravity load on foundation: 

Snow + Foundation 

it = + Live + Dead + Soil 

= 408 plf+ 300 plf+ 1587plf+ 2'(1')(150pcf) + [(24"-8")/ 
12](29)(120pcf) 
-2915plf

= 

The existing foundation is 2'-0" wide, thus the bearing pressure for gravity loads is 
BP = 2915plf/ 2 ft = 1458 psf < 2000 psf allowable 
Existing Foundation is Acceptable. 
(Note: This is a worst case scenario by assuming no buoyancy effects.) 

Step 5: Designof NewFoundation Wall 

Using UBC minimum requirement for masonry walls in Seismic Zone 2B, 

From Table A-24-3-B minimum vertical wall reinforcement for 80 mph wind, Exposure C, 2 
story (first story of 2-story building) unsupported height of 8'-0" 

minimum= #3 rebars @ 72" o.c. 

23 of 44 

VI -E.68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
Januarv 1995 


Elevation Sample Calculation Step 5: Design of New Foundation Wall 

Elevation Sample Calculation 

However, since the house is in seismic zone 2B, Section 2407(h)3 ofUBC applies for minimum 
reinforcement. See typical Hollow -Masonry Unit Exterior Foundation Wall Detail. 

t ;;; i; ..... .--.-.' t. K!'.':.i.:'0
.. .. . ;..i. : : . i i. -.

;, :';;t t. . :. ... 0.' 

i L .... '."E 'E. 

,g,,, :., -.,::.,:: E -,.. , ...
:i. -.. ':..-::".... '.E:::i2<:'<-:fi::::gs4xe.A .......... .::.:

-........ ~~~~~~~~~~~~~~~.i 

.:-E. ?: ............ .. ....... .... :.:.:.: 

,. ". t: ' .,. ' ', ':EC.BX,. , .,::S. ', ......................... . . . . . . . .. . . . . . . . . . . .,:: "

~ ~ ~ ~ ~ R .. ... --.. ..............

i.-X-.-;..,1''ii 
".'':.i'~-~:''.-HL.oW.Y,'l.... '''

~ ~~~~~N .,,: 

............... .6..

M5R 

CHECK SHORT WALLS FOR LATERAL LOADS (SHEAR WALL), TENSION 
AND TORSION 

BIWBE 

Wind shear per wall = 22.1kips /21=1.05 kips per wall 
~~E 

I 

Total seismic shear 18.8 kips
UBC Section 2334(e) requires a 5% x building length induced torsion on seismic loads.

For this house the center of mass and the center of rigidity will coincide. 

5%(60'-0")= 3 ft. of induced torsion
therefre,

18.8kips x 3 ft = 56.4 k-ft
This results in shear in one wall being increased; thus, the total seismic shear for short wall is
18.8kips/2 + 56.4 k -ft/60 ft = 10.3 kips per wall
Therefore,windcontrolsforshortwalls. 24 of 44
Encineerinc Prinninles and Practices of Retrofitting Flood-Prone ResidentialStructures VI -E.69 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Elevation Sample Calculation 

Worst Case, wall with penetrations. 

,NECEO0EC7 

I ~-CN MCORSE

He
.11 11- S = DRPY-I B/

NEAW LINTEL 

II i 

I

II 

I 2: II
i

i 

WALI A. ff-i tZ INER1A. r164 1

AREA 

I |2 .3 . 1 Z2 s 23:2 

SAMPLE ELEVATION 

4 

Assume #4 reinforcing bars @ 48" o.c in solid grouted cores. 

The total load of 1 1.05 kips must now be distributed to the wall according to stiffness of the 
elements ofthe wall. 

(height/length),= 101 /20' = 0.5
(height/length), = 10'/7 = 1.42

Since both height to length ratios are between 0.3 and 10, both shear and flexural deformation 
must be considered. 

With #4@48" o.c. the equivalent solid thickness is 4.6 inches= 0.38 ft. 
Reference: National Concrete Masonry AssociationNotes 
Assume shear modulus, G is 0.4 E where E = modulus of elasticity 

25 of 44 

VI. -E.70 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 

Elevation Sample Calculation Step 5: Design of New Foundation Wall 

Elevation Sample Calculation 

Assume compressive strength of masonry, f m = 2000 psi and type M or S mortar 

per ACI 530-92 Table 5.5.1.3, Em = 2.2 x 1 06 psi 

total deflection, 
U = Uf+ UV 

where:
U = Total Deflection
Uf= VH3/(12EI) Deflection due to Flexure
UV= 3VH/(EA) Deflection due to Shear

thus for this house, 

_ vl (H4l)3 3VjHj 

ul I + 
12EmI EmAi

V1H, 3 3VH

11111 

U" 

12EmI11 E.All 

Since the walls are interconnected by the floor diaphragm, the deflections for parts I and II will 
be equal. This calculation uses two equations, which give the load distribution into walls I and 

II. For more information on the use ofthese formulas, refer to a structural engineering text on 
shear walls. 
thus, 

Vl (H2 3VH1 _ VJH11 
3 3VIIH1 1 

.12EmI1 EmAi 12EmIi EmAII 

26 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.71 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Elevation Sample Calculation 

vl1)3+ 3+{10) V,1(10)3 3V,1(10) 
12(253) 7.6 12(10.9) 2.7 

simplifying results in, 
4.28VI -18.76VII= 0.0 
by IF we get a second equation, 
VI +V =P= ll kips 

Solving the above two equations results in, 
VI 8.96kips=> 8.96 kips/20 ft = 0.45 kips/ft. 
V 1= 2.04 kips=>2.04 kips/7 ft = 0.29 kips/ft. 

Area V1 controls for bolt shear and wall shear. 

From UBC Section 2406(c)7B, 

M 8.96 kips(10')

= 2 ~~=0.75 <1.0 

Vd 8.96 kips(-)(20') 

3 
thus, allowable shear stress is (by equation 6-10 from UBC) 

Fv = 3(4-Vd ) < 80-45 M 

thus, 
F, = (1/3)(4-0.75)(2000)112 = 48.4 psi > 46.25 psi 

Since we will not be specifying "special inspection," UBC 2406(c) states that allowable stresses 
must be reduced by 1/2. 

27 of 44 

VI -E.72 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation 

[Elevation Sample Calculation 

Thus,
Fv = 46.25/2 = 23.1 psi

the applied stress, f is

V 

fv = V/(bjd) 
where: 
b = Width of Section 
j = Ratio of Distance between Centroid of Flexural 

Compressive Forces and Tensile Forces, d 
d Distance from Extreme Compression Fiber to 
Centroid of Tensile Reinforcement 

If we neglect the small axial forces in this wall, and assume equal distribution of reinforcement 

d 20'/2 + (2/3)(20'/2) = 16.67 ft.
j = (2/3)(20')/16.67' = 0.8

forface shell bedding of masonry, width of sectionresisting shear is limited to mortarjoints; 
thus, 

b = 2 (1.25") = 2.5" 

thus, 

f =[8.96/((2.5)(0.8)(1 6.67)(12))]- 1000=22.4 psi 

since f < F wall is O.K. for shear. Use face shell bedding, no special inspections required. 

Does wall go into tension? 

28 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.73 
January 1995 


Chapter VI:General Design Practices 
Elevation 

Elevation Sample Calculation 

maximum flexural uplift = VH/[(2/3)(20')] = 8.96 (10')/13.3 =6.74 kips 

stress block is triangular in shape, thus maximum stress is at end of wall, 

6.74 kips = (l/2)(10') Pma
Pmax=1.35 kips = 1350 lbs t
gravity loads, 
selfweight: 10'(50 psO = 500 lbs 4 
wallabove:8'(18psf) = 144Albs 

644 lbs . 

thus the net tensile force = 1350 lbs -644 lbs = 706 lbs 

consider distributed over 1 foot length 
b = 2.5'1 

thus 
ft= 706/(2.5"1 (12") = 24 psi > Ft = 2512 = 12.5 psi (per UBC 2406(c)4) 

However, since stress is very low, by observation we can say that the minimum reinforcement 
will take the slight tensile load. 

WIND PERPENDICULAR TO SHORT WALL UNDER CONSIDERATION 
(CHECKING VERTICAL SPAN FROM SLAB TO FLOOR) 

P = (8') 14.0 psf)/2 = 56 lbs/ft.
M = wl2/8 = (14)(8)2/8 = 112 lb-ft/ft = 1344 lb-in/ft

Check wall for assumed minimum reinforcement (#4 @ 48" o.c.), assuming T-section assembly. 

290f44

VI -E.74 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 5: Design of New Foundation Wall 

Elevation Sample Calculation 

per ACI 530-92 Section 7.3.2 

1-4 (A .. 4-2 S j-EMPTY CORES 

IN p1-L I wTn I II un a .. us 
_L 

~~~CORE

i X H \ I f 

V -a I _-L~~~~~~~T-SEA4M

ET

WE 

4-II I b.. 

WIND PERPENDICULAR TO WALL 

N T. S. 

I c-c bars = 48"
be min 16 (wall thickness) = 48"

1 72" 

d = 75/8 12 = 3.81 in. 

by the use of working stress design, (T-Beam analysis) it is determined that 
maximum compressive stress, f0 = 35 psi 
maximum tensile stress, f = 1890 psi 

Per UBC 2406(d)A, maximum allowable tensile stress in reinforcement is 

Fs =0.5 (fy) < 24,000 psi 
= 0.5(60,000) 
= 30,000 > 24,000 .-. use F. = 24,000 psi 

For no "special inspections" multiply by 1/2, thus
F5 =12,000 psi >>> f = 1890 psi O.K.

Per UBC 2406(a)3, maximum compressive stress 

Fb =0.33 f'
= 0.33 (2000 psi)
= 660 psi

30 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.75 
January 1 995 


Chapter VI: General Design Practices 

Elevation 

Eevatio S 
Elevation Sample Calculation 

For no "special inspections" multiply by 1/2, thus 

Fb= 660 /2 = 330 psi >>> f O.K. 

Determine Ability of Wall to Withstand Hydrodynamic and Impact Forces 
Moment in wall is, 

186 (8') 14 psf(8')f 43.65 psf(8')2

Qi + w11 + w212 
= 16+ + 
4 16 16 4 16 16 
= 602.6 lb-ft 

Q 3wl W21 186 3(14 psf)(8') (43.65 psf)(8') 

+ + + 
2 8 8 2 8 8 
= 178.7 lbs/ft w/impact 
= 85.7 lbs/ft w/o impact 

M =-+= 

Q w1l 3W21 186 14 (81) 3 (43.65 psf)(8') 

= -+ + = + +
Pbot 2 8 8 2 8 8
= 238 lbs/ft w/impact
= 145lbs/ft w/o impact

Note: Forthe connection design for the top of wall to floor, impact need not be 
considered acting over the entire wall (that would assume a row of debris or logs hits 
the house at one time). 

kV 31 of 44 I 
VI E.
76 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1 995 


Elevation Sample Calculation Step 5: Design of New Foundation Wall 

Elevation Sample Calculation 

For this load, try using #5 @ 48" O.C., assuming a T-section assembly. 
B =48" 
d =3.81" 

By the use of working stress design (T-beam analysis), it is determined that, 

MT = (602.6 lb-ft) (48" ) = 2,401.1 lb-ft 

maximum compressible stress, f'c = 548 psi 
maximum tensile stress, f = 26,253 psi 

S 

Note: f = 26,253 > F, = 24,000 psi allowable by UBC 2406(d)A; however, since an 
impact load is included in the loading under consideration, most building codes consider 
this a "short term" load and allow a 1/3 stress increase. Also note that with this amount 
of loading, it becomes feasible for "special inspections" of the masonry construction, 
and if the owner has qualified personnel to inspect the construction, the 1/2 allowable 
clause in the building codes no longer applies and the design can consider the full 
strength ofthe masonry. Thus, this design may be acceptable if the building code allows 
1/3 stress increase and "special inspections" are performed. 

try #5 @ 24" O.C. 
b = 24" 
d =3.81 

32 of 44 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.77 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Elevation Sample Calculation 

24" 

MT= 602.6lb-ft (--): 1,205lb-ft 

T ~~~12'1 

maximum compressive stress, f 'c = 362 psi
maximum tensile stress, f S = 13,354 psi

This design is acceptable if 1/3 stress increase is allowed for impact however, the "special 
inspections" would not need to be perforned. The owner/engineer should decide which design 
is more cost effective. 

Also note that the above neglects axial load onthe masonry. This was done to simplify the 
calculations. In the wall, compressive stresses will be slightly higher and tensile stresses will be 
slightly lower. See ACI S30 for further information onthis subject. 

8"CMIJ wall w/#5 @ 24" O.C.centeredon grouted cell -2,000 psi masonry (fPm)is acceptable. 

Step 6: Design top of wall connection. (Checking anchor bolts for pullout from masonry) 

Try 1/2"4A307 anchorbolts @ 4'-0" o.c., Wall I is worst case (see above) 

shear per b olt=0.45 k/ft. (4 ft.) 1.8 kips bolt 

It,~~~~~~~~~~~~~~~~~~~~~M 

upliftonbo
P =5.56 (8)120=2.22 kips -ian;
p= 2.22 (2) 15 =0.3 k/ft

by ratio,
thus, uplift on bolt = {(0.22+0.3)/2}(4')=1.04 kips/bolt

try 1/2" 4 A307 anchor bolt, area of bolt, Ab = 0.2 in2
edge distance, Ibe=75/8 /2 -/2/2 = 3.56"
embedment, lb = 4" (chosen)

33 of 44 j 

VI -E.78 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 6: Design Top of Wall Connection 

Elevation Sample Calculation 

Reference: ACI 530-92 Section 5.14 & UBC Section 2406(h)
Ap = min (rlb2 or 7lIb 2) = 7I(3.56)2 3 9 .8 in2

allowable load in tension, 
0.5(Ab)j 
Bt = mm 0.2(Ab)fy 

where: 
Ab = Area of Anchor Bolt 
film = Compressive Strength of Masonry 
f = Yield Strength of Anchor Bolt 

y 

for this anchor bolt pattern, 
Bt = min (((0.5)(39.8)(2000))4),(0.2)(20ksi)) 890,800 = 800 lbs < 1.04 kips 

by inspection the bolt will not work for combined shear and tension, 

Lower bolt spacing to 2'-O" o.c. 
pi =0.3 kips/ft 

by ratio, 
p2 =0.26 kips/ft 
uplift on bolt = {(0.3+0.26)/2}(2')= 0.56 kips < 800 lbs O.K. 
shear per bolt = 0.45 kips/ft (2') = 0.9 kips 

34 of 44 

EnningaarinnPrin,,infa and Pratirce nf Retrnfiffinn Flond-PronA ResidentialStructures VI -E.79 
January 1995 


Chapter VI: General Design Practices 
Elevation 

Elevation Sample Calculation 

allowable load in shear, 

350((f'm) Ab)"14
mnn0.2Abfy)

where: 
AN = Areaof Anchor Bolt 
f'm = Compressive Strength ofMasonry 
f = Yield Strength of Anchor Bolt 

y 

for this anchor bolt pattern, 
Bv=min (350((2000)0.2)M),(0.12(0.2)(20ksi))= 1565,480 480 lbs < 0.9 kips 

If this pattern will not work, try upsizing bolts to 7 2 -0 oc, 

Ab =0.60 in2
Ap= it(751s/2 -7/8/2)2 = 35.78 in2

B.= min (0.5(35.78)(2000)'2),((0.2)(0.6) 20ksi) = 800,2400 = 800 lbs 
B= min (350((2000)(0.6)/),((0. 12)(0.6) 20ksi) = 2060,1440 = 1440 lbs 
Per ACI 530, Section 5.14.2.4,the combined ratio is 

B. +b <1.33(with1/3increase for wind/seismic)
Bt Bv 

where:
bt = ActualBoltTension
bv = Actual Bolt Shear
Bv = Allowable Bolt Shear
Bv = AllowableBoltTension

35 of 44 

VI -E.80 Enaineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Structures 
January1995 


Elevation Sample Calculation Step 7: Design SillSole Plate 

Elevation Sample Calculation 

Forthis case, 

(560/800) + (900/1440) = 0.7 + 0.625 = 1.33 O.K. 
Therefore, use 7/8" 4A307 anchor bolts @ 2'-0" o.c. Embed a 
minimum of 4 inches. Center in cell of masonry. (The embedment of 4 
inches works for the headed anchor bolt and is the minimum required for a 
reinforced wall with a bond beam at the top ofthe wall. However, embedment 
of up to 18 inches is common practice in the engineering industry for 
hooked anchor bolts.) 

Step 7: Design sill/sole plate 

Assume Southern Pine -pressure treated 2x8, No.2 grade 19% moisture content 

Per UBC Table 25-A-1 (and National Design Specification for Wood Construction), 

the following parameters are defined as:
F l = tabulated compression design value perpendicular to grain = 565 psi
Fb= tabulated bending design value = 1400 psi

VF= tabulated shear design value parallel to grain (horizontal shear) = 90 psi 
E = modulus of elasticity = 1,600,000psi 
F = tabulated compression design value parallel to grain = 1200 psi 

C 

Check Bending Stress 

Average uplift per foot in area of concern, = 0.28 kip/ft
Worst bending stress will occur at a splice or end of sill plate.
Note that RI is critical due to prying action.
Section modulus at bolt, Sy is

Sy= Smember bolt hole
Sy =2.719 -bh2/6
Sy =2.719 -(1"1)(1.5"1)26
S= 2.344 in3

36 of 44 

Pnninoarinn Prinecinioeand Practices nf RltrofittinnFlnnd-Prnne Residential Structures VI -E.81 
January 1995 


Chapter VI: General Design Practices 

Elevation 

Elevation Sample Calculation 

The allowable bending stress, Fb' is givenby 
F.' = F.CdC tCCCCCCCCn

b b d m t L F Y fU r C f 

where:
Fb -Tabulated Bending Stress
Cd = LoadDurationFactor
C = Wet Service Factor
Ct = Temperature Factor

= Beam Stability Factor 

CL 
CF = Size Factor 
Cv = Volume Factor 
Cfu = FlatUse Factor 
Cr = Repetitive Member Factor 
Cr = Curvature Factor 
Cf = Form Factor 

For this example, (Reference: National Design Specification for Wood Construction) 
Cd = 1.6 
Cf =1. 15 
all other factors = 1.0 

thus, 
Fb' = 1.6(1.15)(1400psi) = 2576 psi >>> fb O.K. in Bending 

37 of 44 

VI -E.82 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 7: Design SllISole Plate 

Elevation Sample Calculation 

Check horizontal shear, f 

VQ

lv

Ib

where: 
V Shear at Point Under Consideration 
Q = First Moment of Area Above Plane Under Consideration 
I = Moment of Inertia 
b = WidthofMember 

For this example, 
Q = 7.25(1.5/2)(1.5/4) = 2.04 in3 

I Imember Ibait hole 
I = 2.039-(1"#)(1.5")3/12 = 1.76in4 

V = RI z 600 lbs 

thus, 
= (600)(2.04) / (1 .76)(7.25) = 95.9 psi 

Allowable horizontal shear is given by, 
F -FCdCCtCH 

where: 

Fv = Tabulated Shear Stress 
Cd = Load Duration Factor 
Cm = Wet ServiceFactor 
Ct = Temperature Factor 
CH = Shear StressFactor 

For this example, (Reference: National Design Specification for Wood Construction) 
Cd =1.6 
all other factors= 1.0 

thus, 
F,'=1.6(90psi) = 144psi <f O.Kinhorizontal shear 

38 of 44 

Ennineerinn Prindnls .----. of Reatrofittinn Flood-ProneResidential Structures

and PracticesloWr b-.--------y -VI -E.83 

-. M.. T a d M 

January 1995 


Chapter VI: General Design Practices
Elevation

Elevation Sample Calculation 

Check Bearing Around Bolt Hole 

bolt is 78 " -assume a 1 "hole 

For a 8"8 bolt an "N" series washer is 
0.938" inside diameter 
1.47" outside diameter 

if hole is 1"diameter ten 
Acontart= 7(r12 -r22) = 7r((1.47/2)2-(1/2)2) = 0. 91 in2 
thus, f= PA = 600 lbs /0.91 in2 = 659 psi 

The allowable stress is, 
F~i = F.LWCmCICb 

where:
Fcl = Tabulated Stress
Cm = Wet Service Factor
C1 = Temperature Factor
Cb = Bearing Factor

For this example, 

Cb = (lb + 0.375) /b (Reference: National Design Specification 
Cb = (1.47 + 0.375) / 1.47 = 1.26 for Wood Construction) 
all other factors = 1.0 

Allowable stress is therefore, 
F0 =565 psi (1.26) = 712 psi > 659 psi O.K. 

Check single shear wood to concrete connector (due to shear wall load). 

(Reference: National Design Specification for Wood Construction, Section 8.2.3.) 

39 of 44 

VI -E.84 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 7: Design Sil Sole Plate 

Elevation Sample Calculation 

7/8" 4bolt connected to a southern pine (No. 2 grade) 2x8, load parallel to grain, 
tm 2t, 

where: 
t = Thicknessof Main Member 
t -Thickness of Side Member 

For this example, 
to= 2(1.5) =3.0 in 
t=1.5 in 

from Table 8.2A of National Design Specification for Wood Construction, 

Zil = 1160 lbs 

the allowable stress is, 
z11 = 

where: 

ZCdCrmCtCgCA 

For this example, 

Cd = 

Z 
Cd 
Cm 
Ct 

Cg 

CA 

1.6 

= 
= 
= 

= 
= 
= 

Tabulated Allowable Stress 
Load Duration Factor 
Wet Service Factor 
Temperature Factor 
Group Action Factor 
Geometry Factor 

all other factors = 1.0 

thus, 
Z11= (1160 lbs)(1.6)= 1856lbs 

one bolt has a trib length of 2'-0" 
Vbolt= 450 lbs/ft (2') = 900 lbs <Z'l1 
40 of 44 

Pnmineerinn Prinrinkme and Practices of Retrofittina Flood-Prone ResidentialStructures VI -E.85 
January 1995 


Chapter VI:General Design Practices 
Elevation 

Elevation Sample Calculation 

I~ ~ ~~~~~~~~

~~~~~~~~~~~~~~~ 

Checkconnection forwind perpendicular to wail 

Reaction= 14psf(8') = 112lbs/ft (2'bolt spacing)= 224 lbs 

The allowable stress is,
zCeC CCC

ZI = d m 1 g A 

where:
z = Tabulated Allowable Stress
Cd = Load Duration Factor
C = Wet Service Factor
CIC,= Temperature Factor
Cg -Group Action Factor
CA = Geometry Factor

for this example, 

Z_1 = 490 lbs (National Design Specification for Wood Construction)
Cd = 1.6
all other factors = 1.0

thus, 
Z,' = (490 lbs)(1.6) = 784 lbs > 224 lbs O.K. Therefore, a single 2x8 sill plate is 
acceptable with 718" 4 A307 anchor bolts with type "N" washers at 2'-0" o.c. 
grouted into masonry. 

41 of 44 

VI -E.86 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Elevation Sample Calculation Step 7: Design Sill/Sole Plate 

E-

Elevation Sample Calculation 

SAMPLE DETAILS 

Minimum Reinforcement Required by Code for Seismic Zone 2 

.... .. : h b i t0 a~ lR;t0i i 14,ii: : d

E ::i:u-4 i--:; it4: i 

W.4 O05 ARA0(005 4 
O EDR M EmIJRIT 0 T l. 

-oO F4 " VCL~T RIA .3.... . 

NA.S.~~ ~ ~ ~ ~ ~ ~~~;;;b~iSWA 

00

XMASONRY

til -|-tiit;0-t-;MINIMUM ~W2ALLC 033)550O 4S l-t:0i 

I0N

.ti-0yt-it-.t--0-;-REOUILREMENT$t-SEISMICiZONEiNo. 20 :g ;

Sample Bearing Wall Detail 

*4 a 48' 0. C. (MIDDLE OF CORE)
VERTICAL REINFORCEMENT
(FILL CELLS AT REINFORCEMENT
NEW C. M. U. MASONRYWALL WITHGROUT 

HORIZONTAL REINFORCEMENT

HORIZONTAL BARS IN AS REOUIRED
GROUT-FILLED BOND
BEAM NEW 31W' CONCRETESLAB

ON GRADE (TYP.)
UNDISTURBEDGROUND

SURFACE 3. O NOTE:SPLICE NEW BARS
TO EXISTING '4 DOWELS
IN FOOTING a 48' O.C.

PROVIDE CLASS B GROUT-FILLED HOLLOW 

EMBED18' BELOW GRADE LAP FOR No. 4 MASONRYUNIT ALL CELLS
OR BELOW THE FROST BAR FOR MASONRY
LINE, WHICHEVER EXIST. CONC.-t. e-

DEEPER (TYP.) 
IS 
FOOTING J.., .. : l NOTE: 

INFORMATION SHOWN
ON THIS DETAIL
4 / 71 P iNS TO 1THE

CONTINUOUSREINFORCEMENT-~'VA" \ >m BLEM

-' J. EXAMPLE PROBI
REGUIRED

IF ON FILL 

No. 4 HORIZONTAL BARS 

AT 24' O.C. WHEREREOUIRED il 2'-0" BEND ALTERNATE BARS 

HOLLOW-MASONRY UNIT
EXTERIOR FOUNDATION WALL

I B 1 2 3 

42 of 44 

VI-E.87 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.87 

January 1995 


Chapter VI: General Design Practices
Elevation

E, 

Elevation Sample Calculation 

Sample Foundation Detail 

.................. . ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. .......

... ..

,,,~.',,

-.:'jSOLEPLAT

'i'--

::::

,1J,.' ' ' 

SLA TE OW M ...' 85 

WIT O UT AL

GAG 

,.' . "'.'' 'N . .(' f t' :L''''',''W' . 

''5: ' ' ZEW'FLOOR:'~m --

FiLL I:FTLOUt 

E-

. 'WALLS-Y'ST:EMAANC'HANCH

VI~~~~~~~~~HAHNPieOsadPacie fRetoitn lQ-Paa ai~~5nl.+rrila2

EaiLrn-.8 J 

Sa l De43 of 44 W 
VIE.88-Enalnearina PrincinitasD n P-SB

R tfLV 

January 1995 


Elevation Sample Calculation Step7: Design Sil/Sole Plate 

x 
VIZT-' C Qt] 
Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures VI -t.Yw 

January 1995 


j j 

/ Chapter VI: General Design Practices 

Elevation 

CONSTRUCTION CONSIDERATIONS 

PRIOR TO LIFTING ANY HOUSE 

Guidanceon * Obtain all permits and approvals required.
Guidance on the selection of an
elevation or relocation contractor

eisprovided in Chapter VI-R, * Ensure that all utility hookups are disconnected (plumb

sRelocation. ing,phone, electrical, cable, and mechanical). 

* Estimate the lifting load of the house. 
* Identify the best location for the principal lift beams, 
lateral support beams, and framing lumber, and evaluate 
their adequacy (generally performed by a structural 
engineer or the elevation contractor). 
SLAB-ON-GRADE HOUSE, NOT 
RAISING SLAB WITH HOUSE 

* Holes are cut for lift beams in the exterior and 
interior wall. 
* Main lifting beams are inserted. 
* Holes are cut for the lateral beams. 
* Lateral beams are inserted. 
* Bracing is installed to transfer the loads across the 
support walls and lift remaining walls. 
* Jacks are moved into place and structure is prepared for 
lifting. 
VI -E.90 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Construction Considerations 

* Straps and anchors used to attach house to slab-ongrade 
are released. 
* The house is elevated and cribbing installed. 
* Slab around edges is removed to allow for new foundation. 
* The new foundation is constructed. 
* New support headers and floor system are installed. 
* Any required wind and seismic retrofit is completed. 
* House is attached to new foundation. 
* All temporary framing is removed, holes are patched. 
* Reconnect allutilities. 
* Construct new stairways and access. 
* Floodproof all utilities below the FPE. 
SLAB-ON-GRADE HOUSE, RAISING 
SLAB 

* Trenches are excavated for placement of all support 
beams beneath slab. 
* Lifting and lateral beams are installed. 
* Jacks are moved into place and the structure is prepared 
for lifting. 
* The house is elevated and cribbing installed. 
VI -E.91 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.91 
January 1995 


Chapter VI: General Design Practices 

Elevation 

* The new foundation is constructed. 
* Any required wind and seismic retrofit is completed. 
* House is attached to new foundation. 
* Support beams are removed. 
* Access holes are patched. 
* Reconnect all utilities. 
* Construct new stairways and access. 
* Floodproof all utilities below the FPE. 
HOUSE OVER CRAWLSPACE/ 
BASEMENT 

* Remove masonry necessary to allow for placement of 
support beams. 
* Install main liftingbeams. 
* Install lateral beams. 
* Jacks are moved into place and the structure is prepared 
for lifting. 
* All connections to foundation are removed. 
* House is elevated and cribbing installed. 
* Existing foundation walls are raisedor demolished 
depending upon whether the existing foundation walls 
can handle the new loads. 

Vt -L.92 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Construction Considerations 

* New footings and foundation walls are constructed if 
the existing foundation walls/footings cannot withstand 
the additional loading. 
* Backfillbasement where appropriate. 
* House is attached to new foundation. 
* Support beams are removed. 
* Access holes are patched. 
* Reconnect all utilities. 
* Construct new stairways and access. 
* Floodproof all utilities below the FPE. 
HOUSE ON PILES, COLUMNS, OR
PIERS

If the house is to remain in the same location, the house will 
most likely need to be temporarily relocated to allow for the 
footing and foundation installation. If the house is being 
relocated within the same site, the footings should be 
constructed prior to moving the house. 

* Install main support beams. 
* Install lateralbeams. 
* Jacks are moved into place and the structure prepared 
for lifting. 
* House is elevated and cribbing installed. 
Prin-iAnlI f Retrofittina Flood-Prone Residential Structures 
January 1995 

s1yiinaerinn and Prantices a VI -E.93 


Chapter VI: General Design Practices 

Elevation 

o If the house is being relocated, see the Chapter VI 
relocation section. 
 House is attached to new foundation. 
* Remove support beams. 
* Reconnect all utilities. 
* Construct new stairways and access. 
* Floodproof all utilities below the FPE. 
VI -E.94 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Relocation 

Table of Contents 

Step 1-Selection of a House Moving Contractor .................................... VI -R.3
Experience .................................... VI -R.3

-

Financial Capability.................................... VI R.3

ProfessionalismandReputation .................................... VI -R.3

Cost of Services .................................... VI -R.4

Step 2 -Analysis of Existing Site and Structure ..................................... VI -R.6
LiffingBeam Placement .......... . ............................................ . ............... ..... VI-R.7R.7............. 

Step 3 -Selection, Analysis, and Design of the New Site .................................... VI -R. 10
SiteAccess .................................... VI -R.10
Permits.................................... VI -R.10

Step 4 -Preparation ofthe Existing Site .................................... VI -R. 11

Step 5 -Analysis and Preparation ofthe Moving Route ............. ....................... VI -R. 12
IdentifyRouteHazards ..................................... VI -R.12
ObtainApprovals ..................................... VI -R.13
Coordinate Route Preparation .................................... VI -R. 13

Step 6 -Preparation of the Structure..................................... VI -R.14
DisconnectUtilities.................................... VI -R. 14
Cut Holes in Foundation Wall for Beams .................................... VI -R. 14
InstallBeams .................................... VI -R.15
Install Jacks ..................................... VI -R.15

EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures Vi -R.i 
January 1995 


Install Bracing as Required ............................... VI -R. 16
Separate Structure from Foundation .................................. VI -R. 16

Step 7 -Moving the Structure .................................. VI -R. 17
Excavate/Grade Temporary Roadway .................................. VI -R. 17
Attach Structure to Trailer .................................. VI -R. 18
Transport Structure to New Site .................................. VI -R.2 1

Step 8 -Preparation ofthe New Site .................................. VI -R.22
DesignFoundation .................................. VI -R.22
DesignlJtilities.................................. VI -R.22
Excavation and Preparation of New Foundation ........... ....................... VI -R.22
Construction of Support Cribbing .................................. VI -R.23
Construction of Foundation Walls .................................. VI -R.24
Lower Structure onto Foundation .................................. VI -R.24
Landscaping .................................. VI -R.25

Step 9 -Restoration of Old Site .................................. VI -R.26
Demolishand Remove Foundation andPavement . ................................. VI -R.26
DisconnectandRemoveAll Utilities .................................. VI -R,26
Grading and Site Stabilization .................................. VI -R.27

VI -R.ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


RELOCATION 

Relocation is the retrofitting measure that can offer the greatest security from future flooding. It 
involves moving an entire structure to another location, usually outside the floodplain. Selection 
of the new site is usually conducted by the homeowner, often in consultation with the designer to 
ensure that critical site selection factors such as floodplain location, accessibility, utility service, 
cost, and, of course, homeowner preference meet engineering and local regulatory concerns. 
Relocation as a retrofitting measure not only relieves future anxiety about flooding, but also 

offers the opportunity to eliminate future flood insurance premiums. 

Figure VI-RI: House Relocation 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -R.1 
January 1995 


Chapter VI: General Design Practices 

Relocation 

The relocation process, as illustrated in Figure VI-R2, is fairly 

straightforward, but there are a number of design considerations 
to be addressed before embarking on this retrofitting measure. 
The steps involved with the relocation of a structure are discussed 
in more detail throughout this chapter: 

Step 1: Selection of a House Moving Contractor 

Step 2: Analysis of Existing Site and Structure 

Step 3: Selection, Analysis and Design of New Site 

Step 4: Preparation of the Existing Sitel 

Step 5: Analysis and Preparation of the Moving Route 

Step 6: Preparation of the Structure 

Step 7: Moving the Structure 

Step 8: Preparation of the New Site 

Step 9: Restoration of the Old Site 

Figure VI-R2: Relocation Process 

VI -R.2 Enaineerina Princinlas and Prarticesnf Ratrmfiftinet Rai U|UI5

trL 9 ir.eiona 

January 1995 


Step 1 -Selection of a House Moving Contractor 

STEP 1 -SELECTION OF A HOUSE MOVING 
CONTRACTOR 

The selection of a moving contractor is one ofthe most impor

tant decisions a homeowner will make and may ultimately have 

the greatest impact on the success of the project. The designer 

can assist the homeowner in selecting an experienced home 

moving contractor. Some ofthe key elements ofthis selection 

(outlined in the Relocation Contractor Selection Checklist, 

Figure VI-R3) include: 

EXPERIENCE 

The designer/homeowner should visit recent projects the 
contractor has completed and talk to owners who recently 
went through the process to develop an opinion on the 
quality of work done by the contractor. 

FINANCIAL CAPABILITY 

The homeowner/designer should determine whether and to 
what extent the contractor is licensed, insured, and bonded. 
A prudent homeowner will consider the potential risk of a 
failed project before enlisting the assistance of a contractor. 

PROFESSIONALISM AND 

REPUTATION 

The International Association of The designer/homeowner may wish to check the
Structural Movers (ISM) may be ,

contactedat:P.O.Box 1213, contractor's reputation with the state licensig board, the 
Elbridge,NY 13060, (315)689-local Better Business Bureau, local officials, and/orthe 
9498,to obtain informationon International Association of Structural Movers (ISM). A 
houserelocationcompaniesfora critical question is whether or not the contractor is licensed 
retrofittingproject. to work in your area. 

Mnninnnrinn Print-inloa and Practircs nf Ratrnfiffinn Flond-Prona Residential Structures VI -R.3 
January1995 


Chapter VI:General Design Practices 

Relocation 

The designer/homeownershould also interview several 

contractors to determine: 

* how well they may be able to work with this individual; 
* the extent of the contractor's knowledge; and 
I what confidence may be had in the contractor's ability 
to complete the relocation project. 

COST OF SERVICES 

While this should not be the sole determinant of contractor 

selection, cost of services is an important aspect of the 

relocation process. To ensure a comparison of similar 

levels of effort, the designer/homeowner should develop a 

detailed scope of services to be provided and have each 

contractor prepare a bid from the same scope of services. 

Remember, the most qualified contractor may not always 

have the highest cost and conversely, the least qualified 

contractor may not have the lowest cost. 

VI -R.4 Engineerinq Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995 


Qtgn I . Qalao-tinn nf a House MnvinnCnntractnr 

Relocation/Elevation Contractor Selection Checklist 

F

1. Experience of the Contractor:
Recent, successful house relocation/elevation projects? Yes No
Satisfied clients providing good references? Yes__ No
Met time schedules? Yes No
Cleaned up and restored old site? Yes No 

Quality product through your visual inspection 
of recent projects? Yes__ No 

2. Financial Stability of Contractor: 
Bonded? Yes_ _ No ; Amounts:_ 

Licensed? Yes__ No ; Amounts:
Insured? Yes _ No ; Amounts:_

3. Professionalism and Reputation of Contractor: 
State Licensing Agency:
Better Business Bureau:
LocalOfficials:_
International Association of Structural Movers:
Results of the Interview:_

4. Cost of Services: 
5. Summary of References:_ 
I 

Figure VI-R3: Relocation/Elevation Contractor Selection Checklist 

-

Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures VI--. 0 
January 1995 


L % > Chapter VI: General Design Practices 
~~~Relocation 

STEP 2 -ANALYSIS OF EXISTING SITE AND 
STRUCTURE 

The designer should help the homeowner to ensure that the 
contractor conducts an analysis of the existing site and 
structure to determine the critical criteria for the relocation 
of the structure. These criteria will include: 

* Does sufficient space exist around the structure for the 
installation of lifting beams and truck wheels? 
A tP * Can the structure be lifted as one piece or must it be 
separated into sections? 

Usually this analysis is conducted * Dependingupon the final assessment of the structure's 

by the moving contractor and not conditions, how much bracing will be required to suc-
by the homeowner's designer.
However, it is important that the cessftlly move this structure?
designer/homeowner coordinate
and communicate with the * Will this structure survive the lift and a move of the
contractor regarding the afore- distance proposed by the homeowner?

mentioned issues. 

* Which utilities must be disconnected and where? 
* What local regulations govern demolition of the remaining 
portions of the structure (foundation and paved 
areas) and to what standard must the site be restored? 
The contractor usuallyhas experience in analyzing the 
existing structure to determine: 

* the size andplacementofliftingbeams,jacks, andlateral 
or cross beams; 
* whether the structure should be elevated/moved in one 
or several pieces. 
VI -R.6 Enaineerino Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


If the selected contractor is not 
familiarwith these factors, the 
homeownerand designer might 
reconsider their contractor 
selection. 

Step 2 -Analysis of Existing Site and Structure 

The final decision on these items may not be made until an 
evaluation of the moving route is conducted. 

LIFTING BEAM PLACEMENT 

Each of the following factors affecting the placement of 
lifting beams must be taken into consideration during the 
elevation and relocation process: 

* size and shape of the house; 
* existing framing and structural parameters; 
* deflection limitations; and 
* distribution of the structure's weight. 
The major consideration for the placement of lifting beams 
is to limit cracking due to excessive deflections during 
preparation, moving, and settling in place. The lifting 
beams, in tandem with cross or lateral beams, must provide 
sufficient support for the structure. When the house is 
removed from the foundation, the lifting and lateral beams 
should provide as stable a support as the original foundation. 

Deflection of any portion of the structure is normally a 
result of the manner in which the weight of the house is 
distributed, the location of the jacks under the lifting beams, 
and the rigidity of the lifting beam. Proper placement of 
lifting beams, jacks, and lateral beams will protect against 
cracking of both the interior and exterior finishes, as well as 
ensure the integrity of the entire house. 

Enaineerina Principlesand Practices of Retrofittina Flood-ProneResidential Structures VI -R.7 
January 1995 


Chapter VI: General Design Practices 

Relocation 

A second consideration concerning the installation of lifting 
beams is to ensure that they are located so that the house 
can be attached to truck wheel sets forming a trailer. 

The route to be taken during the relocation of the house 
dictates the physical size and weight limitations of the 
structure, due to the horizontal and vertical clearances from 
obstructions. The house may have to be cut into sections, 
which are moved separately to negotiate the available route. 
Lifting beams, therefore, would have to be placed for each 
section to be moved. The entire elevation framing must also 
be rigid enough to take the forces associated with movement. 

The weight of heavier construction materials on certain 
portions of the structure, such as brick veneer, chimneys, 
and fireplaces, causes additional deflection and warrants 
special attention when determining the lifting beam system. 
Even with minimal deflection, brick construction is subject 
to cracking. Therefore, extra precautions will be needed in 
the form of additional beam support or removal of the brick 
for possible later replacement. 

The size and shape of the house also affect the placement 

and number of lifting beams. A simple rectangular floor 

plan allows for the easiest and most straightforward type of 

elevation project. Generally, placement ofthe longitudinal 

VI -R.8 Enaineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


'44 :; IfL; I, t-gf 

Figure VI-R4: When a house is too 
planning is necessary in o 
the pieces separately. 

Step 2 -Analysis of Existing Site and Structure 

lifting beams, with lateral beams located as required, is the 
system utilized for the elevation process. Larger or more 
complex shapes, such as L-shaped or multi-level homes, 
necessitate additional lifting beams and jacks to provide a 
stable lifting support system. Every consideration of the 
load based upon the size and shape of the structure should 
be incorporated into the design and layout of the lifting 
beam system. 

large to be relocated in one piece, careful 
irder to cut the structure in pieces and move 

Enaineerina Princinles and Practices of F 4etrofittina Flood-ProneResidential Structures VI -R.9 

Ja y ____ . -1 9 5 -O

-_

January 1 995 


Chapter VI: General Design Practices 

7 <\ ~ Relocation 

STEP 3 -SELECTION, ANALYSIS, AND DESIGN OF 
THE NEW SITE 

The selection of a new site for a relocated house will require-WI the examination of potential sites with regard to: 

Information on site design * floodplain location;
standards may be obtained from
the local building official, or, if
there is none, from a HUD publica-* utility extensionfeasibility;
tion entitled, Proposed Model
Land DevelopmentStandardsand * accessibility;and
Accompanying State Enabling
Legislation, 1993 Edition.

* permitting feasibility. 
The process is similar to selecting a lot upon which to 
design and build a new home. Local building codes and 
approval processes must be followed. In some instances, 

the homeowner may be required to upgrade existing me

chanical, electrical, and plumbing systems to meet current 

code requirements. 

SITE ACCESS 

An important consideration in the selection of a new site is 

the accessibility of the site for both the house movers and 

the new site construction crews. Severe site access con

straints can increase the cost of the measure and/or require 

clearing and grading activities, which maydiminish the site 

characteristics the homeowner initially desired. 

PERMITS 

The designer/homeowner should make certainthat when the 

house is moved to the new lot, it will conform to all the 

zoning and construction standards in effect at the time of 

relocation. The designer should contact the local regulatory 

VI -R.10 Enaineerina Principlesand Practicas of Ratrmfittinn Flood-Prone RamirigntiaIl Qtrt4irt iras

-v_ g ~---e .--...... a -w * 1995

--r *.g-~-Wwe *Jau-ar

*w * EwV 

January 1 995 


Step 4 -Preparation of the Existing Site 

officials to determine the design standards and submission 
process requirements that govern development of a new 
site. All permits required for construction at the new site 
and for transporting the structure to the new site should be 
obtained prior to initiating the relocation process. 

STEP 4-PREPARATION OF THE EXISTING SITE 

The initial preparation ofthe site includes clearing all vegetation 
from the area in and around the footprint of the house. This is 
done to clear a path beneath the structure to allow the insertion 
of beams for lifting supports. These pathways should be deep 
enough to allow for the movement of both people and machin

ery. 

Figure VI-R5: Clearing Pathways Beneath the Structure for Lifting Supports 
EngineeringPrinciplsandPrcticesfRetrofttinFoodPronResidetialStrcturI I R

Eniern ricpe n Patie ofRtoitn lo-rn eieta tutrsV -R1 

January 1995 


Chapter VI: General Design Practices 

7 <p Relocation 

STEP 5 -ANALYSIS AND PREPARATION OF THE 
MOVING ROUTE 

Once the relocation site has been selected, a route for transport 
must be analyzed and selected. This route should be chosen 
carefully and planned well in advance of the design of the new 
site or the undertaking of any relocation process activities at the 

existing site. 

IDENTIFY ROUTE HAZARDS 

Make certain that the house, as it will be moved, will navigate 

the following: 

Timing may be critical in areas * narrow passages, such as road cuts and widths;
that have heavy traffic during
morning and evening rush hours. bridgeweight limits and widths;
Homes are often relocated during
the late evening and early morn-

ing hours. * utility conflicts, such as light poles, and electric and tele

phone lines; 

* fire hydrants; 
* road signs; 
* trafficsignals; and 
* tight turns around buildings, bridges, and overpasses. 
Care should be taken to ensure that the structure will clear all 
overhead utility lines. Many ofthese can be lifted during the 
move, but utility companies sometimes require the presence of 

their employees and will charge for this service. In some 
instances an overland (non-road) route may be the best alternative. 

VI -R.12 Enaineerina Princinles and Prantices nf RAtrmfittinn Flond-Prne PReideontialQ:rtnptlara

---x7-*--" '-0---1995

_i'--.-

--*_ *r' * -rev *. wvv . *ve-vwJna 

January 1995 


Step 5 -Analysis and Preparation of the Moving Route 

OBTAIN APPROVALS 

It may be necessary to obtain moving permits, not only for 
the area from which the structure is being moved, but also 
in jurisdictions through which the move is passing. Approvals 
for transport in a public right-of-way may be required 
from local governments, highway departments, and utility 
companies. Often approvals may be necessary from private 
landowners whose properties are either crossed or affected 
by the move. 

The time required to obtain approvals and the complexity of 
information some parties may require in order to provide 
approvals may vary widely. The designer/contractor and 
homeowner should investigate this approval process early in 
the relocation effort to minimize potential delays due to 
obtaining permits. 

COORDINATE ROUTE PREPARATION 

The moving contractor should be responsible for the necessary 
coordination made along the moving route. This 
includes: 

* the raising or relocation of utilities by utility companies; 
* any road/highway modifications, such as traffic lights, 
signage, temporary bridges, etc; and 
* clearing/grubbing of overland areas, where necessary. 
The moving contractor should also be responsible for 
making sure that these facilities are returned to their normal 
operating condition as soon as the move is completed. 

Engineering Principles and Practices of F RetrofittingFlood-Prone Residential Structures VI -R.13 
January 1995 


Chapter VI: General Design Practices 

1 < Relocation 

STEP 6-PREPARATION OF THE STRUCTURE 

The steps involved in preparing a structure to be moved are 
described below. 

DISCONNECT UTILITIES 

The first step in preparing the structure is to disconnect all 
the utilities connected to the structure. Specific requirements 
governing the capping, abandoning, and/or removal 
of specific utilities should be available from the local utility 
companies and/orthe local regulatory officials. 

CUT HOLES IN FOUNDATION WALL 
FOR BEAMS 

From beneath the structure, the pathways for lifting beams 
are cut in the existing foundation. 

Figure VI-R6: Pathways for Lifting Beamns 

VI -R.14 Enaineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Strujchiran 
January 1995 


Step 6 -Preparation of the Structure 

.0-,

|~~~~~~~~~~~~~~~~~~~~~~ 

FigureVI-R7: Beams Supported by Cribbing are Placed at Critical Lift Points 

INSTALL BEAMS 

Lifting and lateral beams are placed beneath the structure at all
critical lift points and support cribbing is added as the structure
is separated from its old foundation.

INSTALL JACKS 

Jacks are used to lift the structure from its foundation. Various
types of jacking systems may be employed as long as gradual
and uniform lifting pressures are utilized to lift the structure.

Ennineerina Princinles and Practices of F letrofittina Flood-Prone Residential Structures VI -R.15 
January 1995 


Chapter VI: General Design Practices 

Relocation 

INSTALLBRACING AS REQUIRED 

Bracing may need to be installed to maintain the integrity of the 
structure. 

SEPARATE STRUCTURE FROM 
FOUNDATION 

The structure now stands free from its former foundation. 

Figure VI-R8: Structure is Separated from Foundation 

VI -R.16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Step 7 -Moving the Structure 

STEP 7 -MOVING THE STRUCTURE 

Once the structure has been raised, it is transported to the 
new site. This process is outlined below. 

EXCAVATE/GRADE TEMPORARY 
ROADWAY 

Excavation and grading of a temporary roadway is done at 

one end of the structure. The truck wheels, which will form 

the trailer that will be used to move the house, are brought 

to the site and placed beneath the lifting and lateral beams. 

Figure VI-R9: Excavation of Temporary Roadway 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -R.17 
January 1995 


Chapter VI: General Design Practices 
Relocation 

Figure VI-RIO: Trailer Wheel Sets are Placed Beneath the Lifting Bearns 

ATTACH STRUCTURE TO TRAILER 

The house is attached to the truck wheels and then attached to 

the tractor/dozer in preparation for the moving ofthe structure 

from its original site. The tractor/dozer is used to pull the house 

to street level, while workers continually block the wheels to 

prevent sudden movement. At street level, the house is stabi

lized and a truck is connected to the trailer for the journey to the 
new site. 

VI -R.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Step 7 -Moving the Structure 

Figure Vl-RI 1: House is Lowered onto Trailer Wheel Sets 

Figure Vl-R 12: Trailer is Used to Pull House to Street 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -R.19 
January 1995 


Chapter VI: General Design Practices 

0 % 

~~~~Relocation 

_I 
.''_ 
o street level, workers continually 
dden movement. 
F i g u r 
V I 2-R.2 0,; 
Vj-1 4 Ho s i s S t a b i li'z e d is|. 4 , , ; . 
E n g n e e i n Princi6* E: 

and Connected to Trailer 

s and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Step 7 -Moving the Structure 

TRANSPORT STRUCTURE TO NEW 
SITE 

With connections to the truck completed, the actual transport of 
the structure to the new site begins. 

Figure VI-RI 5: Journey to New Site Begins 

Engineering Principles and Practices of R etrofitting Flood-ProneResidential Structures VI -R.21 
January 1995 


Chapter VI: General Design Practices 

Relocation 

STEP 8- PREPARATION OF THE NEW SITE 

The new site is prepared for the arrival of the structure. 

DESIGN FOUNDATION 

The steps needed to design the new foundation have been 
defined in the Elevation portion of this chapter. 

DESIGN UTILITIES 

Utilities must be available to be brought directly to the 
structure at the new site. Construction should be accomplished 
in accordance with the approved set of design 
documents prepared for the new site and any building 
permit conditions specified by local officials (as explained in 
Step 3). 

EXCAVATION AND PREPARATION OF 
NEW FOUNDATION 

At the new site, excavation and preparation of the foundation 
are underway. 

FigureVI-R16: Foundation PreparationatNewSite 

VI -R.22 Ennineerino PrinCinles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Step 8 -Preparation of the New Site 

CONSTRUCTION OF SUPPORT 
CRIBBING 

Support cribbing is put in place to allow the structure to be 

jacked up and the truck wheel sets are removed. With 
support cribbing in place, materials for completion of the 
foundation are readied. 

Figure VI-RI 7: Support Cribbing is Placed 

A_ 

Figure VI-RI 8: Materials for New I Foundationare Readied 

Engineering Principles and Practices of I Retrofitting Flood-Prone Residential Structures VI -R.23 
January 1995 


Chapter VI: General Design Practices 

Relocation 

CONSTRUCTION OF FOUNDATION 
WALLS 

The foundation wall construction begins. 

LOWER STRUCTURE ONTO 
FOUNDATION 

Once the desired height of the new wall is reached, the house is 
lowered onto its new foundation, cribbing is removed, and 
foundation walls are completed. 

Figure VI-RI 9: New Foundation Wall Construction Begins 

VI -R.24 Engineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Step 8 -Preparation of the New Site 

Figure VI-R20: Once foundation walls are completed, house is lowered and 
connected to foundation. 

LANDSCAPING 

Finishing touches, like preparing the foundation for backfilling, 
are done to blend in the house with its new environment. 

' ! Yi _!,, _.}

1 \ES.. 0tI :0 

heI, -S 

Figure VI-R2 1: Final Preparations foorBackfil ling and Landscaping 

Engineering Principles and Practices of F etrofitting Flood-Prone Residential Structures VI R.25 
January 1995 


Chapter VI: General Design Practices 

19 Relocation 

STEP 9 -RESTORATION OF OLD SITE 

Once the structure is removed from the site, certain steps 
need to be taken to stabilize the site in accordance with 
local regulations. Many homeowners have sold or deeded 
these abandoned properties to local municipalities for the 
development of parkland and/or open space. In any case, 
permits for the demolition of the old site, remaining foundation, 
and remaining utility systems, as well as grading and 
site vegetative stabilization are normally required. 

DEMOLISH AND REMOVE 
FOUNDATION AND PAVEMENT 

The old basement may have to be backfilled to eliminate any 

potential hazard. Check local regulations to see if old 

foundation and utility connections have to be removed. 

DISCONNECT AND REMOVE ALL 
UTILITIES 

Following up on the disconnection and capping of utility 
servicespreviously discussed in Step 2, the homeowner mayA'00 be required to remove all existing utility systems from the 
site. Septic tanks and oil/gas storage tanks on site may be 
Materialfrom drained septic,oil, governedby specific environmental guidelines, which must 
and gas storagetanks must be be followed to ensure that leakage to groundwater sources 
disposed of in a safe and legal... 

manner. does not occur. Depending upon the age and condition of 
the tanks, the homeowner may be required to drain and 
remove these tanks, or drain and stabilize the underground 
tanks against flotation. 

The homeowner may also be required to test the soil around 
an underground tank to determine if leakage has occurred. 
If leakage is confirmed, the homeowner is usually responsible 
for cleaning the contaminated soils. When facing this 

VI -R.26 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Step 9 -Restoration of Old Site 

situation, the homeowner should contact a qualified 
geotechnicalor environmental engineer. Specific requirements 
governing the capping, abandoning, and/or removal of 
specific utilities should be determined from the local utility 
companies and/orthe local regulatory officials. 

GRADING AND SITE STABILIZATION 

The old site may have to be regraded after all the excavation 
and movement by the heavyequipment. The lotwill need 
to be stabilized with vegetation as appropriate to its intended 
future use. 

----Prn^ti~nol

Ef-nooin nilo ::ln-nilFPRtrofittinf, Flrood-Prnne RsidAntial Structures VI -R.27

JnrlylrleerIIly III C -Is V -a l_

15 . 
January 1995 


Dry Floodproofing
Table of Contents

-
Emergency Operations Plan ...................................................... VI -D.3
Inspection and Maintenance Plan ...................................................... VI -D.4
Sealants and Shields ...................................................... VI -D.5
FieldInvestigation............................................................................................................... VI -D.12
Design.......... VI -D. 14
Confirm Ability of Structure to Accommodate Dry Floodproofing Measures ............. VI -D. 14
Selection and Design of Sealant Systems ...................................................... VI -D.23
Coatings...................................................... VI -D.23
WrappedSystems ...................................................... VI -D.24
Brick Veneer Systems ...................................................... VI -D.28
Selectionand Design of Shield Systems...................................................... VI -D.32
PlateShields...................................................... VI -D.32
Construction Considerations for Sealants and Shields ...................................................... VI -D.49
DrainageCollectionSystems...................................................... VI -D.50
FrenchDrains ...................................................... VI -D.52
Exterior Underdrain Systems ...................................................... VI -D.53
InteriorDrainSystem ...................................................... VI -D.56

Dry Floodproofing ...................................................... VI D.1

Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures VI-D.i 
January 1995 


SumpPumps ..................................... VI -D.58
Typesof Sump Pumps .................................... .VI -D.58
Iiltrationvs. Inundation..................................... VI -D.59
Coordination with Other Floodproofing Methods ................. .................... VI -D.5 9
Field Investigation ..................................... VI -D.60
Design.V ................ VI -D.63

BackwaterValves. VI -D.722................ 
Field Investigation ............... VI -D.74
Design............... VI -D.74

Emergency Power ............... VI -D.79
Field Investigation .................................................................................................... VI -D.81
Design .......... VI -D.82
Construction .......... VI -D.91

VI -D.ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


DRY FLOODPROOFING 

Dry floodproofing measures can be described as a combination of adjustments and/or additions 
of features to buildings that eliminate or reduce the potential for flood damage by keeping 
floodwaters out of the structure. Examples ofthese adjustments and additions include: 

* installation of watertight shields for doors and windows; 
* reinforcement of walls to withstand floodwater pressures and impact forces generated by 
floatingdebris; 
* use of membranes and other sealants to reduce seepage of floodwater through walls and wall 
penetrations; 

* installation of drainage collection systems and sump pumps to control interior water levels, 
collect seepage, and reduce hydrostatic pressures on the slab and walls; 
* installation of check valves to prevent the entrance of floodwater or sewage flows through 
utilities;and 

* anchoring ofthe building to resist flotation, collapse, and lateral movement. 
Buildings that are dry floodproofed may be subject to extensive 
hydrostatic and other forces against the foundation and other 
exterior walls and surfaces. As was illustrated in Chapter IV, 

Dry floodproofing is not allowed hydrostatic and soil pressures increase with the depth of flood-
by FEMA for new or substantially ing. For that reason, foundation walls have severe limitations 
improved or damaged residential with regard to the use of dry floodproofing measures. A critical 

structures located in the flood-design consideration is the comparison ofthe ability ofthe 
plain. existing foundation walls to withstand the expected flood-

related and non-flood-related forces with and without additional 
strengthening measures. 

:~ orlr Drenti.J e nf RntnDfittinnMlnnH-Pran Resirdential truirtures Vi -D.1 

-_: -----------

U1 1

Engineering1 r9nc5plubEll0 UC V II U1 Ii I -ow 

January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

In this section (see Figure VI-D 1) the process of selection and 

design ofsealants, shields, drainage collection systems, sump 

pumps, and backflow valves and the provision of emergency 
power to operate necessary drainage systems are discussed. It 
is important that the designer understand that dry floodproofing 

measures are typically needed as part of most retrofitting 

measures. Each link in the retrofitting system must be designed 

to work in concert with the others to provide the level of 

protection desired. 

Field Investigation 
L I 

.4r 

1 
Selection and Design

II 
i 

Confirm Ability of Structure to Accommodate
Dry Floodproofing Measure

t 

Select and Design Sealants and Shields 

Select and Design Drainage Collection Systems 

Select and Design Sump Pumps 

Select and Design Backflow Valves 

Provide for Emergency Power for Drainage System Operation 

I

+~~~~~~~~~~~~ 

Prepare Emergency Operation Plan 

T 

Prepare Operation & Maintenance PlanI 

Construction of Dry
IFloodproofing Measures

Figure VI-D1: Process of Selection and Design for Dry Floodproofing 

VI -D.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Emergency Operations Plan 

One critical aspect of a successful design of a dry floodproofing 

measure is the development of Emergency Operation and 

Inspection and Maintenance Plans. Some of the important 

elements ofthese plans are presented below. 

For additional information on dry 

floodproofing, refer to FEMA
Technical Bulletin 3-93, Non-
ResidentialFloodproofing-
Requirementsand Certification

for Buildings Locatedin Special
Flood Hazard Areas in Accor-
dance withthe NationalFlood
InsuranceProgram.

EMERGENCY OPERATIONS PLAN 

A plan for notifying homeowners (community flood warning 
system) of the need to install dry floodproofing components and 
the chain of command/resources (human intervention) to carry 
out the installation of dry floodproofing measures are two 
critical aspects of an effective emergency operations plan. In 
addition, a suitable evacuation plan and periodic training in the 
installation of dry floodproofing measures are important elements 
in ensuring their effectiveness. 

G o d ~ Patrnittinn FlnrI-Prnna RaidantialStructures vi -D.3 

JaglnuaIr II lu r- III , va -.y .

1995 I I vmnlwwa 
January 1 995 


Chapter VI: General Design Practices

Y y> 

Dry Floodproofing 

INSPECTION AND MAINTENANCE PLAN 

Every dry floodproofing system requires some degree of 
periodic maintenance and inspection to ensure that all components 
will operate properly under flood conditions. Components 
that should be inspected as part of an annual maintenance 

and inspection program include: 

* All mechanical equipment such as sump pumps and generators; 
* Flood shields, to ensure that they fit properly and that the 
gaskets and seals are in good working order, properly 
labeled, and stored where accessible; and 
* Sealed walls and wall penetrations, for cracks and potential 
leaks. 
_. ,; s ---of Rptrnfittinn Fln-nPrPnna >iuvuett QIUL&UIr+ CO

VI -D.4 Enaineerina PrinciolesandPranfimce-..._ ..... .. _z-* .----, .w Iv$ t~*%JvI faoirlantilo OCtrnnhi 

January 1995 


Sealants and Shields 

SEALANTS AND SHIELDS 

Sealantsand shields are methodsthat can be used to protect a 
structure from low-level flooding. Mini-floodwalls (low level) 
can be used as an alternative to shields for protection of windows, 
window wells, or basement doors. These systems are 
easily installed and can be inexpensive in relation to other 
measures such as elevation or relocation. However, by sealing 
(closing) a structure against flood inundation, the owner must 
realize that, in most cases, the typical building will not be 
capable of resisting the loads generated by more than a few feet 

Floodwallsandfloodwallclosures of water. There will be a point beyond which the sealants and 
are discussed in Section F of this shields may do more harm than good and the owner must allow 
chapter. the building to flood to prevent structural failure from 

unequalized forces. 

The U.S. Army Corps of Engineers,National Flood Proofing 
Committee, has investigated the effect of various depths of 
water on brick veneer-over-wood and masonry walls. The 
results of their work show that, as a general rule, no more than 
three feet of water should be allowed on a brick veneer wall or 
ona non-reinforced concreteblockwallthathas not previously 
been designed and constructed to withstand flood loads. While 
no definitive research on floodproofing wood-frame walls 
without brick veneer facing has been undertaken, it is generally 
accepted that wood-frame houses will fail at a lower water 
depth than a masonry or brick veneer home. Therefore, 
application of sealants and shields should involve a deternination 
of the structural soundness of a building and its corresponding 
ability to resist flood and flood-related loads. 

Sealants include compounds that are applied directly to the 
surface ofthe structure to seal exterior walls and floors, or a 
wrapthat is anchoredto the exteriorwallor foundation ator 
below the ground and attached to the wall above grade during 
flooding. The owner may wish to add to the structural strength 
ofthe existing building to aid in resisting flood-induced loads 
(for example adding a brick veneer). 

-

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI D.5 

January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Any dry floodproofing system can be expected to allow some 

water infiltration, and the owner should have a dewatering 

system capable of removing the water. Due to this infiltration 

through exterior walls and floors and percolation ofthe water 

around ground anchored wraps, these systems are not recom

mended for situations where floodwater is in contact with the 

building for more than 12-24 hours. Underlying soils often 

dictate the allowable period of inundation before water starts to 

percolate through the sealant system. 

Existing Brick Veneer Sheathing 

Brick Rowlock ,Wood Frame Wall 
or CMU Block Wall 

Flood Protection Elevation\ C
s F f reebo ard) 

~~(includes :
New Brick Work -Metal Fasteners

Coating and Waterproofing Tie New Brick to Old Brick 

Add Concrete Footing ting Drill and Grout 

Drain to Sump Pump with Connection to
Backup Power Source Existing Footing

Figure VI-D2: The best way to seal an existing brick-faced wall is to add an additional layer of 
brick with a seal in between. Just sealing the existing brick is also an option. 

VI -D.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sealants and Shields 

-A1--A 

_-V L< Flood Protection Elevation 
'WI, (Includes Freeboard) 
1 Freeboard 

Sheathing V, Flood Elevation 

Attach to House 

Wood Frame Wall 6 Mil. Polyethylene Place Loosely on Wall
_ Z Brick Veneer

4' PVC Perforated Pipe (Drain to Sump with 
Backup Power Source) 

Sand Bags 

Loose Sand 

Slabto

Monolithic 

and Footing 

Figure VI-D3: A wrapped house sealing system can be used to protect against low level flooding. 

Shields are watertight structural systems that bridge the openings 
in a structure's exterior walls. They work in tandem with 
the sealants to resist water penetration. Steel, aluminum, and 
plywood are some of the materials that can be used to fabricate 
shields. These features are temporary in most cases, but may 
be permanent when in the form of a hinged plate or a mini-
floodwall at a subgrade opening. Shields transfer flood-induced 
forces into the adjacent structure components and, like sealants, 
can overstress the structural capabilities ofthe building. 

EnnineerinnPrincinles and Practices of Retrofittina Flood-Prone Residential Structures VI -D.7 
January 1995 


Chapter VI: General Design Practices 
Dry Floodproofing 

Figure VI-D4: A shield hinged at its bottom 
could prevent low-level flooding from 
entering a garage or driveway. 

Shield e 1' Freeboard 
Panel 

Shield 
Track 

Figure VI-D5: A door opening may be closed using a variety of materials for shields. 

Vi -D.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sealants andShields

Connection 

Figure VI-D6: A shield can help prevent low-level flooding from entering through a doorway. 

Figure VI-D7: Where a window is exposed to a flood, bricking up the opening could eliminate the 
hazard. 

The use of sealants and shields requires that the house have a 
well-developed interior drain system to collect the inevitable 
leaks and seepage that will develop. This means establishing 
drains around footings and slabs to direct seepage to a central 
collection point where it can be removed by a sump pump. 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -D.9 
January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Additionally, abuilding employing sealants and shields will 
usually need backflow devices and other measures designed to 
eliminate flooding thiugh utility system components. Additional 
information on this topic is presented later in this section. 

-

Never seal a floodprone basement unless a Lower level should only be 
structural analysis indicates the structure can used for parking, storage, 
withstand flood and flood-related loads. and access. 

l~~~~~~~~~~~------

Ie 

Ela Hi lzr 
Downspout 

Aiii -__ ___ii' 

r ->1 Fr ) Sunppurnp

(' -ii C.")i' ") ll-4 ( 2 2 J< dischargeFP

AIL 

,Jim 

Footing 
drain _1 l ~~~~~~~d~r~ain

i nfreeboard)

TT-~Floor drain 

I _ 

Footing ANAL~~

H1lr, 

Sanitarysewerserviceline Back'lowvalve 

Figure VI-D8: Dry floodproofed homes should have an effective drainage system around footings 
and slabs to reduce water pressure on foundation walls and basements. 

VI -D.10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sealants and Shields 

Drain System Around a House 

: | 1.'".' s %7I V 9 I

4" Non-Compacted Gravel, Pipe to Sump 
Crushed Stone Footing Drai _ional 4 

Footing -> 
Waterproofing \ Sewer Backup Valve 
4" Compacted Gravel, 

Crushed Stone Underdrain \ Sump Pump with Backup Power Source 
Figure VI-D9: Drain System Around a Slab-on-Grade House 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-D.11 
January 1995 


Chapter VI. General Design Practices 

() 3 > DryFloodproofing 

FIELD INVESTIGATION 

In addition to, or during consideration of, the field investigation 
information compiledon the existing building/building systems 
data sheet (Figures VI-3 and VI-4), the designer should 
concentrate on collecting or verifying the following items: 

* condition of existing framing, foundation, and footing; 
* determination of existing materials used in the house to 
calculate dead weight; 
* determination oftype of soil, lateral earth pressures, permeability, 
and seepage potential; 
* building's lateral stability system and adequacy of structural 
load transfer connections; 
* foundation wall, footing, and slab information (thicknesses, 
reinforcement, condition spans, etc.); 
* number, size, and location of openings below the FPE; 
* expected flood warning time; 
* evidence of previous, and potential for continued, settlement, 
which could cause cracking after sealant is applied; 
* estimates of leakage through the exterior walls and floor; 
e 

manufacturer's data to determine applicability of sealant 
materials in terms of above- and below-grade applications, 
and duration of water resistance; 

* potential anchorage to secure wrapped systems; 
VI -D.1 2 Enoineerina Princinies and Practices of Retrmfittinri Flood-Prone PRsidlentialSt intiirum

D_ __ wry a . . v. ._ . .__.__ .. l.Hanuar-199

-+;s 

January 1 995r 


Field Investigation 

* preliminary selection of shield material to be used based 
upon the length and height ofthe openings and duration of 
flooding; and 
* preliminary selection oftype of shield anchorage (hinged, 
slotted track, bolted, etc.), to be utilized by considering 
accessibility, ease of installation, and amount oftime available 
for installation. 
Using this information, a designer should be able to determine if 
a system of sealants and shields is an option. Of course, further 
calculations or conditions may dictate otherwise, or that modifications 
should be made to accommodate the system. The 
designer can take the information gathered in the field and begin 
to develop type, size, and location alternatives. 

Sealant alternatives include: 

* cement-and asphalt-based coatings, epoxies and polyurethane-
based caulks/sealants; 
* membrane wraps such as polyurethane sheeting; and 
For additional information concerning 
the performance of various 
sealant systems, refer to the U.S. * brick veneers over a waterproofcoating on the existing 
Army Corps of Engineers research foundation. 

study entitled Flood Proofing
Tests, August 1988, and product Shield alternatives include:
evaluation reports prepared by
model code groups.

* a permanent low wall to protect doors and window wells 
againstlow-levelflooding; 
* bricking in a nonessential opening with an impermeable 
membrane; 
* drop-in, bolted, and hinged shields that cover an opening in 
the existing structure. 
Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -D.1 3 
January 1995 


Chapter VI: General Design Practices 

< m Dry Floodproofing 

Shield alternatives that require human intervention should be 

considered only ifthe flooding situation provides sufficient 

warning time to properly install the shields. The need for both 

sufficient warning time and "human intervention" is critical, since 

shield systems usually require personnel to install them and 

make certain they are properly connected. 

DESIGN 

CONFIRM ABILITYOF STRUCTURE 

TO ACCOMMODATE DRY 

FLOODPROOFING MEASURES 

A critical step in the development of initial type, size, and 
location ofthe sealant and shield systems is to determine the 
ability ofthe existing framing and foundation to resist the expected 
flood-and non-flood-related forces. This process is 
illustrated in Figure VI -D 1 0: Existing Building Structural 
Evaluations. 

Step 1: Calculate flood and flood-related forces. 

The calculation of flood and flood-related forces (hydrostatic, 

hydrodynamic, debris impact, soil, and buoyancy forces) as 

well as determination of seepage and interior drainage rates) 

was presented in Chapter IV. The designer should account for 

any non-flood-related forces (i.e., wind, seismic, etc.) by 

incorporating those forces into Steps 2-6. The determination of 

non-flood related forces was presented in Chapter IV. 

VI -D.14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Existing Building Structural Evaluations 

Calculate Flood and
I Flood-Related Forces I

Figure VI-D 10: Existing Building Structural Evaluations 

Engineering Principles and Practicesof Retrofitting Flood-Prone ResidentialStructures VI -D.15 
January 1995 


Chapter VI:General Design Practices 
K K < Dry Floodproofing 

Step 2: Checkflotation ofthe wood-frame superstructure. 

Residential structures that are determined to be watertight 

should be checked to ensure that the entire sub- and super

structure will not float. However, it is reasonable to assume that 

most residential construction will fail prior to flotation ofthe 

structure. This failure will most likely occur through the slab-

on-grade breaking (heaving/cracking), a window or door failing 

inward, or extensive leakage through wall penetrations. Should 

the designer wishto check the failure assumption, guidance is 

provided in Step 5. If floodwaters come into contact with a 

wood floor diaphragm (elevated floor or crawlspace home) the 

floor system/building superstructure should be checked for 
flotation. 

Check the sum ofthe vertical hydrostatic (buoyancy) forces 

acting upward against the gravity forces (deadload) acting 

downward on the structure. The gravity forces acting down

ward should be greater than the buoyancy forces acting up

ward. If this is not the case, the designer should consider 

choosing another floodproofing method or designing an anti-

flotation system. The homeowner should make this decision 

based upon technical and cost information supplied by the 

designer. 

Step 3: Check ability of walls to withstand expected forces. 

Frames and connections for closures transfer the retained forces 
The typical failure mode for a into the adjacent walls. Typically a vertical strip on each side of 
shield installation is the "kick-in" the opening must transfer the load up to a floor diaphragm and 
of the bottom connection where down to the floor or foundation. This "design strip," shown in 
hydrostaticforces are the greatest. Figure VI-D 11,must be capable of sustaining loads imposed on 

itself and from the openings. The designer should consider all 
forces acting on the design strip, as well as the following additional 
considerations: 

a. Checkdesign strip based on simple span, propped cantilever, 
cantilever, and other end conditions. Consider the 
moment forces into the foundation. 
VI -D.16 Enaineerina Principles and Practices of Retrofittino Flood-Prone Residential Structures 
January 1995 


Design 

Effective design strip width 
based on building code 

Figure VI-D I 1: Typical Design Strip 

b. Check design strip for bending and shear based on concrete, 
wood, masonry, or other wall construction. 
c. Consider the path of forces from shield into the design strip 
through the various connection alternatives including hinges, 
drop-in slots, frames, and others. 

d. The designer may want to refer to the American Institute of 
Steel Construction (AISC) Steel Manual, American Concrete 
Institute (ACI) documents for concrete and masonry 
construction, National Design Specifications of Wood 
Construction (NDS)/ American Institute of Timber Construction 
(AITC) documents for timber construction, APA 
documents for plywood, and other applicable codes and 
standards for more information on the ability of these 
materials to withstand expected flood and flood-related 
forces. 
Fnnineerina Princioles and Practices of FletrofittinaFlood-Prone Residential Structures VI -D.17 
January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Step 4: Check ability of footing to support veneer applications. 

The application of veneer to the exterior of an existing wall must 
be supported at the footing level. The designer should consider 
all forces acting on the existing footing, as well as the following 
additional considerations: 

a. Supporting the masonry veneer on an existing footing can 
add an eccentric load onto the footing and can create soil 
pressure problems. The designer should analyze the footing 
with the additional load considering all load combinations 
including the flooded condition. 
b. The actual pressure on the footing should not overload the 
bearing capacity of the existing soils. Consult a 
geotechnical engineer, ifnecessary. 
c. The designer may want to refer to the ACI Manual for 
Concrete Construction, various soils manuals/textbooks for 
detailed footing design, and applicable codes and standards. 
Step 5: Check slab and connections against uplift forces. 

As floodwaters rise around a structure, a vertical hydrostatic 
(buoyancy) force builds up beneath floor slabs. For floating 
slabs, this buoyancy force is resisted by the structure dead load 
and saturated soil above the footing; for keyed-in slabs, this 
buoyancy force is resisted by the structure dead load, and the 
flexural strength ofthe slab. These slabs must be capable of 
spanning from support to support with the load being applied 
beneath the slab (see Figure VI-D 12). The designer should 
consider all forces acting on the existing slab and connections, 
as well as the following additional considerations: 

VI -D.18 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Design 

Figure VI-D 12: Typical Slab Uplift Failure 

a. Verify the existing slab conditions including thickness, 
reinforcement,joint locations, existence of continuous slab 
beneath interior walls, existence of ductwork in slab, and 
edge conditions. If reinforcement and thickness are not 
easily determinable, make an assumption (conservative) 
based on consultation with the local building official or 
contractors. 
b. Confirm the slab design by checking reinforcement for 
bending and edge connection for shear load. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-D.19 
January 1995 


Chapter VI: General Design Practices 
/X()Dry Floodproofing 

Step 6: Check stability oftop offoundation wall connections. 

Foundation walls may retain water in some situations. These 
walls must transfer the additional hydrostatic load down to the 
footing or slab and up to the floor diaphragm. The designer 
should consider all forces acting on the top ofthe existing 
foundation wall connections, as well as the following additional 
considerations: 

a. Verify existingwall conditions including construction material, 
reinforcement, design conditions (simple span, propped 
cantilever, cantilever, and other end conditions), and connections. 
b. Connections between the wall and floor are of major 
importance in consideration ofthe wall stability. The 
designer should check the following: 
1. masonry/concrete for shear from bolt; 
2. anchor bolt for shear; 
3 . sill for bending from bolt loads; and 
4. transfer of load from sill intojoists into plywood 
diaphragm. 
5. Loads have a pathway out ofthe structure. Additional 
bracing and/or connectors may be required to provide 
this pathway. Analyze framing and be cognizant that all 
sides may be loaded. 
c. The designer may want to refer to the ACI Manual for 
Concrete Construction, ND S/AITC for timber construction, 
AISC for anchor bolts, product literature for wood 
connectors, and applicable codes and standards. 
VI -D.20 Engineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Structures 
January 1995 


Design 

-

Step 7: Design foundation supplementation system, as required. 

If the checks in Steps 2-6 determined that any structural 
members were unable to withstand expected flood and flood-
related loads (wind, seismic, and other forces can be evaluated 
as presented in Chapter IV), the designer can either select 
another retrofitting measure or design foundation supplementation 
measures. These foundation supplementation measures 
could range from increasing the size of the footing to adding 

shoring to the foundation walls, or simply modifying the type, 

size, number and location of connections. The homeowner 

should make this decision based upon technical and cost 
information supplied by the designer. 

Footing Reinforcing: in some cases, the footings for walls 
must be modified to accommodate expected increased loadings. 
The following considerations should be taken into account 
during the design ofthis modification: 

a. The wall footing must be checked for the increased 
soil pressure and sliding. Moment and vertical loads 
from the wall above should be added. 

b. The footing may need more width and reinforcement to
distribute these forces to the soil.
c. For some extreme cases (poor soils, high flood depths, 
flood-related wind and/or earthquake loads), a 
geotechnical engineer may be required to accurately 
determine specificsoil loads and response. 

d. The designer should consider multiple loading situations
taking into account building dead and live loads that are
transferred into the footing, utilizing whatever load
combinations are necessary to design the footing safely
and meet local building code requirements. Consider
the framing of the structure andhow the entirehouse load
is transferred into the foundation.
Pnninnnrmni Prin-inl=s and Practices of Retrmfiftinn Flood-Prone ResidentialStructures VI -D.21 

Januayll IIIV 1 1 | I V A 

IVV 1995| January 
1 995 


ChapterVI: GeneralDesign Practices 

< k~ DryFloodproofing

Dry floodproofing measuresare 

only as good as their weakest link 
(i.e., the connection to the existing 
structure). The designer should 
ensure that all appropriate details 

for making theconnectionwater-
tight as well as allowing for the 
transfer of loads are developed. 

e. The designer may want to refer to the ACI Manual for 
Footing Design, recent texts for wall and footing design, 
and applicable codes and standards. 
Step 8: Repeat process in Steps 1-7 incorporating exterior 
wall foundation supplementation system. 

Once the designer has detenminedthat the existing framing and 
foundation are suitable forthe application ofsealants or shields, or 
that reinforcement can be added to make the existing framing 

and foundation suitable for te application of sealants or dosures, 
the selection/design of a specific system can begin. 

VI -D.22 Enaineerina Principles and Practices of Retrofittino Flond-Prone Resirintili Striinti res 
January 1995 


Selection and Design of Sealant Systems 

SELECTION AND DESIGN OF SEALANT SYSTEMS 

Once the determination is made that a foundation system can 
withstand the expected flood and flood-related forces, the 
selection of a sealant system is relatively straightforward and 
centers on the ability ofthe manufacturer's product to be com

product performance, if available, patible with the length and depth of flooding expected and the 
should be used to supplement the type of construction matenalsusedin the structure. 
manufacturer's literature. Sources 
of test results include model COATINGS 
building code product evaluation C A I S 

reports, a USACE publication 
entitled Flood Proofing Tests, The selection of a coating follows the flow chart presented in 
August 1988, and local building Figure VI-Di 3, Selection of Sealants/Coatings. If additional 

code officials. 
structural reinforcing is required, it should be performed in 
accordance with the guidance presented in the preceding section 
entitled "Confirm Ability of Structure to Accommodate Dry 
Floodproofing Measures." 

r . nnnc ind ~ ,Drmiiem FlRood-ProneResidentialStructures VI-D.23
A -inlp of Rtrnfittinn

Jauayl 1995ll v * w

II IV I rVVI l 

January 1 995 


ChapterVI: General Design Practices 
Dry Floodproofing 

Selection of Sealants/Coatings 

1K 

Design Interior Drainage Collection System 

Figure VI-D 13: Selection of Sealants/Coatings 

WRAPPED SYSTEMS 

The selection and design of a wrapped system follows Figure 

VI-D 14, Selection and Design of a Wrapped Sealant System. 

If additional structural reinforcing isrequired, it should be 

performed in accordance with the guidance presented in the 

preceding section. 

VI-D.24 Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures 
January1995 


Selection and Design of Sealant Systems 

Selection and Design of Wrapped Sealant System 

Figure VI-D14: Selectionand Design of Wrapped Sealant Systems 

VI-D.25 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -D.25 
January 1995 


Chapter VI: GeneralDesign Practices 
O9 > Dry Floodproofing 

Step 1: Selecttype and grade of material. 

Step 2: Checkmanufacturer'sliteratureagainstdurationand 
al-depthof flooding. 

For additional informationconcern-If flooding application is satisfactory, proceed with design; if not 

ingtheperformanceof various satisfactory, select another product or another method. 

sealant systems, refer to the U.S. 

Army Corps of Engineers research 
studyentitledFlood Proofing Step 3: Checkmanufacturer's literature forapplicabilityto 

Tests, August1988,andproduct building materials. Rely on actual test results, if 

evaluation reports prepared by available. 
model code groups. 

If building materials application is satisfactory, proceed with 

design; if not satisfactory, select another product or another 
method. Manufacturer performance claims can be misleading. 
The designer should utilize actual test results rather than rely 
entirely on a manufacturer's performance claim. 

Step 4: Check installation instructions for applicability. 

If installation procedure is satisfactory, proceed with design; if 

not satisfactory, select another product or another method. 

Step 5: Designconnectiontotopofwall. 

Adding a wrap system onto an existing structure will require 
secureconnections atboth the top and bottomofthe wrap. It 
is difficult to determine the actual loads imposed vertically on 

the wrap as this can vary based upon the quality of the installa

tion. Voids left from poor construction may force the wrap to 
carry the weight ofthe water and should be avoided. See 
Figure VI-D 15. The following considerations should be 

followed during selection and design of a top-of-wall connectionsystem: 

VI -D.26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structiures 
January1995 


Selection and Design of Sealant Systems 

Figure VI-D15: Plan View ofWall Section 

a. Use a clamping system that uniformly supports the wrap. A 
smallspacingonthe connectionsand a member with some 
rigidity on the outside ofthe wrap can provide this needed 
support. 
b. The existing wallconstruction is an importantconsideration 
for these connections and canvary widely. Part of 
the connection may need to be a permanent part of the 
wall. 

See Figure VI-D3fordetails on 
wrapped system configuration. 
c. The designer may want to refer to the product literature 
for wrap material, NDS/AITC for connections into 
wood, and applicable codes and standards. 
Step 6: Designfoundationreinforcing. 

Refer to Chapter VI -Dry Floodproofing Section entitled 
"Confirm Ability of Structure to Accommodate Dry Flood-
proofing Measures." 

Step 7: Design drainage collection system. 

Refer to Chapter VI -Dry Floodproofing Section entitled 
"Drainage Collection Systems." 

ResidentialStructures

C^^;naar~n-D0-fn^ ,i f RQtrnfittinn Flonod-Prone VI -D.27 

January 1995 


Chapter VI:General Design Practices 

Dry Floodproofing 

Step 8: Specify connection of wrapping to existing structure 
and existing grade. 

Wrapsystemsmaybe affectedby Anchoring a wrap into the grade at the base of a wall will be the 
freeze-thawcycles.Careful most important link in the wrap system. The following considinstallationin 
accordancewith erations should be followed during selection and design of a 
manufacturerinstructionsand wrap to existing grade connection system:
evaluation ofperformance in frozen 
climates is advisable. 

a. A drain line between the wrap and the house is required 
to remove any water that leaks through the wrap or that 
seeps through the soil beneath the anchor. 
b. As with the top-of-wall connection, wrap forces are 
difficult to determine. It is best to follow details that 
have worked in the past and are compatible to the 
specific structure. 
c. It is recommended that the end of the wrap be buried at 
least below the layer oftopsoil. Additional ballast may be 
needed (sandbags, stone, etc.,) to prevent wrap movement 
in a saturated and/or frozen soil condition. 
d. The designermaywantto referto theproductliterature for 
wrap material and applicable codes and standards. 
BRICK VENEER SYSTEMS 

The selection and design of a brick veneer sealant system 
follows Figure VI-D 16,Selection/Design of a Brick Veneer 
Sealant System, and has many components that are similar to 

SeeFigureVI-D2fordetailson the design of other sealant systems. A typical brick veneer 
brickveneersystemconfiguration. sealant system is shown in Figure VI-D2. Ifadditional structural 
reinforcing is required, it should be performed in accordance 
with the guidance presented in the preceding section. 

VI -D.28 Enaineering Principles and Practices of Retrofitting Flond-ProneRPsidentialStruirtu ires 
January 1995 


Selection and Design of Sealant Systems 

Selection and Design of Brick Veneer Sealant System 

IV 

[--Prepare Plans and Specifications 
Figure VI-D1 6: Selection/Design of a Brick Veneer Sealant System 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.29 
January 1995 


Chapter VI:General Design Practices 

:N>s~ Dry Floodproofing 

Step 1: Check the capacity ofthe existing footing. 

Calculate the weight of the structure and proposed brick veneer 
system on a square foot basis and compare it to the allowable 
bearing capacity for the specific site soils. If the bearing pres

sure from gravity loads is less than the allowable bearing 

pressure, the existing footing can withstand the increased 
loading. If the bearing pressure from gravity loads is greater 

than the allowable soil bearing pressure, the existing footing is 

unable to withstand the increased loading andthe footing must 

be modified, or the designer should select another floodproofing 
measure. 

Step lA: Supplementthe footing, as required. 

If it is found that the existing footing cannot support the loads 

expected from a veneer system or that the configuration ofthe 

footing is unacceptable, the footing can be widened to accom

modate this load. This can be a costly and detailed modifica

tion. The homeowner should be informed ofthe complexity and 

cost of such a measure. The following considerations should be 
followed during design ofa footing supplement: 

a. If additional width is added to the footing, the designer must 
analyze how the footing will work as a unit. Reinforcing 
must be attached to both the old and new footing. This will 
probably involve drilling andepoxy grouting reinforcement 
into the existing footing. The quality and condition ofthe 
existing concrete and reinforcement should be considered in 
the design. 
b. Exercise care when making excavations beside existing 
footings. Take carenotto underminethe footings, which 
could create major structural problems or failure. 
c. Design the footing for the eccentric load from the brick 
weight. Add any flood-related loads and consider all 
possible load combinations. 
VI-D.30 Enaineerina Principles and Practices of RPstrnfittin,FInnri-Prninc PoQ~RantimlQ+ri ntoirm*

- ---_ -Ir------_-.--......~..-*anuary1995

January 1995 


Selection and Design of Sealant Systems 

d. For extreme soilconditions, consult a geotechnical engineer 
to determine soil type and potential response. 
e. The designermaywant to referto the ACI Manualfor 
Concrete Design, a soils manual/textbook for detailed 
footing design, and to applicable codes and standards. 

Step 1B: Designfoundationreinforcing(asrequired). 

Concrete footings can come in a wide variety of configurations. 
Design offootings, especially those involved with retaining of 
materials, can become quite complex. There are many books 
that deal with the design of special foundations, and once the 

stresses are determined the ACI can provide guidelines for 

concrete reinforcement design. 

Steps 2-9 aresimilarto the designof wrapped sealantsystems. 
Refer to the previous section for details on these steps. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.31 
January 1995 


ChapterVI: General Design Practices 
Dry Floodproofing 

SELECTION AND DESIGN OF SHIELD SYSTEMS 

Once the determination is made that a foundation system can 
withstand the expected flood and flood-related forces, the 
selection of a shield system is relatively straightforward and 
centers on the ability ofthe selected material to structurally 
secure the opening, be compatible with the existing construction 

materials, and be responsive to the duration and depth of 
flooding expected. 

PLATE SHIELDS 

The selection and design of a plate shield follows Figure VI-
Industryhas developedmanufac-DI 7, Selection/Design of Plate Shields. Ifadditional existingtured closuresystemsthatmaybe structural reinforcing is required, it should be performed in 
applicableto specificsituations, accordance with the guidance presented in the precedingFor additional information on the 

companies that manufacture these section.
products, contact your local
floodplainmanagementorengi-Step 1: Select the plate shield material.

neering office. 

Plate shield material selection may be driven by the size ofthe 
opening or the duration of flooding. For example, plywood 
shields would not hold up during long-term flooding. 

a. Consider flood duration and select steel or aluminum 
materials for long duration flooding and consider marine 
grade plywood materials for short duration flooding. 
b. Consider opening size and select steel and aluminum 
materials with stiffeners for larger openings and shored 
plywood with appropriate bracing for small openings. 
c. Installation of all shields should be quick and easy. Lighter 
materials such as plywood and aluminum are most suitable 
forhomeowner installation. 
VI -D.32 Engineerina PrinciDlesand Practices of Retrofittino Flood-Prone ResidentialSiS iialruc 
January 1995 


Selection and Designof Shield Systems 

Selection/Design of Plate Shields 

Prepare Details and Specifications 

Figure VI-D 17: Selection/Designof Plate Shields 

Step 2: Determine panel stresses. 

Thedesignershouldcheckthe shieldpanel eitheras a plate or a 

46 horizontal/vertical span across the opening. 
The use of plywood shields in 
long-term exposure situationsmay a. Using end conditions and attachments to determine how the 
induce possible swelling and de-panel will work, calculate stresses based on bending of the 

terioration of the laminating glue. 

I ET ^^

VI-

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-Wd. 
January 1995 


Chapter VI: General Design Practices 

& Y 7P Dry Floodproofing 

plate. In larger plate applications, also compute the end 
shear. 
b. Compare these stresses to the allowable stresses from the 
appropriate source. 
c. Some shieldsmay have a free end at thetop or other 
unusual configuration. These will need to be addressed on 
a case-by-case basis. 
d. Adjust the plate thickness to select the most economical 
section. If the plate does not work for larger thicknesses, 
add stiffeners. 
e. The designer may want to refer to the AISC manual for 
steelplate design, analuminum design manual,APA for 
plywood design, and applicable codes and standards. 
Step 3: Check deflections. 
A plate shield that is acceptable for stresses may not be acceptable 
for deflection. 
a. Calculate deflections forthe panel and evaluate on the basis 
of connections and sealants. 
b. If the deflection is unacceptable, add stiffeners. 
c. Deflection may be controlled by alternative plate materials. 
d. The designer may want to refer to the AISC manual for 
steel plate design, an aluminum design manual, APA for 
plywood design, and applicable codes and standards. 
VI -D.34 Enaineerino -a Princinles and Prantioss nf RPtrnfittinwFlond-Prnne RoioHntial Qtri itfi. -*-r-----v . .--* 
E .w [_|*v7Jauary1995January1995 


Selection and Design of Shield Systems 

Step 3B: Stiffen as required. 

Plate overstress or deflection may be solved through the use of 
stiffeners. 

a. Select the section to be used as a stiffener. Angles may be 
used for steel or aluminum and wood stock for plywood. 
b. Calculate the stresses and deflection based on the composite 
section of stiffener and plate. 
c. Calculate the horizontal shear between the two sections and 
design the connections to carry this load. 
d. Keep plate connections and frame in mind when detailing 
stiffeners. 
e. The designer may want to refer to the AISC manual for 
steel plate design, an aluminum design manual, APA for 
plywood design, Mechanics of Materials tests, and applicable 
codes and standards. 
Step 4: Design the connections. 

Plate connections must be easy to install and able to handle the 
loads from the plate into the frame and surrounding wall. 

a. Determine the type of connection (hinged, free top, bolted, 
latching dogs, or other). 
b. Consider ease of installation and aesthetics. 
c. Connection must operate in conjunction with gasket or
sealant to prevent leakage.
d. Connection must be capable of resisting some forces in the 
direction opposite of surges. 
-------:InADr::ltaiog~ Flood-PronARAsidentialStructures 
January 1995 

Cnnne_ in l e of Ratrnfittinn VI -D.35 


ChapterVI: GeneralDesign Practices 
Dry Floodproofing 

e. The designer may want to refer to the AISC manual for 
bolted connections, ACI manual for connections into 
concrete and masonry, and applicable codes and standards. 
Step 5: Selectthegasketorwaterproofing. 

Gaskets or waterproofing materials, which form the interface 
between shields and the existing structure, are vital elements of 
the dry floodproofing system. They should be flexible, durable, 
and applicable to the specific situation. 

a. Determine the type of gasket orwaterproofmg required. 
b. Consider ease of installation and ability to work with plate/ 
connections as a single unit. 
c. Gasket/waterproofing must be able to withstand expected 
forces. 
d. Gasket/waterproofing must be able to fbinction during 
climatic extremes. 
e. The designer should refer to manufacturer's literature and 
check against duration/depth of flooding and applicability to 
selected building materials. 
Step 6: Checkadjacentwalls, lintels,sills,andtop/bottom 
connections. 

Structural components adjacent to the shield panel, such as 

adjacentwalls, lintels, sills, and top/bottom connections, should 

be checked against maximum loading conditions. Different 

methods of attachment may load the adjacent wall differently. 

VI -D.36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Selection and Design of Shield Systems 

Walls adjacent to the shield should be anchored into the footing 
to resist base shear. Lintels/sills should be checked for biaxial 
bending resulting from lateral loading. Top connections should 
be evaluated for shear resistance and ability to transfer loads to 
thejoists. 

The following design example illustrates the process of selection 
and design of a window opening shield. 

rnt.tirlMa of Structures

C~~nninaari-n O~innccnr RatrofittinnFlonri-Prone Residential VI -D.37 

Januarlvvrlry l~lulv::iallu a .... __

1995 ........ . ..__.__...._.-_..__._. 
January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Sample Calculation for Shield Design 

GIVEN: 

Shield in 12-inch Concrete Masonry Unit wall subjectto hydrostatic (freestanding water) flood 

loading only. 

.'. . N'X N. N. 

';.' N "v,--:.

?r9-aR<t 

: ~:. :.!'t ~ .:-::::N e E sirC 

This example will check only the surrounding wall, design lintel, shield fiwne, and shield panel. 

Seepreviousguidelinesundertheelevationsamplecalculationforremainderofhouse. Previous 

investiigationhas detertined thiatflotation will not occur for thiewater depthisshown. 

-t .' " 'CCSS.-j N.NC C.-g.m

tiSSS'S, .'S.. 

Step l: For an operiing ofthis size, it iis unlikely that plywood would work without stiffening

0 l' 0 . l'-;-'. S'--A g ' --.. \C .C 

(due toitspotentialfor deflection).Terefore,tryusngaflatplateofsteel. 

N C N.'....1 of 11 

D.38 Prioncisles it ftnri 
January 1995 
V tp Enaineering and Practiits of Rutnkfittint Fltpyo-PronwRor sntifl cng 


Sample Calculation for Shield Design 

Sample Calculation for Shield Design 

Calculations: 

Determinewater pressure acrosspanel 

Unit weight ofwater= 62.4lbs/ft3 

Options: 

210

?.~~~~~~~~~ 4 1.2 bf /w 

Note: Designguidanceforthis examplewastakenfrom Roark's Formulasfor Stress 
and Strain, 6th Edition,Warren C.Young. Use ofthis reference isnot an endorsement. 
The book is a standard reference (among others) for structural engineers. 

Panel can be designed as aplate to distribute the load about the perimeter ofthe opening. 

Panel can be designed to span horizontally or vertically (may require stiffeners). 

Whichever option is chosen, the frame and anchors must be capable of transferring the load into 
the wall and/or lintel. The wall must be capable oftransferring the load into the slab or diaphrgms. 

2 of 11 

I .---
Jaulay 11995ll lu I -, . _ -1 .-1 a .. 

r-ni~Mnathin Drin,.inIgmeanri.. PrantiraQ n Ratrnfittinn Floodl-PronaResidential Structures VI -0.39 

January 1 995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Sample Calculation for Shield Design 

Step 2: For this example, design the plate assuming supported on all sides with A36 steel. 

Reference: RoarIs' Formulasfor Stress & Strain,6thedition, Warren C. Young 

Assume simple (hinged) connections forpanel. 

For the calculations it is convenient to divide the loading into two load cases:
the uniform load of 83.2 lbs/ft2 and
the uniformly increasing load of 291.2 -83.2 = 208 lbs/ft2.

PerRoark, Casela, (page458), Uniform Load inthe following calculations, 

a = tabulated coefficient
= tabulated coefficient

1,5 = tabulated coefficient
a = plate dimension horizontal
b = plate dimension vertical
q = maximumpressure onplate
tqplate thickness
E modulus ofelasticity for plate
a = b = 40" thus,

a/b = 1.0 (3=0.2874, a = 0.0444,y = 0.420. Themaximum stress at the center of the 
plate is given by, 

forthis example, 

Pqb2
cYu= 2

t2 

au = {0.2874 (83.2 lb/ft2/144)(40 in)2 }/(3/8 in)2 
= 1889 lbs/ft2 

3 of 11 

VI -D.40 Enaineerina Princioles and Practices of Retrofittinn Flood-Prone Residentiai Struatiuares 
Januaiy 1995 


Sample Calculation for Shield Design 

Sample Calculation for Shield Design 

the maximum deflection is given by, 

4 

-(-ax)qb 

Et 3 

for this example, 

Y. = {-0.0444(83.2/144)(40) 4}/{29x106( 3/8 in)3} = -0.04 in. 
the maximum reaction (at center of sides) is given by, 

R. = ybq 
Per Roark, Case Id, (page 459), Uniform Increasing Load, 
a = b = 40" thus, 
a/b = 1.0 f3=0.16, a = 0.022 

for this example, 
CaT = {0.16 (208 lb/ft 2 1144)(40 in)2 }/(3/8 in)2 = 2630 psi 
YT = {-0.022(208/144)(40) 4}/{29xl0 6 (3/8 in)3 = -0.05 in. 

Assume that these stresses and deflections occur at the same locations and are therefore 
additive (conservative), therefore, 

Cmax = 1889+2630 =4519psi 

Reference: AISC 9t Edition Section F2.1 

Allowable bending stress in plate, 

Fb = 0.75FY 

where:
Fb = allowable bending stress
FY = yield stress of steel

for this example, 
Fb= 0.75(36,000) = 27,000 psi >>> 4519 psi O.K. 

4 of 11 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.41 
January 1995 


Chapter VI: General Design Practices 
Dry Floodproofing 

Sample Calculation for Shield Design 

Step 3: maximum deflection, 
Ymax 0.04 + 0.05 = 0.09 in. 
maximum allowable deflection is recommended to be, 

Yellow = L/240 
where: 
L = sWanofmemberunder consideration ,, _ 

for this example, 

Y.W = 40 in/ 240 = 0.17 in. > 0.09 in. O.K. 
Note: If deflection is a problem, stiffeners can be added to the plate. 
Step 4: CheckConnectiontoWall 
The reaction from the uniform load can be determined from the previous equations. 
Ru = ybq= 0.42(40 in)(83.2/144) = 9.7 lb/in 
To determine the reactions from the sloped loading, assume the plate spans from the top to 
bottom. 

lb.

R 116 

3. 33' 
208 pof 

Rbot. = 231 lb.

ft. 

5 of 11 

VI -D.42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sample Calculation for Shield Design 

Sample Calculation for Shield Design 

Maximum Conservative Reaction is,
[(9.7)(12)] + 231 = 347 lbs

Check Anchor & Masonry 

I/2"0 A307 Anchor Bolt 

Allowable Shear per AISC 9th Edition, (Connection Section) 

(-) (1 0,000) = 1963 lbs>346 lbs O.K 

4 

Check horizontal shear in masonry. Locate bolt in middle of 12" CMU. 

Reference: ACI 530 Section 5.14.2.2 

Area of bolt,
Ab = 0.2 in2

edge distance,
I e-12/2 -I/2 =5.75 <12 db =61

embedment,
lb = 6" (chosen)

allowable load in shear, 

B1= 1(350)" aiT.A)|Q124) 

where: 
Ab = Area ofAnchor bolt 
fm = Compressive Strength of Masonry 
f = Yield Strength ofAnchor Bolt 

y 

6 of 11 

Ennineerihq Principles and Practices of Retrofittina Flood-Prone.Residential Structures VI -0.43 
January 1995 


Chapter VI: GeneralDesign Practices 
Dry Floodproofing 

Sample Calculation for Shield Design 

for this anchor bolt pattern, 

Bv = min (350( (1500)( 0.2))'-),((0. 12) (0.2) (20ksi))
1450,480
480 Ibs > 347 lbs

CheckWalls Adjacent to Opening for Additional Loads 

: . _ _ _ _ _ _ _ i s 0 - . -t --$Df ' 

Chc l'( wde oS 7S f ma-sonry 

,-:,s;tr;7>ip ,D 

Determine the maximum moment and shear (as simple span),
at 5'-0" from top, MM, = 1872lb ft
at bottom, VmK= 1404 lbs

7of 11 

1% 

VI -D.44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995 


Sample Calculation for Shield Design 

Sample Calculation for Shield Design 

Note: for Seismic Zone 2, masonry cores on each side of opening are to be reinforced. 

Check Masonry 

Reference: ACI 530, Working Stress Design 

Assume: 
d 6" (middle) 
b 
Es = 
12" (I1/2cores) 
29x106 psi 
f m 
Em 
n 
= 
= 
1500 psi 
1.6x10 6 psi Table 5.5.1.3 ofACI 
Es/Em= 18 (modular ratio) 
530 

Fb = 1/3(1500 psi) = 500 psi (allowable compressive stress) 
Fs = 24,000 psi (allowable tensile stress) 

Try using 1 -#5 rebar each side of opening, A, = 0.31 in2, full height, 
p = steel ratio = As/bd = 0.31/((6)(12)) = 0.0043 

f ~=

M!A)d 
where: 
M = applied moment 
As = area of steel 

j = ratio of distance between centroid of flexural compressive 

forces and tensile forces = 1 -(K/3) 

K = -pn +(2pn + (pn)2 )1 2 

n modularratio 

p = steel ratio 

8 of 11 

Enaineerina PrinciDlesand Practices of Retrofittina Flood-ProneResidential Structures VI -D.45 
January 1995 


ChapterVI: General Design Practices 
Dry Floodproofing 

Sample Calculation for Shield Design 

II 

K = -0.0043(18)+(2(0.0043)(18)+[(18)(0.0043)]2)1/2 

= 0.3238 

j = 1 -0.3238/3 = 0.8921 

f5 = [(1872 lb ft)(12 in/ft)]/[(0.31)(0.8921)(6)] 

= 13,540 psi < 24,000 psi O.K. 

for tis example, 

fO = MI(1/2bjkd) 

where: 

M = appliedmoment 

b = width of section 

j = ratio of distance between centroid 

of flexural compressive forces and tensile forces 

= 1-(K/3) 

K = -pn+(2pn+(pn)2 )"' 

d = distance to centroid oftensile stresses from the maximum 

compressive stress 

n = modularratio 

p = steel ratio 

t = [(1872 lb ft)(l2 in/fl)]/ 
[1/2(12)(0.8921)(0.3238)(6)2i 
= 360 psi< 500 psi O.K. 

Walls adjacentto closure should have 1-#5 (middle) full height with matching dowel into footing, 
asaminimum. 

9 of 11 

VI -D.46 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sample Calculation for Shield Design 

Sample Calculation for Shield Design 

Check Shear in Masonry at Base 

V = 1404 lb 

Calculate shear stress, 

fV = V/(bjd) 

where: 
V = shear at point under construction 
b = width of section 
j = ratio of distance between centroid 

of flexural compressive forces and tensile forces 

= 1-(K/3) 
K = -pn+(2pn+ (pn)2)1"2 
d = distance to centroid oftensile stresses from the maximum 

compressive stress 
n = modular ratio 
p = steel ratio 

for this example, 
f = 1404/ [(12)(0.8921)(6)] = 21.9 psi 

allowable shear stress, per ACI 530 
Fv= (fm) = (1500)1/2= 38.7 psi >21.0 psi O.K. 

10 of 11 

Enaineerina Princioles and Practices of Retrofiffina Flood-Prone Residential Structures VI -D.47 
January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

S, 

Sample Calculation for Shield Design 

Additional Considerations 

* If water level rises above the top ofthe opening, the closure may laterally load the lintel. In 
this case the lintel should be checked for biaxial bending. 
* Provide any additional code-required reinforcement around openings for the specific seismic 
zone. 
* Different methods of attachment may load the adj acent wall differently. 
* Confirm that gasket is suitable for depth/duration of flooding and selected construction
materials.
11 of 11 

VI -D.48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Construction Considerations 

CONSTRUCTION CONSIDERATIONS FOR SEALANTS 
AND SHIELDS 

The use of sealants and shields may require careful attention to 
critical installation activities. When using shields and sealants, it 
isvitalthat 

* the sealant be applied in accordance withthe 
manufacturer's instructions; 
* wrapped systems are anchored properly and the surrounding 
soil recompacted; 
* shields are tightly installed with associated caulking or 
gaskets, utilizing the proper grade of materials and paying 
close attention to the anchoring details; and 
* multiple closures are accurately labeled and stored in an 
easily accessible space. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.49 
January 1995 


Chapter VI: General Design Practices 

( Q< 

Dry Floodproofing 

DRAINAGE COLLECTION SYSTEMS 

The development ofdrainage collection systems is a critical 

component in the design of many dry floodproofing measures 

and may be utilized in concert with elevation, floodwall, and 

levee measures. These systems collect drainage and seepage 

from areas along, adjacent to, or inside the retrofitting measure 

and the sump pump installation, which transmits the collected 

drainage and seepage away from the building's foundation. 

Determination of the amount of surface water inflow and 

infiltration was presented in Chapter IV. This section presents 

the parameters that govern the design of these systems. 

Typical homes with basements are constructed on concrete 
footings upon which concrete or cinder block foundation walls 
are constructed. In some instances, the foundation walls are 
parged and covered with a waterproof coating, and/or perforated 
pipe underdrains are installed to carry water away from 
the exterior foundation walls (see Figure VI-D 18: Typical 
Residential Masonry Block Wall Construction). Thenthe 
excavations are backfilled and compacted. 

First Floor 

Slope Pway From "Ouse 

Basement Area 

Cement Mortar Parging with Asphalt 
Base Waterproofing Below Grade Concrete or Cinder Block 

Cove Area 

Concrete Basement Slab 

Gravel (may be reinforced with wire mesh) 

PC)rforated Pipe Footing Drain 

111GraveS l Base (sometimes) 

Concrete Footing 

Figure VI-D 18: Typical Residential Masonry Block Wall Construction 

VI -D.50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Drainage Collection Systems 

However, in practice, this fill material is not and often cannot be 
compacted to a density equal to that of the undisturbed soils 
around the house. Because of the density difference, the fill 
material is capable of conducting and holding more water than 
the soil around it and frequently provides a storage area for the 
soil water. As flood levels rise around the structure, the combined 
water and soil pressure in the areas adjacent to the 
foundation increases to the point of cracking foundation walls 
and/or entering the basement through existing cracks to relieve 
the pressure. (See Figure VI-D 19: Common Faults Contributing 
to Seepage into Basements.) 

Settlement of Backfill Creating 
Water Collecting Depression First Floor 
(may occur even with good compaction) 
-Framing 
Slopes T-oward House 
(I 
Basement Area 
Parging Cracked, Does Not 
Extend To and Wrap Footing, 
or Parging Nonexistent 
'a 
_W~ 
_ 
Surface and Subsurface 
Water Collects in Less 
Compact Fill 
Area Excavated and Backfilled ICrack in Wall 
During House Construction Hollow Core Block 
May Fill With Water Basement 
_ ~~~~~~~FloorSlab 
Joint Floor Drain- l 

Drain at or above Basement 
Floor Elevation, or Nonexistent Hydrostatic Pressure Forces 
Water through Wall, Floor 
Joints and Floor Openings 
(Floor Drain) 

Figure VI-DI9: Common Faults Contributing to Seepage into Basements 

Depending upon site-specific soil conditions, high water tables, 
and local drainage characteristics, slab-on-grade homes may 
experience similar seepage problems. In addition, elevating and! 
or dry floodproofing a slab-on-grade home may also necessitate 
the installation of drainage collection systems to counteract 
buoyancy and lateral hydrostatic forces. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.51 
January 1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Drainage collection systems consisting of perforated pipe drains 
are designed to collect this water and discharge it away from 
the structure, thereby relieving the pressure buildup againstthe 
foundation walls. Several types of drainage collection systems 
exist including french drains, exterior underdrains, and interior 
drains. 

FRENCH DRAINS 

French drains are used to help dewater saturated soil adjacent 
to a foundation. They are simply trenches filled with gravel, 
filter fabric, and sometimes plastic pipe. A typical french drain 

French rainsareenerallynotsection is shown in Figure VI-D20. The effectiveness offrench
French drains are generally not dan scoeyte oteeitneoasial icag
suitable for areas subject to drains is existence ofa suitable discharge

requent inundation due to the point and the slope/depth ofthe trench. A suitable discharge 
lack of a gravity discharge point for the drain usually means an open stream, swale, ditch, or 
during a flood. However, they can slope to which the drain can be run. If such a discharge point is a be effective in keeping localized not available, a french drain is generally not feasible. 
drainage away from the foundation 
(providing there is no 
occurrenceof a significant flood). If feasible, the french drain should be dug to a sufficient depth to 

ensure the capture of soil water that might infiltrate the fill 
material inthe footing areaofthe basement. The slope ofthe 
trench should be such that good flow can be maintained between 
the gravel stones. This typically means a minimum slope 
of 1.0% or more. 

Roofing Felt or Filter Fabric 
to Prevent Infiltration of Fine Soil 

Topsoil / Particles in Drain Gravel 

1_9IMinimum 

,,,,,, {~~Typical 

Perforated Pipe in
3/4" to 1"Diameter Gravel Typca

Figure VI-D20: Typical French Drain System 

VI -D.52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Drainage Collection Systems 

Similar to the french drain, an 
exterior underdrain system with 
gravity discharge will not work 
during a flood. Therefore sump 
pump discharge with a backup 
energy source is the preferred 
alternative. 

EXTERIOR UNDERDRAIN SYSTEMS 

Exterior underdrain systems are generally the most reliable 
drainage collection system when combined with some type of 
foundation parging and waterproofing. The advantage of the 
exterior underdrain system is that it will remove water that 
would otherwise exert pressure against the foundation walls and 
floors. Underdrains are normally constructed of continuous 
perforated plastic pipe laid on a gravel filter bed, with drain 
holes facing up. The underdrains are placed along the building 
foundationjustbelowthe footing and carrywaterthat collects 
to a gravity discharge or sump pump for disposal into a public 
drainage system, natural drainage course, or ground surface (as 
permitted by local agencies). (See Figure VI-D2 1: Typical 
Exterior Underdrain System with Sump Pump and Figure VID22: 
Details of a Combination Underdrain and Foundation 
Waterproofing System.) 

Ennineprinn Princinles and Practices of F RetrofittinaFlood-ProneResidential Structures VI -D.53 
January 1995 


Chapter VI: General Design Practices 
Dry Floodproofing 

Exterior Footing Drain 
(perforated pipe in gravel 
bed) around Perimeter 
Plan View 
FloorSlab 
Foundation 
Walls Discha 
Line 

Sump Pump in Pit/ 
(one or more may be used) Floor

/1 i

Discharge Perforated Pipe (in gravel bed) Bel 
Line Floor Slab Along One or More Wal 

Side View 

Discharge Line Alternative Configuration: 
-(through wall at or above ground 
elevation and flood protection level) P Sump

erforated Pit 
_~~~~~~~~~~~~~~~~~~~n

pipe used) 

Sump Pit Basement Floor Slab 

Sump Pump Gravel Sump Pump 
Foundation System Perforated Pipe 
Connected Through Footing Below Floor Slab 

Figure VI-D2 1: Typical Exterior Underdrain System with Sump Pump Showing Two Alternative 
Configurations in the Side View 

VI-D.54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Drainage Collection Systems 

Details of Underdrain and 
Foundation Waterproofing 

Asphalt base (or better) 

waterproofing application 

followed by layer of 
polyethylene sheeting 

3/4"parging applied in two 
layers %" thick each Hollow

\ -~~~~~~~Block

Completely filled 
exterior cove 
\ wake / /1 
Wall 
~~~~~~Expansioin 
Filterfabric Joint 
sloped away 
from wall Basement 
s ~~~~~ ^ t v~~~~~~FloorSlab 
g3 roux a _ ~~~~~Mortar 

1 / 9 ~~~~~~~Conc.Xa 

Drain below / Footing 
top of footing 

NV -1l,'" diametergravel 

/ / ~4"min. 

4" diameter perforated pipe 
Note: gravel may be extended 
to within 9" of finished grade 

FigureVI-D22: Details of a Combination Underdrain and Foundation Waterproofing System 

EngineeringPrinciples and Practices of Retrofitting Flood-ProneResidential Structures VI -D.55 
January 1995 


Chapter VI:General Design Practices 

1n> m~.

Dry Floodproofing 

INTERiOR DRAIN SYSTEM 

Interior drain systems are designed to relieve hydrostatic 
pressure from the exterior basement walls and floors and do not 
require tat the soil be excavated from around the exterior 
basement walls for installation. Sump pumps are perhaps the 
most familiar of all methods used to dewaterbasements. The 
sump is generally constructed so that its bottom is well below 
the base ofthe basement floor slab. Water in the areas adjacent 
to the basement walls and floor migrate toward the area of 
least pressure along the lines of least resistance, in this case 
toward and into the sump. It may be necessary to provide a 
more readily accessible path of least resistance for water that 
has collected in the fill material and around the house to follow. 
To achieve this, pipe segments are inserted and sometimes 
drilled through the basement wall and into the fill behind. These 
pipe segments are then connected to larger diameter pipes 
running along a gravel-filled trench or cove area into the basement 
floor and into one or more sumps. (See Figure VI-D23: 
Typical InteriorDrain Systems.) 

VI -D.56 Enaineerina Principles and Practices of Retrofittino Flood-Prone Residential Structures 
January 1995 


Drainage Collection Systems 

Typical Interior DrainageSystems 

Underdrain System Wall Drainage System
Below Basement Floor Slab Above Basement Floor Slab

1/2" Solid 
Plastic 
Holes Must/ or 

Be Drilled See Copper 
into Cinder ) Section Pipes 
Block Cores "B" 

Sump 

Cl I

riuur ;:ilU Cl -L.L IA..- iviUSIRa-I | 
Pump 
Removed and Replaced 
Note:Water is collectedIn sumpandmust be 
pumpedto a suitable pointof discharge. 

Replacement Slab Around
Perimeter of Basement

Hyrdraulic Existing 

Ce)ment Basemerit
in Cove Slab

-Gravel 

4" Perforated Pipe -X 

Section "A" Section "B" 

Note:Holesmust be drilled Intoblockcoresat 8' 
Intervalsascloseto floor as possible. This 
methodmust be considered an Inexpensive 
alternativeto a below slab system and 
accordinglyhascertainshortcomings:pipe is 
visible;will not drainfromwellbelow floor 
elevation;problemsassociatedwithdampness 
mayremain;hydrostaticpressurebelowfloor 
slabmay not be sufficientlyrelieved. 

I 

Figure VI-D23: Typical Interior Drain Systems 

VI-U..I

x ,. , rag 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -Lv.01 
January 1995 


ChapterVI: General Design Practices 
Dry Floodproofing 

SUMP PUMPS 

TYPES OF SUMP PUMPS 

Two types ofsump pumps commonly used are the submersible 

and the pedestal. The submersible type has a watertight motor 

tat is directly connected to te pump casing. It is installed at 

the bottom ofthe sump. The pedestal sump pump uses an open 

motor supportedon a pipe columnwith the pump at its base. A 

long shaft inside the column connects the motor to the pump 

impeller. Figure VI-D24 depicts both ofthese pumps. Sub

mersible pumps are preferred because they will continue to 

operate if the flood level exceeds the height of the pump. 

Three Wire 
GroundedPower Cord 

Control 

Switch\ 

Three Wire
GroundedPowerCord

Float
Rod
Control Switch 

I 

Chamber 

Motor K
Housing 

Tube1 

Float 

Column 

Float-/ 

Pump /

Case]j 
Impeller \-Screen / \ZOUnn1 

Pump Case LImpeller t-Screen 

Typical Submersible Pump Typical Pedestal Pump 

FigureVI-D24: Types of Sump Pumps 

VI-D.58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sump Pumps 

In selecting a sumppump for use inresidential floodproofing, , 

the designer should consider the advantages of each pump type 

and make a selection based on requirements determined from 

investigation ofthe residence. Considerations include pump 

Batterypoweredmarine-typebilge capacity (gallons per minute or gallons per hour), pump head 

*pumps are an alternative to sump 
pumps/electricalgenerator (vertical height that the water is lifted), and electrical power 
pminstallations. required (residential electrical power is usually 120/240 volts 
AC, single phase). Sump pump motors generally range in size 
from 1/6horsepowerto 1/2horsepowerdesigned to operate 
on either 120 or 240 volts. 

Infiltration vs. Inundation 

The capacities of sump pumps used in residential applications 
are limited. In floodproofing, sump pumps are used to prevent 
accumulations of water within te residence. In conjunction 

with other floodproofing methods, sump pumps can be used to 
protect areas around heating equipment, water heaters, or other 
appliances from floodwaters. Sump pumps are useful to 
protect against infiltration of floodwaters through cracks and 
small openings. Inthe event that there are large openings, or 
that the structure is totally inundated, the pumping capacity of 
sump pumps is often exceeded, but they are useful for controlled 
dewatering after floodwaters slowly recede (if submersible 
pumps are used). 

COORDINATION WITH OTHER 
FLOODPROOFING METHODS 

Design and installation of a sump pump should be coordinated 
with other floodproofing methods such as sealants and shields, 
protection of utility systems (furnaces, water heaters, etc.) and 

emergency power. 

Pnrninarinn Prinnini an.ndPractirce ofRptrofittina Flood-Prone Residential Structures VI-D.59 
January 1995 


# Chapter VI: General Design Practices 
DryFloodproofing 

FIELD INVESTIGATION 

Detailed information must be obtained about the existing 
structure to make decisions and calculations concerning the 
feasibility of using a sump pump. Use the Building/Building 
System Data Sheets (Figures VL-3and VI-4) as a guide to 
record infonnation about the residence. Items that the designer 
may require are covered on the sump pump field investigation 
worksheet, (Figure VI-D25). 

VI -D.60 Enaineerina PrinciDles and Practices of Retrofittinr FIoonr-Prnn ResirdentialIQtriintimrao 
January 1995 


Sump Pumps 

Owner Name: Prepared By: 
Address: Date: 
Property Location: 

Sump Pump Field Investigation Worksheet 

El Document physical location and characteristics of electrical system on sketch plan below.
El Determine base flood elevation:
El Check with local building official's office for version of National Electrical Code (NEC) NFPA70,

and local Electrical Code requirements: 

D Check with local building official's office for established regulations concerning flooded electrical 
equipment: 

El Check with the regulatory agencies to determine which state and local codes and regulations 

regarding the design and installation of plumbing systems may apply to the installation of a sump 
pump: 

El Determine location and condition of any existing drainage collection systems, including sump pits 
and pumps. 

El Does residence have subterranean areas such as a basement? ____Yes No 
El Is there a sump pump installed presently? _Yes -No: If so: 
El Record nameplate data from pump: capacity( 
motor horsepower, voltage, and manufacturer's 
GPH or GPM @FT 
name and model number. 
HEAD), 

EII Sketch plan of basement indicating location of sump, heating and cooling equipment, 
water heaters, and floor drains. 

E1 How high above floor is receptacle outlet serving cord and plug connected to 
sump pumps? 

Figure VI-D25: Sump Pump Field Investigation Worksheet 

Engineering Principles -rndPractices of Retrofitting Flood-Prone Residential Structures Vi -D.61 
January 1995 


ChapterVI: General Design Practices 
Dry Floodproofing 

I 

Once this data is collected, the designer should answer the questions below to develop a preliminary 
concept for the installation of a sump pump. 

D If there is no sump pump and one is needed, note potential location for a sump and tentative 
location for pump discharge piping on above sketch plan. 

D Is there an electrical outlet nearby? Yes No 

D7 Does electrical panel have capacity to accommodate additional GFI circuit if necessary? 
__Yes -No 

El If other floodproofing measures are to be considered, such as placing a flood barrier around 
heating equipment or other appliances, is the existing sump pump in an appropriate location? 
Yes _ No 
Does another sump and sump pump need to be provided? Yes -No 

D Select emergency branch circuit routing from sump pump to emergency panel. Note on above 
sketch plan. 

D Is sump pump branch circuit located above flood protection elevation and is it a GFI circuit? 
___Yes No 

ELI Locate sump pump disconnect or outlet location near sump pump location above FPE. 

Once these questions have been answered the designer can confirm sump pump installation 

applicability through: 

LII Verify constraints because of applicable codes and regulation. 

[I] Sump pump needed? -Yes _ No
L Is sump pump required by code? ____Yes No
D Code constraints known? ----Yes -No
D Proceed to design? Yes No
C: Confirmthat wiring can be routed exposed in unfinished areas and concealed in finished areas. 
___Yes No 
D Confirmthat panel has enough power to support sump pump addition. -Yes -No 

I 

. 

Figure VI-D25: SumpPump Field Investigation Worksheet (continued) 

VI- D.62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sump Pumps 

DESIGN 

The design of sump pump applications follows the procedure 
outlined in the flow chart in Figure VI-D26: Sump Pump 
Design Process. 

Sump Pump Design Process 

Determine Rate of Drainage 

Determine Location for Sump 

Determine Location for Discharge 

Select Pump Size 

Determine Adequate Sump Capacity and Size 

Select Discharge Piping Route 

Size Electrical Components 

Prepare Details and Specifications 

Figure VI-D26: Sump Pump Design Process 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -D.63 
January1995 


Chapter VI: General Design Practices 

< Y~ DryFloodproofing 

Step 1: Determine rate of drainage. 

(Covered previously in Chapter IV.) 

Step 2: Determine location for sump. 

Refer to Figure VI-D27 for typical sump pump installation. 
Considerthe following in locating the sump. 

* Isthere adequateroom for the sump? 
* Are there sub-floor conditions (i.e., structural footings) that 
would interfere with sump installation? 
* If penetration of floor is not recommended, consider using a 
submersible pump design for use on any flat surface. 
* Are other floodproofing measures being considered, such 
as placing a flood barrier around heating equipment or 
plumbing appliances? If so, locate sump or provide piping 
to sump to keep protected area dewatered. Make preliminary 
sketch showing location of sump pump, discharge 
piping, and location of electrical receptacle for pump. 
* Coordinate sump location with design of drainage collection 
system. 
VI -D.64 Enaineerina PrinciDlesand Practices of Retrofittino Flood-Prone Residential Strictures

-in sor _ ----t*-_ -Ju 1 99 

January 1 995 


Sump Pumps 

Typical Sump Detail 

(No Scale) 
Discharge to 
Outdoor or Other_ 
Drainage Systemr Discharge To Battery or 
As Allowed \CPipe and Back Up Power Unit 
ProtectionLevel Check | Sm oe 

Sump Varies

Submersible (1-4 Typical)-~ar, 

Sump Pump 
Varies 
(18"-36" Typical) 

Figure VI-D27: Typical Sump Detail 

Step 3: Determine location fordischarge. 

Check with local authorities having jurisdiction about the 
dischargeof clearwaterwastes. Inmost jurisdictions, itisnot 
acceptable to connect to a sanitary drainage system, nor may it 
be desirable since, in a floodsituation,it may backup. If 
allowable, the desirable location for the discharge is a point 
above the BFE at some distance away from the residence. The 
discharge point should be far enough away from the building 
that water does not infiltrate back into the building. From the 
information obtained during the field investigation, tentatively lay 
out the route ofthe dischargepipingand locatethepoint of 
discharge. 

Fnni D;nn imrinec onri Drotii'.c of RPtrcfittinnFloodrr-ProneResidential Structures VI -D.65

Jaluyll 199t 5I lu r -%-IW

lu I c 

January 1 995 


ChapterVI: General Design Practices 

Dry Floodproofing 

Step 4: Make selection ofpump. 

Sump pumps for residential use generally have motors inthe 

range of 1/6 to 3/4 horsepower and pumping capacities from 8 

to 60 gallons per minute. In selecting a pump, the designer 

needs the following information: 

Estimate of the quantity of floodwater that will infiltrate into 
the space per unit of time (GPM or GPH). 

The total dynamic head for the sump discharge. This equals 
the vertical distance from the pump to the point of discharge 
plus the frictional resistance to flow through the piping and 
fittings. Use the preliminary sketch and field investigation 
information developed earlier to determine these parameters. 
The total discharge head, TH, is computed as 
follows: 

TH=D ~ + h~ig 

| = 111 TH = Ds +h* h~~f 1 9 pipe+ f-fittings 

where: TH is the total head in feet; 

D is the difference in elevation between 
the bottom ofthe sump and 
the point of discharge, in feet; 

hflpipe is the head loss due to pipe friction, 
in feet; and 

hr fittings 

is the head loss through the fittings, 
in feet 

Fonnula VI-D 1: Total Discharge Head 

VI-D.66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Sump Pumps 

The head loss due to pipe friction can be obtained from hydraulic 
engineering data books and is dependent on the pipe material 
and pipe length. The head loss due to pipe fittings is calculated 
as follows: 

N_

hffiuings = Kp (V 2/2g) 

where: hr fiings is the head loss through pipe fittings, 
in feet; 
K P is the resistance coefficient ofthe 
pipe fitting(s), taken from hydraulic 
engineering data books; 
V is the velocity of flowthrough the 
pipe, in feet per second, taken from 
hydraulic engineering data books; 
and 
g is weight of gravity, 32.2 pounds per 
second squared. 

Formula VI-D2: Head Loss Due to Pipe Fittings 

The following example illustrates the use ofthese equations to 
determine the total head requirements for a sump pump installation. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.67 
January 1995 


Chapter VI: General Design Practices 
Dry Floodproofing 

Sample Calculation for Sump Pump 

f 

GIVEN: 

Ds = 10 feet; flow assumed to be 20 gpm; 1.5 inch steel discharge pipe length of 30 feet
includes one elbow, one gate valve and one check valve.

SOLUTION: 

From Hydraulic Engineering Data Books, resistance to flow in a 1.5-inch steel pipe is 2.92 
feet per 100feet ofpipe; 

hfpipe= 2.92 (30/1 00) = 0.876 feet 

resistance coefficients for fittings are 

K (elbow) = 0.63;
K (gate valve) = 0.15;
K (check valve) = 2. 1;
K (sudden enlargementoutlet)= 1.0

K=0.63 +0.15+2.1 + 1.0 =3.88 

velocity converted from gallons per minute to feet per second = 

Vfps4 Q
450 A pipe

fit3 

gal </450se- 

{20 .f75in )2 

ming 4gal -3.14)( 12 in 

ft~~ mnf 

=3.62 f

sec
hffittngs= K0 (V2/2g) = 3.88 (3.62)2/(2)(32.2) = 0.789 feet

TH= D + hfppe + hffliflins = 10 + 0.876 + 0.789 = 1 1.66 feet 

Therefore select a pump capable of pumping 20 gallons per minute at 1 1.66 feet oftotal head. 

VI -D.68 Engineerina Principles and Practioes of Retrofittina Flood-Prone Residential Structures 
January 1995 


Sump Pumps 

Step 5: Determine adequate sump capacity and size.
The capacity and size of the sump depends on several factors:

* Physical size ofthe sump pump 
* Recommendations of the sump pump manufacturer regarding 
pump cycling or other constraints. 
The designer should take these considerations into account in 
locating the sump and configuring the sump pump discharge. 

Step 6: Selectdischargepiperoute. 

* Minimize length of pipe between sump and discharge point. 
* Avoid utility and structural components along route. 
* Attach discharge pipe to structure as required by code. 
* Protect discharge point against erosion. 
Step 7: Size electrical components. 
* Obtain horsepower and full load amperage rating for sump 
pump. 
* Select GFI circuit, as required by code. 
* Size minimum circuit ampacity and maximum fuse size 
* Size maximum circuit breaker size. 
* Obtain recommendedfuse size or circuit breaker size from 
manufacturer and compare to above maximum and minimum 
NEC sizes. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.69 
January 1995 


Chapter VI: General Design Practices 
Dry Floodproofing 

At this point the designer should prepare a floor plan sketch 
showing the location ofthe sump pump, routing of discharge 
line, location of discharge point, and preliminary specifications 
for the sump pump, sump, piping, and appurtenances and 
confirm the preliminary design with the homeowner, covering 
the following items: 

* Verify thatproposed location of sump pump is feasible. 
* Verify electrical availability for sump pump. 
* Verify existing conditions along proposed routing ofdischarge 
piping and at location of discharge pipe termination. 
* Confirm selection and size of sump pump. 
* Confirm size and location of sump. 
* Confirm special considerations regarding existing conditions 
affecting design and installation of sump pump and sump. 
Step 8: Details and specifications. 
Prepare final plans showing: 

* Floor plan with location ofsump and backwater valves 
* Routing of discharge pipe and location oftermination 
* Details, notes, and schedules 
-Sump pump detail 
-Wall, floor, andwall penetration details 
-Sumpconstructiondetails 
VI -D.70 Enaineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Sump Pumps 

-Installation notes
-Equipment notes (or schedule)
-Discharge pipe termination

* Prepare specifications (on drawing or as a specifications 
booklet) 
-Pipe and fittings 
-Insulation 
-Hangers and supports 
-Valves (including backwater valves)
-Sump pumps

* Coordinate plans with work of others on additional 
floodproofing measures that may be proposed at the same 
residence. 
Enaineerina PrinciDlesand Practices of FRetrofittinq Flood-Prone Residential Structures VI -D.71 
January 1995 


Chapter VI: General Design Practices 

7 y > 

Dry Floodproofing 

BACKWATER VALVES 

Backwater valves can help prevent backflow through the 
sanitary sewer and/or drainage systems into the house. 

'00-40 They should be considered for sanitary sewer drainage 

Dependingupon the hydrostatic systems that have fixtures below the FPE. In some in-

pressurein the sewer system, a stances, combined sewers (sanitary and storm) present the 

simple wood plug can be used to greatest need for backwater valves because they can prevent 

close floor drains. both a health and flooding hazard. Backwater valves are 
not foolproof: their effectiveness can be reduced because of 
fouling ofthe internal mechanism by soil or debris. Periodic 
maintenance is required. 

The backwater valve is similar to a check valve used in domes

tic water systems (Figure VI-D28). It has an internal hinged 

plate that opens in the nonnal direction of flow. If flow is 

reversed ("backflow"), the hingedplate closes overthe inlet to 

the valve. The valve generally has a cast-iron body with a 

removable cover for access and corrosion-resistant internal 

parts. The valves are available innominal sizes from two to 

eight inches in diameter. 

As an added feature, some manufacturers include a shear gate 
mechanism that can be manually operated to close the drain line 
when backwater conditions exist. The valve would remain 
open during normal use. A second type of backwater valve is a 
ball float check valve (Figure VI-D29) that can be installed on 
the bottom of outlet floor drains to prevent water from flowing 
up through the drain. This type of valve is oflen built into floor 
drains or traps in newer construction. 

Advanced backwater valve systems have ejector pump attachments 
that are used to pump sewage around the backflow 
valve, forcing it into the sewer system during times of flooding. 
This system is usefull in maintaining normal operation of sanitary 
anddrainagesystemcomponents during a flood. 

VI-D.72 EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Backwater Valves 

II

,~~~~~~~~~~~

I, ~Backwater Valve 

-Handwheel
.A : 'Operator

:_Optional 

Optional-
Manhole 

Check Critical
Valve Part |

Normal Flow
IS Direction

------------------L -Shear-Gate 

Figure VI-D28: Backwater Valve 

Figure VI-D29: Floor Drain With Ball Float Check Valve 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI- D.73 
January 1995 


ChapterVI: General Design Practices 

Dry Floodproofing 

FIELD INVESTIGATION 

Detailed information must be obtained about the existing "a structure to make decisions and calculations concerning the 
feasibility of using a backwater valve. Use the Building/ 
Alternatives to backwate Drvalves Building System Data Sheets as a guide to record informainclude 
overhead sewers and tion about the residence. Once this data is collected, the 
standpipes. Their use sl ould be designer should answer the questions below to develop a 

evaluated carefilly. preliminary concept for the installation of a backflow valve. 

DESIGN 

The designer should follow the process illustrated in Figure 
VI-D30: Backwater Valve Selection, to design, select, and 
specify the backflow valve. 

Backf low Valve Selection 

Determine Relationship of Drains to Flood Protection Elevation 

Confirm Regulations Concerning Backwater Valves I 

I Determine Layout of Drains that Serve Impacted Fixtures I 

I 
Determine Pipe Sizes on Impacted Drains I 

Type, Size and Location for Valves; 

| De~Dvelop 

Figure VI-D30: Backwater Valve Selection 

VI- D.74 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Backwater Valves 

Owner Name: Prepared By: 
Address: Date: 
Property Location: 

Backwater Valve Field Investigation Worksheet 
D Does residence have plumbing fixtures or floor drains below FPE: -Yes -No 
D Is building drainage system equipped with backwater valves, or do floor drains have backwater 
device? -Yes No: If so, locate on a floor plan sketch of the residence. 

D If there are no backwater valves and they are needed, consider the following in selecting a
location for their installation.

D Can adequate clearance be maintained to remove access cover and service valve? 
Yes No 

D Are there any codes that regulate or restrict installation of such valves? 
-___Yes No; If yes, explain. 

D Tentatively locate on sketch box where backwater valves might be installed. 

CD Proceed To Design? _ Yes __No 

Figure VI-D3 1: Backwater Valve Field Investigation Worksheet 

Engineering Principles and Practices of Retrofittina Flood-ProneResidential Structures VI -D.75 
January 1995 


Chapter VI: General Design Practices 

Y 9< ~ Dry Floodproofing 

The elements of this process include: 

Step 1: Determine relationship of drains to FPE. 

If any drain or pipe fixtures are located below the FPE, 
backwater valves should be installed. If all drains and 
fixtures are located above the FPE, backwater valves are 
not necessary. 

Step 2: Determine regulations concerning backwater 
valves. 

Based upon information collected during the field investigation, 
confirm the allowability of and the regulations governing 
the installation of backflow valves. 

Step 3: Determine layout of drains that serve the impacted 
fixtures. 

Make a floor plan sketch showing location of all plumbing 
fixtures and appliances, floor drains, and drain piping that is 
below the FPE. 

Step 4: Determine pipe sizes on impacted drains. 

Obtain from field investigation the size of drainage lines 
below the FPE. 

Step 5: Determine type, size, and location for backwater 
valves. 

Determine type, size, and location of backwater valves 
required, paying considerable attention to any special 
conditions related to installation. Factors to be considered 
include: 

Clearance for access and maintenance 

VI -D.76 Enaineering Principles and Practices of Retrofittina Flood-ProneResidential Structures 
January 1995 


Backwater Valves 

* Cutting and patching of concrete floors 
* Indicate on floor plan sketch the tentative location(s) ofthe 
backwater valve(s). 
At this point the designer should confinr the preliminary design 
with the homeowner, discussing the following items: 

If possible, backwater valves * Verify that proposed locations of backwater valves are
should be located outside a feasible.
structure so as to minimize
damage should the pressurized
line fail. * Verify existing conditions at location of proposed

backwater valve installation. 

Confirm the size and location of needed backwater valves. 

* Confirm special considerations regarding existing 
conditions affecting design and installation of backwater 
valves. 
Step 6: Prepare details and specifications. 

The final plans and specifications should include the following 
items: 

* Floor plan with location of backwater valves 
* Details, notes, and schedules 
-Backwater valve detail 
-Wall, floor, and wall penetration details 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.77 
-January 1995 


Chapter VI: General Design Practices 
Dry Floodproofing 

-Installation notes 
-Equipment notes (or schedule) 

* Prepare specificationsgoverning the installation of: 
-Pipe and fittings 
-Insulation 
-Hangers and supports 
-Valves 
* Coordinate plans with work of others on additional 
floodproofing measures that may be proposed at the 
same residence. 
VI -D.78 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995 


Emergency Power 

EMERGENCY POWER 

Emergency power equipment can be applied to residential 

applications if the proper guidelines are observed. First, it is not 

feasible to apply emergency power equipment to the operation 

of a whole house with electric resistance heat, heat pumps, air 

conditioning equipment, electric water heater, electric cooking 

equipment, or sump pump(s). These large loads would require 

very expensive emergency power equipment that would have 

considerable operating costs. However, small, economical, 

residential portable generators or battery backup units can be 

successfully installed to operate selected, critical electrical 

devices or equipment from the limited power source. 

A list of appliances or equipment that a homeowner might 
choose to operate is shown in Table VI-Dl. It is important 
to note that all of these appliances would most likely not be 
operated at the same time. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.79 
January1 995 


X 

A~ Chapter VI: General Design Practices 

Q v Dry Floodproofing 

Table VI-D Essential Equipment/Appliances to Operate 
from Emergency Power Source 

Critical Items include: 

* Floodwatersump pump -typically 113to 1/2 hp 120 volt single phase. 
* Domestic sewage pump -typically 3/4 hp to 1 hp 120 volt single phase. 
Non-critical items include: 

* Refrigerator -350 watts to 615 watts. 
* Freezer -341 watts to 440 watts. 
* Gas or oil furnace -1,7 hp burner, 1/3 hp to 1/2 hp blower motor. 
* Some lighting or a light circuit -limit to about 400 watts. 
* A receptacle or a receptacle circuit -limit to about 600 watts. 
Several sources of technical information are available to 
assist in the design of emergencyresidential generator set 
installations. 

* Some manufacturers provide application manuals and 
sizing forms to select small gasoline-powered, natural or 
liquid petroleum gas, or battery sets. 
* Other manufacturers even offer software to size the 
small generator/battery sets. 
* Another good source is the supplier of the standby 
generatorlbattery set. These have additional application 
data for sizing the unit to suit the anticipated load. 
* The manufacturer of the set will provide a wattage and 
volt-ampere rating for each size at a particular voltage 
rating. 
Selection of a generator/battery set is a matter of matching 
the unit capacity to the anticipated maximum load. The chief 

VI -D.80 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Emergency Power 

complication in sizing the generator/battery set is the starting 
characteristics of the electric motors in the pumps and 
appliances to be served. 

FIELD INVESTIGATION 

Detailed informationmust be obtained about the existing 
structure to make decisions and calculations concerning the 
feasibility of using an emergency generator or battery 
backup unit. Use the Building/Building Systems Data Sheets 
(Figures VI-3 and VI-4 located in the beginning of Chapter 
VI) as a guide to record information about the residence. 
Among the activities the designer may pursue are: 

* Examine the routing and condition of the existing 
building electrical system, noting potential locations for 
emergency power components (above the FPE and 
away from combustible materials). 
* Determine utility or power company service entrance 
location and routing. 
* Determine utility constraint data. 
* Record these items and locations on an electrical site 
plan/combination floor plan sketches. 
* Confirm space for cable routing between main panel, 
emergency panel, transfer switch, and proposed generator/
battery set. 
* Examine existing panel branch circuit breakers and 
select circuits to be relocated to emergency panel. 
* Confirm utility regulations on emergency power equipment 
with local power company. 
Ennineerinn PrinrinIlA and PrartircAs of FRetrofittino Flood-Prone Residential Structures VI -D.81 

January1995 


ChapterVI: General Design Practices 

Dry Floodproofing 

DESIGN 

The design of emergency power provisions is a straightforward 
process that is illustrated in Figure VI-D32. The steps 
include: 

Emergency Power Design 

Determine Loads to Operate on
Generator or Batterv Set

Identify Start and Run Wattages 

Calculate Maximum and Minimum
KW for Above Loads

I 

|ISelect Generator/Battery Set SizeI| 

E Sele~ctTransfeSwthiz 

Transfer Switch 

Select Emergency Panel Size Manual
Transfer
Switch

Design Wire Conductor and
Raceway Ground SLstem

Prepare Construction Detail Plan 
I and Specifications 

Figure VI-D32: Emergency Power Design Process 

VI -D.82 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Emergency Power 

Step 1: Determine loads to operate on generator set. 

Table VI-D2 presents typical electrical appliance loads for 
Since most power outages are some home equipment. The designer should work with the 
temporary and relatively short owner to select only those pumps/appliances that must be 
lived, a battery backup source for run by emergency power and confirm the estimated appli

sump pumps (only) may be the ance and motor loads.
simplest solution for a
homeowner. However, as the
duration of the power outage Step 2: Identify start and run wattages.
increases, the suitability of battery
backup systems decreases.

Start and run wattages for the appliance loads selected by 

Generator sets are a more secure 
source of power in these situa-the homeowner can be obtained from Table VI-D2, Typical 
tions, especially for those resi-Electric Appliance Loads. 

dents who need/desire power to 
operate medical equipment or 
standard household appliances Step 3: Calculate maximum and minimum KW for operat

during power outages. Battery ing loads. 
systems used in conjunction with 
emergency generators can provide 

service during a limited period if Based upon the loads determined in Step 1, the designer 
the owner is not home when the should develop the range of minimum and maximum watt-
power goes out. ages for the desired applications. Table VI-D2, Typical Electric 

Appliance Loads, can be used to estimate these minimum and 
maximum loads. 

TableVI-D2 Typical Electrical Appliance Loads 

HomeEquipment Typical Wattage Start Wattage 

Critical items: 
Limited lights (safety) 400 400 
Sewage pump (3/4 hp to 1 hp) 1000 4000 
Sump pump (1/3 hp to 1/2 hp) 333 2300 
Water pump 800-2500 800-10000 

Non-critical items: 
Refrigerator 400 -800 1600 
Freezer 600 -1000 2400 
Furnace blower 400 -600 1600 
Furnace oil burner 300 1200 
Furnace stoker 400 1600 
Limited receptacles 600 600 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.83 
January1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Step 4: Select generator/battery unit size: 

At'

Size the generator/battery unit set from load information ob-
Emergency power equipment tained in Step 1. Generator/battery unit set sizing is based upon 
should be located above the flood the approximation that motor starting requirements are three to 
protection level. four times the nameplate wattage rating; thus, generator sets/ 
battery units should be sized to handle four times the running 
watts of the expected appliance loads. 

Small generators/battery unit sets are usually rated in watts. 
Two ratings are often listed-a continuous rating for normal 
operation and a higher rating to allow for power surges. 
Match higher surge ratings with the starting wattage. 

Generator sets can be loaded manually with individual loads 
coming on line in a particular sequence, or the loads can be 
transferred automatically with all devices trying to start at 
one time. This is illustrated by the following examples. 

Table VI-D3 Example of Maximum Generator Sizing Procedure 

RUNNING LOAD STARTING LOAD 
SEWAGE PUMP 1000 4000 
FURNACE 300+400=700 1200 + 1600 = 2800 
SUMP PUMP 333 2300 
REFRIGERATOR 400 1600 
FREEZER 600 2400 
RECEPTACLES 600 600 
LIGHTS 400 400 
TOTALS 4033 WATTS 14100 WATTS 

Select a generator with a continuous rating that is at least as large as the total wattage to start all 
loads at once. 14KW appears to be the minimum size to start all motors at once. 

VI- D.84 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Emergency Power 

TableVI-D4 

Example Step Sequence Manual Start -Minimum Generator Sizing 

Starting Running 

Loads Loads 

Sewage Pump Step 1 4000 

Furnace Step 2 2800 + 1000 =3800 

Sump Pump Step 3 2300 + 700 + 1000 = 4000 

Refrigerator Step 4 1600 + 333 + 700 + 1000 = 3633 

Freezer Step 5 2400 + 400 + 333 + 700 + 1000 = 4833 

Receptacles Step 6 600 + 600 + 400 + 333 + 700 + 1000 = 3633 

Lights Step 7 400 + 600 + 600 + 400 + 333 + 700 + 1000 = 4033 

Largest Load 4,833 Watts; Thus 5KW Generator Set is minimum size. 

For each step or appliance load, add the running wattage of items already operating to the starting
wattage of the items being started in that step. Select the largest wattage value out of all steps.
Compare maximum wattage with continuous wattage rating of the generator.

At this point, the designer has sufficient information to present 
preliminary equipment recommendations to the homeowner, 
prior to the design oftransfer switches, emergency panels, 
wiring, and other miscellaneous items. Among the issues the 
designer should confirm with the homeowner are: 

* The essential power loads proposed for the generator/ 
battery set. Discuss any other essential loads pertaining to 
life or property safety. 
* Generator/battery set siting and proposed location. This 
should be discussed in light of unit weight, portage, 
storage, and handling methods. 
* Provisions for fuel storage and fuel storage safety. 
FnninAerinnPrinrinins and Practices of Retrofittina Flood-Prone Residential Structures VI -D.85 
January1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

The designer should also: 

* Educate the homeowner on battery operating time and/or 
generator operating time vs. fuel tank capacity. 
* Present initial generator/battery set cost and future operating 
costs. 
* Discuss requirements for having equipment located above 
FPE. 
* Discuss generator heat radiation and exhaust precautions to 
prevent carbon monoxide poisoning. 
Step 5: Selectiontransfer switch size. 

Transfer switches are designed to transfer emergency loads 

from the main house system to the generator/battery system 

in the event of a power failure. After power has been 

restored, the transfer switch is used to transfer power from 

the generator/battery set to the house system. Transfer 

switches can be manual or automatic. It is important to 

check with local code officials regarding requirements for 

how transfer switches are set up. 

Manual Transfer Switches generally have the following 
characteristics: 

* Double pole, double throw, nonfrsible, safety switch, 
general duty with factory installed solid neutral, and 
ground bus. Double pole, double throw transfer 
switches are typically required to prevent accidentally 
feeding power back into the utility lines to workers 
servicing the line. This switch also protects the generator 
set from damage when the power is restored. 
* Transfer switches are available with NEMA 1 enclosures 
for indoor mounting and NEMA 3R enclosures for 
outdoor locations. 
VI -D.86 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Emergency Power 

* The voltage rating oftransfer switches is typically 250 volts. 
* Available sizes are 30 amp, 60 amp, 100 amp, and 200 
amp. 
The designer should consider the following items when 
selectinga manual transfer switch: 

* Coordinate amperage to match emergency panel rating, 
continuous current rating of branch circuits, genset 
overcurrent protection, and panel branch feeder circuit 
breaker size. 
* Fusible manual transfer switches are required as service 
entrance equipment and are required if the panel circuit 
breaker size does not correspond to the emergency 
panel size and generator/battery set circuit breaker size. 
* Several manufacturer models are not load break rated 
and require load shedding before transfer operation. 
These switches must be used for isolation only. They do 
not have quick make-quick break operation. 
* Some transfer switches are padlockable in the "off' 
position. 
* Switches should have door interlocks to prevent the 
door from opening with the handle in the "on" position. 
* Avoid locatingthe transfer switch at a meter or service 
entrance outdoor location. Switches are not service 
entrance rated unless they are fusible, and with this 
scenario the total house load is transferred to the genset. 
This method requires a much larger switch and cannot 
be taken out of service without de-energizing the entire 
dwelling. 
Engineering Principles and Practices ofRetrofitting Flood-Prone Residential Structures VI -D.87 
January1 995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Automatic transfer switches are much more expensive than 
manual transfer switches and require an electrical start option 
for the generator/battery set. These switches are usually not cost 
effective forhomeowner generator/battery set installations but 
may, in certain applications involving life safety issues, wanrant 
the added expense. 

Automatic transfer switches automatically start the generator! 
battery set upon loss of regular power and transfer the emergency 
load to the generator/battery source. After power has 
been restored for some time, the transfer switch automatically 
transfers back to normal power source. The generator set 
continues to run for some time unloaded until the set has cooled 
down, then it shuts off. The designer should contact the manufacturers 
for specific applications data for these automatic 
transfer switch devices. 

Step 6: Select emergency panel size. 

Equipment and appliances that need to be powered by a 
generator/battery set are typically wired in an emergency panel 
box. The design of the emergency panel box should be conducted 
with the following considerations in mind: 

* Select branch circuit loads for emergency operation. 
* Size branch circuit over current devices in emergency panel 
to protect equipment and conductor feeding equipment. 
Appliance circuits and motor loads should be sized in 
accordance with NEC requirements. 
d Size panel bus based upon NEC requirements and on 
continuous rating at 125% calculated load for items that 
could operate over three hours. 

o Verify panel box size vs. number and size of circuit 
breakers. 
VI -D.88 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Emergency Power 

* See Tables VI-D5 and VI-D6 for minimum panel bus sizes 
and emergency panel specification criteria. 
TableVI-D6 Emergency Panel Specification 

Criteria 

* Load center type residential panel 
* Main lug 
* Indoor NEMA 1 enclosure above flood protection level 
with isolated neutral for sub panel application 
* Same short circuit current rating as main panel
with ground bar kit
* Pole spaces as required for appliance and motor circuit 
breakers 
At this point, the designer should confirm several items with 
the homeowner including: 

emergencypanel location above flood protection levele 

* transfer switch location above flood protection level 
* no load transfer switch operation 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-D.89 
January1995 


Chapter VI: General Design Practices 

Dry Floodproofing 

Step 7: Design wire conductor and raceway ground system. 

Select route for wiring between panel, transfer switch, and 
generator set and specific wiring materials in accordance 
with local electric codes or NEC. 

Operation and Maintenance Issues: The following 
instructions should be provided to the homeowner with 
generator equipment. 

For manual start generators, operating procedures include: 

1. Turn offor disconnect all electrical equipment including 
essential equipment in emergency panel. CAUTION: 
Make sure solid state appliances remain off while 
standby power is operating. 
2. Connect generator to receptacle. 
3. Place transfer switch in generator position. 
4. Start generator and bring it up to proper speed (1800 
rpm or 3600 rpm). Check generator volt meter; it 
should read 11 5-125 volts; the frequency meter should read 
60 Hz plus or minus three hertz. 
5 . Start the motors and equipment individually, letting the 
genset return to normal engine speed after each load has 
been applied. The load should be applied in the sequence 
used to determine the genset size and generally with the 
CAUTION:if problemsoccur, largest motor load applied first. If the generator cuts out,
turn off existing panel circuit turn offall the electrical equipment and restart.
breaker feeding the transfer
switch before investigating 6. Checkthevoltmeterfrequently. If itfallsbelow200 volts

problemswith faultyconnections for 240-volt equipment or 100 volt for 120-volt equipment,
or wiring, reduce the load by turning off some equipment.

VI-D.90 Engineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Emergency Power 

7. When normal power has been restored, turn off all the 
electrical equipment slowly, one load at a time. Turn offall 
emergency load, place transfer switch in normal load 
position, and turn electrical equipment back on. 
8. Turn off genset circuit breaker. However, allow genset 
approximately five minutes to run for cool-down. Then 
turn off generator engine. Return generator to storage 
location. 

For manual start generators, maintenance procedures include: 

1. Operate generator at about 50% load monthly or bimonthly 
to ensure reliability. 
2. Check for fuel leaks. 
3. Change engine oil per manufacturer's requirements. 
4. Replace or use the fuel supply about every 30 to 45 days 
to prevent moisture condensation in the tank and fuel 
breakdown. Gasoline additives can keep gasoline-powered 
generator fuel from breaking down. 
5. Keep tank full. 
6. Replace air filter element per manufacturer's requirements. 
CONSTRUCTION 

All wiring shallbe installedby licensed electricians to meet 
NEC requirements, local electrical regulations, and requirements 
of the local power company. Bond ground from 
generator emergency panel through transfer switch back to 
main service panel. 

=nningarinn Prinpinineand Practices of Retrnfittinn Flood-Prone Residential Structures VI -D.91 

January19' 95 l._*v --
Januaryl 995 


Wet Floodproofing 

Table of Contents 

Protection of the Structure ........................................................... VI -W.2
Foundations ........................................................... VI -W.2
Cavity Walls ........................................................... VI -W.2
Solid Walls ........................................................... VI -W.3

Design of Openings in Foundation Walls forIntentional Flooding of 
Enclosed Areas Below the FPE ........................................................... VI -W.4 

Use of Flood-Resistant Materials ........................................................... VI -W.6

Building Operation and Maintenance Procedures and Emergency Preparedness Plans ......VI -W.7 
Flood Warning System ........................................................... VI -W.7 
Inspection and Maintenance Plan ........................... ................................ VI -W.7 
Flood EmergencyOperation Plan........................................................... VI -W.8 

Protection of ServiceEquipment ............................................................ VI -W.9
Relocation........................................................... VI -W.9
Elevation............................................................ VI -W.9
In-Place Protection ........................................................... VI -W.10

-

Field Investigation............................................................ VI W.11

Design Overview ........................................................... VI -W. 14
Mechanical Systems ............................................................ VI -W.15
Piping Systems ........................................................... VI -W. 16
Tanks........................................................... VI-W.16
Homeowner Coordination ............................................................ VI -W.17
For Shielding Measures ........................................................... VI-W.17
For Relocation Measures ............................................................ VI -W.17

nnin,...nni nlPri Drn,,+ipqa o~fPatrfffttinn Flond-Prnne Reaidential Structures VI -W.i 
January 1995 


Developing Design Details and Specifications ........... ..................... 
Verify Design with Homeowner ................................ 
Prepare Construction Documents ................................ 
Electrical Systems ................................ 
Central Heating System Alternatives ......................... ................................................ 

Gravity Furnaces .VI 
Forced Warm Air Furnaces .VI 
Hot Water Heating Boilers .VI 
Heat Pump Compressors .VI 

Central Cooling System .VI 
IndoorUnits .VI 
OutdoorUnits .VI 
Ductwork .VI 
Unitary A/C Systems .VI 

Ductwork Systems .VI 
Piping Systems .VI 
Fuel Supply/Storage Applications .VI 

In-Space Heating Equipment .VI 
Room Heaters and Wall Furnaces .VI 
Oil/Kerosene Heaters .VI 
Electric Heaters .VI 

Water Systems .VI 
Drinking Water Wells .VI 
On-Site Portion of Water Systems .............................. 

Sewer Systems ............................... 

On-Site Portion of Sewer Systems .............................. 
SepticTanks .............................. 
Telephone Systems .............................. 
Cable TV Systems .............................. 

Construction .............................. 
Electrical..... 
Mechanical ..... 

VI -W. 18 
VI -W. 18 
VI -W.18 
VI -W.19 

VI -W.22 
-W.23 
-W.24 
-W.25 
-W.26 
-W.26 
-W.26 
-W.27 
-W.27 
-W.27 
-W.27 
-W.29 
-W.30 
-W.3 1 

0 

-W.3 1 
-W.3 1 
-W.32 
-W.32 
-W.32 
VI -W.33 
VI -W.34 
VI -W.34 
VI -W.35 
VI -W.37 
VI -W.3 8 

VI -W.39 
VI -W.39 
VI -W.40 

VI -W.ii Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 

January 1995 


-

WET FLOODPROOFING

Wet floodproofing can be defined as permanent or contingent measures applied to a 

structure and/or its contents that prevent or provide resistance to damage from flooding 

by allowing floodwaters to enter the structure. The basic characteristic that distinguishes 

wet floodproofing from dry floodproofing is that it allows internal flooding of a structure 

as opposed to providing essentially watertight protection. 

Flooding of a structure's interior is intended to counteract hydrostatic pressure on the 

walls, surfaces, and supports of the structure by equalizing interior and exterior water 

levels during a flood. Inundation also reduces the danger of buoyancy from hydrostatic 

uplift forces. Such measures may require alteration of a structure's design and construc

tion, use of flood-resistant materials, adjustment of building operation and maintenance 

procedures, relocation and treatment of equipment and contents, and emergency prepared

ness for actions that require human intervention. This section examines: 

* protection of the structure; 
* design of openings for intentional flooding of enclosed areas below the FPE; 
* use of flood-resistant materials; 
* adjustment of building operation and maintenance procedures; 
o the need for emergency preparedness for actions that require human intervention; and 
o design of protection for the structure and its contents including utility systems
and appliances.
Wet floodproofmg is appropriate
for basements, garages, and
enclosedareas below the flood
protection level.

Fngineerinn Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -W.1 

January 1995 


ChapterVI: General Design Practices

$Q\NWet Floodproofing 

PROTECTION OF THE STRUCTURE 

6 

The NFIP allows wet flood-

proofing only in limited situa

tions. The most common 

application is with pre-FIRM 

structures not subject to substan

tial damage and/or substantial 

improvement criteria. Structures 

in the pre-FIRM category can 

utilize any retrofitting method. 

However, for new structures or 

those that have been substantially 

damaged or are being substan

tially improved, application of 

wet floodproofing techniques is 

limited to the following situa

tions: 

* Enclosed areas below the BFE 
thatare used solely for parking, 
buildingaccess, or limited 
storage. These areas must be 
designed to allow for the automatic 
entry and exit of floodwaters 
through the use of openings, 
and be constructed of flood-
resistant materials. 
* Attached Garages. A 
garage attached to a residential 
structure, constructed with the 
garage floor slab below the BFE, 
must be designed to allow for the 
automatic entry and exit of floodwaters. 
Openings are required in 
the exterior walls of the garage or 
in the garage doors. In addition, 
the areas below the BFE must be 
constructed with flood-resistant 
materials. 
* FEMA has advised communities 
that variances to allow 
(continued on next page) 

As with dry floodproofing techniques, developing a wet 
floodproofing strategy requires site-specific evaluationsthat 
may necessitate the services of a design professional. The 
potential for failure of various structural components 
(foundations, cavity walls, and solid walls) subjected to 
inundation is a major cause of structural damage. 

FOUNDATIONS 

The ability of floodwater to adversely affect the integrity of 
structure foundations by eroding supporting soil, scouring 
foundation material, and undermining footings necessitates 
careful examination of foundation designs and actual construction. 
In addition, it is vital that the structure be adequately 
anchored to the foundation. Uplift forces during a 
flood event are often great enough to separate an improperly 
anchored structure from its foundation should floodwaters 
reach such a height. 

CAVITY WALLS 

Wet floodproofing equalizes hydrostatic pressure throughout 
the structure by allowing floodwater to enter the structure 
and equalize internal and external hydrostatic pressure. 
Thus, any attempt to seal internal air spaces within the wall 
system is not only technically difficult, but also contrary to 
the wet floodproofing approach. Provision must be made 
for the cavity space to fill with water and drain at a rate 
approximately equal to the floodwater rate of rise and fall. 
Insulation within cavity walls subject to inundation should also 
be atypethat is not subject to damage frominundation. The 
design of foundation openings to equalize hydrostatic pressure is 
covered in the next section. 

Vi -W.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Protection of the Structure 

' (continued) 

wet floodproofing may be issued 
for certain categories of structure. 
Refer to FEMA's Technical 
Bulletin #7-93, Wet Floodproofing 
Requirements for Structures 
Located in Special Flood Hazard 
Areas in Accordance with the 
NationalFlood Insurance Program. 

SOLID WALLS 

Solid walls are designed without internal spaces that 
could retain floodwater. Because these walls can be 
somewhat porous, they can absorb moisture and, to 
a limited degree, associated contaminants. Such 
intrusion could cause internal damage, especially in a 
cold (freeze-thaw) climate. Therefore, where solid 
walls are constructed of porous material, the retrofitting 
measures should include both exterior and interior 
protective cladding to guard against absorption. 

Pnninaarinn PrineinIcksand Practirce of I Retrnfittinn Flood-Prone Residential Structures VI -W.3 
January1995 


Chapter VI: General Design Practices 
Wet Floodproofing 

DESIGN OF OPENINGS IN FOUNDATION WALLS FOR 
INTENTIONAL FLOODING OF ENCLOSED AREAS 
BELOW THE FPE 

In buildings that are constructed on extended solid foundation 
walls or that have other enclosures below the FPE (that 
are not designed to resist flooding), it is important that the 

For additional informationonthe foundation contain openings that will permit the automatic 
regulations and design guidelines entry and exit of floodwaters. (See Figures VI-WI and VI-
concerning foundation openings, W2.) 
please refer to FEMA Technical 
Bulletin #1-93, Openings in 

Foundation Wallsfor Buildings These openings allow floodwaters to reach equal levels on both 
Located in Special Flood Hazard sides ofthe walls and thereby lessen the potential for damage 
Areas in Accordance withthe fromhydrostaticpressure. While not arequirement for existing 
National Flood Insurance buildings built prior to a community'sjoining the NFIP, NFIP 
Program. regulations require these openings for all new construction and 

substantial improvements of existing buildings in SFHAs. 

The minimum criteria for design ofthese openings is as follows: 

FoundationOpening' I A minimum oftwo openings shall be provided on different 
with Vent I sides of each enclosed area, having a total net area of not 
\ _7$ less than one square inch for every square foot of enclosed 
BFE area subject to flooding. This is not required if openings are 
-] \ and certified. 

Eengineered 

12' Maximum y-1 Bottom of 
Height L__10 4 9 pening a The bottom of all openings shall be no higher than one foot 
AboveGrade \ above grade. Li|Final Grade 

B!ockFoundation Openings must be equipped with screens, louvers, valves, 

L_ J or other coverings or devices that permit the automatic 
entry and exit of floodwaters. 
Figure VI-W 1: Typical Opening for Solid 
Foundation Wall 

VI -W.4 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Design of Openings in Foundation Walls for Intentional 
Flooding of Enclosed Areas Below the FPE 

Maximum ; \ 

BFE_ _. e / oor J m [Attachedm Maximum

............ g FO G~arage BFE 
X Enclsed )i Lowetloor > -| v

Fiished 

;.?1 Area GradeX x > _ _ = X 1-Opening 

FoundationOpening Enclosed Area 
(Typical) 

Figure VI-W2: NFIP-Compliant Residential Building Built on Solid Foundation Walls with 
Attached Garage 

Fneiinaarinri Prinninlos and Prartircesrof Retrofittino Flood-Prone Residential Structures VI -W.5 
January 1995 


Chapter VI: General Design Practices 
'/Q Wet Floodproofing 

USE OF FLOOD-RESISTANT MATERIALS 

lose 

Detailedguidance is provided in 
FEMA Technical Bulletin 2-93, 

Flood-Resistant Materials 
Requirements for Buildings 
Located in Special Flood Hazard 
Areas in Accordance with the 
National Flood Insurance 
Program. 

POPt 

Additional information on these 
elementscan be obtained from 
FEMA Technical Bulletin 7-93, 

Wet Floodproofing Requirements 
for Structures Located in Special 

Flood Hazard Areas in Accor- 

dance with the National Flood 

Insurance Program. 

In accordance with the NFIP, all materials exposed to floodwater 
must be durable, resistant to flood forces, and retardant to 
deterioration caused by repeated exposure to floodwater. 
Interior building elements such as wall finishes, floors, ceilings, 

roofs, and building envelope openings can also suffer consider

abledamae from inundation by flood-waters, which can lead 
to failure or an unclean situation. The exterior cladding of a 
structure subject to flooding should be nonporous, resistant to 
chemical corrosion or debris deposits, and conducive toeasy 
cleaning. Interior cladding should be easy to clean and not susceptible 
to damage from inundation. Likewise, floors, ceilings, roofs, 

fasteners, gaskets, connectors, and building envelope openings 
should be constructed of flood-resistantmaterialsto minimize 
damagedunng and after floodwater inundation. 

Generally, these performance requirements indicate that masonry 
construction is the most suited to wet flood-proofing in 
terms of damage resistance. In some cases, wood or steel 

structures may be candidates, provided that the wood is 
pressure treated or naturally decay-resistant and steel is galvanized 
or protected with rust-retardant paint. 

Vi -W.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Building Operation and Maintenance Procedures 
and Emergency Preparedness Plans 

BUILDING OPERATION AND MAINTENANCE 
PROCEDURES AND EMERGENCY PREPAREDNESS 
PLANS 

The operational procedure aspect of applying floodproofing 
techniques involves both the structure's functional requirements 
for daily use and the allocation of space with consideration 
of each function's potential for flood damage. Daily 
operations and space use can be organized and modified to 
minimize damage caused by floodwater. 

FLOOD WARNING SYSTEM 

Because wet floodproofing will, in most cases, require some 

human intervention when a flood is imminent, it is extremely 

important that there be adequate time to execute such 

actions. This may be as simple as monitoring local weather 

reports, the National Weather Service alarm system, or a 

local flood warning system. 

INSPECTION AND MAINTENANCE 
PLAN 

Every wet floodproofing design requires some degree of 

periodic maintenance and inspection to ensure that all 

components will operate properly under flood conditions. 

Components of the system, including valves and opening 

covers, should be inspected and operated at least annually. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -W.7 
January 1995 


A A

Chapter VI: General Design Practices 
Wet Floodproofing 

FLOOD EMERGENCY OPERATION 
PLAN 

This type of plan is essential when wet floodproofing 
requires human intervention, such as adjustments to or 
relocation of contents and utilities. A list of specific actions and 
the location of necessary materials to perform these actions 
should be developed. 

VI -W.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Protection of Service Equipment 

PROTECTION OF SERVICE EQUIPMENT

The purpose ofthe retrofitting methods in this section is to 
prevent damage to structure, contents, and equipment caused 
'01* by contact with floodwaters by isolating these components from 
Serviceequipmentincludes floodwaters. Isolation ofthese components can take the form 
heating and air conditioning of relocation, elevation, or protection in place. 
systems, appliances, electrical/ 
plumbing systems, and water RELOCATION 
service/sewerfacilities. 
The most effective method of protection for equipment and 
contents is to relocate (permanently or temporarily) threatened 
items out of harm's way. The interior of the structure must 
be organized in a way that ensures easy access and facilitates 
relocation. 

ELEVATION 

Within the flood-prone structure, elevation of key items could 
be achieved through the use of existing or specially constructed 
platforms or pedestals. Contingent elevation can be accomplished 
by the use of hoists or an overhead suspension system. 
Relocated utilities placed on pedestals are subject to earthquake 
damage and must be secured to resist seismic forces. 

Figure VI-W3: ElevatedAir Conditioning Compressor 

EnaineerinaPrinciDlesand Practices of Retrofittina Flood-ProneResidential Structures VI-W.9 
January 1995 


Chapter VI: General Design Practices 
Wet Floodproofing 

IN-PLACE PROTECTION 

Some components can be protected in place through a variety 
of options, such as: 

* protective waterproof enclosures (flood-resistant bags); 
* anchors and tie-downs to prevent flotation; 
* low barriers or shields; and 
* protective coatings. 
FigureVI-W4: Flood Enclosure ProtectsBasement 
Utilities from Shallow Flooding 

Utility systems as used here are mechanical, electrical, and 
plumbing systems including water, sewer, electricity, telephone, 
cable TV, natural gas, etc. The recommendations presented in 
this section are intended for use individually or in common to 
mitigate the potential for flood-related damage. 

VI -W.10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

FIELD INVESTIGATION 

Detailed information must be obtained about the existing 
structure to make decisions and calculations concerning the 
feasibility of using wet floodproofing. Use the Building/ 
Building System Data Sheets (Figures VI-3 and VI-4) as a 
guide to record information. 

Once this data is collected, the designer should answer the 
questions contained in Figure VI-W5, Wet Floodproofing Field 
Investigation Worksheet, to confirm the measure selected and 
develop apreliminary concept for the installation of wet 
floodproofing measures. 

Once a conceptual approach toward wet floodproofing has 

been developed, the designer should discussthe following 

items with the homeowner: 

* Previous floods and which equipment was flooded in 
prior floods and which previous appliances and branch 
circuits were affected by the floods. 
* Plan of action as to which equipment can be relocated 
and which equipment will have to remain located below 
FPE. 
* Length of power outages for work to be completed. 
* Specific scope of items to be designed. 
* Note any unsafe practices or code violations or exceptions 
to current codes. 
Engineering Principles and Practicesof Retrofitting Flood-Prone ResidentialStructures VI-W.11 
January 1995 


Chapter VI: General Design Practices 
/ Q Wet Floodproofing 

Owner Name: Prepared By: 
Address: Date: 
Property Location: 

Wet Floodproofing Field Investigation Worksheet 

El Flood protection elevation (FPE) required? 

El Can equipment be protected in place? -Yes -No 
O Is it feasible to install a curb or "pony" wall around equipment to act as 
a barrier? Yes No 
El Is it feasible to construct a waterproof vault around equipment below the FPE? 
_ Yes No 

o Can reasonably sized sump pumps keep water away from equipment? 
_ Yes No 
El Can equipment feasibly be relocated? 

O To a higherlocation on same floor level? -Yes -No 

o To the next floor level? -Yes No 
171 Is room available for such equipment? -Yes -No 
E Can existing spaces be modified to accept equipment? _ Yes -No 
a Is additional space needed? Yes No 
a Do local codes restrict such relocations? Yes No 

a Electrical Questions 
al Is it feasible to relocate meter base and service lateral above FPE? -Yes No 
Cl Is it feasible to relocate main panel and branch circuits above FPE? -Yes -No 

El Is it feasible to relocate appliances, receptacles, and circuits above FPE? 

Yes No 
Cl Is it feasible to replace light switches and receptacles below FPE? -Yes No 
1E Can ground fault circuit interrupter protection to branch circuits be added 

below the FPE? -Yes No 
VI Can service lateral outside penetrations be sealed to prevent floodwater entrance? 
Yes No 
E Can cables and/or conduit be mechanically fastened to prevent damage 
during flooding? _ Yes -No 
El Can splices and connections be made water resistant or relocated above FPE? 
_ Yes No 
1 of 2 

Figure VI-W5: Wet Floodproofing Field Investigation Worksheet 

VI -W.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

o MechanicalQuestions 
o If equipment is relocated, examine how related systems will be impacted including hot 
water/steam/condensate piping, cooling condensate drains, ductwork, and fuel supply. 
_ Yes_ No 
0 If equipment is to be relocated, verify that adequate structural support and clearances 

for maintenance and repair exist at the new location. Yes -No 
O Can fire separation requirements be met? -Yes _ No 
SKETCH: 

2 of 2 

Figure VI-W5: Wet Floodproofing Field Investigation Worksheet (continued) 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI-W.13 
January 1995 


Chapter VI: General Design Practices
( Wet Floodproofing

DESIGN OVERVIEW 

In this section we will present the process of design of wet 

floodproofing measures for utilities and appliances address

ing applicable relocation, elevation, and protection in 

place considerations for each type of utility system and 

appliancenoted below: 

* ElectricalSystems 
* Central Heating Systems 
-Gravity Type Furnaces 
-Forced Warm Air Furnaces 
-Hot Water/SteamHeating Boilers 
-HeatPump Compressors 
* Central Cooling Systems 
* Ductwork Systems 
* Piping Systems 
* In-Space Heating Equipment 
* Water Systems 
* Sewer Systems 
* SepticTans 
'Telephone Lines 
VI -W.14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design Overview 

* Cable TV Lines 
The general process of designing wet floodproofing measures 
involves developing apreliminary concept, verifying the concept 
with the homeowner, developing design details and specifications, 
verifying the design with the homeowner, preparing 
construction documents, and providing construction phase 
services. The key components of this process are presented 
below: 

MECHANICAL SYSTEMS 

* Make apreliminary sketch/floor plan showing location of 
mechanical systems. 
* Indicate proposed locations for shielding, relocation, or 
modifications. 
* Indicate modifications or relocations of related components. 
* Indicate materials of construction and means of access 
to equipment. 
* Determine how the shielding, relocation, or modifications 
may affect the structure and coordinate necessary 
modifications with a structural engineer. 

* Develop preliminary details of supports,hangers, piping/ 
ductwork, and equipment modifications. 
Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -W.15 
January 1995 


ChapterVI: General Design Practices 

Wet Floodproofing

K %9 

PIPING SYSTEMS 

* Make preliminary sketchof piping systems affectedby 
flooding. 
* Indicate proposed locations for relocation and/or additional 
anchorage. 
* Determine how relocation or modifications may affect 
the structure and coordinate necessary modifications 
with a structural engineer. 
* Develop preliminary details of supports, hangers, and 
pipingmodifications. 
TANKS 

* Make preliminary sketch of underground tanks and 
necessary provisions to prevent displacement or flotation. 

* Make preliminary sketch of above-ground tanks indicating 
anchoring/ballasting provisions to prevent displacement 
or flotation. 

VI -W.16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Design Overview 

HOMEOWNER COORDINATION 

* Verify existing conditions related to all wet 
floodproofing measures being proposed. 
For Shielding Measures 

* Determine conditions at interface of shields and existing 
walls and floors. 
* Verify structural conditions and necessary provision for 
adequate support of wall. 
* Verify condition for means of access through or over 
wall for service and maintenance of equipment. 
For Relocation Measures 

* Verify existence of sufficient room for access and 
maintenance. 
* Verify structural conditions and necessary provisions for 
supporting equipment. 
* Verify re-routing of piping, fuel supply lines,venting, 
and ductwork. 
* Verify with the homeowner any restriction to proposed 
measures that may be imposed because of deed restrictions, 
zoning laws/subdivision restrictions, and local regulations. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.17 
January 1995 


Chapter VI: General Design Practices 

,' Q Wet Floodproofing 

DEVELOPING DESIGN DETAILS AND 
SPECIFICATIONS 

* Prepare scale drawings of residence floor plans, as 
necessary, to show areas affected by the selected retrofitting 
measure. 
* Prepare details of installation of equipment at new 
locations, including proposed modifications to piping, 
fuel supply lines, venting, and ductwork. 
* Prepare details of new equipment supports or hanging 
provisions. 
* Prepare written specifications for the work, including 
general materials/products, and execution sections. 
VERIFY DESIGN WITH HOMEOWNER 

* Review with the homeowner the proposed retrofitting 
measures and details to ensure that they accurately 
reflect both the existing conditions and proposed improvements. 
PREPARE CONSTRUCTION 

DOCUMENTS 

* Prepare final construction drawings, including details for 
all measures proposed. 
* Make reference to applicable codes and regulations that 
govern the work. 
VI -W.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design Overview 

* Indicate whether or not submission and review by 
authorities having jurisdiction is required. 
* Prepare final specifications. 
ELECTRICAL SYSTEMS 

Electrical system components can be seriously damaged by 
floodwaters when either energized or de-energized. Silt and 
grit accumulates in devices not rated for complete submergence 
and destroys the insulation value of the device. 
Current circuit breakers and fuses are designed to protect the 
wiring conductors and devices from overcurrent situations, 
including short circuit or ground fault conditions. Floodwaters 
seriously affect operation ofthese devices. 

Most homes were not designed to mitigate potential flood 
damage to electrical equipment; however, there are retrofitting 
steps that will provide permanent protection for the 
electrical system. 

* The chief concern is to raise or relocate equipment and 
devices above the FPE. 
* A second step is to seal outside wall penetrations, 
anchor cables and raceway, and mechanically protect the 
wiring system in flood-prone locations. 
* A third step is to seal out moisture. Electrical system 
problems occur as moisture permeates devices causing 
corrosion, which can lead to high resistance of electrical 
connections. 
* A fourth step necessary for retrofitting is the addition of 
ground fault circuit interceptors, which de-energize 
circuits when excessive current leakage is encountered. 
This step ultimately assists life safety protection and may be 
required by local code. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.19 

January 1995 


Chapter VI: General Design Practices 

Wet Floodproofing 

Each residence presents the designer with a unique set of 
characteristics including age, method of construction, size, 
and location. There are different combination systems that may 
need to be modified. When it is not feasible to elevate in place, 
the following information provides the design considerations and 
details that govern the retrofitting of electrical equipment and 
circuits below the FPE. 

* Receptaclesand switches shouldbe keptto aminimumand 
elevated as high as is practical. 
* Circuit conductors must be UL listed for use in wet locations. 
e 

Wiring should be run vertically for drainage after being 

inundated. 

* Outlet boxes should be corrosion-resistant and nonmetallic 
with weatherproof gaskets. 
* Lighting fixtures should be connected via simple screw 
base porcelain lampholders. This will allow for speedy 
removal of lamp or fixture, and the lampholder can be 
cleaned and reused. 
* Sump pumps and generators should have cables long 
enough to reach receptacles above the FPE. 
All circuits below the FPE should be ground fault 

interrupter protected. 

e 

-Wiring splices below FPE should be kept to a minimum. 
If conductors must be spliced, use crimp connectors and 
waterproof with heat shrink tubing or grease packs over 
the splice. 

VI -W.20 Engineerina PrinciDlesand Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design Overview 

* Circuits serving equipment below the FPE should not 
also provide power to equipment above the FPE. This 
means power can be turned off to circuits below the 
FPE and not affect the rest of the home. 
* Electrical equipment and appliances relocated above the 
FPE should have new circuits installed. 
The electrical system should be designed in accordance with 
the National Electrical Code, local codes, and local utility 
company requirements. Prepare construction details and 
specifications as detailed below: 

* Show electrical floor plan and site plans for work to be 
completed by contractors. Include symbols, notes, and 
schedules. 
* Show new riser diagram if service is relocated or replaced. 
Show size of conductors and ground electrode 
conductor. 
* Note demolition of materials and work to be removed. 
* Size new circuit conductors and overcurrent protection 
to devices, equipment, and appliances. 
* Prepare specifications for work to be completed. 
EngineeringPrinciples and Practices of F Retrofitting Flood-Prone Residential Structures VI -W.21 
January 1995 


Chapter VI: General Design Practices 

L Q Y< Wet Floodproofing 

CENTRAL HEATING SYSTEM 
ALTERNATIVES 

The protection of central heating system equipment (i.e., 

furnaces, boilers, fan-coil airhandlers) requires consider

ation of many factors. The designer must be sure that any 

protection or relocation of such equipment conforms to the 

requirementsset forth in local building codes and floodplain 

ordinances, state building codes, and equipment 

manufacturer's installation instructions. Some general 

points to consider are: 

* structural support for relocated equipment; 
 maintenance of required equipment clearances and mainte-
It nance access dictated by code and/or manufacturer; 

Most heating system equipment 

(i.e., furnaces, boilers, fan-coil air * provision of adequate combustion air for fuel-burning 

handling units) is designed and equipment; 

manufactured to operate in a 

particular orientation (i.e., vertical 

or horizontal).In most cases,the * maintenance ofproper venting offuel-burning equipment; 

equipment cannot be reconfigured and 

to operate in a different orientation. 

tion. * extension of fuel supply to relocated equipment. 

VI -W.22 Enqineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995 


Design Overview 

In a post-flooding situation, the 
designer may recommend replacing 
an old furnace with a new 
one that meets current codes, 
is more energy/cost efficient, and 
fits in the desired location. 

Gravity Furnaces 

These furnaces depend on natural convective air circulation 
for operation and do not have a fan or blower. Therefore, 
they are installed at the lowest point in the heating system, 
usually in a basement below the living areas of the house. 
Because of this, alternatives for protection and/or relocation 
are limited. Potential alternatives may include: 

Raise Gravity Furnaces 

* Are non-combustible construction materials required under 
the furnace? 
* Extension or relocation offuel supply lines. 
Provide Protective Ring Wall or Vault 

* Does prevailing code allow waterproofvaults below 
FPE? 
* Can a curb or half-height waterproofpartition be provided 
for protection? 
* Are gravity furnaces allowed under present code? 
Enaineerina Princioles and Practices ofRetrofittina Flood-Prone Residential Structures VI -W.23 
January 1995 


Chapter VI: General Design Practices 

& P< > Wet Floodproofing 

Forced Warm Air Furnaces 

The fiunaces may exist in one of several configurationsupflow, 
downflow, or horizontal-and do not necessarily have 
the same constraints of location as gravity furnaces. In addition 
to the alternatives and considerations listed above, which are 
also applicable to forced wann air furnaces, there are the 
following: 

Relocate Furnace to a Higher Floor or Attic 

* Is space available? 
* Can floor support the weight of the furnace? 
* Is non-combustible flooring required underneaththe furnace? 
* Can furnace be reconnected to existing means for venting or 
is new venting more feasible? 
* Can the ductwork be reconfigured to connect to furnace at 
new location? 
* In case of relocation to an attic, is the furnace labeled for 
such a location? 
* Does a utility room above the FPE need to be constructed 
adjacent to the structure? 
VI -W.24 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Design Overview 

Some local codes recluire that 
piping located in floEA 
hazard zones be cap; ableof 
withstanding stress due to i 
hydrostatic and hydi rodynamic 
forces of floodwaters. 

HotWater Heating Boilers 

Most hot water heating boiler systems utilize a closed loop hot 
water piping loop to distribute heat. Considerations for relocation 
of heating boilers include: 

Can the boiler be placed on a high pedestal base to raise it 
above the FPE? The procedure may include: 

& Reconfiguration of breeching and modifications to 
chimney or vent pipe; 

0 Modification of hot water or steam circulation piping; and! 
or 

* Modification offuel supply lines. 
Can the boiler be placed on an upper floor? 

Is there adequate space (codes generally dictate minimum
clearances)?
Can the boiler be reconnected to existing venting (i.e.,

chimney)?
Is there space for an expansion tank?
Does a utility room above the FPE need to be constructed

adjacent to the structure? 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.25 
January 1995 


ChapterVI: General Design Practices 

o >K WetFloodproofing
Heat Pump Compressors 

The compressor in a heat pump system is generally located 
outdoors. To prevent damage, the compressor can be raised 
above the FPE or be relocated to a constructed above-FPE 
space inside or adjacent to the home, if possible. 

CENTRAL COOLING SYSTEM 

Central cooling systems include split system heat pump and 
air conditioners, ductless split systems, and packaged 
unitary equipment. Common components of all of these 
systems subject to damage from flooding include heat 
transfer coils, electric motors, controls, and compressors. 
Protection of these components from contact with floodwaters 
is strongly recommended for pre-FIRM structures and 
is required for substantially improved (damaged) or new 
structures. The designer should determine whether equipment 
can be protected by shielding or relocation. Shielding 
as used here means to provide a permanent barrier around 
equipment to prevent contact with floodwaters. 

The designer should investigate existing conditions and 
determine shielding and/or relocation measures that may be 
applied to protect cooling equipment. 

Indoor Units 

* Can shielding be provided to prevent floodwaters from 
contacting the indoor air handling unit? 
* Can unit be raised or located on the floor above? 
VI W.26 Enianeerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Design Overview 

Consider reconnection ofthe unit to existing or relocated 
ductwork; extension and/or relocation of refrigerant piping; 
and/or reconnection of the unit to the existing electrical 

power supply. 

Outdoor Units 

* Can outdoor unit feasibly be raised above the FPE? 
Ductwork 

* Refer to the discussion of ductwork under the next section. 
Unitary A/C Systems 

* Can unitary equipment be relocated above the BFE? 
DUCTWORK SYSTEMS 

Effects on flooded ductwork depend on the material of duct 
construction. Typically, galvanized steel or rigid ductboard 
is used for main ducts with flexible round duct runouts to 
individualoutlets. Generally, if wet by floodwaters, ducts 
made up of ductboard or similar materials are not reusable. 
Such duct materials, when wet, usually exhibit degradation 
of physical strength and insulating properties. In addition, 
these materials become soiled by water-borne contaminants 
and cannot be cleaned effectively. Galvanized steel 
ductwork is less susceptible to damage from flooding and 
may be cleaned after flooding. 

Ductwork can be damaged from the weight of infiltrated 

water when floodwaters recede. Access doors installed at 

low points in the duct system can provide a means of 

drainage for any ductwork subject to inundation. Normally 

these access doors would remain closed and would open only 

Engineering Principles and Practicesof Retrofitting Flood-Prone ResidentialStructures VI -W.27 
January 1995 


Chapter VI: General Design Practices 

Q Wet Floodproofing 

when flooding conditions were imminent. These access doors 
may also be used as a means of getting inside ductwork for 
cleaning after a flood. 

Internal acoustical linings or insulations in ductwork cannot be 

reused if they have come into contact with floodwaters. The 
typical linings and insulations are made of glass fiber and, as 
with ductboard, become contaminated from the floodwater and 
cannot be effectively cleaned afterward. Ducts with linings or 
internal insulations that are flooded should be replaced. External 
insulations should also be replaced if wet by floodwaters. 

Although some types of insulation, such as closed cell foam, 
may be water-resistant, all insulations used in the interior of 
ductwork are subject to contamination and should not be 
reused after contact with floodwater. 

To confirm alternatives for floodproofing of ductwork, determine 
the following: 

* Is there any ductwork below the FPE? 
* What is the existing construction material for ductwork 
below the FPE (galvanized steel, ductboard, or flexible duct 
runouts)? 
* If ductboard or flexible duct is checked, verify whether or 
not it can be replaced with insulated steel ductwork. 
* Can ductwork be located at high levels or in the attic? This 
may require reconfiguring air outlet layouts and the use of 
bulkheads to conceal ducts. 
* Does ductwork insulation need replacement? Internally 
insulated ducts probably will have to be replaced, as 
replacement of insulation in existing ductwork is usually not 
feasible. 
VI -W.28 Engineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Design Overview 

* Steel ductwork with no interior insulation wet by floodwaters 
should be inspected, cleaned, and sanitized prior to 
reuse. 
PIPING SYSTEMS 

Potential damage to piping systems because of flooding includes: 

* Damage to thermal insulation of water piping; 
* Contamination of water piping by intrusion of floodwaters; 
* Breakage of piping due to hydrodynamic forces; 
* Clogging of building drain piping because of mud, silt, or 
debris; 
* Infiltration of floodwater into sewer and septic system; and 
* Surcharge (release) of sewage lines. 
Ofthese, only the first three canbe addressed by wet 

floodproofing measures. 

In selecting alternatives involving piping systems, determine the 
answers to the following: 

* Is piping below the FPE? 
* Can piping below the FPE be raised? It shouldbe determined 
whether it is more effective to leave piping at the 
existing location and provide adequate anchors to resist 
hydrodynamic forces or to relocate piping at a higher level. 
Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -W.29 
January 1995 


Chapter VI: General Design Practices 

K Y< ~ Wet Floodproofing 

If relocated, considerations against freezing may be required: 

* Can impervious pipe insulations be installed on pipes 
subject to becoming wet from floodwaters? 
* Can piping outlets be protected against intrusion of 
floodwaters? 
o Are pipes subject to hydrodynamic forces of floodwaters 
properly anchored? 
* Is piping provided with a proper sleeve and caulking at 
penetrations of exterior walls? 
* Surcharge of sewage lines must be considered. 
FuelSupply/Storage Applications 

In conjunction with floodproofing of heating equipment, the 
designer must consider rerouting andlor extending fuel 
supply lines (i.e., fuel oil, natural gas, and LPG) when 
equipment is relocated. Also, fuel storage tanks should be 
checked for proper support and anchorage to resist hydrostatic 
or hydrodynamic forces that act on such tanks during a 
flood. The following should be ascertained with respect to 
fuel supply/storage systems: 

* Can fuel lines be extended from existing point ofentry into 
the residence? 
* Does the fuel tank require relocation because of heating 
equipment relocation? 
* Is the existing fuel tank properly anchored to resist 
hydrostatic, hydrodynamic, and seismic forces? 
VI -W.30 Enaineerina PrinciDtes and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Design Overview 

IN-SPACE HEATING EQUIPMENT 

Residential "in-space" heating equipment refers to equipment 
located directly in the room (or space) to be heated. Such 
equipment may be permanently installed or portable. Gas room 
heaters and wall furnaces, oil/kerosene heaters, electric wall 
heaters, and electric baseboard heaters are examples of in-
space heating equipment. 

If such equipment is below the FPE, the designer must determine 
whether such equipment feasibly can be raised above the 
FPE. The extent to which most equipment may be raised is 
limited by the fact that the equipment must remain in the room 
or space and that raising such equipment may reduce heating 
effectiveness. The designer should consult with the equipment 
manufacturer's installation recommendations before considering 
relocation. 

Room Heaters and Wall Furnaces 

* Can these items be raised? 
* Determine any modifications required to vents and fuel 
supplyprovisions. 
Oil/Kerosene Heaters 

* Can these items be raised? 
* Determine any modifications required to vents and fuel 
supplyprovisions. 
EngineeringPrinciples and Practices of IRetrofittingFlood-Prone ResidentialStructures VI -W.31 
January 1995 


Chapter VI: General Design Practices 

&P27e Wet Floodproofing 

Electric Heaters 

* Can wall units be reinstalled at a higher location in the 
wall? 
* Floor, kickspace, and baseboard units by nature of their 
design usually cannot be raised. If these heaters exist in 
the residence below the FPE, the designer should 
investigate the installation of alternative heaters such as 
electric wall heaters that may be installed above the 
FPE. 
WATER SYSTEMS 

On-site water systems continue to be a source of flood 
damages. Many modifications can be made inexpensively. 
The failure of these systems as a result of flooding can often 
lead to significant repairs that can tax an individual's already 
tight repair budget. 

Drinking Water Wells 

Private water systems can also be threatened by flooding. 

There is little one can do to protect a well that is in the 

floodplain. To avoid contaminating the water system 

beyond the well, residents should turn off the pump motor 

prior to the floodwater reaching the well. This should be 

preceded by the filling of bathtubs and other containers with 

potable water. The storage tank in the building will also 

provide a reservoir of potable water. 

The pump should not be turned on until the well has been 
inspected by a local health official or well repair professional 
followingthe flood. Should the pump not be turned off or if it is 
turned back on prematurely, the contaminated water in the well 
will be pumped into the building, thereby contaminating the 
plumbing in the building. Salt water contamination can damage 

VI -W.32 EngineerinoPrinciples and Practices of Retrofittina Flood-Prone Residential Structures 

January 1995 


Design Overview 

pumps and other mechanical systems like hot water heaters and 
furnaces in hot water-heated buildings. This will, of course, 
significantly increase that cost ofthe restoring the system after a 
flood. 

Shallow wells have a greater risk of being contaminated 
than do deep or artesian wells. Shallow wells are normally 
wider in diameter than artesian wells and therefore are more 
susceptible to surface water entering the well. The liners on 
shallow wells, usually concrete pipe without "O" ring 
gaskets, are generally not as well sealed as those in artesian 
wells, which are normally lined with cast or ductile iron pipe 
with tight-fitting pipejoints. Shallow wells, normally 10to 
20 feet deep, are more susceptible to shallow groundwater 
contamination as well. Bacterial contamination poses the 
greatest threat to public safety. Salt water intrusion can 

leave the water brackish. Though this is distasteful, it is not 

a health risk in itself, but is more an indicator that the well 

has been contaminated and warrants further testing and 

analysis. 

Water service is critical to the continued safe and sanitary 

occupation of a building. Contamination of water systems 
can cause extensive delays in the reoccupancy of buildings 
after a flood. Water systems leading to and inside buildings can 
be a major sourceof flood damage. 

On-Site Portion of Water Systems 

Public water systems can become contaminated during a 
flood event. This contamination can spread to a building's 
water pipe system. Building occupants can do little to prevent 
the contamination of public water systems and should listen to 
instructions of local officials as to how to treat and use public 
water after a flood. To provide a source of potable waterto be 
used during and after a flood, residents should fill their bathtubs 
and various containers with clean water prior to the flood. 
Residents are normally told to do this by local officials as a 
precaution anyway. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.33 
January 1995 


ChapterVI: General Design Practices 

ONZ& Wet Floodproofing 

SEWER SYSTEMS 

On-site sewer systems continue to be a source of flood 
damages. Many modifications can be made inexpensively. 
The failure of these systems as a result of flooding can often 
leadto significant repairs that can tax an individual's already 
tight repair budget. 

On-Site Portion of Sewer Systems 

Sewage systems can generate a large portion of the contamination 
that occurs as a result of a flood. Since sewer 
lines are normally operated by gravity, they areusually 
found along rivers and creeks within the floodplain. In 
communities that have combined sanitary and storm sewers, 
sewage treatment plants are quite frequently overwhelmed, 
and untreated sewage is released into nearby rivers and 
creeks. There is little an individual can do to control this 
problem. 

Before a retrofit method(s) can be chosen, sewage threats 
must be identified as they affect the building under study. 
As an example, before one can predict whether or not a 
particular building is threatened by a sewer backup, one 
must find out if the building is served by a combined sewer 
system. These systems, when threatened with overwhelming 
stormwater, pose the greatest risk of backing up into a 
building. Even sewer systems that do not carry stormwater 
can back up due to floodwater infiltrating the system or sewage 
treatment plants being inundated by floodwater. The designer 
should contact the local sewer utility company to obtain information 
on the type of sewer system that serves the building and 

the history of sewer backups at that address and within the 

general area due to flooding. Only then can the designer decide 

what action(s) to take. 

VI -W.34 Enaineerina Princioles and Practices of Retrofittina Flood-Prone ResidIential Strucintumr 
January 1995 


Design Overview 

Guidance concerning the anchoring 
of septic tanks is applicable to 
other types of underground 
storage tanks. 

In areas with combined sewers or a history of sewer backups, 
the installation of a sewer backflow prevention valve is recommended. 
This can range from a simple flapper type to more 
elaborate configurations that include a wastewater storage area 
for the building and/or a battery-operated wastewater injection 
system that forces the wastewater from the building out into the 
sewer system. These valves are illustrated in the Dry 
Floodproofing section of Chapter VI. This allows the sewer 
system in the building to continue to be used even when the 
public system is overwhelmed. 

Combination check and shear gate valves, also illustrated in the 
Dry Floodproofing section of Chapter VI, provide dual protection 
against backflow. The swing-check responds with instant 
closure when backflow starts. During emergency periods, 
when a serious backwater condition exists or is expected, or 
when the building drainage system is to be shut down, the 
manually operated shear gate is closed until the building drain 
line can be used again. The shear gate valve is kept open when 
the building drainage system is in use. The differential between 
the invert elevations ofthe inlet and outlet provides a cleaning 
action ofthe effluent, which reduces fouling ofthe check seat. 
Simple backflow valves are usually available through local 
plumbing contractors. More elaborate systems are normally 
available through specialty contractors. 

SEPTIC TANKS 

On-site systems consisting of septic tanks and leach fields are 
often seriously affected by flooding. The buoyancy effects on 
tanks and the negative effects caused by the release of sewage 
pose significant health risks. The leach field can be damaged by 
the intrusion of floodwater. Leach field piping partially filled 
with fresh water (sewage water) can become buoyant when 
submerged and result in the possibility that the pipe may lift out 
ofthe ground. This action can obviously result in significant 
damage and resulting repair costs. 

Ennineerina Princinles and Practices of F letrofittina Flood-Prone Residential Structures VI -W.35 
January 1995 


Chapter VI: General Design Practices 
Wet Floodproofing 

I 
When flooding inundates a septic tank, proper anchorage is 
needed to prevent the movement and flotation ofthe tank. If it 
moves, it can rupture connecting piping, burst up out of the 
irces,When subject to flood ft ground, and present a hazardous condition. The worst design 
naturalstorage tanks containing conditions for anchorage of underground tanks occur when the 
rdditonal 
ronmengas 
or oil also pose the a 
risk of explosion or envi 
tal contamination. 
tank is empty and is covered by floodwaters or high ground 
water. Unless proper anchorage is utilized, the buoyancy forces 
acting on the tank will cause the tank to float out of the ground. 
The anchorage of any tank system consists of attaching the tank 
to a resisting body with enough weight to hold the tank in place. 
The attachment, or anchors, must be able to resist the total 
buoyant force acting on the tank. The buoyant force on an 
empty tank is the volume ofthe tank multiplied by the specific 
weight ofwater. it is usually advisable to include a factor of 
safety of 1.3, as is shown in the following buoyancy force 
computation: 
_ w e 
Fb= 0.134 Vt yFS -Wt 
where: Fb is the buoyancy force ofthe tank, in 
pounds; 
Vt is the volume ofthe tank in gallons; 
0.134 is a factor to convert gallons to 
cubic feet; 
y is the specific weight of fresh water 
(62.4 lbHP); 
FS is a factor of safety to be applied to 
the computation, typically 1.3 for 
tanks; and 
Wt is the weight ofthe tank. 
Formula VI-WI: Buoyancy Force on a Tank 

VI -W.36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design Overview 

The volume of concrete required to offset the buoyant force of 
the tank can be computed as follows: 

V = Fb/(Sc

where: VC is the volume of concrete required, 
in cubic feet; 
Fb is the buoyancy force ofthe tank in 
pounds; 
S c is the effective weight of concrete, 
typically 150 pounds per cubic 
foot; and 
or is the specific weight of water (62.4 
lb/ft 3 ). 

Formula VI-W2: Concrete Volume Required to Offset Buoyancy 

To resist this buoyant force, a slab of concrete with a volume, 
VC, is usually strapped to the tank to resist the buoyant load. 

TELEPHONE SYSTEMS 

Telephone systems can be damaged by floodwaters. Exterior 
demarc terminal boxes and transient protectors typically owned 
by the telephone company may require replacement and/or 
relocation above the flood protection elevation. These devices 
receive silt and grit damage, and corrosion may occur on terminals 
and connectors when inundated. 

Four-wire residential telephone cable-type CM is not rated as 
waterproof or for exterior usage. The cables and outlet (type 
RJ- I1) modularjacks should be relocated above the FPE. 
Building penetrations for telephone cable should be sealed to 
keep out moisture and water. All telephone company cables 
from underground or overhead locations should be waterproofed 
with either heavy-duty insulated cable as in aerial drop cable 
or petroleumjelly-filled cable rated for direct burial and submersible 
operation. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.37 
January 1995 


Chapter VI: General Design Practices 

Wet Floodproofing 

CABLE TV SYSTEMS 

Indoor cable (CATV) wiring systems can be damaged by 
floodwaters due to mechanical damage and by corrosion 
and deterioration of the center coax conductor and shield 
wires. CATV terminations (F Connectors) do not readily 
admit moisture due to their design. Exterior-rated coaxial 
cable is petroleumjelly-filled and poses no problems by 
being inundated with floodwaters. 

Relocate CATV cables, outletjacks, and wall plates to 
above the FPE. 

VI -W.38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Construction 

CONSTRUCTION 

ELECTRICAL 

The electrical relocation should follow current NEC (Na

tional Electrical Code NFPA 70) requirements and generally 

involves relocating like equipment or replacing it with similar 

equipment. Local codes and the building officials having 

jurisdiction should be contacted for coordination during 

design to ascertain any special requirements. The local utility 

should be contacted when relocation ofthe service lateral, 

metering equipment, or service location is to be moved or 

relocated. If power is to be disconnected from the house, the 

local utility company should be contacted and advised of this 

condition. Specific electrical system checks should include: 

* Check for correct cable size and breaker sizes per drawings 
in the field. 
* Require inspection before concealing work. 
* Verify that local jurisdiction will provide inspection when 
done. 
* Check grounding; test receptacles with tester. 
* Check light and appliance operation. 
* Review workmanship and wiring methods. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.39 
January1995 


ChapterVI: General Design Practices 
X > Wet Floodproofing 

MECHANICAL 

In conformance with the conditions of the construction contract, 
the designer shall perform inspection of the work during construction. 
Typical mechanical system checks should include: 

Check relocated or modified equipment for proper installation, 
orientation, and operation. 

e 

o 

Require inspection before concealing work. 

* Check wall penetrations for sealing and insulation. 
* Check piping, vent, ductwork, and fuel line connections. 
* Check supports for equipment and piping, vent, ducts and 
fuellines. 
VI -W.40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Floodwalls 

Table of Contents 

Types of Floodwalls ............................... VI -F.2
Gravity Floodwall ............................... VI -F.3
CantileverFloodwall ............................... VI -F.5
Counterfort Floodwall ............................... VI -F.9
ButtressedFloodwall ............................... VI -F.10

FieldInvestigation ............................... VI-F.11

Design ............................... VI -F.14
Floodwall Design (Selection and Sizing) ....... ........................ VI -F.14
Sliding ............................... VI -F.16
Overturning ............................... VI -F.16
Pressure ............................... VI -F.16
Floodwall Sample Calculation ............................... VI -F.36
Floodwall Design -Simplified Approach ............................... VI -F.42
Floodwall Appurtenances ............................... VI -F.46
Floodwall Closures ............................... VI -F.46
Drainage Systems ............................... VI -F.55
Seepage and Leakage ............................... VI -F.60
Seepage Throughthe Floodwall ............................... VI -F.60
Seepage Under the Floodwall ............................... VI -F.61
Leakage Between the Floodwall and Residence ............................ ........... VI -F.62
Architectural Details ....................................... VI -F.63

Maintenance Considerations ....................................... VI -F.70
Construction ....................................... VI -F.73

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi-F.i 
January 1995 


FLOODWALLS

A properly designed and constructed floodwall can often be an effective device for repelling 
floodwaters. Floodwalls are typically used in three roles: 

* as a barrier against inundation, 
* as a defense for unequalized hydrostatic and hydrodynamic loading situa-
tions, and
* to deflect debris and ice away from the structure. 
The selection of a floodwall design is primarily dependent on the type of flooding expected 
at the building's site. High water levels and velocities can exert hydrodynamic and 
hydrostatic forces and impact loads, which must be accounted for in the floodwall design. 
The composition of any type of floodwall must address three broad concerns: 

* Overall stability of the wall as related to the external loads, 
* Sufficient strength as related to the calculated internal stresses, and 
* Ability to provide effective enclosures to repel floodwaters. 
These internal and external forces pose a significant safety hazard if floodwalls are not 
properly designed and constructed, or their design level of protection is overtopped. 
Additionally, a tall floodwall can become very expensive to construct and maintain and 
can require additional land area for grading and drainage. Therefore, in most instances, 
residential floodwalls are practical only up to a height of three to four feet above existing 
grade, although residential floodwalls can be and are engineered for greater heights. 

Under NFIP regulations,
floodwalls are not recognized as
acceptable retrofitting measures
for new and substantially
improved (or damaged) struc-
tures.

Enaineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures VI-F.1 
January 1995 


Chapter VI: General Design Practices 

O19 >~ Floodwalls 

TYPES OF FLOODWALLS 

Figures VI-F 1 and VI-F2 illustrate the use of floodwalls in 46 residential applications. Figures VI-F3 and VI-F4 illustrate 

Placement of floodwalls in the several types of floodwalls including gravity, cantilever, 
floodwayis not allowed under buttress, and counterfort. The gravity and cantilever flood-
local floodplain regulations. walls are the more commonly used types. 

Figure VI-F 1 Typical Residential Floodwall 

Figure VI-F2: Typical Residential Floodwall 

VI -F.2 Enaineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Types of Floodwalls 

Floodwall Types 

FPE _W FPEF 

heel toe 

Gravity Wall Cantilever Wall 

Figure VI-F3: Gravity and Cantilever Floodwalls 

Alternative Floodwall Types 

Buttress Counterfort 

Figure VI-F4: Buttress and Counterfort Floodwalls 

GRAVITY FLOODWALL 

A gravity floodwall depends upon its weight-as its name 
implies-for stability. Thegravity wall's structural stability is 
attained by effective positioning of the mass of the wall, 
rather than the weight of the retained materials. The gravity 
wall resists overturning primarily by the dead weight of the 
concrete and masonry construction. It is simply too heavy 
to be overturned by the lateral flood load. 

EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures VI -F.3 
January 1995 


ChapterVI: GeneralDesign Practices 

Floodwalls 

Frictional forces between the concrete base and the soil 
foundation generallyresist sliding of the gravity wall. Soil 
foundation stability is achieved by ensuring that the struc

ture neither moves nor fails along possible failure surfaces. 

Figure VI-F5 illustratesthe stability of gravity floodwalls. 

Gravity walls are appropriate for low walls or lightly loaded 

walls. They are relatively easy to design and construct. The 
primary disadvantage of a gravity floodwall is that a large 
volume of material is required. As the required height of a 
gravity floodwall increases, it becomes more cost effective 
to use a cantilever wall. 

Stability of Gravity Floodwalls 

A = Height of Floodwall 
C = Width of Top 
L = Width of Bottom 
P = Dead Weight 

\ _ Toe Dt 

If-Point of Rotation 

*_`=_ -Base Friction 

Figure VI-F5: Stability of Gravity Floodwalls 

VI-F.4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Floodwalls 

-'Wh 

Reinforced concrete provides an 
excellent barrier in resisting water 
seepage, since it is monolithic in 
nature. The reinforcement not 
only gives the wall its strength, 
but limits cracking as well. 

CANTILEVER FLOODWALL 

A cantilever wall is a reinforced-concretewall (cast-in-place 
or built with concrete block) that utilizes cantilever action 
to retain the mass behind the wall. Reinforcement of the 
wall is attained by steel bars embedded within the concrete 
or block core of the wall (illustrated by Figure VI-F6). 
Stability of this type of wall is partially achieved from the 
weight of the soil on the heel portion of the base, as illustrated 
in Figure VI-F7. 

Figure VI-F6: Concrete Cantilever Floodwall Reinforcement 

EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures VI-F.5 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Stability of Cantilever Floodwalls 

Figure VI-F7: Stability of Cantilever Floodwalls 

The floodwall is designed as a cantilever retaining wall, 
which takes into account buoyancy effects and reduced soil 

bearing capacity. However, other elements of a 

floodproofing project (i.e., bracing effects of any slab-on

grade, the crosswalks, and possible concrete stairs) may 

help in its stability. This results in a slightly conservative 

design for the floodwall but provides a comfortable safety 

factor when considering the unpredictability of the flood. 

Backfill can be placed along the outside face of the wall to 

keepwater away from the wall during flooding conditions. 

VI -F.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Typesof Floodwalls 

Figure VI-F8: Typical Reinforced Concrete Floodwall 

6 

While the double-faced brick 

floodwall application is used on 

either side of concrete block with 

cores reinforced and grouted, 

experience has indicated it is not 

as strong or leakproof as mono

lithic cast-in-place applications. 

Information and details for a 
standard reinforced concrete 
floodwall are provided in case 
studies 4, 5, and 6 in Chapter VII. 

The concrete floodwall may be aesthetically altered with a 
double-facedbrick application on either side of the monolithic 
cast-in-place reinforced concrete center (illustrated in 
Figure VI-F8). This reinforced concrete core is the principal 
structural element of the wall that resists the lateral 
hydrostatic pressures and transfers the overturning moment 

to the footing. The brick-faced wall (illustrated in Figures 
VI-F9 and VI-F10)is typically used on homes with brick 
facades. Thus the floodwall becomes an attractive modification 
to the home. In terms of the structure, the brick is 
considered in the overall weight and stability of the wall and 
in the computation of the soil pressure at the base of the 
footing, but is not considered to add flexural strength to the 
floodwall. 

Engineering Principles and Practices of IRetrofittingFlood-Prone Residential Structures VI-F.7 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Brick Venee r Over Cast-in-Place Concrete 
Floodwall Typical Section (Cantilever Design) 

not to scale 

NOTE: Face Brick to
Match Ex Brick|

3/4- Chamfer Typ. 

7_ 

e 4' Brick-

Conc. Patio
1/2- Cork_

4-CMU 

3- CLR 

Figure VI-F9: Typical Section of a I Brick-FacedConcrete Floodwall 

VI -F.8 Engineering Principle. s and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Types of Floodwalls 

Figure VI-F IO: Typical Brick-Faced Concrete Floodwall 

When the flood protection elevation requirements of a 
gravity or cantilever wall become excessive in terms of 

material and cost, alternative types of floodwalls can be 

examined. The use of these floodwall alternatives is gener

ally determined by the relative costs of construction and 

materials and amount of reinforcement required. 

COUNTERFORT FLOODWALL 

A counterfort wall is similar to a cantilever retaining wall, 
except that it can be used where the cantilever is long or 
when very high pressures are exerted behind the wall. 
Counterforts, or intermediate traverse support bracing, are 
designed and built at intervals along the wall and reduce the 
design forces. Generally, counterfort walls are economical 
for wall heights in excess of 20 feet, but are rarely used in 
residential applications. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.9 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

BUTTRESSED FLOODWALL 

A buttressed wall is very similar to a counterfort wall. The 
only difference between the two is that the transverse 
support walls are located on the side of the stem, opposite 
the retained materials. 

The counterfort wall is more widely used than the buttress 
because the support stem is hidden beneath the retained 
material (soil or water), whereas the buttress occupies what 
may otherwise be usable space in front of the wall. 

VI -F.10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

FIELD INVESTIGATION

Detailed information must be obtained about the site and 
existing structure to make decisions and calculations concerning 
the design of a floodwall. The designer should 
utilize the guidance presented in this chapter where detailed 
information and checklists for field investigation are presented. 
Key information to collect includes the low point of 
elevation survey, topographic and utilities surveys, hazard 
determinations, local building requirements, and homeowner 
preferences. Once the designer has developed the above-
mentioned low point of entry and site and utility survey 
information, a conceptual design of the proposed floodwall 
can be discussed with the homeowner. This discussion 
should cover the following items: 

* Previous floods and which areas were flooded or affected 
by floods. 
* A plan of action as to which opening(s) and walls of the 
structure can be protected by a floodwall and floodwall 
closures. 
* Evidence of seepage/cracking in foundation walls, which 
would indicate the need to relieve hydrostatic pressure 
on the foundation. 
* A plan of action to use a floodwall to relieve hydrostatic 
pressure on the foundation and other exterior walls. 
* The various floodwall options and conceptual designs 
that would provide the necessary flood protection. 
Obtain consensus on the favored type, size, location, 
and features of the floodwall(s). 
* A plan of action as to which utilities need to be adjusted 
or floodproofed as a result of the floodwall. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures vi -F.1 1 
January 1995 


Chapter VI: General Design Practices 

Floodwalls 

A plan of action for construction activity and access! 
egress to convey to the owner the level of disruption to 
be expected. 

The designer of a floodwall should be aware that the con

struction of these measures may not reduce the hydrostatic 

pressures against the below-grade foundation of the struc

ture in question. Seepage beneath the floodwall and the 

natural capillarity of the soil layer may result in a water level 

inside the floodwall that is equal to or above grade. This 

condition is worsened by increased depth of flooding out

side the floodwall and the increased flooding duration. 

Unless this condition is relieved, the effectiveness of the 

floodwall maybe compromised. This condition is illus

trated in Figure VI-F 11. 

-I \_ Zone of 
Phreatic Surface Saturated Soil 

Figure VI-FI 1: Seepage Underneath a Floodwall 

It is important that the designer check the ability of the 
existing foundation to withstand the saturated soil pressures 
that would develop under this condition. The computations 
necessary for this determination are provided in Chapter IV. 

VI -F.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

The condition can be relieved by installation of foundation 
drainage (drainage tile and sump pump) at the footing level, 
and/or by extending the distance from the foundation to the 
floodwal. The landside seepage pressures can also be decreased 
by placing backfill against the flood side of the floodwall 
to extend the point where floodwaters submerge the soil, 
but the effectiveness of this measure depends on the relative 

Determination of an appropriate characteristics of the soils in the foundation and the backfill. 
distance from the structure for the The design of foundation drains and sump pumps is presented 

floodwall is a function of the 

in the Chapter VI Dry Floodproofing section. 

depth of the foundation. The 
deeper the lowest level of the 
structure, the furither away the Computation of the spacing required to obviate the problem is 
floodwall should be placed. a complicated process that should be done by an experienced 

geotechnical engineer. Figure VI-F12 illustrates the change in 

phreatic surface as a result of increasing the distance between 

the foundation and the floodwall and/or the installation of a 

foundation drain and sump pump system. 

ir External Floodwall 

Floodwall 

r nFlood Protection Elevation

Patio 

Foundation Drain to S 

:p 'SK,16No 

Phreatic Surface Saturated Soil 

Figure VI-F12: Reducing Phreatic Surface Influence by Increasing Distance from Foundation to
Floodwall

Enaineerina Principles and Practices of RetrofittingFlood-Prone Residential Structures VI -F.13 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

DESIGN 
FLOODWALL DESIGN (SELECTION 
AND SIZING) 
The permeability of concrete The design of floodwalls consists of the proper selection 
block may necessitate the use of a 
monolithic core or the application sizig of the actual floodwall and the specification of 
of sealants to eliminate seepage appurtenances such as drainage systems; waterproof materithroughthe 
wall. als to stop seepage and leakage; and miscellaneous details 
to meet site and homeowner preferences for patios, steps, 
wall facings, and support of other overhead structures 
(posts and columns). 
The structural design of a floodwall to resist anticipated 
flood and flood-related forces presented in Chapter IV 
follows the seven-step process outlined in Figure VI-F 13. 

VI -F.14 Enaineerina PrinciDlesand Practices of RetrofittinaFlood-Prone Residential Structures 
January 1995 


Design 

Floodwall Design Process 

Calculate Factor of Safety against
Overturning, FS(OT)

Figure VI-F13: Floodwall Design Process 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.15 
January 1995 


ChapterVI: General Design Practices 

Floodwalls 

Failure by Sliding
FPE ,

Sliding Force :
Heel, _ Toe

Figure VI-F14: Failure by Sliding 

Figure VI-F15: Failure by Overturning 

Figure VI-F16: Failure Due to Excessive 
Pressure 

In general the stability of the floodwall should be investigated 
for different modes of failure. 

Sliding 

A wall including its footing may fail by sliding if the sum of 
the lateral forces acting upon it is greater than the total 
forces resisting the displacement. The resisting forces 
should always be greater than the sliding forces by a factor 
of safety. (See Figure VI-F14.) 

Overturning 

Another mode of failure is overturning about the foundation 
toe. This type of failure may occur if the sum of the overturning 
moments is greater than the sum of the resisting 
moments about the toe. The sum of resisting moments 
should be greater than the sum of the overturning moments 
by a factor of safety. (See Figure VI-Fl 5.) 

Pressure 

Finally, a wall may fail if the pressure under its footing 
exceeds the allowable soil bearing capacity. (See Figure VIF16.) 

In the following paragraphs, the step-by-step process for 
completing the structural design of a floodwall is presented, 
followed by an example illustrating the use of the formulas. 
Table VI-F I provides soil information that is necessary in 
the computations that follow. 

VI- F.16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

TableVI-FI Soil Factors for Floodwall Design 
Soil Type Allowable Bearing Coefficient of Friction, Cf 
Pressure, S,, In pounds 
per square foot 
Clean, dense sand and 
gravel, GW, GP, SW and 2,000 0.55 
SP 
Dirty sand and gravel of 
restricted permeability, 2,000 0.45 
GM, GM-GP, SM, and 
SM-SP 
Firm to stiff slits, clays, 
silty fine sands, clayey 1,500 0.35 
sands and gravel, CL, 
ML, CH, SM, SC, and GC 
Soft clay, silty clay, and 600 0.30 
silt, CL, ML, and CH 
Step 1: Determine wall height and footing depth. 
1. Determine wall height based on flood protection elevation, 
which equals the design flood elevation plus one 
foot. The extra one foot is the minimum recommended 
freeboard as a safety measure against future flood levels 
that exceed the design flood. 
2. Determine minimum footingdepth based on the frost 
depth, local code requirements, and the soil condition. 
The footing should rest on suitable natural soil or on 
controlled and engineeredbackfill material. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.17 
January 1995 


Chapter VI: General Design Practices 

Floodwalls 

Step 2: Determinedimensions. 

Based on the following guidelines or reference to engineering 
handbooks, assume dimensions for the wall thickness, 
footing width, and footing thickness. 

1. The choice of wall thickness depends on the wall material, 
the strength of the material, and the height of the 
wall. Typical wall thicknesses are 8, 12, and 16 inches 
for masonry, concrete, or masonry/concrete walls. 
2. The footing width depends on the magnitude of the 
lateral forces, allowable soil bearing capacity, dead load, 
and the wall height. The typical footing width is the 
proposed wall height. Typically the footing is located 
under the wall in such a manner that 1/3 of its width 
forms the toe and 2/3 of the width forms the heel of the 
wall as shown in Figure VI-F 17. Typical footing thicknesses 
are based upon strength requirements and include 
8, 12, and 16 inches. 
Step 3: Determine forces. 

There are two types of forces acting on the wall and its 
footing: lateral and vertical. These forces were discussed in 
Chapter IV and are illustrated in Figure VI-F 17. 

VI -F.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Forces Acting on a Typical Floodwall 

6 

A -Hydrostatic 

Buoyancy 
Pressure

F62 

2Bearingqmex)

~'-L4..JJIIIIII Soil 

_M~n)___ _ Pressure 

Figure VI-F17: Forces Acting on a Floodwall 

1. Lateral forces: These forces are mainly the hydrostatic 
and differential soil/water forces behind the wall, and 
the saturated soil force in front of the wall. Hydrostatic 
and soil forces are as described in Chapter IV -Determination 
of Hazards. 
=nnindmrinn Prinninlha andl Practircme of Retrnfittine Flood-Prone Residential Structures VI -F.19 
Januarv 1 995 


Chapter VI: General Design Practices 

Floodwalls 

2. Vertical forces: The vertical forces are buoyancy and 
the various weights of the wall, footing, soil, and water 
acting upward and downward on the floodwall. The 
buoyancy force, FbW acting at the bottom of the footing 
is computed as follows: 
;ODD I' 

Fb= Fbi* b2 = lbs 

with F bi and Fb2 computed as follows: 

Fbl=1/2yHB 

(From Formula IV-8) 

F 2 =1/2yD B 
(From Formula IV-8) 

where: Fb is the total force due to buoyancy, 
in pounds; 

Fbl is the buoyancy force, in pounds, 
due to hydrostatic pressure at the 
floodwall heel acting at a distance 
of B/3 from the heel; 

Fb2 is the buoyancy force, in pounds, 
due to hydrostatic pressure at the 
floodwall toe, acting at a distance 
of B/3 from the toe; 

Y is the specific weight of water 

(62.4 pounds per cubic foot); 
B is the width of the footing, in 
feet; 
H is the floodproofing design depth, 
in feet; 
Dt is the depth of soil above the 
floodwall toe, in feet. 

(See Figure VI-F17) 
Formula VI-FI: Buoyancy on a Floodwall 

VI-F.20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

The gravity forces acting downward are: 

* the unit weight of floodwall (Ww.1); 
I wall ll lbs/LF 

where: Wwali is the weight of the wall, in 
pounds; 
H is the floodproofing design depth 

in feet; 
tftg is the footing thickness, in feet; 
twall is the wall thickness, in feet; 
Sg is the unit weight of wall material 

(concrete is 150 pounds per cubic 
foot); 

(See Figure VT-F17) 

Formula VI-F2: Floodwall Weight 

* the unit weight of the footing (Wftg); 
= B tftgSg = lbsALF

ik W~~'ftg 

where: Wftg is the weight of the footing, in 
pounds; 
B is the width of the footing, in 

feet; 
tftg is the footing thickness, in feet; 
Sg is the unit weight of wall material 

(concrete is 150 pounds per cubic 
foot) 

(See Figure VI-F17) 

Formula VI-F3: Footing Weight 

Engineerinrgi ri. rh --' and Practices of Retrofitting Flood-Prone Residential Structures VI -F.21 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

* the unit weight of the soil over the toe (WYQ; 
flu 

I1oI loII 

LMs': 

Wst= C(D' -tftg)(701i) = lbs/LF 

where: WN, is the weight of the soil over the 
toe, in pounds; 
C is the width of the footing toe, in 
feet; 
Dt is the depth of the soil above the 

floodwall toe, in feet; 
tftg is the footing thickness, in feet; 
y7oj is the unit weight of the soil, in 

pounds per cubic foot. 

(See Figure VI-F17) 

The unit weight of the soil, yl.o Formula VI-F4: Weight of Soil Over Floodwall Toe 
can be obtained from the soil 

survey, engineering texts, or a * the unit weight of the soil over the heel (W1h); and 

geotechnical engineer. 

Wah = Ah(Dh-tfg)(ysoi-62.4) = lbs/LF 

where: Wb, is the weight of the soil over the 
heel, in pounds; 
Ah is the width of the footing heel, in 
feet; 
Dh is the depth of the soil above the 
heel, in feet; 
tags is the footing thickness, in feet; 
, is the unit weight of the soil, in 
pounds per cubic foot. 

(See Figure VI-F17) 

Formula VI-F5: Weight of Soil Over Floodwall Heel 

VI- F.22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

* the unit weight of the water above the heel (Wwh). 
i Q I .I 

Wvh = (Ah)(H -tftg)(62.4)= _bs/LF 

where: Wwh is the weight of the water above 
the heel, in pounds; 
Ah is the width of the footing heel, in 
feet; 
H is the floodproofing design depth, 
in feet; 
tftg is the footing thickness, in feet; 

(See Figure VI-F17) 

Formula VI-F6: Weight of Water Above Floodwall Heel 

The total gravity forces acting downward, WG,in pounds 
can be computed as the sum of the individual gravity forces: 

Formula VI-F7: Total Gravity Forces Per Linear Foot of Wall 

Therefore the net vertical force, Fv,is then calculated as: 

Formula VI-F8: Net Vertical Force 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.23 
January 1995 


Chapter VI: General Design Practices 

FloodwalIs 

Step 4: Check sliding. 

This step involves the computation of the sliding forces, the 
forces resisting sliding, and the factor of safety against 
sliding. For a stable condition, the sum of forces resisting 
sliding should be larger than the sum of the sliding forces. 

1. Sliding Forces: The sum of the sliding (lateral hydrostatic, 
hydrodynamic, and impact) forces, FH' is computed 
as follows: 
FH= Fh+ Fdif+ (Fdh or Fd)+ 
(F. or F) = lbs 
where: FH is the cumulative lateral hydrostatic 
force acting at a distance 
H/3 from the point under consideration, 
in pounds; 
Fh is the lateral hydrostatic force due 
to standing water in pounds; and 
F jf is the differential soil/water force 
acting due to combined freestanding 
water and saturated soil 
conditions, in pounds. 
Fdh is the equivalent hydrostatic 
pressure due to low velocity. 
flood flows, in pounds; 
Fd is the hydrodynamic force against 
the structure due to high velocity 
flood flows, in pounds; 
Fn is the normal impact force in 
pounds, and 
Fs is the special impact force in 

pounds. 

The computation of FH 9 Fdp Fdh9 F 
FATand F. is presented in Formulas IV-4, 
IV-6, IV-10, IV-13, IV-14, and IV-15. 

(See Figure IV-17) 

Formula VI-F9: Sliding Forces 

VI -F.24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

2. Resisting Forces: The forces resistant to sliding are the 
frictional force, Ffrqbetween the bottom of the footing; 
the cohesion force, FC,between the footing and the soil; 
and the soil and the saturated soil force, Fp, over the toe 
of the footing. These resisting forces are computed as 
follows: 
a. Frictional Foc: The frictional force, Ffrpbetween 
the bottom of the footing and the soil is a function 
of net vertical force, FVqtimes coefficient of friction, 
Cr The coefficient of friction, C. between 
the base and the soil depends on the soil properties. 
(See Table VI-F 1). 
Ffr = Cf FV= lbs 

where: Ffr is the friction force between the 
footing and the soil, in pounds; 

C, isthe coefficient of friction 
between the footing and the soil; 
and 

FY is the net vertical force acting on 
the footing, in pounds, as was 
previously presented in Formula 
VI-F8. 

Formula VI-FIO: Frictional Forces 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.25 
January 1 995 


Chapter VI: General Design Practices 

Floodwalls 

b. Cohesion Force: The cohesion force between the 
base and the soil, F,, is obtained by multiplying the 
width of the footing, B, by the allowable cohesion 
value of the soil. This allowable cohesion value is 
usually obtained from a geotechnical analysis of 
the soil. The cohesion between the footing and 
the soil may be destroyed or considerably reduced 
due to contact from water. Due to potentially high 
variations in the allowable cohesion value of a soil, 
the cohesion is usually neglected in the calculations; 
unless the value of cohesion is ascertained 
by soil tests or other means, it should be taken as 
zero in the calculations. 
F = CB= lbs 

- ~~~~~C

S 

where: F is the cohesion force between the 
base and the soil in pounds; 

C is the allowable cohesion in 
pounds per square foot (usually 
assumed to be zero), and 

B is the width of the footing, in 
feet. 

(See Figure VI-F17) 

Formula VT-Fl 1: Cohesion Force 

VI -F.26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


.

Design 

c. Saturated Soil Force Over the Toe: The saturated 
soil force over the toe, FP,is calculated as: 
Fp =2 [kP (Yso_ y)+y]Dt= lbs 

where: FP is the passive saturated soil force 
over the toe, in pounds; 
7'.iI is unit weight of the soil (pounds 
per cubic foot); and 
Dt is the depth of the soil over the 
floodwall toe, in feet. 
kp is the passive soil pressure 
coefficient 
Y is the specific weight of water in

The passive soil pressure coeffi-
cient, k , typically ranges from 2-lbs/ft3 .

5. Typical values are 2 for plastic 
clays, 3 for clayey silts and poorly (See Figure VI-F17) 
graded gravels, and 3-4 or well 
graded sands. Consult a Formula VI-F12: Saturated Soil Force Over Floodwall Toe 
geotechnical engineer for more 
precise values. The sum of the resisting forces to sliding, FR, is calculated 
as the sum of the individual resisting forces to sliding, as 
shown below. 

FRFII 

X ~FR =Ff + FC+ F= Ilbs 

Formula VI-F 13: Sum of Resisting Forces to Sliding 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.27 
January 1995 


/ <p~ h 
Chapter VI: GeneralDesign Practices 
Floodwalls 
3. Factor of Safety Against Sliding: For the stability of 
the wall, the sum of resisting forces to sliding, FR'should 
be larger than the sum of the sliding forces, F H. The 
ratio of FR over FHis called the Factor of Safety against 
sliding, FS(SL) and is calculated as: 
[X FS(SL) = FRF H= > 1.5 
where: FS(SL) is the factor of safety against 
sliding (should be greater than 
1.5); 
FR is the sum of the forces resisting 
sliding in pounds; and 
FH is the sum of the sliding forces 
(cumulative lateral hydrostatic 
force) in pounds. 
Formula VI-F14: Factor of Safety Against Sliding 
The factor of safety against sliding should be at least 1.5. If 
the factor of safety is determined to be less than 1.5, the 
designer should lower the footing, increase the amount of fill 
over the footing, and/or change the footing dimensions, then 
go back to Step 3 and try again (as is illustrated in the flow 
chart for design of floodwall). 
Step 5: Check overturning. 
The potential for overturning should be checked about the 
bottom of the toe (Figure VI-F5). For a stable condition, 
the sum of resisting moments, MR,should be larger than the 
sum of the overturning moments, MO' The ratio of MRover 
MO is called the Factor of Safety against overturning, FS(OT). 
1. Overturning Moments: The overturning moments are 
due to hydrostatic and hydrodynamic forces, impact 
loads, saturated soil, and the buoyancy forces acting on 
VI -F.25 cgqineerinq Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


'-I,'~~~~~~: 

When hydrodynamic input loads 
act on the floodwall sections 
parallel to the flow and the 
downstream facing wall, Formulas 
VI-F9 and VI-F15 will produce 
conservative results. Further 
detailed analysis may result in 
smaller sections and a corresponding 
reduction in cost. 

Design 

the footing. The sum of the overturning moments, Mo, 
is calculated as: 

-M' MO =Fh(H/3)+Fdif(D/3)+Fbl(2B/3)+ 

r,-.0g I 

[Fdh(H/2) or Fd(H-Dh/2 + Dh)] 

+(FnH or FSH)+Fb2(B/3)= foot-lbs 

Vihere: MO is the sum of the overturning 
moments, in foot-lbs; 

Fh is the lateral hydrostatic force due 
to standing water, in pounds 
(Formula IV-4); 

Fdif is the differential soil/water force 
acting due to combined freestanding 
water and saturated soil 
conditions (Formula IV-6); 

Fbi is the buoyancy force, in pounds, 
due to hydrostatic pressure at the 
floodwall heel acting at a distance 
of B/3 from the heel, (Formula 
VI-Fl); 

Fb2 is the buoyancy force, in pounds, 
due to hydrostatic pressure at the 
floodwall toe, acting at a distance 
of B/3 from the toe, (Formula 
VI-Fl); 

Fdh is low velocity force (Formula 
IV-10); 
Fd is hydrodynamic force (Formula 
IV-13); 
Fn is normal impact force (Formula 
IV-14); 
Fs is special impact force (Formula 
IV-1 5); 
B is the width of the footing, in 

feet; 
H is the height of the wall, in feet; 
D is the height of the soil above the 

heel, in feet; and 

* h is the depth of the soil above the 
heel, in feet. 
Formula VI-F15: Sum of Overturning Moments 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.29 
January 1995 


Chapter VI: General Design Practices 

Floodwalls 

2. Resisting Moments: The resisting moments are due to 
all vertical downward forces and the lateral force due to 
soil over the toe. The sum of resisting moments, MR,is 
calculated as: 
10001

[.ilMR = W W.,,(C+(tw 1I2)) + Wftg (B/2) + 
Ws (C/2) + WSh (B-(Ah/2)) + WWh (B(
Ah/2)) + Fp (Di/3)= foot-lbs 

where: MR is the sum of the resisting moments 
in foot-lbs; 
Wwa81 is the weight of the wall, in 
pounds; 
t is the wall thickness, in feet; 
Wftg is the weight of the footing, in 
pounds, (Formiula VI-F3); 
B is the width of the footing, in 
feet; 
Wst is the weight of the soil over the 
toe, in pounds, (Formula VI-F4); 
C is the width of the footing toe, in 
feet; 
Dt is the depth of the soil above the 
floodwall toe, in feet; 
Wsh is the weight of the soil over the 
heel, in pounds, (Formula VL-F5); 
Ah is the width of the footing heel, in 
feet; 

WWh is the weight of the water above 
the heel, in pounds, (Formula 
VI-F6); and 

Fp is the passive saturated soil force 
over the toe, in pounds (Formula 
VI-F 12). 

(Refer to Figure V I-F1 7) 

Formula VI-F16: Sum of Resisting Moments 

VI-F.30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
Januarv 1995 


Design 

3. Factor of Safety Against Overturning: As mentioned 
earlier, for a stable condition, the sum of resisting 
moments, MR should be larger than the sum of the 
overturning moments, Mo, resulting in a factor of safety 
greater than 1.0. However, the factor of safety against 
overturning, FS(OT),should not be less than 1.5. If 
FS(OT)is found to be less than 1.5, the designer should 
increase the footing dimensions, then go back to Step 3 
and try again (see the flow chart for design of floodwall). 
I= DI

Inca 0, 

FS(OT)=MR/MO= _ 1.5 

where: FS(OT) is the factor of safety against 
overturning (should be greater 
than 1.5); 

MR is the sum of the resisting moments, 
in foot-lbs, (Formula VIF15); 
and 

MO is the sum of the overturning 
moments, in foot-lbs, (Formula 
VI-F 1 6). 

Formula VI-F17: Factor of Safety Against Overturning 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.31 
January 1995 


Chapter VI: General Design Practices 

Floodwalls 

Step 6: Calculate eccentricity. 

The final resultant of all the forces acting on the wall and its 
footing is a force acting at a distance, e, from the centerline 
of the footing. This distance, e, is known as eccentricity. 
The calculation of eccentricity is important to ensure that 
the bottom of the footing is not in tension. The eccentricity 
value is also needed for the calculation of soil pressures in 
Step 7. The eccentricity, e, is calculated as: 

e= (BI/2)-((MR -MO)/F) = feet 

where: e is the eccentricity, in feet; 
B is the width of the footing, in 
feet; 
FV is the net vertical force acting on 
the footing, in pounds, (Formula 
VI-F8); 
MO is the overturning moment, in 
foot-lbs, (Formula VI-F15); and 
MR is the resisting moment, in footlbs, 
(Formula VI-F 16). 

(Refer to Figure VI-F17) 

FormulaVI-F18: Eccentricity 

This eccentricity, e, should be less than 1/6 of the footing 
width. If e is found to exceed B/6, then change the footing 
dimensions, go back to Step 3, and try again (see flow chart 
for design of floodwall). 

VI -F.32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design

Step 7: Calculate soil pressures. 

The soil pressures, q, are determined from the following 
formula. 

001j q = (FV/B)(1 (6e/B)) = lbs/ft2 

where: q is the soil pressure created by 
the forces acting on the wall, in 
pounds per square foot; 

Fv is the net vertical force acting 
on the footing, in pounds, (Formula 
VI-F8); 

B is the width of the footing, in 
feet; and 
e is the eccentricity, in feet (Formula 
VI-F 18). 

(Refer to Figure VI-F17) 

Formula VI-F19: Soil Pressure 

The maximum value of q should not exceed the allowable 

soil bearing capacity. The bearing capacity of soil varies 
with the type of soil, moisture content, temperature, and 
other soil properties. The allowable values should be 
determined by a geotechnicalengineer. Some conservative 
allowable bearing values for a few soil types are given in 

Table VI-Fl Soil Factors for Floodwall Design. If the 
computed value of q is more than the allowable soil bearing 
value, increase the footing size, then go back to Step 3 and 
try again (see flow chart for design of the floodwall). 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.33 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

-t

The bending moment (Mb) for 
sizing reinforcing steel in the 
vertical floodwall component is 
the product of the lateral hydrostatic 
force (FH) and the distance 
between the point of force application 
and the bottom of the vertical 
floodwall component (H/3 -ta.) 

Step 8: Select reinforcing steel. 

Select an appropriate reinforcing steel size and spacing to 
resist the expected bending moment, Mb. Figure VIF18 
illustrates a typical floodwall reinforcing steel installation. 
The cross-sectional area of steel reinforcing required 
can be computed using Formula VI-F20. This formula 
assumes use of steel with a F = 60 ksi. 

N 

I0E a 

Mb 
A-= 1000 = in2/one-footwidth ofwall 

1.76df 
where: A, 
Mb 
1000 

df 

is the cross-sectional area of 
reinforcing steel required per foot 
width of wall, in square inches; 
is the bending moment, in footlbs; 
is a factor used to convert foot-
pounds to foot-kips; and 
is the distance between the 
reinforcing steel and the 
floodwall face opposite retained 
material, in inches. 

(Refer to Figure Vl-F 18) 
Formula VI-F20: Cross-Sectional Area of Steel 

s

VI -F.34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

d, is typically the floodwall 
thickness minus 3-1/2" to allow a 
minimum of 3" between the 
reinforcing steel and the floodwall 
edge. 

The selection of reinforcing steel 
in the footing portion of a floodwall 
is computed using Formula 
VI-F20 while modifying Mb for 
top and bottom steel considerations. 
For top steel, the moment 
is the product of the weight of soil 
and water over the heel (wsh+wvh) 
and the heel length (Ah) divided 
by 2. 

The selection of bottom steel is a 
function of the soil bearing 
pressure. The moment can be 
computed by adding the soil 
bearing pressure at the toe edge of 
the vertical floodwall section to 
twice the maximum soil bearing 
pressure (q + 2q,,,) and multiplying 
this sum by toe length squared 
over 6 (C2/6). The soil bearing 
pressure at the toe edge of the 
vertical floodwall section (q) can 
be computed by ratio from the 
calculations (for q.., qma)shown 
in step 7. 

Using the computed cross-sectional area of reinforcing 
steel, refer to ACI to select the most appropriate steel 
reinforcing bar sizeand spacing. 

..aII. 

Figure VI-F 18: Typical Reinforcing Steel Configuration 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.35 
January 1995 


Chapter VI: General Design Practices 

Floodwall Sample Calculation 

[ 

FLOODWALL SAMPLE DESIGN 

Objective: 

Design a cantilever floodwall to protect a residence subject to 3 feet of flooding. Site soil 

conditions are as follows: Clean Dense Sand, Unit Weight = 120lbs/ft3; Allowable Soil 
Bearing Capacity = 2,000 lbs/ft2;Equivalent Fluid Pressureof Soil = 78 lbs/ft3; Coefficient 
of Friction (Cf)= 0.47; Passive Soil Pressure (k) = 3.69; and Cohesion = 0. The floodwall 
is in an area of potential normal impact loading and expected flood velocities are 5 
fps. 

Step 1: Assume wall height and footing depth (refer to Figure VI-F 17). 

H = 7.0 feet
D = 4.0 feet
Dh = 5.0 feet
tfg = 1.0 feet

Step 2: Determine dimensions (refer to Figure VI-F17). 

B = 5.0 feet
Ah = 2.5 feet
C = 1.5 feet

twalt 1.0 feet 

.

Wall and footing to be reinforced concrete having unit weight of 150lbs/ft3 

1 of 6 

VI -F.36 Enaineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Desian 

Floodwall Sample Calculation 

Step 3: Calculate forces. 

DetermineLateral Forces: 

Formula IV-4 Fh = 1/2(62.4)(7)(7) = 1,528.8 lbs/LF. 
Formula IV-6 Fdif= 1/2(78-62.4)(5)(5)= 195.0 lbs/LF. 
Formula IV-9 dh = (1.25)(5)(5)/(2)(32.2) = 0.49 feet. 
Formula IV-10 Fdh= (62.4)(0.49)(7) = 211.96 lbs/LF. 
Formula IV-14 Fj= (1,000)(5)/(32.2)(1) = 155.28 lbs. 
Formula IV-9 F H= 1,528.80+195.00+211.96=1,935.76 lbsALF. 

Since Fnacts only at a single point, we will not include loading into the uniform lateral 

floodwall loading. Once the floodwall is sized, we will evaluate the wall perpendicular to 

flow to determine ability to resist the impact loading. If necessary this wall will be rede

signed to resist impact loads. This process will avoid overdesigning of the entire flood

wall. 

FormulaVI-F12 Fp = 1/2(3.69(120-62.4)+ 62.4)(4)(4) = 
2,199.55 lbs/LF. 

Determine Vertical Forces: 

Formula VI-F1 Fbi = 1/2(62.4)(5)(7) = 1,092.00 lbs. 
Formula VI-F1 Fb2 = 1/2(62.4)(5)(4) = 624.00 lbs. 
Formula VI-F1 Fb = 1,092 + 624 = 1,716.00 lbs. 
Formula VI-F2 WW.11= (7-1)(1)(150) = 900.00 lbs. 
FormulaVI-F3 Wftg= (5)(1)(150) = 750.00 lbs. 
FormulaVI-F4 W= (2)(5-1)(120-62.4) = 720.00 lbs. 
FormulaVI-F5 WSh= (4)(5-1)(120-62.4) = 921.60 lbs. 
FormulaVI-F6 WWh = (2.5)(7-1)(62.4) = 936.00 lbs. 
Formula VI-F7 WG = 900 + 750 + 576 + 540 + 936 

= 3,702.00 lbs. 
Formula VI-F8 Fv = 3,702.00 -1,716.00 = 1,986.00 lbs. 

2 of 6 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.37 
January 1995 


Chapter VI: General Design Practices 

e 

Floodwall Sample Calculation 

( 

Step 4: Check sliding. 

Formula VI-F10 Ffr=0.47(1,986) = 933.42 lbs. 
Formula VI-F13 FR=933.42 + 2,199.55 = 3,132.97 lbs. 
Formula VI-F14 FS(SL)= 3,132.97/1935.76 = 1.62. 

OK for sliding since 

1.62 > 1.5 (recommended) 
Step 5: Check overturning. 

Formula VI-F15 MO= (1,935.76)(7/3) + (195)(5/3) + 
(1,092)(1013)+ (624)(5/3) + 
(211.96)(7/2) = 9,314.05 foot-lbs. 

FormulaVI-F16 MR= (900)(1.5(1/2)) + (750.00)(5/2) + 
(540)(1.5/2) + (576)(5-(2.5/2) + 
(936)(5-(2.5/2)) + (2,199.55)(4/3) 
= 12,682.74 foot-lbs. 
Formula VI-F17 FS(OT)=12,682.74/9,314.05 = 1.36. 

No good. Try increasing the footing size to overcome the overturning momement. Assume 
B = 7.0 feet; Ah = 4.0 feet; and C = 2.0 feet. This requires revision of Steps 3 and 4 
for which the results are shown below. FhWF Fdh FH FP,Wwallwill not change. Recom

pute vertical forces. 

FormulaVI-F1 F = 1/2(62.4)(7)(7) = i,528.80 lbs. 
FormulaVI-F1 Fb2 = 1/2(62.4)(7)(4) = 873.60 lbs. 
FormulaVI-F1 F= 1,528.80+ 873.60 = 2,402.40 lbs. 
Formula VI-F2 Ww,,l = (7-1)(1)(150) = 900.00 lbs. 
Formula VI-F3 Wf = (7)(1)(150) = 1,050.00 lbs. 
Formula VI-F4 W, = (2)(5-1)(120-62.4) = 720.00 lbs. 
Formula VI-FS W h= (4)(5-1)(120-62.4) = 921.60 lbs. 

3 of 6 

VI-F.38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Floodwall Sample Calculation 

Formula VI-F6 

Formula VI-F7 

Formula VI-F8 

Recheck Sliding 

Formula VI-F10 
FormulaVI-F13 
Formula VI-F14 

Recheck Overturning 

Formula VI-F15 

Formula VI-F16 

Formula VI-F17 

Step 6: Determine eccentricity. 

Formula VI-F18 

WWh = (4)(7-1)(62.4) = 1,497.60 lbs. 

WG= 900.00 + 1,050.00 + 921.60 + 

720.00 + 1,497.60 = 5,089.20 lbs. 
F, = 5,089.20 -2,402.40 = 2,686.80 lbs. 
Ffr = 0.47(2,686.80) = 1,262.80 lbs. 

FR = 1,262.80 + 2,199.55 = 3,462.35 lbs. 

FS(SL) =3,462.35/1,935.76 = 1.79. 

OK for sliding. 

MO = (1,528.80)(7/3) + (195)(5/3) + 
(1,528.80)(2(7)/3) + (873.60)(7/3) + 
(211.96)(7/2) = 13,806.85 foot-lbs. 

MR = (900)(2t(1/2)) + (1,050.00)(7/2) + 
(720)(2/2) + (921.60)(7-(4/2)) + 
(1,497.60)(7-(4/2)) + (2,199.55)(4/3) 
= 21,673.74 foot-lbs. 

FS(OT)= 21,673.74/13,806.85 = 1.57 

OK for overturning since 

1.57 > 1.5 (recommended) 
e = 7/2 -(21,673.74 -13,806.85)/2,686.80 = 

0.57 < 7/6 OK 
4 of 6 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.39 
January 1995 


Chapter VI: General Design Practices 

Floodwall Sample Calculation 

Step 7: Check soil pressures. 

Formula VI-F19 q = (2,686.80/7)(1  6(.57)/7))) 
q..= (2,686.80/7)(1 -(6(.57)/(7))) = 

195.64 lbs/ft2 
qmx= (2,686.80/7)(l+(6(.57)/(7))) = 
572.64 lbs/ft2 < 2,000 OK 
Step 8: Select reinforcing steel. 

For steel in the vertical floodwall section: 

Formula VI-F20 A, = (1935.76)(7/3-1)/1000/(1.76)(8.5) = 

0.17 in2 
For top steel in the footing section: 

Formula VI-F20 As = ((921.60 + 936.00)(2.5)/2)/1000/ 
(1.76)(8.5) = 0.13 in2 

For bottom steel in the footing section: 

ratio q from q.jn' qmg1 q = 572.64 -(1.5/8)(572.64-195.64) = 

501.95 lbs/ft2 
Formula VI-F20 As = ((1.5)2/6)(501.95+ 2(572.64))/1000/ 
(1.76)(8.5) = 0.04 in2 

From American Concrete Institute Reinforced Concrete Design Handbook Table 9a: use
#4 bars on 14 inch centers in the vertical floodwall section, use #4 bars on 18 inch centers
for the top steel in the footing section, and use #2 bars on 12 inch centers for the botom

steel in the footing section. Other ACI documents have similar information. 

5 of 6 j 

VI -F.40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design

Floodwall Sample Calculation 

Since this floodwall design situation also includes normal impact forces, we must check 
the wall perpendicular to the flow for this loading situation. However, since impact loads 
do not act uniformly along the wall, the factor of safety of sliding/overturning can be 
lowered as long as it is above 1.0. This check will change only FH'MO, FS(SL) FS(o0 , and 

e. 
Formula IV-14 F. = (1,000)(5)/(32.2)(1) = 155.28 lbs. 
Formula IV-9 FH = 1,528.80+ 195.00+211.96+ 155.28= 
2,091.04 lbsILF. 
Formula VI-F14 FS(SL)= 3,462.35/2,091.04 = 1.65. 

OK for sliding since 

1.65 > 1.0 (recommended) 
Formula VI-F15 MO = (1,528.80)(7/3) + (195)(5/3) + 
(1,528.80)(2(7)/3) + (873.60)(7/3) + 
(211.96)(7/2) + (155.28)(7) = 
14,893.81 foot-lbs 

Formula VI-F17 FS(OT)= 21,673.74/14,893.81 = 1.45 

OK for overturning since 

1.45 > 1.0 (recommended) 
Formula VI-F18 e = 7/2 -(21,673.74 -14,893.81)/2,686.80 = 

0.97 < 7/6 OK 
OK for eccentricity. Therefore the wall as designed will withstand the anticipated impact 
loading. If the factors of safety for overturning/sliding and the eccentricity had not been 
acceptable, the footing should be resized or enlarged (B, Ah, and C). 

6 of 6 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.41 
January 1995 


Chapter VI: General Design Practices 

Floodwalls 

FLOODWALLDESIGN -SIMPLIFIED 

APPROACH 

This simplified approach uses The following Table VI-F3 presents general factors used in 
assumed site conditions. The 

designer should be aware that the developig a standardized approach to floodwal design. If 
previous process is normally used the soil conditions at the site in question do not reflect the 
in the design of most floodwalls. assumed conditions below, the standard criteria approach 
However, this design process can cannot be utilized, and the detailed design process pre-
be shortened for floodwalls of less sented earlier in this section must be used. 

than three feet in height by 
assuming certain site-specific soil 
conditions and design parameters. Based on the stability requirements (assuming no cohe-
Presented later in this section is a sion), footing dimensions for various wall heights, footing 
table of typical floodwall design

sizes r .anfloremen s esi depths, and two different soil types have been calculated. 

sizes and reinforcement schemes 
that would be applicable in certain The calculation results are shown in Tables VI-F4 and VI-
situations. The designer should be F5. The designer can utilize the followingtablesto specify 
awarethat unless the situationin floodwall/footing dimensions required for heights up to 7.0 aquestion meets the assumptions feet, which reflect flooding levels from 1.0to 4.0 feet 
andstandarddesign criteria minimum of three feet of soil over the 
established herein, it would be (icludig a footing). 
prudentto completethe entire Flooding levels can be computed as (H -Di). It is impor

designprocessfor the floodwall tant to note that these dimensions are very conservative and 
application. the designer may be able to reduce the dimensions. 

VI -F.42 Enaineerina Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design

In these calculations, the following assumptions have been 
made: 

1-Wall and footing are of concrete 

2 -Wall thickness = F -0" 

3 -Footing thickness = 1' -0" 

4 -Minimal debris impact potential 

5 -Minimal velocity (<5fps) 

6 -Reinforcing consisting of #4 steel bars on 12-inch 

centers in both the wall and footing 

Table VI-F2 Assume d Soil Factors for Simplified Floodwall Design 

Allowable kP Equivalent Fluid 
Soil Type 
ure,Bearing Press 
Ibs./ft.2 
Passive Soil 
Pressure Coefficient 
C, 
Friction Factor 
Pressure for 
Saturated Soil 
Unit Weight 
of Soil lbs/R3 
Clean, dense sand and 
gravel 2,000 3.70 0.55 75 120 
GW, GP, SW, SP 
Dirty sand and gravel 
of restricted permeability 2,000 3.00 0.45 77 115 
GM, GM-GP, SM, SM-SP 

Engineering Principles and Practice s of Retrofitting Flood-Prone Residential Structures Vi -F.43 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Table VI-F3 Typical Floodwall Dimensions for Clean, Dense, 
I Sand and Gravel Soil Types: (GW. GP, SW, SP) 1 

Height of Depth of Depth of Base Width* Heel Width* Toe Width* 
Floodwayl* Soil on Soil on B (ft) Ah(ft) C (ft) 
H (fIt) Water Land* 
Side Dh (ft) Side D,(ft) 
41'-oi 31-o0l 3 -O3i 2' -6" 1'-0" 6 

51 -0t 31 -311 31-OQi 41-6"t 2'-6"1 1t-Oi 

41'-0" 31-4'-2'-Oil 1by-

0" Oil O" 
41 -Ol 41-Oil 41-61" 21 -6" 1'3-O1 
61-O" 31-3' -0" 6'-6" 31-61" 2' -0" 

41-011 31-3"l 61 -0" 3' -611 11 -611 
59-QiI 31 -0l 51-6" 3' -0"1 11 -61" 
41-Oil 4' -O" 41-6" 2' -6" 1' Oil 
51 -Oil 41 -Ot 41-Oil 2'-6" 6" 

71-Oil 31 -Oil 39 -Oil 91 -3tt 6' -6"' it -6"1 
70 3' 41-0" 3-0" 71 0"l 3-6" 21'-6" 
59 -Oi 4 -0" 6' -6" 31 -611 21 -0" 
45-31-0" " 53-" 2' -0"

4'-8'6'-
0"1 31 -Ot 71-Q" 41-6" 1'- 6" 
61-0" 4.-0" 6' -O11 3' -69 1 -6" 

*Refer to Figure VI-FI 7 

VI -F.44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Table VI-F4 Typical Floodwall Dimensions for Dirty Sand and Gravel of 
Restricted Permeability Soil Types: (GM, GM-GP, SM, SM-SP) 

Depth Depth 
Height of of Soil on of Soil on Base Width* Heel Width* Toe Width* 
Floodwall* Heel* Toe* B (ft) Ah (ft) C (ft) 

H (ft) Dh (ft) Dt (ft) 
4'-i 3' -0i" 39-0I" 2'-61" 11- Oi 0'-6" 
51 -0t 31-0i 3' -0" 5' -0" 2' -6" 1'-6" 

41 -Ott 39 -oil 41 -612' -6 1 ' -0" 
4' -Of 4' -Of$ 49-Ot 2' -0" 1'-0" 
61 -0" 31-Ot 31-0i 8' -Olt 5' -6" 1i'-6" 
4' -Of 39-0i" 7-6" 5' -61" 1'-0" 

5'-Oit 3'-Off 7'-Off 5'-6"O -611 

41 -Ol 41 -Ol 59 -6"1 31 -0i 11 -6"1 

5' -Of 4' -Qil 5' -Of 31-oi 1 -6" 
7'- 0 4' -Of 4'-0" 8'-0'' 5'- 0 2'-0" 
51-opt 41-Of' 7' -Olt 49-oi 2' -0 
6' -Ol 41 -0i 6' -6" 49-0i" 1' -5"9 
*Refer to Figure Vl-F1 7 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.45 
January 1995 


Chapter VI: General Design Practices 

> y > Floodwalls 

FLOODWALL APPURTENANCES 

Floodwall appurtenances include drainage systems, stair 

details, wall facings, patios, existing structure connections 

(sealants), existing structure support (posts and columns), 

and closure details. Each will be discussed with illustra

tions, details, and photographs provided to help the de

signer develop details that meet the needs of their specific 

situation. The designer is reminded that it is likely that a 

local building code may have standards for the design and 

construction of many of these items. 

Floodwall Closures 

In designing floodwall closures, many of the principles 
discussed earlier in the dry floodproofing section apply. 
Watertight closures must be provided for all access openings 
such as driveways, stairs, and ramps, and seals should 
be provided for all utility penetrations. Figure VI-F19 
illustrates typical floodwall closures. Structural analysis for 
the design of closures should follow the procedures outlined 
previously for shield design. 

VI -F.46 Engineerina Principlesand Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Water 

Latching Dogs Are Commonly Used To Secure a Closure Panel. 

Water 

Side-Hinged Closure 

Track 

Drop-In Closure 

Figure VI-F 19: Typical Floodwall Closures 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.47 
January 1995 


Chapter VI: General Design Practices 

Floodwalls 

0////z///,X//7,//// 

/~ 

Free 

I . 
I Width of Opening 

0:Th

I. .. 
Supporte I 
I 
. 
Closure I .,Supported 

I. .. 
I. 
..I.

,1.'. --. . 

.I -. -. 

t Bottom of Opening 

Supported or Sealed 
W1-I 

Figure VI-F20: Closure Variables 

The type of closure used depends primarily on the size of 
the opening that needs to be protected. This will determine 
the type of material to be used and how the closure is to be 
constructed and operated. 

Longer and larger closures, such as for a driveway, must be 

able to withstand significant flood forces, and therefore 

should be made of a substantial material. Normally this 

would be steel plate, protected against rust and corrosion. 

Heavy aluminum plate may also be used, although it will 

likely need to be reinforced. In either case, due to the 

weight of the closure, it is usually best that it be hinged so 

that it can swing into place. Hinging can be located along 

the bottom so the closure lies flat when not in use, or it can 

be placed along one side, so the closure can fold back out 

of the way. 

For normal passage openings, aluminum is probably the 
most common material used. It is a lightweight material, 
allowing for easy fabrication and transport, and it is resistant 
to corrosion. Aluminum can buckle under heavy water 
pressure, so it may need some additional reinforcement. 

VI -F.48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

For smaller openings, exterior grade plywood is also 
commonly used. It is relatively inexpensive and is easily 
fabricated. However, plywood is subject to warping if not 
properly stored. In addition, it will collapse under relatively 
low flood forces, and will usually require significant reinforcement, 
usually some type of wood frame. 

Aluminum and plywood are both light enough to be used 

for temporary closures that can normally be stored in a safe 

location and installed only when floodwaters threaten. 

There are many different arrangements that can be used to 

install these movable closures. The more common methods 

include the "drop-in" shield that fits into a special slot 

arrangement and the "bolt-on" shield that is affixed over an 

opening. There are several different types of hardware that 

can be used to secure a closure in place, such as T-bolts, 

wing nuts on anchored bolts, or latching dogs. 

It is absolutely essential that closures be made watertight. 

This is normally accomplished through the use of some 

type of gasket. Neoprene and rubber are materials com

monly used, but there are a number of other materials 
readily available that perform equally as well. 

The successful performance of a closure system also requires 
that it be held firmly against the opening being 
protected. Although the hydrostatic pressure of the water 
may help to hold the closure in place, floodwater surges can 
result in negative pressure that can pull off an improperly 

installed closure. 

Whatever material is used, it must be of sufficient strength 

and thickness to resist bending and deflection failures. The 
ability of a specific material to withstand bending stresses 
may be substantially different from its ability to withstand 
deflection stresses. Therefore, to provide for an adequate 
factor of safety, the required closure thickness should be 

calculated twice: first taking into account bending stresses, 
and second taking into account deflection stresses. The 
resulting thicknesses should be compared and the larger 
value specified in the final closure design. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.49 
Januarv 1995 


Chapter VI: General Design Practices 
Floodwalls 

Orientation of Openings: It is 
highly recommended that 
openings in floodwalls and levees 
nQl be placed on the upstream 
side. In the event that they are, 
Formulas VI-F21, VI-F22, VIF23 
and VI-F25 should be 
modified to include the expected 
hydrodynamic forces. Closures 
should not be used on upstream 
sides where impact loads are 
expected. 

One method of determining the thickness of the closure for 
steel and aluminum is presented in Formulas for Stress and 
Strainby Roark and Young. For a flat plate supported on 
three sides, the plate thickness required due to bending 
stresses may be determined by the following formula: 

t = |Ph + (PdjorPd) c -inches 

Maxac 

where: t plate thickness; 

Ph hydrostatic pressure due to 
standing water, in psi from 
Formula IV-4; 

We width of closure, in inches 

Max cr allowable stress for the 
plate material (from material 
handbooks), in psi; and 

13 moment coefficient from Table
VI-F5;
Pdhand Pd are defined in Formulas IV-10
and IV-12.

Formula VI-F21: Plate Thickness due to Bending Stresses 

Similarly, for a steel or aluminum flat plate supported on 
three sides, the plate thickness required due to deflection 
stresses may be determined by the following formula: 

PE_ 

ECt= (Pdh orPd)Wc inches

1 Ph + E= 

where: oc deflection coefficient from Table
VI-F5; and

E modulus of elasticity for the plate 
material (from material handbooks) 
in psi. 

Formula VI-F22: Plate Thickness due to Deflection Stresses 

VI -F.50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

Januarv1995 


Design 

The variables used in the above equations for plate thickness 
are illustrated in Figure VI-F20. Table VI-F5, Moment 
Coefficients details the moment and deflection coefficients 
as a function of the ratio of plate height to width. 

Table VI-F5 Moment (P3) and Deflection 

(a) Coefficients 
hjWcI 0.05 0.67 1.00 1.50 2.00 2.50 3.00 3.50 4.00 

a 0.11 0.16 0.20 0.28 0.32 0.35 0.36 0.37 0.37 

13 0.03 0.03 0.04 0.05 0.06 0.06 0.07 0.07 0.07 
*See Figure VI-F19 

Allowable values for carand E may be found for steel plates 
in Manual of Steel Construction, American Institute of 
Steel Construction, and for aluminum plates in Aluminum 
Construction Manual, the Aluminum Association. 

The method of designing plywood closure plates is similar 
to that for steel and aluminum closure plates except that the 
varying structural properties of plywood make using a 
single formula inappropriate. Because these structural 
properties are dependent upon the grades of plywood sheet, 
the type of glue used, and the direction of stress in relation 
to the grain, determination of the thickness and grade 
required for a plywood closure is best achieved by assuming 
a thickness and grade of plywood and calculating its 
ability to withstand bending, shear, and deflection stresses. 
This involves calculating the actual bending, shear, and 
deflection stresses in the plywood closure plate for the 
thickness and grade specified. These actual stress values 
are then compared with the maximum allowable bending, 
shear, and deflection stresses (taken from APA Plywood 
Design Specifications). 

If the actual stresses computed are less than the maximum 
allowable stresses for bending, shear, and deflection, then 
the thickness and grade specified are acceptable for that 
application. However, if either of the actual bending or 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.51 

Jlamnlni 1QQ.9; 


Chapter VI: General Design Practices 
Floodwalls 

shear stresses or deflection exceeds the maximum allowable 
values, the closure plate is not acceptable and a new 

6 

The designer is referred to 

Plywood Design Specifications, 

American Plywood Association, 
for a detailed discussion of design 
guidelines. 

thickness and/or grade of plywood closure plate should be 
specified and the calculations repeated until all actual 
stresses are less than the maximum allowed. The following 
guidance has been prepared to illustrate one method of 
designing plywood closure plates. Note that a one-way 
horizontal span is assumed because the variability of 
plywood properties is dependent upon grain and stress 
direction. 

Compute bending moment on horizontal one-way span 
(supported on two sides only). 

a 

ME Mb= 
Ph + (dhr Pd ))We2 = in-lbs/in

8 

where: Mb is the bending moment in 
in-lbs/in; 

Ph is the hydrostatic pressure due to 
standing water, in psi from 
Formula IV-4; 

We is the width of the closure in 
inches; and 
Pdh an( d Pd are defined in Formulas IV-lO 
and IV-12. 

Formula VI-F23: Bending Moment 

Check bending stress. 

Mt,_ 

~KS ' 

where: fb is the bending stress in psi; 
Mb is the bending moment in 
in-lbs/in; and 
KS is the effective section modulus 
from a reference in in3/in. 

Formula VI-F24: Bending Stress 

VI -F.52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

If the calculated bending stress for the specified plate (Qb)is 
less than the maximum bending stress allowed (Fb)(from 
references), the closure plate is adequately designed for 
bending applications. If not, the closure should be redesigned 
and the calculation repeated. 

Compute shear force. 

l 

vs 
(Ph+(PdhorPd))WC _ 
pounds2 
where: V5 is the shear force in pounds; 
Ph is the hydrostatic force in psi 
Formula IV-4; 
WC is the width of the closure plate 
in inches; and 
PA an(I Pd are defined in Formulas IV- 10 
and IV-12. 

Formula VI-F25: Shear Force 

Check shear stress. 

__~~~v 

CRS _ pounds 

where: f is the shear stress in pounds; and 
CRS is the rolling shear constant 
dimensionless. 

Formula VI-F26: Shear Stress 

If the calculated shear stress for the specified plate (f5) is 
less than the maximum shear stress allowed (F), the closure 
plate is adequately designed for shear applications. If 
not, the closure should be redesigned and the calculations 
repeated. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.53 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

-0 

Compute deflection for a single one-way span. 

I II 

I A= Pdhor Pd))(W}C 4

i_(PIh,( +y) 
I b 921.6(E)(I) -inches

where: Ab is the computed deflection in 
inches; 
Ph is the hydrostatic pressure, in psi. 
from Formula IV-4; 
WC is the unsupported width in 
inches; 
y is a support width factor in 
inches; 
E is the Modulus of Elasticity in 
psi; 
I is the Effective Moment of 
Inertia in in4/ft; and 
Pdhand Pd are defined in Formulas IV-lO 
and IV-12. 

Formula VI-F27: Plate Deflection for a One-Way Span 

Check deflection. 

A customary and acceptable level of deflection may be 
expressed as 

| E ~~Ab(allowable)= 24 = _ inches 

where: Ab is the allowable deflection in 
inches; and 
WC is the unsupported width in 
inches. 

Formula VI-F28: Allowable Deflection 

VI -F.54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

If the calculated deflection (Ab) is less than the allowable 
deflection (Ab), the closure plate is adequately designed for 
deflection situations. If not, the closure should be redesigned 
and the calculations repeated. 

Closure plates of plywood are limited to short spans and 
low water heights. It should also be noted that most plywood 
will deteriorate when exposed to high moisture. 
Therefore, plywood closure plates should be examined 
periodically and replaced as necessary. 

Drainage Systems 

When designing a floodwall system, the designer must 
verify that it will not cause the flooding of adjacent property 
by blocking normal drainage. Specific information and 
local requirements can be obtained from the local zoning 
commission, the building inspector, or the water control 
board. Before deciding on a design, the designer should 
check local building codes, floodplain and/or stormwater 
management ordinances, zoning ordinances, or property 
convenents that may prohibit or restrict the type of wall 
planned. 

The flood protection design should be developed to divert 
both floodwater and normal rainfall away from the structure. 
By directing the floodwater and rainfall away from the 
structure, the designer can minimize potential erosion, 
scour, impacts, and water ponding. Typical design provisions 
include: 

* Regrading the site 
* Sloping applications 
* Drainage system(s) 
=nninagrinn Prinninlaim anrd PracticesQ of PatrnfittinmFlond-Prone Residential Structures VI -F.55 
iftna mloi, I 00O. 


Chapter VI: General Design Practices 
Floodwalls 

Regrading the site basically involves contouring. The 
surface can be contoured to improve the drainage and 
minimize floodwater turbulence. Ground covers or grasses, 
especially those with fibrous root systems, can be effective 
in holding soil against erosion and scour effects of floodwa

ters. 

Sloping applications include providing a positive drainage 
for engineered applications such as patios, sidewalks and 
driveways. The material is slightly inclined, typically at a 

1% to 2% grade, to an area designed for collection, which 
includes inlets, ditches, or an existing storm drain pipe 
system. Figures VI-F21 and VI-F22 show two patio drainage 
options, and Figure VI-F23 shows a floor drain section 
typically used to provide positive drainage for patio areas 
enclosed by floodwalls. These configurations can also be 

used with sump and sump pump installations. 0 

Sample Patio Gravity Drainage 

Stairs |Stairs 

Figure VI-F21: Sample Patio Drainage to an Outlet 

VI-F.56 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Sample Patio Sump Pump Drainage 

Splash Blbcks 

Figure VI-F22: Sample Patio Drainage to a Sump 

Typical Gravity Floor Drain Section Through Floodwall 

Gatv. Wre Mesh 

Rodent Scrn 

w/1/4 Square

OpenNt 

Cut to 

MatchGrad. // 

Figure VI-F23: Typical Gravity Floor Drain 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.57 

January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Figure VI-F24: Typical Patio Sump Pump Installation 

Figure VI-F25: Typical Patio Gravity Floor Drain Installation 

Drainage systems are a series of pipes that collect and route 
interior drainage to a designated outfall. Usually the 
drainage operation is underground and works through a 
gravity process. However, when grading and sloping will 
not allow the gravity system to function, provisions for a 
pumping method, such as a sump pump, should be made. 
Information on the design of sumps and sump pump applications 
is provided in the Dry Floodproofing section of this 
chapter. 

VI -F.58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

lanioanr IQQ4; 


Design 

For example, in its simplified form, a gutter and downspout 
outlet, which can be found on almost all houses, is a type of 
storm drainage system. Provisions at the downspout outfall 
should also be developed in the site drainage design. 

Included in the drainage system application is a backflow 
valve. The unit, sometimes referred to as a check valve, is a 
type of valve that allows water to flow one way but automatically 
closes when water attempts to flow in the opposite 
direction. Figure VI-F26 shows a typical floodwall 
with a check valve for gravity drainage. The elevation of 
the drain outlet should be as high as possible to delay 
activating the backflow valve, while maintaining a minimum 
of 2% slope on the drain pipe. 

Typical Floodwall with Check Valve 

FloodLevel 1 x b a 

,Concrete or Block Wall 

Cast-in Place or Grout 0 

Flap Valve -AdM7 

Concrete Splash Block C sh B 

_ />--Zigoncretef Sp~~~~~lash Block 

Concrete Footing 

Figure VI-F26: Typical Floodwall With Check Valve 

The success of the gravity drainage system is predicated on 
the fact that the floodwater will reach its maximum height 
after the rainfall at the site has lessened or stopped. Therefore, 
when the backflow valve is activated, little or no 
water will accumulate on the patio slab (usually after the 
rainstorm). However, should this condition not exist, the 
use of a sump pump and/or design of runoff storage within 
the enclosed area should be provided. 

=nrdnaarinn Prinrinaes and Pratices of Rptrnfittinn Flood-Prona RAsidential Structures VI- F.59 

January 1 995 


/ \ Chapter VI: General Design Practices 

Floodwalls 

SEEPAGE AND LEAKAGE 

Floodwalls should be designed and constructed to minimize 

seepage and leakage during the design flood. Without 

proper design considerations, floodwalls are susceptible to 

seepage through the floodwall; seepage under the flood

wall; leakage between the floodwall and residence; and 

leakage through any opening in the floodwall. 

Seepage Through the Floodwall 

All expansion and construction joints shall be constructed 
with appropriate waterstops and joint sealing materials. To 
prevent excess seepage at the tension zones, the maximum 
deflection of any structural floor slab or exterior wall shall 
not exceed 1/500 of its shorter span. Figure VI-F27 illustrates 
the use of waterstops to prevent seepage through a 
floodwall. 

Waterstop 

Wetted Face- ; Shear Key 

Waterstop 

Figure VI-F27: Waterstop 

VI -F.6O Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Design 

Seepage Under the Floodwall 

The structure design may also include the use of impervious 
barriers or cutoffs under floodwalls to decrease the 
potential for the development of full hydrostatic pressures 
and related seepage. These cutoffs must be connected to the 
impervious membrane of the building walls to operate 
effectively. 

To meet these requirements, it may be necessary to provide 
impervious cutoffs to prevent seepage beneath the floodwall. 
This requirement is critical for structures that are 
designed on highly pervious foundation materials. It may 
also be necessary to construct a drainage system parallel to 
the interior base of the floodwall to collect seepage through 

or under the structure and normal surface runoff from the 
watershed. All seepage and storm drainage should be 
diverted to an appropriate number of sumps or gravity 
drains, or pumped to the floodwater side of the structure. 
Normal surface runoff (during non-flood conditions) must 
also be taken into account in the drainage system. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.61 
January 1995 


Chanter VI: General Desian Practices 

Floodwalls 

Leakage Between the Floodwall and 
Residence 

1111111=111M

The connection between the existing house wall and the 
floodwall is normally not a fixed connection, because the 
floodwall footing is not structurally tied to the house 
foundation footing. Therefore, a gap or expansion joint 

The effectivenss of house 

reasedby may exist between the two structures that offers the poten

floodproofing can be inc 

placing fill against the hc ruseto tial for leakage. This gap should be filled with a water-

keep floodwaters from cc oming proof material that will work during seasonal freeze-thaw 

into direct contact with tl he cycles. 

structure. 

One alternative, illustrated in Figure VL-F28, is to utilize a 

1/2-inchbituminous expansion material, high-density 

caulking, and 1/2-inch polyurethene sealant. 

:-~

VI -F.62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
.1antimmr 1QQ! 


Design 

,,-1/2" Bituminous Expansion Material 

I 77I1NS1 

'o < :.t |00 Concrete Grout 

Lo 1 

ZTwo Alternative 
Connection 
Details 

1/2" Bituminous Expansion Material 

-Concrete Grout 

Figure VI-F28: Floodwall to House Connection 

ARCHITECTURAL DETAILS 

Floodwalls can be constructed in a variety of designs and 
materials. By taking into account the individual house 
design, topography, and construction materials, and with 
some imagination, the designer can build a floodwall to not 
only provide a level of flood protection, but also enhance 
the appearance of the home. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.63 
.laniiarv I Q.A 


Chapter VI: General Design Practices 

Floodwalls 

The floodwall design can be a challenge to landscape or to 
blend into the terrain. By using natural topography and 
employing various types of floodproofing techniques, such 
as waterproofing, sealants, or decorative bricks or blocks, 
the designer can make a floodwall not only blend in with 
the house and landscape, but also make an area more 
attractive by creating a privacy fence or by outlining a patio 
or garden area. 

The two most common applications of cosmetic facing of a 
floodwall consist of brick facing and decorative block 
facing. This is illustrated in Figure VI-F29. 

Figure VI-F29: Typical Cosmetic Facings 

VI -F.64 Enaineerina PrinCiDlesand Practices of Retrofitting Flood-Prone Residential Structures 
Januarv 1995 


Design 

Typical floodwall design often incorporates the use of a 
patio, which is enclosed by the floodwall. A concrete slab-
on-grade or decorative brick paving can be constructed 
between the house and the floodwall, which will create an 
attractive and useful feature. The slab-on-grade or brick 
paving can serve four very functional purposes: 

* Patio area for the homeowner; 
* Additional bracing for the floodwall; 
* Positive drainage away from the building towards 
drainage collection points; and 
* Impervious barrier inside the floodwall to reduce 
infiltration of water into the soil adjacent to the structure. 
The patio floor or slab-on-grade is set four inches below the 
door openings to provide for a reasonable amount of water 
storage to accommodate rainfall and roof-gutter spillage 
that may occur after the floodwater has reached the elevation 
that will have closed the backflow valve on the patio 
drain. The concrete slab is sloped to a floor drain (or 
drains) which discharge, if existing grade allows, through a 
gravity pipe or sump pump installation. 

In addition to designing patio applications, a qualified 
design professional can develop architectural and structural 
modifications that will accommodate existing/future wood 
decks or roof overhangs (illustrated in Figures VI-F30 and 
31). These supports can bear on the floodwall's cap, 
provided additional structural modifications to the floodwall 
and foundations are furnished to sustain the increased 
load from above. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -F.65 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Typical Floodwall Supporting Columns 

Wood Column 

Galv. Post Base 

10d Galv. Comm. 

Nails (4 Total) -'. 
-1/2" x 12" Galv. Anchor vwith2" Hook 

and Foundation 
Loads 

Figure VI-F30: Floodwall Supporting Columns 

Figure VI-F3 1: Floodwall Supporting Columns 

VI-F.66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1 995 


Design 

Residential access requirements, such as driveways, sidewalks, 
doors, and other entrances, will need to be examined 
during the design. These entrances may create gaps in the 
floodwall. Every effort should be made to design passages 
that extend over the top of the wall and not through it. A stile 
stairway over a floodwall provides access while not creating 
an opening in the floodwall. 

The stile is a series of steps up and over the floodwall and to 

the designed grades, which thereby closes the floodwall gap 
and provides a permanent flood protection. Handrails, 
railings, and stair treads and other safety features must be 
incorporated into the stile stairway in accordance with local 
building codes. 

ypical Step Detail 

Scale: 3/4" = 1'-0" 

Varies(See Plans) 

Atitn Flod-PoneResdenialStu1(Typ

Radius

) 

< < Soo ~~~~~~~Plans_ 

3\i7F~~~~~~~~~~1,2' E.J 2 

4Mn H Conc.
4, Grae + So Plan^Pns 

Paio for 

Figure VI-F32: Typical Step Detail 

Engineering Principles and Practices of F Retrofitting Flood-Prone Residential Structures VI -F.67 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Figure VI-F34: Typical Floodwall Steps 

In addition to the architectural qualities the floodwall can 
provide, the entire site area can be finished with landscaping 

-Vt features such as planter boxes, trees, and shrubs. Vegetative 

cover and stone aggregate can also be utilized not only to 
Landscaping inside and enhance the flood protection, but also as a method of erooverchanging 
a protected area may sion and scour prevention. A qualified landscape architect 
generate organic debris that could should be consulted when selecting material coverage for a 
clog drains. Plants should be particular area. Roots, foliage, leaves, and even potential 

selected that do not result in 

clogged drains from falling leaves growth patterns of certain trees and shrubs should be ac

or fruit. counted for in the selection of landscaping materials. Figure 
VI-F35 shows a typical landscaping alternative. 

VI -F.68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Figure VI-F35: Typical Floodwall Landscaping 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.69 
January 1995 


Chapter VI: General Design Practices 

Z 9 ~ Floodwalls 

MAINTENANCE CONSIDERATIONS 

Once the flood protection has been constructed, a maintenance 
schedule should be adopted to ensure the system will 
remain operational during flooding conditions. Floodwalls 
should be inspected annually for structural integrity. The 
visual investigation should include a checklist and photographic 
log of: 

* Date of inspection 
* General floodwall observations involving wall cracking 
(length, width, locations), deteriorated mortar joints, 
misalignments, chipping, etc. 
* Sealant observation, including displacement, cracking, 
and leakage. 
* Overall general characteristics of the site including 
water ponding/leakage, drain(s), and drainage and site 
landscaping. 
* Operation of the sump pump, generator/battery, and 
installation of any closures. 
* Testing of drains and backflow valves 
Additionally, the entire flood protection system should be 

inspected after a flood. A complete observation including a 

photographic record similar to the annual report should be 

developed and may also include: 

* damages associated with impacts and flood, 
* excessive scour and erosion damage, 
VI -F.70 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Maintenance Considerations 

* floodwater marks, and 
* functional analysis regarding the flood protection system. 
The following floodwall inspection worksheet (Figure VIF36) 
can be used to record observations during the annual 
and post-flood inspections. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.71 
January 1995 


Chapter VI: General Design Practices 
Floodwalls 

Owner Name: Prepared By: 

Address: Date: 
Property Location:_ 

Floodwall Inspection Worksheet 

FLOODWALL COMPONENT YES NO OBSERVATIONS 

Cracking in Wall 

Mortar Joint Separation _ 

Wall Misalignment 

Miscellaneous Chipping & Spalling 

Possible Leakage Spots 

Sealant Displacement 

Water Ponding 

Drains Functional 

Sump Pump Operational 

Landscaping 

Sketch Area: 

General Observations and Summary: 

Figure VI-F36: Floodwall Inspection Worksheet 
I 
VI F.
72 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Maintenance Considerations 

CONSTRUCTION 

During the construction of a floodwall, periodic inspections 
should be conducted to ensure that the flood protection 
measure has been built per the original design intent. As a 
minimum the designer, owner, or owner's representative 
should inspect and observe the following improvements: 

e 

Confirm adequate slope drainage, including drain pipes, 
patio, and grading outside the floodwall; 

* Confirm that floodwall foundation was prepared in 
accordance with plans and specifications; 
* Confirm that sealants, waterproofing, and caulking were 
applied per the manufacturer's requirements for installation; 
* Confirm that the sump pump is operational; 
* Check sample brick or decorative block (before installation) 
for patterns or match to existing conditions; and 
* Confirm that a maintenance requirement checklist was 
developed and used, which included all of the 
manufacturer's recommendations for passive flood 
protection applications, sealants, drains, etc. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.73 
January 1995 


Levees 

Table of Contents 

Field Investigation................................................................................................................ I-L.I

Design................................................................................................................................ VI-L.4
Standard Criteria ........................................... VI -L.4
Maximum Settled Height of Six Feet ............. .............................. VI -L.4
MinimumCrestWidthofFiveFeet ........................................... VI -L.5
Floodwater Side Slope of 1 Vertical on 2.5 Horizontal ........................................ VI -L.5
Land Side Slope ........................................... VI -L.5
One Foot of Freeboard ........................................... VI -L.5
InitialPhases.................................................................................................................. VI- L.6
Locate Utility Lines That Cross Under the Levee ........................................... VI -L.6
Provide "Cut-Off' for Levee Foundation Seepage ........................................... VI -L.7
Identify Foundation Soil Type ........................................... VI -L.7
Clay Foundation................................................................................................ VI-L.7
Sandy Foundation ........................................... VI -L.7

Seepage Concerns .................. VI -L.8
Scouring/Slope Protection .................. VI -L.9
InteriorDrainage .................. VI -L.10
Maintenance .................. VI -L. 11
Cost .................. VI -L.12

Construction .................. VI -L.14
Soil Suitability .................. VI -L.14
Compaction Requirements .................. VI -L. 14
SettlementAllowance .................. VI -L. 15
Borrow Area Restrictions .................. VI -L.15
Access Across Levee .................. VI -L. 15

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -L.i 
January 1995 


Field Investigation

LEVEES 

Levees are embankments of compacted soil that keep shallow to moderate floodwaters from 
reaching a structure. A well designed and constructed levee should resist flooding up to the 
design storm flood elevation, eliminating exposure to potentially damaging hydrostatic and 
hydrodynamic forces. 

This chapter outlines the fundamentals of levee design and provides the designer with an empirical 
design suitable to a limited range of situations. The design criteria outlined in the USACE 
manual number EM 110-2-1913, entitled Design and Construction ofLevees, are complex 
and intricate because they must provide for a wide variety of design conditions that are not 
always applicable to residential levees. These additional factors could result in construction 
costs that are considerably higher than the value ofthe benefits (damages avoided) associated 
with construction. If certain design parameters are controlled, the costs should be greatly 
reduced, allowing the individual homeowner to consider this retrofitting technique an economically 
feasible option. 

FIELD INVESTIGATION 

Certain conditions must exist before levees can be considered a 

viable retrofitting option. The questions that should be asked 

before proceeding any further are listed below: 

Under NFIP regulations, levees are 

not recognized as acceptable Does the natural topography around the structure in ques-
retrofitting measures for new and tion lend itselfto this technique?
substantially damaged or improved
structures.

A significant portion of the cost associated with the construction 
of a levee hinges upon the amount of fill material 
needed. If the topography around the structure is such that 

--... only one or two sides of the structure need to be protected, 
a levee may be economical. 

Placement of levees in the 

floodway is not allowed under 

local floodplain regulations. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -LA 
January 1995 


Chapter VI: General Design Practices 

Levees 

Is a suitable impervious fill material readily available? 

6 A suitable impervious fill material, such as a CH, CL, or 

A settled height of six feet is the SC, as defined in American Society for Testing and 
maximumelevationrecommended Materials (ASTM) designation D-2487, entitled Classiforindividualresidentiallevees. 
fication ofSoils, is required to eliminate concerns of 

seepage and stability. 

* Do local, state, or federal laws, regulations, or ordinances 
restrict or prevent the construction of a levee? 
Coordination with local, state, and federal officials may be 
necessary to determine if the levee retrofitting option is 
permissible. Certaincriteriaexistprohibiting construction 
within a FEMA-designated floodway, the main portion of a 
stream orwatercourse that conveys flow during a storm. 

a Will the construction of a levee alter, impede, or redirect the 
natural flow of floodwaters? 

Previous calculations from Chapter IV to determine both 
the depth and velocity of flood flows around the structure in 
question should be checked to ensure that the levee will not 
result in increased flood hazards upstream. Also, in many 
cases the local floodplain administrator may require an 
analysis ofthe proposed modification to the floodplain. 

* Will flood velocities allow for the use of this technique? 
If the flood velocities along the water side of the levee 
embankment exceed eight feet per second, the cost of 
protecting against the scour potential may become so 
great that a different retrofitting technique should be 
considered. 

The designer of a levee should be aware that the construction of 
a levee may not reduce the hydrostatic pressures against a 

VI -L.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Field Investigation 

below-grade foundation. Seepage underneath a levee and the 
natural capillarity ofthe soil layer may result in awater level 
inside the levee that is equal to or above grade. This condition 
If the assumptions listed in this 
is worsened by increased depth of flooding outside the levee 
chapter are not applicable to the and increased flooding duration. Unless this condition is 
site being considered, an experi- relieved, the effectiveness ofthe levee may be compromised. 
enced levee designer should be This condition, which involves the intersection ofthe phreatic 
consulted or another method line with the foundation, is illustrated in Figures VI-FI 1 and VI-
considered. F 12. 
It is important that the designer check the ability ofthe existing 
foundation to withstand the saturated soil pressures that would 
develop under this condition. The computations necessary for 
this determination are provided in Chapter [V. 
The condition can be relieved by installation of foundation 
drainage (drainage tile and sump pump) at the footing level, 
and/or by extending the distance from the foundation to the 
levee. The land side seepage pressures can also be decreased 
by placing backfill against the flood side of the levee 
to extend the point where floodwaters submerge the soil 
away from the structure, but the effectiveness of this measure 
depends on the relative characteristics of the soils 
investigation. The design of foundation drains and sump 
pumps is presented in Chapter VI Dry Floodproofmg section. 
An experienced geotechnical engineer should compute the 
spacing required to obviate the problem. 

Enaineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures VI -L.3 
January 1995 


Chapter VI: General Design Practices 

y Y  Levees 

DESIGN 

STANDARDCRITERIA 

The following parameters are established to provide a 
conservative design while eliminating several steps in the 2V' .JUSACEdesign process, thereby minimizing the design cost. 
These guidelines pertain to the design and construction of 
Thesedesign recommendations are localized levees with a maximum settled height of six feet. 
conservative.Alternativeparam-Techniques of slope stability analysis and calculation of 
eters for a specific site may be 
developed by an engineer qualified seepage forces are not addressed. The recommended side 
in levee design. slopes have been selected, based on experience, to satisfy 

__________________________ requirements for stability, seepage control, and maintenance. 
The shear strength of suitable impervious soils compacted 
to at least 95 percent of the Standard Laboratory density as 
determined by ASTM Standard D-698 will be adequate to 
assure stability of such low levees, without the need for 
laboratory or field testing or calculation of safety factors. 

The minimum requirements for crest width and levee side 
slopes are defined below. In combination with the toe 
drainage trench (which will be defined later in this section) 
and the cutoff effect provided by the backfilling of the 
inspection trench, these minimum requirements will provide 
sufficient control of seepage, and do not require complex 
analyses. Flatter land side slopes are recommended for a 
levee on a sand foundation to provide a lower seepage 
gradient, because a sand foundation is more susceptible to 
seepage failure than a clay foundation. 

Maximum Settled Height of Six Feet 

This is a practical limit placed due to available space and 
material costs. 

VI -L.4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Minimum Crest Width of Five Feet 

This is required to minimize seepage concerns and allow for 
ease of construction and maintenance. 

Floodwater Side Slope of 1 Vertical 
on 2.5 Horizontal 

This is required to minimize the scour and erosion potential, 
to provide adequate stability under all conditions including 
rapid drawdown situations, and to facilitate maintenance. 

Land Side Slope 

The land side slope may vary based upon the soil type used in 
the levee. If the levee material is clay, a land side slope of one 
vertical to three horizontal is acceptable. If the levee material is 
sand, a flatter slope of one vertical to five horizontal is recommended 
to provide a lower seepage gradient. 

One Foot of Freeboard 

This is required to provide a margin of safety against over

topping and allow for the effects of wave and wind action. 

These forces create an additional threat by raising the height of 

the floodwater. 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -L.5 
January 1995 


Chapter VI: General Design Practices 
Levees 

| ~~~~~~~~~~mmn.

I ~n 'S 2' 

Figure VI-L 1: Typical Residential Levee 

INITIALPHASES 

Because ofthe importance ofthe characteristics of the soil that 
makes up the levee foundation, the excavation of an inspection 
trench is required. The minimum dimensions ofthe inspection 
trench are shown in Figure VIL 1. The inspection trench, which 
shall run the length of and be located beneath the center of the 
levee, provides the designer with information that will dictate the 
subsequent steps inthe design process. The mandatory requirement 
of an inspection trench is fundamental to the assumptions 
made for the rest of the design process. The inspection 
trench will accomplish the following objectives: 

Locate Utility Lines That Cross Under 
the Levee 

Once identified, these must be further excavated and backfilled 

with a compacted impervious material to prevent development 

of a seepage path beneath the levee along the lines. 

VI -L.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Design 

Provide "Cut-Off" for Levee 
Foundation Seepage 

The trench itselfwill be backfilled with ahighly impervious soil, 
such as a CH, CL, or SC, as previously referenced, to create 
an additional buffer against levee foundation seepage. 

Identify Foundation Soil Type 

The construction ofthe inspection trench should provide the 
designer with a suitable sample to identify the foundation soil 
type through the use of the Unified Soil Classification System, 
(USCS). This variable will further direct the design ofthe levee. 

Clay Foundation 

If, after inspection, it is determined that the in situ foundation 

material is composed of a clay soil, as defined by the NRCS, a 

land side slope of 1 vertical on 3 horizontal should be utilized. 

Sandy Foundation 

If, after inspection, it is determined that the in situ foundation is 
composed of a sandy soil,as definedby theNRCS, a land side 
slope of 1 vertical on 5 horizontal should be utilized. 

Fnniniarinn PrinninleQanrd Practices of RetrofittinnFlood-ProneResidential Structures VI -L.7 
January 1995 


Chapter VI: General Design Practices 
Z/k ~ cI Levees 

SEEPAGE CONCERNS 

Durationoffloodingis a critical 

consideration in the design of 

leveeseepagecontrolmeasures. 

Thelongerthe duration of 

flooding(i.e.,thelongerfloodwa-

tersare in contact with the levee), 

the greater the potential for 

seepageandthe greater the need 

for seepage controlmeasures 

such as cutoffs, drainage; toes, 

andimperviouscores. 

If inspection determines that the 

Two types of seepage must be considered in the design of a 
residential levee system: levee foundation seepage and embankment 
seepage. The amount of seepage will be directly related 

to the type and density of soils in both the foundation and the 
embankmentofthelevee. Whiletheinstallationandbackfllling 
of themispection trench with impervious material willhelp 
reduce concerns of foundation seepage, further steps must be 
taken to minimize any embankment seepage for levees between 
three and six feet in height. The mandatory inclusion of a 

drainage toe will control the exit of embankment seepage while 
also controlling seepage in shallow foundation layers. 

The inclusion of a drainage toe for a levee of varying height will 

be limited to those areas with a height greater than three feet. If 
the levee height varies due tothe natural topography, a drainage 
toe will be required only for those portions of the levee that 
have a height greater than three feet. 

foundation consists of a deepThmaoresnfrteicuonfhseesrsiso 

depositof sandor gravel that will 
permitseepageunderthe shallow 
inspectiontrench,a deeper trench 

wouldbe required, especiallyif 

basempoentfonedinucur

haRsa 
daefinedsaunde This-

or gavl 
scenariomay make the use of a 
leveeuneconomical. 

ffid 

Long duration floodingmay 
negatively impact the ability of the 
drainage toe and inspection trench 
to control the seepage through and 
under the levee. 

Temjrrao o h nlso fteemaue st 

relieve the pressure of seepage through or under the levee so 
that piping may be avoided. Piping is the creation of a flowpath 
for water through or under a soil structure such as a levee, dlarn, 

or other embankment, resulting in a pipe-like channel carrying 

water through or under the structure. Piping can lead to levee 
failure. Piping becomes a more serious problem as the permeability 
of the foundation soil increases. 

VI -L.8 Enaineerina Princioles and Practices of Retrofittino Flood-Prone Residential Strimrtiirss 
January 1995 


Seepage Concerns 

The drainage toe should be sized as shown in Figure VI-L2, 
and should be filled with sand conforming to the gradation of 
standard concrete sand as defined by ASTM standards. 

Figure VI-L2: Drainage Toe Details 

SCOURINGISLOPE PROTECTION 

The floodwater side of the levee embanknent may require 
protection from erosion caused by excessive flow velocities. 
For flow velocities of up to three feet per second, a vegetatively 
stabilized or sodded embankment will generally provide adequate 
erosion protection. Some vegetative covers, such as 

Bermuda grass, Kentucky bluegrass, and tall Fescue, provide 
erosion protection from velocities of up to five feet per second. 
The grasses should be those that are suitable for the local 
climate. An alternative or supplement to a vegetative cover is 
the use ofa stone protectionlayer. The layer shouldbe placed 
onthe entirefloodwaterface ofthe levee and be sizedin 
accordance with Table VI-L 1: 

Table Stone Protection Layer 

VI-Li Guidance 

VeloctiesMinimum 

These values are from USACE DiameterofAgainst Slope 
Manual Design and Construction 
of Levees. < 2 fps 0.5 inches 
< 5 fps 2.0 Inches 
< 8 fps 9.0 Inches 

. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -L.9 
January 1995 


Chapter VI: General Design Practices

<~ Levees 

INTERIOR DRAINAGE 

Constructing a levee around a house will not only keep floodwater 
out, but also will act to keep seepage and rainfall inside 
the levee unless interior drainage techniques are utilized. One 
method of draining water that collects from rain and from 
seepage through and under a levee is to install drainpipes tat 

Guidanceon estimating interior extend through the levee. While this will allow for drainage by

drainagequantitiesis presentedin gravity, the drains must be equipped with flapgates, which close 

ChapterIV. to prevent flow of floodwaters through the pipe. The flap gates 
will open automatically when interior floodwaters rise above 

exterior floodwaters. 

Normal Conditions 

River Side, 

/ ~~Levee\ 

FlapGate0Ope_ _ _ 

River Flood Conditions Local Drainage

Side_ 

losed-

Figure VI-L3: Drain Pipe Extending through Levee 

To ensure that water from precipitation or seepage within a 

leveed area is removed during flooding, a sump pump should be 
installed in the lowest area encompassed by the levee. All 
interior drainage measures should lead to this.pump, which will 

discharge the flow up and over the levee. The sump pump 

should have an independent power source sothat it will stay in 

operation should there be an interruption of electrical power, a 

common event during a flood. 

VI -L.10 Enaineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


FloodwaterSide 
Slope 
Top 

Land Side Slope 

Top_ 

FigureVI-L4: InteriorStorage Area 

Seepage Concerns 

Analternativeto theuse of a sump pump (for minor storms),is 
the creation of an interior storage area that will detain all interior 
flow until the floodwaters can recede. See Figure VI-L4. 
Typically the storage area is sized for the 2- or 10-year recurrence 
interval event. 

Drain Pipe 

Ponding areas 
for when flap 
valves are 

_ D Drain Pipe 

MAINTENANCE 

Levee maintenance should include keeping the vegetation in 

good condition and preventing the intrusion of any large roots 

from trees or bushes or animal burrows, since they can create 

openings or weak paths in the levee through which surface 

water and seepage can follow, enlarging the openings and 

causing a piping failure. Planting oftrees and bushes is not 

permitted on the levee. 

Any levee design should include a good growth of sod on the 

top and slopes of the levee to protect against erosion by wind, 

water, and traffic, and to provide a pleasing appearance. 

Regular mowing, along with visual inspection several times a 

year, should identify critical maintenance issues. 

Pnninaarinn Printcinipq and Pranticesq of Ratrofittino Flood-Prone ResidentialStructures VI -L.11

Januy 1 A gay A--995 ---

January 1995 


'Chapter VI: General Design Practices 

Levees 

COST 

The accuracy of a cost estimate is directly related to the level of 
detail in a quantity calculation. The following example provides 
a list ofthe common expenses associated with the construction 
of a residential levee. Unit costs vary with location and wholesale 
price index. To obtain the most accurate unit prices, the 
designer should consult construction cost publications or local 
contractors. The designer should also budget an additional five 
percent ofthe total construction capital outlay annually for 
maintenance ofthe levee. 

Table VI-L2, Cost Estimate Example, illustrates the estimated 
cost (based on 1985prices)for constructionof a three-foothigh, 
21 6-foot-long levee, which was built to protect a 1,600SF 
house in Montgomery County, Maryland. 

TableVI-L2 Cost Estimate Example 
Item Cost 
Strip Topsoil $335.00 
Dig Inspection Trench $750.00 
Import Fill $1,800.00 
Compact Fill $600.00 
Riprap $2,700.00 
Drain Tile (4" PVC) $215.00 
Check Valve $900.00 
Sewer Gate Valve $1,200.00 
Sump Pump $1,000.00 

Discharge Piping $100.00 
Total First Cost $9,600.00 

VI -L.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Table VI-L3 Levee Cost Estimating 

Owner Name: 
Address: 
Property Location:

Item 

Clearing & Grubbing 
Stripping Topsoil 
Seeding 
Sod 
Import Fill (1 -5 miles) 
Import Fill (5-15 miles) 

Import Sand 
Compact Fill 
Riprap/Stone Slope 

Protection 

Dig Inspection 
Trench -2' x 4'
Drain Gate Valve 

Drain Check Valve 
Sump Pump 
(gasoline, up to 3 h.p.) 

Sump Pump Generator 

Sump Pump 
(gasoline, 3 to 8 h.p.) 

Drain Tile 
4"-6" DIAPVC 

DrainTile 
8"-10" DIA PVC/RCP_

Discharge Piping for 

Unit 

T.S. F.* 
T.S. F.* 
T.S.F.* 
T.S.F.* 
Cubic Yards 
Cubic Yards 
Cubic Yards 
Cubic Yards 
Cubic Yards 

_ 

Linear Feet 

Each 
Each 
Each 

Each 

Each 

Linear Feet 

LinearFeet 

Linear Feet 

Worksheet 

Prepared By: 
Date: 

Unit Cost 
1994 Dollars 

$50.00 to $100.00 
$40.00 to $100.00 
$30.00 to $40.00 
$350.00 to $450.00 
$2.50 to $7.00 
$7.00 to $21.00 
$8.50 to $12.00 
$0.75 to $2.00 
$25.00 to $35.00 

$2.50 to $4.50 

$600.00 to $1900.00 

$650.00to $1300.00 

$850.00 to $1400.00 

$350.00 to 1,000.00 

$1500.00 to $2250.00 

$7.00 to $10.00 

I 

$10.00 to $12.00 

$3.00 to $7.00 

Seepage Concerns 

# Units 
Needed Item Cost 

(1-2 inch DIA) Sump Pump 
*T.S.F. = Thousands of Square Feet 

Total Cost 

-

L7I3

J L | ~~~~~~vI

_ 

_ 

_

_ 

_ 

Engineering Principles and Practicesof Retrofitting Flood-ProneResidential Structures VI -LAO 

January1995 


Chapter VI: General Design Practices 

Levees 

CONSTRUCTION 

To prepare forthe construction of a levee, all ground vegetation 
and topsoil should be removed over the full footprint of the 
levee. If sod and topsoil are present, they should be set aside 
and saved for surfacing the levee when it is finished. 

SOIL SUITABILITY 

Most types of soils are suitable for constructing residential 
levees. The exceptions are very wet, fine-grained, or highly 
organic soils, defined as OL, MH, CH, OH type soils by the 

NRCS. The best are those with a high clay content, which are 

highly impervious. Highly expansive clays should also be 

avoided because of potential cracking due to shrinkage. 

COMPACTION REQUIREMENTS 

As the levee is constructed, it should be built up in layers, or, 
lifts, each ofwhich must be individually compacted. Each lift 
should be no more than six inches deep before compaction (see 
Figure VI-L5). Compaction to at least 95 percent of standard 

laboratory density should be performed at or near optimum 

moisture content with pneumatic-tired rollers, sheepfoot rollers,: 

or other acceptable powered compaction equipment. In some 

situations, certain types of farm equipment can effect the needed 
compaction. 

VI -L.14 EngineeringPrfnciplesand Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Construction 

6 

Settlement allowances vary by 
geographic region and geologic 
conditions. Therefore, a five 
percent allowance may not be 
applicable in all situations. 

Consult the state or local floodplain 
managementofficials for 

firther information. 

SETTLEMENT ALLOWANCE 

The levee should be constructed at least five percent higher 
than the height desired to allow for soil settlement. 

BORROW AREA RESTRICTIONS 

A principle concern for the construction of the levee is the 
availability of suitable fill for levee construction, but 
caution should also be taken as to the location of the fill 
borrow area. For the purpose of this manual a general rule 
is to avoid utilizing a borrow area within 40 feet of the 
landward toe of the levee. 

ACCESS ACROSS LEVEE 

The complete encirclement of a structure with a levee can 
create access problems not only for the homeowner but also 
for emergency vehicles. If the levee is low enough, additional 
fill material can be added to provide a flat slope in 

Drine-inidn andi Practirac nf RptrnfittinnFlood-ProneResidential Structures VI -L.1:5

PIi~iii ii~e~ If r 1---A -* A --I --

I'll les . --

January 1995 


Chapter VI: General Design Practices 

Y<Q~ Levees 

one area for a vehicle access ramp running over the levee as 
shown in Figure VI-L6. Careshouldbe taken to prohibithigh 
volumes oftraffic across the levee, which could result in the 
formation of ruts or the wearing away ofthe vegetative cover. 

Access over the Levee AdditionalFillPlaced 
Adtiona FlloPAcceds 

Figure VI-L6: Access over the Levee 

If it is necessary to have a gap in the levee, this can be 

closed during flooding through the use of a gate or closure 
structure. Additional details are provided in the section of 
Chapter VI entitled Dry Floodproofing. It should be noted 
that the use of a closure structure requires human interven

tion. If the structure in question is susceptible to flood 
hazards with little or no warning time, or if human intervention 
cannot be guaranteed, the use of a closure is not recommended. 

:eafl0 

VI -L.16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995 


CHAPTERVII

CASE STUDIES

Featuring: 

Elevation Wet Floodproofing
Relocation Dry Floodproofing

Levees and Floodwalls 


---~~ ~ ~ ~ ' 

Case Studies 

Table of Contents 

Elevation ..............................

Case Study #1, Elevating Houses on Masonry Walls, Masonry Piers, and Wood Posts, 

TugForkValley,WestVirginia................. ..I II -

.V 
RetrofittingOptions. ................... . 
Retrofitting DesignParameters ..................... .. I I 
RetrofittingCosts............................................. 

............. 

AppliedRetrofitting Technology . . 
ElevationUsingaMasonry WallFoundation ............................ 
ElevationUsingaMasonry PierFoundation.. ......... .. I I I I ... 

ElevationUsingaWoodPostandBeamFoundation ............... ............... 

Case Study #2, Elevating Homes on Crawlspace, Dry Creek, Goodlettsville, 
Tennessee: 1989-1990 .V ..... , I 

... 
ProjectImplementation.................................hi ................... II.I.II. . .....

... 6... 
ScopeofWork, Proposals,and Contract . .......................... 
Construction .. 
Costs ...................... 
Inspection, Approval, and Payment ..................... .. I I ... . 
UsingDryCreekasanEstimatingTool ....................... 
Conclusions .............................. .................... 

HouseRelocation ............................................................

Case Study #3, Relocating a Slab-On-Grade House With Slab Attached, 
Tampa,Florida: 1990. . ...

. 

RaisingandMovingthe Structure ..

RaisinginPlace ........ . .

Relocation ........ .

. ... 

FoundationDesignConsiderations.. ........................... 
Elevating the Structure Cost Considerations .......... ...... I... ........

I I I 

Construction ofthe New Foundation and Attaching the Elevated Structure Cost 
Considerations.............................................................................................. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January1995

VII.-3 

3 

VII -3 
VII-5 
VII-6 
VII -7 
VII -8 
VII-12 
VII-16 

VII-188........... 
VII-18 
VII-18 
VII -21 

VII-21

VII -22 

VII -23 

VII -25 

VII-.30 

VII -30 

VII -31 

VII-39

VII-46 

VII-48 

VII -49 

VII -50 

VI -i 


New or Raised Utilities, and Raised Air-Conditioning Equipment Cost 
Considerations.............................................................................I ..................

VII -50 
ArchitecturalModification Cost Considerations . .............................. VII -50 
Cost Estimates .............................. VII -50 
Conclusions ..... VII -51 

Small Levees and Perimeter Floodwalls ........................... VII -54

Case Study #4, Floodwalls, Levees, and Perimeter Drains, Bailey Creek,
Madison,Connecticut ..................... VII -54
General Design Criteria ..................... VII -54
ProjectSummary..................... VII -55
Engineering Analysis Summary ..................... VII -55

Case Study #5, Perimeter Floodwall, Henson Creek, Prince George's County,

Maryland....VII-64 

Malyland~.........................-.........................!.............................................................. .VI-6
Retrofitting Methodology .................................. VII -64
Engineering Analysis Summary .................................. VII -68

Proposed ................................... VII -.70

Work 

Plan, Elevation, and Construction Details .................................. VII -72

WetFloodproofing .................................. VII -78

Case Study #6, Wet Floodproofing a House on a Crawlspace, Henson Creek,
Prince George's County, Maryland ............................ VII -78
Engineering Analysis Summary ............................ VII -78
Dry Floodproofing Option ............................ VII -78
Wet Floodproofing Option ............................ VII -82
Engineering Analysis .............................. VII -85
Cost Estimates .................................................................................................... VII -85
Proposed Work ............................ VII -86

VII -ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


DryFloodproofing .................................. VII -90

Case Study #7, Dry Floodproofing a House with a Walk-out Basement, Henson Creek, 

Prince George's County, Maryland ............................ VII -90
Engineering Analysis Summary ............................ VII -90
Engineering Calculations and CostData ............................ VII -92
Proposed Work ............................ VII -95
Plan, Elevation, and Construction Details .......................... VII -96

Case Study #8, Veneer Wall, Dry Floodproofing, Tug Fork Valley, West Virginia ...... VII -105 
VeneerWall ................................................................ ...................................... VII-105 
Construction Cost.............................................................................................. VII-108 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VII -iii 

January 1995 


CASE STUDIES 

This chapter presents case studies of actual structural and nonstructural retrofitting 
measures. The studies illustrate some of the procedures presented in previous chapters in 
actual practice. The cases include elevation, relocation, small levees and floodwalls, and 
wet and dry floodproofing methods. 

The case studies were extracted from the following reports: 

Flood Proofing Technology in the Tug Fork Valley, US Army 
Corps of Engineers, National Flood Proofing Committee, April, 

1994. 

A Flood Proofing Success Story Along Dry Creek at 
Goodlettsville, Tennessee, US Army Corps of Engineers, National 
Flood Proofing Committee, September, 1993. 

Raising and Moving the Slab-on-Grade House with Slab Attached, 

US Army Corps of Engineers, National Flood Proofing Committee, 
1990. 

Bailey Creek Flood Prevention, Resource, Conservation and 
|I , 
US. DEPARmmENrOF AGRICULURE 
SOIL CONSERVATON SERVICE I 
Development Project, Madison, Connecticut, Connecticut 
Department of Environmental Protection, New Haven County Soil 
and Water Conservation District, US Department of Agriculture 
Natural Resources Conservation Service. 

Henson Creek Floodplain Study, Prince George's County, Maryland, 
Department of Environmental Resources, Watershed Protection 
Branch. 

Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VIl -1 
January 1995 


Case #1: Elevation 

ELEVATION 

This section presents two case studies that identify procedures, methodology, and design 
parameters used to elevate houses. Case Study #1 illustrates the elevation of houses on 
masonry walls, masonry piers, and wood posts in the Tug Fork Valley, West Virginia. 
Case Study #2 illustrates the elevation of homes on a crawlspace in Goodlettsville, 
Tennessee. 

CASE STUDY #1
Elevating Houses on Masonry Walls, Masonry Piers
and Wood Posts
Tug Fork Valley, West Virginia

The Tug Fork Valley is located on the border of southern West Virginia and northeastern 
Kentucky (see Figure VII-1.1). The April 1977 flood provided the impetus for formulating 
a flood damage reduction plan, which used both structural and nonstructural measures 
to achieve a cost-effective and socially acceptable solution to the flooding problems in the 
valley. 

As a result of the April 1977 flood, Congress enacted legislation within the Energy and 
Water Development Act of 1980. This Act was unique in that it authorized the Chief of 
Engineers to take whatever measures were necessary and advisable to reduce flood 
damages at federal expense. In effect, the Act provided a fertile legislative environment 
for the formulation and implementation of an array of both structural and nonstructural 
measures in the Tug Fork Valley. 

Retrofitting Options 

Structures located in the floodplain that would suffer damages to the first habitable floor 
during a recurrence of a flood of the magnitude of the April 1977 flood were eligible for 
either voluntary retrofitting or acquisition. Eligibility for retrofitting required that: 

* the structure would suffer damages to the first floor or to mechanical 
systems below the first floor; 
* the structure not be located within the regulatory floodway; 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII-3 
January 1995 


Chapter VII: Case Studies 

e$Iu 
Ohio IV 
West Virginia 
Tug Fork 
Bsin 
Kentucky-( Virginia 
T e n e s s e. ... .. C . 
Tennese M.Carolina 
i VICINITY MAP 
SCALEIN MILES 
t .a 
Figure V11- 1. 1: Tug Fork Valley 
0 5 10 IS 
SCALEIN MILES 
10 
TUG FORK BASIN 

VII -4 Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation 

* raising the structure to an elevation one foot above the April 1977 flood 
level would not place the first floor more than 12 feet above the adjacent 
ground surface; and 
* the structure was structurally sound and could be raised safely. 
The method chosen for retrofitting was based upon engineering feasibility and cost-
effectiveness. The options available included the following: 

* elevation of the livable area on a solid masonry wall foundation, masonry 
pier, or wood post/beam foundation; 
* construction of a veneer wall against the structure with sealed openings at 
entrances (see Case #8); 
* construction of floodwalls or levees around an individual or group of 
structures; or 
* construction of a replacement floodproofed structure on-site. 
For those structures for which elevation was the most cost-effective option, the owner 
was required to execute an agreement, prior to start of construction, that restricted future 
use of the enclosed lower area below the elevated first floor. Future enforcement of 
owner operation and maintenance of the retrofitting construction and owner compliance 
with the restrictive agreements was transferred to the local government sponsor following 
the final construction inspection. 

Retrofitting Design Parameters 

The following series of design parameters was developed for the retrofitting program: 

* The Design Flood -Established by legislation as the April 1977 flood or the 100year 
flood level if it was higher at the project site. 
* Freeboard -A one-foot freeboard for elevated structures was measured from the 
elevation of the design flood to the bottom of the subfloor material or floor slab of 
the first floor. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -5 
January 1995 


Chapter VII: Case Studies 

* Veneer Wall Design -The maximum height for the design of a veneer wall is 
dependent upon the strength of the existing structure walls and the soil conditions 
supporting the structure (see Case #8). 
* Height of Rise -The height limit for elevating structures was determined to be 12 
feet from the adjacent ground surface. This tall height limit resulted in a substantial 
savings in program costs by reducing the number of structures for which 
acquisition/relocation was the only option. 

* Floodwater Velocity -Hydrologic and engineering studies for foundation designs 
showed that retrofitting structures by elevation or veneer wall could only occur 
where floodwater velocities did not exceed eight feet per second. 
* Structure Condition -Structures found to be deteriorated beyond a point 
where limited rehabilitation would not permit safe elevation were not raised. 
* Adjacent Structures -In some situations, portions of adjacent structures 
were temporarily demolished in order to place steel lifting beams for raising the 
structure to be elevated. Justified temporary demolition costs were reimbursed as 
a part of the total construction costs. 

RetrofittingCosts 

Retrofitting existing structures by elevation can be a complicated and labor-intensive 
process. The factors described above all contribute to the cost of elevating an existing 
structure. The key factors influencing the cost of retrofitting by elevation include: 

* size, condition, and construction type (frame or masonry) of the structure; 
* the height of elevation required and the type of foundation needed to 
support the structure; 
* the need for structure rehabilitation; 
* the type, condition, and location of mechanical and utility systems; 
* requirements for structure access, including handicapped access; and 
* access to the site. 
Vil -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation 

Table VII-1. 1 below shows the percentage contribution to elevate a structure.
TableVII-l.1 RetrofittingCost for Structure Elevation

Construction Items Percent of Total Construction 
Structure Lifting 27 
Foundations 21 
Mechanical and Utilities 9 
Carpentry and Finishings 14 
Site Work, Mobilization, and Cleanup 29 

100
From "Floodproofing Technology in the Tug Fork Valley," U.S. ArmyCorps of Engineers

Applied Retrofitting Technology 

The choice of a particular foundation for an elevated structure and the basic design of the 
supporting foundation were critical cost and coordination elements in the retrofitting 
program. Several factors influenced the basic design and application of foundations in 
the Tug Fork Valley, including: 

* floodplain location of the structure and the inherent hydraulic characteristics of 
that location; 
* height of house raising required to reach the design flood elevation with 
freeboard; 
* type of building construction such as frame or masonry; 
* use and condition of structure; 
* architectural character of the structure; and
. cost effectiveness of the solution.
Pnninaarinn PrininipIQ and Practices nf RptrnfittinnFlood-Prone Residential Structures VII -7 
January 1995 


Chapter VII: Case Studies 

Generally, three types of supporting foundations were used to raise the structures in the 
Tug Fork Valley: 

* reinforced solid masonry wall; 
* masonry pier construction; and 
* wood post and beam. 
Elevation Using a Masonry Wall Foundation 

The majority of structures completed in the first three approved phases of the Tug Fork 
Valley project were raised on reinforced masonry wall foundations. The decision to use 
this type of foundation was based upon the architectural styles of structures located in 
those project areas and the increased support strength needed in areas of higher floodwatervelocity. 

Normally, existing foundations and footings on eligible structures were deteriorated due 
to repeated flooding or were unsuitable as a base for the new walls due to poor construction. 
For this reason, most, if not all, portions of the existing footing and foundation 
walls were demolished during the raising process. Where possible, the existing footing 
and portions of the existing foundation walls were used as a base for the extended masonry 
wall. 

The basic design of the reinforced masonry wall foundation (see Figure VII-1.2) consisted 
of a continuous perimeter wall of concrete block (8 x 8 x 16 or 8 x 12 x 16 inch block) 
resting upon an appropriately sized (12 x 18 or 12 x 24 inch) reinforced concrete footing. 
The masonry wall contained vertical steel reinforcing grouted into every third cell of the 
concrete block. 

The vertical steel was placed in two-foot lengths with 12-inch lap spacings. All concrete 
block cells were grouted solid below grade, and block sealer was applied to the exterior 
block face below grade to prevent moisture penetration. The exterior surface of the block 
was painted with a coating of block filler and two coats of latex paint (owner's choice of 
colors). The vertical steel was tied to the footing reinforcing and a continuous bond-
beam course positioned near the top of the foundation wall. Generally, number four steel 
rebar was used in the footing as vertical reinforcing, and in the bond-beam course. 

VII -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation

In addition to the vertical reinforcing, steel reinforcing (standard truss "dur-o-wal") was 

added to alternating horizontal mortar joints. Steel anchor bolts were extended into 

grouted block cells from the bond-beam course to the new sill plate, or steel strapping 

was included in the grouted block cells and attached to the existing joists for anchoring 

the first floor to the new foundation (see Figure VII-1.2). 

In those limited cases where the existing footing was suitable as a base for the new 
foundation, the existing footing was drilled, new number four steel reinforcing bars were 
grouted in, and a strip footing cap was poured on top of the old footing before laying new 
foundation block. A continuous grout layer was placed on top of all footings before 
laying the initial block course. 

In cases where the structure had an existing below-grade basement, the existing basement 
wall was removed two feet below grade and a new footing was constructed on top of the 
existing wall before laying the new foundation block. The existing basement floor was 
fractured and the basement area was filled with compacted free-draining material to the 
elevation of the exterior grade. Interior supporting masonry or steel pipe columns, when 
required, were founded on unfractured portions of the existing basement floor or on new 
footings and extended to the required design height (see Figure VII-1.3). 

An integral part of the solid wall foundation design was the equalization of hydrostatic 
water pressures between the interior enclosure and the exterior flood heights. With the 
exception of one structure (see Case #8) the entire Tug Fork Valley retrofitting program 
was based upon elevation with flooding below the first floor. 

In the case of the solid masonry wall foundation system, openings to allow filling and 
drainage of the enclosed area were designed based upon FEMA criteria (one square inch 
of free opening per one square foot of enclosed floor space). The design used on 88 
percent of the structures elevated on masonry wall foundations was a 2 x 2 foot square 
galvanized sheet metal louver, providing 50-percent free opening with alternating louvers 
for both filling and drainage of the enclosure. 

Louvers were placed within eight inches of the interior grade and at least two louvers 
were used in each enclosure, regardless of the enclosed square footage. Owners were 
allowed to press-fit one-inch thickness styrofoampanels into the louvered opening from 
the interior to reduce cold air penetration into the enclosed area beneath the first raised 

floor (see Figure VII- 1.4). In the event of flooding, these panels would dislodge at low 

water pressure and permit hydraulic equalizationto occur. 

EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures VII -9 

January 1995 


Chapter VII: Case Studies 

In the case of the other foundation designs (wood post/beam and masonry pier) the area 
beneath the first floor was not entirely enclosed or was enclosed with wood lattice, 
allowing free passage of floodwater both into and out of the space without louvers. 

II

9 
S S 

craw~~am Ma 

-L4 ANOD0 %V01 
-RF.. 4-p; Of~~S VIt 
_%

Hu 

Figure VII-1.2: Typical Wall Detail Section 

Vii -10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation 

*L-A4 *oL1TV 
-5 ID 0%N9AlP WEI=&4 

BAWL cOWrl'

A AFVDM-I-

Figure VII-1.3: Interior Column Detail 

Figure VII-1.4: Flood Louver Detail 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII-11 
January 1995 


Chapter VII: Case Studies

Elevation Using a Masonry Pier Foundation 

One residence in the Tug Fork Valley program was raised approximately 11 feet on 
masonry piers. A steel frame structure was designed to span the masonry piers and 
support the existing floor system, which was in poor condition from past flooding damages 
(see Figure VII-1.5). All of the masonry piers were individually designed to fit the 
structure and the expected hydrostatic and hydrodynamic loading at the site. 

Figure VII-I.5: Masonry Pier Plan 

VII -12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation 

The piers were constructed of 8 x 8 x 16 inch concrete masonry block founded on concrete 
footings. All cells of the block pier were grouted solid with concrete. Vertical steel 
reinforcing was placed in all piers with ladder-style masonry joint reinforcing in alternating 
horizontal joints. Number five reinforcing steel bars were used for footings and 
vertical reinforcing as shown in Figure VII-1.6. 

Utilities were collected into a single insulated pipe chase constructed to resist flood 
damages (see Figures VII-1.7 and VII-1.8 ). The structure floor was fully insulated to 
reduce the increased heating demands caused by unimpeded air flow beneath the structure. 
The perimeter of the masonry pier foundation was clad with treated wood planking 
and wood lattice to reduce the visual impacts of this design. 

Two additional factors that require consideration in the elevation process are weather and 

safety. Weather-related problems were solved, in part, by installing plastic skirting 
around the bottom of the raised structure. Once the plastic skirting was installed, the area 
beneath the structure was protected from precipitation and could be heated to a tempera

ture that protected utilities and allowed concrete and mortar work to proceed. 

Safety was most important during the construction activities of the retrofitting program. 

Contractors, inspectors, Corps of Engineers personnel, and the staff of the state housing 

agencies were informed of the inherent construction dangers. Standard precautions 

regarding the use of personal safety equipment (helmets, safety footwear, eye and ear 

protection, etc.), the use and storage of potentially hazardous solvents and fluids, fire 

protection, use of heavy equipment and power tools, and control of the job site perimeter 

were discussed frequently with contractors. The safety efforts resulted in the successful 

retrofitting of 136 structures without a single serious injury or fatality. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -13 
January 1995 


I Chapter VII: CaseStudies 

'&eT

Figure VII-1.6: Masonry Pier Detail Section 

VII -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation 

10A

PDOW ,ft w 

Pie Deai

Figue VI-l.7Inulatd Utlit Chasej 

Figure VII-1.7: Insulated Utility Pipe Chase Detail 

.

I~~~I ~*~ ** ..-. 

C-.~~Arir DinenloaI~ anei Pmnrtinp nf RetmnfittingFlood-ProneResidentialStructures VII -15 
January 1995 


Chapter VII: Case Studies 

Elevation Using a Wood Post and Beam 
Foundation 

Two frame residences were raised using this design. The basic design uses 
eight-inch diameter round or square pressure-treated wood posts founded 
at least four feet deep with a continuous six-inch concrete encasement 
below grade. Spacing of posts is dependent upon structure size and 
configuration, size and number of supporting beams required, soil bearing 
capacity, and legal uses of the area below the raised first floor. 

The superstructure consisted of pressure-treated wood beams positioned to 
support the main bearing walls of the structure. Pressure-treated wood sill 
plates were placed between the post/beam framework and the structure's 

floor system. The beams were connected to the notched posts using 
galvanized bolts, washers, and nuts. Additional lateral and horizontal 
wood bracing was added to resist lateral wind and floodwater loading. 
Figure VII-1.9 shows the basic design elements of the wood post/beam 
foundation. 

tLW~pCfl~t 

"S.&"Wt,

3cW 

Figure VII-1*9: Wood Post/Beam Detail Section 

VII -16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #1: Elevation 

Materials used for aesthetic treatment were resistant to water damage and did not impede 
high water flows. Rather than using breakaway walls that may require replacement after a 
flood event, the panels were hinged at the top to swing in the direction of the flood flow, 

thus reducing hydrodynamic loading on the foundation, reducing the obstruction of floodwater, 
and reducing operation and maintenance cost for the owner. 

STRUCTURE LIFTING PROCESS 

One of the most important and relatively expensive elements in elevating structures is the process 
of physically lifting the structure to the design elevation. Structure lifting contractors 
were employed as both subcontractors and prime contractors depending on their 

management, insurance, and financial capabilities in the retrofitting program. 

Several elements contributed to the successful elevation of structures in the program. 

First, each lifting contractor was required to submit for review a lifting plan that de

scribed the number and placement of support beams, cribbing supports, and any special 

support systems for porches or building additions required to raise the structure. 

Prior to lifting a structure, a survey was made of the structure interior to locate critical 

stress points and concentrated weights. Critical areas in residences included bathrooms, 

kitchens, interior supporting walls, floor slabs, fireplaces, chimneys, and room additions. 

Each of these areas received special attention in the lifting plan due to the presence of 

non-flexible wall and floor coverings, which were subject to cracking. Also required in 

the lifting plan was the proposed hydraulic jacking system, which allowed collective or 

individual control of hydraulic jacks located within the cribbing supports. As a by-

product of the elevation process, the unified hydraulic jacking system determined the 

weight of the structure, which proved useful in foundation design. Use of the unified 

hydraulic jacking system facilitated the elevation of most structures in the program to the 

design flood height in a single work day. 

Two additional factors that require consideration in the elevation process are weather and 

safety. Weather-related problems were solved, in part, by installing plastic skirting 

around the bottom of the raised structure. Once the plastic skirting was installed, the area 

beneath the structure was protected from precipitation and could be heated to a tempera

ture that protected utilities and allowed concrete and mortar work to proceed. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vil -17 
January 1995 


Chapter VII: Case Studies 

CASE STUDY #2
Elevating Homes on Crawlspace, DryCreek
Goodlettsville, Tennessee: 1989-1990

This case study is included because it represents a departure from the traditional way the 
Corps of Engineers has elevated houses by the standard government process of "plans and 
specs -advertisement -sealed bid -award -construction," where the homeowner has little 
or no input, and the contractor's work is directed and inspected by the Corps of Engineers. 
The goal of the Dry Creek Project was to reduce the Corps of Engineers' involvement 
and increase homeowner participation. This was accomplished by changing the 
standard procedure and allowing the homeowners to select their own contractors and 
direct the work. In very simple terms, the Corps of Engineers said to each homeowner, 
"We will give you technical assistance; then you get your house raised and we will pay 
for it." 

The project is located about ten miles north of downtown Nashville, Tennessee. Dry 
Creek is the boundary between the city of Goodlettsville and metropolitan Nashville (see 
Figure VII-2.1). The purpose of the project was to reduce damages as a result of flooding 
in the Gateway Subdivision, where 46 homes were within the 100-year floodplain. Nineteen 
of the homes were eligible for elevation. The project began in March 1989 and was 
completed in June 1990. 

Project Implementation 

Project implementation began with an information phase. Each homeowner was given a 

package explaining the house elevating program in general, the Corps of Engineers' role, 

and the homeowner's responsibilities. The homeowners were also given information to 

pass along to prospective contractors. 

Scope of Work, Proposals, and Contract 

The homeowners were required to obtain at least three proposals from contractors of their 

choice and submit them to the Corps of Engineers. It was emphasized to the owners that 

their meetings with the contractors were very important since that would be their opportu

nity to exchange ideas and recommendations, and to gain familiarity with the contractors. 

The Corps of Engineers supplied estimating forms for the contractors in the information 
packages. 

VII -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #2: Elevation 

Figure VII-2. 1: Dry Creek Project 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -19 
January 1995 


Chapter VII: Case Studies 

The Corps of Engineers' project manager and a cost engineering representative measured 
and inspected each home so that cost estimates could be developed. Following a review 
of the particular aspects of each home, the project manager and the cost engineer's representative 
independently developed estimates for each home. Since plans and specifications 
were not prepared, the Corps of Engineers essentially developed generic "fair and 
reasonable" estimates for each home. After two Corps of Engineers estimates were 
prepared, a single amount was agreed upon (usually the average of the two), and that 
value became the government cost estimate. 

Before the offer to the homeowner was finalized, the Corps of Engineers reviewed the 

contractor's proposal to verify (as much as possible) the assumed scope of work. On 

occasion, the government estimate was adjusted after review of the proposals. After the 
government estimate was finalized, a Memorandum of Record was prepared to document 
the costing process. The Corps of Engineers' "offer" included construction costs and a 
$200 legal allowance to the homeowner. 

The next step was the homeowner's negotiation of a contract with the selected contractor. 
Without exception, the Corps of Engineers' offer was less than the lowest contractor 
proposal, but all the homeowners were able to negotiate an agreement within the Corps of 
Engineers' allowance. After the Homeowner-Contractor contract was executed, it was 
forwarded to the Corps of Engineers for review. The review was to insure that the fundamental 
requirements were covered, and other major items of work were agreed upon, 

such as the size of porches and decks, sidewalks, driveways, landscaping, etc. 

The last step prior to construction was the execution of the Corps-Homeowner Agreement. 
It was very simple, with only four Corps requirements: 

* the house must be raised at least one foot above the 100-yearflood elevation as 
specified by the Corps of Engineers; 
* the construction must pass the codes inspection by the City of Goodlettsville; 
c 

a provision for flow through the foundation was required to eliminate hydrostatic 

pressure; and 

* the homeowner must execute a covenant provided by the Corps and later recorded 
at the courthouse stating that the space below the new first floor would never be 
converted into living space. The space could be used for parking, building access, 
and storage only. 
VII -20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #2: Elevation 

Construction 

All the homes in the program were one-story brick veneer, in sound structural condition. 

The homes were approximately 1,000 to 1,475 square feet, and the required elevation 
heights ranged from two to six feet. All homes had crawlspaces under the main portion 

of the structure. Several residences had finished garages on slabs about 1.5 feet lower 
than the first floor; the slabs were not raised. 

Costs 

The cost of elevating the 19 homes in place ranged from $25,900 to $35,350 each, including 
government administrative cost. Table VII-2.1below identifies the cost of retrofitting 
each structure. The major variables that influenced the costs were the number of entrances/
exits, height of the elevation, foundation perimeter, size of existing porches, 
offsets, and finished garages. Administrative costs of about $4,000 per structure were 
incurred. 

Table VII-2. 1 DRY CREEK FLOODPROOFING PROJECr SUMMARY 

SIZE of RAISE CONST.
HOUSE HEIGHT COST**,---COMMENTS
(sq.ft.) (ft.)

1000 5.33 200 3 exits 

1000 6.00 $29,500 3exits
1000 5.33 S29,500 3 exits
1000 4.67 $29.500 3exits.A/C

1420 4.67 535,000 3 exits, finishedgarage,offset
1450 4.00 35,350 2 exits, ANC,fin. garage, offset,

paveddrive,bigporch 
1430 3.33 534.050 2 exits, fin.garage,offset,fireplace,paved drive,2 big porches 
1475 4.00 $33.000 3 exits,offset 

1425 3.33 532,600 2 exits, garage,offset. veddrivealum.sidina.bigfrontporch 
1425 2.67 31,000 offset, b frontporch

2 exits, garage, 
1450 2.00 S30,800 2 exits, finishedgarage,largeattachedcarport 
1065 4.67 529,700 2 exits, offset 
1275 2.00 530.200 2 exits, finishedutilityroom(onslab),A/C,partialstoneface 
1450 2.00 531.800 2 exits,finishedgaragew/falseceiling,C/Lfence 
1400 2.00 531.80 2 exits,finishedgaragewIfalseceiling,N IC 
1450 2.00 528,500 frontporch,garage(rehang2 doors&window Interorsteps) 

1014 2.00 525.900 2 exits,paveddriveway
1000 200 527,200 2exits,attachedutilityroomwoodfence concretepatio
1450 2.00 531,600 garagew s An front

2 exits, finished 

BrickveneerhousesIn sound structuralconditionwithcrawlspaces.
Includes$4,000perstructureforCorpsof Engineers' costs.

administrative 

1989-1990prices. 

'Try fl4

VII Engineering 
Principles and Practices of Retrofitting Flood-Prone Residential Structures vil -d 
^4ltoI 

January 1995 


Chapter VII: Case Studies 

_ 

The steps listed below were typical. 

* Building permit and electrical and plumbing permits were obtained. 
* A pre-construction inspection and inventory was conducted by some contractors 
and homeowners at the Corps of Engineers' suggestion. 
* Site work in advance of the elevation took from three to five days. This included 
brick removal and disposal, dismantling fences and moving shrubbery to allow 
access for the mobile equipment, knocking holes in the foundation walls, cutting 
garage slabs to allow placement of the house lifting beams, and other miscellaneous 
activities. 

* On the day of the actual house elevating, water and sanitary drainage lines were 
disconnected and the owners vacated the home. 
* The elevation was usually accomplished with synchronized hydraulic jacking 
systems and timber cribbing. This activity took about one to two hours per vertical 
foot. 

* Temporary utility reconnections were made and temporary steps were built. 
* The remainder of the work can be characterized as "routine" home construction 
activities. The time involved for the construction varied greatly, from two weeks 
to three months. Factors impacting the time included the weather, capability of 
the contractor, and availability of subcontractors. 
Inspection, Approval,and Payment 

Because the contractor worked directly for the homeowner, the Corps of Engineers did 

not direct the work. The only formal "inspection" by the Corps of Engineers was to 

certify that the terms of the Corps-Homeowner agreement were met prior to payment. 

The Goodlettsville Building Code Department provided the "quality control" for the 

construction (along with the homeowners). Payment was made by check and was issued 
jointly to the homeowner and the contractor for the amount specified in the Corps-

Homeowner agreement. 

VII -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #2: Elevation 

Using Dry Creek as an Estimating Tool 

As discussed earlier, the homes on Dry Creek were structurally sound, brick veneer, one-

story homes with crawlspaces. The homes ranged from 1,000 to 1,475 square feet. 
Building materials and skilled labor were readily available, and there was a competitive 

environment within the local contractor community. This does not mean that the Dry 
Creek costs are not representative; it means that extracting cost data from this project for 
use elsewhere should be done with caution and with an understanding of the applicability 

of such cost data. 

A number of factors influence the cost of retrofitting a home; some include: size of 
structure, height of raise, condition of the home, number of entrances, size of porches, 
fireplaces, type of construction (brick veneer vs. frame), access, additions or offsets, and 

others. For homes in fair condition or better (no serious structural deficiencies), the 

dominant factors are usually the size of the home and the raise height. After the Dry 

Creek retrofitting project was completed, the cost data was evaluated to see if any rela

tionships could be derived that might be used as a planning-level estimating tool. An 

equation was developed that computes the Dry Creek house-raising costs. The variables 

in the equation are size of structure and raise height, and the equation takes the form: 

I-I 

Computed cost = K + (Ks)(size) + (K h)(raise height) = $_ 

Where: K is 11,360; 
Ks is 12.6/square feet; 
KI is 970/raise height; 
size is square feet of the ground floor, 
including attached garage; and 
raise height is raise height in feet. 

Fornula VII-2. 1: Dry Creek House Raising Costs 

ZA_ n^ r::...D.;n.inl .. A M-n4-,f 0~+rnfitininn Floo-iProne Residential Structures VII -23

Janguaryngr1995 LIUVLIq'VO %WIW. * -_ -I _s 

I 

January 1995 


Chapter VII: Case Studies

The following Cost Analysis Table (Table VII-2.2) shows the actual cost, the computed 
cost using this formula, and the percent difference for each house raised in the Dry Creek 
Retrofitting Project. 

The above equation should give reasonable planning-level estimates for screening alternatives. 
Anyone using the equation or its results should recognize the limitations of this 
method. The equation should not be applied to situations that are drastically different 

from those at Dry Creek. Specifically, the equation should not be used on homes in poor 
(unsound) condition or homes on slab. 

Table VII-2.2 COST ANALYSIS TABLE 

STRUCTURE SIZE RAISE ACTUAL COMPUTED PERCENT 

NUMBER (squarefeet) HEIGHT COST COSr* DIFFERENCE 
(feet) (Computled

Ai. Adual) 

1 1000 533 $26,200 S29,130 +10 
2 1000 6.00 $29,500 $29,780 + 1 
3 1000 5.33 S29,500 S29,130 -I 
4 1000 4.67 $29,500 S28,490 -4 
5 1420 4.67 $35,000 $33,782 -4 
6 1450 4.00 S35,350 $33,510 -5 
7 1430 3.33 $34,050 S32,608 -4 
8 1475 4.00 $33,000 $33,825 + 2 
9 1425 3.33 $32,600 $32,545 0 
10 1425 2.67 $31,000 $31,905 +3 
11 1450 2.00 $30,800 $31,570 + 2 
12 1065 4.67 $29,700 $29,309 I 
13 1275 2.00 $30,200 $29,365 3 
14 1450 2.00 $31,800 $31,570 . 1 

15 1400 2.00 S31,800 $30,940 3 
1 6 1450 2.00 $28,500 $31,570 +10 
17 1014 2.00 $25,900 $26,076 + 1 
18 1000 2.00 $27,200 25,900 -5 
19 1450 2.00 $31,600 $31,570 0 

Includes$4,000per structure for Corps of Enginercs'administrativecosts
' ComputedCostWhereK= 11,36A,Ks=12 6 ; Kh=9 7 0

JAMPLE: 

Hon No. S. 

COMPUTEDCOST= K+(K5Xsizcof house insquarefect)+ KXraisc heightin fcet)
= 11,360+ (121)(sizeof house)+ (970)(rmbe height)
; 11,360 + (12.6)(1420)+ (970)(4.67)
= $33,782

VI.-24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #2: Elevation 

Conclusions 

The Dry Creek retrofitting project was a success. The project objectives were achieved: 
retrofit the homes in a cost-efficient manner and maximize homeowner satisfaction. 

There was nothing unique about retrofitting the homes along Dry Creek; no new construction 
techniques were developed, and no unusual techniques were used. The uniqueness of 
the project was the administrative philosophy. This philosophy was to "keep things 
simple, and stay out of the way as much as possible." 

Unless there are special conditions, plans and specifications are not required for elevation 
projects, and the Corps of Engineers' presence is not necessary to direct and inspect the 
work. Special conditions can include multi-hazard concerns such as velocity, debris 
impact, high wind, and/or seismic activity for example. A straightforward agreement was 
created with the necessary conditions to insure that retrofitting objectives were met. The 
Corps of Engineers allowed the homeowners to make decisions regarding their homes and 
work with the contractors of their choice. Cost-efficiency was achieved by limiting the 
administrative cost throughout the process. 

The Homeowners at Dry Creek included factory workers, bankers, single parents, elderly 

couples, and others. Approximately two years after project completion, the Corps of 

Engineers sent a questionnaire to each of the 19 homeowners requesting their opinions 

about the project and how it was administered. Twelve of the homeowners returned the 

questionnaire. The results indicate that they favored the high level of homeowner in

volvement that the project provided. The results of the post-project questionnaire are 

shown in Table VII-2.3 

EngineeringPrinciplesand Practices of Retrofitting Flood-Prone Residential Structures VII -25 
January 1995 


Chapter VII: Case Studies 

Table V1-2.3 Post -Project Questionnaire Results 

1 2 3 4 5 0 

I'm glad I was given the opportunity to choose
my own contractor. 9 2 1

I'm glad I was allowed to direct the work and
make decisions concerning the final appearance 9 1 2
and function of my house.

I don't feel my responsibilities (soliciting
proposals, negotiating with my contractor 9 2 1
agreements, etc.) were too much handle.

I think the Corps exercised about the right
amount of control over the project. 9 2 1

I think the overall appearance of my home is at
least as good as before my house was raised. 9 2 1

I think the value of my home increased by
having it raised. 9 2 1

Overall, I consider the house raising project a
success. 8 4

All things considered, I'm glad I had my house
raised. 10 2

KEY 

Strongly Strongly No
Agree Disagree Response

1 12 13 14 15 0

I 

Customer satisfaction is always important, particularly when something as personal as 
elevating an individual's home is involved. The best formula is to allow the homeowner 
as much freedom and flexibility as possible while maintaining control of the "federal 
interest," cost, and project integrity. The procedures used in the Dry Creek Project should 
be considered when cost efficiency and customer satisfaction are project objectives. 
Figures VII-2.2 through VII-2.7 are examples of homes raised during the Dry Creek 
project. 

V1I -26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Case #2: Elevdlon 

'5I 

1. 
,' 

Figure VII-2.2: Typical Home Raised About Two Feet 

Figure VII-2.3: Typical Home Raised About Five Feet 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII-27 
January 1995 


Chapter VII: Case Studies 

2

' I i~ '1

tk "tf 

tI !"~ ( 

iw1, 

-.:

;]'sA ~]t 14 , IU, 

Figure VII-2.4: Example of a Home Raised With the Brick Veneer in Place -During 
Construction 

Figure VII-2.5: Example of a Home Raised With the Brick Veneer in Place -
Completion

VII-28 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #2: Elevation 

I 

Figure VII-2.6: Provision for equalization of hydrostatic head was accomplished 
with foundation vents and/or flexible flaps on crawlspace access door. 

Figure VII-2.7: Example of a Home Raised With Air Conditioner Compressor Unit on 
Elevated Platform 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -29 
January 1995 


Chapter VII: Case Studies 

HOUSE RELOCATION 

This section presents a case study that identifies procedures, methodology, and design 

parameters used to raise and move a slab-on-grade house with the slab attached. 

CASE STUDY #3
Relocating a Slab-On-Grade House With Slab Attached
Tampa, Florida: 1990

Many approaches to flood protection and flood loss reduction have been developed and 
used with varying degrees of success, including raising existing structures above expected 
flood levels, or relocating them to flood-free areas. Those approaches are relatively 
simple for structures originally constructed on piers; however, they are not as well recognized 
as economically viable practices for structures on concrete slab foundations. In the 
case of slab foundations, there are two practical possibilities: detaching the structure 
from the floor slab, or moving the entire structure with the slab attached. The latter 
practice is not widely known and understood, and is often believed to be infeasible. It is, 
however, technically feasible, is often economically feasible, and presents many advantages 
in the hands of an experienced structural mover. 

The procedures and techniques described here are based primarily on those employed by a 
professional structural mover operating in the Tampa, Florida area. Other professionals in 
the field may employ different but equally effective methods. No undertaking of this 
magnitude should be attempted without the advice and assistance of professional struc

tural movers and structural engineers or architects. 

Keeping the slab attached has a number of advantages over the detached-from-slab 

approach. In the case of raising the structure in place, or moving it only a short distance 

so that temporary utility connections can be maintained, a major advantage to the 

homeowner is the possibility of continued residence in and use of the house during the 

process. The presence of the floor slab adds greatly to the structural integrity of the 

building or building segments during the move, and somewhat simplifies the internal 

shoring and bracing required. The presence of the slab is especially advantageous, if not 
absolutely essential, for some types of construction, such as concrete block. 

VII -30 Engineering Principles and Practices of Retrofittinq Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

Raising and Moving the Structure 

A system used extensively in Florida, where construction with concrete block is widely 
practiced, involves excavating the soil from beneath the structure, inserting a system of 
two heavy steel longitudinal beams and numerous closely-spaced cross members, and 
cutting the plumbing connections and any footings or piers encountered. Procedures will 
vary somewhat from structure to structure, and must be planned on a case-by-case basis. 
The slab-on-grade is typically designed to be continuously supported by the underlying 
soil. This demands careful planning for the systematic removal of the soil and for supporting 
the slab throughout the process as shown in Figure VII-3 .1. Special care is 
required for concentrated loads such as fireplaces and chimneys as indicated in Figure 
VII-3.2. 

Figure VII-3. l: Temporary Supports for the Slab 

Hydraulic jacks are placed at three points beneath the steel beam system, two near one 
end of the structure beneath each of the main longitudinal beams, and one at the other end 
of the structure midway between the two longitudinal beams. The lifting points are thus 
positioned to form an isosceles triangle in the horizontal plane of the slab. The three-
point lift minimizes the possibility of cracking of the slab due to twisting or differential 
movement. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -31 
January 1995 


Chapter VII: Case Studies 

, :,; 'V . L.

X~_f'-, .. . ~ 

Figure VII-3.2: Fireplaces Require Special Attention 

If the structure is to be raised in place without relocation, once it is raised to the desired 
elevation the jacks are replaced with timber cribbing. If it is to be moved to another 
location, large wheeled dollies are inserted at the two jacking points under the main 
beams, and the hauling equipment takes the load at the third jacking point, centered 
between the main beams. At the new location, the moving equipment is replaced by 
timber cribbing supporting the structure at the desired elevation, and the new foundation 
is constructed beneath it. Figure VII-3.3 shows one of the timber cribbing supports 
placed beneath a main longitudinal beam. 

If piers or portions of grade beams must be removed, they are first scored along appropriate 
cut lines with an air saw equipped with a concrete blade, then broken with a hammer. 
Figures VII-3.4 and VII-3.5 show where previously existing piers have been cut away. 
Any reinforcing steel encountered is cut with a torch as shown in Figure VII-3.6. 

VII -32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

Figure VII-3.3: Timber Cribbing 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -33 
January 1995 


Chapter VII: Case Studies 

Figure V1I-3.4: Piers Cut Away Using Air Saw 

Figure VII-3.5: Piers From Original Foundation 

VII -34 Engineering Principles and Practices of FRetrofittingFlood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

Figure VII-3.6: Cutting Reinforcing Steel 

If the structure's size or shape prevents raising or moving it one piece, it can be cut into 
manageable segments. If the structure is too tall for vertical clearances available along 
the route, the roof can be partially or completely removed. It is frequently necessary to 
remove chimneys for this reason. It may also be advantageous to remove the floor from 
attached garages, many of which are constructed at a slightly lower elevation than the 
remainder of the house. 

Cuts in walls are made between studs in frame construction. In concrete block construction, 
a whole section of blocks may be removed (see Figures VII-3.7 through VII-3. IO) 
and replaced at the new site, sometimes incorporating a new pilaster at the location of the 
removed blocks. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -35 
January 1995 


Chapter VII: Case Studies 

Figure VII-3.7: Garage Floor Slab Removed 

Figure VII-3.8: Holes in Garage Wall to Insert Steel Beams 

VII -36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Riokeon 

Figure VII-3.9: Excavation Below Slab to Allow Access 

FIg E and T l Completed
Figure VII-3. I10: Excavation and Tunneling Completed

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vn -37 
January 1995 


L Chapter VII: Case Studies 

Vertical cuts through roofs are usually made between rafters or joists, or immediately 

alongside a rafter or joist. Reconnections at cuts between rafters are made with 2 x 6 or 2 

x 8 timbers laid flat against the underside of the roof. Reconnections of cuts immediately 

adjacent to a rafter can be made by nailing additional rafters to the old rafter. 

Cuts through the slab are made with "street saws" equipped with diamond blades. Usually 
no attempt is made to reconnect the slab at the new site. The joints will merely be 
sealed with grout. New foundation piers can be located directly under slab cuts to prevent 
differential movement of the two edges. Figure VII-3. 11 shows a cut through a slab prior 
to raising the structure. 

According to experienced structural movers, about two weeks are required for the average 
residential structure for initial site preparations, excavation and tunneling, and jacking. 
This time can be substantially increased by site conditions such as large trees preventing 
or limiting access by the excavating and earth moving equipment, the need for dewatering, 
the presence of rock, etc. Construction of the new foundation, reconnecting utilities 
and air conditioning equipment, architectural adjustments, and final site cleanup and 
landscaping involve additional time. 

_E . ~~~~~~~~~~~~.. w .)-I 

.-v.. 

. 

T'-,*it. 4..,.
%I 1:7, i -.1:

1i i 

I. I I, 
._~~~~~~~~~ 

A:~~~~~~~~~

I 

Figure VII-3.11: Slab Cut With a Street Saw 

VII -38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

Additional time is required if the structure is to be cut into sections, (see Figure VII-3.24) 
moved to a new location, and reassembled. This additional time is highly variable, 
depending on the design of the structure involved, distance of the move, and difficulty of 
the route. Speed of the equipment along the route can be as high as 20 miles per hour 
under extremely favorable road conditions, but usually ranges between three and eight 
miles per hour. 

Raising in Place 

The following steps are generally required, although not necessarily in the sequence 
presented. The operations listed below assume continued occupation of the home during 
the process. 

* Obtain the necessary building permits and arrange with utility providers for 
necessary disconnections, reconnections, and inspections. Regulations vary 
greatly from jurisdiction to jurisdiction. 
* Prepare site as required to allow access for necessary equipment. This includes 
removal and protection of trees and shrubs, removal of fences, etc. 
* Excavate around the perimeter of the slab to allow access for subsequent operations. 
Excavation is carried to an elevation below the base of the perimeter grade 
beams. 
* Excavate and tunnel under the foundation to allow placement of support beams. 
Excavation and tunneling are accomplished both manually and mechanically. 
Specialized earthmoving equipment has been developed to facilitate this process. 
One such piece of equipment, termed a "long nose bucket" or a "snoot" by its 
developer, is designed for attachment to a front end loader. The "snoot" is pushed 
under the slab to remove the earthen materials. This equipment and its use are 
shown in Figures VII-3.12 through VII-3.14. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -39 
January 1995 


Chapter VII: Case Studies 

Figure VII-3.12: Long Nosed Shovel Attachment 

Figure VII-3.13: Perimeter Grade Beam Being Removed 

VII-40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

VlI-J.14: Snoot Being Used to Funnel Under Slab 

* Provide temporary access facilities to the structure. (Temporary entrance, steps, 
landings, etc.) 
* Provide temporary, flexible utility connections. Water, electricity, telephone, and 
natural gas are generally above-ground connections and relatively simple. Sanitary 
sewer connections will generally require excavation, usually in connection 
with the excavation and tunneling under the slab. 

* Detach driveways, sidewalks, porches, and garage, if applicable, or remove the 
slabs from these areas. 
* Remove or secure fragile home furnishings. Most of the contents can remain in 
the home throughout the raising process. 
* Place support beams and jacks. A system of main beams and smaller cross beams 
is used. The main beams are placed under the structure and positioned onjacks. 
The cross beams are placed over the main beams and jacked upward until close to 
the slab, then shimmed against the underside of the slab. Unevenness in the 
underside of the slab is compensated by the shims and wedges as shown in Figures 
VII-3.15 and VII-3.16. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -41 
January 1995 


Chapter VII: Case Studies 

* Elevate the structure and support it on temporary cribbing as shown in Figure VII3.4. 

* Construct the new foundation as shown in Figures VII-3.18 through VII3.21. 

* Elevate and reconnect the air conditioning equipment, if any. 
* Permanently reconnect the utilities. 
* Construct and install architectural and aesthetic adjustments, as required. This 
will include new entrances and closing in under the elevated floor slab, which 
must give consideration to floodplain regulations such as a requirement for openings. 
* Restore the site, including landscaping. 
I 4-, ,.~~~~~~

M_ 

FigureVIl-3.15: Shims Used on Underside of Slab 

VII -42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocaton 

Figure VII-3.16: Wedges Used on Underside of Slab 

; -.''Ai t, -.p

Figure VII-3.17: Relocated Concrete Block Home 

EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures VII -43 
January 1995 


Chapter VII: Case Studies 

Figure VII-3. 18: Concrete Block Counterbalance 

r ,1 N
Figure VII-3.19: New Piers and Wood Cribbing

VII-44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

_ ii 'qw 

PSSt IAW w f I

7 

gu r et V I E x er

?Fi 0 o Co c r teM a son r Bl c W a l l 

,,i 

Aue VI -4 

Figure VII-3.21: Breakaway Exterior Walls 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Struc 
January 1995 


Chapter VII: Case Studies 

Relocation 

Relocating the structure entails all or most of the operations required for elevating in 
place, plus some additional procedures related to the move to a new location. Temporary 
utility connections are usually not required as it is generally not possible to continue 

living in the home during the moving process. If the structure must be moved in sections, 
most or all of the contents must be removed and stored, possibly including even carpets, 
plumbing fixtures, water heaters, air conditioning systems, etc. With those exceptions, all 
of the operations are similar to elevating in place. Additional operations that would be 
required are listed below. 

* Investigate possible routes to the new location and arrange for necessary
permits and utility company assistance along the selected route.
* Prepare the new site, including installation of utility service. Timing of
utility service construction must be planned to avoid damage from heavy
equipment during the house moving process.
* Cut the structure into sections small enough for the route, placing interior
shoring and weatherproofing the openings as shown in Figures VII-3.22
and VII-3.23. Vertical clearance limitations may require removal of roof
sections. Cut locations must be carefully chosen to minimize damage and
maximize internal support. Cuts through hallways can minimize damage
to interior walls. Cutting through roofs can be delayed until the final cut
to minimize weather damage. 

* Place the dollies and hauling equipment at the jacking points of each
section, and move them to the new location as shown in Figure VII-3.24.
* Reassemble the structure at the new site. 
* Construct new walks and driveways. 
Vill -46 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocatlon 

No

'Of ,

c', : , In~~~~~~~~~~~~~ 

. i,_ 

Figure V11-3.22: Interior Shoring 

Figure VII-3.23: Plastic Sheeting for Weather Protection 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII-47 
January 1995 


Chapter VII: Case Studies 

Figure VII-3.24: One Section of the House Has Been Raised, Prior to Insertion of 
Dollies 

Foundation Design Considerations 

The system described requires the use of construction materials and methods suitable for 

the limited vertical clearance provided beneath the raised or relocated structure. Al

though it might be possible to move an elevated structure onto an already constructed 

foundation of driven piles, it would undoubtedly be extremely difficult and expensive, as 

would building a new foundation to fit the under surface of an existing slab prior to 

moving the slab into place. Attachment of the old slab to a timber pile foundation would 

also present difficult problems. The usual practice, therefore, is to move the structure to 

the desired location and elevation, and construct the new foundation beneath it. Rein

forced concrete or concrete block are the most commonly used construction materials. 

Other than the restrictions on materials dictated by the presence of the structure overhead, 
foundation design considerations would be no different than for new construction. 
Although intended primarily for use in coastal high hazard areas, excellent information 
and recommendations on design of foundations for elevated structures is contained in the 
Coastal Construction Manual published in 1986 by the Federal Emergency Management 
Agency (FEMA). 

VII -48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

The publication suggests a number of foundation types and materials suitable for construction 
of raised structures in coastal high hazard areas. Several of those suggested 
would lend themselves to construction in the restricted space beneath a raised or relocated 
structure. Among them are reinforced concrete or reinforced masonry unit (concrete 
block) piers on spread footings, or on grade beams under concrete slab; and reinforced 
concrete or reinforced masonry unit shear walls parallel to the likely direction of 
flow of floodwaters or waves. 

Design of the new foundation should consider wind and wave forces, and the potential 
for erosion and scour. Also, in coastal high hazard areas, careful attention should be 
given to the connections between the new foundation and the raised slab. 

The design should take into account the fact that the original slab was intended to be 
continuously supported on the underlying soil. Unsupported spans of floor slab should 
probably be limited to ten feet or less, and piers should be spaced as required to insure 

integrity of the slab. Some designers recommend four inches on center. 

Elevating the Structure Cost Considerations 

Costs include site preparation, excavation and tunneling, removal of unwanted slab areas, 
utility disconnections (and temporary flexible connections, if required), jacking and 
leveling, utility reconnections, and site cleanup. Information from structural movers 
experienced with the process indicates that the basic cost of these procedures would be 
about $12.00 per square foot of foundation area for a 1,200- to 1,800-square-foot one-
story residence. Costs per square foot would increase somewhat for either smaller or 
larger structures, and for multistory structures. There is a practical lower limit to the time 
for initial site preparation, excavation, jacking, and mobilization costs, all of which 
increase the cost per square foot for the smaller structures. Larger structures require 
more time and labor for the increased volume of material to be excavated. Within limits, 
up to 10 to 12 feet, the height to which the structure is to be elevated does not significantly 
affect the cost. Costs are affected, however, by site conditions such as large trees 
preventing or limiting access by the excavating and earth moving equipment, the need for 
dewatering, the presence of rock, etc. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -49 
January 1995 


Chapter VII: Case Studies 

Construction of the New Foundation and Attaching the
Elevated Structure Cost Considerations

Foundations for elevated residential structures can be constructed by a variety of methods, 
and with a variety of materials. The costs are dependent on site conditions, materials 
used, and labor costs, and differ between different regions of the country. Reinforced 
concrete grade beams ranging in size from 8 x 16 to 24 x 24 inches cost from $7.70 to 
$27.50 per linear foot. Reinforced concrete masonry unit piers, typically 8 x 16 or 12 x 12 
inches, could cost from $2.00 to $14.00 per linear foot including the footing. Reinforced 
concrete piers 12 x 24 inches could cost from $14.00 to $48.00 per linear foot of elevation. 

Newor Raised Utilities, and Raised Air-Conditioning
EquipmentCost Considerations

Again according to the FEMA, Coastal Construction Manual, raising the water utility 

costs $4.00 to $8.80 per foot; the sewer utility costs $6.00 to $16.50 per foot; the gas 

utility costs $4.00 per foot; and the electrical utility costs $3.00 per foot. Varying permit 

requirements, protection against freezing, etc., may influence costs for these items in 

various regions of the U.S. 

Architectural Modification Cost Considerations 

These include enclosing the area beneath the raised floor slab (with breakaway walls if 

required), new entranceways, stairs, landings, porches, and patios, new sidewalks, and 

driveways, etc. Breakaway walls would cost about $0.75 per square foot of lattice work, 

$1.50 to $2.00 per square foot for stud wall and plywood sheathing, and $2.70 to $3.10 

per square foot for block walls. Landscaping and site restoration costs are highly variable. 

Cost Estimates 

Detailed cost estimates for elevating a hypothetical residential structure in place two feet 

and ten feet above grade are shown in Tables VII-3 .1 and VII-3 .2 The estimates assume 

the structure to be 36 x 36 feet, single story (1,296 square feet), with a detached garage. 

The foundation is assumed to be typical slab-on-grade with a perimeter grade beam and 

interior beams beneath bearing walls poured monolithically. 

VII -50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

The new foundation consists of 14-inch-square reinforced concrete piers with two-teetsquare 
by eight-inch-deep footings set three feet ten inches below grade. The piers are 
nine feet on centers both ways, for a total of 25 piers. 

The project site is assumed to have no unusual or difficult soil conditions, and to have 

adequate clearances for equipment and operations. The equipment required for elevating 

structures is highly specialized and expensive. 

Major costs in the procedures described above are involved in mobilization and demobi

lization of this equipment. Some reductions in the cost per residence can be realized if 
work on more than one structure can be undertaken within a reasonably limited area and 
within a limited time. The sample cost estimates assign these mobilization costs to one 
structure. 

The cost estimates reflect 1988 price levels in the Houston-Galveston area of the Texas 
Gulf coast. These cost estimates were derived from various sources, primarily the FEMA 
Coastal Construction Manual, and Means Site Work Cost Data 1988. The estimates are 
intended only to indicate the general range of costs involved in a slab raising project for 
comparison with other possible flood protection measures or with new construction, and 
should not be used as a basis for estimates for specific projects. Costs in addition to 
those shown would be incurred for landscaping, and for temporary housing during the 
construction if the work prevented remaining in residence during the process. 

Conclusions 

Raising and moving a slab-on-grade structure with the slab attached can be both practical 
and cost-effective when undertaken by competent, experienced, and adequately equipped 
structural movers. In some cases, the procedure may provide the only practical retrofitting 
option. Each structure will have highly individual engineering and architectural 
characteristics affecting economic feasibility and aesthetic desirability. Some advantages 
of this procedure include: 

* continued occupancy and use of the structure during the process; 
* avoiding or simplifying interior shoring and bracing, better preserving the structural 
integrity of the building; and 
* the technique is applicable to some construction materials not otherwise feasible 
to move or raise, such as concrete masonry block. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -51 
January 1995 


Chapter VII: Case Studies 

Table VlI-3. 1 Detailed Cost Estimate Elevation of a 36 x 36 (1296 st) 
One-Story Home 2 Feet Above Ground 

ITEM QUANTITY UNIT PRICE COST 

Elevation of Home 1296 SF 12 15,552 

New Concrete Pier Foundation
(see note) 25 EA 170 4,250
Pier-Slab Connection 25 EA 21.20 530
Hurricane Clips 50 EA 1.50 75

Raise Water, Sewer & Gas 2 LF 28.14 56
Elevate Air Conditioner

Wooden Deck, 5x5 treated 25 SF 7.54 188
Extend Downspouts LS 30 30
Architectural Modifications

New Front Porch (see note) 36 SF 7.54 271
Wood Front Stair & Rails 2 LF 239 478
Concrete Stair Pad I EA 50 50
New Back Porch (see note) 100 SF 7.54 754
Wood Back Stair & Rails 2 LF 239 478
Concrete Stair Pad EA 50 50
Wooden Lattice 288 SF I 288
Painting, Decks & Stairs 125 SF 0.39 * :~~% 49
Painting Lattice, Spray 288 SF 0.14 : 40
New Sidewalks 30 LF 5.52 166

Subtotal 23,306 

Contingencies 25% 5,826
Subtotal Construction Cost 29,132
Engineering & Design 5% 1,457
Supervision & Administration 3% 874

Total Construction Cost $31,463 

Const. Cost Per Sq. Foot of Slab $24 

NOTES:
Concrete piers, 9' c.c., 14x14x5'-10" pier in place. Includes 2' x 2' x 8" footing in place, ,
4 #4 bars each way.
New Front Porch: Wood Deck, 6' x 6'. treated 2x6.

New Back Porch: Wood Deck, 10' x 10', treated 2x6. 
Source: U.S. Army Corps of Engineers 

VII -52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #3: Relocation 

I I 

TableVII-3.2 Detailed Cost Estimate Elevation of a 36 x 36 (1296 sf)
One-Story Home 10 Feet Above Ground

I

I 

ITEM QUANTITY UNIT PRICE COST 

I 
Elevation of Home 1,296 SF 12 15,552. 

New Concrete Pier Foundation 
(see note) 25 EA 190 4,750 
Pier-Slab Connection 25 EA 21.20 530 

Hurricane Clips 50 EA 1.50 75 
Raise Water, Sewer. & Gas 10 LF 28.14 281 
Elevate Air Conditioner 

* Wooden Deck, 5x5 treated 25 SF 7.54 188
Extend Downspouts 1 LS 150 150
Architectural Modifications
New Front Porch (see note) 36 SF 7.54 271 
Wood Front Stair & Rails 10 LF 239 2,390 
Concrete Stair Pad 1 EA 5050 

New Back Porch (see note) 100 SF 7.54 754 
Wood Back Stair & Rails LF 239 2,390 
Concrete Stair Pad 
10 EA 5050 
Wooden Lattice 1,440 SF 1,440 
Painting, Decks & Stairs 150 SF 0.39 58 
Painting Lattice, Spray 1,440 SF 0.14 202 
New Sidewalks 30 LF 5.52 166 

Subtotal 29,298 

Contingencies 25% 7,325 
Subtotal Construction Cost 36,623 
Engineering & Design 5% 1,831 
Supervision & Administration 3% 1,099 

Total Construction Cost $39,552 

Const. Cost Per Sq. Foot of Slab $31 

NOTES:
Concrete piers, 9' c.c., 14x14x13'-10" pier in place. Includes 2' x 2' x 8" footing in place,
4 #4 bars each way.
, New Front Porch: Wood Deck, 6' x 6', treated 2x6.
New Back Porch: Wood Deck, 10' x 10', treated 2x6.

i 

Source: U.S. Army Corps of Engineers 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -53 
January 1995 


Chapter VII: Case Studies 

SMALL LEVEES AND PERIMETER FLOODWALLS 

This section presents two case studies that identify procedures, methodology, and design 

parameters used to construct small, low-level levees and perimeter floodwalls. Case 

Study #4 illustrates a variety of measures used in Madison, Connecticut, and Case Study 

#5 illustrates a perimeter floodwall in Prince George's County, Maryland. 

CASE STUDY #4
Floodwalls, Levees, and Perimeter Drains
Bailey Creek, Madison, Connecticut

This case study discusses retrofitting methods that were successfully used to protect 
houses located along Bailey Creek, in Madison, Connecticut. The Bailey Creek Flood 
Prevention, Resource, Conservation and Development (RC&D) Project was sponsored by 
the Town of Madison, Connecticut, Department of Environmental Protection, and New 
Haven County Soil and Water Conservation District, in cooperation with King's Mark 
RC&D and the US Department of Agriculture, Natural Resources Conservation Service. 
Construction was completed in 1991 and worked successfully during Hurricane Bob 
(August 1991). 

General Design Criteria 

The following design criteria were applied to all the retrofitted houses along Bailey 
Creek: 

 minimum protection from flooding is the 100-year level.; 
e 

freeboard for floodwalls less than three feet high will be 0.5 feet; 

2 

freeboard for earth levees less than three feet high will be 1.0 feet; 

e 

a cementitious waterproof coating is applied to all walls up to the design flood 
level; 

* concrete floodwall footings must be 42 inches below the ground surface (primarily 
for frost protection); 
VII -54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #4: Small Levees and Perimeter Floodwalls 

* a 4,000-watt generator is required to power the sump pump, emergency lights, 
well pump, and other emergency equipment; 
* drainage and sump pumps are installed within the protected area; and 
* existing poured concrete foundation walls and floors are assumed to be structurally 
sound enough to withstand three feet of hydrostatic pressure. However, the 
floors were only able to withstand 1.5 feet. 
Project Summary 

The projects required continuous inspection during construction, and were expensive. The 

Natural Resources Conservation Service was directly involved with the contractor to limit 
homeowner-requested changes and for quality assurance and contract compliance. Since 
installation, the measures have experienced significant flooding conditions and have 

proven to be very successful. 

Engineering Analysis Summary 

SURFACE WATER FLOODING 

The flooding threat to one of the homes consisted of surface water flooding of the basement 
and attached garage. Figure VII-4.1 depicts the preexisting surface water problems. 
The basement floor was 2.5 feet below the 100-year flood level, causing water to enter the 
basement. Figure VII-4.2 depicts the engineering solutions developed to retrofit the 
house and garage. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -55 
January 1995 


Chapter VII: Case Studies 

Figure VII-4.1: Surface Water Problem (Before) 

Figure VII-4.2: Surface Water Problem (After) 

VII -56 Engineering ,-'nnciptes and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #4: Small Levees and Perimeter Floodwalls 

The site required the construction of floodwall, levee, and sump pump with an underground 
drain as shown on the site plan at Figure VII-4.3. A concrete floodwall (see 
Figure VII-4.4) was constructed around the existing patio and deck and a sump pump 
installed (see Figure VII-4.5). An earth levee was built to protect three sides of the 
house. The levee was built to a height ranging from 0.5 feet to 3.0 feet with a top width 
ranging from two to five feet. An earth backfill with a four-inch perforated drain (see 
Figure VII-4.6) was placed along one corner of the existing foundation to complete the 
encirclement.VThe earth backfill was filled to a top elevation of 11.6 NGVD with a three-

foot-wide top width. The project was completed at a total cost of $25,000. Figure VII

4.7 and VII-4.8 show the completed parts floodwall and earth backfill. 
Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures VII -57 
January 1995 


Chapter VII: Case Studies 

0a 

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v /51-a/a r

vitk 

\\ / 3r^ 

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"I M 

I ijj/ 
I fII 

! If Jr~ 

s,&c % rmt 

Figure VII-4.3: Site Plan 

VII -58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #4: Small Levees and Perimeter Floodwalls 

SUc wilir 4. 
FNl~tNG E { 
TOP Or REINFORC 
LNNfRirE WALLELEV. 11.6 4VA*f"4. 
SCC.NU 4 _CK SM 
(APPOcILIMA-) 
ORIGINALMIUOUNOUNC 
!PC 417 10 CLCV1hA 61611IGA 
X ~ :-_ _ _ 

Figure VI4. Typical Detail Section Floodwall 

REWR I:ED s

, *' Itn~~~tUUOPRUo I-C 

rfnCPR-ns 

.i., 1M M. GRACEI 
Figure V11-4.4: Typical Detail SectionofBcileFloodwall 
nnnPcenEXVMO n F NON

SWAMS~~~~~~~~~~~E~SIM

ofRRacticEs rne Resc 

10 MEW .

ff r~~~~ttiCKTE41 it. 

4.-SIM1V s

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rt~n~t4A"E \ # 

. iur /I-. yia Deai SetionofBakle Flod 

EngneenPrincpe an PatincesofRtoiinFld-re =ResietialStuctures V 5 

January 1995 


Chapter VII: Case Studies 

FIN. -&LJL*" ------ -19, I 
(,'t#$&,FICC4v"AUnATMWM WUT W K

IWAM 

NSWAM M VML K 

USIA= 

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WIL,

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PULO172Wu gm 

v 4w mm 

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02M N IrAVIM

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exas'TtIce vpa'""Ap Mr-MO 
foam F.*.Om* 

Figure VII-4.6: Patio Area Sump Pump Detail 
Ar 
.LO DI. 9. . I 
'4. 
CO&x C CA-0DI.ZY _2.4 
CLAS 
417 S 
Figure VII-4.7: Footing Drain Detail 
244. r Kqi.S ecgfe jO PtJ N_ 

VII -60 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #4: Small Levees and Perimeter Floodwalls 

Figure V11-4.8: Completed Patio Floodwalls 

SUBSURFACE WATER FLOODING 

The threat to another house, on the other side of Bailey Creek, consisted of surface and 
subsurface flooding. Figure VII-4.9 depicts the location of the house with respect to 
Bailey Creek and the engineering solution developed to retrofit the house. Figure VII

4.11 depicts details on the sump pump and drain installation. An earth backfill against 
the existing foundation was constructed on the Bailey Creek side of the house with an 
elevation of 11.6 feet NGVD and a top width of three feet. A drain (see Figure VII-4. 10) 
and sump pump (see Figure VII-4.1 1) were constructed inside the basement to handle 
subsurface water. This project was completed at a total cost of $9,280. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -61 
January 1995 


Chapter VII: Case Studies 

I I 
// w 
I 
I I 
A. 
I I 
l I 
I I .#,pm0 
4p 
-S 
4P 
'p 'p 
I 11 
"a'I 
I I 1k a 
(7> I iv! ecl sPU*S . 1W 
II Qua U UItt 
Figure VII-4.9: Site Plan: House on Opposite Side of Bailey Creek and Engineering Solutions 

VI!-62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1 995 


Case #4: Small Levees and Perimeter Floodwalls 

-_w@.WAI 

RDNWu 

WAn 6M

..,- *a MNaAN 

a~WI a

410=10SIM 

Figure VII-4.IO: Typical Drain Detail Lev~~~i s 0 SAgo 
w~~~~a "SVO Al 

N* W~u. Ala Io ansmoo 

-. ., 

Figure VII-4.1 1: Sump Pump and Sur np Detail 

Engineering Principles and Practices of Ret rofitting Flood-Prone Residential Structures VII -63 
January 1995 


Chapter VII: Case Studies 

CASE STUDY #5
Perimeter Floodwall
Henson Creek, Prince George's County, Maryland

This case involves the construction of a floodwall around the perimeter of a slab-on-grade 
house located along Henson Creek in Prince George's County, Maryland. The actions 
taken (sponsored by the Prince George's County, Maryland, Department of Environmental 
Resources, Watershed Protection Branch) were in keeping with the county's policy to 
protect houses within the 100-year floodplain and/or remove the threat of flooding to 
these private residences. 

The Henson Creek watershed area is a relatively narrow watershed, ranging from 2.5 to 

3.0 miles in width and about 11 miles in length. Its combined drainage area, which 
includes tributary flows, is in the range of about 30 square miles. Various areas along 
Henson Creek were subject to flooding, and the problems were expected to increase 
because of development growth within the watershed boundaries. 
The initial analysis was conducted to examine the feasibility of widening and improving 
Henson Creek channel for the purpose of flood control. In an effort to remove affected 
houses from the I 00-year floodplain, five alternative designs were investigated. Four of 
the studies involved the hydraulic analysis of an existing culvert, and widening and 
improving the creek's banks. The fifth alternative was to retrofit individual houses. 

Based on the results of the alternatives evaluated, home retrofitting was the most cost-
effective solution to provide 100-year flood protection. The four designs involving 
culvert structure modification were rejected due to costs that ranged from $1,245,000 to 
$3,095,000. The retrofitting of individual houses (elevation, floodwalls, wet and dry 
floodproofing measures) was estimated at $246,800. 

Retrofitting Methodology 

DETERMINATION OF FLOOD DEPTH 

Computer analysis through the use of HEC-2 and TR-20 modeling was used to determine 
water-surface elevations that would result from a 1 00-year flood based on ultimate 
watershed development. Cross sections were located at critical locations and at predetermined 
distances along the stream channel. The flood depth at a particular structure 

VII -64 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

(residence) was interpolated from the water-surface elevations at the nearest cross section 
both upstream and downstream. 

DETERMINATION OF LOW POINT OF FLOODWATER ENTRY 

Each residence was field surveyed to determine the elevation of all openings into 
crawlspaces or basements, and ground at the house, first floor, and basement slab. A 
county engineer reviewed the survey data and determined what elevation the floodwater 
would have to reach before the residence would begin to flood. Many times this elevation 
was a vent, an entrance into a crawl space, a walkout from a basement, or the top of a 
stairwell into a basement. 

DETERMINATION OF TYPE OF CONSTRUCTION 

Each residence was reviewed by a team of engineers to determine the type of construction 
used in the residence. Three types of structures were identified: slab on grade, crawl-
space, and full basement. 

DETERMINATION OF STRUCTURAL COMPETENCE 

The team of engineers reviewed the construction and condition of each residence to 
determine if the residence could be successfully retrofitted. 

DETERMINATION OF RETROFITTING METHOD 

Each residence was evaluated separately, but structures of similar construction were 
considered receptive to similar- retrofitting methods. 

DETERMINATION OF RETROFITTING COSTS 

The county developed a database of current costs (1988) associated with the retrofitting 

of residential structures. Personal knowledge and contacts with other individuals in

volved in similar work in other jurisdictions as well as cost data from publications includ

ing Engineering News-Record (ENR) and Mean 's Guide were used to develop the esti

mates. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -65 
January 1995 


Chapter VII: Case Studies 

DETERMINATION OF DESIGN CRITERIA 

The structural analysis of the houses was performed in full accordance with the design 
requirements set forth in the following codes and regulations: 

* Prince George 's County Building Code, 1983 
* BuildingOfficialsand CodeAdministrators(BOCA)NationalBuilding
Code, Ninth ed., 1984
* AmericanStandardBuildingCode Requirementsfor Masonry(ANSI
A41.1-1953, Reaffirmed 1970)
* Flood-Proofing Regulations (EP 1165 2 314), U.S. Army Corps of Engi-
neers, June 1972
In addition, the following references were used as guidelines in the structural computa-
tions: 

* Specificationfor the Design and Constructionof Load-BearingConcrete 
Masonry (TR75B) National Concrete Masonry Association (NCMA)
February, 1987

* Basement and Foundation Walls (TR68-A), NCMA, 1971 
* Nonreinforced Concrete Masonry Design Tables (TR03), NCMA, 1971 
* Reinforced Concrete Masonry Design Tables (TR84), NCMA, 1971 
* DesignManualforRetrofittingFlood-proneResidentialStructures(FEMA
114), Federal Emergency Management Agency, September 1986
* CostReportonNon-StructuralFloodDamageReductionMeasuresfor
Residential Building Within the Baltimore District, U.S. Army Engineer
Institute for Water Resources, IWR Pamphlet #4, July 1977
VII -66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

The following design values were used in the structural analysis of the foundation walls: 
Soil: Soil unit weight = 120pcf 
Internal friction angle = 30 degrees 
Active pressure coefficient = 0.33 

Masonry: Allowable tension in flexure (normal to bed joints) Type M or S 
mortar 
Hollow Units: 23 psi 

Solid Units: 39 psi 
Allowable Shear (Type M or S mortar) 
All Units: 34 psi 
Compressive Strength, fm = 1,000psi 
Unit Weight (ASTM C-140) = 120 pcf 
Allowable stress for grade 60 reinforcing steel, f 24,000 psi 

S 

Dead Loads: Floor and Roof: 15 psf 

Foundation Walls: Density of masonry block = 120 pcf 

Density of wood: 40 pcf 

Live Loads: Lateral Earth Pressures: 

Saturated Soil: 40 psf 

Water: 62 psf 
Water plus buoyant soil: 82 psf 
Wind Pressure: 16 psf 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -67 

January 1995 


Chapter VII: Case Studies 

Engineering Analysis Summary 

Site #1: The site is a one-story, brick veneer over wood-frame slab-on-grade house 
located south of Henson Creek (see Figure VII-5.1). The first floor elevation (FF) and 
low point of entry (LPE) is 198.4and the 100-yearwater-surface elevation (WSEL) is 

199.0 (see Figure VII-5.2). 
HENSON CREEK 

(7%)ROAD r(

rm 

n\\\iI Ig o

I 

Figure VII-5.l: Location Plan 

VII-68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

100 YR. FUTURE V 
_ ERICKFACEE 
WOEL 10.09 
FINISHED FLOOR 
ELEV. 106.40 

Figure V11-5.2: Preexisting Slab-on-Grade Construction Detail 

Since the 100-year water surface elevation (WSEL) was only 0.6 feet above the finished 
floor, the construction of a floodwall around the perimeter of the house proved to be the 
best option in terms of overall cost (approximately $18,000) and risk to the building. 
This would allow the house to stand as is and be protected by a separate structural element. 
The owners were advised of the elevation and/or relocating problems associated 
with their house and that the county selected the floodwall alternative. The recommendations 
listed below were developed based on the engineering analysis: 

* Construct a floodwall around the perimeter of the house. The wall must be at 
least one foot above the 1 00-year WSEL, or approximately 2.6 feet high to comply 
with the county code. 
* Provide at least two step-up/step-down accesses over the wall to the entrances 
into the house. 
* Rebuild the concrete patio located in back of the house inside the floodwall. 
* Provide a gravity drainage system behind the floodwall to rid the ringed area of 
the trapped water. 
* Tie down the tool sheds to resist flotation. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -69 
January 1995 


Chapter VII: Case Studies 

Proposed Work 

The proposed work is keyed to Figure VII-5.3, Site Plan. 

1. Construct floodwall (see Figure VII-5.4). 
2. Construct concrete steps for access over the floodwall (see Figure VII-5.9 and 
VII-7. 12). 
3. Install steel pipe railing. 
4. Construct a concrete slab on four-inch gravel base inside the floodwal. Provide 
positive drainage to sump pump. 
5. Relocate telephone junction box vertically to elevation 200.5. 
6. Limits of grading, seeding, and mulching. 
7. Provide four-inch-high concrete equipment pad under air conditioner, (see Figure 
VII-5.10). 
8. Apply waterproofing between existing wall and topsoil. 
9. Install new downspout drain with new coupling through landing. 
10. Plant new shrubs. 
11. Remove existing concrete pad. 
12. Install 6 x 6-inch treated timber retaining wall (see Figure VII-5.9). 
13. Fill planter with topsoil. 
14. Remove existing concrete slab in its entirety. 
15. Furnish and install new sump pump and pit (see Figure VII-5.8). 
Vll -70 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

-

16. Tie down existing shed. 

17. Remove and dispose of fence. 

18. Install one-inch round PVC schedule 40 conduit for sump pump electrical cables. 

19. Install outside rated double receptacle in 6 x 6-inch exterior lockable box. 

20. Verify location of gas line prior to excavation. 

21. Limit of disturbance and sod. 

22. Provide concrete encasement of three-inch diameter PVC sleeve around existing 
gas line. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -71 
January 1995 


Chapter VII: Case Studies 

Plans,Elevation, and Construction Details 

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FIN. FL. EL.-198.4!. ~~~18 

ONESTORY2 TX4D' .; 

/ONESTORY RICKFACESLAB ON GRADE i r 

NOT.iWINDOW D VENT ROT t WINDOW ASP 

~ 201,0 8OT.t9t.4ILOR Jr, ~ / ' _1

/ ~~~~~ act~ 9DOOR 220D WN~ 

_OtW.7 INDOW 

139. 
WdTER

98.
,1i \ 42 4 1CO

--r---ON/ 

1 

AD OZ.N PAD 

I991 

:kV,4 
9.2_4 _4 > /

6w

R 

/ i I'll 

It 

a 710roMAreH ... /MjS/ZOA/ IOU 

S_ 

Figure VII-5.3: Site Plan 
VII -72 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

"@TE: FACESUCKTO UATCH
EX. SUCK

S 

JOINTSTOLet UPWM 

erx1111 TSa 

04.O 12csaC C COBoetN 
4Ir MAXlt

b1

_-4CMU SOP 

u'i riLA14 

*HOW. REINF.A 
I" CONTINUOUS. an TOM
01*OWA

rTnNE. 

-GROUTINTERIOR SOLID 
;WITN4000 PSI PEA 
GRAVELCONCE 

,4_ 4012 

Figure VII-5.4: Typical Floodwall Detail Section 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -73 
January 1995 


Chapter VII: Case Studies 

Figure VII-5.5: Footer Detail 

Figure VII-5.6: Wall-to-House Connection Detail 

VII-74 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

e* 0 

* : 
| | | 
W~~ 

Figure VII-5.7: Drain Detail 

1.itnaFod-rn Reietal tutrs V-7 

Figure VII-5.8: Sump Detail 

Ennineerinn Princinles and Practices of Reti 
January 1995 


Chapter VII: Case Studies 

. _ A ___ A.... MIAV 

Figure VII-5.9: Floodwall Steps and Landscaping Timber 

Figure VII-5.10: Sump Pump Outlet and Raised Air Conditioner Unit 

VII-76 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #5: Perimeter Floodwall 

Figure VII-5.1 1: Completed Project 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -77 
January 1995 


Chapter VII: Case Studies 

WET FLOODPROOFING 

This section presents a case study that identifies procedures, methodology, and design 
parameters used in wet floodproofing. 

CASE STUDY #6
Wet Floodproofing a House on a Crawlspace
Henson Creek, Prince George's County, Maryland

This case study discusses wet floodproofing measures that were taken to protect houses 
located along Henson Creek in Prince George's County, Maryland. (See Chapter VII, 
Case #5 for complete background and retrofitting methodology.) 

Engineering Analysis Summary 

Site #2: The site is a two-story wood-frame house on a crawlspace with a first-floor (FF) 
elevation of 199.3 (see Figure VII-6.1). The bottom of the crawlspace vent is 197.5 and 
the bottom of the crawlspace access door or low point of entry (LPE) is 196.9. The 1 00year 
water-surface elevation (WSEL) is 198.4 (see Figure VII-6.2). 

The types of forces imposed by the floodwater will be lateral hydrostatic pressure on the 
exterior masonry walls and a buoyant force on the first floor timber framing. The house 
was analyzed under dry floodproofing and wet floodproofing conditions in order to 
investigate the feasibility of each condition. Figure VII-6.2 is the preexisting foundation 
wall section. 

Dry Floodproofing Option 

On the field inspection, the existing masonry walls appeared to be in good condition; 
therefore, the mortar joints were assumed to have a structural capacity equal to their 
capacity at construction. In addition, the calculations are based on the assumption that 
the bottom of the footing is exactly 30 inches below grade as required by code. 

The dry floodproofing option was rejected because the analysis showed that the flexural 
stress in the mortar joints exceeds the allowable stress under 1 00-year flood conditions. 
Moreover, dry floodproofing would be difficult to achieve since the soil around the 

VII -78 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Case #6: Wet Floodproofing 

foundation was relatively permeable sandy soil and would allow water to seep into the 
crawlspace. This is due to the difference in water level between the inside and outside of 
the wall during flood conditions and the permeability of the soil. The dry floodproofing 

calculations are shown in Figure VII-6.3. 

190 

_ 

\LJFIRE 

Figure V11-6.1: Location Plan 

Ennineerina PrinciDlesand Practices of Retrofitting Flood-Prone Residential Structures VII -79 
January 1995 


L Chapter VII: Case Studies 

311ItNQ1.. 

100 YR. FUTURE 

WSEL. 196.4 

EXIST. GRADE 

Figure VII-6.2: Preexisting Foundation Wall Section Detai I 

VII -80 Engineering Principles and Practices of R(etrofitting Flood-Prone Residential Structures 
January 1995 


Case #6: Wet Floodproofing 

IOYM1T-ko0 O<ttlav 

-v 
I 1A4

) ~~ wAl9S:. __ 

_

vOCAC._.V~~~ a,

aj ^lvo , ~~~~~.;.

_ 

Q

0 I---

_ _610. _"-V 

C_2~~~6 hi: 11, 
bM; 

La^.~ ' NGWW4 

lA, = 11Z = 01 16 z .q0 

( I8 ' 

V 1-6) (I.-, ) .Z SI1 16 O.qs 

R V.s I ' I., 

4t ( 87') ( I.,*O'L _t 46bpg O . QP,5 
Hr = OZ %IV 

t. = (ic 80(z-So) i (1U5)(*<cJ) + (I4e1)(.5) -3 (5 
V-'A 4 6 -l44' 
Or"0)(Z) _ CP07.5 f 

(S.7)t 
S~c<, g A 42 1 p-r 

4 betv> r10 ;n CD 

L4'<tl tr' 3 1cx) z

' \t 1}^X)]

( S *1 

i~.lb,~ S3S-p', 
Figure VII-6.3: Dry Floodproofing Calculations 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -t51t , .... nVll -81 
January 1995 


L Chapter VII: Case Studies 

Co rnSssite Ste.r : 4s. o at t-mnvok0 . 

u\-4.i-t *wsAth stress %.9 -S5.Cto -Z g 

> ZS.O t~  

S i n e . 4-' p l e A d t n + k u t i W t 1 

4+ b\oa C?*;on

Th ib t r'< .

"'V> 

% I rwsw#Ottcs -NCMA Nsernn4 CoocVab. 
rlsv-er DeiesiaKT4LaS I p. Zfl 

2%4 Scc 1 e cr5c eioCS' 

Figure VII-6.3: Dry Floodproofing Calculations (continued) 

Wet Floodproofing Option 

This option allows the water to enter the crawlspace through vents or the access doors. 

This results in a reduction in the mortar joint stress to below the allowable limit. It is 

imperative that the openings are free of debris to sufficiently allow the water to flow 

through. When the water reaches its peak elevation, the wood floor framing will be 

partially submerged and will cause an upward buoyant force on the first floor. A conser

vative approach was taken in the structural calculations, which checked the buoyant force 

with the entire floor joists submerged. The analysis showed that the dead load of the first 

floor alone is sufficient to resist the upward force caused by the water. The main floor 

beam and possibly the floor joists will be inundated by the water for a period of two to 

three hours, and structural damage could occur to the floor joists, beam, and possibly to 

the subflooring. Therefore, waterproofing should be applied to the floor joists to allow 

the implementation of the wet floodproofing option. The wet floodproofing calculations 

are shown in Figure VII-6.4. 

V1I -82 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #6: Wet Floodproofing 

\j'4c+I. 
-
Fior. PvO&,iw! 0?*i -kvrrir +kyaoun Yant 
I 
Slubw p~Nme"+ 
.1/. (Xx .4) (-15)1 
(<e*t-COt) 
'1t ( i.q 
VAtolip 
-14-5%6 
9I.Py O 
Figure V11-6.4: Wet Floodproofing Calculations 
* tA % -
A C.5 
Z.%l 
0 X(3 It 
a 

VII -83 

Engineering.Principles and Practices of Retrofitting Flood-Prone Residential Structures VI] -83 
January 1995 


Chapter VII: Case Studies

Z -.

tS-e )(.s) -+ -2.8c(-2)Ctz.8i) (I*6)(o.-W) 

FA (A0 16 

PIi 1Z5Z0AblSob 

F;^1~~~~~~(oz ' j --

a1 

-

Te = t zis) <~i

(X) . n Z .Z 
II^l 16f

e =(I5)(Zn) tI| + ; ) -T = 

lb('t5.a)L~ 1;f5a z
IL I Zs --18Z5 I" 

C I= %.'7 (se r. Z j4 )
h4bUm+ -tb"L# &,cA -M 18.s -am,-7 -M8 rs

viv4 La.% 5 tht. Oh U.."p ze 

IF.~a -( 1e, ., 4 (z2zz) -~ lIUO tip 
%6/

(0Z I dm , 4 , = 3S (v to .-0 

IL.O_. 

,,, MS O-S) -= 14. 
.: \lm AVa *A4 iWNI S z|3 O tc 

fKM;+Uw44 L-A w-% aw;\81 *' 

1'5 rX3. $ e.we<-e Oj beZeIAYA.4 

3iAEw+ ?bvc. t1'5)(_'<5)Y.6,-4--s 4-~ p.4A 'I *' rq ' 
5u 7om i~O WI. lo 5 -3 .7 -113 rsi t 0c 

Figure VII-6.4: Wet Floodproofing Calculations (continued) 

VII -84 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #6: Wet Floodproofing 

Engineering Analysis 

The following recommendations were developed based upon the engineering analysis: 

* Waterproof the floor joists, main beam, and the bottom of the subflooring to 
eliminate possible structural/water damage. 
* Replace any electrical wiring that has any bare wire exposed due to deterioration, 
splices, or connections with a water-resistant romex cable. 
* Outside oil and gas tanks need to be anchored to the ground. 
* The fuse and junction box on the back of the house should be raised to at 
least 1.0 feet above the 100-year future WSEL. 
* Replace, clean, or add any vent openings to meet the current building code 
requirements and water flow requirements. 
* Provide drainage from the crawlspace interior. 
* Provide a water permeable access door to the crawlspace. 
* Tie down tool shed in back yard to resist flotation. 
Cost Estimates 

The following are cost estimates in 1988dollars to wet floodproof the house: 

Waterproofjoists & subfloor $ 300 
Misc. electric and plumbing $ 500 
Oil and gas tank foundations $ 1,200 
New vents $ 300 
Water permeable access door $ 150 
Tie down tool shed $ 200 

TOTAL $ 2,650 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vii -85 
January 1995 


Chapter VII: Case Studies

Proposed Work 

The proposed work is keyed to Figure VII-6.5. 

1. Remove existing block vent. Furnish and install new block vent into existing 
opening. Rework opening as required to accommodate new vent (see Figure VII6.6). 
2. Furnish and install new water-permeable access door (see Figure VII-6.7). 
3. Remove existing concrete pad in its entirety. 
4. Provide new concrete pad. 
5. Final grade in crawlspace adjacent to all exterior walls shall not be lower 
than six inches below bottom of crawlspace access door. In addition the grade in 
the crawlspace shall not differ by more than one foot. 
6. Waterproof floor joist and underside of subfloor in crawlspace. 
7. Tie down tool shed (see Figure VII-6.8). 
8. Gas meter to be raised to elevation of 199.4. 
9. Fumish and install new block vent (see Figure VII-6.6). Remove existing concrete 
masonry block and locate vent within three feet of comer. Remove existing 
adjacent vent and replace with new concrete masonry block. Paint as necessary to 
match existing colors. Seal opening where hose bib penetrates the new concrete 
masonry block. 
VII -86 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #6: Wet Floodproofing 

Figures VII-6.5: Site Plan 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -87 
January 1995 


L Chapter VII: Case Studies 

".f~rIN vrip Jm.I* 

EtL"inx VN L L$1i

S&JP 

hocX (ebAtL Ago 

tire 0 0W

AFF14o,114,J

vezr e6,csi GOe L.l.,-
C'rf DgAFto4P CO4

& L 

Ml"t 4OCA* Of %Cr

B 4 foo1'N(C 4~ 

L _l 

Figures VIl-6.6: Block Vent Detail 

-I.

1A4~IJ&,N
F10xAL4 IiLL 41 OftIN

pbC2Ii4Lr~s.Jt p m t --

W#idl~r6:AVN 4

.

P64ec..HL 8A~f~4

td.1. 

'EI

I.JAU. IK~b..._j37IM"E f 3F : ; 

I .cfN, 

.fL

Lx,,S,*-I.-teJ4"rlo --1 I->f_. _ _ _ _._ 

... "... _." 

Figures VII-6.7: Access Door Detail 

VII -88 Engineering Principles and Practices of Re&trofittingFlood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

GALV. CABL

,1 ~~~CONT. 

L~~~~~~~~~~~~~~~~ 

ANCHORING SYSTEM " MANUFACTURED.BY _
fARROW; -CHANCE OR APPROVED EQUAL

I | 0 SPACING OF ANCHOR ASSEMBLY SHALL 9 LONGtv ANCHOR$ 

AI.~ _____

0 ~NOTEXCEED S o/e 1F orY

L1 

9/ Li; 

:)-0 'I 
Figure V11-6.8: Anchorage Detail for Sheds 
Sheds are anchored so they do not become floating debris. 

VII

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vll --89 
January 1995 


ChapterVII: Case Studies 

DRY FLOODPROOFING 

This section presents two case studies that identify procedures, methodology, and design 
parameters used to dry floodproof houses. Case Study #7 illustrates dry floodproofing of 
a house with a walkout basement in Prince George's County, Maryland. Case Study #8 
illustrates dry floodproofing using a veneer wall in the Tug Fork Valley, West Virginia. 

CASE STUDY #7
Dry Floodproofing a House with a Walk-out Basement
Henson Creek, Prince George's County, Maryland

The site is a two-story wood-frame house with a walk-out basement. The first floor 
elevation is 211.7 and the basement floor elevation is 204.0. The top of the existing retaining 
wall that encompassed the walkout is 207.0 (see Figure VII-7.3). The 100-year water-
surface elevation (WSEL) is 206.0 based on future upstream land use conditions (see 
Figure VII-7. 1). A flood protection elevation of 207.0 was utilized in this design. 

The foundation consists of a full basement with a walkout on the Henson Creek side of 
the house. The existing grade varies in elevation along the foundation wall where the 
highest elevation occurs in the front and slopes down toward the walkout (see Figure VII7.4). 

Engineering Analysis Summary 

The foundation walls were checked for structural adequacy against the lateral pressures 
exerted by the soil and the floodwater (see Figure VII-7.2). The worst case, which occurs 
along the front, was investigated in the structural calculations similar to Case #6. The 
existing walls prove to be structurally sound and able to resist the lateral forces imparted 
by the 1 00-year flood. 

Since the house has a walk-out basement with a finished floor 2.0 feet below the 100-year 
WSEL, the proposed replacement floodwall that wraps around the back of the house will 
have to retain the floodwater in addition to the soil. The present condition of the existing 
wall is questionable due to the numerous cracks in the joints and the cracks around the 
grouted pockets at the wood columns and unknown wall foundation conditions. Furthermore, 
the wall was not designed to resist the relatively high lateral forces occurring 
during the flood. Therefore, it was recommended that the wall be replaced with a reinforced 
concrete floodwall. Temporary supports will be required for the first-floor over-

VII -90 Enaineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

hang during the construction of the wall. The wood columns supporting the overhanging 

room should bear on top of the wall with a bearing plate to distribute the column load. A 
step-up/step-down entrance over the wall is required for ingress and egress to the basement. 

Figure VII-7. 1: Location Plan 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -91 
January 1995 


Chapter VII: Case Studies 

The following recommendations were developed based upon the engineering analysis: 

* Construct a new reinforced concrete wall to replace the existing wall. Top of wall 
must be at elevation 207.0 or higher. 
* Apply waterproofing to the inside basement wall to prevent leakage into the living 
areas of the basement. 
Engineering Calculations and Cost Data 

The cost to dry floodproof the house was estimated in 1988 dollars at $4,800. The following 
calculations (see Figure VII-7.2) were applied to the existing foundation to determine 
if the house could be retrofitted using dry floodproofing techniques. 

Demolish existing wall $ 500 
Waterproofing $ 400 
Rebuild wall $3,900 
TOTAL $4,800 

:II : 0 

VII -92 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

Figure VII-7.2: Dry Floodproofing Calculations 

Engineering Principles and Practices of Retrofitting Flood-Prorie Residential Structures VII -93 
January 1995 


Chapter VII: Case Studies 

F;i^ -A Vw 

(4.-i' z 44.~

s4.

in(+15

) (4-/ 
Im 7 lb > RAm-79Jb 

co /7.0 

.: a 1loawin6 rO mm+ 1uovt^*io-i5s\ItI:n1X1 Ge4.rtr4C 

m",4 (4s")(4. ) z.8 + L f4z'I F

3Of 16' 

f t a 5Is IXlz 71,j z?.4 4

A i5Qj;5 IzS ,OpOc 

*I = 

Tj-em.4.tlu^ 4 OL 01.,.~1 AW14.

* S4,a ;%4. :iHi -h
tc~~~~u .<J -Le"S ICt^ 

iw~~~~~~~~~~,rv

i-+ 

+ Sectiol pots &v-~NC-MA
COcy Mahsevfrt Qezi's To%6Lue'?. L
1* sIl_ I li-n CT_; tV^I L 

Figure VII-7.2: Dry Floodproofing Calculations (continued) 

VII -94 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

: ; . : i f 

FINISHED FLOORELEV 
211.7 

aL 

SIDING -JOIST 

100 YR. FUTUR a
WSEL. 200.0

ELEV. 207.0 

12"CONC. BLOCK 

Is EXIST. 

GRADE ELEY. 204.0 

CONC. FOOTING 

Figure VII-7.3: Preexisting Walk-out Basement Foundation Wall Detail Section 

Proposed Work 

See Figures VII-7.4 through VII-7. 17. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI[ -95 
January 1995 


Chapter VII: Case Studies 

Plans, Elevations, and Construction Details

OF 
DISTURBANCE 

W"LIMIT 

* I /-
'm. . __

Figure VII-7.4: Site Plan 

VII -96 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodprooflng 

. 1:.A 

*~~ e _

44. 
*-s--1.2.l giNkSfN' 

feat, Kf>:WKAW

e a.a 11 Oo

. FF %AL). 

-,~cirTg'J'; ~ ~ d'ti~iI4 vLO -N 

Figure VII-7.5: Concrete Patio, Replacement Floodwall, and New Access for Basement Detail 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -97 
January 1995 


Chapter VII: Case Studies

I 

Figure VIl-7.6: Step and Wall Detail Elevations 

S

VII -98 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

41: . . z,i , i i I 
_ ~7 ~ i~ ~. Set. MAW' 46f t li Folz 

^ ~~~~~~I. ' r*%>

4P1 

4144~iO4

fAw 

x ot rI 

p 114~~~~~~~~_ _ _ _ _ _ _ _. 

l 

^ 8 

4XC~~~g

2 4 lZ~tg> 

Figure VII-7.7: Concrete Floodwall Detail 

VII-7.8: Downspout Connection to Drain Detail 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vil -99 
:January 1995 


Chapter VII: Case Studies 

. r' HIG DENSITY CAULAINOMOTH0WE$S FU 
KEIGHTOF WALL S3UBMI SAMPLE To COUKTy. 
*1/2' MT. MANSION MATERIAL 
FULL KEIGHT OF WAL.L 

I i. 11 J 

<p l,- ateS~~I 

:% I 

Figure V11-7.9: Floodwall Connection to House Detail 

-ACE4 :toR k~p WUMH 

.ZAV SILLR_ 

GALV.,,PO4, BASE By SIMPSON

TYPE A:; OR APPROVEDEOUAL 

lOd NALVS / ,GRIND LEVEL TO RECEIVE
( 4-TOTAL)3 -< < POSTBASE _

I/2 x 12"GALV.ANCHOR 

W./2-HOOXK 

TOP OF PROPOSED 
BACKFILLSEEPLAN 

*. 7C ELEVATiON

. -S E SEE FLOOOWALL DETAIL I 

. . ,, .., . 

.*"' "A ' '.'-

Figure V11-7.I0: Floodwall Supporting Columns Detail 

Vil -100 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

,'% COMppC.TfD 

fILL 

c0'Mc46J. eqrNg,Jr 
I~.M. f 

_--

.-----4 

Figure VII-7. 11: Step Detail 

Figure VII-7.12: Step Detail 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -101 
January 1995 


Chapter VII: Case Studies 

I S

-

,- *JMOICOUP~LOSECEPTAcLCMP6 g24 LMWWS &*]( 
?AYiat A Mii.CUMAXAs&la LU&tWof w 

ts wtC.L Tvit M"lt SO$ AMOTE.Mo AXtdi PIPt 
Of At LCVST6' 

r-SI.Onfi/0'T. TOPit 
r,,ae DRAW" $AT& A:OPKELICT*r CAR14a

0 ri AIN I'titte

OftAIM 

Figure V11-7.13: Sump Pump Detail 

Figure V11-7.14: Stair Section 

VII -102 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #7: Dry Floodproofing 

I ..-I.-.1...... -.-.. 

Figure VII-7.15: Air Conditioning Pad and Sump Pump 

-N 

El. I . 

Cetal Stutue V -10 

Figure VII-7.16: Floodwall and Supporting Columns 

Engineering Principles and Practices of Retrofitting Flood-Prone Resic 
January 1995 


Chapter VII: Case Studies 

VII-7.17: Stairs and Supporting Columns 

VII -104 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #8: Veneer Wall Dry Floodproofing 

CASE STUDY #8
Veneer Wall, Dry Floodproofing
Tug Fork Valley,West Virginia

A two-story church of 1,920 square feet located within the floodway fringe experienced 
only 1.82 feet of flooding to the first floor area during the 1977 flood. The first floor of 
the church was constructed with masonry walls and the second story was wood-frame 
construction. The 1 00-year floodwater velocity at the church site was between two and 
three feet per second. This church was determined eligible for the retrofitting program 
since it met the criteria needed for construction of a veneer wall. This method has proven 
effective on residential structures, as well. 

Veneer Wall 

This type of perimeter wall is included under the category of dry floodproofing. In this 
category, water is prevented from entering the first floor of the structure by the use of 
veneers, closures, and sealants. Several factors limit the use of veneer walls for protecting 
structures, including: 

* the inherent strength of the structure's existing perimeter walls, 
* the depth of flooding at the structure, 
* floodwater velocity and debris impact potential at the structure, 
* size and number of closures needed to service the structure, and 
* the structure owner's capability to operate and maintain the aspect of the
retrofitting system that requires human intervention.
A detailed engineering analysis of the structure's walls, closures, and utilities determined 
that the structure could be dry floodproofed by constructing a veneer wall attached to the 
existing first-floor masonry wall. The owners of the church exhibited a willingness and 
capability to operate and maintain the veneer wall, closures, and utilities to prevent future 
flood damages to the structure. 

The veneer wall was constructed of reinforced poured concrete. The wall was six inches 
thick and extended from the existing footing to an elevation one foot above the design 
flood (see Figure VII-8. l). The wall was attached to the existing masonry wall with 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI] -105 
January 1995 


Chapter VII: Case Studies 

metal anchors (see Figure VII-8.2), and formed rubber waterstops were installed be

tween all concretejoints. Aluminum flashing was installed along the top of the wall to 

prevent rainwater from seeping between the veneer wall and the existing masonry wall 

(see Figure VII-8.3). 

god.

W -& AWMii4l%cmVLJ 

WAL 1 1T R 

I l 

iL--L -a 

~~~~~-Lftv61Aft 

Figure VII-8. 1: Veneer Wall Detail Section 

| r1 n is ~ 

WON. X~A V 

Figure VII-8.2: Veneer Wall Metal Anchor Detail Section 

VII -106 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 

January 1995 


Case #8: Veneer Wall Dry Floodproofing 

mot:gr-1Tf OF WAL W/MiGc YAW= 

1Wt

IMJ As_ WIM.Ut~iq~u ,4hJ

__1 &W curm

VA_ / re" NONV4Y awy 4ge

1A~F~, Mct4T. 

'FT)I * ; I .. .MbM4 6 w,

1---Sir -4-'r 

-

~~~. ...CoF l .*,"' WVdoA

s~~~~t~ss2 

Bobvet~~~~~5z 

~~OU -I~O 

Figure VII-8.3: Aluminum Flashing Detail Section 

Asphaltic waterproofing was applied to the veneer wall surface below ground and a 
waterproof silicone sealant was applied to the veneer wall surface above the exterior 
grade (see Figure VII-8.1). 

Only one entrance to the first floor required a closure. The remaining door accessed an 
equipment room on the first floor and was shortened to avoid the need for a second 
closure in the veneer wall. A three-by-two-foot solid aluminum panel with perimeter 
seals and lock bolts was used to seal the closure (see Figure VII-8.4). The second floor 
was accessed by exterior concrete steps and interior steps. 

An exterior air-conditioning unit was relocated onto a raised pressure-treated wood 
platform. A water line was relocated to avoid penetration of the veneer wall, and a valve 
box and gate valve were installed on the underground sewer line to prevent backflows 
into the first floor area. 

Detailed instructions regarding the operation and maintenance of the veneer wall, closure, 
and utility valve were placed on wall placards both on the exterior wall next to the 
closure and inside the church. These items were included in the agreement executed 
between the church owners and the Corps of Engineers. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -107 
January 1995 


Chapter VII: Case Studies

_A MAHI~~ _

V -C A,_,. lb 41SU fa M 

Figure VII-8.4: Watertight Closure for Opening 

Construction Cost 

Key factors that influence the construction cost of veneer walls include: 

* height of design flood at the structure; 
* type and condition of the structure walls; 
 type, extent, and condition of structure footing; 
* number and size of structure access closures needed; 
* number, size, and location of underground utilities entering the structure; 
and 
* permeability and bearing capacity of soils at the structure. 
Additional factors that influence the cost of floodproofing include the availability of 
skilled contractors and competitively priced building materials. Table VII-8. 1 below 
shows the percentage contribution to construct a veneer wall against the structure. 

VII -1 08 Enaineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Case #8: Veneer Wall Dry Floodproofing 

Table V11-8.I Floodproofing Cost for a Veneer Wall 
Construction Items Percent of Total Construction 

Site Work, Mobilization, and Cleanup 40
Concrete and Masonry 24
Metals 26
Carpentry and Finishes 7
Mechanical and Electrical 3
100

Flood Proofing Technology in the Tug Fork Valley, U.S. Army Corps of Engineers, National Flood 
Proofing Committee, April 1994. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -109 
January 1995 


APPENDIX A

THE NATIONAL FLOOD
INSURANCE PROGRAM


Appendix A: The National Flood Insurance Program (NFIP) 

THE NATIONAL FLOOD INSURANCE PROGRAM (NFIP) 

Flood insurance coverage is available from the NFIP to all owners and 
occupants of insurable property (buildings and certain contents) in participating 
communities. Walled and roofed structures that are principally above ground 
and not entirely over water may be insured. Flood insurance is available for 
all buildings in a participating community whether the buildings are located 
inside or outside of the floodplain. This coverage is available for 
manufactured homes that are anchored to permanent foundations. Up to 10 
percent of the policy value for building coverage may apply to a detached 
garage or carport on the same lot. Contents within insured buildings also may 
be insured under separate coverage. 

The purchase of flood insurance is required for buildings located in the 100year 
floodplain as a condition of obtaining a federally regulated or insured 
mortgage or home improvement loan. NFIP flood insurance is available 
through private insurance companies and agents, as well as directly from the 
federal government. All companies offer identical coverage and rates as 
prescribed by the NFIP. 

PRE-FLOOD INSURANCE RATE MAP (PRE-FIRM) 
CONSTRUCTION VERSUS POST-FLOOD 
INSURANCE RATE MAP (POST-FIRM) 
CONSTRUCTION 

For flood insurance rating purposes, buildings are classified as being either 
pre-FIRM or post-FIRM. 

* Pre-FIRM construction means construction or substantial improvement 
started on or before December 31, 1974, or before the effective date of 
the community's initial FIRM, whichever is later. 
* Post-FIRM construction means construction or substantial improvement 
started after December 31, 1974, or on or after the effective date of the 
community's initial FIRM, whichever is later. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures A -1 
January 1995 


Appendix A: The National Flood Insurance Program (NFIP) 

Insurance rates for pre-FIRM buildings located in Special Flood Hazard Areas 
are set on a subsidized basis, while insurance rates for post-FIRM buildings 
located in Special Flood Hazard Areas are set actuarially on the basis of 
designated flood hazard zones on the community's NFIP maps (FIRMs) and 
the elevation of the first floor of the building in relation to the expected 100year 
flood level. For both pre-FIRM and post-FIRM buildings located outside 
a Special Flood Hazard Area, insurance rates are set actuarially, as well. This 
rate structure provides an incentive to property owners to elevate buildings in 
exchange for receiving the financial benefits of lower insurance rates. 
Subsequent to substantial improvements, a pre-FIRM building may become a 
post-FIRM building for flood insurance rating purposes. The enclosed Flood 
Insurance Rate Tables (Figures A-1 and A-2) provide information on costs of 
coverage for different buildings subject to various flooding scenarios. 

HYPOTHETICAL CASE STUDY 

To illustrate the impact of elevating a building on flood insurance premium 
rates and how the Flood Insurance Rate Tables are used, the following 
hypothetical example is provided: 

A family purchased a home located within a Special Flood 
Hazard Area (Zone AE) identified on their community's 

A t4 FIRM. The home was a one-floor single-family dwelling

with no basement. As a condition of receiving a federally-
The limits of coverage used in backed mortgage, a flood insurance policy was required by 
these examples became effective the lending institution. Because the home was constructed 
on March 1, 1995. before the initial FIRM for this community became effective, 

I this home was rated as pre-FIRM construction. The 
homeowners chose to purchase the maximum amount of 
coverage available for the building and its contents: $50,000 
of basic coverage plus an additional $200,000 of coverage 
for the building. For contents, they purchased the basic 
$15,000 of coverage plus an additional $85,000 of coverage. 
Thus, the total flood insurance coverage for the building and 
contents was $350,000. 

A -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix A: The National Flood Insurance Program (NFIP) 

To determine the annual rate to purchase this coverage, the Flood Insurance 
Rate Tables were utilized. Because their community participated in the regular 
program of the NFIP and the building is pre-FIRM construction, the Regular 
Program -Pre-FIRM Construction Rate Table was utilized. In this table, the 
flood insurance rates for buildings located in a Special Flood Hazard Area are 
subsidized in that (1) they are independent of the relationship between the first 
floor elevation and the BFE (2) the rates are below actuarial rates. In this 

table, a single-family home with no basement located in Zone AE has a rate of 

.60/.18 listed for building coverage. This means that for every $100 of basic 
building coverage, the annual premium would be $0.60. For every $100 of 
additional building coverage, the annual premium would be $0.18. There is a 
separate column in the table to determine premiums for basic and additional 
contents coverage, in this case $0.70 and $0.32 for every $100 of coverage, 
respectively. Figure A-1 shows the computations of the annual flood insurance 
premium for this example home providing maximum coverage allowable under 
the NFIP. 

Engineering Principles <i Practices of Retrofitting Flood-Prone Residential Structures A -3 
January 1995 


Appendix A: The National Flood Insurance Program (NFIP) 

Coverage 

(Hundreds Of Annual 
Dollars) Rate' Premium 

Basic Coverage 

Building 500 $0.60 300.00 

Contents 150 $0.70 105.00 

$405.00 

Additional Coverage 

Building 2,000 $0.18 360.00 

Contents 850 $0.32 272.00 

$632.00 

Federal Policy Fee 30.00 

Expense Constant 45.00 

Total Premium For This Policy = $1,112.00 

'Annual rate per $100 of coverage. Values taken from pre-FIRM insurance rate tables dated October
1,1994.

iFigure A-1: Annual Fiood Insurance Premium for Sample Home (Pre-FIRM) Before Elevating 

Subsequently, the home was substantially damaged in a flood. When repairing 

the building, the owner elevated the first floor to the BFE shown on the 

community's FIRM in order to comply with the community's floodplain 

management ordinance. Because the building was substantially improved, it 

was now considered post-FIRM for flood insurance rating purposes. Thus, the 

flood insurance premium was adjusted accordingly. Because the building is 

now considered post-FIRM construction, the new premium is determined 

actuarially based on the elevation of the first floor relative to the BFE. The 

computations for the new premium are made in a manner similar to that used 

for pre-FIRM, except that the Regular Program Post-FIRM-Construction Rate 

Tables were used. Note that there are separate tables for building and contents 

coverage for post-FIRM construction located in Zone AE. Because the first 

floor of this home was elevated to the BFE, the computations for the new 

premium are shown in Figure A-2, assuming the same maximum level of 

coverage that was previously purchased. 

A -4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix A: The National Flood Insurance Program (NFIP) 

Coverage 

(Hundreds Of Annual 
Dollars) Rate' Premium 

Basic Coverage 

Building 500 $0.36 180.00 

Contents 150 $0.72 108.00 

$288.00 

Additional Coverage 

Building 2,000 $0.07 140.00 

Contents 850 $0.12 102.00 

$242.00 

Federal Policy Fee 30.00 

Expense Constant 45.00 

Total Premium For This Policy = $605.00 

'Annual rate per $100 of coverage. Values taken from flood insurance rate tables dated January 1, 1994. 

Figure A-2: Annual Flood Insurance Premium for Sample Home (Post-FIRM) After Elevating 

By elevating the home to meet NFIP requirements, the property owners were 

able to reduce the annual flood insurance premium by $507.00. Over the life 

of a mortgage, this can be a significant savings. Elevating the structure higher 

would have resulted in an additional reduction in the annual flood insurance 

premium. 

Elevating a building above the BFE does not eliminate the requirement to 

purchase flood insurance but will reduce the insurance rate. Even though a 

building is elevated, the potential exists for damage to the foundation system 

which, in turn, could result in structural damage to the home. This is one 

reason why continued flood insurance is required. 

Many flood-prone homes were built prior to their community's adoption of 

NFIP regulations. Therefore, those flood-prone homes do not meet current 

floodplain management standards. Consequently, owners wanting to 
substantially modify, improve, repair, or retrofit their home as a result of 

preference or damage are subject to the NFIP substantial improvement 
(substantial damage) requirements discussed previously. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures A -5 
January 1995 


APPENDIX B 

i, 1192 go 
GLOSSARYOF TERMS 


Appendix B: Glossary of Terms 

GLOSSARY OF 

A Zone 
Alluvial Fan 

Anchor 

Armor 

Backflow Valve 

Base Flood 
Elevation (BFE) 

Berm 
Borrow Area 
Building Code 

TERMS 

See Special Flood Hazard Area. 

Area of deposition where steep mountain drainages empty into 
valley floors, usually in arid regions. Flooding in these areas 
often includes characteristics that differ from those in riverine or 
coastal areas. 

A series of methods used to secure a structure to its footings or 

foundation walls so that it will not be displaced by forces acting 

on the structure. 

To protect fill slopes from erosion or scouring by floodwaters. 

Techniques of armoring include the use of riprap, vegetation, 

gabions, or concrete mats. 

See Check Valve. 

The flood elevation having a one-percent chance of being 
equaled or exceeded in any given year. The BFE is determined 
by statistical analysis for each local area and designated on the 
Flood Insurance Rate Maps. The BFE is also known as the 
100-Year Flood Elevation. 

A bank or mound of earth, usually placed against a foundation 

wall. 

An area where material has been excavated for use as fill at 

another location. 

Regulations adopted by local governments that establish 
standards for construction, modification, and repair of buildings 
and other structures. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures B -1 
January 1995 


Appendix B: Glossary of Terms 

Caulking Flexible material used to fill joints in a structure, such as around 
windows or doors, which is able to resist the passage of 
moisture. 
Check Valve A type of valve that allows water to flow one way, but 
automatically closes when water attempts to flow in the opposite 
direction. 
Closure A shield made of strong material, such as steel, aluminum, or 
plywood, used to temporarily fill gaps in floodwalls, levees, or 
sealed structures and protect against water entrance through 
areas that have been left open for day-to-day convenience at 
entrances such as doors and driveways. 
Coastal 
High-Hazard 
Area 
Designated as V Zone on Flood Insurance Rate Maps, this is the 
portion of the coastal floodplain subject to storm-driven velocity 
waves of three feet or more in height. 
Column Upright support units for a building, set in pre-dug holes and 
backfilled with compacted material. They are also known as 
posts, although columns are usually of concrete or masonry 
construction. 
Concrete 
Masonry 
Unit (CMU) 
Block of concrete used in construction. 
Crawl Space Low space below the first floor of a house, where there has not 
been excavation deep enough for a basement, but where there is 
often access for pipes, ducts, and utilities. 
Debris Impact 
Loads 
Sudden loads induced on a structure by debris carried by floodwater. 
Though difficult to predict, impact loads must be 
considered when floodproofing a structure. 
Dry 
Floodproofing 
A retrofitting method used in areas of low-level flooding to 
completely seal a home against water, by making the walls 
substantially impermeable to the passage of water. Also 
referred to as sealing in this manual. 

B -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix B: Glossary of Terms 

Elevation 

Existing 

Construction 

Extended 
Foundation 

Federal 
Emergency 
Management 
Agency 

(FEMA) 

Federal 
Insurance 
Administration 

(FIA) 

Fill 

Flash Flood 

Flood (For NFIP 
flood insurance 
policies) 

The raising of a structure to place the lowest floor at or above 
the flood protection elevation on an extended support structure. 

For floodplain management purposes; a structure already 
existing or under construction prior to the effective date of a 
community's floodplain management regulations. For flood 
insurance purposes, a structure for which the "start of 
construction" commenced before the effective date of the FIRM 
or before January 1, 1975, for FIRMs effective before that date. 

The construction of additional height of foundation wall above 
existing foundation walls in order to elevate a structure to or 
above the design flood elevation. 

Agency created in 1978 to provide a single point of 
accountability for all federal activities related to disaster 
mitigation and emergency preparedness, response, and recovery. 

The governmental unit, a part of the Federal Emergency 
Management Agency, that administers the flood insurance 
aspects of the National Flood Insurance Program. 

Material such as earth, clay, or crushed stone that is placed in 
an area and compacted to increase ground elevation. 

A flood that crests in a short length of time and is often 
characterized by high velocity flow. It is often the result of 
heavy rainfall in a localized area. 

A partial or complete inundation of normally dry land areas 
from 1) the overland flood of a lake, river, stream, ditch, etc.; 
2) the unusual and rapid accumulation or runoff of surface 
waters; and 3) mudflows or the sudden collapse of shoreline 
land. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures B -3 
January 1995 


Appendix B: Glossary of Terms 

Flood Depth The height difference between the flood elevation and the lowest 
grade adjacent to the structure. 
Flood Fringe That portion of the floodplain that lies beyond the floodway and 
serves as a temporary storage area for floodwaters during a 
flood. This section receives waters that are generally shallower 
and of lower velocities than those of the floodway. 
Flood Hazard 
Boundary Map 
(FHBM) 
The official map of a community, issued by FEMA, where the 
boundaries of the flood, mudslide, and related erosion areas 
having special hazards have been designated as Zones A, M, 
and/or E. 
Flood Insurance 
Rate 
Map (FIRM) 
The official map of a community issued by FEMA that shows 
the Base Flood Elevation (BFE), along with the special hazard 
areas and the risk premium zones applicable to the community. 
Flood Insurance 
Study (FIS) 
A study performed by any of a variety of agencies and 
consultants to delineate the special flood hazard areas, base 
flood elevations, and risk premium zones. The study is funded 
by FEMA and is based on detailed site surveys and analysis of 
the site-specific hydrologic and hydraulic characteristics. 
Floodplain Normally dry land adjacent to a body of water, such as a river; 
stream, lake, or ocean, that is susceptible to inundation by 
floodwaters. 
Floodplain 
Management 
A program of corrective and preventive measures for reducing 
flood damage, including but not limited to flood control 
projects, floodplain land-use regulations, retrofitting (or 
floodproofing) of buildings, and emergency preparedness plans. 
Floodproofing 
Design Depth 
The height difference between the flood protection elevation and 
the lowest grade adjacent to the structure. 
Floodproofing Any combination of measures taken on a new or existing 
structure for reducing or eliminating flood damage to a 
structure. For existing structures, it is also known as 
retrofitting. 

B -4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix B: Glossary of Terms 

Flood Protection 
Elevation 

Floodwall 

Floodway 

Footing 

Foundation 
Walls 

Freeboard 

Human 
Intervention 

Hydrodynamic 

Loads 

Hydrostatic 

Loads 

The height, in feet, above NGVD or NAVD to which 
floodproofing measures are designed. It is normally the sum of 
the expected flood elevation plus freeboard. (Also referred to as 
the Flood Protection Level). 

A constructed barrier of resistant material, such as concrete or 
masonry block, designed to keep water away from a structure. 

The central portion of the floodplain that carries the greatest 
portion of the waterflow in a flood. Obstructions in the 
floodway will result in increased flood levels upstream. 

The enlarged base of a foundation wall, pier, or column 
designed to spread the load of the structure so that it does not 
exceed the soil bearing capacity. 

A support structure that connects the foundation, or the building 
substructure, to the main portion of the building, or the building 
superstructure. 

An additional amount of height used as a factor of safety in 
determining the design height of a flood protection measure to 
compensate for unknown factors, such as wave action and the 
hydrologic effect of urbanization. Certain guidelines and 
restrictions apply for establishing freeboard on levees and 
floodwalls in Special Flood Hazard Areas. 

The required presence and active involvement of people to enact 
any type of flood protection measure prior to flooding. 

Forces imposed on an object, such as a structure, by water 
moving around it. Among these loads are positive frontal 
pressure against the structure, drag effect along the sides, and 

negative pressure on the downstream side. 

Forces imposed on a surface, such as a wall or floor slab, by a 

standing mass of water. The water pressure increases with the 

square of the water depth. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures B -5 
January 1995 


Appendix B: Glossary of Terms 

Interior Grade 
Beam 

Levee 

Lift 

Mean Sea Level 

Mitigation 
Directorate 

National Flood 

Insurance 
Program 

(NFIP) 

One Hundred 
(100)-Year Flood 

Openings 
Permeability 
Phreatic Surface 

Pier 

A section of a floor slab that has a thicker section of concrete to 
act as a footing to provide stability under load-bearing or critical 
structural walls. 

A barrier of compacted soil designed to keep floodwater away 
from a structure. 

A layer of soil that is compacted before the next layer is added 
in the construction of a fill pad or levee. 

The average height of the sea for all stages of the tide, usually 
determined from hourly height observations over a 19-year 
period on an open coast or in adjacent waters having free access 
to the sea. 

The governmental unit, a part of the Federal Emergency 
Management Agency, that administers the floodplain 
management aspects of the National Flood Insurance Program. 

The federal program created by an act of Congress in 1968 that 
makes flood insurance available in communities that enact 
satisfactory floodplain management regulations. 

The flood elevation that has a one-percent chance of being 
equaled or exceeded in any given year. It is also known as the 
base flood elevation. 

See venting. 

The property of soil or rock that allows water to pass through it. 

The upper boundary of a subsurface area which contains 
saturated soil. 

An upright support member of a building with a height limited 
to a maximum of three times its least lateral dimension. It is 
designed and constructed to function as an independent structural 
element in supporting and transmitting building and 
environmental loads to the ground. 

B -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Pile 

Post 

Regulatory 
Floodway 

Relocation 

Retrofitting 

Riprap 

Scouring 

Slab-on-Grade 

Special Flood 
Hazard 
Area 

Stile 

Structural Mat 
Slab 

Appendix B: Glossary of Terms 

An upright support member of a building usually long and 

slender in shape, driven or jetted into the ground by mechanical 

means and primarily supported by friction between the pile and 

the surrounding earth. 

Long upright support units for a building, set in pre-dug holes 

and backfilled with compacted material. Each post usually 
requires bracing to other units. They are also known as 
columns, although posts are usually made of wood. 

As referenced in a floodplain management ordinance, this is the 
portion of the floodplain needed to discharge the 100-year flood 
without increasing the flood elevation by more than a designated 
height; under the NFIP this is one foot. Severe restrictions 
apply to development within regulatory floodways. 

Moving a structure from a flood-prone area to a new location, 
normally to one where there is no threat of flooding. 

Floodproofing measures taken on an existing structure. 

Broken stone, cut stone blocks, or rubble that is placed on 
slopes to protect the slopes from erosion or scouring caused by 
floodwaters or wave action. 

The localized erosion around flow obstructions caused by the 
entrainment of soil or sediment. 

A structural design where the first floor sits directly on a poured 
concrete slab, which sits directly on the ground. 

An area having a special flood hazard and shown on a Flood 
Hazard Boundary Map or Flood Insurance Rate Map as Zones 
A, AO, A1-30, AE, AR, A99, VO, V1-30, VE, V, M, or E. 

A set of stairs to allow access over an obstruction, such as a 
floodwall. 

The concrete slab of a building that includes structural 
reinforcement to help support the building's structure. 

EngineeringPrinciplesand Practices of Retrofitting Flood-Prone Residential Structures B -7 
January 1995 


Appendix B: Glossary of Terms 

Substantial Damage of any origin sustained by a structure whereby the cost 

Damage of restoring the structure to its before-damaged condition would 
equal or exceed 50 percent of the value of the structure before 
the damage occurred. 

Substantial Any reconstruction, rehabilitation, addition, or other 

Improvement improvement of a structure, the cost of which equals or exceeds 
50 percent of the value of the structure before the "start of 
construction" of the improvement. This term includes structures 
which have incurred "substantial damage,1 " regardless of the 

actual repair work performed. The term does not, however, 
include either: 

1.) Any project for improvement of a structure to 
correct existing violations of state or local health, 
sanitary, or safety code specifications which have 
been identified by the local code enforcement 
official and which are the minimum necessary to 
assure safe living conditions, or 

2.) Any alteration of a "historic structure" provided 
that the alteration will not preclude the structure's 
continued designation as a "historic structure." 

Venting A system designed to allow floodwaters to enter an enclosure, 
usually the interior of foundation walls, so that the rising water 
does not create a dangerous differential in hydrostatic pressure. 
This is usually achieved through small openings in the wall, 
such as a missing or rotated brick or concrete block, or a small 
pipe. Also known as openings. 

V Zone See Coastal High Hazard Area. 

Watershed An area that drains to a single point. In a natural basin, this is 
the area contributing flow to a given place or stream. 

Zero Flood The elevation of the lowest finished floor of a structure.
Depth

B -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


APPENDIXC 

I N 

-~~~~~~~~~~~~~~~~ --IMI"E 

-GLOSSARYOF RESOURCES 


Appendix C: Glossary of Resources 

GLOSSARY OF RESOURCES 

This appendix presents information on resources available to the engineer, 
code official, or architect interested in floodproofing. Recommendations for 
establishing a basic retrofitting library, information on programs and 
organizations that can provide assistance, and a bibliography of references 
utilized in this manual are included. Much of this information was taken from 
Flood Proofing: Techniques, Programs and References, prepared by the U.S. 
Army Corps of Engineers National Flood Proofing Committee in February 
1991. 

THE BASIC RETROFITTING LIBRARY 

This section lists readily available references that form a basic floodproofing 

library. People interested in more detailed information on this subject are 

encouraged to obtain copies of these publications, as they cover most of the 

technical and programmatic aspects of retrofitting. They are listed below by 

agency source. Single copies of USACE and FEMA publications are free. 

The next section discusses how to obtain more references on specific topics. 

State floodplain management coordinators usually know of any additional 

publications that may be available from state and local offices. 

PUBLICATIONS AND SOURCES 

Order the following publications from the U.S. Army Corps 

of Engineers, Attn: CECW-PF20 Massachusetts Avenue, 

NW, Washington, D.C. 20314 

Flood Proofing Regulations, U.S. Army Corps of Engineers, Pittsburgh 

District, 1992, 96 pages (Corps publication EP 1165 2-314). The definitive 

work by the Corps of Engineers that provides construction specifications for 

retrofitting new buildings. It includes detailed lists of materials for areas to be 

wet floodproofed. The manual is organized to facilitate easy adoption by 

reference to a building code and provides both technical data and guidelines 

for ordinance administration. Illustrated with line drawings. Note: This 

document supersedes EP 1165-2-314 dated June 1972. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -1 
January 1995 


The Basic Retrofitting Library 

Flood Proofing Systems & Techniques, U.S. Army Corps of Engineers, L.N. 

Flanagan, editor, 1984, 100 pages. An illustrated, easy-to-read review of 40 
different buildings that have been elevated, dry and wet floodproofed, leveed, 
or otherwise protected. Buildings include new construction and retrofitted 
houses, businesses, schools, office buildings, and factories. Narrative includes 

costs. Many examples include photos of flooding. 

Flood Proofing: Techniques, Programs and References, U.S. Army Corps of 
Engineers, National Flood Proofing Committee, with French and Associates, 
Ltd., February 1991, 22 pages. This report addresses retrofitting techniques 
and government retrofitting programs, references, and terminology. It presents 
a general overview of retrofitting measures and provides the reader with 
information on government agencies that offer more specific assistance and 
detailed retrofitting information. 

Flood Proofing: How to Evaluate Your Options, U.S. Army Corps of 
Engineers and National Flood Proofing Committee, July 1993, 55 pages. This 
document was prepared to help answer the question "should floodproofing be 
used?" It is intended as a tool to assist in the preliminary evaluation of 
whether floodproofing is appropriate and what may be the best floodproofing 
measure to consider. It includes an introduction to floodproofing, the various 
measures, factors to consider, flooding characteristics, and thd thought process 
for evaluating physical, economic, and other factors influencing the 

floodproofing decision. Finally, an appendix provides a detailed explanation on 
how to perform an economic analysis comparing flood proofing benefits with 
floodproofing costs. 

Raising and Moving the Slab-on-Grade House with Slab Attached, U.S. Army 

Corps of Engineers and National Flood Proofing Committee, 1990, 28 pages. 

This report presents an overview of the raising and relocation process 

including advantages, methods and techniques, the steps involved, foundation 

design consideration, and costs. A photographic study of jobs in process is 

also included. 

Local Flood Proofing Programs, U.S. Army Corps of Engineers and National, 
Flood Proofing Committee, June 1994, 54 pages. 

C -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

A Flood Proofing Success Story Along Dry Creek at Goodlettsville, Tennessee, 

U.S. Army Corps of Engineers and National Flood Proofing Committee, 
September 1993, 20 pages. This report documents a successful floodproofing 
project where 19 homes were raised in place. Included are detailed 
descriptions of the homes involved, implementation procedures, and project 
costs. 
Flood Proofing Technology in Tug Fork Valley, West Virginia and Kentucky, 

U.S. Army Corps of Engineers and National Flood Proofing Committee, 
August 1993, 32 pages. This report documents elevation and dry floodproofing 
actions taken to reduce flooding in the Tug Fork Valley. Included are design 
details, cost information, and examples from the 136 homes that were 
floodproofed. 
Order the following publications from the Federal Emergency 
Management Agency, Attn: Publications, P.O. Box 2012, Jessup, 
Maryland, 20794-2012. 

DesignManualfor Retrofitting Flood-ProneResidentialStructures, 

Federal Emergency Management Agency, 1986, 265 pages (FEMA-114). An 
extensive review that discusses all aspects of protecting an existing house from 
flood damage. The book has many drawings and photographs. Each chapter 
covers a different technique with an introduction and sections on considerations 
(e.g., flood hazard, building type, regulatory restrictions), cost, and technical 
design criteria. 

FEMA Technical Bulletins, Federal Emergency Management Agency, 1993. 

FEMA has developed seven technical bulletins providing guidance on
Openings in Foundation Walls (TB #1-93), Flood Resistant Material

Requirements (TB #2-93), Non-Residential Floodproofing Requirements (TB 

#3-93), Elevator Installation (TB #4-93), Free-of-Obstruction Requirements 

(TB #5-93), Below-Grade Parking Requirements (TB #6-93) and, Wet 

Floodproofing Requirements (TB #7-93). Refer to the bibliography (page C

22) for a complete reference on each Technical Bulletin. 

Elevated Residential Structures, Federal Emergency Management Agency, 
1984, 135 pages (FEMA-54). A review of how to build an elevated building. 

Concepts, examples, and performance criteria are given, but technical 

specifications are not. Numerous examples are discussed with architectural 

drawings and photographs. Cost analyses are covered and calculation forms 

are included. Sources of information and assistance are listed. 

EngineeringPrinciplesand Practices of Retrofitting Flood-Prone Residential Structures C -3 
January 1995 


The BasicRetrofitting Library 

Flood ProofingNon-ResidentialStructures,FederalEmergencyManagement 
Agency, 1986, 200 pages (FEMA-102). An overview of retrofitting new and 
existing buildings designed to familiarize the reader with a variety of 

techniques. Retrofitting is divided into two parts: permanent (elevation, dry 
floodproofing, and levees and floodwalls) and emergency wet floodproofing. 
There are many drawings and photos to illustrate key points. Selection 

processes, case studies, sources of assistance, and performance criteria are also 
covered. 

Coastal Construction Manual, Federal Emergency Management Agency, 1986, 
210 pages (FEMA-55). A technical document that provides guidance on the 
design and construction of coastal residential structures (single-family and low-

rise multi-family) able to resist flood, wind, and erosion damage. The book 

discusses new construction, nonresidential structures, and retrofitting existing 

structures. Photographs and figures are used throughout. Detailed appendixes 

provide design data, design equations and procedures, cost information, and a 

sample coastal construction code. 

Order the following publications from the Association of State Floodplain 

Managers, Attn: Publications, P.O. Box 2051, Madison, WI 53701-2051. 

FloodplainManagement1995: State andLocal Programs,Associationof State 
Floodplain Managers, 1995, 100 pages, $15 for Association members, $20 for 
nonmembers. This publication discusses what the states are doing in 
floodplain management. There are numerous tables that identify what is being 

done by all 50 states and the District of Columbia, including state retrofitting 

activities. Each state's programs and selected local programs are reviewed. 

NationalDirectoryof FloodplainManagers,Associationof State Floodplain 
Managers, 1994, 157 pages, free to Association members, $20 for 
nonmembers. A directory of all members of the Association that includes 
sections on federal agencies, summaries of their programs, publications, 
committee progress reports, and cross references of members by area of 
interest and state. This is the only national directory of state floodplain 
management staff. Note: revised versions of this document are published every 
year. 

C -4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

GOVERNMENT RETROFITTING PROGRAMS 

Local, state, and federal government agencies perform a variety of activities 
that implement or support retrofitting. This chapter groups the activities into 
six categories: general information, technical assistance, regulations, financial 
assistance, projects, and research and technology transfer. 

GENERAL INFORMATION 

The most common way government agencies support retrofitting is by 
providing publications and general information to interested persons. Several 
federal and state agencies have published manuals on the topic that are 
available to individuals and local governments for free distribution. Some of 
the publications are listed in the previous section of this Appendix. 

Many local governments have prepared their own brochures that address local 
flooding and building conditions. Often these are distributed free to all 
residents of the floodplain or, particularly in the case of basement flooding, to 
all residents of the community. These federal, state, and local publications 
usually discuss retrofitting in general terms and provide property owners with 
an idea of what techniques would work for their situation. 

Agencies also answer general questions about retrofitting and related topics. 
Local building, housing, and community development departments refer callers 
to the publications or state and federal agencies that provide assistance. Some 
maintain lists of retrofitting contractors or consultants. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -5 
January 1995 


Government Retrofitting Programs 

TECHNICAL ASSISTANCE 

While many agencies provide general information, a few provide more specific 
information to advise property owners about retrofitting individual buildings. 
This can include a range of services such as providing flood and building 
elevations, discussing options for protecting a building, recommending specific 

techniques, and reviewing the owner's building plans. 

Several agencies have developed flood audit programs. These include a site 
investigation, discussions with the owner, and a written report that 
recommends specific retrofitting and other preparedness steps, such as 
purchasing flood insurance. Flood audits have been conducted for residences 
as well as large commercial or industrial complexes. 

Technical assistance is specific and usually provides more help to a property 
owner than general information, such as that found in a brochure or other 
publication. However, few governmental agencies provide technical assistance 
for individual buildings due to the staff time necessary. In addition, free 
technical assistance service may not be based on careful examination of a 
building's structural condition, tests of wall strength, etc. Government agencies 
are hesitant to make specific recommendations based on what can only be a 
relatively cursory inspection. 

REGULATIONS 

Most regulations for retrofitting are based on the minimum standards of the 
National Flood Insurance Program. The NFLP sets minimum regulatory 
standards for constructing, modifying, or repairing buildings located in the 
floodplain to keep flood losses to a minimum. Over 18,000 flood-prone 
communities have adopted and enforce the minimum standards, and many have 
more restrictive requirements. The NFIP limits some retrofitting: it prohibits 

obstructions, such as berms or levees in floodways. 

The NFIP requires that a building that is substantially improved or 
substantially damaged be elevated so its lowest floor is at or above the BFE. 
Substantial damage is defined as "damage of any origin sustained by a 

structure whereby the cost of restoring the structure to its before-damaged 

condition would equal or exceed 50 percent of the value of the structure before 
the damage occurred." Houses that have been substantially damaged or are 
being substantially improved (renovated) must be elevated to or above the 100-

year flood level. 
C 6 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

Many states and communities have more restrictive standards than the NFIP. 
The most common is freeboard, requiring an extra margin of safety in the 
design and construction of flood protection measures to account for waves, 
debris, hydraulic surge, or lack of flooding data. Some prohibit buildings or 
residences in certain areas, such as a floodplain or conservation zone. In these 
communities, substantially damaged buildings may not be allowed to be rebuilt 
unless they are relocated. 

FINANCIAL ASSISTANCE 

It is clear that homeowners' decisions to retrofit and the retrofitting measures
they choose are directly related to their financial condition. This is
particularly true after a flood, when opportunities for retrofitting are most
evident and the homeowners' interest levels are high, but they are in a difficult
financial position to take action. In many cases, availability of financial
assistance is the determining factor in whether or not a property will be
retrofitted.

Financial assistance can come in a variety of forms. For example, local
governments could use property tax incentives to encourage retrofitting. Most
financial assistance programs provide low-interest loans and grants.
Generally, grants are limited to lower income families.

There are several federal, state, and local financial assistance programs for
which retrofitting is a secondary objective. Usually, the owner must show that
retrofitting is related to the program's primary concerns of rebuilding after a
disaster, improving housing, or preserving or increasing employment
opportunities.

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -7 
January 1995 


Government Retrofitting Programs 

PROJECTS 

The greatest degree of government involvement is in the construction of public 
retrofitting projects. The agency prepares the construction plans, gets the 
owner's agreement, hires the contractor, and inspects the work. The more 
common projects include public buildings such as schools and waterfront park 
buildings. 

There are a few examples of government-built retrofitting projects on private 
property. Some of these start as financial assistance programs but evolve into 
projects because the homeowners are unable to handle the technical aspects of 
managing a construction project. Others begin when flood control project 
plans find that retrofitting is the most cost-effective approach to reduce flood 
damages. 

RESEARCH AND TECHNOLOGY TRANSFER 

Several federal and some state agencies have conducted or sponsored research 
into retrofitting materials and measures, as well as ways to assist property 
owners with retrofitting. Two of the largest research programs are sponsored 
by the U.S. Army Corps of Engineers' National Flood Proofing Committee 
and FEMA. The USACE has conducted studies and tests of the ability of 
structure walls to withstand flooding, waterproofing compounds and materials, 
raising and moving structures (including slab-on-grade houses), and other 
miscellaneous retrofitting measures, including the use of a flexible, waterproof 
membrane to wrap a house. 

Other agencies have investigated retrofitting measures, ways to motivate 
owners, alternative assistance arrangements, and methods for disseminating 
technical information. 

While research itself is important, it is equally important to disseminate both 
the findings from research and lessons learned from practical experience. For 
example, FEMA and the USACE often inspect buildings after a flood to 
determine how well retrofitting measures have performed. The findings are 
published in papers and books and explained at conferences and workshops. 

C -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

There have been a few retrofitting training programs, most of them for disaster 
assistance workers or local officials who implement state or federal technical 
or financial assistance programs. The USACE and the Model Building Code 
Groups conduct training programs under contract to FEMA. Some agencies 
also hold or sponsor public meetings or workshops for property owners. 

ORGANIZATIONS THAT SUPPORT RETROFITTING 
ACTIVITIES 

This section reviews the retrofitting programs conducted by six federal 
agencies. Programs that are usually undertaken by state and local agencies are 
also covered. 

U.S. ARMY CORPS OF ENGINEERS (USACE) 
The U.S. Army Corps of Engineers is the nation's oldest and largest water 

resources organization. Through its flood control program, the Corps 

conducts feasibility studies and builds flood control projects. Where it is 

shown to be economically feasible, these projects can include retrofitting. 

Major projects require specific authorization and funding by Congress, while 

small projects can be implemented with agency authority. 

The Corps Floodplain Management Services Program provides flood hazard 

determinations, technical data on flood hazards, and guidance on retrofitting, 

floodplain regulations, flood warning, emergency preparedness, and evacuation 

planning. It also staffs the National Flood Proofing Committee, which 

supervises research and provides technology transfer on relocation, elevation, 

and other retrofitting measures. The Committee also coordinates with other 

agencies and associations involved in floodproofing. 

Point of Contact: The Corps' civil works programs are organized in 
divisions and districts that cover the entire country. The 
main point of contact at these divisions and districts is 
the Floodplain Management Services office, whose 
telephone numbers and addresses are presented below. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -9 
January 1995 


Organizations that Support RetrofittingActivities 

U.S. ARMY CORPS OF ENGINEERS OFFICES 
Alabama 

Mobile District 

P.O. Box 2288 
Mobile, AL 36628-0001 
Attn: CESAM-PD-P 
205/694-3879 

Alaska 

Alaska District 

P.O. Box 898 
Anchorage, AK 99506-0898 
Attn: CENPA-EN-PL-FP 
907/753-2610 

Arkansas 

Little Rock District 

P.O. Box 867 
Little Rock, AR 72203-0867 
Attn: CESWL-PL-F 
501/378-5611 

California 

Los Angeles District 

P.O. Box 2711 
Los Angeles, CA 900532325 
Attn: CESPL-PD-WF 
213/894-5375 

Sacramento District 
650 Capitol Mall 
Sacramento, CA 95814-4794 
Attn: CESPK-PD-F 

916/551-1881 

San Francisco District 
211 Main Street 
San Francisco, CA 941051905 
Attn: CESPN-PE-W 

415/974-0460 

South Pacific Division 
Room 720 
630 Sansome Street 
San Francisco, CA 941112206 
Attn: CESPD-PD-P 

415/705-1637 

District of Columbia 

Headquarters 
20 Massachusetts Ave., NW 
Washington, D.C. 203141000 
Attn: CECW-PF 

202/272-0169 

Florida 

Jacksonville District 

P.O. Box 4970 
Jacksonville, FL 322320019 
Attn: CESAJ-PD-FP 
904/791-1102 

Georgia 

Savannah District 

P.O. Box 889 
Savannah, GA 31402-0889 
Attn: CESAS-PD-F 
912/944-5339 

South Atlantic Division 
Room 313 
77 Forsyth Street, SW 
Atlanta, GA 30335-6801 
Attn: CESAD-PD-A 

404/331-4441 

Hawaii 

Pacific Ocean Division 
Ft. Shafter, HI 96858-5440 
Attn: CEPOD-ED-PH 

808/438-7009 

Illinois 

Chicago District 
219 S. Dearborn Street 
Chicago, IL 60604-1797 
Attn: CENCC-PD-R 

312/353-4078 

North Central Division 
536 S. Clark Street 
Chicago, IL 60605-1592 
Attn: CENCD-PD-FP 

312/353-6531 

C-10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

Rock Island District 

P.O. Box 2004 
Clock Tower Building 
Rock Island, IL 61204-2004 
Attn: CENCR-PD-F 
309/788-6361 

Kentucky 

Louisville District 

P.O. Box 59 
Louisville, KY 40201-0059 
Attn: CEORL-PD-S 
502/582-5742 

Louisiana 

New Orleans District 

P.O. Box 60267 
New Orleans, LA 701600267 
Attn: CELMN-PD-FG 
504/862-2507 

Maryland 

Baltimore District 
Supervisor of Baltimore 
Harbor 

P.O. Box 1715 
Baltimore, MD 21203-1715 
Attn: CENAB-PL-B 
301/962-3235 

Massachusetts 

New England Division 
424 Trapelo Road 
Waltham, MA 02254-9149 
Attn: CENED-PL-B 

617/647-8255 

Michigan 

Detroit District 

P.O. Box 1027 
Detroit, MI 48231-1027 
Attn: CENCE-PD-PF 
313/226-6773 

Minnesota 

St. Paul District 
1135 USPO & Custom 
House 
St. Paul, MN 55101-1479 
Attn: CENCS-PD-FS 

612/220-0280 

Mississippi 

Lower Miss. Valley 
Division 

P.O. Box 80 
Vicksburg, MS 39181-0080 
Attn: CELMV-PE-F 
601/634-5827 

Vicksburg District 

P.O. Box 60 
Vicksburg, MS 39181-0060 
Attn: CELMK-PD-F 
601/631-5416 

Missouri 

Kansas City District 
700 Federal Building 
Kansas City, MO 641062896 
Attn: CEMRK-PD-P 

816/426-3674 

St. Louis District 
1222 Spruce Street 
St. Louis, MO 63103-2833 
Attn: CELMS-PD-M 

314/331-8480 

Nebraska 

Missouri River Division 

P.O. Box 103, Downtown 
Station 
Omaha, NE 68101-0103 
Attn: CEMRD-PD-F 
402/221-7273 

Omaha District 
Room 6014 USPO & 
Courthouse 
Omaha, NE 68102-4978 
Attn: CEMRO-PD-F 

402/221-4596 

New Mexico 

Albuquerque District 

P.O. Box 1580 
Albuquerque, NM 871031580 
Attn: CESWA-ED-PH 
505/766-2635 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C-11 
January 1995 


Organizationsthat Support Retrofitting Activities 

New York 

Buffalo District 
1776 Niagara Street 
Buffalo, NY 14207-3199 
Attn: CENCB-PD-FP 

716/879-4143 

New York District 
Supervisor of New York 
Harbor 
26 Federal Plaza 
New York, NY 10278-0090 
Attn: CENAN-PL-FP 

212/264-8870 

North Atlantic Division 
90 Church Street 
New York, NY 10007-9998 
Attn: CENAD-PL-FP 

212/264-7482 

North Carolina 

Wilmington District 

P.O. Box 1890 
Wilmington, NC 284021890 
Attn: CESAW-PD-F 
919/251-4720 

Ohio 

Ohio River Division 

P.O. Box 1159 
Cincinnati, OH 45201-1159 
Attn: CEORD-PD-J 
513/684-3012 

Oklahoma 

Tulsa District 

P.O. Box 61 
Tulsa, OK 74121-0061 
Attn: CESWT-PL-GF 
918/581-7896 

Oregon 

North Pacific Division 

P.O. Box 2870 
Portland, OR 97208-2870 
Attn: CENPD-PL-FS 
503/326-3823 

Portland District 

P.O. Box 2946 
Portland, OR 97208-2946 
Attn: CENPP-PL-CF 
503/326-6411 

Pennsylvania 

Philadelphia District 

U.S. Customs House 
2nd & Chestnut Streets 
Philadelphia, PA 191062991 
Attn: CENAP-PL-F 
215/597-4808 

Pittsburgh District 
William S. Moorehead Fed. 
Bldg. 
1000 Liberty Avenue 
Pittsburgh, PA 15222-4186 
Attn: CEORP-PD-J 

412/644-4180 

South Carolina 

Charleston District 

P.O. Box 919 
Charleston, SC 29402-0919 
Attn: CESAC-EN-PH 
803/727-4682 

Tennessee 

Nashville District 

P.O. Box 1070 
Nashville, TN 37202-1070 
Attn: CEORN-ED-P 
615/736-5055 

Memphis District 
B-202 Clifford Davis Fed. 
Bldg. 167 North Main Street 
Memphis, TN 38103-1894 
Attn: CELMM-PD-M 

901/544-3968 

Texas 

Galveston District 

P.O. Box 1229 
Galveston, TX 77553-1229 
Attn: CESWG-PL-P 
409/766-3023 

Fort Worth District 

P.O. Box 17300 
Forth Worth, TX 761020300 
Attn: CESWF-PL-F 
817/334-3207 

Southwestern Division 
1114 Commerce Street 
Dallas, TX 75242-0216 
Attn: CESWD-PL-M 

214/767-2310 

C-12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

Virginia 

Norfolk District 
Supervisor of Norfolk 
Harbor 
803 Front Street 
Norfolk, VA 23510-1096 
Attn: CENAO-PL-FP 

804/441-7779 

Washington 

Seattle District 

P.O. Box C-3755 
Seattle, WA 98124-2255 
Attn: CENPS-EN-HH 
206/764-3660 

Walla Walla District 
Bldg. 602 City-County 
Airport 
Walla Walla, WA 993629265 
Attn: CENPW-PL-FP 

509/522-6589 

West Virginia 

Huntington District 
502 8th Street 
Huntington, WV 257012070 
Attn: CEORH-PD-S 

304/529-5644 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -13 
Januarv 1 995 


Organizations that Support Retrofitting Activities 

FEDERAL EMERGENCY MANAGEMENT AGENCY (FEMA) 

Created by the Congress in 1968, the National Flood Insurance Program aims 
to reduce future damage to existing and new construction through prudent 
floodplain development and to transfer the risk of that development from the 
public to the private sector through an insurance mechanism that protects the 
financial interest of the property owner while requiring a premium to be paid 
for that protection. 

The Federal Emergency Management Agency identifies and maps flood 
hazards nationwide. Flood Insurance Rate Maps distinguish several flood 
hazard zones, including the 100-year floodplain, which is defined as an area 
inundated by a flood that has a one-percent chance of being equalled or 
exceeded in any year (i.e., the 100-year flood, also called the Base Flood 
Elevation). In riverine areas and tidal areas subject to waves of less than three 
feet in height, the 100-year floodplain is referred to as the Special Flood 
Hazard Area and is designated Zone A. In coastal areas where wave heights 
equal or exceed three feet, the 100-year floodplain is referred to as the Coastal 
High Hazard Area and is designated Zone V. 

In communities that participate in the program, construction is allowed within 
the Special Flood Hazard Area if it complies with local floodplain ordinances 
that meet National Flood Insurance Program requirements. A fundamental 
requirement is that any new or substantially improved residential building must 
have its lowest floor elevated to or above the Base Flood Elevation. A 
building is considered substantially improved when the cost of any 
rehabilitation, addition, or other improvement, or repair or reconstruction after 
damage, equals or exceeds 50 percent of the pre-improvement/pre-damage 
value of the building. In A Zones, the lowest residential floor must be elevated 
either on earthen fill or solid or open foundations to or above the Base Flood 
Elevation. In V Zones, the lowest horizontal structural member must be 
elevated to or above the Base Flood Elevation on an open foundation. 

The foundation of the NFIP is a quid pro quo: if a community will adopt and 
enforce ordinances to reduce future flood risks, the federal government will 
make flood insurance available to property owners in the community. 

C -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

Lending institutions require the purchase of flood insurance for buildings 
located in the Special Flood Hazard Area as a condition of obtaining a 
federally sponsored or insured mortgage or home improvement loan. Flood 
insurance policies are available through both private insurance agents and the 
federal government. 

Point of contact: FEMA's work is conducted through ten regional offices 
as shown on the following page. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -15 
Januarv 1995 


Organizations that Support Retrofitting Activities 

FEMA REGIONAL OF FICES 

Region I 
CT, ME, MA, NH, RI, VT 

J.W. McCormack POCH, 
Room 442 
Boston, MA 02109-4595 
617/223-9540 
Region II 
NJ, NY, PR, VI 

26 Federal Plaza, Room 
1338 
New York, NY 10278-0002 
212/238-8208 

Region III 

DE, DC, MD, PA, VA, 
WV 

Liberty Square Building, 
2nd floor 
105 South Seventh Street 
Philadelphia, PA 191063316 
215/931-5500 

Region IV 
AL, FL,GA, KY, MS, NC, 
SC, TN 

1371 Peachtree Street, NE 
Suite 700 
Atlanta, GA 30309-3108 
404/853-4200 

Region V 
IL, IN, MI, MN, OH, WI 

175 West Jackson 
4th Floor 
Chicago, IL 60604-2698 
312/408-5500 

Region VI 
AR, LA, NM, OK, TX 

Fed. Reg. Center, Room 
206 
800 North Loop 288 
Denton, TX 76201-3698 
817/898-9399 

Region VII 
IA, KS, MO, NE 

911 Walnut Street, Room 
200 
Kansas City, MO 641062085 
816/283-7061 

Region VIII 
CO, MT, ND, SD, UT, 
WY 

Denver Federal Center Bldg 
710 
Box 25267 
Denver, CO 80225-0267 
303/235-4811 

Region IX 
AZ, CA, HI, NV 

Building 105 
Presidio of San Francisco 
San Francisco, CA 941291250 
(415)923-7100 

Region X 
AK, ID, OR, WA 

Federal Regional Center 
130 228th Street, SW 
Bothell, WA 98021-9796 
206/487-8800 

C-16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

TENNESSEE VALLEY AUTHORITY (TVA) 

Since 1953, the TVA has assisted state and local officials and property owners 
in planning and implementing sound floodplain management practices within 
the Tennessee River watershed. Since October 1994, floodplain management 
assistance has been provided by the USACE and local/state governments. 
Information on TVA reservoirs is presently available from TVA. 

Point of contact: Tennessee Valley Authority 

524 Union Avenue 

Evans Building, Room 1A 

Knoxville, TN 37902-1499 

615/632-2101 

NATURAL RESOURCES CONSERVATION SERVICE 
(NRCS) 

As part of the U.S. Department of Agriculture, the NRCS, formerly known as 
the Soil Conservation Service (SCS), primarily serves rural areas. NRCS staff 
provides information on land-use planning, conservation planning, resource 
development, water management, and flood prevention to farmers, community 
officials, and land developers. While mostly a general information and 
technical assistance operation, NRCS also funds flood protection projects that 
can include retrofitting elements. 

Point of contact: NRCS work is conducted through local soil and water 
conservation districts. The point of contact is the district 
conservationist. (Check the local telephone directory.) 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -17 
January 1 995 


Organizations that Support Retrofitting Activities 

SMALL BUSINESS ADMINISTRATION (SBA) 

The SBA administers the federal government's major disaster loan program. 
In spite of its name, SBA disaster loans are available for any privately owned 
property, including businesses and residences. The low-interest loans are 
provided to rebuild a damaged building, including the cost of bringing a 
building up to the current building code standards. The loans can pay for 
code-required retrofitting of substantially damaged buildings and some smaller 

projects. 
Point of contact: SBA loans are only available following either an SBA or 
Presidentially declared disaster. Disaster Application 
Centers are established to process applications. The 
location and hours of these centers are well publicized. 

DEPARTMENT OF HOUSING AND URBAN 
DEVELOPMENT (HUD) 

HUD programs are designed to improve housing conditions, local economies, 
and neighborhoods. As the nation's housing agency, HUD has been active in 
protecting both public and privately owned houses from flood damage. HUD's 
major retrofitting program is the Community Development Block Grant 
(CDBG), which provides funds directly to larger cities and counties. States 
handle CDBG funds for smaller communities. 

The block grant concept allows states and communities to set their funding 
priorities as long as the local projects relate to program objectives, i.e., they 
must benefit low and moderate income people, prevent or eliminate slums and 
blight, or meet other urgent community development needs. Many 
communities have used CDBG funds to retrofit buildings as a way to provide 
low-income residents with safe and sanitary housing. Some states have 
reserved block grant funds for special post-disaster projects that have included 
retrofitting. 

Point of contact: Each state has a HUD Area Office, located in its capital 

or largest city. State departments of community affairs 

are also points of contact on the Community Develop

ment Block Grant. (Check the local telephone directory.) 

C -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

ASSOCIATION OF STATE FLOODPLAIN MANAGERS 
(ASFPM) 

While not a government agency, the ASFPM supports many government 
retrofitting programs. Its Floodproofing/Retrofitting committee works on 
coordinating and publicizing federal, state, and local retrofitting activities. 
The Mitigation Committee focuses on post-disaster activities, especially 
programs that can provide funding help to property owners. 

The Association is a provider of general information and has published several 
reports on retrofitting activities. Its conferences are the largest in the nation 
on floodplain management and usually include many sessions on retrofitting. 
The Association is also a good source of information on state and local 
floodplain management programs and contacts. 

Point of contact: ExecutiveDirector 
Association of State Floodplain Managers 

P.O. Box 2051 
Madison, WI 53701-2051 
608/266-1926 
STATE HOUSING AND COMMUNITY AFFAIRS 
AGENCIES 

Most states have a department of community affairs or similar office that is 
responsible for managing the Community Development Block Grant (see 
HUD). Some states have their own funding programs that operate similar to 
the block grant program. They fund housing or economic improvement 
projects, including protecting buildings from floods. Some agencies provide 
technical assistance to communities undertaking floodplain management 
planning or establishing programs to help property owners. 

Point of contact: The title and duties will vary from state to state, but 
most will have a community affairs agency located in the 
state capital. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -19 

Iwnlnrv 1 QQR 


Organizations that Support Retrofitting Activities 

S 

STATE FLOODPLAIN MANAGEMENT 
COORDINATORS 

Most states have a floodplain management coordinator whose duties include 
advising and assisting local officials and property owners about the National 
Flood Insurance Program (NFIP), particularly its regulatory aspects. These 
offices are also the best sources of information about related floodplain 
management issues, including programs that affect or support retrofitting. A 
few state coordinating offices provide technical assistance or manage financial 
assistance programs. 

Point of contact: State coordinators can be located by contacting the 
appropriate FEMA Regional Office, the Association of 
State Floodplain Managers or local floodplain 
administrators. 

LOCAL BUILDING AND FLOODPLAIN 
MANAGEMENT AGENCIES 

Regulations that affect retrofitting are implemented by local building, zoning, 
floodplain, or housing code departments. These offices sometimes provide 
general information and technical assistance to property owners. Several have 
developed handbooks on retrofitting for their residents. 

Point of contact: Generally, county regulatory departments operate only in 
unincorporated areas. Municipal departments have 
jurisdiction in incorporated cities, towns, and villages 
(check the local telephone directory). State NFIP 
coordinators and FEMA Regional Offices may know of 
local departments particularly active in retrofitting. 

LOCAL HOUSING, COMMUNITY DEVELOPMENT, 
AND PLANNING AGENCIES 

There are many different kinds of city, county, and regional agencies involved 
in housing, planning, urban renewal, and community development. 
Community development departments and housing authorities work to improve 
local housing conditions through both public housing and programs to help low 
and moderate income residents. This work can be in the form of building 
inspections, technical assistance, and financial assistance. Other local and 

C -20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1 995 


Appendix C: Glossary of Resources 

regional agencies include regional planning commissions, sanitary districts, and 
water management districts. 

Most provide general information to residents and technical assistance to local 

officials. Some sanitary districts have regulatory authority based on the need 

to keep floodwater out of sewer lines. Some of these agencies have active 

technical and financial assistance programs to help property owners in 

retrofitting projects. 

Point of contact: These agencies may be listed in the local telephone 
directory. State NFIP coordinators, FEMA Regional 
Offices, and local floodplain administrators may know of 
agencies particularly active in retrofitting. 

VIDEOTAPES 

Valuable retrofitting information and training are available on video cassette. 
Floodproofing information videos have been prepared for general distribution 
by the following entities. 

FEMA and the National Association of Home Builders Best Build Series, 

which may be purchased from the NFIP at a cost of $10, includes these titles: 

* Constructing a Sound Coastal Home (20 minutes) 
* Construction in a Riverine Floodplain (24 minutes) 
0 Protecting a Flood-ProneHome (30 minutes) 
(The regional offices of FEMA are listed on page C-16.) 

USACE National Flood Proofing Committee 

* House Raising with Slab Attached (7 minutes) 
(The USACE address nearest you can be found on pages C-10 through C-13.) 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -21 
January 1995 


Bibliography 

BIBLIOGRAPHY 

Association of State Floodplain Managers -Floodplain Management Resource Center, 
Flyer, How to Get Information. 

Colorado Water Conservation Board and Colorado Water Resource
Research Institute, Colorado State University, Colorado Flood
Proofing Manual, October 1986.

Department of Housing and Urban Development, Design and Construction Standards 
for Residential Basements in Non-Coastal High Hazard Areas, February 9, 
1979. 

Department of Housing and Urban Development, Manual for the Construction of 
Residential Basements in Non-Coastal Flood Environments Contract No. H3849, 
March 1977for FIA, DHUD. 

Federal Emergency Management Agency, Community Rating System Coordinators 
Manual, FIA-15, July 1994. 

Federal Emergency Management Agency, Alluvial Fans: Hazards and Management, 
FEMA-165, Federal Insurance Administration, Office of Loss Reduction, 
February 1989. 

Federal Emergency Management Agency, Reducing Losses in High Risk Flood 
Hazard Areas: A Guidebookfor Local Officials, FEMA 116, Chapter 3, 
February 1987. 

Federal Emergency Management Agency, Hazards & Management, February, 1989. 

Federal Emergency Management Agency, Design and Construction Manualfor 
Residential High Hazard Areas. 

Federal Emergency Management Agency (FEMA 54), Elevated Residential 
Structures, 1984. 

C -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
Januarv 1995 


Appendix C: Glossary of Resources 

Federal Emergency Management Agency (Office of Loss Reduction), Technical 
Informationon ElevatingSubstantiallyDamagedResidentialBuildingsin Dade 
County, Florida, Washington, D.C., January 29, 1993. 

Federal Emergency Management Agency and American Red Cross, Repairing Your 
Flooded Home, FEMA 234/ARC 4477, August 1992. 

Federal Emergency Management Agency, Code Compatibility Report, Volumes 1-3, 
October, 1992. 

Federal Emergency Management Agency, Detailed Chronology of Significant National 
Flood Insurance Program Events, June 1, 1991. 

Federal Emergency Management Agency, Following a Flood...Steps to Recovery, 
November, 1990. 

Federal Emergency Management Agency, Guidelines and Specifications for Wave 
Elevation Determination and V Zone Mapping, Third Draft, July 1989. 

Federal Management Agency, TB #1-93, Openings in Foundation Walls for Buildings 
Located in SpecialFlood HazardAreas in Accordance with the NFIP, April 
1993. 

Federal Emergency Management Agency, TB #2-93, Flood Resistant Material 
Requirementsfor BuildingsLocatedin Special FloodHazardAreas in 
Accordance with the NFIP. April 1993. 

Federal Emergency Management Agency, TB #3-93, Non-Residential Floodproofing 
Requirementsand Certification for BuildingsLocated in Special Flood Hazard 
Areas in Accordance with the NFIP, April 1993. 

Federal Emergency Management Agency, TB #4-93, Elevator Installation for 
BuildingsLocated in Special Flood HazardAreas in Accordance with the 
NFIP, April 1993. 

Federal Emergency Management Agency, TB #5-93, Free-of-Obstruction 
Requirementsfor BuildingsLocatedin Coastal High HazardAreas in 
Accordance with the NFIP, April 1993. 

Federal Emergency Management Agency, TB #6-93, Below-Grade Parking 
Requirementsfor BuildingsLocatedin Special FloodHazardAreas in 
Accordance with the NFIP, April 1993. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -23 
January 1995 


Bibliography 

Federal Emergency Management Agency, TB#7-93, Wet Floodproofing for 
Requirements for Structures Located in Special Flood Hazard Areas in 
Accordance with the NFIP, December 1993. 

Flo Engineering, Inc., (Letter) Outline Delineating Alluvial Fan Flooding in Colorado 
Relative To Mitigation and Structural Floodproofing, January 13, 1993. 

Flo Engineering, Inc., (Letter) Bibliography Related to Alluvial Fan Floodproofing 
and Mitigation for Water Floods, Mud Floods, and Mud Flows, January 11, 
1993. 

Flo Engineering, Inc., Report on Residential Floodproofing on Alluvial Fans, January 
22, 1993. 

French & Associates, Ltd., Midwest Floodproofing Conference and Exposition 
Evaluation Report, April, 1991. 

French & Associates, Ltd., Floodproofing Home Utilities: Flood Hazards, Hazard 
Mitigation Monograph Series. 

French & Associates, Ltd., Performance of Flood Proofing Measure -Partial Draft, 
May 1992. 

French & Associates, Ltd., Letter Regarding Contractor's Survey, February 3, 1993. 

French & Associated, Ltd., Downey Manor Flood Protection Planning Consultants 
Report: Village of Homewood, IL, March 10, 1992. 

French & Associates, Ltd., Floodproof Sites in Illinois, June 23, 1992. 

French, Richard H., Fuller, Jonathan E., and Waters, Steve, Alluvial
Fan: Proposed New Process-Oriented Definitions for Arid
Southwest, ASCE Journal of Water Resources Planning and
Management, Vol. 119, No. 5, September/October, 1993.

Goldman, Steven J., Katherine Jackson and Taras A. Bursztynsky, P.E., Erosion and 
Sediment Control Handbook, McGraw-Hill Book Company, 1986. 

Interagency Task Force for Floodplain Management, Association of State Floodplain 
Managers and Soil Conservation Service, Floodproofing and Flood Warning 
and Response Workshop, September 9, 1992. 

C -24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

Prince Georges County, MD, Residential Drainage: Dealing With Wet Basement and 
Erosion Problems (revised October, 1987), February 1979. (2 copies) 

Prince Georges County, MD, Department of Environmental Resources, Watershed 
Protection Branch, Henson Creek Floodplain Study at Suitland Road Crossing 
Town of Morningside, July, 1988. 

Prince Georges County, MD Department of Environmental Resources Watershed 
Protection Branch, Henson Creek Floodplain Study at Suitland Road Crossing 
Town of MorningSide (Residential Home Floodproofing) Alternate "E" 
Analysis, November, 1988. 

Prince Georges County, MD Department of Environmental Resources Watershed 
Protection Branch, Structural Floodproofing General Conditionsand Standard 
Specifications, June, 1989. 

Prince Georges County, MD Department of Environmental Resources Watershed 
ProtectionBranch,ResidentialFloodproofingSite Plan/Notes and Details, 
1214 Waterford Drive District Heights, MD, February 25, 1991. 

Prince Georges County, MD Department of Environmental Resources Watershed 
ProtectionBranch,ResidentialFloodproofing Site Plan/Notesand Details, 
3400 29th Avenue, Hillcrest Heights, MD, July 11, 1991. 

Prince Georges County, MD Department of Environmental Resources Watershed 
Protection Branch, Site Grading and Sediment and Erosion Control Plans for 
the Casey Property, 7801 Rosaryville Road, Woochyard, MD, May 2, 1991. 

Prince Georges County, MD Department of Environmental Resources Watershed 
ProtectionBranch, Site Grading and Sediment and Erosion Control Plans for 
the Birlatt Residence, 14813 Livingston Road, May 2, 1991. 

Prince Georges County, MD Department of Environmental Resources Watershed 
Protection Branch, Site Grading and Sediment and Erosion Control Plans for 
the Holmes Residence, Accoceek, MD, May 2, 1991. 

Prince Georges County, MD, Site Grading and Sediment and Erosion Control Plans, 
The Lollis Residence, 7803 Knollwood Street, Brandywine, MD, April 12, 
1991. 

Sheatter, John R., University of Chicago, IL, The Center for Urban Studies, 

Introduction to Floodproofing, 1967. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -25 
January 1995 


Bibliography 

Soil Conservation Service, Basin and Area Planning Division, Washington, D.C. 
Upstream Flood Loss Task Force Report, April 30, 1991. 

University of Colorado at Boulder, The Natural Hazards Research and Applications 

Information Center (FIA-17), Floodplain Management in the United States: 

'An Assessment Report, Volume I, May, 1992. 

U.S. Army Corps of Engineers, Los Angeles, CA, Engineering Standards for Flood 
Protection of Single Lot Developments on Alluvial Fans. 
U.S. Army Corps of Engineers, National Flood Proofing Committee, Flood Proofing 
Bibliography, June 1988. 
U.S. Army Corps of Engineers National Flood Proofing Committee, Raising and 
Moving the Slab on Grade House with Slab Attached, 1990. 
U.S. Army Corps of Engineers, Pittsburgh District, Flood Proofing Regulations, 
EP1165 -314, June, 1972, Revised March 1992. 
U.S. Army Corps of Engineers, Flood Proofing: Techniques, Programs and 
References, February 1991. 
U.S. Army Corps of Engineers National Flood Proofing Committee, How to Evaluate 
Your Options, July 1993. 
U.S. Army Corps of Engineers National Flood Proofing Committee, A Flood 
Proofing Success Story along Dry Creek at Goodlettsville, Tennessee, 
September 1993. 

U.S. Army Corps of Engineers National Flood Proofing Committee, Flood Proofing 
Technology in the Tug Fork Valley, West Virginia and Kentucky, 
August 1993. 

C -26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix C: Glossary of Resources 

THE RESOURCE CENTER 

This appendix has introduced 14 publications that are readily available and that 
provide overviews of retrofitting, as well as our bibliography for this 
publication. There are many more references on various technical aspects of 
retrofitting. Most of them have been collected and cataloged at the Floodplain 
Management Resource Center. This chapter explains how to locate these 
additional publications. 

Any person may use the Resource Center. It is a public service established by 

the Association of State Floodplain Managers with financial support from the 

Corps of Engineers, the Federal Insurance Administration, the Tennessee 

Valley Authority, and other public and private organizations. 

OPERATION 

The Floodplain Management Resource Center is located at the Natural Hazards 
Center in Boulder, Colorado. It houses the nation's largest collection of 
documents on retrofitting. Each document has been categorized and 
summarized. The summaries have been entered into a computer data base that 
enables Center staff to quickly identify those documents most appropriate for 
an inquirer's needs. 

Contact the Center by calling 303/492-6818 between 9:00 and 4:00 Mountain 
Time, Monday through Friday, or by writing to the Natural Hazards Center, 
IBS No.6, Campus Box 482, Boulder, Colorado, 80309-0482. Upon receiving 
an inquiry, a Center staff person will review the database and retrieve 
summaries of those documents that appear most useful. 

The Center staff person may read excerpts from the document summaries over 
the telephone or mail printed document summaries to the inquirer. The 
Resource Center does not send a document to the inquirer; it only tells the 
inquirer how to obtain a copy. The staff may copy all or portions of a 
document that are in the public domain (especially those that are out of print). 

The cost of answering inquiries, including printing and mailing up to ten 
document summaries, is borne by the Resource Center. There is no cost for 
these services to any caller. The Center may charge a fee for copying a 
document or providing additional services. The fee is based on the actual cost 
of duplicating or performing the service. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures C -27 
January 1995 


The Resource Center 

DOCUMENT SUMMARIES 

All records on the Center's retrofitting publications are kept on document 
summaries. The summaries follow the adjacent format. This format provides 
all necessary data about a document on one page so the Center staff and the 
inquirer can quickly and easily identify that the document is appropriate. 
While no document takes more than one page, a different summary page may 
be used for each article in publications such as conference proceedings and 
edited collections of articles by different authors on different topics. 

KEYWORDS 

The Resource Center's computer program can search for any word. Three 

sections of the document summary list selected keywords that help the Center 

and the inquirer locate the documents they need. The Topic Keywords 

identify the floodplain management activity, the Focus Keywords explain how 

the topic is addressed, and the Audience Keywords list the type of reader the 

publication is directed to. 

Using the keywords can greatly assist in the document search. For example, a 
request for a book on retrofitting basements will yield more than 25 
publications. In most cases, the inquirer has a more specific interest. For 
example, if a caller wants a book that explains protecting basements from 
hydrostatic pressure to homeowners, the Center staff's search would be: 

Topic="pressures" and "basement" 

Focus= "techniques" 

Audience="lay persons" 

This particular search will locate two books (more will probably be added over 
time). The inquirer will be told about the books and how to obtain them and 
will also be sent the document summaries. 

C -28 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


AOPPENDIX D 

mEffmommlffilfflilo EMNr, 

ALLUVIAL FAN FLOODING


Appendix D: Alluvial Fan Flooding 

ALLUVIAL FAN FLOODING 

In mountainous regions in the 
west, floodwaters may spread out 
in a fan shape as they flow from 

the mouth of a watershed to the 
valley below. The floodwaters 
erode the steep slopes of the 
watershed and deposit sediment in 
a cone or fan shape over the flatter 
land. Overtime, this process 
creates a land form known as an 

alluvial

fan. 

Alluvial fan flooding is a hazard to communities in the mountainous 
regions of the western United States. Alluvial fan flooding 
is characterized by a sudden torrent of water capable of carry

ing rocks, mud, and debris that debouches from the steep 
valleys and canyons and spreads over the fan surface. The type 
of detailed flood damage mitigation information available for 
other flood-prone areas is limited for alluvial fan situations, but a 
profile of this type of flooding and general measures to mitigate 

its Impact arebeginning to emerge. 

Across the western United States alluvial fans are appealing to 
residential developers for their vistas, and pressure to construct 

rsdnildvlpr o hi its n rsuet osrc 

on fans is increasing as the valley floors become populated. 

Fan fofwacDevelopment over the last several decades has proceeded with 

by surging, rosion,

e scour, 
channel avulsion, mud and debris 
flows, and sheet flows on the lower 
portions of the fan surface. Each 

fan flood event and each fan can 
exhibit different flood characteris- 

tics. 

Water flowing from the narrow 
mouth of a basin and spreading 
out as it leaves the opening is said 
to debouch.* 

little cognizance of the potential for flood hazards. On most 
fans, there is evidence of past floods, but the history of development 
is relatively short and the consequences of a 100-year 
flood have not been confronted. Many fan communities are 

now preparing flood management and mitigation plans, but 
existing structures may have to rely on floodproofing measures 

to reduce flood damage. 

Contained in this appendix is a discussion of: 

* alluvial fan physical processes and how fan flooding differs 
from riverine flooding; 
an overview the code

of regulatory framework and buildig 
issues unique to fan areas; 

* techniques for integrating floodproofing/retrofitting with fan-
wide mitigation and master drainage plans; and 
* guidance on retrofitting design criteria. 
Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures D -1 
January 1995 


Appendix D: Alluvial Fan Flooding 

, I 

4i 

Figlure D- 1: Telluride, Colorado Fan 

It is recognized that development on alluvial fans may vary in 
density and may include large commercial, single- and multifamily 
residential, and/or municipal structures that can significantly 

affect local hydraulic conditions. Where high density development 
exists or where there are major structures oriented across 
potential flow paths, upfan channel-related mitigation measures 
such as channelization, flow diversion, and debris basins are the 
most feasible approach for hazard avoidance. Fan-wide master 
plans for zoning and fan-wide mitigation measures are crucial 
for successful protection of the community as a whole. Where 
master plans or mitigation schemes are inadequate or nonexistent, 
floodproofing and retrofitting of residences may provide the 

' only reasonable methods for flood loss reduction. Retrofitting 
can reduce future flood damage but is seldom recognized by the 
NFIP, particularly with respect to insurance premium rates. 

In the desert Southwest, alluvial fans are subject to clear water 
flooding and debris-laden frontal waves. In parts of the mountainous 
West, mudflows dominate fan evolution. Fans in the 

'I i1Pacific Northwest are prone to flood hazards related to sedi-. 
ment transport from less common sources, such as volcanic 
activity and logging practices. The following sections provide 

some general concepts and definitions of terms related to 

alluvial fans and floodproofing design. 

aid 

Figure D-2: Alluvial Fan Flooding Damage, Telluride, Colorado 

D -2 Enaineerinq Principles and Practices of Retrofiftinq Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

INTRODUCTION TO ALLUVIAL FANS

FAN MORPHOLOGY 

Both the hydraulic and hydrologic flood characteristics of alluvial 
fans are highly variable from fan to fan, which may be in different 
stages of episodic growth. A geologist, geomorphologist, 
hydrologist, or hydraulic engineer experienced in alluvial fan 
technology should be consulted to identify alluvial fan characteristics 
and the possible response to flooding. 

An alluvial fan is a conical- or fan-shaped land form located at 
the mouth of a watershed, where floodwaters debouch from the 
basin and spread over the valley floor. Alluvial fans evolve over 
geologic time as sediments (boulders, gravel, sand, and fines), erode 
from the steep watershed slopes and are transported by flood 

flows to the flatter fan surface. Sediments accumulate on the fan 

as the slope decreases, flows spread out, and the flow loses its 
ability to transport sediment The alluvial fan surface may be punctuated 
by deep channels or irregularly-shaped deposits formed by 
infrequent, often large flash flooding events. 

teobogic Apex 

Apex ~FFan 
Figure D-3: Rancho Mirage, California Channelized Zone 
Fan Damage (1979) Bid 
BraletdZone 
N 

_ e Termninus

n~~~~~~~~~~a 
ValleyFloor 

Figure D-4: Oblique View of an Alluvial Fan 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures D -3 
January 1995 


Appendix D: Alluvial Fan Flooding 

The fan apex, usually located near the intersection of the 
mountain watershed and the top of the fan, is the point where 
storm runoffemerging from the confined mountain channel onto 
the alluvial fan diverges into either multiple channels or uncon

fined flow. 

The fan terminus, or toe, is the intersection of the alluvial fan 
and the valley floor. Fan slope may become milder approaching 
the fan terminus, resulting in a concave profile. 

Alluvial fans emerging from adjacent mountain watersheds may 
coalesce and form an apron of alluvial material along the 
mountain front, disguising the presence ofthe fan. This apron is 
called a bajada. 

Three zones may be identified on the surface of an alluvial fan, 
reflecting the hydraulic and sediment-transport processes during 
a flooding event: 

* the channelized zone (not always noticeable below the apex 
of an active fan); 
* the braided zone; and 
* the sheet flow zone. 
The exact location of each zone on a given fan is dependent on 
flooding characteristics, but usually can be identified on the fan 
surface after a recent flood event. These zones are discussed 
throughout the text in relationship to feasible retrofitting alternatives. 

D -4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

The channelized zone is generally located at and below 
(downstream of) the fan apex. Flow within this zone is confined 
to well-defined channels, although channels may split or 
abruptly change direction. This zone is associated with hazardous 
flooding conditions related to high flow velocities, boulder 
and debris impact, and channel scour. If channels are deeply 
incised, this zone may extend further down the fan. 

As channels progress over an alluvial fan, they may become 
shallower and wider, and split into a system of multiple channels 
in an area ofthe fan defined as the braided zone. Flow in the 
braided zone has an unstable pattern of numerous interlacing 
shallow channels. Flood hazards in this zone are related to 
flood inundation and sediment deposition, rather than high flow 
velocity or debris impact. Large boulder transport is generally 
absent in this zone. 

Flow depths normally decrease in the downfan direction. 
Smaller channels may aggrade while other areas are subject to 
erosion or scour. Flow may continue to spread laterally until 
sheet flow is predominant. Sheet flow generally refers to flow 
depth less than 0.5 ft. Flood hazards in this sheet flow zone 
are usually limited to inundation by low velocity floodwater. 

Streets and buildings can change the composition of a fan zone 
by redistributing floodwaters over the fan surface. The altered 
flood response can impact areas on the fan that may have been 
considered outside the originally delineated flood hazard zone. 
As a fan is developed, delineation of flood hazards may 
change. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures D -5 
January 1995 


Appendix D: Alluvial Fan Flooding 

TYPES OF FAN FLOODING 

Water flooding dominates alluvial fan flows in the desert South

west. The fan flows are generally characterized by relatively 

stable channels near the apex ofthe fan, with sheet flow and 

sediment deposition on lower portions ofthe fan surface. Flood 
damage occurs from water inundation, scour around structures, 
and sediment deposition requiring cleanup. In contrast, the 
alluvial fans of the Pacific Northwest, Rocky Mountains, and 
the West Coast ranges can experience severe mud and debris 
flows whose surges can engulf entire buildings, resulting in 
structural damage, movement, or complete collapse. 

Alluvial fan processes and the resultant fan morphology are 
dependent upon hydrologic conditions of the upstream watershed. 
Factors contributing to devastating fan flooding include: 

I high intensity rainfall events on sparsely vegetated steep 
slopes; 

* steep watershed slopes with highly erosive soils or unstable 
geologic formations; 
* sediment buildup and storage in watershed channels; 
* saturated soil conditions from antecedent rain and snowmelt; 
* recent forest fires, logging, or other soil-destabilizing 
activities in the watershed; 
* intensity and configuration of development on the fan; and 
* failure of flood mitigation measures. 
Fan flooding can occur through the continuum of sediment 
transport processes from clear water flows to 
hyperconcentrated sediment flows such as mud floods and 
debris flows. 

D -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


'.1* 

The July 24, 1977 mud flows in 
Glenwood Springs, Colorado, 
resulted in approximately $500,000 
(1977 dollars) in damage, most of 
which involved mud removal. 

Appendix D: Alluvial Fan Flooding 

A water flood is the inundation ofthe fan surface from 
overbank discharge or rainfall/snowpack runoff. Fan water 
floods are common in the desert Southwest. Water flooding 
can cause damage by inundating the lower floor, scouring and 
undermining structures, displacing buildings from foundations, 
physically ripping or tearing apart structures, or depositing 
sediment in basements and yards. Sediment loads are less than 
20 percent ofthe total flow and do not significantly affect fluid 
flow properties. 

When the concentration of sediment in the flow reaches 20 to 
40 percent by volume, the flow is considered to be 
"hyperconcentrated" and can be defined as mud flow. Mud 
flows with 20 to 40 percent volume are more common in the 
Rocky Mountains and along the West Coast. These concentrations 
of sediment cause an increase in viscosity of the flow 
matrix and a corresponding increase in the flow competence 
(ability to transport large boulders). Mud flows can be destructive 
to buildings because they are usually associated with high 
velocity flows. In addition to the property damage cited above 
for a water flood, mud flows can cause severe property damage 
related to sediment deposition. Cleanup costs can be significantly 
higher for a mud flood than a water flood. 

Mud flows having a flow matrix with a sediment concentration 
ranging from 40 to 55 percent by volume are common in the 
alluvial fans ofthe Pacific Northwest and also occur in the 
Rocky Mountains. Damage results from inundation by mud, 
impact of mud frontal waves, and high lateral loading, which can 
result in structure collapse. Mud flows can raft large boulders 
and debris on their flow surfaces, causing substantial impact 
damage. Cleanup costs after a mudflow event can be severe. 

Debris flows are hyperconcentrated flows with a sediment 
concentration that may be greater than 55 percent by volume. 
They consist primarily of rolling and tumbling boulders and 
debris and only a limited amount of fluid for lubrication. Fifty 
percent or more of the particles in a debris flow are generally 
larger than sand. 

Engineering Principles and Practices of R etrofitting Flood-Prone Residential Structures D -7 
January 1995 


Appendix D: Alluvial Fan Flooding 

Debris flows are less likely than 
water or mud floods to occur, but 

can cause moredamagedue to the 
impactof high velocity bouldersor 
debris waves, which crash through 
building walls or knock structures 

off foundations. 

.DV 11 

A key characteristic of active fans 
is the presence of evidence of 
relativelyrecent (in geologic terms) 
floodflows. 

Channel avulsion is the episodic, and often erratic, shift of a 
channel's path. Channel avulsion maybe initiated by sediment 
deposition that can fill or block the channel, forcing the flow to 

create a new path, or by bank erosion, through which the flow 
will be diverted. The new flow path will often follow a steeper 
course. Structures located in the path of a newly forming 

channel are often undermined and destroyed. 

FAN TYPES 

Three types of alluvial fans are discussed in this manual; they are 
differentiated based on hydraulic and sediment transport 
processes: active alluvial fans, distributary flow systems, and 
inactive alluvial fans (French et al, 1993). Alluvial fans are also 
differentiated on the basis of flow conditions present on the fan 
between flooding events. Dry fans are associated with ephemeral 
streams; wet fans are associated with perennial streams. 
Virtually all alluvial fans in the southwestern states are dry fans. 

Active alluvial fans are generally associated with steep-

sloped watersheds with high sediment yields. Active fans 

aggrade overtime and are subject to debris flows, 

hyperconcentrated sediment flows, flash flooding, and aggrada

tion and degradation related to sediment transport processes. 

Channels near the apex avulse episodically in response to the 

high sediment supply. Fan growth is relatively uniform. Active 

fans are generally regarded as high flood hazard fans. Portions 

of active alluvial fans may have inactive surfaces. 

Distributary flow fan systems exhibit divergent or braided 

flow patterns. The channel proceeding downfan will split into 

one or more channels that may possibly recombine further 

downfan. These fan types are associated with watersheds 

where the sediment supply is in approximate equilibrium with 

the sediment transport conveyance through the system. 

Debris flow activity on the fan surface is limited to frontal 

waves. The flood hazard associated with distributary fans is 

generally water inundation, sediment deposition, and scour, 

resulting in a moderate or low flood hazard. 

D -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

Inactive alluvial fans are associated with watersheds in more 
geologically stable regions where the sediment transport processes 
on the fan exceed the sediment supply from the watershed. 
Inactive fans degrade over geologic time and channels 
are generally stable, creating a convergent pattern over the 
surface ofthe fan. The fan may actually be developing its own 
small watershed or drainage system. Recent sediment deposition 
on the fan surface, channel avulsion, and debris flows are 
absent. The flood hazard on inactive alluvial fans is usually 
moderate or low, although the steep fan slopes still have potential 
for severe erosion or sediment deposition if drainage conditions 
are altered. 

ALLUVIAL FAN FLOOD HAZARDS 

While alluvial fans present flood hazards found in riverine 
flooding such as inundation and differential hydrostatic loading, 
they are often compounded by high velocities, 
hyperconcentrated sediment flows, severe erosion, and extensive 
sediment deposition. Structures on alluvial fans may be 
susceptible to damage caused by high velocity water; lateral 
loading that forces structures off foundations or induces wall 
collapse; water inundation; scour and undermining of buildings; 
impact of mud, debris, and boulders; sediment burial; and 
landscape erosion. 

Most alluvial fan floods are caused by high-intensity, short-
duration summer thunderstorms. This is particularly true in the 
desert Southwest and Rocky Mountain region. Fan flooding on 
the western slopes of the West Coast mountains is often caused 
by longer duration rainstorms (e.g., West Coast frontal weather 
systems). Less common causes of fan flooding include spring 
snowpack melt, volcanically-induced flooding, and failure of 
water storage facilities. The flooding is often characterized by a 
frontal wave or "wall of water" that may carry boulders, trees, 
and debris; scour large channels; and carry off cars and property. 
The peak discharge in the flood wave may even overtake 
and become the frontal wave. If there is no rainfall in the valley 
or on the fan, the flood may arrive without warning. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

Floods debouching from the watershed onto the alluvial fan are 
initially confined to a channel or between canyon walls. Structures 
located near the fan apex can be subjected to high velocities 
(greater than 10 fps), deep flow depths (greater than three 
feet), and debris. Flows cutting new channels or eroding 

-existing channel beds may scour around buildings, tilting foundations 
and leaving unstable structures and large scour holes. 
After the flood event, layers of sediment deposition must be 
removed from yards, basements, or even first floors. 

On desert fans, the flow distributing itself between buildings and 
down streets can cause shallow flooding damage associated 
with high velocity flow in the streets include the inundation and 
transport of vehicles, filling of lowest floors with water and 

The frontal wave may collapse sediment, structural damage the upstream side of buildings from 

-t 
walls, topple structures, and rip
buildings from their foundations. flow and debris impact, landscape erosion, local scour at
building corners, and shallow sediment deposition. The block-
age of flood conveyance facilities, such as bridges and culverts,
or the failure of the storm sewer system can be exacerbate local
_ flooding on lower portions of the fan.

A very large, high velocity mud flood can be devastating, 
On fans with a history of mud and I resulting in the collapse of buildings and/or loss of life. Mud and 
debris flows, residents can debris flows can have frontal waves up to 15 feet high and have 

experience a more devastating level been known to sweep houses offtheir foundations, as in the 

of flood hazard. Lake Whatcomb, Whatcomb County, Washington, 1983
torrent debris flows, which deposited two houses into the lake
below. Mud flows have been found to travel at a rate ofthree
to 20 feet per second with flow depths of up to 15 feet.

Similarto frontal waves, surging will increase the flood hazard 
by subjecting structures to significantly higher flow depths and 
velocities. Surges have been observed at eight feet high, more 
than double the flow depth. 

Some watersheds are more prone to surges during flooding 
events due to channel geometry or sediment supply. Surges 
may entrain large boulders and other debris, increasing damage 
due to impact. In some cases, surging may also be due to the 
development of roll waves, a flow instability phenomenon often 
observed in open channels. 

D-10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


ok 

FandManagement 989)provides: 
and Management (o1989)provides 

related management issues, and 
briefly discusses retrofitting of 
individual residential structures. 

Another FEMA publication 

Risk Flood Hazard Areas: A 
Guidebookfor Local Officials 

specifically addresses alluvial fan 
flooding as a regulatory problem 
and provides outlines for the 
development of regulations and 
master plans for communities. This 
guidebook also summarizes the 
Dawdy Method for estimating 
flood frequency on alluvial fans 
and presents the Colorado Statute 
HB-1041 asamodel geologic 
hazard ordinance that includes 
alluvial fan flooding hazards. 

Appendix D: Alluvial Fan Flooding 

The hydrostatic pressure exerted on structural walls by sediment 
deposits can also be a significant flood hazard. Once the 
mud or debris flowhas ceased, the resulting deposition against 
a building can exert large lateral pressures that may be nonuni-

Hform across the face of the wall. In addition to the impact and 

differential hydrodynamic loading related to mud flows, the high 

specific weight ofthe deposited mud and the resulting differential 
loads can cause structural damage to buildings designed to 
withstand predicted water hydrostatic and hydrodynamic loads. 

Often large boulders, trees, or other debris will come to rest 

against the upfan side of a building, contributing to the nonuni

form lateral load on a wall. 

REGULATORY FRAMEWORK 

THE FEMA/NFIP FRAMEWORK AND 
ALLUVIAL FAN CONSIDERATIONS 

A detailed description of the National Flood Insurance Program 

(NFIP) and its minimum regulations for floodplain management, 

as well as a discussion of building codes are provided in earlier 

chapters. Within this regulatory context, alluvial fan flooding 

poses special problems for individuals and agencies trying to 

interpret guidelines that were prepared specifically for riverine 

flooding conditions. Although FEMA recognizes alluvial fan 

flooding hazards, guidelines do not specifically address mud and 

debris flow hazards or sheet flow inundation on urbanized 
alluvial fans. 

Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures D -11 
January 1995 


Appendix D: Alluvial Fan Flooding 

Unmapped urbanized fans are not subject to FEMA/NFIP 
insurance ormitigation criteria. In response to increased 
exposure to fan flooding, some communities have undertaken 
flood hazard delineation and have instituted local ordinances 
and regulations for fan development. In most states, there are 
no guidelines or regulations governing hazard delineation, zoning 
regulations, or mitigation for new construction. 

Mapping of alluvial fans forthe NFIP is conducted by a statistically 
based computer model called "FAN." FEMA provides a 
user's manual and program disk for those interested in performing 
the computations. The computations are based on certain 
assumptions regarding typical behavior of flow as it passes from 
the apex across the fan. The computations are not based on 
actual routing of flood hydrographs as applied in the normal 
riverine community flood insurance maps. Engineering firms 
with specialized alluvial fan analysis expertise have the capability 
to perform reasonable estimates of the physical processes that 
take place as the alluvial floods aggrade, degrade, change 
direction, and change concentration of sediment and debris 
loads. Such computations are generally not attempted for 
active fans because oftheir propensity to change physical 
configuration ofthe fan during floods. However, inactive alluvial 
fans with stabilized channels can often be successfully modeled. 
In view ofthe above concerns, retrofitting of buildings inthe 
floodplains must be based on estimated design parameters 
(velocity, scour, depth, sediment, debris, etc.) in order to 
reduce future flood damages. However, future damage must be 
expected when the parameters are exceeded. Homeowners 
can expect some relief from the more frequent flood events wit 
retrofitting, but this type of mitigation is recognized by FEMA 
only in its community rating system. 

D- 12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

The depth of flooding shown on 

the FIRMs for alluvial fans should 

be considered an estimate for the 
entire fan area, not an absolute 
value. Alluvial fan flood depths 
may vary from the given flood 

depth by several feet, depending 

upon local conditions. For that 

reason, site-specific analysis 

should be undertaken to accu

rately determine flood depth for a 

retrofitting project. 

A well-integrated approach to 
floodproofing and fan flood 
mitigation can reduce flood losses 
and possibly lower flood insurance 

costs where the measures are 
approved by FEMA. 

LOCAL FLOODPLAIN 
ADMINISTRATION 

In communities that have not adopted specific alluvial fan flood 
hazard regulations and ordinances, it is left to the developers 
and homeowners to mitigate flood hazards or implement 
floodproofing. Progressive communities have conducted 
geologic!geomorphic surveys and hydrologic studies to more 
effectively determine the extent of flood hazards. Once the 
potential for the flood hazard is understood, a permitting and 
review body can draft ordinances and regulations governing 
development on alluvialfans. 

In the communities investigated forthis manual, flood hazard 
delineation methods and flood hazard zoning regulations varied 
widely. Some existing alluvial fan flood hazard ordinances and 
zoning regulations establish "no build" zones and zones where 
development is allowed contingent on mitigation or retrofitting. 
A few ordinances address impact loading, downfan flood 
impacts, and freeboard. Tasks, such as mitigatingfan flood 
hazards, recommending floodproofing techniques, and providing 
comprehensive fan flood protection are being accomplished in 
differentways locallyfrom community to community. 

INTEGRATION WITH COMMUNITY 
PLANNING 

Residential retrofitting methods should be compatible with 

comprehensive alluvialfan flood hazard mitigation and master 

drainage plans. Integration of the retrofitting method with 

existing drainage and mitigation measures (such as streets 

designed as conveyance channels) can reduce flood damage in 

densely populated neighborhoods. 

Enainearinn Princiriles Practices of Retrofitting Flood-Prone Residential Structures D -13 

. and c __ 
January 1995 

Fnniaar i .--_ni_,_ --. __ __.e 


Appendix D: Alluvial Fan Flooding 

There are areas on virtually every fan of such extreme flood 
hazard tat hazard avoidance is essential. If"no build" zones 
6 have been designated, building permits should be denied within 
these zones (often in the fan channelized and braided zone). 
Flood damage incuvedon densely 
Residences constructed in these high hazard zones prior to the 
berms, floodwalls, reinforced walls, or landscaping may result in 
disagreement regarding historical deflection ofthe flow. Buildings orientedto reduce hydrodyflooding 
conditions or newly namic loading may also redirect flows. Flow deflection may 
created flooding from flow result in increased flood hazards to residences that historically 
deflection. were subject to little or no flood hazard. Elevation of the 
structure on supporting members or the conveyance of flow 
between buildings potentially exposes a downfan property to 
increased flooding. Thus all proposed retrofitting measures 
should be designed to avoid increasing flood hazards to other 
properties. Local ordinances may specify that the proposed 
retrofitting must be able to pass the flood through the property 
or development without increased damage to others. NFIP 
regulations concerning conveyance around a new structure in 
AO Zones may also be applied to retrofitting situations. 

Integration offloodproofing methods with master drainage and 
fan-wide comprehensive mitigation plans will have the benefit of 
reducing downfan flood damage. Floodproofing should direct 
flows into desirable paths such as streets or dedicated flow-
through areas. Regulations may require setbacks from existing 
channels. Floodproofing should not encroach on setback 
distances. 

Finally, structural flood mitigation and floodproofing measures 
should also be integrated into the community master emergency 
plan to avoid impeding emergency services during a flood event. 
The diversion of flow by a floodwall into a designated emergency 
route may eliminate access to areas of the fan by emer

gency equipment. Community emergency planning information 
is available through the community planning department. 

D -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

STRUCTURAL FLOOD PROTECTION 
SOLUTIONS AND PLANNING 

Ideally, communities will have implemented master drainage and 
flood mitigation plans prior to development on alluvial fans. 
Master plans can address hazard avoidance alternatives that set 
aside areas with high flood hazard potential as open space or 
parklands. In addition, master drainage plans can include 
structural mitigation aimed at protection of developed portions 
of the fan, such as flow diversion channels and debris basins. 
These mitigation measures may eliminate the need to retrofit 
residences and may be more technically and economically 
feasible for the community. 

Master development or drainage plans can prohibit development 
in high flood hazard areas (zone near the fan apex) where 
the potential for catastrophic flooding, particularly related to 
mud and debris flows, exists. Most master plans, however, 
permit development in moderate to low flood hazard areas. 
Within the context of the master plans for drainage or development, 
regulation of unit layout and density can enhance hazard 
avoidance by designing for passage of floodwaters, dedicating 
areas for sediment deposition and ponding, and assigning 
emergency access routes. Approval of residential retrofitting 
measures should be contingent on compatibility with the master 
plan components. Retrofitting can negatively impact the 
downfan flood hazards when not considered in the context of a 
master drainage plan. 

Residential retrofitting measures may include elevation, floodwalls, 
levees, site grading, dry floodproofing, wet 
floodproofing, landscaping, or building reinforcement. Retrofitting 
measures can be either permanent, contingent, or emergency. 
In general, fan flooding occurs with very little warning, 
limiting the effectiveness of contingency or emergency measures 
that require human intervention. 

Fnninpprinn Prinrin~lpsand Practices of F RetrofittinoFlood-Prone Residential Structures D -15 
January 1995 


Appendix D: Alluvial Fan Flooding 

_V' 

SanDiego County, California, 
amendedits flood damage preven- 
tion ordinance (Ordinance No. 
7534) to require that any develop- 
ment on alluvial fans must not 
disrupt natural alluvial fan processes. 
The intent of this ordi-1) 
nance is that unhinderedflow 
conditionswill cause less damage 
than if the flow is disturbed in a 
haphazard way. At an enforcement 
level, the ordinance requires that 
flood flows must be returned to 
natural conditions upon exiting a 
property. This approach is more 
feasible where development 
density is low and engineered 
obstructionscause only limited 
disruptionto fan hydraulics. 
Where development density is 
moderateto high, this approach is 

not feasible because natural fluvial 
conditions no longer exist. 

POTENTIAL DOWNFAN IMPACTS OF 

FLOODPROOFING 

Homeowners,community officials, and design professionals 
must consider the hydraulic effects of proposed retrofitting 
measures on downfan properties. Flood protection must not 
create additional damage and liability during a flood event. The 
potential impacts of retrofitting measures fall into two categories: 

damage resulting fromthe diversion of flowfromoneproperty 
onto another; and 2) constriction of flow upstream resulting 
in higher flow depth and velocities. Three scenarios are presented 
to illustrate the potentially damaging impacts related to 
retrofitting. 

Scenario I: Flow diversion to contiguous properties as a 
result of retrofitting. 

Retrofitting measures such as a floodwal levee, or fill embankment 
divert the flow to an adjoining property or property across 
the street that has not been delineated within the flood hazard 
zone orhas not been historically inundated. Potential flood 

damage to the unprotected property may be avoided by 
redirecting the flows back to natural drainage ways or open 

spaces or insuring sufficient street and stormiwater system 
capacity. 

Scenario IT: Altered upfan flow depths and velocities as a 
result of retrofitting. 

An existing residential structure located with no development 
upfan has been retrofitted to protect against shallow sheet flow. 
In proposed fbrther development of the subdivision, two houses 
would be built directly upfan ofthis house. The two new 
houses would constrict the flow between them, subjecting the 
original house to a greater inundation flow depth, velocity 
impact, and scour than predicted. The retrofitting measures 
against shallow flows are then inadequate to protect the original 
structure against the new flooding conditions. 

D -16 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

This flooding scenario may be avoided by diverting the flow 

upfan of the new houses to existing drainage ways or streets. A 

community should place performance requirements on develop

ments in fan areas to avoid this situation, requiring the construc

tion of a diversion facility. 

Scenario III: Increased flow volumes to specific downfan 
areas as a result of retrofitting. 

Streets may be designed on alluvial fans to convey floodwaters 

as a mitigation measure. The capacity ofthese streets to 
convey upfan floodwaters may be exceeded if upfan urbanization 
or diversion measures are allowed that increase runoff into 

the streets. The volume of water reaching the lower developed 
portion of the fan will increase, thus subjecting potential buildings 
to greater flow and potential damage. To avoid increased 
damage to the downfan properties, upfan storage or flow 
diversion to an undeveloped location would have to be designed. 
Increasing the street conveyance capacity is generally 
not cost effective. This scenario illustrates the need for wise 
community planning prior to new development. 

DETAILED DESIGN PRACTICES 

OPEN SPACE AND STRUCTURE 
RELOCATION 

There is potential for flooding over the entire surface of active 
alluvial fans. The channelized zone experiences the greatest 
depths, velocities, and sediment transport capability and is 
particularly prone to severe flood hazards. NFIP regulations 
may not adequately address all the hazards presented on the 
fan. Existing pre-FIRM structures are subject to substantial 
damage/substantial improvement criteria. 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures D -17 
January 1995 


Appendix D: Alluvial 

Fan Flooding 

As part of a master drainage or development plan on the fan, 
some communities may considerpurchasing areas of high flood 
hazard and relocating existing homes. Public ownership of these 
lands allows the greatest flexibility in comprehensive fan flood 
hazard management. The floodplain administrator can use the 
channelized zone to build flood mitigation structures such as 
debris basins and channels and dedicate open space for sediment 
deposition. Removing development from areas of highest 
hazard relieves the community of all or part ofthe costs related 
to flood mitigation studies, regulation of building improvements, 
and cleanup costs following a flood event. Open space also 
enhances the aesthetics ofthe fan. 

Master drainage plans, hazard zone delineation, building codes, 
public purchase of land, open space dedication, and land trades 
are all considerations for structure relocation. (Often, however, 
properties in the fan are quite expensive, which would preclude 
a buyout.) Although relocation is a significant undertaking, it 
may be economically feasible considering the potential threat to 
lives and property on the upper reaches of the fan. 

STRUCTURAL DESIGN -BUILDING 
CODES 

Minimum structural design requirements for buildings in flood-

prone areas have been established by the NFIP and the Interna

tional Conference of Building Officials Uniform Building Code 

(UBC). The UBC, generally adopted in most western states, 

addresses building requirements for structures located in riverine 

flood hazard areas designated by approved flood insurance 

maps or the local floodplain management ordinance. Although 

the UBC does not specify building requirements related to 

alluvial fan flood hazards, many ofthe floodproofing concepts 

discussed can be applied. 

D -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

Under the UBC, building design is required to withstand the 
forces associated with the base flood level of the 1 00-year 
flood event. The UBC requires the use of well-established 
engineering principles in the design of structural members to 
resist flotation, stress increases, overturning, collapse, or 
permanent lateral movement due to flood-induced loads (hydrostatic, 
hydrodynamic, and impact loads). Reconciliation of 
discrepancies between the different codes can be made by 
referring to the Code Compatibility Report, Appendices A 
through F, (FEMA, Oct. 1992). 

Within designated A zones (equivalent to FEMA FIRM Zone 
A), the UBC requires that the lowest floor of new or substantially 
improved residential buildings be situated at or above the 
base flood elevation. The Code makes an exception for 
enclosed spaces below the base flood elevation, provided that 
the space is used only as "building access, exits, foyers, storage, 
orparking garages." 

ELEVATION TECHNIQUES 

New or substantially improved/damaged structures must be 
elevated at least to the flow depth indicated on the FIRM, or at 
least two feet if no depth is given. Elevation can effectively 
remove the habitable positions of a structure from contact with 
floodwaters and in most instances mud and debris flows. The 
NFIP and UBC require that residential structures be elevated to 
the height of the base flood elevation (or flow depth in the case 
of alluvial fans). Local regulations may also require additional 
freeboard. In areas of potential mud, debris, and high-velocity 
flows, additional freeboard should be considered. Although 
elevating structures may be an expensive flood protection 
technique for retrofitting homes, itmay still present a viable 
retrofitting option and should be evaluated for feasibility. 

Elevation on posts or piles permits floodwaters to pass underneath 
the structure, causing little obstruction to flow. A properly 
designed pile will carry all inherent structural loads and lateral 
loads (hydrodynamic and impact) expected during the design 
flood. In addition to normal geotechnical concerns, the most 
important design consideration for piles is potential scour (refer 

Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures D -19 
January 1995 


Appendix D: Alluvial Fan Flooding 

to discussion of scour in Chapter IV). Spacing of posts and 
piles should be relatively wide to minimize flow constriction or 
the collection of debris found in the watershed or on the fan. 
The failure of supporting members could potentially cause more 
damage than inundation of a non-elevated structure. 

Elevation of a residence on fill is a design practice for new 

homes on alluvial fans in the southwestern United States and is 
regulated by local ordinances. This floodproofing technique is 
most viable on fans regulated by a master drainage plan that 
specifies flood conveyance facilities and drainage ways. Fill 
slopes can be oriented to divert flow in a desired direction. 
Elevation on fill, in contrast to piles and posts, may impose a 
significant obstruction to the flood path; therefore, constriction 
and diversion of flow onto adj acent properties is a concern. Fill 
should consist of easily compactible sand or gravel. Application 
and compaction should follow standard engineering practices. 
The toe ofthe fill slope must be protected from scour. This 
slope protection should be extended at least two feet below 
ground surface. The fill slope above the ground surface should 
be protected by rock riprap or vegetation to at least the base 

flood level. 

DRY FLOODPROOFING 

Dry floodproofing consists ofthe application of an impermeable 
membrane to the walls of a structure to the flood protection 
elevation. Dry floodproofing is appropriate for shallow flooding 
zones where the base flood elevation is not determined. This 
technique can be used for brick veneer and masonry structures 
where floor slabs are rigidly connected to walls. 

External dry floodproofimg consists of an impervious layered 
sheet material such as tar or asphalt bitumen applied to the 
exterior ofthe building. Excavation around the foundation may 
be required to externally floodproof building material below the 
Dry floodproofing is not allowed ground surface subj ect to soil saturation during the flooding 
by FEMA for new or substantially event. Membrane materials should be designed to resist all 
improved or damaged residential expected flooding conditions including scour, abrasion, impact, 
structures located in a SFHA. and hydrostatic and hydrodynamic pressures. On alluvial fans 
subject to mud and debris flows, the external membrane cannot 
be exposed to the flow. External membranes may not be 
required onthe downfan side of a building. 

D -20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

Internal membranes may also be used but, in general, are more 
prone to leaks than external membranes, which are held tightly 
against the structure by hydrostatic pressure. As with external 
membranes, any points of discontinuity may leak and require 
additional floodproofing during installation. Leaks are most 
likely to occur at membrane seams, construction joints and 
corners, and where pipes and ducts penetrate the membrane. 

Waterproofing materials that may be considered include polyethylene, 
PVC, polyurethane, and polyisobutylene. This 
method also requires rigid connections between floor slabs and 
walls to prevent leaking. The foundation and walls should be 
protected against scour, decay, and cracking with the use of 
treated building materials and armored backfill. For existing 
structures being considered for remodeling or rehabilitation, this 
will require the application of additional foundation materials to 
standing walls. 

BUILDING REINFORCEMENT 

Structures located in areas subject to hydrodynamic and impact 
forces from water, mud, and debris flows can be protected 
against damage and collapse through structural reinforcement of 
upfan walls. Reinforcement may include the addition of structural 
supporting members or an exterior facade, or the removal 
and replacement of existing walls. 

In conjunction with the reinforcement of upfan walls, removal of 
openings in the upfan wall should be investigated. If these 
openings are removed, they may need to be replaced with 
openings on other walls. Weak points in the bearing wall, such 
as windows, doors, and utility connections, may leak or fail 
under flooding conditions and should be reinforced and 
floodproofed or eliminated. Window wells should be retrofitted 
with reinforced waterproof coverings and backfilled. Doors 
and windows located wholly or partially below the expected 
base flood level should likewise be eliminated or replaced with 
reinforced water-tight coverings up to the level of the base flood 
plus freeboard. Reinforcement of upfan walls should be designed 
for impact pressures and hydrodynamic loading related 
to mud and debris flows. 

Engineering Principles and Practices of F RetrofittingFlood-Prone Residential Structures D -21 
January 1995 


Appendix D: Alluvial Fan Flooding 

Figure D-5: Reinforced Upfan Walls 

I t: 

Figure D-6: Reinforced Upfan Walls 

D-22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

FLOODWALLS AND LEVEES 

Floodwalls and levees may be constructed on the upfan portion 

of a building to protect it from the forces of moving water and 

inundation. This method of floodproofing may consist of blocks 

(brick or cinder), concrete, railroad ties, and other construction 
materials that would withstand the design hydrostatic, hydrodynamic 
and impact loads. The height of floodwalls should be 
based on a specified design maximum flow depth plus freeboard. 
The estimated freeboard should include velocity head, 
wave height, potential flow runup, potential for sediment deposition 
against the wall, and surging. Floodwalls should be 
constructed below grade to provide protection from scour. 
Stability design should take into account material removed by 
scour. 

Protecting IK.esidencein Colorado

Figure D-7: Floodwall 

CnninnarinnnuaIy 1w995" ' Prinninlac" alndPracticae of RatrnfiftinniFlood-Prone Residential Structures D -23 

. -

January 1 995 


Appendix D: Alluvial Fan Flooding 

Levees are raised fill embankments along an existing or planned 
conveyance channel designed to confine or prevent inundation 
ofthe floodplain. Frequently utilized on riverine floodplains, 
leeves may require some modification when applied on alluvial 
fans. On alluvial fans, levees can divert flow around a subdivision 
or residence, or they may provide protection along a 
natural or engineered channel through a developed area. 
Levees should be designed to protect against scour and levee 
slope erosion. 

Figure D-8: Debris Flow Levee 

On steep alluvial fan slopes, the complete enclosure of a 

structure by a floodwall and levee is not usually necessary. The 

downfan side of the property does not require a floodwall when 

the ground slopes significantly. On the other three sides, the 

retrofitting design should consider access to the building and 

grounds. Closures should not be included in the protective 
structure because failure of the closure may cause complete 

failure of the floodwall/levee. In some instances, floodwalls 
have been used primarily for protection against mud and debris 
flows, without restricting seepage but assuring structural stabil

ity. 

D -24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 
January 1995 


Appendix D: Alluvial Fan Flooding 

The U.S. Army Corps of Engineers (draft report, undated) 
recommends avoiding this retrofitting alternative for mud and 
debris flows where the overtopping or failure of levees and 
floodwalls can cause catastrophic damage in excess of the 
damage that would have occurred in an area devoid of protection. 
In addition, mud and debris flow deposition on the upfan 
side of the wall or levee may increase the potential for overtopping 
or runup. 

Floodwalls and levees are an excellent method of flood protection 
for an existing structure. Their use is most appropriate in 
fan flood hazard zones characterized by low and moderate 
velocity flows or mud flows in low density development. 
Design height for floodwalls and levees should be limited to 
three to four feet. This restricts their use where scour and 
debris conditions are prevalent. 

: It bro .M arW I II 
Figure D-9: Diversion Levee in Col lorado 

Enaineerina PrinciDles and Practices of I:IetrofittincaFlood-Prone Residential Structures D -25 
January 1995 


SITE GRADING 

Site grading on alluvial fans is constrained by the fan slope, 
street and driveway cuts, and drainage. Site grading can be 
effective as a flood protection method for existing homes if the 
predicted flooding is relatively shallow and the rnoff from the 
property can be incorporated into and handled by the 
stormwater facilities designed as part of a drainage plan. Site 
grading should be considered for the sheet flow zone of alluvial 
fans (< 1 foot in depth). Grading a lot for flood protection may 
consist of grading the lawn away from the house at 1:12 slope 
for a minimum distance of six feet perpendicular to the house 
(UBC, 1991), creating a swale around the house, sloping the 
lawn or yard to the street or driveway, or establishing grading to 
work in conjunction with other damage reduction measures 
such as levees. It is important to determine if waters concentrated 
by a grading plan will cause unnecessary erosion or flow 
on adjacent properties or overload existing storm facilities or 
streets. 

Typical Plot Plan 

Stb. 

Figure D- 10: Typical Subdivision Plot Plan 


Appendix D: Alluvial Fan Flooding 

Care should be taken to avoid the risk of flood damage through 
negative site grading. Drainage ways and depressions should 
be located to minimize ponding and diversion of floodwaters 
near the structure. Excavation of the fan slope for a lawn may 
direct floodwaters toward the structure, causing more damage 
than if the yard were left at grade. Finally, any natural drainages 

or levees should remain undisturbed. 

A ditch or shallow trough excavated around a structure or the 
property perimeter will collect and convey floodwater. The site 
may be graded to convey floodwater to the ditch. The disposal 
of ditch water should be considered with respect to the fan-
wide master drainage plan. It may be possible to pass the 
water around the protected structure, then disperse the flow 
before leaving the property. Even in fan areas where the 
sediment loads are not important, ditches or troughs will require 
frequent maintenance for maximum effectiveness when a flood 
event occurs. 

Rural Plot Plan 

STREET 

Figure D-l 1: Typical Rural Plot Plan 

Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures D -27 
January 1995 


Appendix D: Alluvial Fan Flooding 

LANDSCAPING 

Standard landscaping designs may be applied for floodproofing 

measures in fan zones of shallow flooding (less than one foot). 

Flood flows may be dispersed with landscaping that splits the 

flow with wedged flow barriers or spreads the flow through 

vegetated areas. Landscaped low mounds may be oriented to 

divert flows to an on-site drainage path or off-site flow convey

ance area, such as the street or dedicated flow-through area. 

Mounds may be vegetated or armored to withstand erosion 

from low-velocity water flow and raindrop impact. Landscap

ing may not be compatible with flows having high sediment 

loads. Sediment deposition may render the landscaping design 

ineffective. 

Uniform Sheet Flow 

Depressed
Flow Through
Dispersion Area

A

Wedge 

Tree 

Uniform Sheet Flow 

Uniform Sheet Flow 

Figure D- 12: Typical Dispersion Design 

D -28 Enaineering Principles and Practices of Retrofittina Flood-Prone Residential Structures 
January 1995 


APPENDIX E

BENEFIT/COST ANALYSIS OF 
HAZARD MITIGATION PROJECTS 
USER'S GUIDE 


BENEFIT-COST ANALYSIS
OF
HAZARD MITIGATION PROJECTS

RIVERINE
and
COASTAL A-ZONE
FLOOD

MANUAL VERSION 1.0 

January 5, 1995 

Applicable to All Software Versions 1.0x 

Prepared for the Federal Emergency 
Management Agency 


TABLE OF CONTENTS 

CHAPTER 1 THE ROLE OF BENEFIT-COST ANALYSIS 
IN HAZARD MITIGATION PROJECTS ....................... 1-1 

Introduction ..................................................... 1-1
Acknowledgements .......................................... 1-1
Hazard Mitigation Projects ............... ..................... 1-1
The Benefit-Cost Program ............... ..................... 1-1
Level One vs. Level Two B-C Analyses ........ .................. 1-2
What Data are Needed for B-C Analysis? ........ ................. 1-2
Myths and Misconceptions About Benefit-Cost Analysis ...... ............. 1-3
Overview of User's Manual .......................................... 1-4

CHAPTER 2 GETTING STARTED . ..................................... 2-1

Hardware and Software Required ............... ..................... 2-1
Computer Hardware .......................................... 2-1
Computer Software .......................................... 2-2
Windows ............................................ 2-2
Quattro Pro for Windows ........... ..................... 2-3
Installing the Benefit-Cost Programs ............. ..................... 2-5
Network Systems ........................................... 2-5
Stand-Alone Computers . ...................................... 2-5

CHAPTER 3 PROGRAM BASICS ...................................... 3-1
Starting Quattro Pro for Windows (QPW) .......... .................... 3-1
Start Windows ............................................. 3-1
Start QPW .............................................. 3-1
Opening Files .............................................. 3-2
Screen Display ............................................. 3-3
Zoom List .............................................. 3-3
Moving Around in the Programs . ..................................... 3-4
Several Easy Ways .......................................... 3-4
Benefit-Cost Menu Tree . ..................................... 3-4
Basic Commands and Procedures ............... ..................... 3-7
Naming and Saving Files ................ ..................... 3-7
Save ............................................... 3-7
Save As . .............................................. 3-7
OOPS! . ..............................................

3-9
Start a New Benefit-Cost Analysis .......... .................... 3-9
Exit From a Benefit-Cost Program .......... .................... 3-9
Run a Different Benefit-Cost Program ........ .................. 3-10
Exit from QPW ............................................ 3-10
Exit from Windows .......................................... 3-10
Cell Colors .............................................. 3-11
Unprotected Blocks .......................................... 3-11
Protected Blocks ........................................... 3-11
Data Entry .............................................. 3-12
Correcting Errors .......................................... 3-12
Entering Commas and Dollars ........... ..................... 3-13

ii 


Entering Addresses ........................................ 3-13
Syntax Error .............................................. 3-13

CHAPTER 4 TUTORIAL . ........................................ 4-1
Level One and Level Two Benefit-Cost Analyses ........ ................ 4-1
Level One (Minimum Data) B-C Analysis ......... ................ 4-1
Level Two (Detailed) B-C Analysis ............ .................. 4-2
Starting the Tutorial . ........................................ 4-3
Level One Data .................................................. 4-4
Project Information .......................................... 4-4
Building Data .......................................... 4-6
Building Contents .......................................... 4-8
Displacement Costs Due to Flood Damage ....... ................ 4-9
Value of Public/Nonprofit Services .......... ................... 4-10
Rent & Business Income . ................................... 4-11
Mitigation Project Data ...................................... 4-12
Flood Hazard . .......................................... 4-14
Benefit-Cost Results .......................................... 4-15
Print Menu .............. ............................ 4-17
To End the Tutorial .......................................... 4-17

CHAPTER 5 BENEFIT-COST MODEL: GUIDANCE ....... ................. 5-1
Introduction. ........................................... 5-1
Exact Data vs. Estimates .......................................... 5 -2
Data Requirements ............................. 5-2
Level One (Minimum Data) B-C Analysis ............................. 5-3
Level Two (Detailed) B-C Analysis . ............................. 5-5
Expediting B-C Analysis ............................. 5-6

CHAPTER 6 BENEFIT-COST MODEL: LEVEL ONE ANALYSIS ............. 6-1
Introduction .................................................... 6-1
Data Differences: Public, Commercial, & Residential Buildings ..... ........ 6-1
Data Input: Color Codes . ........................................... 6-2
Level One Data .................................................. 6-3
Introduction................................................. 6-3
Project Information . .......................................... 6-3
Building Name, Address, City, State, Zip ..... ............... 6-3
Owner . .............................................. 6-3
Contact Person ............. .......................... 6-4
Disaster Number ...... I ............................... 6-4
Project Number ............. .......................... 6-4
Application Date ............ .......................... 6-4
Discount Rate .............. .......................... 6-4
Scenario Run ID ....... I .............................. 6-5
Analyst ......................................... 6-5
Building Data ............. 6-5
Building Type ......... 6-5

............................... 

iii 


BuildingInformation . ................................... 6-6
Zero Flood Depth Elevation ........ ................ 6-6
Numberof Stories above Grade .......... ........... 6-6
ConstructionDate . ................................. 6-6
HistoricBuilding Controls ......... ................. 6-7
Building Size and Use ................ .................. 6-7
Total Floor Area ............. .................... 6-7
Area Occupied by Owner or Public/Nonprofit Agencies ... 6-7
BuildingValue ........................................ 6-7
BuildingReplacementValue ($/sf ....... ............ 6-8
Total Building Replacement Value ................... 6-8
DemolitionThreshold ............................... 6-8
Building Contents ................................. 6-9
Contents Description ................................. 6-9
Total Value of Contents ................................. 6-9
Value of Contents ($/so ..................... 6-10
Displacement Costs Due to Flood Damage ...................... 6-10
Rental Cost of Temporary Building Space ($/sf/month) ........ 6-10
Rental Cost of Temporary Building Space ($/month) ... ...... 6-10
Other Displacement Costs ............................ 6-10
Total Displacement Costs ............................ 6-10
Value of Public/Nonprofit Services ............................ 6-11
Description of Services Provided .......... ........ , 6-11
Annual Budget ............. ............... 6-11
Is Rent Included? ............................ 6-12
Proxy Rent .................. 6-12
User-Entered Rent Estimate ............................ 6-12
Cost of Providing Services...........-.......... 6 12
Post-DisasterContinuityPremium ......... .... . 6-12
Total Value of Lost Services ............ ................ 6-13
Rent & Business Income .................................... 6-14
Total Monthly Rent from All Tenants .... 6-14
Estimated Net Income of Commercial Businesses ............ 6-14
Mitigation Project Data ................... 6-14
Select Mitigation Measure .............. ................. 6-14
Project Description .................. 6-15
Project Useful Life .................................... 6-15
MitigationEffectivenessEstimates ......... .............. 6-15
Elevation.................................... 6-15

Relocation/Buyout

...... .. .......... 6-16

Flood Barriers ......... ......... 6-16 
O ther ................................ ........ 6-16 
Mitigation Project Costs ......... ......... 6-17 
ProjectCost ...................... 6-17 
Base Year of Costs ................... 6-17 
Annual Maintenance Costs . ..... 6-17 
Relocation Costs for Mitigation Project . . 6-17 
Relocation Time Due to Project . . 6-18 
Rental Cost During Occupant Relocation .. 6-18 

iv 


Other Relocation Costs ...... ............... 6-18
Total Relocation Costs ...... ............... 6-18
Total MitigationProject Costs ...... ................ 6-18

CHAPTER 7 BENEFIT-COST PROGRAMS: FLOOD HAZARD RISK ..... ........ 7-1
Introduction . ................................................ 7-1
Level One Analysis .. . ........................................ 7-1
Level Two Analysis .7-1
Flood Hazard Risk .7-2
Carry Over Information . 7-2
Flood Hazard Data -Riverine .7-2
Flood Discharge Data .7-2
Flood Elevation Data .7-2
Figure 7-1 Example Flood Profile Graph ........ .................. 7-4
Flood Hazard Data -Coastal A-Zone ............. ..................... 7-5
Flood Elevation Data ......................................... 7-5
Figure 7-2 Typical Transect Schematic ........ ................... 7-7
Figure 7-3 Transect Location Map ......... ..................... 7-8
Expected Annual Number of Floods ............. ..................... 7-9
Default Flood Estimates . ...................................... 7-9
User-Entered Flood Estimates ........... ..................... 7-10
Level Two Flood Analysis ............... ..................... 7-10
Flood Hazard Risk: Technical Appendix ........... ................... 7-11
Flood Recurrence Intervals .............. ..................... 7-11
Flood Elevation vs. Flood Depth .......... ..................... 7-11
Review of Scientific Notation ............ ..................... 7-12
Flood Exceedance Probabilities .......... ..................... 7-12
Expected Annual Number of Floods -Riverine ...... .............. 7-13
Expected Annual Number of Floods -Coastal A-Zone ..... ......... 7-14

CHAPTER 8 BENEFIT-COST PROGRAMS: LEVEL TWO ANALYSIS .........8-1

Introduction .................................................... 8-1 
Level Two Data: Building Depth-Damage Function ....................... 8-2 
Reference Information From Level One Data ...................... 8-2 
Building Depth-Damage Function (DDF) ......................... 8-2 
Building Depth-Damage Table .8-3 
Default Building DDF .8-3 
FIA Depth-Damage Table. 8-4 
User-Entered Building DDF .8-6 
Modified Building DDF .8-6 
Comments: Building DDF .8-7 
Level Two Data: Contents Depth-Damage Function .8-8 
Reference Information from Level One Data .8-8 
Contents Depth-Damage Function (DDF) .............. 8-9 
Contents Depth-Damage Table .8-9 
Default Contents DDF .8-9 
User-Entered Contents DDF .8-9 
Contents DDF ($) . ; 8-10 

v 


Comments: ContentsDDF ............. ....................... 8-10
Level Two Data: Displacement Time .......... ...................... 8-11
Reference Information From Level One Data .......... v .......... 8-11
DisplacementTime Estimates .......... ...................... 8-12
Displacement Time Estimate Table ....... ................. 8-12
Default Displacement Time Estimates ...... ............... 8-12
User-Entered Displacement Time Estimates ..... .......... 8-12
DisplacementCosts($) .......... ...................... 8-13
Rental IncomeLosses ........... ...................... 8-13
Comments: Displacement Time Estimates ...... ................. 8-13
Level Two Data: Functional Downtime .......... ................... 8-14
Reference Information from Level One Data ...................... 8-14
Functional Downtime Estimates ............................... 8-15
Functional Downtime Table ............................. 8-15
Default Functional Downtime Estimates ..... .............. 8-15
User-Entered Functional Downtime Estimates ..... ......... 8-15
Value of LostServices ......... ........................ 8-16
Lost BusinessIncome ......... ......................... 8-16
Comments: Functional Downtime ............................. 8-16
Level Two Data: Mitigation Project Effectiveness ....................... 8-17
Reference Information from Level One Data ...... ............... 8-17
Mitigation Effectiveness (Percent of Damages Avoided) ..... ........ 8-18
Mitigation Effectiveness Table ........................... 8-18
Building Damages Default Effectiveness (%) ..... ........... 8-18
Building Damages User-Entered Effectiveness (%) .... ....... 8-19
Contents Damages Default Effectiveness (%) ..... .......... 8-19
Contents Damages User-Entered Effectiveness (%) .... ...... 8-19
Other Effectiveness Assumptions ........................ 8-20
Comments: Mitigation Effectiveness Estimates ..... .............. 8-20

CHAPTER 9 BENEFIT-COST MODEL: RESULTS ......................... 9-1
Introduction .................................................... 9-1
Summary of Damages Before Mitigation ............................... 9-2
Scenario Damages Before Mitigation ............................ 9-2
Expected Annual Damages Before Mitigation ...... .................. 9-3
Interpreting Damages Before Mitigation .......................... 9-3
Summary of Damages After Mitigation ............................ ...9-4
Scenario Damages After Mitigation .............................. 9-4
Expected Annual Damages After Mitigation ....................... 9-5
Interpreting Damages After Mitigation ............................ 9-6
Benefits .................................................... 9-7
Expected Annual Benefits from Mitigation ........................ 9-7
Benefit-CostResults . ............................................. 9-8
Reference Information from Level One Data ...................... 9-8
DiscountRate .............. .......................... 9-8
Project UsefulLife ........... .......................... 9-9
Present Value Coefficient ............................... 9-9
Summary of Expected Annual Damages and Benefits ..... ......... 9-10

Vi 


Expected Annual Damages and Losses Before Mitigation ...... 9-10
Expected Annual Damages and Losses After Mitigation ....... 9-10
Expected Annual Benefits ......... ..................... 9-10
Present Value of Benefits ......... ..................... 9-11
Summary of Project Benefits and Project Costs ...... ............. 9-11
Project Benefits ................ ...................... 9-11
Project Costs . ........................................ 9-11
Benefits Minus Costs ........... ....................... 9-11
Benefit-Cost Ratio ............. ....................... 9-11
Interpreting Benefit-Cost Results ....... .................. 9-12
Summary ............................................ 9-14
Single-Valued Data Entries ........ ...................... 9-14
Data that Vary by Flood Depth ....... ................... 9-14
Summary of Benefits and Costs ......................... 9-14

CHAPTER 10 BENEFIT-COST MODEL PRINT-OUT .......................10-1

CHAPTER 11 GLOSSARY ........................................... 11-1

..... A-1

APPENDIX 1 ECONOMIC ASSUMPTIONS AND EQUATIONS ............. 
Benefit-Cost Program .............. ............................... A-1
Economic Assumptions for Modeling Benefits ........................... A-3
Underlying Assumptions ...................................... A-3
Detailed Economic Assumptions and Equations .................... A-5
Scenario Damages .................................... A-5
Building Damages ..................................... A-5
Contents Damages .................................... A-6
Displacement Costs .................................... A-6
Lost Business Income ................................. A-7
Rental Income Losses ................................. A-7
Public/Nonprofit Services Lost ............................. A-8
Expected Annual Damages ............................... A-8
Expected Annual Benefits ............................... A-9
Total Expected Annual Benefits ........................... A-9
Benefits .............................. A-10
Costs .............................. A-10
Benefit-CostRatio. .............................. A-11
Present Value Criterion .............................. A-1I
Technical Economic Terms ........... ................... A-12
Benefit-Cost Analysis ............ .................. A-12
Cost-Benefit Analysis . ................................. A-12
Cost-Effectiveness Analysis ............................... A-12
Economic Efficiency . ................................. A-12
Economic Impact Assessment ................................ A-13
Informal Benefit-Cost Analysis ................................ A-13
Risk-Benefit Analysis . ................................. A-13
References............................................... A-14

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VERSION 1.0 12129/94 THE ROLE OF BENEFIT-COST ANALYSIS

CHAPTER 1 

THE ROLE OF BENEFIT-COST ANALYSIS 

Acknowledge-
ments

Hazard
Mitigation
Projects

The Benefit-Cost 
Program 

IN HAZARD MITIGATION PROJECTS 

Introduction 

This manual and accompanying software were prepared by Goettel & 

Horner Inc. for the use of the Federal Emergency Management Agency 

(FEMA) in conducting benefit-cost analyses of hazard mitigation 

projects. This manual is applicable to both the Riverine and Coastal 

A-Zone Flood Benefit-Cost software for the assessment of hazard 

mitigation projects; other modules are applicable to Coastal V-Zone 

Flood, Hurricane Wind, and Seismic hazard mitigation projects. 

Hazard mitigation projects are specifically aimed at reducing or 

eliminating future damages. Although hazard mitigation projects may 

sometimes be implemented in conjunction with the repair of damages 

from a declared disaster, the focus of hazard mitigation projects is on 

strengthening, elevating, relocating or otherwise improving buildings, 

infrastructure or other facilities to enhance their ability to withstand the 

damaging impacts of future disasters. In some cases, hazard 

mitigation projects may also include training or public-education 

programs if such programs can be demonstrated to reduce future 

expected damages. 

Benefit-cost analysis provides estimates of the "benefits" and "costs" of 

a proposed flood hazard mitigation project. The benefits considered 

are avoided future damages and losses which are expected to accrue 

as a result of the mitigation project. In other words, benefits are the 

reduction in expected future damages and losses (i.e., the difference in 

expected future damages before and after the mitigation project). The 

costs considered are those necessary to implement the specific 

mitigation project under evaluation. 

Costs are generally well determined for specific projects for which 

engineering design studies have been completed. Benefits, however, 

must be estimated probabilistically because they depend on the 

improved performance of the building or facility in future floods, the 

timing and severity of which must be estimated probabilistically. 

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VERSION 1.0 12/29/94 THE ROLE OF BENEFIT-COST ANALYSIS 

VERSION 1.0 12/29/94 THE ROLE OF BENEFIT-COST ANALYSIS 

LEVEL ONE vs. 
LEVEL TWO 

B-C Analyses 

What Data are 
Needed for B-C 
Analysis? 

The benefits considered in the Benefit-Cost Program include: avoided 
damages to the building and contents, avoided displacement costs, 
avoided rental and business income losses, and avoided loss of 
public/nonprofit services. 

The "benefits" calculated by the program are expected future benefits 
which are estimated over the useful lifetime of the mitigation project. To 
account for the time value of money, a net present value calculation 
must be performed. This calculation is done automatically in the 
program, using the discount rate and project useful lifetime entered by 
the user. Results of benefit-cost calculations are presented two ways: 
first, the benefit-cost ratio (benefits divided by costs) and second, the 
present value criterion (benefits minus costs). 

The Benefit-Cost Program is designed to facilitate two different levels 
of analysis. A LEVEL ONE (Minimum Data) analysis relies heavily on 
default values built into the model and requires the minimum data input 
from users. A LEVEL TWO (Detailed) analysis allows the user to 
override default values with user-entered, building-specific estimates. 

The validity of any benefit-cost calculation and the robustness of 
conclusions drawn therefrom depend entirely on the validity of the data 
used in the calculations. Calculations based on detailed, building-
specific engineering analysis will be much more accurate (and 
correspondingly more useful) than calculations based largely on typical 
or default values of input parameters. 

For any benefit-cost analysis of a hazard mitigation project, basic 

information about the building/facility under evaluation is required, 

including: building type, size, replacement value, contents value, and 
various economic data about the use and function of the building. 

Estimates of the vulnerability of the building and contents to flood 
damage both before and after mitigation are particularly important. 

In most cases, few of the data inputs will be exact numbers. Rather, 

approximate data or informed, reasonable estimates will be used. See 

Chapter 5, Benefit-Cost Program: Guidance for helpful hints 

regarding exact data vs. reasonable estimates. 

In addition to data about the building under evaluation, benefit-cost 

analysis of flood hazard mitigation projects requires a quantitative 

assessment of the degree of flood risk at the site. This assessment is 

performed automatically by the Benefit-Cost Program using flood data 

input from a Flood Insurance Study and a Flood Insurance Rate Map, 

along with data on the Zero Flood Depth elevation of the building. The 

degree of flood risk at a given site profoundly affects the benefit-cost 

results. 

1-2 


VERSION 1.0 12/29/94 THE ROL O F BENFlT-eosT ANALYSRIS 

Myths and Misconceptions About Benefit-Cost Analysis

.I 

1. The benefits of hazard mitigation projects are avoided future 
damages. Benefits are not the damages experienced in the 
declared event, even if such damages would be 100% avoided 
by the mitigation project. Rather, benefits are the present value 
of the sum of expected avoided future damages for all levels of 
intensity of future disasters (e.g., floods). 
2. To estimate future damages (and the benefits of avoiding them), 
the probabilities of future events must be considered. The 
probabilities of future events profoundly affect whether or not a 
proposed hazard mitigation project is cost effective. The 
benefits of avoiding flood damage for a building in the 10-year 
flood plain will be enormously greater than the benefits for an 
identical building situated at the 1000-year flood elevation. 
3. Mitigation may not be cost-effective even though a particular 
facility experienced great damage in the declared event, if the 
event were a low probability (i.e., a 500- or 1 000-year) event. 
Conversely, mitigation may be cost effective even though the 
particular facility experienced little or no damage in the declared 
event, if the probability of future damage is high. 
4. The benefits of hazard mitigation projects for critical facilities 
such as hospitals, emergency operations centers, and fire 
stations, and for high occupancy facilities such as schools tend 
to be higher than the benefits of projects for non-critical or low 
occupancy facilities. The higher benefits arise because future 
damages and losses may be high if the hazards are not 
mitigated. However, just because a proposed hazard mitigation 
project is for a critical facility does not guarantee that the. project 
is cost-effective. On the contrary, even for critical facilities, 
hazard mitigation projects may not be cost-effective if the project 
is too expensive or the risk of future damage is not high enough. 
5. Each proposed hazard mitigation project must be evaluated on 
its own merits to compare the benefits and costs of a specific 
project. There are no "rules of thumb" which determine eligible 
and ineligible projects because the costs and benefits of each 
project are different. The benefits of a particular project may 
vary markedly depending on the vulnerability of the existing 
facility to damages and losses, the probabilities of future 
damages, and the effectiveness of the mitigation measure in 
avoiding future damages. 
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VERSION 1.0 12129/94 THE ROLE OF BENEFIT-COST ANALYSIS

Overview of User's Manual 

The User's Manual provides a comprehensive guide to conducting 
Benefit-Cost Analysis of Riverine and Coastal A-Zone Flood Hazard 
Mitigation Projects. 

Chapter 2, Getting Started, provides elementary guidance for novice 
users about loading and starting the Benefit-Cost program. 

Chapter 3, Program Basics, provides basic information about how to 
move around within the program, how to make data entries, etc. 

Chapter 4, Tutorial, provides a worked example illustrating the process 
of entering data and obtaining benefit-cost results. 

Chapter 5, Benefit-Cost Program: Guidance, provides helpful hints 
for conducting benefit-cost analysis, including data requirements, 
LEVEL ONE and LEVEL TWO analyses, and expediting benefit-cost 
analysis. 

Chapter 6, Benefit-Cost Program: Level One Analysis, provides a 

detailed discussion of all the data inputs necessary for a LEVEL ONE 
(Minimum Data), Benefit-Cost Analysis. 

Chapter 7, Benefit-Cost Program: Flood Hazard Risk, provides 
detailed information about modeling, flood hazards, and determining 
annual probabilities of floods. 

Chapter 8, Benefit-Cost Program: Level Two Analysis, provides a 
detailed discussion of the data inputs necessary for a LEVEL TWO 
(Detailed) Benefit-Cost Analysis, including guidance on overriding 
default values with user-specified, building-specific data. 

Chapter 9, Benefit-Cost Program: Results, provides a detailed 
discussion of the results of benefit-cost analysis, including guidance on 
interpretation of results. 

Chapter 10, Benefit-Cost Program: Print-Out, is a full print-out of a 
sample benefit-cost analysis, including all of the data entry screens, 
results screens, and the graphical presentation of data and results. 

Chapter 11, Glossary, defines technical terms used in the program 
and in the user's manual. 

Appendix 1, Equations, summarizes all of the underlying equations in 
the Benefit-Cost Program and defines all technical terms used in the 
equations. 

1-4 


VERSION 1.0 12/29/94 GETTING STARTED

.s 

COMPUTER 
HARDWARE 

CHAPTER 2
GETTING STARTED

This chapter describes the computer hardware and software required to 
run the Benefit-Cost Programs and how to install them on your 
computer. Chapter 3, Program Basics, describes the basics of using 
Quattro Pro for Windows (QPW), how to get around in the Benefit-
Cost Programs, and how to enter the data requested. Chapter 4, 
Tutorial, provides a fully worked example of a benefit-cost analysis 
with guidance for the novice user. 

QPW works very much like other spreadsheet programs such as Lotus 
1-2-3, or Excel, so that experience with any of them is almost 100% 
transferrable to QPW. However, even if you have little or no 
experience with spreadsheet programs, the Benefit-Cost Programs 
are self-contained and easy to use. 

Hardware and Software Required 

This Benefit-Cost Programs require an IBM-compatible computer 
(PC). The CPU must be a 386 or higher; the programs will run faster 
with a 486 or Pentium CPU. In addition, the computer MUST have: 

1. at least 4 (more is better) megabytes of memory (RAM), 
2. a hard drive with at least 15 (more is better) megabytes 
of free disk space, and 
3. a high density (HD) 3.5" floppy disk drive. 
The Benefit-Cost Program files require a large amount of disk space, 
about 3 megabytes per file saved (i.e., for each worked benefit-cost 
analysis for a mitigation project). Therefore, it is desirable to have a 
large hard disk if you anticipate saving a substantial number of files. 
Alternatively, files can be saved on high density (HD) floppy disks. 
However, because of the file size (HD floppy disks hold only about 1.4 
megabytes), the files MUST be compressed using utility programs 
available on recent versions of DOS or a separate utility program (such 
as PKZIP). When compressed, each file is less than 1 megabyte. 
Files can also be saved on tape or Bernoulli drive back-up systems. 

2-1 


GETTING STARTED

VERSION 1.0 1:2/29/9i4 GETTING STARTED

VERSION 1.0 12/29/94 

COMPUTER These Benefit-Cost Programs are WINDOWS programs; therefore, 
SOFTWARE your computer must have Windows (Version 3.1 or higher) installed 
beforeyou loador run the Benefit-Cost Programs. Windows Version 

3.11 is recommendedbecause of additional features and somewhat 
less propensity to "crash" than Version 3.1. 
All Windows programs require the use of a mouse; thus your computer 
system must have a mouse properly installed and operational. 

Windows To install Windows: 

1. Turn on your computer. 
2. Insert the Windows Disk I in the drive (A: or B:) that you want 
to use for the installation and close the drive door. Windows 
Setup letsyou use any activefloppy disk drive. 
3. At the DOS prompt, C:X>, to make the installation drive active, 
type the drive letter desired followed by a colon (A: or B:) and 
press Enter. Your DOS prompt will change to A:> or B:> 
depending on which drive you made active. 
4. Type SETUP and press Enter. This command initiates the self-
installing Windows Setup program. 
NOTE: DOS commands are not case-sensitive and may be 
entered either in upper or lower case. For clarity, all DOS 
commands in this manual are shown in upper case. 

5. Follow the instructions on the screen. 
The Setup program's instructions should be self-explanatory. But, if 
you do have questions about any of the procedures or options, you can 
request on-line Windows Help by pressing the F1 key. For more 
information, see the Microsoft Windows User's Guide. 

HINT: The installation routine will ask if you want to choose a "custom" 
installation or allow Windows to perform a "standard" installation. Most 
computers will operate well if you allow Windows to self-install (i.e., 
select the "standard," not the "custom" installation). 

2-2


VERSION 1.0 12/29/94 GETTING S~TARTED

I 

Quattro Pro for The Benefit-Cost Programs run in QUATTRO PRO FOR WINDOWS 

Windows (QPW) (QPW). You must have QPW (VersIon 5.0) installed on your computer 
before loading or running the Benefit-Cost Programs. 

To Install QPW: 

1. Be sure you are in Windows (i.e., install Windows first): open 
Windows if it does not automatically come up when you turn on 
your computer. At the DOS prompt, C:\>, to open Windows, 
type WIN 
If this command opens Windows, proceed to Step 2. If not, then 

an error message, "bad command or file name," will appear. If 

this error message appears, it means that Windows is not in the 

path list and you must change directories before opening 

Windows. At the DOS prompt, C:\>, to change directories, type 

CDWINDOWS 

This command changes the DOS prompt to C:\WINDOWS>. At 
the DOS prompt, C:1WINDOWS>, to open Windows, type WIN 

2. Insert the QPW Disk I in the drive (A: or B:) you want to use for 
the installation and close the drive door. 
3. With your mouse, point the cursor on Elie on the menu bar (at 
the top of your screen), press and hold the left button of your 
mouse. While holding down the left mouse button, move the 
mouse until Run... is highlighted and release the mouse button. 
Or, Click on Eile, then click on Run... 
2-3


VERSION 1.0 12/29194 GETTING STARTED 

4. On the Command Line (i.e., inside the box which will appear 
next on your screen, as shown below), type 
-A:INSTALL.EXE 

or B:INSTALL.EXE 

depending on which drive the QPW disk is in. Be sure to type 

the command exactly as written: do not add spaces or change 

punctuation. Then left-clickthe mouse on OK. 

3 : 
5. Enter the requested information in the Installation Dialog Box 
which will appear on your screen. Accept the default choice of 
QPW for the Quattro Pro directory. 
6. Quattro Pro will ask you for various information during the 
installation. Simply type the response and press Enter or click 
the mouse on OK. The default (standard) settings are usually 
suitable for your first installation of Quattro Pro. 
7. After entering the information requested in the Installation Dialog 
Box (e.g., your name), click on Install to continue. 
8. Follow instructions (e.g., change from Disk I to Disk 2 to Disk 3 
etc.) as they appear. 
9. After you have completed these steps, your QPW installation will 
be complete! 
I 

2-4


VERSION 1.0 12/29/94 GETTING START-ED

installing the Benefit-Cost Programs

Network Computer networks may be set up and managed in many different 

Systems ways. Therefore, this manual cannot give detailed instructions for 
installing the Benefit-Cost Programs on a specific network system. 
To install the programs on a computer which is connected to a network 
system, give the program disks and the User's Manual to your 
computer system operator or network administrator. After installation is 
completed, go to the Start QPW section on page 3-1. 

Stand-Alone 1. Turn on your computer. 
Computers: I 

2. If you are not at a DOS prompt (such as C:\>) either exit from 
Windows to DOS, or select a DOS prompt from within Windows. 
To exit from Windows, click on Eile on the menu, then click on 
Exit. The program will display: "This will end your Windows 
Session." Click on OK. Your screen will show: C:\> 

If your hard disk drive is designated D, or some other letter, that 
letter will appear in place of C; 

3. To install either the Riverine or Coastal A-Zone programs, 
insert the first Benefit-Cost Program disk (3.5") in either the A 
or B drive of your computer (whichever floppy drive is the high 
density 3.5" drive); 
4. At a DOS prompt (C:\>), 
If the Program diskette is in the A drive, type: 
A:INSTALL A: C: 

If the Program diskette is in the B drive, type: 
B:INSTALL B: C: 

The install routine will automatically ask for the second Program 
disk at the proper time. 

5. The install routine will automatically create a new subdirectory 
on your C drive: C:%BCFLOOD or C:ABCCSTA for the 
Riverine and Coastal programs, respectively. 
2-5


VERSION 1.0 12/29/94 GETTING :STARTED 

VERSION i .0 12/29/94 GETTINGSTARTED 

6. Two files will be loaded into the C:XBCFLOOD or 
C:IBCCSTA directory: 
A. An example file with all data entries filled in: 
BCEXAMP.WBI 
B. A blank file, for user data input: 
BCBLANK.WBI 
7. PROGRAM INSTALLATION IS COMPLETE! 
is

2-6


VERSION 1.0 12/29/94 PROGRAM BASICS
VERSION 1.0 12/29/94 PROGRAM BASICS

Start Windows 

Start QPW 

CHAPTER 3
PROGRAM BASICS

This chapter provides basic information about starting and running 

Quattro Pro for Windows and the Benefit-Cost Programs, along with 

helpful hints. 

Starting Quattro Pro For Windows (QPW) 

Quattro Pro For Windows (QPW) is a Windows program; therefore 

you must first start Windows before starting Quattro Pro. If you are not 
already in Windows, type WIN at a DOS prompt (e.g., C:\>) to start 
Windows. See page 2-3 for more information. 

After starting Windows, click the left mouse button on 

the symbol (the "icon") or the group window labeled
Quattro Pro for Windows (QPW). Then, double-click the
left mouse button on the QPW icon within the window.

Quattro Pro for Windows works very much like any other Windows 

spreadsheet (e.g., Lotus 1-2-3 or Excel) or.any other Windows 
program, including word processors (e.g., WordPerfect or Microsoft 
Word). Quattro Pro commands are initiated by clicking on pull-down 
menus at the top of the screen or by clicking on the speed buttons 
below the menu lines. 

To use the Benefit-Cost Programs, you need to know only a little about 
Quattro Pro. Once a Benefit-Cost Program is loaded, the data entry, 
calculations, and printing of results can be accomplished entirely within 
the program, with minimal use of Quattro Pro commands. 

3-1 


VERSION 1.0 12/29/94 PROGRAM BASICS

Opening Files The menu bar along the upper edge of the QPW window will display a 

Eile command at the left side. Click on the File command. When the 

menu opens, click on the Open... line. 

The screen will display the Open File Dialog Box which contains two 
boxes side by side: File Name and Directories. 

If the C: drive is not listed at the top of the Directories list, double click 
on the C: in the Drives box on the bottom center of the screen. Use 
the mouse to move the cursor to the BC_ FLOOD or BCCST_A 
directory where the Benefit-Cost Programs are located, and double 
click. All of the files ending in .WB1 will be listed in the File Name box 
at the left. 

Double click on the BCEXAMP.WBI line to load a completed 
example, or on BCBLANK.WBI to load a blank spreadsheet. Or, files 
may be opened by clicking once on the file name and then on OK. 

3-2


VERSION 1.0 12/29/94 PROGRAM BASICS 
VERSION 1.0 12/29/94 PROGRAM BASICS 

The computer will load a Benefit-Cost Program. Loading may take 

from a few seconds up to several minutes, depending on the computer. 

The bottom right corner of the screen (Status line) will display WAIT 

while the model is loading and READY when the model is loaded. Do 

not attempt to enter any commands while WAIT is displayed! 

As you continue to use the Benefit-Cost Programs and save files, the 
File Name box will contain the names of all of your files which have the 
.WB1 ending. Double-clicking on the desired file will open any of these 
files. Please see Naming and Saving Files on page 3-7. 

I
Screen Display I When a Benefit-Cost Program is loaded, the first screen visible is the
Sign-On Screen which identifies the program title, version, and date.

Zoom List If the words extend past the right-hand side of your computer screen or 

if the image is too small, change the Zoom List by following these 

steps: 

1. Click on the Zoom List arrow, located in the 
second row of symbols (the productivity tools 100 
SpeedBar) at the top of the screen; 
2. While holding down the left-hand mouse button, move the 
mouse until the correct value (e.g., 80) is highlighted. It may 
take a little trial-and-error to determine the best value for your 
screen. Changing the Zoom List setting changes the size of 
the screen display.

I 

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VERSION 1.0 12/29/94 PROGRAM BASICS 

VERSION 1.0 12/29/94 PROGRAM BASICS 

Moving Around in the Programs W 

Several Easy There are several easy ways to move around in a Benefit-Cost
Ways Program:

1. Use the mouse to place the cursor wherever you want to be on a 
page and click on that location. 
2. To move left-right on a page, use the cursor arrows on the 
keyboard, or the horizontal scroll bar at the bottom right of the 
screen. 
3. To move up-down on a page, use the cursor arrows on the 
keyboard? or the vertical scroll bar at the right hand edge of the 
screen. 
4. To move to the top of any page in a program, press the Home 
button on the keyboard. 
5. To proceed sequentially through a Benefit-Cost Program, click 
on the Next Screen Button, at the bottom of each page. 
6. To move to a specific location within a program, use the custom 
Menu Tree (described next) which appears at the top of the 
screen. Click on the desired menu item; the submenu (a list of 
available choices) appears. Click on the desired submenu item. 
Benefit-Cost The Benefit-Cost Programs are driven from a customized menu tree.
Menu Tree The menu appears at the top of the display screen (after the model is
loaded):

tIlei E'odeI aarRis~le

.i..evelOne ,e/Dat\Lees~trst~ 

Menu items can be accessed by clicking on the desired menu label or 
by the IX keyboard command, where "X"indicates the underscored 
letter in the menu name. For example, Results can be accessed by 
clicking on Results or by typing IR. 

In addition to the main menu, there are submenus which appear when 
a main menu heading is clicked on. Submenus are accessed in the 
same manner as the main menu headings. S 

3-4


VERSION 1.0 12/29/94 PROGRAM BASICS 
VERSION 1.0 12/29/94 PROGRAM BASICS 

For example, to move to the Depth-Damage Function screen, click on 
Level Two Data,then Click on luilding Depth-Damage Function. 

7 : S * . I __ 
Mtg~to~rj~ Ef E z .e X 

The complete Benefit-Cost Menu Tree is given below. 

CUSTOMIZED BENEFIT-COST MENU TREE 

File
Save
Save As...
Quit

Model 

Version 

Color Codes 

Level One Data 
Project Information 
Bluilding Data 
Building Contents 
Displacement Costs 
Value of Public/Nonprofit Services 
Bent & Business Income 
Mitigation Project Data 

Elood Hazard Risk 

Level Iwo Data 
fluilding Depth-Damage Function 
Contents Depth-Damage Function 
Displacement Time 
Eunctional Downtime 
Mitigation Project Effectiveness 

Results 
Damages Before Mitigation 
Damages After Mitigation 
Benefits 
Benefit Cost Results 

Summary 

I 

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VERSION 1.0 12/29/94 PROGRAM BASICS

10 12/29194

VERSION PROGRAM BASICS 

I Print 

i 

summary 
Report 
Graph HazardData 
Graph Damages Before Mitigation 
Graph Damages After Mitigation 
Graph Benefit-Cost Results 
All Graphs 

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VERSION I.0 12/9/9Q14 PROGRAM BASICS 

VER.IflN 1fl 12129/94 PROGRAM BASICS 

Basic Commands and Procedures

Naming and Each benefit-cost analysis file you wish to save MUST have a unique 
Saving Files name to avoid writing over the original file. If you choose (i.e., click on) 
the Save command, the model will automatically name your file 
NEWBC.WB1.

I 

Save 

However, if you choose the Save command subsequently to save a 

different file, you will be asked if you wish to replace (write over) the 
existing file. If you choose Replace your NEWBC.WB1 file will be 
replaced. 

Save As... If you choose Save As... a unique name can be entered as a file is 
saved. Click on Eile (in the menu on the top line of the screen), then 
click on Save As... 

Muidel 

3-7


VERSION 11.0~12/29/94 PROGRAM BASICS 

VERSION 1.0 12/29/94 PROGRAM BASICS 

The screen will display the Save BC File As Dialog Box. Click on the 

Eile Name box, then type in the new name, e.g., RUNI7.WB1, as 
shown below. Use the Backspace or Delete keys to edit any name 
which automatically appears in the box. After entering the desired new 
file name, click on OK and the file will be saved with its new name. 

Names can have up to eight letters or numbers, then a period, followed 
by three letters or numbers, e.g., RUN12345.WBI 

3-8


VERSION 1.0 12129/94 PROGRAM BASICS 

VERSION 1.0 12/29/94 PROGRAM BASICS 

l 

OOPSI If you accidentally overwrite one of the original Benefit-Cost Program 

If you overwrite files by saving a file with user-entered data without changing the name, 

the programfile the original program file will be lost (overwritten by the new file). To 
recreate the original program file, check to see if a backup copy exists: 
it will have the same name as the original, followed by a .bak extension 

(ending), e.g., BC_EXAMP.BAK or BCBLANK.BAK. Rename this 
file with the original name. 

1. Click on the File menu at the top of the screen. 
2. X Click on Open, to open the Open File Dialog Box. 
3. Type *.bak in the File Name box to see if any back-up files exist. 
4. Next, Qpen the .bak file (see page 3-2 for instructions on 
opening a file). 
5. Select Save As and save the file with the desired name, as 
describedon page3-7, Naming and Saving Files. 
Helpful Hint: If all else fails, reinstall the file from the original floppy 
disk as described on page 2-5, Installing the Benefit-Cost Programs. 

Start a New If you want to do another benefit-cost analysis (i.e., run the same
Benefit-Cost Benefit-Cost Program again, with different inputs):
Analysis

1. Save the existing open file with a new name (see Naming and 
Saving Files, page 3-7). 
2. Click on Eile (in the menu at the top of the screen), hold down 
the left mouse button until Quit is highlighted. 
0~~~~~~~ 

3. Click on Eile, then click on _Qpen to start a new analysis (see 
Opening Files, page 3-2). 
Exit From a 1. Save your work with a new name, by using the 

Benefit-Cost FilelSave As command described above. 

Program 

2. Click on Eile, then click on Quit to leave the Benefit-Cost 
Program. 
I 

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VERSION 1.0 12/29/94 PROGRAM BASICS

Run a Different 
Benefit-Cost 
Program 

Exit from QPW 

If you want to run a different Benefit-Cost Program (e.g., the Coastal 
A-Zone Program instead of the Riverine Program): 

1. See Opening Files on page 3-2. 
2. Select the appropriate directory (e.g., BCFLOOD or 
BCCSTA) for the desired Benefit-Cost Program. 
3. Open BCEXAMP.WBI or BCBLANK.WBI or another 
previously named file. 
To exit from QPW, you must first exit from the Benefit-Cost Program. 
With the mouse, highlight Elie and Quit. This closes the program 
without saving it (so save the file first, if desired, as described 
above). 

Next, with the mouse, highlight Elue, then Exit to close QPW and 
return to the Windows screen. 

Exit from To leave Windows, click on Elue, then on Exit. The screen will display 
Windows a dialog box with "This will end your Windows Session.t' Click on OK to 
return to a DOS prompt. 

3-10 


VERSION 1.0 12/29/94 PROGRAM BASICS

Cell Colors 

Unprotected 
Blocks 

Protected Blocks 

Before you begin the data entry process, note that all areas 
(blocks or "cells") of the program screens are color coded to remind the 
user what type of information each cell contains. 

The cell type appears in the Style List window when the cursor is 
clicked on a cell. The Style List window is in the upper SpeedBar. 

liformation 112 

In the Benefit-Cost Programs, background space is white and 
identifying labels (which cannot be changed) have black text on white 
backgrounds. There are seven colors which indicate different types of 
data entries or calculated results: 

User data entries can be made ONLY in PINK, GREEN, BLUE, or RED 
blocks. "Unprotected" means that data entries CAN be made within 
these blocks. 

Blocks colored ORANGE, YELLOW, and PURPLE are protected. The 
background, or normal blocks, which appear WHITE are also protected. 
User entries CANNOT be made in these blocks. To change 
information in PURPLE blocks (Carry Over) the original data entries in 
the PINK or GREEN blocks must be changed. To change entries in the 
ORANGE or YELLOW blocks, the underlying selections or data entries 
which affect these blocks must be changed. 

3-11 


VERSION 1.0 12/29/94 PROGRAM BASICS

Data Entry 

Correcting 
Errors 

To enter data into a block (cell) in the program, first move the cursor to 
the block where you want to enter the data. Then, type the desired 
information. As you type, the characters appear in the Input Line 
below the menus and speed buttons. 

i Cross Headquarters I 

Only when you press Enter or an arrow key or click the check mark 
button (/) does Quattro Pro move the characters into the block (cell). 
Thus, you must press Enter or an arrow key or click the check mark 
button (V) to actually make the data entry which you have typed. 

If you attempt to enter data in cells which are not GREEN, PINK, 
BLUE, or RED you will see a "protected cell' error message. Other 
cells are "protected" to prevent inadvertent changes to the program. As 
with other error messages, click on OK or press the Esc key to return 
to data entry. 

If you make a mistake while typing, press the Backspace key on the 
keyboard to erase. To clear the entire entry, click the X box or press 
the Esc button on the keyboard. 

3-12


VERSION 1.0 12/29/94 PROGRAM BASICS

Entering 
Commas 
and Dollars 

Entering 
Addresses 

Syntax Error 

After pressing Enter, if you find you made a typing mistake or want to 
change an entry, first select the cell which you wish to change by 
clicking on the cell. Then, type the entry over again or click inside the 
text on the Input Line (see Data Entry above) and edit it there. To 
delete an entry without replacing it, just select the cell (by clicking on 
the mouse in the desired cell) and press the Del button on the 
keyboard. 

Another option is to use the Delete button to delete the 
entry. Click on the cell with the mistake, then move the 
mouse to the Delete button (on the left side of the bottom 
Tool Bar) and click. 

To Undo any entry or change, move the cursor to the cell 
and left click the mouse, then highlight and click on the 
Undo (pencil eraser) icon (on the bottom right of the Too l 

Bar). 

QPW can't accept number entries which include a dollar sign "$" or 
commas ",". Thus, twenty thousand square feet must be entered as 
20000 and a cost of $10,000 must be entered as 10000. The "$" and 
"," are inserted automatically. If you forget and include a "$" or a "," the 
model will respond with a "Syntax error" message. Click on the OK, or 
press the Esc keyboard button, then enter correctly the information 
requested. 

When entering the address (or any combination of letters and numbers 
which beggin with a number), first type an apostrophe (') followed by the 
number and street name. The'tells Quattro Pro that the entry is text, 
not numbers. If you forget to include the apostrophe, a "Syntax error" 
message will appear. Click on the OK, or press the Esc keyboard 
button, then enter correctly the information requested. 

3-13


VERSION 1.0 12/29/94 TUTORIAL

CHAPTER 4
TUTORIAL

II

This chapter reviews the process of loading Quattro Pro for Windows 
and a Benefit-Cost Program, and works through a sample LEVEL ONE 
(see definition below) data entry exercise and benefit-cost analysis. 
This tutorial is provided primarily for the less experienced computer 

user. 

To examine an example of a complete benefit-cost analysis, open the 
BCQEXAMP.WBI file in either the BCFLOOD or the BCCST_A 
directory. These BC EXAMP.WB1 files have all of the data entries 
already completed. To use the tutorial to enter data in a blank benefit-
cost model, follow the instructions which start on page 4-3. 

LEVEL ONE and LEVEL TWO Benefit-Cost Analyses 

A LEVEL ONE (Minimum Data) Benefit-Cost Analysis, relies heavily 
on default values and requires the minimum of user-specified data 
entries. A LEVEL TWO (Detailed) Benefit-Cost Analysis, relies less 
on default values and incorporates much more building-specific data. 

LEVEL ONE 
(Minimum Data) 
B-C Analysis 
By entering the information on the LEVEL ONE Data pages and the 
Flood Hazard Data, the program will perform a Benefit-Cost analysis of 
the proposed mitigation project. Additional numerical values which the 
model requires for its calculations are already included in the program 
as "default values." 
For general guidance on how to perform a benefit-cost analysis, see 
Chapter 5, Benefit-Cost Programs: Guidance. 

For a detailed explanation of the data entries for a LEVEL ONE 
analysis, see Chapter 6, Benefit-Cost Programs: Level One 

Analysis. 

For a detailed explanation of flood data entries, see Chapter 7, 
Benefit-Cost Programs: Flood Hazard Risk. 

4-1 


VERSION 1.0 12/29/94 TUTORIAL
VERSION 1.0 12/29/94 TUTORIAL

LEVEL TWO 
(Detailed) 
B-C Analysis 

Users are encouraged to perform a LEVEL TWO (Detailed) analysis 
whenever possible. LEVEL TWO analyses will provide the most 
accurate results by incorporating much more building-specific data and 
judgments than a LEVEL ONE analysis. See Chapter 8, Benefit-Cost 
Programs: Level Two Analysis for a detailed discussion of Level Two 
data entry. 

The following tutorial is for the LEVEL ONE (Minimum Data) Benefit-
Cost Analysis. 

4-2


VERSION 1.0 12/29/94 TUTORIAL

Step One
Step Two

Step Three

Step Four

VERSION12/29/94 TU TORIA 

1.0 

Starting the Tutorial 

Start Quattro Pro for Windows (QPW). See page 3-1. 

Open the desired Benefit-Cost Program file. See instructions (Opening 

Files) on page 3-2. For the tutorial, open the BC BLANK.WBI file in 

the BCFLOOD directory. 

The Sign-On screen appears after a Benefit-Cost Program is loaded. 
Adjust the Zoom List factor which controls the size of the screen 
display, if necessary. See instructions on page 3-3. 

Proceed through the Data Input process, as outlined below in the 

tutorial example. This example leads you through the LEVEL ONE 

(Minimum Data) benefit-cost analysis data input process. Click on the 

NEXT SCREEN button at the bottom of the Sign-On Screen to begin 

the data entry process. 

Clicking this button on the Sign-On screen moves you to the LEVEL 
ONE DATA screen, where the data entry process begins. 

4-3


VERSION 1.0 12/29/94 TUTORIAL

VERSION TUTORIAL

1.0 12129/94 
Building Name 

Address 

OOPSI 

Help 

City, State, Zip 
Code 

PINK Blocks (Information Only). With your mouse, move the cursor 
to the first pink-colored block, Building Name, and click on the cell. 
IMPORTANT:the cursor must be in the first space inside the pink 
box, not to the left of it. Type the name of the building, i.e., City Office 
Annex. Press the Enter key. As you make data entries, remember 
that PINK blocks are for information only;they serve to identify the 
project under evaluation, but do not affect numerical benefit-cost 
results. Entries in the RED block and the GREEN blocks do affect 
numerical results. 

Then, with the mouse or the arrow keys, move the cursor to the street 
Address and enter it in the followingway: 
'55 A Street 

If you forget to start your entry with an apostrophe (') an error 
message will be displayed. 

The address (and all combinations of numbers and letters which begin 
with a number) MUST be entered with a single apostrophe (') 
preceding the address, e.g., '55 A Street. Ifnot entered this way, a 
"Syntax error" message willappear: click on the OK of the error 
message and add the apostrophe (see page 3-13). Then, press Enter. 

Move to the next entry. 

PINKBlock (Information Only). Enter the city, state and zip code for 
the building: Cape Squirrel, VA 22222. Move to the next entry. 

4-4 


VERSION 1.0 12/29/94 TUTORIAL 

VERSION 1.0 12/29194 TUTORIAL 

Owner PINK Block (Information Only). Enter the name of the building's
owner. This may be an agency, a private party,4etc. Enter: City of
Cape Squirrel. Move to the next entry.

Contact Person : 'PINK1Block (Information Only). Enter Sam Smith, City Manager,
for the building's manager, or other contact person who could provide
information about the building to the analyst. Move to the next entry.

Disaster Number PINK Block (Information Only). Enter disaster number FEMA-000-
IDR-VA. Move to the next entry.

Project Number PINK Block (Information Only). Enter project number 123456. Move
to the next entry.

Application Date PINK Block (Information Only). Enter January 1, 1994. Move to the
next entry.

Discount Rate RED Block (OMB Policy). The discount rate of 7% is already entered.
Move to the next entry.

Scenario Run ID PINK Block (Information Only). Enter the scenario run number 1.
Move to the next entry.

Analyst PINK Block (Information Only). Enter your name. Move to the next
entry.

4-5


VERSION I1.0 12/29/94 TUTORIAL 

VERSION 1.0 12/29/94 TUTORIAL 

BUILDING TYPE 

BUILDING 
INFORMATION 

Zero Flood Depth 
Elevation 

Numberof 
Stories 

Construction 
Date 

Historic Building 
Controls 

3 flAA~~~~~~~~ 

You must use the mouse to click on the appropriate button; the arrow 
keys will not operate these buttons. For this example, click on the 
button labeled: 2 story w/o basement. This choice will automatically 
appear in the purple cell labeled "Building Type Selected." 

GREENBlock (Data Input). Enter 6 as the Zero Flood Depth 

Elevation (top of the lowest finished floor) for this building. Move to the 
next entry. 

PINK Block (Information Only). Go to the Number of Stories Above 
Grade box and enter 2. Move to the next entry. 

PINK Block (Information Only). Go to the Construction Date box 

and enter 1965. Move to the next entry. 

PINKBlock (Information Only). Go to the Historic Building 
Controls box and enter No. Move to the next entry. 

4-6


VERSION 1.0 12/29/94 TUTORIAL

BUILDING SIZE 
AND USE 

Total Floor Area 
(Sf) 

Syntax Error 

Area Occupied 
by Owner or 
Public/Nonprofit 
Agencies 

BUILDING 
VALUE 

Building 
Replacement 
Value ($/sf) 

GREEN Block (Data Input). Enter 2000 (two thousand) without a 
comma. The screen will display this as 2,000 when you confirm the 
entry by pressing Enter or move to the next data entry block. If you 
make a mistake, use the backspace key to erase, then enter the 
information correctly. If you made a mistake and have already pressed 
the Enter key, you will see an Error Message. Follow the instructions 
below. 

Spreadsheets such as Quattro Pro can't accept numbers which include
a dollar 'sign ($)or commas. Thus, twenty thousand must be entered
20000 and a cost of $1 0,000 should be entered as 1 0000: the I$" and
the "," are entered automatically. If you forget and include a "$" or a ","
the program will respond with a "syntax error" message. Click on the
OK, then enter correctly the information requested.

GREEN Block (Data Input).
Enter 1500 for the total amount of space (in square feet) occupied by
the owner or public/nonprofit agencies. Move to the next entry.

Relacement

Buldn Vatlue($ 

-. :T.otal 

BuildingReplacementVaill
BuildingDamage that would Ren

Re 

GREEN Block (Data Input). Enter 75 as the building's value per 
square foot. Move to the next entry. 

4-7


VERSION 1.0 12/29/94 TUTORIAL 

VERSION 1.0 12/29194 TUTORIAL 

Total Building 
Replacement 

Value 

Building Damage 
that would 
Result in 
Demolition 

Contents 

Description 

Total Value of 

Contents 

Value of 

Contents ($Isf) 

YELLOW Block (Result). The program automatically calculates
$150,000 as the building's total replacement value and displays it in the
yellow block. Move to the next entry.

DemolitionPercent
GREEN Block (Data Input). Enter 50 (fifty) for the percent of building
damage at which demolition and replacement (rather than repair) would
be expected to occur; this value is also known as the "demolition

threshold." Move to the next entry. 

Demolition Value
YELLOW Block (Result). The programdisplays$75,000 for the
dollars of building damage at which demolition and replacement (rather

than repair) would be expected to occur. Move to the next entry. 

1:-Ul M00Ej k v_ 

PINK Block (Information Only). Enter office furniture, computers &
files as the description of the building's contents. Move to the next
entry.

GREEN Block (Data Input). Enter 60000 as the total contents value.
The "$" sign and the comma are entered automatically. Move to the
next entry.

YELLOW Block (Result). The program displays $25.00 as the value
of contents in dollars per square foot of building space. Move to the
next entry.

4-8


VERSION 1.0 12/29/94 TUTORIAL

: A 0 3 0 SOUAIA 

Rental Cost of 
Temporary 

BuildingSpace 

($/sflmonth) 

Rental Cost of 
Temporary 
Building Space 
($/month) 

Other Costs of 
Displacement 

($/month) 

Total 
Displacement 
Costs ($Imonth) 

GREEN Blocks (Data Input). Enter 1.50 (one decimal point five zero) 
as the rental cost of temporary building space in dollars per square foot 
per month. Move to the next entry. 

YELLOW Block (Result). The program displays $2,250 as the 
monthly rental cost of temporary building space. Move to the next 
entry. 

GREEN Block (Data Input). Enter 500 (five hundred) as the estimated 
cost of all other non-rent costs associated with this displacement. 
Other costs include moving costs, temporary equipment, temporary 
furnishings, etc. Move to the next entry. 

YELLOW Block (Result). The program will display $2,750 as the 
calculated total displacement cost per month. Move to the next entry. 

4-9


VERSION 1.0 12/29/94 TUTORIAL 

VERSION 1.0 12/29/94 TUTORIAL 
s _A*lS 

Description of 
Services 

Provided 

Annual Budget 
of 
Public/Nonprofit 
Agencies 

Is Rent Included 
in this Budget? 

User-Entered 

Rent Estimate 

($/month) 

Cost of 
Providing 
Services ($/day) 

PINK Block (Information Only). Enter City Planning Office. Move 

to the next entry. 

GREEN Block (Data Input). Enter 195000 (one hundred ninety five 
thousand) as the annual budget for allthe public/nonprofitagencies 
operating out of this building. This is the total annual operating budget 

0 

for public or nonprofit agencies in this building. The total budget should 
exclude pass-through amounts such as Social Security payments. 
Move to the next entry. 

Click on the YES button to indicate that rent is included. The program
displays "Rent Included" under the $195,000 annual budget cell just
above. When rent is not included in the annual budget, the program
calculates a default or proxy rent based on the value of the building and
displays it in the YELLOW Block (Result) on the next line. Move to the
next entry.

GREEN Block (Data Input). Leave this entry blank, because rent is 

already included in the budget estimate. Move to the next entry. 

YELLOWBlock (Result). The programcalculates $534 as the 

estimated daily cost of providing services from this building. Move to 

the next entry. 

I 

4-10


VERSION 1.0 12/29/94 TUTORIAL

Post-Disaster 
Continuity 
Premium ($/day) 

Total Value of 
Lost Services 
($/day) 

Monthly Rent 
from Tenants 

Net Income of 
Commercial 
Businesses 

GREEN Block (Data Input). Enter 500 for a $500 per day continuity 
premium. Move to the next entry. 

YELLOW Blocks (Results). The program displays $1034 as the total 
value of lost services per day. Move to the next entry. 

__ I 

GREEN Block (Data Input). Enter 600 (five hundred), as the total 
monthly rent received from all tenants in the building, excluding 
public/nonprofit agencies ($/month). Move to the next entry. 

GREEN Block (Data Input). Enter 1500 (one thousand five hundred) 
as the estimated net income of commercial businesses in the building 
($/month). Move to the next entry. 

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VERSION 1.0 1 2/29/94 TUTORIAL 
VERSION12/29/94 TUTORIAL

1.0 

A A_

* 3k
** 

Select Mitigation 
Measure 

Project 

Description 

Project Useful 

Life 

Mitigation

Effectiveness 

Estimates 

F

eCt ?=IF Ea 

With the mouse, click on the Elevation button. The program will 
display this choice in the purple cell. 

PINK Block (Information). Enter Elevate 5 feet. Move to the next 
entry. 

GREENBlock (Data Input): Enter 30 as the years of useful life 
expected from this mitigation measure. Move to the next entry. 

EtrEfc~eesEtmtsfrteMtgto esr
IOSta'froEfftitDettive

at Deh 

Enter 4 in the Elevation row under the 100% Effective to Depth 
column header (see Chapter 6, Benefit-Cost Programs: Level One 
Analysis for a discussion of mitigation project effectiveness). The 
program displays NIA(not applicable) in the 0% Effective at Depth 
column for the Elevation row because this is calculated automatically 
from the building depth-damage function. NIAalso appears in the 
Relocation/Buyout rowbecause such measures are assumed to be 
100% effective at all depths. Although values may appear in other rows 
(from previous uses of the program), the program only "reads" (uses) 
the values in the row which corresponds to the mitigation measure type 
selected. Move to the next entry. 

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VERSION 1.0 12/29/94 TUTORIAL

MITIGATION 
COSTS 

Mitigation 
Project Cost 

Base Year of 

Costs 

ANNUAL 

MAINTENANCE 
COSTS ($NYEAR) 

Present Value of 
Annual 
Maintenance 
Costs 

RELOCATION 

COSTS FOR 

MITIGATION 

PROJECT 

Relocation Time 

Due to Project 

Rental Cost 
During Occupant 
Relocation 

GREEN Block (Data Input). Enter 40000 (forty thousand) as the 
mitigation project cost, excluding relocation costs. Move to the next 
entry. 

PINK BLOCK (Information Only). Enter 1994. Move to the next 
entry. 

GREEN Block (Data Input). Enter 500 (five hundred) as the annual 
maintenance costs. Move to the next entry. 

YELLOW Block (Result). The program calculates $6,205 as the 
present value of annual maintenance costs. This calculation is based 
on the annual maintenance costs, the project useful lifetime, and the 
discount rate. Move to the next entry. 

In this section, the time and costs associated with occupant relocation 
during the construction of the mitigation project are estimated. 

GREEN BLOCK (Data Input): Enter 2, for two months of relocation 
time necessary for the mitigation project. Move to the next entry. 

GREEN Block (Data Input): Enter 2.00 for $2.00 per square foot per 
month as the rental cost during occupant relocation for the mitigation 
project. Move to the next entry. 

YELLOW Block (Results): The program displays $3,000, as the 

monthly rental cost incurred during occupant relocation for the 

mitigation project. Move to the next entry. 

4-13 


VERSION 1.0 12129f94 .TUTORIAL 

VERSION 1.0 12/29/94 TUTORIAL 

Other Relocation GREEN Block (Data Input). Enter 500 (five hundred) dollars in other 

Costs ($/month) relocation costs per month. Move to the next entry. 

Total Relocation YELLOW Block (Result). The program displays $7,000 as the total 

Costs relocation costs for the mitigation project. Move to the next entry. 

TOTAL YELLOW Block (Result): The program displays $53,205 as the total 
MITIGATION mitigation project costs. This total includes the mitigation project costs, 
PROJECT the present value of the annual maintenance costs, and the relocation 
COSTS costs for the project. Move to the next entry. 

A A, 

Flood Data 

GREEN Blocks (Data Input). Complete the Flood Data chart with the 
data as shown above, for Flood Frequency, Discharge and Elevation. 
These data, along with the Zero Flood Depth elevation of the facility 
under evaluation determine the extent of flood risk at the site. For more 
information about how flood hazards are modeled in the program, see 
Chapter 7, Benefit-Cost Programs: Flood Hazard Risk. 

To view the calculated flood estimates, move down on the flood hazard 
page with the arrow keys or mouse. The flood estimates are updated 
automatically whenever you move to any page, other than the Flood 
Hazard page. 

NOTE: This tutorial is for a Riverine flood example. The Coastal A-
Zone flood data entry is slightly different. See Chapter 7, Benefit-Cost 
Programs: Flood Hazard Risk. 

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VERSION 1.0 12/29/94 .TUTORIAL 

*-ilW::@u S-E~uP 

mfI0 

Use the mouse to highlight Results on the menu, and then, while 
holding down the left button, move the mouse until Benefit-Cost 
Results is highlighted. The program will then move to the Results 
screen. 

Present Value 
Coefficient 

YELLOW Block (Result). The program displays 12.41 as the present 

value coefficient. The Present Value Coefficient is the present value of 

$1.00 per year in benefits received over the project useful life time 

period. The Present Value Coefficient is calculated from the Project 

Useful Lifetime and the Discount Rate, which are carried over, 

PURPLE Blocks (Carry Over), from the LEVEL ONE Data entry page 

and displayed here for reference. 

Summary of Expected Damages and Benefits 

Expected 
Damages and 
Benefits Table 

YELLOW Blocks (Results). For each category listed in the table 
above, the program displays the calculated results: Expected Annual 
Damages Before and After Mitigation, Expected Annual Benefits, 
and the Present Value of the Annual Benefits. See Chapter 9, 
Benefit-Cost Programs: Results, for a detailed discussion of these 
results and how to interpret them. 

4-15 


VERSION 1.0 12129194 TUTORIAL

BENEFITS AND 

COSTS 

Project Benefits 

Project Costs 

Benefits Minus 

Costs 

Benefit-Cost 
Ratio 

Next 

YELLOW Block (Result). The program displays $36,691 as the present 
value of damages avoided, which are the calculated benefits for the 
mitigation project. This value is the "bottom line" -the calculated 
benefits of the project -- corresponding to all of the data inputs made 
previously. 

YELLOW Block (Result). The program displays $53,205 as the total 
costs of the proposed mitigation project. 

YELLOW Block (Result). The program displays ($16,513) as the 
difference between the Project Benefits (i.e., the present value of total 
damages and losses avoided) and -the total Project Costs of the 
mitigation project. This result indicates that for the particular project 
evaluated the benefits are less than the costs by $16,513. 

YELLOW Block (Result). The program displays 0,69 as the ratio of 
benefits to costs for the proposed mitigation project. This means that 
each $0.69 in benefits from the project carries a cost of $1.00. Thus, 
project costs are greater than the benefits. 

Click on the NEXT SCREEN button and go to the next results screen, 
SUMMARY. 

The summary contains a concise compilation of all of the data inputs 

which affect the numerical benefit-cost results. 

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VERSION 1.0 12/29/94 TUTORIAL

I 

PRINT MENU

TO END THE 
TUTORIAL 

The Print Menu controls printing of the Summary page, the Report, and 
any or all of the graphs included in the Benefit-Cost Program. The 
Summary page contains a one-page compilation of all of the data inputs 
which affect the numerical benefit-cost results. The Report is a printout 
of the Data and Results screens from the Benefit-Cost Program, 
without the Help buttons and without the bright color shadings. 

Click on the Print menu label to access the printing options. The 
program will automatically display the range of available choices to 
print. Click the mouse button on the appropriate item in the Print menu 
to print any desired item. 

After completing the tutorial session, please EXIT from the tutorial 
Benefit-Cost Program. 

To save your tutorial example: 
First, save your work (if desired) with a new name, by using the 
FilelSave As command described above. 

To closethe tutorial file: 
Click on File then click on Quit. 

To conduct another benefit-cost analysis: 
Use the mouse to move the cursor to File and hold down the left 
button. Then highlight Qpen... Open the new file, either 
BCEXAMP.WB1 or BCBLANK.WB1, as described in the 
section, OPENING FILES on page 3-2. 

If you don't wantto do anotherbenefit-costanalysis: 
Click on File, then click on Exit to leave Quattro Pro and return 
to Windows. To exit from Windows, click on Eile, then on Exit. 
The screen will display a dialog box with "This will end your 
Windows session." Click on OK to return to a DOS prompt. 

4-17 


VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance 

VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance 

CHAPTER 5

BENEFIT-COST PROGRAMS: GUIDANCE 

I I

Introduction The accuracy, validity, and usefulness of any benefit-cost analysis 
depends on the correctness of the input data. Any benefit-cost analysis 
in which input data such as the building depth-damage function or the 
effectiveness of the mitigation measure do not realistically reflect the 
particulars of the building and mitigation project under evaluation cannot 
provide useful results. 

Each analyst conducting benefit-cost analysis has the responsibility to 
ensure that all data inputs are reasonable, defensible, and well-
documented. The programs process all of the data inputs in a 
mathematically correct manner, but the programs cannot produce 
correct results when incorrect data are entered. The analyst has 
control over the data inputs and thus responsibility for the results. 

Thus, a good faith effort must be made to obtain accurate input data for 
benefit-cost analysis. The zero flood depth elevation of the building 
under evaluation is particularly important because this markedly affects 
the degree of flood risk to the building and thus markedly affects the 
benefits of avoiding future flood damages. 

I e nE efi th c ost a al ysi s n diusx b

~ 

re Hieweditoensu e hat data pu ts I 

jilding i ~deevlaion '-' E I 

5-1


VERSION 1.0 12129/94 B-C PROGRAMS: Guidance 

Exact Data 
vs. Estimates 

Data 

Requirements 

Despite the importance of accurate data input for benefit-cost analysis, 
very few of the data inputs for benefit-cost analysis of hazard mitigation 
projects will be exact numbers. However, if exact numbers are 
available for some of the data inputs, enter them. For example, if the 
zero flood depth elevation,the square footage of the building and the 
value of contents are known, then enter the known values. In most 
cases, however, only a few of the required data inputs will be known 
exactly. 

Typically, most of the data inputs for benefit-cost analysis willbe 
estimates, rather than exact numbers. Ifexact values are not 
available, it is acceptable to use approximate values or your best 
judgement. For example, if a neighborhood has houses of 
approximately 1000 square feet and an average value of $60,000, then 
it is acceptable to use these values as the average for the 
neighborhood. It is not necessary to determine that one house is 927 
square feet and another 1083 square feet, or that one house is worth 
$56,000 because the roof leaks and another is worth $62,500 because 
it has an elegant fireplace in the living room. 

For most small projects, approximate values may provide an acceptable 
benefit-cost analysis. As project size (i.e., cost) increases, or for 
projects whose benefit-cost ratio is very close to one, it may be 
worthwhile to devote more time and effort to obtaining better estimates 
or more exact values. 

The level of detail, amount of data required, and level of effort 
necessary to conduct a benefit-cost analysis of a hazard mitigation 
project may vary substantially depending on the scale of the project and 
the desired accuracy of the analysis. 

The benefit-cost software is flexible and is designed to accommodate 
different levels of analysis corresponding to different scales of projects 
and desired level of accuracy. The simplest analysis, requiring the least 
project-specific data, can be completed using "default" or reference 
data built into the programs, along with a minimum amount of required 
project-specific data. More detailed analyses can, if desired, 
incorporate a large body of project-specific data. 

5-2 


VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance 

VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance 

LEVEL ONE A LEVEL ONE (Minimum Data) benefit-costanalysis can be
(Minimum Data) conducted using "default" or reference data built into the programs.
B-C Analysis See Chapter 6, Benefit-Cost Programs: Level One Analysis for

more detailed information. 

A LEVEL ONE (Minimum Data) analysis relies heavily on default data 
built into the Benefit-Cost Programs. Completing a LEVEL ONE 
benefit-cost analysis requires entering the following information: 

1. All "required" data on the LEVEL ONE Data screens, 
which include: 
a. Project Information. These data, discussed in 
Chapter 6, page 6-3, identify the facility, the 
project under evaluation, and the discount rate. 
Except for the discount rate, these entries do not 
directly affect the numerical benefit-cost results. 
5-3


VERSION 1.0 12/29/94 0B-C PROGRAMS: Guidance 
Specification of an appropriate discount rate is 
discussed in Chapter 6, Benefit-Cost Programs: 
Level One Analysis. The discount rate is fixed 
by the Office of Management and Budget (OMB) 
and FEMA policy and is NOT a user-adjustable 
data variable for FEMA-funded projects. This 
entry should be checked for appropriateness. The 
appropriate rate for Section 404 or 406 Hazard 
mitigation projects is defined by OMB and updated 
annually. 
b. Building Data. These data, which are discussed 
in Chapter 6, page 6-5, contain essential 
information, including the zero flood depth of the 
building, and building replacement value. 
c. Building Contents. These data, which are 
discussed in Chapter 6, page 6-9, identify the 
contents and the contents value. 
d. Displacement Costs Due to Flood Damage. 
These data, which are discussed in Chapter 6, 
page 6-10, identify the cost of temporary building 
space and other costs associated with displacement 
from the building due to flood damage. 
e. Value of Public/Nonprofit Services. These 
data, which are discussed in Chapter 6, page 61, 
describe the type of services provided, the 
daily cost of providing these services from this 
building, the post-disaster continuity premium, and 
the total value of lost services per day. 
f. Rent & Business Income. These data, which are 
discussed in Chapter 6, page 6-14, identify the 
total monthly rental income and estimated net 
business income of commercial tenants (if any). 
g. Mitigation Project Data. These data, which are 
discussed in Chapter 6, page 6-14, specify the 
type of mitigation project, lifetime of the project, 
the total costs, and the effectiveness of the project 
in avoiding future damages and losses. 

5-4


VERSION 1.0 
VERSION 1.0 
12/29/9412/29/94 
B-C PROGRAMS: 
B-C PROGRAMS: 
Guidance 
Guidance 
I 
2. Flood Hazard Data on the "Flood Hazard" data entry 
screen. The required data on the "Flood Hazard" screen, 
discussed in Chapter 7, consist of information from the 
Flood Insurance Study (FIS): flood elevations and 
discharges for 10-, 50-, 100-, and 500-year floods. If a 
FIS is not available, then comparable data may be 
obtained elsewhere or estimated. In any case, good 
estimates of the flood hazard at the site under evaluation 
are essential for benefit-cost analysis. 

LEVEL TWO For large, high-cost projects, projects which are politically sensitive, or 

(Detailed) projects where initial screening indicates that benefit-cost ratios are 

B-C Analysis close to one, more detailed analysis may be desirable. Detailed 
analysis is also necessary whenever the default values, used in the 
LEVEL ONE (Minimum Data) analysis, do not accurately reflect a 
specific project under evaluation. See Chapter 8, Benefit-Cost 
Programs: Level Two Analysis, for detaileddiscussion. 

The Benefit-Cost Programs allow the user to "override" (i.e., replace) 
any of the default values by entering building-specific data in the BLUE 
data entry blocks. All entries in BLUE blocks override default data 

which are always shown in ORANGE blocks. 

Users may enter a complete building-specific analysis by entering data 
in all of the BLUE blocks, or simply enter a few building-specific data 
where desired. 

There are several circumstances when entering building-specific data is 
highly recommended, including: 

1. for non-residential buildings, because the FIA depth 
damage data (see Chapter 6) are predominantly for 
residential buildings, 

2. whenever high water velocities, debris or ice flows are 
expected during flooding, because the default depth 
damage data are for damage resulting predominantly 
from water depth only, 
3. for buildings which are unusually susceptible or resistant 
to flood damage because of construction details or 
contents, 
I 

5-5


VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance 

VERSION 1.0 12129/94 B-C PROGRAMS: Guidance 

I 

4. for buildings in which loss of function impacts (relocation 
costs, rental and business income losses, loss of 
government services) are high, and 
5. any large, high-cost, or politicallysensitive projects, 
especially when a preliminary LEVEL ONE analysis 
indicates a benefit-cost ratio near one. 
R g WAR

m Ji~ Xo 1 (nd rforall 

Expediting Benefit-cost analysis of most common hazard mitigation projects is 

B-C Analysis easy and simple: many of the required data inputs are built into the 
software as default values and most of the other required data are 
readily obtainable. 

There are data collection requirements necessary in order to conduct 

benefit-costanalyses. Some data, such as flood hazard information 

and zero flood depth elevations, are particularly important for the 

analysis and accurate values must be obtained. Often the necessary 

data are not particularly difficult to obtain. 

By providing a quantitative, defensible framework, benefit-cost analysis 

of hazard mitigation projects may expedite the approval process for 

good projects by providing solid documentation of eligibility. Benefit-

cost analysis may also minimize the appeal process for projects which 

are rejected by providing quantitative, rather than purely subjective 

decision-making criteria. Furthermore, if there are disputes between 

FEMA and applicants over the results of the benefit-cost analysis, all of 

the input data are clearly on the table for review and discussion. 

Thus, when the whole project evaluation process is considered, benefit-
cost analysis may actually reduce the effort required rather than 
increase it. 

Furthermore, there are several ways to conduct benefit-cost analyses 
efficiently, including: 

5-6


VERSION 1.0 12129/94VERSION 1.0 12/29/94 B-C PROGRAMS: GuidanceB-C PROGRAMS: Guidance 
1. Use common data to evaluate projects in a single 
neighborhood. Many of the data may be applicable to 
numerous structures in a single neighborhood. For 
example, flood elevations of 10, 50, 100, and 500-year 
floods may be applicable to an entire neighborhood. 
Other data inputs such as replacement value per square 
foot, depth-damage function, etc., may be the same or 
very similar for many structures in a neighborhood. 
2. Evaluate projects in a single neighborhood 
consecutively. To maximize the use of common data 
and for consistency, it may be desirable to conduct all the 
benefit-cost analyses required for a given neighborhood 
consecutively, changing only the data which differ from 
project to project. Changes in only a small number of 
input parameters (or sometimes only one, such as zero 
flood elevation) may suffice to conduct many analyses, 
once the first analysis is completed. 
3. Group similar projects. If a large number of structures 
are similar (such as a housing development), then it may 
not be necessary to conduct individual analyses of each 
structure. Rather, group projects with the same flood 
hazard risk (i.e., at the same elevation or closely similar 
elevations) can be grouped or averaged. A buyout or 
relocation of one hundred 1,000 square foot houses can 
be analyzed as 100,000 square feet of single family 
residences, or analyzed by calculating the benefits for 
one (average) house, multiplied by one hundred, and 
then compared to the total cost of the buyout. 
4. Consider projects at the same or closely similar, Zero 
Flood Depth Elevation with the same flood hazard 
risk. Flood hazard risk will be identical for structures at 
the same or closely similar Zero Flood Depth Elevation in 
the same neighborhood. Once the flood hazard 
information is compiled, many single analyses can be 
conducted using the flood hazard information, or groups 
of buildings at the same Zero Flood Depth Elevation can 
be grouped for one analysis. 
I 

5-7


VERSION 1.0 12/29/94 B-C PROGRAMS: M11idant-A 

VERSION 1.0 12/29/94 B-C PROGRAMS. Guidnn. 

If a large number of similar structures at varying 
elevations are to be evaluated for a buyout, relocation, or 

S 

for a single type of flood mitigation measure (e.g., 
elevation or protection by a levee) then structures may be 
grouped in bands (contours) of elevation. One or two feet 
of elevation difference can markedly change flood 
hazard, so it is very important to only group structures of 
the same or closely similar elevations. If a large group of 
structures varies in elevation, the structures may be 
grouped in one-foot elevation bands: for example, 
consider all structures between 6.5 and 7.5 feet of 
elevation to be at 7 feet. Grouping structures in wide 
bands of elevation (e.g., covering several feet of elevation 
difference) will almost certainly produce substantially 

inaccurate results. 

5. Use your good judgement and make reasonable 
estimates. Remember that exact data are generally not 
available. Always use judgement and reasonable 
estimates whenever exact data are not available. 
Although it may be necessary to gather additional data for 
large (high-cost), controversial, or high-visibility projects, 
or projects with Benefit-Cost ratios near one, many 
decisions will be clear-cut and can be made with 
approximate data only. 

5-8


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

CHAPTER 6

PROGRAMS: LEVEL ONE ANALYSISI

jBENEFIT-COST 

Introduction 

This chapter provides guidance on conducting a LEVEL ONE 

(Minimum Data) benefit-cost analysis; defines the data input terms; 

and provides hints on making reasonable estimates when exact data 

are not available. The LEVEL ONE Data entries MUST be completed 

whether or not a LEVEL TWO analysis is subsequently conducted. 

See Chapter 5, Benefit-Cost Programs: Guidance, for general 
guidance on benefit-cost analysis, including: the use of exact data vs. 
estimates, when to use LEVEL ONE (Minimum Data) vs. LEVEL TWO 
(Detailed) benefit-cost analysis, and other helpful hints. 

See Chapter 3, Program Basics, and Chapter 4, Tutorial, for basic 
information on moving around within data entry screens, entering data, 
erasing mistakes, etc. See the Quattro Pro Manual for detailed 
technical information about the spreadsheet program. 

DataDifferences:Public, Commercial, & Residential Buildings 

The Benefit-Cost Programs can be used to evaluate hazard mitigation 
projects for a wide range of building uses, including public/nonprofit, 
commercial, residential, and mixed-use buildings. 

Generally, the data requirements are similar for different building uses. 
However, any data entries which are not applicable to the building 
under evaluation may be left blank or zeros may be entered. For 
example, in a completely public or residential building, leave blank or 
enter zeros for any entries which pertain to rental or business income. 

There are six types of avoided damages and losses (i.e., benefits) 
which are considered in the programs: building damages, contents 
damages, displacement costs, business income losses, rental income 
losses, and lost public/nonprofit services. In some circumstances it 
may not be necessary to consider all of these avoided damages and 
losses, even if they are applicable to the building under evaluation. 

6-1 


VERSION 1.0 

VERSION 1.0 

12/29194 B-C PROGRAMS: Level One Analvsls 

12/29/94 B-C PROGRAMS: Level One Analysis 

If benefit-cost analysis is being used ONLY to establish minimum 

eligibility for funding and NOT to prioritize projects, then once sufficient 

benefits are considered to exceed the project costs, it may not be 

necessary to consider additional benefits. For example, if the benefits 

of only avoiding building damage exceed costs, then it may not be 

necessary to consider any of the other damages and losses avoided. 

If desired, data can be entered sequentially. For example, enter data 
applicable to building damages only, then review the benefit-cost ratio 
to see if it is greater than one. If so, then other data entries can be left 
blank. If not, then contents damage data, displacement costs, etc., can 
be entered sequentially until benefits exceed costs, i.e., the benefit-cost 

ratio is greater than one. In other words, it may not be necessary to 

consider some of the more complicated damages and losses, such as 
the value of government services lost if projects can be demonstrated 
to be cost-effective by avoiding only building and contents damages. 

However, if benefit-cost ratios are used to prioritize among projects with 

benefit-cost ratios greater than one, then it is important to count fully all 
of the benefits applicable to each project. 

Data Input: Color Codes 

Each entry is color coded. See Cell Colors, page 3-11, or Model I 

Color Codes on the Benefit-Cost Programs menu. 

User data entries can be made only in PINK, GREEN, BLUE or RED 

blocks: 
PINK BLOCK Information Only: entries do not 
affect the numerical results; 
GREEN BLOCK Data Input: entries affect the 
numerical results; 
BLUE BLOCK Override Default Values: entries 
affect the numerical results; 
RED BLOCK OMB Policy: entries determined by 
OMB/FEMA policies and affect the 

numerical results. 

Blocks colored ORANGE, YELLOW, and PURPLE and all other parts 

of the programs are protected. User entries cannot be made in these 
blocks. To change information in PURPLE blocks (Carry Over) the 
original data entries in the PINK or GREEN blocks must be changed. 

As you enter data, remember the color codes! 

6-2 


:VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis

VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

FLUisthmi A 

Introduction To conduct a LEVEL ONE (Minimum Data) benefit-cost analysis, only 

the LEVEL ONE Data and the Flood Hazard Data must be entered. 
To conduct a LEVEL TWO (Detailed) benefit-cost analysis, additional 
building-specific data may be entered. See Chapter 5, Benefit-Cost 

Programs: Guidance, for a discussion of the differences between 

LEVEL ONE and LEVEL TWO analyses. See Chapter 8, Benefit-

Cost Programs: Level Two Analysis, for a detailed review of 

conducting a LEVEL TWO analysis. 

Me1 I Sm 

These data entries describe the building and hazard mitigation project 
under evaluation. 

Building Name 
Address 
City, State, Zip 
PINK Blocks (Information Only). These entries contain basic 
identifying information about the building being evaluated: Building 
Name, Address, City, State and Zip Code. 
Help When entering the address (or any combination of letters and numbers 
which begin with a number), remember to first type an apostrophe (') 
followed by the number and street name. See Chapter 3, page 3-13. 
Owner PINK Block (Information Only). The building's Owner may be an 
agency, a private party, etc. Building ownership may affect eligibility for 
hazard mitigation funding. 
6-3 


VERSION 1.0 12/29/94 B-C PROGRAMS, Level One Analysis 

Contact Person 

Disaster Number 

Project Number 

Application Date 

Discount Rate 

(%) 

PINK Block (Information Only). The Contact Person is someone 
who could, if needed, provide additional information about the building 
to the analyst. 

PINK Block (Information Only). The Disaster Number is a unique 
number assigned by FEMA for each disaster. 

PINK Block (Information Only). The Project Number may be the 

DSR number assigned by FEMA or any other identifying number. 

PINK Block (Information Only). The Application Date is the date 
when the application was submitted to FEMA. 

RED Block (OMB Policy). The Discount Rate entry is determined by 
OMB/FEMA policy and cannot be varied by the user on a project-byproject 
basis. 

On October 29, 1992, OMB issued Circular A-94, Revised (Transmittal 
Memo No. 64), "Guidelines and Discount Rates for Benefit-Cost 
Analysis of Federal Programs." In this Circular, OMB states that the 
appropriate discount rate varies depending on whether or not the 
investment (i.e., project) is an "internal Federal government 
investment." 

For FEMA-funded hazard mitigation projects for state and local 
governments (or eligible nonprofits), the OMB-mandated discount rate 
is the rate applicable for investments which are not internal Federal 
government investments. The OMB-mandated discount rate 
corresponds approximately to the 30-year Treasury bond rate, but the 
appropriate rate is specifically fixed by OMB annually. Currently, the 
OMB-mandated discount rate is 7% (see Appendix C of Circular A-94). 

For each disaster, an appropriate discount rate should be determined 
by FEMA, in accordance with the OMB guidance, and applied 

uniformly to all hazard mitigation projects being considered. 

The discount rate determined for each disaster is entered in the RED 
Block. After this rate is determined and entered ONCE, it can then be 
used for analysis of ALL hazard mitigation projects for this disaster. 

6-4


VERSION 1.0 12129194 B-C PROGRAMS: Level One Analysis 

Scenario Run ID PINK Block (Information Only). The Scenario Run ID provides a
place to enter a Run Number or identifying name to distinguish this
particular benefit-cost analysis from others. In some cases, multiple
analyses of the same project may be run with different sets of input
assumptions to explore the sensitivity of results to changes or
uncertainties in input data.

Analyst PINK Block (Information Only). The Analyst block identifies the
person principally responsible for the benefit-cost analysis. The
analyst's name is displayed automatically in small type on the bottom of
each printed page and on the cover page of the printed report.

II L =_11]I 

BUILDING TYPE The building's construction type is very important for the benefit-cost
analysis because many of the numerical values in the programs,
including the amount of damage a particular building type is expected to
sustain under different flood depths, depend on the building type.

GREEN Button (Data Input). Select the Building Type by clicking on 
the appropriate green and gray button which applies and determines 
many of the default parameters. The selected building type appears in 
the purple cell labeled "Building Type Selected." 

l~~~~~~~~, _-X 

MANSX ORSt~ ffiff'.'i>R4mmet -I-,~ 11---_ .<1 4 _ I I 

I --,X,,<....... 'ev. |

_~~~~~~~1= ,9..-,:i _ ,.' St.>t-'2:. 

8

, 18.f,<i.,,*,, 3 ."-',X',~'.;~j,~ 

The building types on the Select Building Type buttons are the six 

Federal Insurance Administration (FIA) building types. If one of these 

six types is selected, default depth-damage functions are used by the 

programs to estimate flood damages. To view the default depth-

damage function for the building type selected, choose Level Two Data 
I Building Depth-Damage Function from the program menu, or see 

the Default Depth-Damage Function Table on page 8-4. 

If the building under evaluation is not one of these FIA types, then a 
LEVEL TWO analysis of the building depth-damage function MUST be 
done. The closest type building type may be selected to provide a 
depth-damage function for reference, but a building-specific depth-
damage function appropriate for the building MUST be entered. See 

6-5 


VERSION 1.0 12/29./94 B-C PROGRAMS: Level One Analysis 

BUILDING 
INFORMATION 

Zero Flood Depth 
Elevation 

Number of 
Stories Above 
Grade 

Construction 
Date 

Chapter 8, Benefit-Cost Programs: Level Two Analysis, page 8-2, 
for information about entering building-specific depth-damage functions. 

Similarly, if Other is selected for building type, no default (LEVEL ONE) 
depth-damage function can be provided and a LEVEL TWO analysis 
MUST be conducted. 

This section contains entries for the Zero Flood Depth Elevation and 
three descriptive categories for the building. 

GREEN Block (Data Input). The Zero Flood Depth Elevation, as 
defined by the Federal Insurance Administration, is the elevation in feet 
of the top of the finished flooring of the lowest finished floor. 

The Zero Flood Depth Elevation of the building under evaluation is 
particularly important because it markedly affects the degree of flood 
risk for the building, and thus markedly affects the benefits of avoiding 
future flood damages. 

Zero Flood Depth Elevations can be obtained from surveying data if 
available, or may be estimated from observed flood data. For example, 
if the flood was known to have had an elevation of 463 feet in a 
neighborhood and the flood depth in a building was 4.5 feet above the 
Zero Flood Depth Elevation, then the Zero Flood Depth Elevation 
for the building (i.e., the elevation of the top of the finished flooring of 
the lowest finished floor) must be 458.5 feet. 

PINK Block (information Only). The Number of Stories Above 
Grade may affect engineering judgment about the building's 
vulnerability to flood damage. Taller buildings will have lower 
percentages of flood damage at a given flood depth, because only the 
lower story or stories will be directly affected by flood waters. 

PINK Block (Information Only). The Construction Date is included 
to provide guidance about the building's vulnerability to flood damage 
because construction practices change with time. In the absence of 
more detailed information, knowing the construction date may help a 
knowledgeable engineer to make informed judgements about probable 
construction materials and details which may be relevant to a building's 
depth-damage function. 

6-6 


VERSION 1 .0 1-2129/94 B-C PROGRAM\S: Level One Analysis 

VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

Historic Building 
Controls 

BUILDING SIZE 
AND USE 

Total Floor Area 

Area Occupied 
by Owner or 
Public/Nonprofit 
Agencies 

BUILDING 
VALUE 

PINK Block (Information Only). Enter a "YES" or "NO" in Historic 
Building Controls to indicate whether this building has been entered 
or is eligible to be entered in the Register of Historic Buildings, or is 
affected by any similar legislation. Historic status may limit allowable 
flood hazard mitigation projects and result in higher than normal costs 
for both flood damage repair and mitigation projects. 

GREEN Block (DataInput). The Total Floor Area in square feet 
(sf) is the size of the entire building. 

GREEN Block (Data Input). The Area Occupied by Owner or 
Public/Nonprofit Agencies (sf) may be the same as the total area or 
less if commercial businesses occupy part of the building. For single 
family residences, the total area and area occupied by the owner are 
generally the same. 

These two areas are distinguished because some of the economic data 
(displacement costs, rental and business income, value of government 
services) depend on the space occupied by public/nonprofit agencies 
and commercial businesses. 

Remember to enter numerical values without a dollar sign ($) or 
commas; see page 3-13 for more information. 

The data entries in these blocks describe several aspects of the value 
of the building. 

B ILDING VALUE 

>Totat~Buildng t ($n).e

Repaceme valu 

6-7


VERSION 1.0 12/29/94 B-POGAS:Lee O gnenls'

VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

Building 
Replacement 
Value ($Isf) 

Total Building 

Replacement 
Value 

Demolition 

Threshold 

GREEN Block (Data Input). Building Replacement Value ($Isf) is a 

measure of the economic value of the building, including the structural
and non-structural permanent parts of the building, but excluding
contents.

Replacement value means the cost to provide a functionally-equivalent
structure of the same size. Replacement value does not include
recreating historical or archaic materials, finishes or features.

For historic buildings, the distinction between "reproduction" and
"replacement" value may be important. Reproduction duplicates the
design and architectural details of a specific building. For historic
buildings, the reproduction value rather than the replacement value may
be a more appropriate measurement of a building's value. If desired,
an historic building's reproduction value (in $Isf) can be entered in the
"Building Replacement Value" block.

YELLOW Block (Result). Total Building Replacement Value ($)is
calculated from the value per square foot and the building size.

GREEN Block (Data Input). Building Damagethat would Result in
Demolition, the "demolition threshold," is the percentage of building
damage at which demolition and replacement (rather than repair) would

0

be expected to occur as the economically efficient choice. Many
buildings will be demolished rather than repaired when the cost to repair
the damage exceeds some percentage of the replacement cost.

I 

~ A 

For older, somewhat substandard buildings, the demolition threshold
may be quite low (e.g., 20 or 30%). For typical, relatively modern
buildings, the threshold will generally be higher (e.g., 50 or 60%). For
some particularly important historical buildings, the demolition threshold
may approach 100%.

6-8 


VERSION 1.0 i12/29/94 B-C PROGRAMS: Level One Analysis 

The demolition threshold damage percentage is an important policy 
parameter which may significantly affect the benefit-cost results 
because it may have a major impact on the depth-damage function. 
Therefore the demolition threshold damage percentages should be 
chosen carefully in accord with the condition and viability of the existing 
building. For example, a brand new city hall building would probably be 
repaired from a higher level of damage than would a decrepit building 
badly in need of refurbishing. 

YELLOW Block (Result). The demolition threshold in dollars of 

damage is calculated from the entered percentage and the building 

replacement value. 

3 S~~~~

: 

Contents PINK Block (Information Only). The Contents Description block is 
Description for a brief summary of the building's contents (e.g., computers, office 
furniture). 

Total Value of GREEN Block (Data Input). -Total Value of Contents is the estimated 

Contents total value of the building's contents, including furniture, carpet, 
equipment, computers, supplies, etc. 

The exact value of building contents is rarely known. Estimates can be 
obtained from owners, or from a general knowledge of the nature of the 
contents and common sense. For example, an art museum or a 
building filled with computers will have a much higher contents value 
than a building storing used bricks or recycled newspapers. 

For most buildings, the value of contents is significantly smaller than the 
building value. However, in some cases where contents are unusually 
valuable (e.g., an art museum) or usually vulnerable to flood damages, 
then avoiding contents damage may be as important or more important 
than avoiding building damages in determining total project benefits. 

Default estimates of the Contents Depth-Damage Function (i.e., 

contents damage as a percentage of total contents value) are based on 

the building type selected. To view the default contents depth-damage 

function for the building type selected, choose Level Two Data I 

Contents Depth-Damage Function from the Benefit-Cost Program 

menu; for more information see page 8-8. 

6-9 


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

Value of
Contents

($/sf1 

Rental Cost of 
Temporary 
Building Space 
($/sf/month) 

RentalCost of 
Temporary 
Building Space 
($/month) 

Other 

Displacement 

Costs 

Total 

Displacement 

Costs 

YELLOW Block (Result). The Value of Contents ($Isf) is calculated 
from the Total Value of Contents and the Total Floor Area of the 
building. The Value of Contents ($/sf) may be useful in comparing 
contents values from building to building and as a guide as to whether 

estimated contents values are reasonable. 

3 A S 3 0 0033k O 

Displacement Costs due to Flood Damage may be incurred when 

owners must operate from a temporary site while flood-related damage 

to the original building is repaired. Costs for temporary rent and other 

displacement expenses are entered here. 

GREEN Block (Data Input). Rental Cost of Temporary Building 

Space ($lsflmonth) is an estimate of the rental rate paid for temporary 

quarters. Major floods may cause extensive damage to many 

structures, thus reducing the available supply of alternate space and 

leading to higher rental costs throughout the area. 

YELLOW Block (Result). The Rental Cost of Temporary Building 
Space ($lmonth) is calculatedfrom the Area Occupied by Owner or 
PubliclNonprofit Agencies (sf) and the Rental Cost of Temporary 
BuildingSpace ($1sf/month). 

GREENBlock (Data Input). Other Costs of Displacement 

($/month) include moving and extra operating costs incurred because 

of the disruption and displacement from normal quarters. 

YELLOW Block (Result). Total Displacement Costs ($/month) are 

calculatedas the sum of Rental Cost of Temporary 

Building Space ($Imonth) and Other Costs of Displacement 

($/month). 

Default estimates of displacement times depend on building damages 
at each flood depth. To view the default displacement time estimates 
choose Level Two Data I Displacement Time from the Benefit-Cost 
Program menu. For more inforniation, see page 8-11. 

i 

6-10


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

Description of 
Services 
Provided 

Annual Budget 

Displacement costs for tenants are approximated in the programs by 
counting the rental income losses to the owner. Counting tenant 
displacement costs and rental income losses would be double counting. 

For public/nonprofit agencies, Displacement Time is distinct from 
Functional Downtime (i.e., service interruption); estimates for each will 
generally be quite different. For example, a public agency which is 
relocated in temporary quarters for six months will incur six months of 
displacement costs, but the loss of service is only two weeks if the 
agency is functioning in temporary quarters two weeks after the flood. 
To view the Default Functional Downtime estimates, choose Level Two 
Data I Functional Downtime from the Benefit-Cost Program menu; or 
see page 8-14. 

l * a

S * I

The value of public/nonprofit services is included in the benefit-cost 
programs to count fully the benefits of avoiding flood damage for such 
facilities. If the building under evaluation is a commercial or residential 
building, then leave these entries blank or enter zeros. 

PINK Block (Information Only). This block provides a place to enter a 
brief summary of the type of services provided from this location. 

GREEN Block (Data Input). The Annual Budget of Public/Nonprofit 
Agencies is the total annual operating budget of all the public/nonprofit 
agency functions located in this building. The total should include 

rental costs but exclude "pass-through" monies (e.g., Social Security 
payments) which the agency receives and redistributes. The annual 
operating budget is used to estimate the value of services provided. 

For example, if a public/nonprofit Egency spends $10,000 per day 

6-11 


VERSION 1.0 012/29/94 :7I ; B-C PROGRAMS: Level One Analysis 
VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

providing a service to the public, then this service is valued at $10,000 
per day and the loss of this service due to flood damage is also valued 
at $10,000 per day. 

Is Rent GREEN Buttons (Data Input). Select whether the Annual Budget 

Included? includes or excludes any rent paid (by an agency which does not own 
the structure) by clicking on the appropriate button. Your choice willbe 
displayed next to the rent buttons. 

Proxy Rent ORANGE Block (Default). If rent is NOT included in the annual
budget, the programs calculate a default or proxy rent based on the
value of the building and the discount rate.

User-Entered BLUE Block (Override Default). Enter a User-Entered Rent 
Rent Estimate Estimate ($Imo) in place of Proxy Rent if the proxy rent displayed is 
not an accurate estimate for the building under evaluation. 

Cost of YELLOW Block (Result). The programs calculate the daily Cost of 
Providing Providing Services from this Building ($/day)based on the annual 
Services budget and, if rent is not included in the annual budget, from the default 

proxy rent or, ifprovided, from the user-entered rent estimate. 

Post-Disaster GREEN Block (Data Input). Some public/nonprofit services may be 
Continuity very littlein demand after a disaster, while others may be vital to 
Premium maintain. Public/nonprofit services that are important for post-disaster 

response and recovery are worth more to the community after the 
disaster than in normal circumstances. The Post-Disaster Continuity 
Premium ($/day) is a way of assigning an extra value to these post-

disaster services. 

For example, emergency services would be vital in the hours and days 

immediately followinga disaster, whereas routine services such as 
employment referral would not. Based on the nature of the services in 
this building, the continuity premium is how much extra daily cost the 
tenant agencies would be willing to spend to maintain agency functions 

after a disaster. 

The magnitudeofthe Post-Disaster Continuity Premium depends on 
how critical the services are in the post-disaster environment. 
Emergency response services such as medical, fire, and police are 
particularly important post-disaster and continuity premiums for such 
services are generally high. Services which are only moderately 
important post-disaster should have moderate premiums. Routine 
services that can be delayed with littleor no impact should not have 
continuity premiums. 

6-12 


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

Continuity premiums of 50-100% of the normal daily costs of providing 

services may be appropriate for services which are moderately 
important in the post-disaster environment. Continuity premiums of 

several times normal daily costs may be appropriate for emergency 
response services. Continuity premiums of five or ten times the normal 

daily costs may be appropriate for services which are critical to the 

disaster response. 

The Post-Disaster Continuity Premium, like all other inputsfor the 

benefit-cost analysis, must be reasonable and defensible for the 

specific public/nonprofit service being valued. If the continuity premium 

is unreasonable, this portion of the analysis will be invalid. 

Total Value of YELLOW Block (Result). TheTotal Value of Lost Services ($/day) 

Lost Services is calculated by summing the daily cost of providing services under 
normal conditions and the Post-Disaster Continuity Premium. 

Estimates for the value of lost public/nonprofit services for each flood 

depth are based on the daily cost of providing services and estimates of 

Functional Downtime. Functional Downtime is the time period for 

which public/nonprofit services are lost due to flood damage. Default 

estimates of Functional Downtime are based on the building depth-

damage function. To view the default Functional Downtime estimates 

choose Level Two Data I Functional Downtime from the Benefit-Cost 

Program menu; or see page 8-14. 

6-13


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

IV * mF11 0I-1 

I .8'.C: 1''9fv.A'... :'.''sR . g X->t'o.Gs'SKwiS1O.-^' '-y S
;'A::' :.'. ->S S 

Gal~ MoiithlRent from All~isth >:enatws,
stm'ate'dNet 
T yf (S,>mahl m hl | l-

Icoe iCommrc~EBisnesesrrS Hi 

Total Monthly GREEN Block (Data Input). Total Monthly Rent ($/month) entered 
Rent From All here is the amount paid by all tenants in the structure. For a 
Tenants commercial or residential building which is rented, this amount is 

included to value the loss of rental income from flood damages. For a 
public/nonprofit building, the rent value entered should be only the rent 
for that portion, if any, rented to private tenants. Rent costs for 
public/nonprofit agencies are included in the Value of PubliclNonprofit 

Services section discussed above. 

Estimated Net GREEN Block (Data Input). Estimated Net Income of Commercial 
Incomeof Businesses ($/month) is the net, not gross, income per month of 
Commercial commercial businesses in the building. Exact figures will generally not 
Businesses be available, so reasonable estimates may be made. If there are no 

commercial businesses in the building, then leave this entry blank or 
enter a zero. 

011M * snSNli 

Select Mitigation 
Measure 
Select Mitigation Measure 
GREEN Buttons (Data Input). Select the mitigation measure by 
clicking on the appropriate green and gray button. The selected 
mitigation measure appears in the purple cell labeled "Type of 
Mitigation Selected." 

6-14


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

VERSION 1.0 12129/94 B-C PROGRAMS: Level One Analysis 

Project PINK Block (Information Only). This space is provided to enter a 
Description brief summary of the proposed mitigation project, for example, "buyout," 
"relocate," or "elevate ten feet." 

Project Useful GREEN Block (Data Input). The project's useful life is the estimated 

Life number of years during which the mitigation project will maintain its 
effectiveness. Useful life is the time period over which the estimated 
economic benefits of the proposed mitigation project are counted. The 
useful life which the user enters MUST be commensurate with the 
actual project being considered. 

Useful lives of 5 to 10 years for equipment purchases, and 30 
(residential) to 50 (non-residential) years for building projects are 
typical. For major infrastructure projects, or for historically important 
buildings, useful lives of 50 to 100 years may be appropriate. For 
buyouts/relocations an entered lifetime of 100 years will capture fully 
the benefits of the mitigation measure. 

Mitigation 
Effectiveness 
Estimates 

GREEN Block (Data Input). The effectiveness of most flood mitigation 
projects varies with the depth of flood water. For the flood mitigation 
type selected, enter estimates of the depth at which the mitigation is 
100% and 0% effective: 

Elevation 
Elevating buildings by N feet is generally 100% effective to 
N-1 feet. For example, elevating 8 feet is 100% effective to 7 
feet, elevating 12 feet is 100% effective to 11 feet. This result 
arises from the fact that, for example, an "8-foot flood" is 
considered in the programs to be all floods between 7.5 and 8.5 
feet. Therefore, elevating a structure 8 feet will convert an 8foot 
flood into a 0-foot flood (from -0.5 to 0.5 feet), and there is 
still damage from a 0-foot flood. Thus, an 8-foot elevation is 
100% effective to only 7 feet. 

6-15 


B-C PROGRAMYS: Level One Analysis

VERSION 1.0 12/29/94 AayiVERSION-1.--22/9 RORM:Lee-n 

For buildings with basements, the situation can be more 

complicated depending on the degree of flood proofing of the 

basement. Unless there is detailed information available 
aboutan individual structure, assuming that elevating N feet is 
100% effective to N-1 feet is a reasonable assumption for 
structures with and without basements. This assumes that flood 
proofing of the basement occurs along with elevation. 

The flood depth at which elevations are 0% effective is 
calculated automatically by the programs and need not be 
entered by the user. 

Relocation/Buyout 
Relocation/Buyout projects are assumed to be 100% effective at 
all flood depths and thus effectiveness depths need not be 
entered by the user. 

Flood Barriers 
The flood depth at which flood barriers are 100% and 0% 
effective depends on how the barrier is constructed and on 
assumptions about freeboard. Freeboard is defined as the 
height of a flood barrier above a flood height which is necessary 
to insure satisfactory flood performance. For example, to 
provide 100-year flood protection for flood insurance purposes 
levees must be constructed 3 feet above the 100-year flood 
elevation (i.e., with 3 feet of freeboard). 

In the absence of detailed engineering analysis, a simple 
assumption about flood barriers is that a flood barrier of height N 
feet is 100% effective to N-1 feet and 0% effective at N feet. 

Other 
Other flood hazard mitigation projects include wet flood proofing 
and any other measures not covered by the three mitigation 

types discussed above. 

The depths at which "Other" flood hazard mitigation projects are 
100% and 0% effective must be estimated on a case-by-case 
basis. 

The programs calculate effectiveness only for the selected mitigation 
project type. Other entries should be deleted (see Delete button, page 
3-13) to avoid confusion; however, the programs ignore any other 
values in the table. 

I 

6-16


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

MITIGATION 
PROJECT 
COSTS 

Project Cost 

Base Year of 
Costs 

Annual 
Maintenance 
Costs 

Present Value of 
Annual 
Maintenance 
Costs 

Relocation Costs 
for Mitigation 
Project 

The effectiveness of flood hazard mitigation projects at every flood 
depth is calculated by the programs from the depths of 100% and 0% 
effectiveness. To view the default Mitigation Effectiveness estimates 
at each flood depth select Level Two Data I Mitigation Project 
Effectiveness from the Benefit-Cost program menu; for more 
information see page 8-17. 

GREEN Block (Data Input). The Mitigation Project Cost includes all 
direct construction costs plus other costs such as architectural and 
engineering fees, testing, permits, and project management, but 
excludes relocation costs. 

PINK Block (Information Only). The Base Year of Costs is the year 
in which the mitigation project's costs were estimated. If cost estimates 
are several years old, they may need to be adjusted by the user to 
account for inflation in costs between the base year and the present. 

GREEN Block (Data Input). Annual Maintenance Costs ($/year) 
may be required to maintain the effectiveness of some mitigation 
projects, particularly levees where annual inspection and vegetation 
removal may be required. For most other mitigation projects, Annual 
Maintenance Costs will be negligible or zero. 

YELLOW Block (Result). Based on the discount rate, the Annual 
Maintenance Cost for each year of the project's useful life is reduced 
to its present value and summed. 

For some mitigation projects, occupants may have to be relocated for 
construction of the project. In such cases, the Relocation Costs are 
an integral part of the mitigation project and must be counted in the total 
mitigation project costs. 

6-17


VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis 

Relocation Time 
Due to Project 

Rental Cost 
During Occupant 
Relocation 

Other Relocation 
Costs 

Total Relocation 
Costs 

Total Mitigation 
Project Costs 

To Continue... 

GREENBlock (Data Input). Relocation Time Due to Project 
(months) is the number of months for which the building must be 
vacated in order for the mitigation project to be completed. Note 
that this relocation time is completely distinct from the displacement 
time needed to repair flood-related damages. 

GREEN Block (Data Input). Rental Cost During Occupant 
Relocation ($/sf/month) is an estimate of the rental rate paid for 
temporary quarters. Major coastal floods may cause extensive damage 
to many structures, thus reducing the available supply of alternate 
space and leading to higher rental costs throughout the area. 

YELLOWBlock (Result). Rental Cost During Occupant Relocation 
($/month) is calculatedfromthe Rental Cost ($lsflmonth) and the 
Total Floor Area (sf). 

GREENBlock (Data Input). Other Relocation Costs ($/month) 
include moving and extra operating costs incurred because of the 
temporary relocation. 

YELLOWBlock (Result). The Total Relocation Costs are calculated 
fromthe entered Relocation Time Due to Project (months), Rental 
Cost During Occupant Relocation ($/month), and Other Relocation 
Costs ($/month). 

YELLOWBlock (Result). Total Mitigation Project Costs are 
calculated by summingthe Mitigation Project Cost, the Present 
Value of the Annual Maintenance Costs, and the Total Relocation 
Costs. 

This completes the LEVEL ONE (Minimum Data) Benefit-Cost 
Analysisdata entry process except for the Flood Hazard data. To 
enter Flood Hazard data, click on the Next Screen button at the bottom 
of the second LEVEL ONEData page, or select Flood Hazard from 
the Benefit-Cost Program menu. 

6-18


VERSION 1.0 12129/94-B-C PROGRAMS: Flood Hazard Risk 

: -CHAPTER 7 
BENEFIT-COST PROGRAMS: FLOOD HAZARD RISK 

Introduction 

This section contains data entries for flood frequencies, discharges and 
elevations which are necessary to specify quantitatively the extent of 
flood hazard at the site under evaluation. From the entered flood data, 
the programs calculate the expected annual number of floods in one-
foot elevation increments. "Expected" annual number means the long 
term statistical average number per year, not that this number of floods 
occurs every year. 

The degree of flood risk at a particular site profoundly affects the 
expected flood damages at a site and thus profoundly affects the 
benefits of avoiding flood damages at the site. Therefore, the flood 
hazard data entered in this section are among the most critical data 
inputs for benefit-cost analysis of flood hazard mitigation projects. 

LEVEL ONE A LEVEL ONE Flood Hazard Risk Analysis is performed using 
Analysis Information from a FIS and a FIRM, or equivalent information, for the 
location under evaluation. Data on flood frequencies and elevations are 
entered into the Flood Data table shown on page 7-2. 

LEVEL TWO 
Analysis 
If a FIS and a FIRM are not available, or if the user desires to use other 
estimates of flood hazard risk, then a LEVEL TWO Analysis must be 
performed. 
7-1 


VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

A AW9 m 

Carry Over PURPLE Blocks (Carry Over). Information from the LEVEL ONE 

Information DATA page is displayed to identify the building under consideration and 
to provide reference information and guidance for LEVEL TWO 
(Detailed) evaluations. 

**9 AU9 A -

A *A 

I 

Flood Data 

Flood frequency, discharge and elevation data MUST be entered in the 

flood hazard table in order to calculate the degree of flood risk at the 

site under evaluation. Flood data for 10-, 50-,100-, and 500-year 

floods are generally available from the Flood Insurance Study (FIS) for 

the area under evaluation. However, if flood data for other frequencies 

are available, the frequencies and corresponding discharge and 

elevation data may be entered in this table. 

The table showing the expected annual number of floods is 
automatically recalculated whenever the flood data are revised. 

Flood Discharge The FIS contains a table of flood frequencies and discharges similar to 
Data the two left hand columns of the table above. If more than one set of 
discharge data are shown for the stream, use the discharges for the 
closest location downstream from the building location. 

Flood Elevation The FIS also contains Flood Profile graphs which show the elevations 

Data of 10-, 50-, 100-, and 500-year floods along the stream. The elevation 
of a 100-year flood, for example, varies with location along the stream 
because water runs downhill. To characterize flood risk at a given 
location, it is necessary to know the elevation of the 10-, 50-, 100-, and 
500-year floods at this location. These data may be obtained from the 
Flood Profile graphs in the FIS. 

I 

7-2


VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

Flood Profile graphs show the variation of flood elevations with distance 
* X f . upstream from a waterway confluence, bridge, or street crossing. To 
: :: 
. determine the elevations for the building under evaluation, the distance 
upstream from a landmark on the Flood Profile graph must be 
measured on a map. The Flood Insurance Rate Map (FIRM) may be 
used for this purpose. Once the location has been properly identified, 
then flood elevations for 10-, 50-, 100-, and 500-year floods are read 
from the Flood Profile graph. 
An example of a Flood Profile graph from an FIS is shown on the 
following page. In this example, stream distance is shown in thousands 
:: of feet above the confluence with Overpeck Creek. The house under 
,: 
evaluation is located about 7850 feet above the confluence, or 45 feet 
upstream from Vanostrand Avenue overcrossing. Flood, elevations for 
the 10-, 50-, 100-, and 500-year floods are read from this section of the 
Flood Profile graph. 
In this example, the 500-year elevation is 128.1 feet; the 100-year 
. . elevation is 127.1 feet; the 50-year elevation is 125.9 feet; the 10-year 
elevation is 124.5 feet; and the channel bottom is 119.5 feet. See the 
Flood Profile graph on the next page. 
Flood elevations may vary markedly along the stream course, 
depending on the gradient of the individual stream. Therefore, it is very 
important to read properly the flood elevation data on the Flood Profile 
graph for the specific site under evaluation. 
I ..; 

7-3


mni 
Co 
125 _ 
FD 
120 
mxA) 
-L 
ID 
3 115 m l-3 N) 
-'I 
z , 0n -w 
C)0r CO, 
110 
-I a 
025 X 
105 -
0 
00.N 
ma) 
7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.0 8.1 3 
-w 
STREAMDISTANCEIN THOUSANDSOF FEET ABOVECONFLUENCEWITHOVERPECKCREEK 0. 
0 

0


VERSION 1.0 12i29/94 B-C PROGRAMS: Flood Hazard Risk 

VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

eeaA TA0A I

A~~~~9 I NAIA 

Flood Data 

Flood frequency and elevation data MUST be entered in the flood 
hazard table in order to calculate the degree of flood risk at the site 
under evaluation. Flood data for 10-, 50-, 100-, and 500-year floods are 
generally available from the Flood Insurance Study (FIS) for the coastal 
floodplain area under evaluation. However, if flood data for other 
frequencies are available, the frequencies and elevation data may be 
entered in this table. 

The table showing the expected annual number of floods is 

automatically calculated whenever any of the screens which display 

results calculated from these flood data. However, to view the 

expected annual number of floods before going to results, the Update 

Flood Data Button must be clicked to run the regression calculation 

which provides the expected annual number of floods estimates. 

Flood Elevation The FIS usually contains tables which show the elevations of 10-, 50-, 

Data 100-, and 500-year floods. Unlike riverine floods, where flood
elevations vary with distance along the stream, coastal floods are
assumed to be at the same elevation throughout an area to which a

particular transect or a group of transects applies. A transect (see 
Figures 7-2 and 7-3) is a line drawn perpendicular to the coastline 
showing the A-Zone and V-Zone regions. Thus, if a 1 00-year flood has 
an elevation of 6.5 feet, this elevation applies along the transect as 
shown in the FIS. 

The "1-year" flood elevation data entry can be estimated from the 

highest expected annual tide level or from other local flood gauge data. 

The flood frequency and flood elevation data are very important for the 
benefit-cost analysis and accurate data from a FIS or other reasonable 
estimates must be entered in the Flood Hazard Table. 

I 

7-5 


VERSUION1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

For additional guidance on obtaining flood information from Flood 
Information Studies and Flood Insurance Rate Maps, users are 
referred to the following publications: 

1. Guide to Flood Insurance Rate Maps (FIA-14), FEMA, 
May, 1988. 
2. Flood Proofing, How to Evaluate Your Options, U.S. 
Army Corps of Engineers, 1993. 
3. Flood Retrofitting Manual, FEMA, 1994. 
7-6


m 

0

z 

MB 

CD 

A ZONE |

V Z0O E 

LWAVEHEIGHT X 

WAVE HEIGHT GREATER THAN 3FT. 
t
BASEFLOODELEVATION 
INCELUDINGWAVE EFFECTSS aC)

0f 
_l~~MEAN ~~~~~~~~~~~~~~~~~~~~~~~~

-'I 

G) 

FEC AN WAET 
w~~~~~~~~~~~~~~~~WN 

C) 

0

0

en 

ent: Wave x~~~~~~~~~~~NDWAE 

Source: Flood Insurance Study Suppleent W e Height Analysis 5.

T0

FEMA, 1983. 

Pr 


m 

CO 

0 

7I3 

_ C)~~~~~~~~~~~~~~)' 

0_ .I i O 

rn -4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

FERCHARLOTTE COUNTY, FL Ad0..0f
TRANSECTLOCATIONMAP:I 16 E ---. 0

_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l .I CO) 
l~ 

Source: Flood Insurance Study Supplement: Wave Height Analysis 
_-MA, 1983. 


VERSION 1.0 12/29194 B-C PROGRAMS: Flood Hazard Risk 

VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

~ 

~

i A : ;:'

~

RUJA~

ff*,749X01:1#XA~~~~~~~~~~~~~~~~

Expected Annual 
Numberof 
Floods by Flood 
Depth 

Default Flood The default estimates of the Expected Annual Number of Floods of 

Estimates each flood depth from -2 to 18 feet are shown in the ORANGE 
(Default) column. These estimates are calculated from the flood 
frequency, discharge and elevation data entered previously. "Expected 

annual number" of floods does not mean that this number of floods 

occurs every year, but rather "expected" indicates the long term 

statistical average number of floods per year. The default estimates of 

the expected annual number of floods at each depth are shown in 

scientific notation because these numbers may vary over an extremely 

wide range, including very small numbers. For an explanation of 

scientific notation, see the Technical Appendix to this chapter, page 7

12. 
Except when annual probabilities approach one, the expected annual 
number of floods and the annual probability for each flood depth are 
virtually identical. 

i 

For a LEVEL ONE analysis, these default estimates of the expected 

annual number of floods at the site under evaluation should be used. 

7-9


VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard RIRk 

User-Entered If desired, user-entered estimates of the annual probabilities of floods of 

Flood Estimates each flood depth can be entered in the BLUE (Override Default) 
column of the Flood Hazard Table. Making such estimates and other 
possible modifications of the default flood estimates are discussed 
below in the Level Two Flood Analysis section. 

LEVEL TWO There are two ways to conduct a LEVEL TWO Flood Hazard Risk 

Flood Analysis Analysis: 
1. The flood data entry table (above) can be filled in with 
estimates based on limited data or informed judgement. 
Such an analysis will be less accurate than analyses 
using full FIS/FIRM (or equivalent) data, but flood 
estimates will be approximately correct as long as the 
input estimates are reasonable for the area under 
evaluation. Such an analysis is a LEVEL TWO analysis 
because it requires interpolation or extrapolation of 
limited data and/or other professional judgement about 
flood risks. 
2. The default values of the Expected Annual Number of 
Floods for each flood depth can be overridden with user-
entered estimates. This option requires an independent 
source of flood data, such as a U.S. Army Corps of 
Engineers study or other data from a professional 
hydraulics engineer experienced in flood modeling. Such 
flood data MUST be expressed as Expected Annual 
Numbers of Floods at the appropriate location and 
elevation under evaluation. To override the default 
estimates in the ORANGE column, user-entered values 
are entered in the BLUE column. Whenever user-
estimates of the expected annual number of floods are 
entered, the programs use these values rather than the 
default values, although the default values are displayed 
for comparison to the user-entered values. 

7-10


VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

Flood Hazard Risk: Technical Appendix

Flood 
Recurrence 
Intervals 

Flood Elevation 
vs. Flood Depth 

Floods are a probabilistic natural phenomenon: it is impossible to 
predict in what years floods will occur or how severe the floods will be. 
Flood hazards are often expressed in terms of flood frequencies or 

recurrence intervals, such as a 1 0-year flood or a 1 00-year flood. 

A "100-year" flood means that there is a 1 % chance per year of a flood 
at the 1 00-year or higher flood elevation. A 1 0-year flood means that 
there is a 10% chance of a flood of the 1 0-year or higher flood 

elevation. In general, the annual probability of a flood of X-years is 11X. 
Thus, the annual probability of an 83-year flood is 1/83 or 0.012. 

Flood recurrence intervals do not mean that floods occur exactly at 

these intervals; rather they only express the probabilities of floods. 

Thus, a given location may experience two 100-year floods in a short 

time period or go several decades without experiencing a 10-year flood. 

Flood recurrence intervals (in years) and annual flood probabilities 

contain exactly the same probabilistic information. The previous 

paragraphs explained how to convert recurrence intervals in years into 

annual probabilities. Conversely, annual probabilities can be converted 

to recurrence intervals. The recurrence interval in years of a flood 

depth with Y annual probability is 1N. For example, the recurrence 

interval for a flood with an annual probability of 0.01234 is 1/0.01234 or 

81 years. 

In the benefit-cost programs, flood probabilities are expressed in terms 

of annual probabilities. If desired, these probabilities can be converted 

to recurrence intervals by the procedure discussed above. 

For a given Riverine Flood (e.g., a 100-year flood), the elevation of the 

flood water surface varies with location along the stream as shown by 

the Flood Profile (see pp. 7-2 to 7-4). For a given Coastal Flood (e.g., 

a 1 00-year flood), the elevation of the flood water surface is 

approximately constant along a given transect (see pp. 7-5 to 7-7). At a 

given location the flood depth corresponding to a 1 00-year flood varies 

depending on the Zero Flood Depth Elevation of the building under 

evaluation. In the Benefit-Cost Programs, Expected Annual Numbers 

of Floods are shown for each flood depth from -2 to 18 feet for the 

building under evaluation. For a different building with a different 

Zero Flood Depth Elevation, the Expected Annual Number of Floods 

for each flood depth will be different. Thus, for example, the depth of a 

1 00-year flood will differ for buildings at different Zero Flood Depth 

Elevations. 

I 

7-11


VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

VERSION 1.0 12129/94 B-C PROGRAMS: Flood Hazard Risk 

Review of The annual probabilities of floods are expressed in scientific notation 
Scientific because the probabilities may vary from nearly 1 to much less than 1 in 
Notation a million (0.000001). Scientific notation is a widely-used convenient 

method of expressing numbers which vary over a very wide range. 

In scientific notation, as in the Calculated Annual Probability of Floods 
table, numbers are expressed in two parts: a prefix and a power of 10. 
For example, 6E+02, where 6 is the prefix and +02 is the power of 10, 
means 6 times 102, or 6 times 100, or 600. 

Another way of thinking about scientific notation is that the power of 10 
part of the number tells which direction and how much to move the 

decimal place. Thus, 6E+02 is 6 with the decimal placed moved to 
places to the positive (right) direction or 600. Thus, 6E+03 is 6000. 
Scientific notation with negative powers of ten, means to move the 

decimal place to the negative (left) direction. Thus, 6E-02 is 0.06; 6E

03 is 0.006 and so on. E+00, means don't move the decimal place. 

Thus, 6E+00 is simply 6. 

Scientific notation may seem cumbersome with routine numbers, but it 

is very convenient when numbers are very large or very small or to 

compare the relative sizes of very large or small numbers. Thus, 6E11 
is a more convenient way of expressing 0.00000000006. 

Flood The Expected Annual Numbers of Floods for each flood depth, 
Exceedance correspond closely to Annual Probabilities of floods. Such probabilities 
Probabilities are interval probabilities; that is, they express the probabilities for each 

flood depth. For example, in the Benefit-Cost Programs, the annual 

probability of a 2-foot flood is considered to be the annual probability for 

all floods between 1.5 and 2.5 feet of depth at that site. 

Flood probabilities are often expressed as exceedance probabilities. 

An exceedance probability means the probability of all floods greater 

than or equal to some specified flood. Thus, the annual exceedance 

probability for a 2-foot flood means the annual probability for all floods 

greater than or equal to 2 feet. 

To avoid confusion, the distinction between interval probabilities and 

exceedance probabilities must be clearly made. The commonly used 

term 1 00-year flood, is actually an exceedance probability. In other 

words, the 100-year flood level with an annual probability of 0.01 means 

all floods greater than or equal to this level. The interval probability of a 

flood at exactly (within plus or minus 0.5 feet) the 1 00-year flood level 

will be smaller (sometimes much smaller) than the exceedance 

probability for a 1 00-year flood, because the exceedance probability 

includes ALL floods greater than or equal to the 1 00-year flood. 

7-12 


:-VERSION 1.0 12/29194 -B-C PROGRAMS: Flood Hazard Risk 

VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

For completeness, the benefit-cost programs tabulate both exceedance 
probabilities and interval probabilities, although all calculations are done 
using the interval probabilities. Graphs of flood probabilities (both 
exceedance and interval) may be viewed by clicking on the graph 

buttons at the end of the flood hazard screen in the Benefit-Cost 
Programs. 

Expected The Riverine Flood modeling uses an approach outlined by the U.S.
Annual Number Army Corps of Engineers for riverine flooding (Flood Proofing, How to
of Floods-Evaluate Your Options, 1993).
Riverine

The Expected Annual Number of Floods at each flood depth are 

calculated from the flood frequency and flood elevation data entered by 
the user, along with the Zero Flood Depth Elevation of the building 
under evaluation. 

The flood frequency data (i.e., 10, 50, 100, or 500 years) correspond to 

exceedance probabilities (see Flood Recurrence Intervals section on 
page 7-7). The computer program does a regression analysis fit 
between the logarithm of exceedance probability and flood discharge to 

obtain a smooth curve relating exceedance probability and flood 

discharge. Then, flood elevations are read (by the program) from the 
"rating curve," which is the relationship between flood discharge and 
elevation. The regression analysis is done in this manner because the 

relationship between stream discharge and probabilities is smooth 
whereas the relationship between flood elevation and probabilities may 
be very irregular because of variations in stream valley shape. Flood 
probabilities for floods below the 10-year flood elevation are determined 
using the standard A-1 to A-30 flood curves used previously on FlRMs. 

This analysis gives the annual exceedance probability for all floods, in 
one-foot increments of depth. From the annual exceedance 
probabilities, calculated as described above, the expected annual 

number of floods in a given one-foot increment are calculated from the 
difference in exceedance probabilities of two flood depths. For 
example, the expected annual number for a 2-foot flood (i.e., all floods 
between 1.5 and 2.5 feet) at a given site (with a given Zero Flood Depth 
Elevation) is calculated as the exceedance probability for a 1.5-foot 
flood minus the exceedance probability tor a 2.5-foot flood. 

I 

7-13 


VERSIONA1.0 12/29194 B-C PROGRAMS: Flood Hazard Risk 

VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk 

Expected The Coastal A-Zone flood modeling uses an approach similar to that
Annual Number outlined by the U.S. Army Corps of Engineers for riverine flooding
of Floods -(Flood Proofing, How to Evaluate Your Options, 1993).
Coastal A-Zone

Coastal A-Zone flood models are based on storm surge models which 

predict flood elevations. Depending on the date of the Flood Insurance 

Study, various elevation standards may be used in the FIS (e.g., 

National Geodetic Vertical Datum of 1929, NGVD or others). 

Regardless of the elevation standard used, the FIS always gives flood 
elevations relative to some benchmark elevation. 

The Expected Annual Number of Floods at each flood depth are 

calculated from the flood frequency and flood elevation data entered by 

the user, along with the Zero Flood Depth Elevation of the building 
under evaluation. 

D&>f6bmFlood 1nsau FIS od Inrce' RatekM' 

Xm MA F1 "1W 

The flood frequency data (i.e., 10, 50, 100, or 500 years) correspond to 
exceedance probabilities (see Flood Recurrence Intervals section on 
page 7-7). The computer program does a regression analysis fit 
between the logarithm of exceedance probability and flood depth to 
obtain a smooth curve relating exceedance probability and flood depth. 
This regression fit gives the annual exceedance probability for all 
floods, in one food increments of depth. 

From the annual exceedance probabilities, calculated as described 
above, the expected annual number of floods in a given one foot 
increment are calculated by difference.. For example, the expected 
annual number of a 2-foot flood (i.e., all floods between 1.5 and 2.5 
feet) is calculated as the exceedance probability for a 1.5-foot flood 
minus the exceedance probability for a 2.5-foot flood. 

For a given coastal area covered by a FIS and a FIRM, the elevations 
of the 10-, 50-, 100-and 500-year floods are constant over the entire 
area. However, the probability of a given flood depth occurring at a 
specific site depends very strongly on the elevation of the particular site. 
Thus, the Zero Flood Depth Elevation of the facility underevaluation 
has a profound impact on the degree of flood risk experienced at the 
site. 

7-14


VERSION 1.0 12/29/94 LEVEL TWO: Introduction 

CHAPTER 8 
BENEFIT-COST PROGRAMS: LEVEL TWO ANALYSIS 

Introduction 

Chapter 6, Benefit-Cost Programs: Level One Analysis, reviewed 

the data entries necessary to conduct a LEVEL ONE (Minimum Data) 

Benefit-Cost Analysis, relying heavily on default values built into the 

programs. This chapter provides guidance on LEVEL TWO (Detailed) 
analyses which may incorporate much more building-specific data. 

ALL of the data input for a LEVEL TWO (Detailed) analysis involves 

making building-specific estimates which override the default values 

used in a LEVEL ONE (Minimum Data) analysis. 

For a LEVEL TWO (Detailed) analysis, there are five data tables where 
default information may be overridden by the user with building-specific 
information: 

1. Building Depth-Damage Function 
2. Contents Depth-Damage Function 
3. Displacement Time 
4. Functional Downtime 
5. Mitigation Project Effectiveness 
This chapter reviews these five data tables and provides guidance 
about making building-specific estimates. 

I 

8-1


VERSION 1.0 12/29194 LEVEL TWO: Buildina DDF 

VERSION 1.0 12/29/94 LEVEL TWO: Bulidina DDF 

I MI 

9 IA M 

The Building Depth-Damage Function (DDF) indicates a building's 
vulnerability to flood damage by showing the expected levels of 
damage, both as a percentage of building replacement value and as 
dollars of damage for each flood depth. The Building Depth-Damage 
Function is the damage estimated to occur to a building at each flood 
depth. 

The following three sections, Reference Information from Level One 
Data, Building Depth-Damage Function, and Comments: Building 
DDF, all pertain to the Building Depth-Damage Function. 

The Building Depth-Damage Function section of the LEVEL TWO 
(Detailed) benefit-cost analysis is reached via the menu tree: 
Level Two Data I Building Depth-Damage Function 

3 3 

0jlqj 

Carry Over 4

Information ii'go. Sri;r g-

PURPLE Blocks (Carry Over). Information from the LEVEL ONE 

Data page is displayed to identify the building under consideration and 

to provide reference information and guidance for the LEVEL TWO 

(Detailed) evaluation. 

8-2


VERSION 1.0 12/29/94 1.0 12/29/94 LEVEL TWO: Buildina DDF

VERSION LEVEL TWO: Building DDF~~~~~~~~~~~~ 
0:1111193II3311 "", ITA" I0 0I E 

I

Building, 

Depth-Damage . D EtiED 

Table fD ) DDFt0il 

There are five columns in the Building Depth-Damage Table. The 

first column shows the range of flood depths considered, from -2 to 18 

feet. The next three columns contain damage estimates in percentages 

of the building's replacement value: Default DDF, User-Entered DDF, 

and Modified DDF (to account for the demolition damage threshold 

percentage). The fifth column converts the Modified DDF from 

percentages of damage into dollars of damage. 

Default ORANGE Blocks (Default). The Default Building DDF estimates 

Building DDF shown are based on the building type selected earlier and on Federal 
Insurance Administration (FIA) data.. FIA data on hundreds of 
thousands of flood damage claims are categorized into six classesof 
structures. These FIA data are predominantly, but not entirely, for 
residential buildings. 

In conformance with the FIA depth-damage data, the depth-damage 

table runs from -2 to 18 feet, with all depths relative to the Zero Flood 
Depth Elevation of the building (i.e., the top of the first finished floor). 
Damage data is included for depths below 0 feet because damage 
occurs at these flood levels for buildings with basements. 

The default depth-damage estimates have several limitations: 

1. Only six classes of buildings are included. 
2. No distinction is made between different types of 
construction. For example, one-story wood frame and 
masonry buildings are grouped in the same class. 

3. No distinction is made for differences in construction 
practices or age of structures. 
I 

8-3


VERSION 1.0 12/29/94 LEVEL TWO: Building DDF 

FIA 

Depth-Damage 
Table 

4. FIA depth-damage estimates include all claims including 
flood damage due to high velocity flows, ice or debris 
flows, or erosion and soil/foundation failures. However, 
the preponderance of claims are due to water depth only 
and thus these depth-damage estimates approximate 
water depth only damages. 
5. Damage estimates do not consider the flood duration. 
6. Depth-damage data at high flood depths are based on 
many fewer claims than at lower flood depths and thus 
may be less reliable. 
For the above reasons, the Default DDF data should be regarded as a 
useful approximation to actual expected water depth-damages, but 
certainly not as absolute truth for all circumstances. 

The following table displays the default depth-damage estimates by 
flood depth for the six classes of building types plus the "other" 
classification included in the programs. These estimates are from the 
FIA flood damage claim data; values at a few depths have been 
interpolated between FIA data points. 

8-4


VERSION 1.0 12/29/94 LEVEL TWO: Building DDF 
FIA DEPTH-DAMAGE DATA 

1 
Building I Story, 2 Story, Split I or 2 Split Mobile Other 
Type w/o W/o Level with Story, Level, Home 
Basement Basement Basement with with 
Flood Basement Basement 
D e p th _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
-2 0 0 0 4 3 0 0 
-1 0 0 0 8 5 0 0 
0 9 5 3 11 6 8 0 
1 14 9 9 15 16 44 0 
2 22 13 13 20 19 63 0 
3 27 18 25 23 22 73 0 
4 29 20 27 28 27 78 0 
5 30 22 28 33 32 80 0 
6 40 24 33 38 35 81 0 

7 43 26 34 44 36 82 0 
8 44 29 41 49 44 82 0 
9 45 33 43 51 48 82 0 
10 46 38 45 53 50 82 0 
11 47 38 46 55 52 82 0 
12 48 38 47 57 54 82 0 
13 49 38 47 59 56 82 0 
14 50 38 47 60 58 82 0 
15 50 38 47 60 58 82 0 
16 50 38 47 60 58 82 0 
17 50 38 47 60 58 82 0 
18 50 38 47 60 58 82 0 

8-5


VERSION 1.0 12/29/94 LEVEL TWO: Building DDF 

User-Entered BLUE Blocks (Override Default). If the Default DDF does not 

Building DDF accurately reflect the specific building under evaluation, users may 
enter more appropriate estimates based on engineering judgement and 
common sense. If the OTHER building type is selected, then no default 
values are provided and the user MUST enter building-specific 
estimates. Whenever a user enters a depth-damage estimate, the 
programs use these values rather than the default values, although the 
default values are displayed for comparison to the user-entered values. 

If building damage data at one observed flood depth are available, this 

value may be used to calibrate the user-entered building DDF. The 

percent damage at this flood depth can be set to agree with the actual 

damages, and damages at other flood depths can be smoothly adjusted 

to be consistent with the observed damage data point. However, it is 

important to note that the damages in a single flood may not or may not 

be representative of future expected damages, depending on whether 

or not unusual circumstances affected the observed damages. 

Overriding the default depth-damage estimates is perfectly acceptable, 

indeed it is required in order to get a valid benefit-cost analysis, 

whenever the default estimates do not accurately reflect the building 

under evaluation. For example, if a building is unusually resistant or 

unusually vulnerable to flood damage, this information should be 

reflected in the user-entered depth-damage function. 

Also, the default depth-damage estimates consider predominantly water 
depth. If high velocity flows, ice or debris-induced damage, erosion and 
soil/foundation failure, or unusually long-duration flooding are likely, 
then default depth-damage estimates MUST be adjusted accordingly. 

Modified 
Building DDF 
YELLOW Blocks (Results). The Modified DDF (%) takes into 
account the demolition threshold damage percentage entered on the 
LEVEL ONE Data page and adjusts the DDF accordingly. For 
example, if the demolition percentage is 40% then all damages at or 
above 40% are assumed to be 100%, because the building would be 
expected to be demolished as a total loss at that level of damage. 
YELLOW Blocks (Results). The depth-damage percentages of the 
Modified DDF (%) are converted to dollars in the final column of the 
depth-damage table. 
I 
8-6 


VERSION 1.0 12/29194 LEVEL TWO: Building DDF 

_ I I_ 

Comments PINK Block (Information Only). This comment box may be used to 
record specific information about the building which affects its 
vulnerability to.flood damage or any other information or assumptions 
which affect the user-entered depth-damage estimates (such as floods 
with debris or long duration flooding). Additionally, if OTHER was 
selected as the building type, a description of the building and its 
estimated depth-damage function should be entered here. 

8-7


VERSION 1.0 12129/94 LEVEL TWO: Contents DDF 

VERSION 1.0 12/29/94 LEVEL TWO: Contents DDF 

PCeel -TA 

The Contents Depth-Damage Function (DDF) indicates the building 
contents' vulnerability to flood damage by showing the expected levels 
of damage, both as a percentage of contents value and as dollars of 
damage for each flood depth. 

The following three sections, Reference Information from Level One 
Data, Contents Depth-Damage Function, and Comments: 
Contents DDF, all pertain to the Contents Depth-Damage Function, 
the damage estimated to occur to the building's contents at each flood 
depth. 

The Contents Depth-Damage Function section of the LEVEL TWO 
(Detailed) benefit-cost analysis is reached via the NEXT SCREEN 
button at the bottom of the Building Depth-Damage Function screen 
or the menu tree: 

Level Two Data I Contents Depth-Damage Function 

~M WJI

Carry Over 
InformationtV ntariti 
zrs b 777.7~j 
PURPLE Blocks (Carry Over). Information from the LEVEL ONE 
Data page is displayed to identify the building under consideration and 
to provide reference information and guidance for the LEVEL TWO 
(Detailed) evaluation. 

8-8


VERSION 1.0 12/29/94 LEVEL TWO: Contents DDF 

_ 3MIPMS 

I 

Contents 
Depth-Damage 
Table 

Default 
Contents DDF 

User-Entered 
Contents DDF 

There are five columns in the Contents Depth-Damage Table. The 
first column shows the range of flood depths considered, from -2 to 18 
feet. The second carries over the Default or User-Entered Building 
DDF (if entered) from the Building Depth-Damage Function for 
reference. The next two columns contain estimated contents damage 
in percentages of the contents' value: Default DDF (%) and User-
Entered DDF (%). The fifth column, DDF ($), converts the Default 
DDF (%)or, if entered, the User-Entered DDF (%) values into dollars. 

ORANGE Blocks (Default). The Default Contents DDF values shown 
are 150% of the default building damage percentages for the building 
type selected. The 150% multiplier assumes that typical contents are 
more vulnerable to flood damage than are typical buildings. 

The Default Contents DDF depends ONLY on the building type 
selected, NOT on the contents in any particular building. The vulnerability 
of contents to flood damage may vary markedly depending on the 
type of contents. For example, rare books are much more vulnerable 
than are used bricks. Therefore, users should enter building-specific 
estimates of the contents Default DDF whenever possible. 

BLUE Blocks (Override Default). If the Default DDF does not 
accurately reflect the Contents DDF of the specific building under 
evaluation, the user may enter more appropriate estimates based on 
engineering judgement, actual contents, and common sense. Also, if 
the OTHER building type is selected, then no default values are 
provided and the user must enter building-specific Contents DDF 
estimates. Whenever a user enters a depth-damage estimate, the 
programs use these values rather than the default values, although the 
default values are displayed for comparison to the user-entered values. 

8-9 


VERSION 1.0 12129/94 LEVEL TWO: Contents DDF 

VERSION 1.0 12/29/94 LEVEL TWO: Contents DDF 

Contents DDF ($) 

Comments: 
Contents DDF 

If contents damage data at one observed flood depth are available, then 
this value may be used to calibrate the user-entered Contents DDF. In 
this case, the percent damage at the observed flooddepth can be set to 
agree withthe observed damages, and damages at other flood depths 
can be smoothlyadjusted to be consistent withthe observed damage 
data point. However, it is important to note that the damages in a single 
flood may not or may not be representative of future expected 
damages, depending on whether or not unusual circumstances affected 
the observed damages. 

Overriding the default depth-damage estimates is perfectly acceptable, 
indeed it is required to get a valid benefit-cost analysis, whenever the 
default estimates do not accurately reflect the building under evaluation. 
For example, if a building's contents are unusually resistant or unusually 
vulnerable to flood damage, this information should be reflected in the 
user-entered Contents Depth-Damage Function. 

Also, the default depth-damage estimates consider predominantly water 

depth. If high velocity flows, ice or debris-induced damage, erosion and 
isoil/foundation failure, or unusually long-duration flooding are likely, 

then the default depth-damage estimates MUSTbe adjusted 

accordingly. 

YELLOWBlocks (Results). The contents depth-damage percentage 
estimates are converted to dollars in the final column of the Contents 
Depth-Damage Table. 

S40 II S SI 

PINK Block (Information Only) This comment box may be used to 

record specific information about the building contents which affects 
their vulnerability to flood damage or any other information or 

assumptions whichaffectthe user-entered contents depth-damage 

estimates (such as long duration flooding). 

8-10 


VERSION 1.0 12/29194 LEVEL TWO: Displacement Time 

Additionally, if OTHER was selected as the building type, a description 

of the building contents and their estimated depth-damage function 

should be entered here. As with the Building DDF, if OTHER is 

selected, no default values for the Contents DDF are provided. 

ff AAYMATORRDA0 AM 9 MA29174#10 

The Displacement Time Estimates indicate the occupants' 

vulnerability to flood damage by showing the expected levels of 

displacement time, displacement costs, and rental income losses for 

each flood depth. Displacement Time is the number of days 

occupants must vacate the building because of flood damage. 

Displacement Time may be shorter than the repair time, because 

some flood damage repairs can be made with occupants in the building. 

The following three sections, Reference Information from Level One 

Data, Displacement Time Estimates, and Comments: 

Displacement Time Estimates, all pertain to the Displacement Time, 

the number of days of displacement estimated to occur to a building's 

occupants at each flood depth. 

The Displacement Time section of the LEVEL TWO (Detailed) 
benefit-cost analysis is reached via the NEXT SCREEN button at the 
bottom of the Contents Depth-Damage Function screen or the menu 
tree: 

Level Two Data I Displacement Time 

l I 

Carry.Over 
Information :t C o ua mj Gon;a 

PURPLE Blocks (Carry Over). Information from the LEVEL ONE 

Data page is displayed to identify the building under consideration and 

to provide reference information and guidance for the LEVEL TWO 

(Detailed) evaluation. 

8-11 


VFR92:ICnNI n 19190/QA LEVEL TWO: .Displacement Time 

VFD.IAM I fl 1919 QIQeI LEVEL TWO: Displacement Time 

lflwffmoail -| 

Displacement
Time Estimate
Table

There are six columns in the Displacement Time Due to Building 

Flood Damage Table. The first column shows the range of flood 

depths considered, from -2 to 18 feet. The second column carries 

forward the Modified DDF (%) from the Building Depth-Damage 

Table for guidance. The third column, Default (days), shows the 

estimated number of days of displacement by flood depth. The fourth 

column, User-Entered (days), is for the user to override the default 

estimates by entering building-specific estimates. The fifth column 

calculates the Displacement Costs by flood depth from the Default or, 

if entered,the User-Entered Displacement Time Estimates (days) 

and the Total Displacement Costs($/day). The sixth column 

calculates the Rental Income Losses by flood depth from the Default 

or User-Entered Displacement Time Estimates and the Total 

Monthly Rent From All Tenants. 

Default ORANGEBlocks (Default). The Default Displacement Time 
Displacement Estimates (days) are derived from the Modified DDF (%) shown in the 
Time Estimates Building Depth-DamageTable. The Default estimates assumethat 

no displacement (i.e., renting of temporary space) occurs if the building 
sustains less than 10% damage. However, if the estimated building 
damage is greater than 10%, then the Default estimates of 

Displacement Time are scaled between 30 and 365 days. The 30 day 

minimum assumes that occupants won't relocate to temporary space if 
the damage is repairable within 30 days. The 365 day maximum 
assumes that all repairs will be completed and occupants will be back in 

the original space within one year. 

User-Entered BLUE Blocks (Override Default). If the Default Displacement Time 

Displacement Estimates do not accurately reflect the displacement times estimated 

Time Estimates for the occupants of the specific building under evaluation, users may 
enter more appropriate estimates based on engineering judgement, 
actual days of displacement observed, and common sense. 

8-12 


VERSION 1.0 12/29194 LEVEL TWO: Displacement Time 

Displacement 
Costs ($) 

Rental Income 
Losses 

Also, if the OTHER building type is selected, then no default values are 

provided and the user must enter building-specific estimates of the 

number of days of displacement. Whenever a user enters a 

Displacement Time Estimate, the programs use these values rather 
than the default values, although the default values are displayed for 

comparison to the user-entered values. 

If data on actual Displacement Time at one observed flood depth are 
available, then this information may be used to calibrate the user-
entered Displacement Time Estimate. In this case, the 

Displacement Time at the observed flood depth can be set to agree 
with the observed displacement time; estimated displacement times at 
other flood depths can be smoothly adjusted to be consistent with the 
observed Displacement Time data point. However, it is important to 
note that the Displacement Time in a single flood may not or may not 
be representative of future expected times, depending on whether or 

not unusual circumstances affected the observed time. 

Overriding the Default Displacement Time Estimates is perfectly 
acceptable, indeed it is required to get a valid benefit-cost analysis 
whenever the default estimates do not accurately reflect the building 
under evaluation. For example, if local conditions suggest that 
unusually long or short displacement times are likely, this should be 
reflectedin the User-Entered Displacement Time Estimates. 

YELLOW Blocks (Results). The Default Displacement Time 
Estimates, or, if entered, the User-Entered Displacement Time 
Estimates are converted into Displacement Costs based on the Total 
Cost of Displacement per day (from the LEVEL ONE Data page) and 
the estimated days of displacement for each flood depth. 

YELLOW Blocks (Results). The Default Displacement Time 
Estimates, or, if entered, the User-Entered Displacement Time 

Estimates are converted into Rental Income-Losses based on the 
Total Monthly Rent from All Tenants ($/month, from the LEVEL ONE 
Data page) and the days of displacement for each flood depth. 

* 3 A A 
Comments PINK Block (Information Only). This comment box should be used to 
record specific information about the Displacement Time Estimates 
and how they are governed by the building's vulnerability to flood 
damage and any other information, assumptions or local conditinns. 

8-13 


VERSION 1.0 12129194 LEVEL TWO: Functional Downtime 

VERSION 1.0 12/29/94 LEVELTWO: Functional Downtime 

*DA A~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A 

Functional Downtime is the number of days a public/nonprofit agency 
cannot provide services due to disaster-caused damage. For example, 
an agency may have to relocate out of its building for 60 days, but may 
resume service provision from temporary quarters after only 7 days. 
Thus, in this case, the functional downtime due to disaster damage is 7 
days. Functional Downtime is also used to estimate business income 
losses (if applicable) due to flood damage. 

The following three sections, Reference Information from Level One 

Data, Functional Downtime Estimates, and Comments: Functional 
Downtime Estimates, all pertain to the Functional Downtime 
Estimates, the days of lost function estimated to occur to at each flood 
depth. 

The Functional Downtime section of the LEVEL TWO (Detailed) 

benefit-cost analysis is reached via the NEXT SCREEN button at the 
bottom of the Displacement Time screen or the menu tree: 

Level Two Data I Functional Downtime 

9MMMUlii 

CarryOver ~fo hsBidn tdy 
Information Ptat P a' 'ut ''-

Etiae Nt ivco, o-Cdommercia A eBusine 

PURPLE Blocks (Carry Over). Information from the LEVEL ONE 
Data page is displayed to identify the building under consideration and 
to provide reference information and guidance for the LEVEL TWO 
(Detailed) evaluation. 

8-14


VERSION 1.0 12/29/94 LEVEL TWO: Functional Downtime 

* A ** A 
Functional 
Downtime Table 

Default 
Functional 
Downtime 
Estimates 

User-Entered 
Functional 
Downtime 
Estimates 

There are six columns in the Functional Downtime Estimates table. 
The first column shows the range of flood depths considered, from -2 to 
18 feet. The second column carries forward the Building DDF from the 
Building Depth-Damage table for guidance. The third column, Default 
Downtime, shows the estimated number of days of lost agency 
functioning by flood depth. The fourth column, User-Entered 
Downtime, is for the user to override the default estimates by entering 
building-specific estimates. The fifth column calculates the Value of 
Lost Services by flood depth from the Default or, if entered, the User-
Entered Functional Downtime Estimates (days) and the Total Value 
of Lost Services ($/day). The sixth column calculates the Lost 
Business Income by flood depth from the Default or User-Entered 
Functional Downtime Estimates and the Estimated Net Income of 
Commercial Businesses ($/month). 

ORANGE Blocks (Default). The Default Downtime Estimates (days) 
are derived from the Building DDF (%) carried over from the Building 
Depth-Damage Function Table. The Default Downtime Estimates 
assume that if the building sustains less than 10% damage, then one 
day of Functional Downtime occurs for each 1% of damage. 
However, if the estimated building damage is greater than 10%, then 
the Default Downtime Estimates are scaled between 10 and 30 days. 
It is assumed that public/nonprofit agencies and businesses will resume 
function in temporary quarters, if necessary, within 30 days; thus the 
Default Functional Downtime Estimates are capped at 30 days. 

BLUE Blocks (Override Default). If the Default Functional 
Downtime Estimates do not accurately reflect the Functional 
Downtime estimated for the specific building under evaluation, users 
may enter more appropriate estimates based on engineering 
judgement, actual days of downtime experienced, and common sense. 
Also, if the OTHER building type is selected, then no default values are 

8-15 


VERSION 1.0 12/29194 LEVELTWO: Functional Downtime 

Value of Lost 
Services 

Lost Business 
Income 

Comments 

provided and the user must enter building-specific estimates of the 
number of days of functional downtime. Whenever a user enters a 
Functional Downtime Estimate, the programsuse these values rather 

than the default values, although the default values are displayed for 
comparison to the user-entered values. 

If data on actual Functional Downtime at one observed flood depth 
are available, then this information may be used to calibrate the user-
entered Functional Downtime Estimate. In this case, the Functional 
Downtime at the observed flood depth can be set to agree with the 
observed time and estimated times at other flood depths can be 
smoothly adjusted to be consistent with the observed Functional 
Downtime data point. However, it is important to note that the 
Downtime in a single flood may not or may not be representative of 
future expected Downtimes, depending on whether or not unusual 
circumstances affected the observed Downtime. 

Overriding the default Functional Downtime estimates is perfectly 
acceptable, indeed it is required in order to get a valid benefit-cost 
analysis whenever the default estimates do not accurately reflect the 
building under evaluation. For example, if local conditions suggest that 
unusually long or short downtimes are likely, this information should be 
reflected in the user-entered Functional Downtime Estimates. 

YELLOW Blocks (Results). The Default Functional Downtime 
Estimates, or, if entered, the User-Entered Functional Downtime 
Estimates are converted into the Value of Lost Services based on the 
Total Value of Lost Services per day (from the LEVEL ONE Data 
page) and the estimated days of Functional Downtime for each flood 
depth. 

YELLOW Blocks (Results). Similarly,the Lost BusinessIncomefor 
each flood depth is based on the Estimated Net Income of 
Commercial Businesses ($/month) from the LEVEL ONE Data page, 
and the estimated days of Functional Downtime for each flood depth. 

_ 6 aO I 

PINK Blocks (Information Only). This comment box should be used 

to record specific information about the occupants' Functional 

Downtime as it is governed by the building's vulnerability to flood 

damage or any other information, local conditions, or assumptions 

which affect the user-entered Functional ilnwntime Estimates. 

8-16 


VERSION 1.0 12/29/94 LEVEL TWO: Mitigation Project Effectiveness 

M 7ZJA&MTi%# I #J'Ji--I FAIF422441

_JJ1J.t1AJ1#[ q A721111 

Mitigation Effectiveness indicates the estimated percentage of 

damages and losses avoided by the mitigation measure for each flood 

depth. Mitigation Effectiveness estimates are made separately for 

avoiding building and contents damages. 

The following three sections, Reference Information from Level One 

Data, Mitigation Effectiveness, and Comments: Mitigation 

Effectiveness Estimates, all pertain to the Mitigation Project 

Effectiveness, the estimated percentage of damages avoided at each 

flood depth. 

The Mitigation Effectiveness section of the LEVEL TWO (Detailed) 
benefit-cost analysis is reached via the NEXT SCREEN button at the 
bottom of the Functional Downtime screen or the menu tree: 

Level Two Data I Mitigation Project Effectiveness. 

-. S  

Carry Over

Information Tt Fr fi 

Tit, uIlrdingRp~cmotauX

dIl 

PURPLE Blocks (Carry Over). Information from the LEVEL ONE 

Data page is displayed to identify the building under consideration and 

to provide reference information and guidance for the LEVEL TWO 

(Detailed) evaluation. 

8-17


VERSION 1.0 12/29/94 LEVELTWO: Mitigation Project Effectiveness 

Mitigation 
Effectiveness 
Table 

Building 
Damages Default 
Effectiveness (%) 

AS 

-*

0. S S. .I. *S.S 

There are seven columns in the Mitigation Effectiveness Table. The 
first column shows the range of flood depths considered, from -2 to 1 8 
feet. The second column shows Building Depth Damage Function 
Before Mitigation, for reference. The third column shows the Default 
Building Effectiveness Estimates. The fourth column is for the user 
to override the Default Building Effectiveness Estimates with User-
Entered estimates. The fifth column shows the Contents Depth-
Damage Function Before Mitigation, for reference. The sixth column 
shows the Default Contents Effectiveness Estimates. The seventh 
column is for the user to override the Default Content Effectiveness 
Estimates with User-Entered estimates. 

ORANGE Blocks (Default). The Building Damages Default 
Effectiveness (%) of the mitigation measure in avoiding building 
damages is calculated from the mitigation measure selected and the 
heights where the mitigation measure is 100% and 0% effective. These 
estimates of the Mitigation Project Effectiveness are entered in the 
Project Data section of the LEVEL ONE Data entry (see page 6-15). 

For relocation/buyout projects, the Default Mitigation Effectiveness of 
100% for all flood depths is correct and need not be modified by user-
entered input. Similarly, for elevation projects, the default values are 
generally applicable and probably should not have to be modified by 
user-entered input. 

8-18


VERSION 1.0- 12/29/94 LEEL TOMiiainPoetEffectvns 

VERSION 1.0 12/29194 LEVEL TWO: Mitigation Proj.... Effectiveness 

Building 
Damages 
User-Entered 
Effectiveness (%) 

Contents 
Damages Default 
Effectiveness (%) 

Contents 
Damages User-
Entered 
Effectiveness (%) 

For flood barrier projects, there may be more variation in effectiveness 
depending on the engineering details and thus the default values may 
or may not accurately reflect the effectiveness of all flood barrier 
projects. If the Other category is selected for mitigation measure then 
default estimates based on the heights of 100% and 0% effectiveness 
may also have to be modified. 

BLUE Blocks (Override Default). Users may override the Building 
Damages Default Effectiveness estimates by entering building-
specific estimates in this column. Whenever a user enters a mitigation 
effectiveness estimate, the programs use these values rather than the 
default values, although the default values continue to be displayed for 
comparison to the user-entered values. 

If the Building Damages Default Effectiveness estimates do not 
accurately reflect the specifics of the building under evaluation, then 
enter more appropriate estimates based on engineering judgement and 
common sense. Overriding the Default Effectiveness Estimates is 
perfectly acceptable, indeed it is required in order to get a valid benefit-
cost analysis, whenever the default estimates do not accurately reflect 
the building under evaluation. For example, if the particular mitigation 
measure under evaluation is expected to be unusually effective or 
unusually ineffective, this information should be reflected in the User-
Entered Effectiveness Estimates. 

ORANGE Blocks (Default). The Contents Damages Default 
Effectiveness of the mitigation measure in avoiding contents damages 
is assumed to be the same as the Building Damages Default 
Effectiveness. See the Building Damages Default Effectiveness 
section above for a review of these assumptions. 

BLUE Blocks (Override Default) Users may override the Default 
Mitigation Effectiveness estimates by entering building-specific 
estimates in this column. Whenever a user enters effectiveness 
estimates, the programs use these values rather than the default 
values, although the default values continue to be displayed for 
comparison to the user-entered values. 

If the default mitigation effectiveness estimates do not accurately reflect 
the specific building under evaluation, then enter more appropriate 
estimates based on engineering judgement and common sense. 
Overriding Default Effectiveness Estimates is perfectly acceptable, 
indeed it is required to get a valid benefit-cost analysis whenever the 
default estimates do not accurately reflect the building under evaluation. 
For example, if the proposed mitigation measure is expected to be 
unusually effective or unusually ineffective, this information should be 
reflected in the user-entered Effectiveness Estimates. 

8-19 


VERSION 1.0 12/29/94 LEVEL TWO: Mitigation Project Effectiveness 

VERSION 1.0 12129/94 LEVEL TWO: Mitigation Project Effectiveness 

Other The effectiveness of the mitigation measure in reducing Displacement 
Effectiveness Time and Functional Downtime is assumed to be the same as the 
Assumptions effectiveness in avoiding building damages. 

0U A& 

M3111 m E_ 

Comments PINK Blocks (Information Only). This comment box should be used 
to record specific information about the mitigation measure's 
effectiveness for both the building and content damages or any other 
information or assumptions which affect the User-Entered Mitigation 
Effectiveness Estimates. 

8-20


VERSION 01.0 12/29/94 B-C PROGRAMS: Results 

CHAPTER 9 
BENEFIT-COST PROGRAMS: RESULTS 

Introduction 

This chapter summarizes all of the results which are calculated from the 
data inputs. There are four main types of results: 

. Summary of Damages Before Mitigation, 

2. Summary of Damages After Mitigation, 
3. Benefit-Cost Results, and 
4. Summary. 
Results should always be reviewed for reasonableness. If any of the 
results appear unreasonable, then check the corresponding input 

parametersl~~~Miiinwhich lead 1toDaathe results.a i~E TW11 

| Each analyst conducting benefit-cost analysis has the responsibility to 
ensure that all data inputs are reasonable, defensible, and well-
documented. The programs process all of the data inputs in a 

|mathematically correct manner, but the programs cannot produce 
correct results when incorrect data are entered. The analyst has 
control over the data inputs and thus responsibility for the results. 

I 

9-1


VERSION 1.0 12/29/94 RESULTS: Damages Before Mitigation 

I A A: e 
This section of results characterizes the vulnerability of the EXISTING 
building to flood damages and losses BEFORE undertaking any 
mitigation measures. The estimated scenario damages and losses for 
the existing building at each flood depth depend directly on the depth-
damage functions for building and contents, displacement, and 
functional downtimes, and all of the other data input parameters. The 
expected annual damages and losses also depend very strongly on the 
degree of flood risk at the site under evaluation. 
_WaBS_& 
~p E~ X -
A 
Scenario 
Damages Before 
Mitigation 
($per event) 
Scenario Damages are defined as damages and losses per flood 
event (occurrence). Scenario damages indicate the estimated 
damages which would result from a single flood of a particular depth at 
the building under evaluation. For example, the scenario damages for a 
3-foot flood are the expected damages and losses each time a 3-foot 
flood occurs at a particular site. Scenario damages do NOT depend on 
the probability of floods at that location. 
Scenario 
Damages Table 
The Scenario Damages Table contains scenario damages for each 
flood depth from -2 to 18 feet for six categories of damages and losses: 
building damages, contents damages, displacement costs, business 
income losses, rental income losses, and lost public/nonprofit services. 
In addition, the total damages and losses are shown for each flood 
depth. 
The information in this Scenario Damages Before Mitigation table 
shows the total vulnerability of the existing building to flood damage, 
how these damages are distributed among different categories of 
damages, and how these damages vary with flood depth. 
9-2 


VERSION 1.0,12129/94 RESULTS: Damages Before Mitigation 

I LINALi M

IlJ, I I I LeY.A 3 E: 

---am

-

-

Expected Annual
Damages Table

Interpreting 

Damages Before 
Mitigation 

The Scenario Damages discussed above do NOT depend on flood 
hazard risk. Two identical buildings located at different elevations in a 
flood plain will have identical scenario damages at each flood depth. 
However, the probability of flood damage varies markedly with elevation 
in a flood plain. 

Expected Annual Damages take into account the annual probabilities 

of floods of each depth. Expected Annual Damages are the 
AVERAGE damages per year expected over a long time period. 
"Expected annual" does NOT mean that these damages will occur 
every year. 

For each flood depth, Expected Annual Damages are calculated by 
multiplying the Scenario Damages times the expected annual number 

(probability) of floods of each depth. 

The Expected Annual Damage Table contains expected annual 

damages for each flood depth from -2 to 18 feet for six categories of 
damages and losses: building damages, contents damages, 
displacement costs, business income losses, rental income losses, and 
lost public/nonprofit services. In addition, the total damages and losses 
are shown for each flood depth. 

Expected Annual Damages will generally be much smaller than 
Scenario Damages because the expected annual number or annual 
probability of a flood of a given depth is usually much less than one. 

Scenario Damages and Expected Annual Damages provide different 
information. Scenario Damages describe how much flood damage 
there will be each time a given flood occurs. However, because 

Scenario Damages DO NOT consider flood probabilities, they do not 

provide sufficient information for decisionmaking. Scenario Damages 

for a given flood depth may be high, but if the flood Probability is very 

9-3 


VERSION 1.0 12/29/94 ` Results: Damaaes After Mitioation 

VERSION 1.0 12/29/94 Results: Damaaes After Mitiantion 

low, no mitigation action may be warranted. For example, if a 5-foot 
flood causes $50,000 damages but such a flood is expected to occur 
only once in 1,000 years, then simply repairing the very infrequent flood 
damage may be the most sensible and cost-effective strategy. 

The Scenario Damages Before Mitigation and the Expected Annual 

Damages Before Mitigation provide, in combination, a complete 

picture of the vulnerability of the building to flood damage before 

undertaking a mitigation project. 

Expected Annual Damages DO consider flood probabilities. A 

building with high Expected Annual Damages means that not only are 

Scenario Damages high, but also that flood probabilities at the depths 

that cause considerable damages are relatively high. High Expected 

Annual Damages means that there are high potential benefits in 

avoiding such damages through mitigation projects. 

Even for buildings with high Expected Annual Damages, all mitigation 

projects are not necessarily cost-effective. Cost-effectiveness depends 

on the cost of the mitigation project and on the effectiveness of the 

mitigation project in avoiding damages, as well as on the Expected 

Annual Damages. 

A* *A ~rf ~A&Ala AA 

This section of results characterizes the vulnerability of the building to 

flood damages and losses AFTER undertaking a particular mitigation 

measure. Scenario damages after mitigation depend on the damages 

before mitigation and on the effectiveness of the mitigation measure in 

avoiding damages. The Expected Annual Damages and Losses 

after mitigation also depend very strongly on the degree of flood and 

flood-related risks at the site under evaluation. 

IMJH--61 eiSVI-11YA3I A A a -T1 111 &110

OEM=~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

-~~~~ 

Scenario Damages After Mitigation are the damages and losses 
expected to occur per flood event after the mitigation project is 
implemented. For some mitigation projects, such as relocation or 
buyout, the Scenario Damages After Mitigation will be zero. For 
other projects, such as elevation or flood barriers, Scenario Damages 
After Mitigation will be lower than before mitigation but not zero at 
those Rood depths where the mitigation measure is partially effective. 

9-4 


VERSION 1.0 12/29/94 Results: DamagesAfter Mitigation 

Scenario 
Damages Table 

Scenario Damages After Mitigation indicate the estimated damages 
which would result from a single flood of a particular depth at the 
building under evaluation after completion of the mitigation project. For 

example, the scenario damages for a 3-foot flood are the expected 
damages and losses each time a 3-foot flood occurs at a particular 
site. Scenario damages DO NOT depend on the probability of floods at 

that location. 

The Scenario Damages After Mitigation Table contains scenario 
damages for each flood depth from -2 to 18 feet for six categories of 
avoided damages and losses: building damages, contents damages, 
displacement costs, business income losses, rental income losses, and 
lost public/nonprofit services. In addition, the total damages and losses 
are shown for each flood depth. 

The information in this Scenario Damages After Mitigation table 
shows the total vulnerability of the building after mitigation to flood 
damage, how these damages are distributed among different categories 
of damages, and how these damages vary with flood depth. In the 
example table above, Scenario Damages After Mitigation are zero for 
flood depths through 4 feet, because the mitigation measure (elevation) 
is 100% effective in avoiding damages at these flood depths. 

WC419 l3 lkl WA myA lA

3 

A I -

Expected Annual Damages After Mitigation take into account the 
annual probabilities of floods of each depth. Expected Annual 
Damages are the AVERAGE damages per year expected over a long 
time period. "Expected annual" does not mean that these damages will 
occur every year. 

9-5


VERSION 1.0 12/29194 Results: Damaaes After Mitiaation 

VERSION 1.0 12/29194 Results: DamaaesAfter Mitloation 

Expected Annual Damages After Mitigation also take into account 
the effectiveness of the mitigation measure at each flood depth. For 
some mitigation projects, such as relocation or buyout, the Expected 
Annual Damages After Mitigation will be zero. For other mitigation 
projects, such as elevation or flood barriers, Expected Annual 
Damages After Mitigation will be lower than before mitigation but not 
zero. 

For each flood depth, Expected Annual Damages After Mitigation 
are calculated by multiplying the Scenario Damages times the 
expected annual number (probability) of floods of each depth. 

The Expected Annual Damages After Mitigation table (shown above) 
contains expected annual damages AFTER mitigation for each flood 
depth from -2 to 18 feet for six categories of avoided damages and 
losses: building damages, contents damages, displacement costs, 
business income losses, rental income losses, and lost public/nonprofit 
services. In addition, the total damages and losses AFTER mitigation 
are shown for each flood depth. 

Interpreting The Scenario Damages After Mitigation and the Expected Annual 
Damages After Damages After Mitigation provide, in combination, a complete 
Mitigation picture of the vulnerability of the building to flood damages after 
undertaking a mitigation project. 

9-6


VERSION 1.0 12/29/94 Results: Expected Annual Benefits 

U~~~~~~1 

Expected Annual 

Benefits Table 

Benefits are damages and losses avoided because of the mitigation 
project. In other words, benefits are the difference in damages before 
and after the mitigation project. The Expected Annual Benefits of a 
mitigation project are the expected annual AVOIDED damages and 
losses. Thus, Expected Annual Benefits are the difference between 
Expected Annual Damages Before Mitigation and Expected Annual 
Damages After Mitigation. 

A

I I 

i|iA_ 

FloogudC 

0 t Daae aam C 

The final table in the Damages after Mitigation section shows the 

Expected Annual Benefits arising from the specific mitigation project 

under evaluation. 

The Expected Annual Benefits Table (shown above) contains 

expected annual benefits for each flood depth from -2 to 18 feet for six 
categories of avoided damages and losses: building damages 
avoided, contents damages avoided, displacement costs avoided, 
business income losses avoided, rental income losses avoided, and lost 
public/nonprofit services avoided. In addition, the total damages and 
losses avoided after mitigation are shown for each flood depth. The 
Total Expected Annual Benefits due to the mitigation project are the 
sum of the total avoided damages and losses over all of the flood 
depths. 

9-7


VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results 

VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results 

e -~~~~~~~-

This section of results has three subsections: 

1. Reference Information From LEVEL ONE Data, 
2. Summary of Expected Annual Damages and Benefits, 
and 
3. Summary of Project Benefits and Project Costs. 
U U 

Sm . 0 -, 0 

Discount Rate The Discount Rate entry is determined by OMB/FEMA policy and 
cannot be varied by the user on a project-by-project basis. 

On October 29, 1992, OMB issued Circular A-94, Revised (Transmittal 

Memo No. 64), "Guidelines and Discount Rates for Benefit-Cost 

Analysis of Federal Programs." Inthis Circular, OMB states that the 

appropriate discount rate varies depending on whether or not the 

investment (i.e., project) is an "internal Federal government 
investment." 

For FEMA-funded hazard mitigation projects for state and local 

governments (or eligible nonprofits)-,the OMB-mandateddiscount rate 

is the rate applicable for investments which are not internal Federal 

government investments. The OMB-mandateddiscount rate 

corresponds approximately to the 30-year Treasury bond rate, but the 

appropriate rate is specifically fixed by OMB annually. Currently, the 

OMB-mandated discount rate is 7% (see Appendix C of Circular A-94). 

For each disaster, an appropriate discount rate should be determined 

by FEMA, in accordance with the OMB guidance, and applied 

uniformly to all hazard mitigation projects being considered. The 

discount rate determined for each disaster is entered in the RED box 

under LEVEL ONE Data. After this rate is determined and entered 

ONCE, it can then be used for analysis of ALL hazard mitigation 

projects for this disaster. 

9-8 


-VERSION 1.0 12Z/29/94 RESULTS: Benefit-Cost Results 

Project Useful PURPLE Block (Carry Over). The Project Useful Life, entered on the 
Life LEVEL ONE (Minimum Data) screen, is carried over for reference. 

Present Value YELLOW Block (Result). The Present Value Coefficient is 

Coefficient mathematically determined by the discount rate and the project useful 
lifetime. The Present Value Coefficient is the present value of $1.00 
per year in benefits received over the project useful lifetime. In other 
words, the Present Value Coefficient is a multiplier of the expected 
annual benefits which determines the net present value of the expected 
annual benefits. 

Calculated benefits and benefit-cost ratios are directly proportional to 

the Present Value Coefficient. However, in every case the discount 

rate and project useful lifetime entered by a user MUST be 

commensurate with the actual funding source for the project (see 

Discount Rate, pg. 9-8) and the actual mitigation project (see Project 

Useful Life, pg. 6-15). 

The following table shows the Present Value Coefficient for a wide 
range of discount rates and project useful lifetimes. 

an

. ~~~ ~~~~~~ . I~~~~~~~~ . ~._ ---I. . D I .1 -i--.. < ,.x;ik9.s 

9-9


VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results 

Summary of 
Expected Annual 
Damages and 

Benefits Table 

Expected Annual 
Damages and 
Losses 
Before Mitigation 

Expected Annual 
Damages and 
Losses 
After Mitigation 

Expected Annual 
Benefits 

0 12 t 3 l l i l 
A 

YELLOW Blocks (Results). There are five columns in the Summary 
of Damages and Losses table. The first column contains the six types 
of damages and losses considered, along with a total. The second 
column is the Expected Annual Damages and Losses Before 
Mitigation. The third column is the Expected Annual Damages and 
Losses After Mitigation. The fourth column is the Expected Annual 
Benefits. The fifth column is the Present Value of Annual Benefits. 

The Expected Annual Damages and Losses Before Mitigation 
indicate the estimated average annual damages that are expected to 
occur before the mitigation project is completed. These figures indicate 
the vulnerability of the existing building to flood damages. See page 93 
for more discussion. 

The Expected Annual Damages and Losses After Mitigation are the 
expected annual residual damages after completion of the mitigation 
project. In some cases, these damages and losses will be zero-(e.g., 
for buyout or relocation projects). See page 9-5 for more discussion. 

The Expected Annual Benefits of the mitigation project are the 
Expected Annual Avoided Damages. The Benefits of the mitigation 
project are exactly the amount of damages and losses which do not 
occur (i.e., are avoided) because of the mitigation measure. See page 
9-6 for more discussion. 

9-10


WERSION 1.0 12/29194 RESULTSI: Benefit-cost R esutst 

or ---w

VERSION 10 12/29/94 RESULTS: Benefit-Cost Results 

Present Value of The Benefits are the present value (over the lifetime of the mitigation 

Benefits project under evaluation) of the Expected Annual Benefits or, 

equivalently, the present value of damages avoided. The last column of 
the Summary of Expected Annual Damages and Benefits table 
shows the Benefits (present value of damages avoided) for each of the 
six categories of damages and losses and in total. 

The final section of the Benefit-Cost Results page summarizes the 

results of the benefit-cost analysis. 

U 

A111-*nF1 Xft A il

I Y9121a 1119* 

a 

Project Benefits
and Project
Costs

k:4 
PROJECT YELLOW Block (Result). The Project Benefits, whichwere 

BENEFITS calculated and displayed as the last entry in the bottom right corner of 

the Summary of Expected Annual Damages and Benefits Table, are 
presented again here. Project Benefits (i.e., the net present value of 
the Expected Annual Benefits over the lifetime of the project) are the 

productof the Present Value Coefficient andthe Expected Annual 

Benefits. 

PROJECT YELLOW Block (Result). The Project Costs are carried over from
COSTS the LEVEL ONE Data entry page where they were entered for
comparison to the calculated Project Benefits.

BENEFITS YELLOW Block (Result). The difference between Project Benefits 
MINUS and Project Costs is displayed here in dollars. This value, also known 
COSTS as the present value criterion, shows the magnitude of the difference 

between Benefits and Costs. The present value criterion may be 
greater than zero (if benefits exceed costs) or less than zero (if costs 
exceed benefits). 

BENEFIT-COST YELLOW Block (Result). The Benefit-Cost Ratio is the Project 

RATIO Benefits divided by the Project Costs. For hazard mitigation projects 
under either Section 404 or Section 406, the Benefit-Cost Ratio MUST 
be equai to-or greater than one for funding eligibility. 

I 

9-11 


VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Resrnltsq 

VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results 

Interpreting 

Benefit-Cost 

Results 

Benefit-Cost Ratios, like all of the results of benefit-cost analysis, 

depend directly on the input data. Varying any of the input data which 

affect numerical results (i.e., changing any of the entries in green data 

entry blocks) will change the benefit-cost ratio. 

The sensitivity of calculated benefits and/or benefit-cost ratios to 
changes in the values entered in the model may be explored by varying 
input parameters one at a time (within credible or justifiable limits) 
and noting the impact on the resulting calculated benefits. Some of the 
input parameters have little impact on the benefit-cost ratio because 
they only govern a tiny portion of the benefits. Other input parameters 
have a major impact on benefit-cost results. The relative importance of 
each input parameter will vary from project to project depending on the 
specifics of each individual project. 

Because of the inherent uncertainties, benefit-cost results, like any 

calculation, should not be interpreted blindly or in disregard of the 

uncertainties. For example, three prospective flood hazard mitigation 

projects with benefit-cost ratios of 0.2, 1.2, and 2.2 are almost certainly 

distinguishable. Three prospective projects with benefit-cost ratios of 

0.95, 1.00, and 1.05 are probably not significantly different. Three 

projects with ratios of 0.8, 1.0, and 1.2 may or may not be significantly 
different, depending on the validity of the input data. 

Benefit-cost ratios near one will always be in a gray area of 

interpretation. Depending on the accuracy of the input data, benefit-

cost ratios near one (e.g., 0.9 or 1.1) may not be significantly different 
from 1. That is, with reasonable and defensible variations in estimates 
made in the input parameters, the benefit-cost results can come out 
either somewhat above or somewhat below one. 

The real power of benefit-cost analysis is to separate projects with 
benefit-cost ratios substantially below one from projects with 
benefit-cost ratios substantially above one. There will always be 
projects on the borderline, subject to results indicating benefit-cost 
ratios greater than or less than one, depending on variations in input 
data assumptions. 

In this context, the relative rankings of benefit-cost results may be more 

significant than the absolute benefit-cost ratios. Thus, if similar 
assumptions are made about roughly similar projects, the ranking of 
benefit-cost ratios accurately reflects relative differences between the 
projects, while the absolute numerical values of benefit-cost ratios 
reflect the general assumptions made in conducting the analyses. 

In comparing a range of projects with varying costs, benefits, and 
benefit-cost ratios, it is essential to consider the scale of the projects as 
well as the simple benefit-cost ratio. For example, a $5,000 project with 
a benefit-cost ratio of 2.0 (i.e., benefits of $10,000, present value 
criterion of $5,000) is not intrinsically a "better" project than a $500,00u 

9-12 


VERSION 1.0 

VERSION 1.0 

12/29/94 RESULTS: Benefit-Cost Results 

12/29/94 RESULTS:Benefit-CostResults 

project with a benefit-cost ratio of 1.5 (i.e., benefits of $750,000 and a 
present value criterion of $250,000). Thus, in comparing projects it is 
necessary to consider both the benefit-cost ratios and the present value 
criterion (or the total amount of dollar benefits). Simple comparisons of 
projects using only the benefit-cost ratios are valid if and only if the 
projects are of closely similar size (cost). 

As discussed in Chapter 5, Benefit-Cost Model: Guidance, the 
accuracy, validity, and usefulness of any benefit-cost analysis depends 
on the correctness of the input data. A benefit-cost analysis in which 
ANY of the input data do not realistically reflect the particulars of the 
building and mitigation project under evaluation will be inaccurate and 
potentially misleading. 

As discussed in Chapter 5, many of the data inputs for benefit-cost 
analysis are not exact numbers, but rather informed estimates or 
judgements. Nevertheless, all of the data inputs as well as the results 
must be reviewed for reasonableness and defensibility. 

Benefit-cost analyses are subject to review and audit. Therefore, any 
analyses where the input parameters are not reasonable for the specific 
building and mitigation project under evaluation may be challenged. 

9-13


VERSION 1.0 12/29/94 RFSULTS: siimmarv 

Single-Valued 
Data Entries 

Data that Vary by 
Flood Depth 

Summaryof 
Benefits and 
Costs 

The Summary page is in three parts: the first part contains all of the 
single-valued data entries, the second part contains a table of all data 
entries which vary by flood depth, and the third section contains a 
summary of the benefit-cost results. 

The three sections of the Summary Table are shown below: 

:wnmts CW 

100

XSBE4V1 R 
100R100 
1 M3E4,f~9 

'1l5174E028 

100' 3S58AED0 
A-100 1.t34E-03: 

77' 4.45BE~-44

RRJb|EE1S v 26,17:6tI

--~~~~tk, E#5097

PROJE4T,5!ENEFITSMINUS9WXM0 T$, E' E24.121) 
BENEFIT-COSTMRATIOV AmE.52~J'

: 

9-14


VERSION 1.0 12/29194 BENEFIT-COST PROGRAMS: Print-Out 

VERSION 1.0 12/29/94 BENEFIT-COST PROGRAMS: Print-Out 

CHAPTER 10

BENEFIT-COST PROGRAMS: PRINT-OUT 

I I

The print-out which follows contains all data tables, results tables, and graphs from the
Riverine Flood Benefit-Cost Program. The print-outconsists ofthree parts:

1. a one-page summary of data inputs; 
2. a twelve-page report containing all of the data entry and results pages from the 
Benefit-Cost Program; and 
3. seven pages of graphs illustrating flood hazard, damages, and benefit-cost 
results. 
The print-out from the Coastal A-Zone Benefit-Cost Program is virtually identical other 

than page three of the report which summarizes flood hazard data. The Riverine Flood data 

include frequency, discharge, and elevation data while the Coastal A-Zone Flood data 

include only frequency and elevation data. 

10-1


RlverineFloodMitigatonProjecs 

V-i..~~~ -t-qAg laoi 

IR.e,1d1ericod Mltt.sU.nPtojeda V..,, 10Ia . IA 4O.A 

SUMMARY Scenario Run ID: L I 

City Office Annex 55 A Street Cape Squirrel, VA 22222
Mitigation Project: Elevate 5 feet
Building Type: 2 Story wlo Basement

DATA USED FOR THIS ANALYSIS:
Building Replacement Value ($Isf) $75.00
Total Floor Area (square feet): 2,000
Total Building Replacement Value: $150,000
Demolition Threshold Damge Percentage: 50%
Total Contents Value $50,000
Total Displacement Costs ($Imonth): $2,750
Cost of Providing Services from this Building ($Iday) $534
Post-Disaster Continuity Premium ($Iday) $500
Total Value of Lost Services (Sday) $1,034

Total Monthly Rent from All Tenants ($/month) $500 
Estimated Net Income of Commercial Businesses ($lmonth) $1,500 
Total Mitigation Project Costs $53,205 
Discount Rate 7.00% 

Project Useful Life (years) 30 

IDATA THAT VARY BY FLOOD DEPTH: 
Flood Building Modified Contents Displacement Functlonl| BuildingMIt. ContentsMii Annual# 
Depth(It) DDF DDF ( Time (days) Downtime(days) Effectiveness(%Effectiveness(OA of Floods 
-2 0 0 0 0 0 100 100 1.123E-01 
-1 0 0 0 0 0 100 100 5.751E-02 
0 5 5 8 0 5 100 100 6.450E-02 
1 9 9 14 0 9 100 100 2.943E-02 
2 13 13 20 54 13 100 100 1.208E-02 
3 18 18 27 94 18 100 100 3.677E-03 
4 20 20 30 110 20 100 100 1.221 E-03 
5 22 22 33 126 22 77 77 4.494E-04 
6 24 24 36 142 24 63 63 1.801E-04 
7 26 26 39 158 26 50 50 7.752E-05 
8 29 29 44 152 29 38 38 3.547E-05 
9 33 33 50 214 30 39 39 1.711E-05 
10 38 38 57 254 30 42 42 8.645E-06 
11 38 38 57 254 30 37 37 4.548E-06 
12 38 38 57 254 30 32 32 2.481E-06 
13 38 38 57 254 30 24 24 1.397E-06 
14 38 38 57 254 30 13 13 8.102E-07 
15 38 38 57 254 30 0 0 4.822E-07 
16 38 38 67 254 30 0 0 2.939E-07 
17 38 38 57 254 30 0 0 1.831E-07 
18 38 38 57 254 30 0 0 1.163E-07 

SUMMARY OF PROJECT BENEFITS AND COSTS 
PROJECT BENEFITS $36,691 
PROJECT COSTS $53,205 
PROJECT BENEFITS MINUS PROJECT COSTS : ($16,513) 
BENEFIT-COST RATIO: 0.69 

FEMADisclaimer:Theresults producedbythis analysisareneitherconclusiveevidencethat theproposedprojectIs cost-effective,nor a 

guaranteethat a prolectIs eligible for any governmentgrantforwhateverpurpose. 

AnMst Goatal&Homer 

1212&'41,0h9:28:24, Gorttel&HomnerInc..2725 DoonerWay,Sacrneiant CA 93818,(i16)45i-4180

10-2 


Rvm FIood mWSIen PMe VernWn 1.0, N.-It. 18. 1334 

FEMA I Benefit-Cost Analysis of Hazard Mitigation Projects

-ME

RIVERINE FLOOD

Version 1.0
November 18, 1994

Report of Benefit-Cost Analysis 

Building Name City Office Annex 
Address 65 A Street 
Cape Squirrel, VA 22222 
Analyst 
Project Description 
Goettel & Horner 
Elevate 6 feet 
Project Number 123456 
Application Date January 1, 1994 
Scenario Run ID 1 

Benefit-Cost Program Prepared for the 

FederalEmergency Management Agency 

by 

GOETTEL & HORNER INC.
2725 Donner Way
Sacramento, Ca 95818
(916) 4514160
FAX (916) 451-3460

rEMA Dis;;Ialmer:
The results produced by this analysis are neither conclusive evidence that the proposed project Is cost-effective,
nor a guarantee that a project is eligible for any governmentgrant for whateverpurpose.

1212NS4. G."I uHo-lrln, CA M18, (018) 451-4160 

0:25:34. & 2725 D-My, S 
10-3 


Rivenne Flood Mibgation Projects Verloin 1.0, Novembr 18, 1994 

LEVELONE DATA Page .1I 

PROJECT INFORMATION 

Building Name City Office Annex 
Address 55 A Street 
City, State, Zip Cape Squirrel, VA 22222 
Owner City of Cape Squirrel 
Contact Person Sam Smith, City Manager 

. 

. 

Disaster Number FE MA-000-D R-VA. 
Project Number N42 5 6 
Application Date JanuFii 1, 11994 
Discount Rate 7.00% 
Scenario Run ID I I 
Analyst JGoettel& Hor qr 

BUILDING DATA 

Building Type Selected | 2 Story wlo Basement 

BUILDING INFORMATION 
Zero Flood Depth (elevation in feet) 
Number of Stories Above Grade 
Construction Date 
Historic Building Controls 

BUILDING SIZE AND USE 
Total Floor Area (sf) rz2,000 
Area Occupied by Owner or PubliclNonprofit Agencies (sf) 1 1500 . 

BUILDING VALUE 
Building Replacement Value ($Isf) $75.00 
Total Building Replacement Value ($) $150,000 
Building Damage that would Result in Demolition Percent 

Value 575,000 

BUILDING CONTENTS 

Contents Description lofficefurniture, computers & files 
Total Value of Contents $50,000 
Value of Contents ($lsf) 1 $25.00 

DISPLACEMENT COSTS DUE TO FLOOD DAMAGE 

Rental Cost of Temporary Building Space ($1sflmonth) E 1.50 
Rental Cost of Temporary Building Space ($/month) $2,250 
Other Costs of Displacement ($/month) $500 
Total Displacement Costs ($Imonth) $2,750 

12128194,09:26:35, Goeltel & Homer Inc., 2725 Donner Way, Sacramento CA 95818, (916) 451-4160 

10-4 


Riverine Flood Mitigation Projects Version 1.0, November 18, 1994 

LEVEL ONE DATA (Continued) Page 2 

City Office Annex 55 A Street Cape Squirrel, VA 22222 

Scenario Run ID 1 

VALUE OF PUBLIC/NONPROFIT SERVICES 

Description of Services Provided City Planning Office 

Annual Budget of Public/Nonprofit Agencies $195,000 

Is Rent Included in this Budget? | Rent Included 
If Rent is NOT Included, a Proxy Rent is Added to the Budget ($/month) l 
User-Entered Rent Estimate, in Place of Proxy Rent ($lmonth) $0 

Cost of Providing Services from this Building ($/day) $534 
Post-Disaster Continuity Premium ($/day) $500 
Total Value of Lost Services ($/day) $1,034 

RENT & BUSINESS INCOME 

Total Monthly Rent from All Tenants ($/month) $500 l 
Estimated Net Income of Commercial Businesses ($/month). $1,500 

MITIGATION PROJECT DATA 

Type of Mitigation Selected Elevation 

Project Description [Elevate 5 feet I 

Project Useful Life (years) 30 
Mitigation Effectiveness ,__ 
Mitigation Measure 100% Effective to Depth 0% Effective at Depth 
Elevation 4 NIA 

Relocation/Buyout NIA NIA 
Flood Barriers 
Other 

Mitigation Project Cost (excluding relocation costs) $40,000 
Base Year of Costs 1994 
Annual Maintenance Costs ($/year) $500 
Present Value of Annual Maintenance Costs ($) $6,205 

Relocation Costs for Mitigation Project 
Relocation Time Due to Project (months) 2 
Rental Cost during Occupant Relocation ($Isflmonth) $2.00 
Rental Cost during Occupant Relocation ($/month) $3,000 
Other Relocation Costs ($/month) $500 
Total Relocation Costs $7,000 

Total Mitigation Project Costs $53,205 

12128/94. 09:26:37. 10-5 Goettel& Homer Inc., 2725 Donner Way, Sacramento CA 95818, (916) 451-4160 


RiverineFRod Midgaion PrcIects Version 10, November 1. 1994 

IFLOODHAZARD RISK Page 3 

City Office Annex 55 A Street Cape Squirrel, VA 22222 

Scenario Run ID I 1 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Zero Flood Depth (elevation in feet): I r,6 

FLOOD HAZARD DATA 

Data from Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM)
Flood Frequency Discharge Elevation

(years) (cfs) (ft) 
10 279,000 5.8 
60 351,000 7.4 
100 377,000 8.0 
500 444,000 9.5 

EXPECTED ANNUAL NUMBER OF FLOODS 

Flood Depth Default User 

(feet) Estimate Estimate 
-2 1.12E-01 
-1 5.75E-02 

0 6.45E-02 

1 2.95E-02 

2 1.21 E-02 
3 3.68E-03 
4 1.22E-03 
5 4.49E-04 
6 1.80E-04 
7 7.75E-05 
8 3.55E-05 
9 1.71 E-05 
10 8.64E-06 
11 4.55E-06 
12 2.48E-06 
13 1.40E-06 
14 8.10E-07 
15 4.82E-07 
16 2.94E-07 
17 1.83E-07 
18 1.16E-07 
COMMENTS: FLOOD HAZARD RISK ESTIMATES 

12123/94, 0:26:39, Gosptel&HomerInc., 2725 DonnerWay,SacramentoCA 95518, (916) 451-4160 

10-6 


RivenneFlood Mitigation Projects Verslon10, November 18 1994 
LEVEL TWO DATA: BUILDING DEPTH-DAMAGE FUNCTION Page 4 | 
[City Office Annex 55 A Street Cape-Squirrel, VA 22222 
a&w Scenario Run ID I I .1 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Building Type: 1 2 Story wlo Basement 

... 

Number of Stories Above Grade 2 
Construction Date 1965 
Historic Building Controls No 

Total Floor Area (square feet): 2,000 
Total Building Replacement Value: $150,000 
Demolition Threshold Damage Percentage: 50% 

BUILDING DEPTH-DAMAGE FUNCTION (DDF) 

ESTIMATED BUILDING DAMAGE 

Flood Depth Default User-Entered Modified Modified
(feet) DDF (%) DDF (%) DDF (%) DDF ($)
-2 0 0 $0

-1 0 0 $0 

0 5 5 $7,500 
1 9 9 $13,500 
2 13 13 $19,600 
3 18 18 $27,000 
4 20 20 $30,000 
5 22 22 $33,000 
6 24 24 $36,000 
7 26 26 $39,000 
8 29 29 $43,500 
9 33 33 $49,500 
10 38 38 $57,000 
11 38 38 $57,000 
12 38 38 $57,000 
13 38 38 $57,000 
14 38 38 $57,000 
15 38 38 $57,000 
16 38 38 $67,000 
17 38 38 $57,000 
18 38 . 38 $57,000 

COMMENTS: BUILDING DDF 

0926:411

2i28194, 
10-7 Gottfl &Homer Inc., 2725 Donner Way. Samcmento CA 95818, (916) 451-4160 


RN*ern Flood UW1gagon "acts Venlon 1.0, Nowrbor 18, IM1 

RloeriM Flood lJfligation Prc.eCtI Varloo 1.0, November18.1004 

I~LEVELTWO DATA: CONTENTS DEPTH-DAMAGE FUNCTION Page 5 I 

jCit OfficeAnnex 55 A Street Cape Squirrel,VA 22222 
Scenario Run ID F I 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Contents Description Iofficefurniture, computers & files
Total Value of Contents $

S50,000 
Value of Contents ($Isf) F_ $25.00 

CONTENTS DEPTH-DAMAGE FUNCTION (DDF) 

ESTIMATED CONTENTS DAMAGE 
Flood Depth Building Default User-Entered 
(feet) DDF(%) DDF (%) DDF (%) DDF ($) 
-2 0 0 $0 
-1 0 0 $0 
0 5 8 $3,750 
1 9 14 $6,750 
2 13 20 $9,750 
3 18 27 $13,500 
4 20 30 $15,000 
5 22 33 $16,500 
6 24 36 $18,000 
7 26 39 $19,500 
8 29 44 $21,750 
9 33 60 $24,750 
10 38 57 $28,500 
11 38 57 $28,500 
12 38 57 $28,500 
13 38 57 $28,600 
14 38 57 . $28,500 
15 38 57 $28,500 
16 38 57 $28,500 
17 38 57 $28,500 
18 38 57 . $28,600 

COMMENTS: CONTENTS DDF

12128/94,09:28:43, Gouete & Homer Inc., 2725 DonnerWay. Sacramento CA 95818, (916) 451-4160

in-s 


Riveine Flood Miigaton Projects Version1.0. Novernber 18. 994 
LEVEL TWO DATA: DISPLACEMENTTIME Page6 
City Office Annex 55A Street Cape Squirrel, VA 22222 

Scenario Run ID I 1 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Rental Cost of Temporary Building Space($Isflmonth) 

Rental Cost of Temporary Building Space($/month) 

Other Costs of Displacement ($/month) 

Total Displacement Costs ($/month) 

Total Monthly Rent from All Tenants ($/month) I $500 

DISPLACEMENT TIME DUE TO BUILDING FLOOD DAMAGE 

Flood Depth Modified Default User-Entered Displacement Rental Income 
(feet) DDF (%) (days) (days) Costs Losses 
-2 0 0 $0 $0 

-1 0 0 $0 $0 
0 5 0 $0 $0 
1 9 0 $0 $0 
2 13 54 _ $4,950 $900 
3 18 94 $8,617 $1,567 
4 20 110 $10,083 $1,833 
5 22 126 . $11,550 $2,100 
6 24 142 $13,017 $2,367 
7 26 158 $14,483 $2,633 
8 29 182 $16,683 $3,033 
9 33 214 $19,617 $3,567 

10 38 254 $23,283 $4,233 
11 38 254 $23,283 $4,233 
12 38 254 $23,283 $4,233 
13 38 254 $23,283 $4,233 
14 38 254 $23,283 $4,233 
15 38 254 $23,283 $4,233 
16 38 254 $23,283 $4,233 
17 38 254 $23,283 $4,233 
18 38 254 $23,283 $4,233 

COMMENTS: DISPLACEMENT TIME ESTIMATES 

1212894,09:25:45. 
10-9 Goettel & Hornarlc 2725DonnerWay.Sarwnento CA95818.(916)451t41 


Rtwfine Flood Mitlgaton Projeds V4ruon1.0, November 18, 1994 

LEVEL TWO DATA: FUNCTIONAL DOWNTIME Page 7 

CIty Office Annex 55 A Street Cape Squirrel, VA 22222 

Scenario Run ID I 0 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Cost of Providing Services from this Building ($/day) 5534 
Post-DisasterContinuity Premium ($/day) $500 
Total Value of Lost Services ($Iday) $1,034 
Estimated Net Income of Commercial Businesses ($/month) $1,500 

FUNCTIONAL DOWNTIME ESTIMATES 

Flood Depth Building Default User-Entered Value of Lost Business 
(feet | DDF (%) Downtime (days) Downtime (days) Lost Services Income 

-2 0 0 __ _ _ _ _ _ _$0 $07 

-1 0 0 $0 $0 
0 5 5 $6,171 $250 
1 9 9 $9,308 $460 
2 13 13 $13,445 $650 
3 18 18 $18,616 $900 
4 20 20 $20,685 $1,000 
5 22 22 $22,763 $1,100 
6 24 24 $24,822 $1,200 
7 26 26 $26,890 $1,300 
8 29 29 $29,993 $1,450 
9 33 30 $31,027 $1,500 
10 38 30 $31,027 $1,500 
11 38 30 $31,027 $i,600 
12 38 30 _ $31,027 $1,500 
13 38 30 $31,027 $1,600 
14 38 30 _ $31,027 $1,500 
15 38 30 _ $31,027 $1,500 
16 38 30 $31,027 $1,500 
17 38 30 $31,027 $1,500 
18 38 30 ._____ ._$31,027 $1,500 

COMMENTS: FUNCTIONAL DOWNTIME ESTIMATES 

12l28194.09:26:47. Goettal&Homer Inc.. 2725 DonnorWey. SacrawmntoCA 95818, (915) 4514160 

10-10 


RiverineFloodMitgationProjects Verslon1.0,November18,1994 

[LEVEL TWO DATA TION PROJECT EFFECTIVENESS Page 8 I 

lCityOffice Annex 65A Street Cape Squirrel, VA 22222 

Scenario Run ID I 1 | 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Building Type towoBasement 
Total Floor Area (sf) 2,000 
Total Building Replacement Value 

Demolition Threshold Damage Percentage 50% 

Type of Mitigation Selected II Kiw;Elevation 
Project Description IElevate 5 feet 

Total Mitigation Project Costs I $53,205 

MITIGATION EFFECTIVENESS (percent of damages avoided) 

BUILDING DAMAGES CONTENTS DAMAGES 
Flood Depth Building Default User-Entered Contents Default User-Entered 

(feet) DDF (%) Eff. (%) Eff.(%) DDF (%) Eff. (%) Eff. (%) 
-2 0 100 0 100 
-1 0 100 0 100 

0 5 100 8 100 

1 9 100 14 100 
2 13 100 20 100 
3 18 100 27 100 
4 20 100 30 100 
5 22 77 33 77 

6 24 63 36 63 
7 26 50 39 50 
8 29 38 44 38 
9 33 39 50 39 
10 38 42 57 42 
11 38 37 57 37 
12 38 32. 57 32 
13 38 24 57 24 
14 38 13 57 13 
15 38 0 57 0 
16 38 0 57 0 
17 38 0 57 0 
18 38 0 57 0 

COMMENTS: MITIGATION EFFECTIVENESS ESTIMATES 

12M2N. 09:26:50. 

10-11 Goettel&Homerlnc.,2725DonnerWay.SacramentoCA95818.(916)4514180 


thwine Flood M~artion Prmicts VasoIA .,N&MIM, 

SUMMARY OF DAMAGES BEFORE MITIGATION Page 9 

City Office Annex 55 A Street Cape Squirrel, VA 22222 
Scenario Run ID | 
Building Type 2 Story wlo Basement I 
SCENARIO DAMAGES BEFORE MITIGATION($ per event) 

Flood Building Contents Displacement Business Rental Pubilc/ 
Depth Damages Damages Costs Losses Losses Nonprofit Total 
-2 $0 $0 $0 $0 $0 $0 $0 
-t $0 $0 SO SO $0 $0 $0 
0 $7,500 $3,750 $0 $250 $0 $5,171 $16,671 
1 $13,500 $6,750 $0 $450 $0 $9,308 $30,008 
2 $19,500 $9,750 $4,950 $650 $900 $13,445 $49,195 
3 $27,000 $13,500 $8,617 $900 $1,567 $18,616 $70,200 
4 $30,000 $15,000 $10,083 $1,000 $1,833 $20,685 $78,602 
5 $33,000 $16,500 $11,550 $1,100 $2,100 $22,753 $87,003 
6 $36,000 $18,000 $13,017 $1,200 $2,367 $24,822 $95,405 
7 $39,000 $19,500 $14,483 $1,300 $2,633 $26,890 $103,807 
8 $43,500 $21,750 $16,683 $1,450 $3,033 $29,993 $116,410 
9 $49,500 $24,750 $19,617 $1,500 $3,567 $31,027 $129,961 
10 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
11 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
12 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
13 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
14 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
15 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
16 $57,000 $28,soo $23,283 $1,500 $4,233 $31,027 $145,544 
17 $57,000 $28,600 $23,283 $1,500 $4,233 $31,027 $145,544 
18 $57,000 $28,500 $23,283 $1,S00 $4,233 $31,027 $145,544 

EXPECTED ANNUAL DAMAGES BEFORE MITIGATION($ per year) 

Flood Building Contents Displacement Business Rental Public]
Depth Damages Damages Costs Losses Losses Nonprofit Total

-2 SO $0 $0 $0 $0 $0 $0 
-1 S0 $0 $0 $0 $0 $0 $0 
0 $484 $242 $0 $16 $0 $334 $1,075 
I $398 $199 $0 $13 $0 $274 $885 
2 $236 $118 $60 $8 $11 $162 $594 
3 $99 $50 $32 $3 $6 $68 $258 
4 $37 $18 $12 $1 $2 $25 $96 
s $15 $7 $5 $0 $1 $10 $39 
6 $6 $3 $2 $0 $0 $4 $17 
7 $3 $2 $1 $0 $0 $2 $8 
8 $2 $1 $1 $0 $0 $1 $4 
9 $1 S0 $0 $0 $O $1 $2 
10 $0 $0 $0 $0 $0 $0 $1 
11 $0 $0 $0 $0 $0 $0 $1 
12 $0 $0 $0 $0 $0 $0 $0 

13 $0 $0 $0 $0 S0 $0 $0 
14 $0 $0 $0 $0 $0 $0 $0 
1S $0 $0 S0 $0 $0 $0 $0 
16 $0 $0 $0 $0 S0 $0 $0 

17 sob $0 -__$0 _ __ $0 _ _ $0 
18 $0 $0 $0 $0 $0 $0 $0 
Total $1,281 $641 $114 $43 $21 $883 $2,982 

12/2994,09:26:53. Goettel & Homer inc., 2725 Donner Way. Sacramento CA 95515, (916) 4514150 

10-12 


Riverne FloodMitigation Pmjects _in1 n w~h~ 1A -ul 
SUMMARY OF DAMAGES AFTER MITIGATION Page 10 | 
City Office Annex 55 A Street CapeSquirrel, VA 22222 

Scenario Run ID 

Project Description |Elevate5 feet 

SCENARIO DAMAGES AFTER MITIGATION ($ per event) 
Flood Building Contents Displacement Business Rental Public/ 
Depth Damages Damages Costs Losses Losses Nonprofit Total 
-2 $0 $0 $0 $0 $0 $o so 
.1 $0 $0 $0 $0 $0 $0 $0 
0 $0 $0 $0 $0 $0 $0 $0 
1 $0 $0 $0 $0 $0 $0 So 
2 $0 $0 $0 $0 $0 $0 $o 
3 $0 $0 $0 $0 $0 $0 $0 
4 $0 $0 $0 $0 $0 $0 $0 
5 $7,500 $3,750 $2,625 $250 $477 $5,171 $19,774 
6 $13,500 $6,750 $4,881 $450 $888 $9,308 $35,777 
7 $19,500 $9,750 $7,242 $650 $1,317 $13,445 $51,904 
8 $27,000 $13,500 $10,355 $900 $1,883 $18,616 $72,254 
9 $30,000 $15,000 $11,889 $909 $2,162 $18,804 $78,764 
10 $33,000 $16,500 $13,480 $868 $2,451 $17,963 $84,262 
11 $36,000 $18,000 $14,705 $947 $2,674 $19,596 $91,923 
12 $39,000 $19,500 $15,931 $1,026 $2,896 $21,229 $99,583 
13 $43,500 $21,750 $17,769 $1,145 $3,231 $23,679 $111,073 
14 $49,500 $24,750 $20,220 $1,303 $3,676 $26,945 $126,394 
15 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
16 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
17 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 
18 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 

EXPECTED ANNUAL DAMAGES AFTER MITIGATION ($ per year) 

Flood Building Contents Displacement Business Rental Publicl 
Depth Damages Damages Costs Losses Losses Nonprofit Total 

-2 $0 $0 $0 $0 $0 $0 $0 
-1 $0 $0 $0 $0 $0 $0 $0 
0 $0 $0 $0 $0 $0 $0 $0 
I $0 $0 $0 $0 $0 $0 $0 
2 $0 $0 $0 $0 $0 $0 $0 
3 $0 $0 $0 $0 $0 $0 $0 
4 $0 $0 $0 $0 $0 $0 $0 
5 $3 $2 $1 $0 $0 $2 $9 
6 $2 $1 $1 $0 $0 $2 $6 
7 $2 $1 $1 $0 $0 $1 $4 
8 $1 $0 $0 $0 $0 $1 $3 
9 $1 $0 $0 $0 $0 $o $1 
10 $0 $0 $0 $0 $0 $0 $1 
11 $0 $0 $0 $0 $0 $0 $0 
12 $0 $0 $0 $0 $0 $0 $0 
13 $0 $0 $0 $0 $0 $0 $0 
14 $0 $0 $0 $0 $o $0 $0 
15 $0 $0 $0 $0 $0 $0 $0 
16 $0 $0 $0 $0 S 0 $0 $0 
17 $U $0 $0 $0 $0 $0 $0 
18 $0 $0 $0 $0 $0 $0 $0 

Toal $9 $5 $3 $0 $1 $6 $25 

17nA/G u,;co;3

n,

li:6ZEli4, U8:Z0:55, 

10-13 Goettel& Homer Inc.,2725 Donner Way. Sacnamento CA 95318, (91e) *45141W0 


Rfernra FloodmlffoaimnProlicts Venslon1.0,Novamber18, 1994 

SUMMARY OFBENEFITS FROMMITIGATION Page 11 

_

City Offlce Annex 55 A Street Cape Squirrel, VA 22222 
Scenarlo Run ID 1 

Project Description |Elevate6 feet 
EXPECTED ANNUAL BENEFITS FROM MITIGATION ($ per year) 

Flood Building Contents Displacement Business Rental Public/ 
Depth Damages Damages Costs Losses Losses Nonprofit Total 
-2 $0 $0 $0 $0 $0 $0 $0 
-1 $0 $0 $0 $0 $0 $0 $0 
0 $484 $242 $0 $16 $0 $334 $1,075 
1 $398 $199 $0 $13 $0 $274 $885 
2 $236 $118 $60 $8 $11 $162 $594 
3 $99 $50 $32 $3 $6 $68 $258 
4 $37 $18 $12 $1 $2 $25 $96 
5 $11 $6 $4 $0 $1 $8 $30 
6 $4 $2 $1 $0 $0 $3 $11 
7 $2 $1 $1 $0 $0 $1 $4 
8 $1 $0 $0 $0 $0 $0 $2 
9 $0 $0 $0 $0 $0 $0 $1 
10 $0 $0 $0 $0 $0 $0 $1 
11 $0 $0 $0 $0 $0 $0 $0 
12 $0 $0 $0 $0 $0 $0 $0 
13 $0 $0 $0 $0 $0 $0 $0 
14 $0 $0 $0 $0 $0 $0 $0 
15 $0 $0 $0 $0 $0 $0 $0 
16 $0 $0 $0 $0 $0 $0 $0 
17 $0 $0 $0 $0 $0 $0 $0 
18 $0 $0 $0 $0 $0 $0 $0 
Total $1,272 $636 $110 $42 $20 $877 $2,957 

Gottel & HovmerInc., 2725 DonnerWay, SacramentoCA 95818, (916) 4514180 

1228094,10:05:08, 

10-14 


Riverinn Flood MitigationProjects Version1 0, November 18, 1994 

BENEFIT-COST RESULTS Page 1 

City Office Annex 55 A Street Cape Squirrel, VA 22222 

Scenario RunIDID 
Building Type L 2 Story wlo Basement 
Project Description IElevate5 feet 

REFERENCE INFORMATION FROM LEVEL ONE DATA 

Discount Rate 7.00% 
I Project Useful Life (years) 30 
Present Value Coefficient 12.41 

SUMMARY OF EXPECTED DAMAGES AND BENEFITS 

Expected Annual Expected Annual Expected Annual Present Value of 
Damages Damages Benefits Annual Benefits 
Before Mitigation After Mitigation V 
Building Damages $1,281 $9 $1,272 $15,779 
Contents Damages $641 $5 $636 $7,890 
DisplacementCosts $114 $3 $110 $1,369 
Business Income Lost $43 $0 $42 $526 
Rental Income Lost $21 $1 $20 $249 
Gov't Services Lost $883 $6 $877 $10,879 
Total Losses $2,982 $25 $2,957 $36,691 
A: 
PROJECT BENEFITS L_ ~$36,691 
PROJECT COSTS I ~~$53,205 I 
BENEFITS MINUS COST S ($1 6,513) 
BENEFIT-COST RMIkTIO 1 0.69 L 

FEMADisclaimer: The results produced by this analysis are neitherconclusive evidencethat the proposedproject is cost-effective, nor a 
guaranteethat a project is eligible for any governmentgrant for whateverpurpose. 

12f214,0C9:27:0J0, 

10-15 Goettel&Homer Inc. 2725 DonnerWay, Sacramento CA95818,(916) 451-4160 


Annual ExceedanceProbability 
vs. Flood Depth 

0.3 

U 

0.25 

._ . 

co-0.2 

0 ._
L-

a) 0.15

0 

am 0.1

x

0) 

X 

w 

0.05 
0 Il I I I I oI***** 
-~A 6 I F l o o 1D 1e 1t 1 14 1h 16 17 18 

Flood Depth 

Office Annex

A.-City 


ExpectedAnnual Numberof Floods 
vs. Flood Depth 

0.12 

*0

to

0 

0 0.1 -------------------------------------------0 
0.08

.hm 

a) 

EC 

0.06 
b 

0.04
ft) 

LU 

0.02 A ~ ~ ~ ~ ~ ~ ~ ~ R 
0 

-2 -iI 6 2 1 a 6 6 1 9 . fofl f21Tf)3Q fS f6 fl 

Flood Depth 
-.-City OfficeAnn 


Scenario Damages
Before Mitigation

$160,000

$140,000 -

Gov'tServices Lost

$120,000RentalIncomeLost

$100,000 ---

----------d

Business IncomeLost 

$80,000 --------: ---4 1 N 

DisplacementCosts 

$60,000 -------------U
Contents Damages

$40,000 --------A 

Building Damages

$20,000 -
$0 -

e1t

2 4 6 8D141l 1d 1 

Flood Depth 


ExpectedAnnual Damages
Before Mitigation

$1,200 

$1,000 ----

Gov't Services Lost 
Rental Income Lost 

z 

$600 -l--------BusinessIncomeLost 

U 

Displacement Costs 

U 

$200 --------
Contents Damages 

Building Damages 
$0 

Flood Depth 


Scenario Damages
After Mitigation

$160,000 -
$140,000-

$120,000 -Gov'tServices Lost 

E

$100,000 --- -------------------RentalIncomeLost 
$80,000-Business IncomeLost 
$60,000 -DisplacementCosts

X

$40,000-Contents Damages
$20,000-BuildingDamages

$0-I I I I I I 

4 d6D t 1 14 16 18 
Flood Depth 


ExpectedAnnual Damages 
AfterMitigation 

$10 

$8-E 

Gov't ServicesLost 

_ 

$6-RentalIncome Lost 

Business IncomeLos

E

$4 

0 DisplacementCostsContentsDamages 

$2 

Building Damages

---1----------

$0 I I I I I I 

T 

-2 6 .4 1 F I b I I6 k 1 

FloodDepth 


Expected Annual Benefits

AnnualBenefits 

from Mitigation

$1,200$
1,000 -
$800 -l 
$ t600 --------------------
$400 
$ 2 00 
-I 
----I ------------
$0-L I l i 1-I L I I I I I 
Flood Depth 


MitigationProject Benefits

Lost Services (29.65%) 

-BuildingDamages (43.00%) 

Rent Losses (0.68%o)

BusinessLosses (1.43%o)
DisplacementCosts (3.73%.Y) 

ContentsDamages(21.50%)-' 


VERSION 1.0 12/29/94 GLOSSARY

Annual Budget 
of Public/ 
Nonprofit 
Agencies 

Avoided 
Damages and 
Losses 

Base Year of 
Costs 

Benefit-Cost 
Ratio 

Benefits 

Block Colors 

CHAPTER 11
GLOSSARY

The annual budget of public/nonprofit agencies is the total annual 
operating budget of all the public/nonprofit agency functions located in a 
building, excluding "pass-through" monies (e.g., Social Security 
payments) which the agency receives and redistributes. The annual 
budget is used to value the loss of public/nonprofit services due to flood 
damages. 

Avoided damages and losses are the "benefits" counted in benefit-cost 
analysis. Six types of avoided damages and losses are counted in this 
benefit-cost program: building damages, contents damages, 

displacement costs, business income losses, rental income losses, and 
lost public/nonprofit services. 

The base year of costs is the year in which the mitigation project's costs 
were estimated and allows cost estimates made in prior years to be 
adjusted for any inflation in costs between the base year and the 
present time. 

The benefit-cost ratio is the ratio of the present value of benefits to 
project costs for the proposed mitigation project. 

The benefits counted in a benefit-cost analysis are the present value of 
the sum of the expected annual avoided damages over the lifetime of 
the mitigation project. 

Each block (cell) of data entry or data display areas of the program 

screens is color coded to inform the user what type of information each 

block contains. See Color Code chart, below. Also, see Style List. 

11-1


VERSION 1.0 12/29/94 GLOSSARY

Building 
Damages 

Building Depth-
Damage 
Function (DDF) 

Building 

Replacement 
Value 

Building 

Reproduction 
Value 

Bu5lding-Specific 
Data 

Seven cell colors indicate different types of entries: 

GREEN Blocks (Data Input) require the user to enter data concerning 
the building or project and directly affect the calculated results. 

PINK Blocks (Information Only) contain information about the building 
or project and do not affect the calculated results. 

PURPLE Blocks (Carry Over) contain information that was entered by 
the user in other screens. 

ORANGE Blocks (Default) contain default data and cannot be 
changed. 

BLUE Blocks (Override Default) can be used to override default data 
with project-specific data. 

YELLOW Blocks (Results) contain calculated results from the model. 

RED Blocks (OMB Policy) contain entries that are defined by OMB or 
FEMA policy and thus are not user-defined entries. 

Building damages are the estimated damages to a structure, expressed 
as a percentage of the building's replacement value. Building damages 
include both structural and non-structural elements (mechanical, 
electrical, and plumbing systems) but exclude the building's contents. 

The building depth-damage function (DDF) indicates the building's 
vulnerability to flood damage by showing the estimated building 
damage for the range of flood depths from -2 to 18 feet above the top of 
the lowest finished floor. 

Building replacement value is the cost to provide a functionally-
equivalent structure of the same size, generally of a more modern 
construction type. Replacement value does not include recreating 
historical or archaic materials, finishes or features. 

Building reproduction value is the cost of duplicating the design and 
architectural details of a specific, usual historic, building. 

Building-specific data are values which apply to the specific building 
under evaluation rather than to a generic building construction type. 

11-2


VERSION 1.0 12/29/94 GLOSSARY,

I 

Building Type 

Business Income 
Losses 

Buyout, 
Mitigation 
Measure 

Coastal Transect 

Construction 
Date 

Contents 

Damages 

Contents Depth-
Damage 
Function 

Contents Value 

Building types considered in the model are the six Federal Insurance 
Administration (FIA) building types (1 story without basement, 2 story 
without basement, and split level without basement; 1 or 2 story with 
basement, split level with basement; and mobile home) plus an "other" 
category. The "other" category allows data inputs for building types not 
covered by the six FIA building types. 

Business income losses are the value of lost net business income due 
to flood damage. 

Buyout is a type of mitigation measure in which the owner's interest in 
the building is purchased and the building demolished. Buyouts are 

assumed to be 100% effective mitigation measures at all flood depths. 

Used in the Coastal-A Zone and Coastal-V Zone programs (but not in 

the Riverine Flood program), a coastal transect is a line drawn 

perpendicular to the coastline showing the A-Zone and V-Zone regions. 

Coastal transects are shown on maps in coastal Flood Information 

Studies. 

The construction date is the year during which the building's 

construction was started. 

Contents damages are the estimated damages to the building's 
contents, expressed as a percentage of the total contents' replacement 
value. Contents damages include furniture, office equipment, carpet, 
and other items specific to individual tenants' usages, but exclude 
mechanical, electrical, and plumbing systems which are non-structural 
parts of the building. 

The contents depth-damage function (DDF) indicates the content's 

vulnerability to flood damage by showing the estimated contents 

damage for the range of flood depths from -2 to 18 feet. 

The contents value is the estimated total value of the building's 

contents, including furniture, carpet, equipment, supplies, etc. 

I 

11-3


VERSION 1.0 12/29/94 GLOSSARY

Continuity 
Premium 

Cost of 
Occupant 
Displacement 

Default Building 
Depth-Damage 
Function 

Default Values 

Demolition 
Threshold 
Damage 
Percentage 

Depth-Damage 
Function (DDF) 

Discharge 

Discount Rate 

The post-disaster continuity premium is a means of more highly valuing 
public/nonprofit services which are particularly important in the post-
disaster environment. The continuity premium is the extra dollar 
amount per day an agency would be willing to pay to maintain its 
functions after a flood. This premium is appropriate for those 
public/nonprofit services which may be more valuable than normal in 
the post-flood time period. 

The cost of occupant displacement is the total cost of displacement 
after a flood, including rent for temporary quarters, moving, and extra 
operating costs incurred because of displacement. The total cost of 
displacement of occupants is calculated from the displacement time and 
cost per month. 

The default building depth-damage function indicates a typical building's 
vulnerability to flood damage by showing the estimated levels of 
damage at each flood depth, based on the building type selected. 

Default, or reference, values are the estimated "typical" values 
contained in the program which are used in a LEVEL ONE (Minimum 
Data) analysis to facilitate a benefit-cost analysis for a "typical" building 
of the type selected. 

The demolition threshold damage percentage is the level of building 
damage, expressed as a percentage of the building's replacement 
value, at which the building is likely to be demolished rather than 
repaired. This percentage will vary depending on the type, style, age, 
condition, and historic significance of the structure. 

See Building Depth-Damage Function or Contents Depth-Damage 
Function. 

Discharge is the volume of water flow in a river or stream, usually 
measured in cubic feet per second. 

The discount rate is an interest rate which accounts for the time value 
of money. The discount rate is used to convert expected annual 
benefits over the lifetime of a project to a net present value. For 
Federally-funded hazard mitigation projects, the discount rate is 
determined by U.S. Office of Management and Budget (OMB) 
guidance. 

11-4 


VERSION 1.0 12/29/94 GLOSSARY 

VERSION 1.0 12129/94 GLOSSARY 

Displacement 
Costs 
Displacement costs are the product of displacement costs per month 
and the expected period for which the building will be unusable due to 
flood damage. Displacement costs are incurred when owners are 
displaced to a temporary site while flood-related damage to the original 
building is repaired and include costs for rent and other displacement 
expenses. 
Displacement 
Time 
Displacement time is the time during which an agency must operate 
from a temporary location due to flood-related damage while repairs are 
made to the original building. Compare with Functional Downtime. 

Economic Economic parameters used in the benefit-cost program are the 
Parameters Discount Rate, Project Useful Life, and Present Value Coefficient. 

Elevation, Elevation is a type of mitigation measure in which an existing building is 
Mitigation elevated to reduce future flood damages. 
Measure 

Estimated "Estimated" is used to denote data inputs which are based on 

judgement rather than exact values, and also to denote calculated 
results derived from other input parameters. In benefit-cost analysis 
"estimated" is distinct from "expected." See Expected. 

Exceedance The exceedance probability is the likelihood (probability) of exceeding a 
Probability particular value in a stated time period. For example, the annual 
exceedance probability for a 3-foot flood is the probability for all floods 
greater than or equal to a 3-foot flood. 

Expected "Expected" in benefit-cost analysis means a statistical, average value. 
For example, "expected" annual damages are the statistical average 
damages "expected" over a long time period. "Expected" annual 
damages do not occur every year. 

Expected Annual The expected annual avoided damages are the expected annual 
Avoided benefits counted in benefit-cost analysis. In other words, the expected 

Damages annual avoided damages are the difference between expected annual 

damages before and after mitigation. 

11-5


VERSION 1.0 12/29/94 GLOSSARY
VERSION 1.0 12/29194 GLOSSARY

Expected Annual Expected annual damages before mitigation are the average damages 
Damages Before per year expected over a long time period. For each flood depth, 
Mitigation expected annual damages are calculated by multiplying the scenario 
damages before mitigation by the annual probability that a flood of each 
depth will occur. 
In this program, expected annual damages are calculated for six 
categories of damages and losses: building damages, contents 
damages, displacement costs, business income losses, rental income 
losses, and lost public/nonprofit services. 

Expected Annual Expected annual damages after mitigation are the average damages 
Damages After per year expected over a long time period. For each flood depth, 
Mitigation expected annual damages after mitigation are calculated by multiplying 

the scenario damages after mitigation times the annual probability that 
a flood of each depth will occur. 

Expected Annual The expected annual number of floods is the long term average annual 
Number of number of floods of a particular depth, from -2 to 18 feet. The expected 
Floods annual number of floods is closely similar to the annual probability of 

floods at each depth. 

Expected Net The expected net present value of a flood hazard mitigation project is 

Present Value the present value of benefits arising from the mitigation project. 
Expected annual benefits in each year of the useful lifetime of the 
project are discounted to present value and summed to obtain the net 
present value of benefits. 

Flood Barrier, A flood barrier is a type of mitigation measure in which barriers such as 
Mitigation flood walls, levees, or enclosures are constructed to prevent flood water 
Measure from reaching a structure. 

Flood Depth-The flood depth-damage table displays the estimated damage by flood 
Damage Table depth for the six classes of building types plus the "other" classification 
included in the program. 

Flood Risk The flood risk for a particular building is the expected annual number of 
floods, in one-foot increments from -2 to 18 feet in the program, at the 
building site. Flood risk varies markedly with elevation. See Zero 
Flood Depth Elevation. 

11-6 


VERSION 1.0 12/29/94 'GLOSSARY

Freeboard 

Functional 
Downtime 

Income, 
Estimated Net 

Level One 
(Minimum Data) 
B-C Analysis 

Level Two 

(Detailed) 

B-CAnalysis 

Main Menu 

Menu Bar 

Menu Tree 

Freeboard is the additional height of a flood protection measure above 
an expected flood height which will provide an extra measure of flood 
protection. For example, to provide 1 00-year flood protection, levees 
normally are constructed with 3 feet above the 1 00-year flood elevation 
(i.e., with 3 feet of freeboard). 

Functional downtime is the time during which an agency/organization is 
unable to provide its services due to flood damage. Compare with 
Displacement Time. 

The estimated net income of commercial businesses is the net monthly 
income of commercial businesses in the building. 

A LEVEL ONE (Minimum Data) benefit-cost analysis uses "default" or 
reference data built into the program, and requires the minimum amount 
of building-specific and project-specific data. A LEVEL ONE analysis 
may be appropriate for small, low-cost projects or as an initial screening 

of larger projects. See LEVEL TWO (Detailed) benefit-cost analysis. 

A LEVEL TWO (Detailed) benefit-cost analysis is a highly detailed 

analysis in which default, or reference, values may be overridden with 

project-specific data. A LEVEL TWO analysis may be desirable for 

large, high-cost projects, projects which are politically sensitive, or 

projects where initial screening indicates that benefit-cost ratios are 

close to one, whenever the default values used in the LEVEL ONE 

(Minimum Data) analysis do not accurately reflect a specific project 

under evaluation, or where the results of a LEVEL ONE analysis 

indicate that a more detailed analysis is required to determine whether 

the project is cost-effective. 

The main menu is the list of headings which appears at the top of the 

display screen, customized for the benefit-cost program. The main 

menu headings in the Benefit-Cost Program are shown below: 

fEile Model tLevel OGneData7 Foodaard Risk HLevel Iwo ty 

The menu bar displays all the main menu headings of the benefit-cost 

program in the row near the top of the screen (i.e., word commands), 

under the words "Quattro Pro for Windows." 

The menu tree is the complete list of items which can be accessed by 

the menu bar. 

11-7 


VERSION 1.0 12/29/94 GLOSSARY

Mitigation 

Measure 

Mitigation 

Project Cost 

Modified 
Building Depth-
Damage 
Function 

Net Present 
Value (NPV) 

Other, Mitigation 
Measure 

Planning Horizon 

Post-Disaster 
Continuity 
Premium 

Present Value 

Present Value 
Coefficient 

A flood hazard mitigation measure is any project undertaken to mitigate 
the flood hazard. See Elevation, Flood Barrier, Relocation, and 
Buyout. 

The mitigation project cost is the sum of all direct construction costs 

plus other costs such as architectural and engineering fees, testing, 

permits, and project management but excludes relocation costs. See 

Relocation Costs. 

The modified building depth-damage function is the building DDF 
modified to account for the demolition threshold damage percentage. 

See Expected Net Present Value. 

The "Other" category of flood hazard mitigation projects includes wet 
floodproofing (see previous discussion on this subject) and any other 
measures not covered by the Elevation, Buyout, Relocation, or Flood 
Barriercategories. 

The planning horizon is the expected useful lifetime of the flood hazard 
mitigation project. See Project Useful Life. 

See ContinuityPremium. 

See Expected Net Present Value. 

The present value coefficient is a multiplier determined by the discount 
rate and the planning period which indicates the present value of $1.00 
per year in benefits over the useful lifetime of the project. See Present 
Value. 

11-8


VERSION 1.0 12/29/94 GLOSSARY

Productivity The productivity tools SpeedBar is an additional row of symbols, usually 
Tools SpeedBar underneath the first SpeedBar, which provides access to more Quattro 
Pro features. 

Project Costs 

Project Useful 
Life 

Protected Blocks 

Public/ 
Nonprofit 
Services Lost 

Recurrence 
Intervals 

Relocation, 
Mitigation 
Measure 

Relocation Costs 

Rent, Total 
Monthly 

Project costs are the total mitigation project costs. See Mitigation 
Project Cost. 

The project's useful life is the estimated time period over which the 
mitigation project will maintain its effectiveness. Project useful life must 
be commensurate with the actual project being considered. 

Protected blocks cannot be changed by the user. Blocks colored 
orange, yellow, and purple are protected. 

Public/nonprofit services lost are those services which cannot be 
provided when a building becomes unusable during a flood. Avoided 
public/nonprofit services lost are one of the benefits counted in the 
benefit-cost program. 

A recurrence interval is the average time period between similar events 
(e.g., 100 years). A 1 00-year flood means a flood with a 1% annual 
probability of occurring. 

Relocation is a flood hazard mitigation alternative available in some 
situations. Relocation entails moving a structure out of the flood plain. 
Relocations are assumed to be 100% effective measures at all flood 
depths. 

Relocation costs are incurred when occupants must be relocated for 
construction of the mitigation project. In such cases, the Relocation 
Costs are an integral part of the mitigation project and must be counted 
in the total mitigation project costs. 

Total monthly rent is the amount of rent paid by all tenants in the 
structure. For a public/nonprofit building, the rent value entered should 
be only the rent for that portion, if any, rented to private tenants. 

11-9 


VERSION 1.0 12/29/94 GLOSSARY 

Rental Income Rental income losses are lost payments normally paid by private 

Losses tenants for all or a portion of the building. Inter-or intra-agency rents 

Scenario 

Damages 

Scenario 

Damages After 
Mitigation 

Scenario 
Damages Before 
Mitigation 

Scenario Run 
Identification 

SpeedBar 

Stories Above 

Grade 

.Style List 

within the Federal Government are not counted because such 
payments are generally transfers and their loss does not represent a 
true economic loss. 

Scenario damages are the damages per flood occurrence (i.e., event) 
of a given flood depth. In the program, scenario damages are 
expressed in 1-foot flood-depth increments from -2 to 18 feet. 

Scenario damages after mitigation are the estimated damages and 
losses from a single flood of a particular depth at the building after 
completion of the mitigation project. Scenario damages do NOT 
depend on the probability of floods at a location. 

Scenario damages are the damages and losses from a single flood of a 
particular depth at the building under evaluation before completion of 
the mitigation project. Scenario damages do NOT depend on the 
probability of floods at that location. 

The scenario run identification is a number or name which will 
distinguish this particular analysis from others. 

The SpeedBar is the row of icons (small pictures) just under the menu 
bar, i.e., the first row of buttons and tools. As the cursor moves across 
each item in the SpeedBar, an explanation of the button (or symbol) 
appears in the bottom left corner of the screen. 

Stories above grade are the number of stories above ground level in 

this building. 

The style list is the set of names which appear in the Style List window 

(located on the SpeedBar) which indicates the type of information 

contained in that block. The seven categories are the same as for the 

Block Colors. 

11-10


VERSION 1.0 12/29/94 GLOSSARY

Total Building 
Replacement 
Value 

Total Mitigation 
Project Costs 

Transect 

Zero Flood Depth 
Elevation 

Zoom List Box 

The total building replacement value is the product of the building 
replacement value per square foot and the building size 

Total mitigation project costs are the sum of the project costs and 
relocation costs necessary for the project. 

See Coastal Transect. 

The zero flood depth elevation of the building is the elevation of the top 
of the finished flooring of the lowest finished floor, as defined by the 
Federal Insurance Administration in compiling flood damage data. 

The zoom list box is the rectangular box in the third row at the top of the 
QPW window, which may be adjusted for the size of an individual 
computer screen display. 

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APPENDIXI
ECONOMIC ASSUMPTIONS AND EQUATIONS

I I 

The economic assumptions and equations which define the benefit-cost 
analysis of flood hazard mitigation projects are summarized in this 
appendix. 

Benefit-Cost Program 

The benefits of a flood hazard mitigation project are the avoided future 
damages and losses (i.e., the extent to which the mitigation project is 
effective in reducing expected future damages and losses). The net 
present value of benefits accounts for the time value of money, 
because benefits are expected to accrue in the future and dollars 
received in the future have a present value which is less than dollars 
received immediately. The expected net present value of a flood 
hazard mitigation project is the sum of the present value of net benefits 
expected to accrue each year over the life of the project, minus the 
initial cost of the mitigation project. The expected net present value, 
NPV, is defined as: 

NPV=-+ B B2 Bt BT INV 
1+i (1+1)2 01+it (1+itr 

where: 

NPV is the expected net present value of a flood hazard 
mitigation project; 

B. is the expected annual net benefit of the hazard 
mitigation project for year t; 
i is the annual discount rate; 

T is the useful lifetime of the hazard mitigation project; and 

INV is the initial investment (the cost of the project). 

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Each year's expected net benefit is discounted to its present value, then 
all years' expected net benefits are summed together to yield the total 
expected net present value. The planning horizon, or useful lifetime, of 
the hazard mitigation project varies depending on the type of project, 
with 30 to 50 years being common for building projects. The discount 
rate corrects benefits expected to be received in the future to their net 
present value. 

If expected net benefits are constant each year over the life of the 
project, the expected net present value equation is simplified to the 
constant annual benefits and one discount term representing the 
present value for the entire planning horizon. With this simplification, 
the expected net present value equation is reduced to: 

NPV = Bt t1-1+wT1_ INV 

For completeness, we mention two other factors which could be 
included in the expected net present value calculation: the salvage 
value of the mitigation investment at the end of the planning horizon 
and the annual costs to maintain the effectiveness of the mitigation 
project. However, the present value of the salvage value of flood 
hazard mitigation projects is generally quite small, because of the long 
planning horizons appropriate for building projects. Thus, salvage value 
is not considered in the program. The annual maintenance costs of 
typical Section 404 or 406 flood hazard mitigation projects are generally 
small, but may be significant, especially for levee projects. Therefore, 
for completeness, the annual maintenance costs are included in the 
benefit-cost program. The net present value of the annual maintenance 
costs is included in the total mitigation project costs. 

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EconomicAssumptions for Modeling Benefits

Underlying 
Assumptions 
The benefits of a flood hazard mitigation project are the reduction in 
damages that would otherwise be expected. Expected annual benefits 
are defined as the sum of expected avoided damages and losses. 
There are three different types of damages which are considered: 
scenario damages, expected annual damages, and expected annual 
avoided damages. Definitions of these terms are: 
Scenario Damages: 
the expected damages per flood of a given flood depth at the 
building, 
Expected Annual Damages: 
the product of scenario damages and the expected annual 
number of floods of a given flood depth at the building, and 
Expected Annual Avoided Damages (Expected Annual Benefits): 
the product of expected annual damages and the effectiveness 
of the mitigation measure in reducing damages at the building. 
A schematic example illustrating these damage terms is given below: 
Table 1 
Flood 
Depth 
(ft) 
Scenario 
Damages 
Expected 
Annual 
Number of 
Floods 
Expected 
Annual 
Damages 
Effectiveness 
of Mitigation 
Measure 
Expectea 
Annual 
Benefits 
-2 $20,000 .10 $2000 100% $2,000 
-1 $25,000 .05 $1250 80% $1,000 
o $35,000 .02 $700 50% $350 
1 $50,000 .01 $500 26% $125 
2 $85,000 .005 $425. 15% $64 
In this example, the scenario damages indicate the expected damages 
each time a flood of the given depth occurs at the building site. 
Scenario damages do not depend on how frequently such floods are 
expected to occur. The annual flood probabilities indicate the degree o-
flood-related risk at the specific site under consideration. The expected 
annual damages are the product of scenario damages and annual flooa 
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Benefits are 
AVOIDED 
Damages 

probability. Expected annual damages are the best estimate of the 
average damages per year expected at this site; such estimates do not 
indicate that these damages will occur every year. Expected annual 
damages are those damages which are expected to occur without 
undertaking the mitigation measure. The effectiveness of the mitigation 
measure is an estimate of how much expected damages will be 
reduced by the mitigation measure under consideration. 

The expected annual avoided damages (i.e., the annual benefits) are 
the product of expected annual damages and the effectiveness of the 
mitigation measure. The expected annual avoided damages are thus 
the expected annual benefits of undertaking the mitigation measure. 

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Scenario 

Damages 

Building
Damages

Detailed Economic Assumpti-ons and--Equations 

Scenario damages (SCD) are the total damages per flood event. Thus, 
scenario damages are the sum of building damages (BD), contents 
damages (CD), displacement costs (DIS), lost business income (LBI), 
rental income losses (RENT), and the value of lost public/nonprofit 
services (VLS) per scenario (flood event). Scenario damages are 
calculated separately before and after the mitigation measure for each 
flood depth from -2 to 18 feet: 

SCD = BD + CD + DIS + LBI + RENT + VLS 

where: 
SCD is the total scenario (per event) damages; 
BD is the total building damage per scenario; 
CD is the total contents damage per scenario; 
DIS is the total displacement costs per scenario; 
LBI is the total lost business income per scenario; 
RENT is the total rental income losses per scenario; and 
VLS is the total value of lost public/nonprofit services 
per scenario. 

Building damages (BD) are estimated as the product of the modified 
depth damage function (MDDF), the floor area of the building (FA), and 
the replacement value of the building per square foot (BRV). Building 
damages are calculated separately before and after the mitigation 
measure for each flood depth from -2 to 18 feet: 

BD = (MDDF) (FA) (BRV) 

where: 

BD is the total amount of building damage per 
scenario; 

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MDDF is the modified depth damage function, the 
expected damage by flood depth expressed as a 
percentage of building replacement value; 
FA is the floor area of the building (in square feet); 
and 
BRV is the building replacement value (per square 
foot). 

Contents Contents damages (CD) are estimated as the product of the contents 

Damages depth-damage function (CDDF) and the total building contents 
replacement value (CRV). Contents damages are calculated separately 
before and after the mitigation measure for each flood depth from -2 to 
18 feet: 

CD = (CDDF) (CR19 

where: 

CD is the total contents damage; 

CDDF is the contents depth damage function, expressed 
as a percentage of contents replacement value for 
each flood depth; and 

CRV is the total building contents replacement value. 

Displacement Displacement costs (DIS) are the product of displacement days 

Costs necessary (DD), the displacement costs per square foot per day (DC), 
and the total area occupied by the owner agency or public or nonprofit 
agencies (TA). Displacement costs are calculated separately before 
and after the mitigation measure for each flood depth from -2 to 18 feet: 

DIS = (DD) (DC) (TA) 

where: 

DIS is the displacement costs per flood event; 

DD is the estimated number of displacement days 
necessary for each flood depth; 

DC is the displacement costs per square foot per day; 
and 

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Lost Business 
Income 

Rental Income 
Losses 

TA is the total area occupied by the owner agency or 
public/nonprofit agencies. 

Lost business income (LBI) is included if all or a portion of the building 
are rented to commercial businesses. Lost business income (LBI) is 
the product of the net income of commercial businesses per day (NICB) 
and the number of days of functional downtime (FDD). Lost business 
Income is calculated separately before and after the mitigation measure 
for each flood depth from -2 to 18 feet: 

LBI = (NICB) (FDD) 

where: 
LBI is the total business income lost; 
NICB is the net income of commercial businesses per 
day; and 
FDD is the number of days of functional downtime. 

Rental income losses (RENT) are included if all or a portion of the 
building are rented to private tenants. Inter- or intra-agency rents within 
the federal, state, or local governments are not counted because such 
payments are generally transfers; loss of such payments does not 
represent a true economic loss. Other private sector economic losses 
(such as lost wages) are not considered because they are assumed to 
be generally negligible for public/nonprofit buildings. 

Rental income losses (RENT) are; the product of displacement days 
necessary (DD) and the daily rental rate (DRR). Rental income losses 
are calculated separately before and after the mitigation measure for 
each flood depth from -2 to 18 feet: 

RENT = (DD) (DRR) 

where: 

RENT is the total rental income lost; 

DD is the number of displacement days necessary; 
and 

DRR is the daily rental rate. 

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Public/ For public/nonprofit sector buildings, the value of services lost (VLS) SNonprofit when the building becomes unusable during a flood must be included. 

Services Lost 

Expected Annual 
Damages 

Public/nonprofit services are valued using the Quasi-Willingness to Pay 
(QWTP) model. QWTP is a simple methodology that assumes that 
public/nonprofit services are worth what we pay to provide the services. 

VLS is the product of the total value of lost services per day (VOLS) 
and the number of days of functional downtime (FDD). The period of 
lost services depends on the agency's ability to find alternative quarters 
and to establish normal functions. This period may vary depending on 
the structure, size and function of the agency and the availability of 
suitable quarters after the flood. Note that the period of loss of agency 
function may be much shorter than the period of displacement 
necessary due to flood damage, because agencies will resume their 
functions in temporary quarters. The value of public/nonprofit services 
lost are calculated separately before and after the mitigation measure 
for each flood depth from -2 to 18 feet: 

VLS = (VOLS) (FDD) 

where: 
VLS is the value of lost agency services for a flood of a 
given depth; 
VOLS the total value of lost services per day; and 
FDD is the total number functional downtime days for a 
flood of a given depth. 

Expected annual damages (AD) are the product of scenario damages 
(SCD) and the expected annual number of floods of a given depth 
(EAE). Expected annual damages are calculated separately before and 
after the mitigation measure for each flood depth from -2 to 18 feet: 

AD = (SCD) (EAE) 

where: 

AD is the expected annual damages; 

SCD is the total scenario damages (as defined 
previously); and 

EAE is the expected annual number of floods of a given 
depth. 

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ExpectedAnnual 
Benefits 
Expected annual benefits (EAB) are the product of expected annual 
damages (ADB) before mitigation and the effectiveness of the mitigation 
measure (EFF). Expected annual benefits are calculated for each flood 
depth from -2 to 18 feet: 
EAB = (AD B) (EFF) 
where: 
EAB is the expected annual benefits; 
ADW is the expected annual damages before mitigation; 
and 
EFF is the effectiveness of the mitigation measure in 
reducing expected damage from a flood of a given 
depth. 
Equivalently, expected annual benefits (EAB) are the difference 
between expected annual damages before mitigation (AD") and 
expected annual damages after mitigation (ADA). Expected annual 
benefits are calculated for each flood depth from -2 to 18 feet: 
EAB = AD" -AD A 
where: 
EAB is the expected annual benefits; 
ADW is the expected annual damages before mitigation; 
and 
ADA is the expected annual damages after mitigation. 
Total Expected 
Annual Benefits 
The total expected annual benefits (AB) of a flood hazard mitigation 
project are the expected annual benefits (EAB) summed over the full 
range of damaging floods considered (e.g., -2 feet to 18 feet). 
AB 
max 
= E EAB 
RF=mln 
where: 
AB is the total expected annual benefits of a flood 
hazard mitigation project; 
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I 
RF 
min 
max 
EAB 
is the flood depth considered; 
is the minimum damaging flood considered (-2 feet 
in the Benefit-Cost Program); 
is the maximum flood considered (18 feet in the 
Benefit-Cost Program); and 
is the expected annual benefits from each flood 
depth being considered. 
Benefits The benefits (B) of a flood hazard mitigation project are the net present 
value of the total expected annual benefits (AB) over the useful lifetime 
of the hazard mitigation project (T) at an annual discount rate (I): 
B = AB 1i 
where: 
B 
AB 
T 
i 
is the benefits of a flood hazard mitigation project; 
is the expected annual benefits of the hazard mitigation 
project; 
is the useful lifetime of the hazard mitigation project; and 
is the annual discount rate. 
S 
Costs The total mitigation project costs (C) is the sum of the mitigation project 
costs (PC), the present value of the annual maintenance costs 
(PVAMC), and the relocation costs for the mitigation project (RC). 
C = PC + PVAMC + RC 
where: 
C 
PC 
is the total mitigation project costs; 
is the mitigation project costs including 
construction and other costs but excluding 
relocation costs; 

I 

PVAMC is the net present value of the annual maintenance 
costs of the mitigation project; and 

S 

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__VERSIOECONOMI ,N1.0 ./29/94 gUAI

2 I

A-% %U 

RC is the relocation costs necessary for construction 
of the mitigation project. 

Benefit-Cost The benefit-cost ratio (BCR) is the benefits of the mitigation project (B),
Ratio divided by the costs of the mitigation project (C). 

BCR = (B)I(C) 

where: 

BCR is the Benefit-Cost ratio of the hazard mitigation 
project; 

B is the benefits of the hazard mitigation project; and 

C is the total mitigation project costs. 

Present Value The present value criterion (PVC) is the benefits of the mitigationCriterion project (B), minus the costs of the mitigation project (C). 

PVC = B-C 

where: 

PVC is the present value criterion of the hazard 
mitigation project; 

B is the benefits of the hazard mitigation project; and 

C is the total mitigation project costs.

I 

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Benefit-Cost 

Analysis 

Cost-Benefit 
Analysis 

Cost-
Effectiveness 
Analysis 

12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS 

12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS 

Technical Economic Terms 

Benefit-cost analysis provides estimates of the "benefits" and "costs" of 
a proposed project or change. The term "benefit-cost analysis" is used 
to denote economic analyses that apply either the maximum present 

value criterion or the benefit-cost ratio criterion to evaluate prospective 

actions. Both costs and benefits are discounted to their net present 

value. The maximum present value criterion subtracts costs from 

benefits to determine if benefits exceed costs. Benefit/cost ratios 

provide an alternative evaluation: prospective actions in which benefits 

exceed costs have benefit-cost ratios above one. The logic of benefit-

cost analysis requires that benefit-cost ratios, and/or the present value 

criterion, be compared across competing alternatives. 

Cost-benefit analysis has identical economic assumptions to benefit-
cost analysis and differs only in the nomenclature used to describe the 
analysis. Subtle differences in meaning between benefit-cost and cost-
benefit analysis have been discussed (Hurter et al., 1982). These 
authors prefer the term benefit-cost for three reasons: 

1 ) determining benefits is often the most difficult aspect of the 
analysis; if costs are placed first, the emphasis is wrong; 
2) when ratios are used to compare projects, the ratio used is 
benefit-cost, not cost-benefit; and 

3) placing the word "costs" first seems to suggest a negative 
attitude toward projects. It should be noted, however, that 
economic concepts, particularly as reflected in benefit-cost 
analysis, are completely neutral with respect to the undertaking 

of projects. 

Cost-effectiveness analysis identifies the least-cost way to achieve a 
stated objective; it is strictly a comparison among means to a given end 
(Andrews, 1982). Thus, cost effectiveness is the ability to achieve a 
given benefit at a minimum cost. In cost effectiveness analysis. the 
merits of the objective itself are not evaluated ineconomic terms. This 

approach is typically used to select methods of achieving specific 

environmental standards. 

The Stafford Act uses cost-effectiveness when it means that benefits 

exceed costs in 404, Hazard Mitigation, and 406, Public Assistance. 

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Economic 
Efficiency 

Economic Impact 
Assessment 

Informal Benefit-
Cost Analysis 

Risk-Benefit 
Analysis 

Economic efficiency is attained when the economy is functioning in a 
way that maximizes the value of society's consumption over time (Ward 
and Deren, 1991). Economic efficiency may also be viewed as the 
contribution to overall social welfare (Leman, 1989). It is generally 
accepted that a benefit-cost ratio above one indicates an improvement 
in economic efficiency. Benefit.cost analysis however does not indicate 
whether the project is the "most efficient" allocation of scarce resources 
for two reasons. First, benefit-cost analysis is an average rather than a 
marginal concept. The ratio indicates the relationship between benefits 
and costs for a given project size. Economic efficiency, however, 
requires that a project be sized where marginal benefits equal marginal 
costs, which maximizes the total net benefits. Second, the typical 
project benefit-cost analysis does not survey the complete array of 
spending alternatives for all public projects/programs unrelated to the 
project under analysis. Economic efficiency under a budget constraint 
would require that the marginal benefits for all public spending 
alternatives be equal. 

Economic impact assessment is both simpler and broader than either 
benefit-cost analysis or cost-effectiveness analysis in that it does not 
necessarily require aggregation or even categorization of effects as 
costs or benefits. It requires only the projection of economic effects of 
proposed actions and the listing of these for consideration. Impact 
assessment is broader than benefit-cost or cost-effectiveness analysis 
because it includes identification of all economic impacts: the changes 
in total (direct, indirect and induced) regional employment and income 
created by the proposed project. The inclusion of indirect and induced 
regional economic benefits and costs in the formal benefit-cost analysis 
is not generally accepted by the economics profession. Many 
economists maintain that such indirect and induced economic impacts 
represent a change in the distribution of economic activity and should 
not be confused with true gains in economic efficiency. 

Informal benefit-cost analysis embraces an indefinite range of 
procedures for the general identification and balancing of desirable and 
undesirable effects of proposed actions on society. Thus, informal 
benefit-cost analysis simply approximates pure common sense, and it 
should not be compared with formal economic analyses of prospective 
projects. 

Risk-benefit analysis compares the economic benefits of a proposed 
project with the environmental and/or health-safety risks that are also 
created by the project. Ideally, the environmental and/or health-safety 
risks should be quantified in economic terms which in many cases is 
almost, if not impossible. 

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References 

Andrews, R.N.L. (1982) Benefit-Cost Analysis as Regulatory Reform, in Cost-Benefit 
Analysis and Environmental Regulations: Politics. Ethics and Methods, D. Swartzman, R.A. 
Liroff, and K.G. Croke (editors), The Conservation Foundation, Washington, D.C. 

Hurter, A.P. Jr., G.S. Tolley and R.G. Fabian (1982) Benefit-Cost Analysis and the Common 
Sense of Environmental Policy, in Cost-Benefit Analysis and Environmental Regulations: 
Politics. Ethics and Methods, D. Swartzman, R.A. Liroff, and K.G. Croke (editors), The 
Conservation Foundation, Washington, D.C. 

Leman, C.K. (1989) The Forgotten Fundamental: Successes and Excesses of Direct 
Government, in Beyond Privatization: The Tools of Government Action, L.M. Salamon (editor), 
The Urban Institute Press, Washington, D.C. 

Ward, W.A. and B.J. Deren (1991) The Economics of Project Analysis, A Practitioner's 
Guide. Economic Development Institute of the World Bank. 

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