Floodproofing 

Non-Residential Buildings

FEMA P-936 / July 2013

FLOODPROOFING NON-RESIDENTIAL BUILDINGS i

Floodproofing 

Non-Residential Buildings

FEMA P-936 / July 2013
ii FLOODPROOFING NON-RESIDENTIAL BUILDINGS

All illustrations in this document were created by FEMA or a FEMA contractor unless otherwise noted.

All photographs in this document are public domain or taken by FEMA or a FEMA contractor, 

unless otherwise noted.

Questions or comments on this manual are welcome and should be addressed to 

FEMA Building Science (http://www.fema.gov/building-science) through the 

FEMA Building Science Helpline at FEMA-BuildingscienceHelp@fema.dhs.gov or call (866) 927-2104.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS iii

Acknowledgements

Acknowledgements

Authors and Key Contributors

David K. Low, P.E., DK Low and Associates

Amit Mahadevia, CFM, URS Group, Inc.

Manuel Perotin, P.E., CFM

Adam Reeder, P.E., CFM, Atkins Global

Adrienne Sheldon, P.E., CFM, URS Group, Inc.

Lauren Seelbach, E.I.T., CFM, URS Group, Inc.

Jennifer Sparenberg, CFM, URS Group, Inc.

John Squerciati, P.E., CFM, Dewberry

Reviewers and Contributors

Gene Barr, CFM, CH2M Hill, Inc.

Randy Behm, P.E., CFM, USACE, Omaha District

William Coulbourne, P.E., URS Group, Inc.

Jhun de la Cruz, FEMA Headquarters

Bret Gates, FEMA Headquarters

Michael Gease, FEMA Region VIII

Michael Grote, Gulf Coast Community Design Studio, Mississippi State University

Paul Gugenheim, Delta Structural Technologies

John Ingargiola, EI, CFM, CBO, FEMA Headquarters

Dick Jones, FEMA Region IV

Vasso Koumoudis, CFM, URS Group, Inc.

Stephen O’Leary, AIA, CFM, USACE, Huntington District
iv FLOODPROOFING NON-RESIDENTIAL BUILDINGS

A ACKNOWLEDGEMENTS

John “Bud” Plisich, FEMA Region IV

Rebecca Quinn, CFM, RCQuinn Consulting

Jody Springer, FEMA Headquarters

Alan Springett, FEMA Region II

Amy Tarce, AICP Assoc., AIA, National Capital Planning Commission

Paul Tertell, P.E., FEMA Headquarters (Retired)

Zachary Usher, FEMA Headquarters

Steven Van Dyke, FEMA Headquarters

Ronald Wanhanen, FEMA Region VI

Gregory Wilson, CFM, FEMA Headquarters

Wallace Wilson, P.E., CFM, URS Group, Inc.

Technical Editing, Layout, and Illustration

Diana Burke, ELS, URS Group, Inc.

Young Cho, URS Group, Inc.

Julie Liptak, Stantec

Lee-Ann Lyons, URS Group, Inc.

Ivy Porpotage, URS Group, Inc.

Billy Ruppert, URS Group, Inc.

Amy Siegel, URS Group, Inc. 

Claude Tybaert, URS Group, Inc.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS v

Table of Contents

1 Introduction ......................................................................................................... 1-1

1.1 Objective and Scope...................................................................................................................1-1

1.2 Definitions and Key Concepts ....................................................................................................1-2

1.3 Limitations of Floodproofing and Precautionary Measures..........................................................1-3

1.4 Assumptions...............................................................................................................................1-4

1.5 Evaluation of Floodproofing Options .........................................................................................1-4

1.6 Icons...........................................................................................................................................1-7

1.7 Organization...............................................................................................................................1-8

2 Design Considerations in Floodproofing .............................................................. 2-1

2.1 Regulatory Requirements, Building Codes, Design Standards, and Guidance Documents .........2-2

2.1.1 National Flood Insurance Program................................................................................. 2-2

2.1.2 Floodproofing Certificate for Non-Residential Buildings in Zone A............................... 2-6

2.1.3 Floodproofing Historic Buildings .................................................................................. 2-7

2.1.4 National Policies for Federal Actions in Floodplains....................................................... 2-8

2.1.5 Local Floodplain Management Regulations.................................................................. 2-10

2.1.6 Model Building Codes ................................................................................................. 2-10

2.1.7 Consensus Standards.................................................................................................... 2-13

2.1.8 Additional Federal Guidance Documents..................................................................... 2-15

2.2 Design Loads and Site Characteristics.......................................................................................2-16

2.2.1 Identifying the Base Flood Elevation ............................................................................ 2-16

2.2.2 Design Flood Elevation ................................................................................................ 2-17

2.2.3 Determining the Flood Depth...................................................................................... 2-18

2.2.4 Determining Hydrostatic Loads ................................................................................... 2-20

2.2.5 Determining Hydrodynamic Forces ............................................................................. 2-25
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2.2.6 Determining Impact Loads .......................................................................................... 2-28

2.2.7 Interior Drain Systems ................................................................................................. 2-28

2.2.8 Determining Site Drainage for Floodwalls and Levees.................................................. 2-30

2.2.9 Understanding the All-Hazards Approach .................................................................... 2-33

2.3 Other Flood Characteristics .....................................................................................................2-34

2.3.1 Duration of Flooding ................................................................................................... 2-34

2.3.2 Rate of Floodwater Rise and Fall .................................................................................. 2-35

2.3.3 Flood Frequency........................................................................................................... 2-35

2.3.4 Future Conditions........................................................................................................ 2-36

2.4 Site Factors ...............................................................................................................................2-36

2.4.1 Flood Hazard Boundaries............................................................................................. 2-36

2.4.2 Erosion......................................................................................................................... 2-37

2.4.3 Geotechnical Considerations........................................................................................ 2-38

2.5 Functional, Operational, and Economic Factors ......................................................................2-38

2.5.1 Functional Use Requirements of the Building .............................................................. 2-39

2.5.2 Occupant Safety........................................................................................................... 2-39

2.5.3 Flood Warning Time.................................................................................................... 2-40

2.5.4 Flood Emergency Operations Plan ............................................................................... 2-41

2.5.5 Inspection and Maintenance Plan................................................................................. 2-42

2.5.6 Economic Factors ........................................................................................................ 2-43

2.6 Building Vulnerability Assessments...........................................................................................2-43

2.6.1 All-Hazards Vulnerability Assessment........................................................................... 2-44

2.6.2 Structural Condition Assessment ................................................................................. 2-44

2.6.3 Vulnerability Assessments for Electrical and Mechanical Utilities and Systems ............ 2-48

2.6.3.1 Utilities General ........................................................................................... 2-49

2.6.3.2 Electrical Utilities ......................................................................................... 2-49

2.6.3.3 Mechanical Utilities...................................................................................... 2-50

2.6.3.4 Electrical Systems ......................................................................................... 2-50

2.6.3.5 Mechanical Systems...................................................................................... 2-51

3 Dry Floodproofing Measures .............................................................................. 3-1

3.1 Design Considerations for Dry Floodproofing Project ................................................................3-2

3.1.1 Flood Warning Time ..................................................................................................... 3-2
FLOODPROOFING NON-RESIDENTIAL BUILDINGS vii

TABLE OF CONTENTS

3.1.2 Site and Building Evaluation .......................................................................................... 3-3

3.1.3 Building Standards and Codes........................................................................................ 3-3

3.1.4 Verification and Testing of Systems................................................................................. 3-5

3.2 Continuous Impermeable Walls..................................................................................................3-5

3.2.1 Openings ....................................................................................................................... 3-6

3.2.2 Wall Systems .................................................................................................................. 3-7

3.3 Flood Resistance of Interior Core Areas ....................................................................................3-10

3.4 Shields for Openings.................................................................................................................3-11

3.4.1 Doors .......................................................................................................................... 3-12

3.4.2 Windows...................................................................................................................... 3-12

3.4.3 Utility Connections...................................................................................................... 3-13

3.5 Flood Shields for Openings in Exterior Walls............................................................................3-14

3.5.1 Types of Flood Shields.................................................................................................. 3-14

3.5.2 Flood Shield Materials.................................................................................................. 3-18

3.5.3 Gaskets and Seals ......................................................................................................... 3-18

3.5.4 Plate-Style Flood Shields .............................................................................................. 3-19

3.5.5 Case Study: Retrofit Dry Floodproofed Building, New Castle, DE............................... 3-22

3.6 Backflow Valves ........................................................................................................................3-24

3.7 Internal Drainage .....................................................................................................................3-27

3.7.1 Sump Pumps................................................................................................................ 3-27

3.7.2 Pressure Relief Systems................................................................................................. 3-32

3.8 Flood Emergency Operations Plan and Inspection and Maintenance Plan ...............................3-33

3.9 Dry Floodproofing in New Construction .................................................................................3-34

3.10 Case Study: University of Texas Perimeter Wall and Dry Floodproofing Project .......................3-38

4 Other Flood Protection Measures......................................................................... 4-1

4.1 Floodwalls and Levees.................................................................................................................4-1

4.1.1 Floodwalls...................................................................................................................... 4-1

4.1.1.1 Types of Floodwalls ........................................................................................ 4-2

4.1.1.1.1 Gravity Floodwalls .......................................................................................... 4-3

4.1.1.1.2 Cantilever Floodwalls ...................................................................... 4-4
viii FLOODPROOFING NON-RESIDENTIAL BUILDINGS

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4.1.1.1.3 Buttress and Counterfort Floodwalls................................................ 4-5

4.1.1.2 Building and Site Considerations in Floodwall Design ................................... 4-5

4.1.1.3 Floodwall Design Process................................................................................ 4-8

4.1.2 Levees........................................................................................................................... 4-10

4.1.2.1 Building and Site Considerations in Levee Design........................................ 4-10

4.1.2.2. Basic Levee Design Parameters...................................................................... 4-11

4.1.2.3 Levee Design Process .................................................................................... 4-13

4.2 Wet Floodproofing Measures ....................................................................................................4-14

4.2.1 Flood Damage-Resistant Materials ............................................................................... 4-14

4.2.2 Protection of Vulnerable Equipment and Contents ..................................................... 4-16

4.2.3 Flood Openings for Equalization ................................................................................. 4-17

4.3 Floodproofing Electrical and Mechanical Utilities and Systems ................................................4-18

4.3.1 Electrical Utilities and Systems..................................................................................... 4-21

4.3.2 Mechanical Utilities and Systems.................................................................................. 4-23

4.4 Emergency Measures.................................................................................................................4-24

4.4.1 Sandbags...................................................................................................................... 4-24

4.4.2 Temporary Flood Barriers............................................................................................. 4-25

4.4.3 Flood Wrapping Systems.............................................................................................. 4-26

4.5 Combination of Floodproofing Measures..................................................................................4-29

4.5.1 Wet and Dry Floodproofing Techniques....................................................................... 4-30

4.5.2 Other Combinations.................................................................................................... 4-32

4.5.3 Case Study: Application to Historic Buildings.............................................................. 4-32

Appendix A: FEMA Assistance

Appendix B: Understanding the FEMA Benefit-Cost Process

Appendix C: Checklist for Vulnerability of Flood-Prone Sites and Buildings

Appendix D: References

Appendix E: Resources

Appendix F: FEMA Region Contact Information
FLOODPROOFING NON-RESIDENTIAL BUILDINGS ix

TABLE OF CONTENTS

Figures

Figure 2-1 Satisfying NFIP requirements through building codes.................................................... 2-2

Figure 2-2 FEMA’s 8-step decision-making process for compliance with Executive 

Order (EO) 11998 and 44 CFR Part 9........................................................................... 2-9

Figure 2-3 Building and stream location on a FIRM .................................................................... 2-17

Figure 2-4 Flood depth.................................................................................................................. 2-20

Figure 2-5 Equal (A) and unequal (B) hydrostatic pressures applied to the exterior 

elements of a building; (B) shows the building protected by dry 

floodproofing methods applied..................................................................................... 2-21

Figure 2-6 Hydrostatic forces acting on a foundation wall............................................................. 2-24

Figure 2-7 Hydrodynamic and impact loads.................................................................................. 2-26

Figure 2-8 Frontal impact from debris........................................................................................... 2-28

Figure 2-9 Typical interior drain systems....................................................................................... 2-29

Figure 2-10 Rectangular area enclosed by a floodwall or levee.......................................................... 2-30

Figure 2-11 Rectangular area partially enclosed by a floodwall or levee............................................ 2-32

Figure 2-12 Relationship between flood recurrence intervals and the probability of an 

event occurring within a given period........................................................................... 2-36

Figure 2-13 Basic building components exposed to flood loads ....................................................... 2-45

Figure 2-14 Significant differential settlement in the foundation causing slab failure....................... 2-47

Figure 2-15 Typical systems in buildings ......................................................................................... 2-49

Figure 3-1 Filled window opening................................................................................................... 3-7

Figure 3-2 Application of a waterproof membrane on the exterior (positive side) of 

a wall (left) and fiber-reinforced polymer wrap applied to the interior 

(negative side) of a wall (right) ....................................................................................... 3-8

Figure 3-3 Decision process for selecting type of sealant.................................................................. 3-9

Figure 3-4 Interior drain in a dry floodproofed retail building....................................................... 3-10

Figure 3-5 Watertight door used to protect mechanical rooms subject to flooding......................... 3-11

Figure 3-6 Equipment room with watertight door......................................................................... 3-12

Figure 3-7 Door opening protected from low-level flooding by a flood shield................................ 3-14

Figure 3-8 Window protected from low-level flooding by a flood shield and wall sealant............... 3-15

Figure 3-9 Aluminum flood shield used for flooding less than 3 feet deep ..................................... 3-15

Figure 3-10 Types of flood shields ................................................................................................... 3-17
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Figure 3-11 Selection/design of plate-style flood shields ................................................................. 3-19

Figure 3-12 Front of retrofit dry floodproofed building where drop-in flood shields 

protect doors ............................................................................................................... 3-23

Figure 3-13 Rear of retrofit dry floodproofed building with permanently installed flood shield ....... 3-23

Figure 3-14 Backflow valve ............................................................................................................. 3-24

Figure 3-15 Floor drain with a backflow valve with a ball float check valve...................................... 3-25

Figure 3-16 Backflow valve selection process ................................................................................... 3-25

Figure 3-17 Typical sump detail ...................................................................................................... 3-27

Figure 3-18 Sump pump design process .......................................................................................... 3-30

Figure 3-19 A deteriorated flood shield gasket that must be replaced for the shield to 

seal and function properly ............................................................................................ 3-34

Figure 3-20 Dry floodproofed fuel pump room adjacent to generator fuel tank vault ..................... 3-35

Figure 3-21 Door to a dry floodproofed generator fuel tank vault servicing multiple 

generators in high-rise building ................................................................................... 3-36

Figure 3-22 Cross section of the test mock-up used for the SERRI tests of a 

substantially impermeable CMU wall system .............................................................. 3-37

Figure 3-23 Flood doors incorporated into the existing building façade .......................................... 3-39

Figure 3-24 Ross Sterling Avenue was raised to protect the MSB to the level of the base flood ....... 3-40

Figure 3-25 Three sets of stairs that provide building egress during the design flood 

event, but still allow normal use of the building .......................................................... 3-40

Figure 4-1 Typical masonry floodwall with engineered closures, which protected the 

Oak Grove Lutheran School in Fargo, ND, from flooding in 2001 ................................ 4-2

Figure 4-2 Gravity, cantilever, buttress, and counterfort floodwalls ................................................. 4-3

Figure 4-3 Concrete cantilever floodwall reinforcement .................................................................. 4-4

Figure 4-4 Stability of a cantilever floodwall ................................................................................... 4-5

Figure 4-5 Floodwall successfully safeguards Lourdes Hospital from Tropical Storm 

Lee flooding (source: FloodBreak).................................................................................. 4-7

Figure 4-6 Aerial view showing effective protection of Lourdes Hospital from flooding 

as a result of Tropical Storm Lee..................................................................................... 4-7

Figure 4-7 Floodwaters surround Columbus Regional Hospital in 2008 ......................................... 4-8

Figure 4-8 Columbus Regional Hospital schematic of floodwall plan .............................................. 4-8

Figure 4-9 Floodwall design process ............................................................................................... 4-9

Figure 4-10 Levee design parameters for a typical non-residential levee .......................................... 4-12
FLOODPROOFING NON-RESIDENTIAL BUILDINGS xi

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Figure 4-11 Basic levee design process ............................................................................................. 4-13

Figure 4-12 The Duval Beach Club after wet floodproofing retrofits................................................ 4-16

Figure 4-13 Typical openings in walls of enclosures......................................................................... 4-17

Figure 4-14 Non-residential structure retrofitted with flood openings following 

Hurricane Katrina (New Orleans, LA, 2008)................................................................ 4-18

Figure 4-15 Equipment in an electrical control panel that was mostly destroyed 

when approximately two-thirds of the height of panel was inundated by 

floodwaters (Columbus Junction, IA, 2008)................................................................. 4-19

Figure 4-16 Main electrical service switchboard inundated by floodwaters that rose to 

the red mark on the doorframe (Cedar Rapids, IA, 2008) ............................................ 4-19

Figure 4-17 Undamaged secondary switchgear located at the University of Texas 

Medical Branch. The switchgear had been constructed on an upper floor 

that remained above flood levels. The switchgear was not damaged during 

Hurricane Ike (Galveston, TX, 2008)........................................................................... 4-20

Figure 4-18 Emergency generator elevated above flood levels at the University of Texas 

Medical Branch, Hurricane Ike (Galveston, TX, 2008) ................................................ 4-20

Figure 4-19 Pad-mounted transformer and 15 kilovolt switchgear, both vulnerable to 

damage when inundated with floodwaters (Cedar Rapids, IA, 2008)............................ 4-21

Figure 4-20 Electrical cables and an example of an electrical installation using cables...................... 4-22

Figure 4-21 Example of installation using electrical conduits and insulated conductors .................. 4-22

Figure 4-22 Techniques for proper placement of sandbags .............................................................. 4-25

Figure 4-23 Three-foot-high water-filled temporary barrier protecting a structure in Tunica, MS .... 4-26

Figure 4-24 Gravel-filled containers that formed a barrier to protect the University of 

Iowa (2008) ................................................................................................................. 4-26

Figure 4-25 Plan view of wall section showing the deflection of a wrap at a doorway....................... 4-27

Figure 4-26 Plastic sheeting attached to a brick-faced wall to seal it from water intrusion................ 4-27

Figure 4-27 Decision process for the selection and design of a flood wrapping system..................... 4-28

Figure 4-28 Commercial structure in Darlington, WI mitigated using a combination of 

wet and dry floodproofing techniques .......................................................................... 4-30

Figure 4-29 A non-critical break room, originally located on an upper floor was 

relocated to create space for the critical control room ................................................... 4-31

Figure 4-30 Flooding of businesses in historic downtown Darlington, WI, Midwest Flood (1993).. 4-32

Figure 4-31 Businesses along Main Street in Darlington, WI, mitigated with an 

elevated interior first floor ............................................................................................ 4-33
xii FLOODPROOFING NON-RESIDENTIAL BUILDINGS

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Figure 4-32 Hardware store on Main Street in Darlington, WI, mitigated with a raised 

interior first floor and flood damage-resistant materials ................................................ 4-33

Figure 4-33 Hardware store on Main Street in Darlington, WI, showing ramp to 

elevated interior first floor for ADA compliance........................................................... 4-33

Tables

Table 1-1 Consideration of Floodproofing Measures for Non-Residential Buildings ...................... 1-5

Table 2-1 NFIP General Requirements for Dry Floodproofing ...................................................... 2-5

Table 2-2 NFIP General Requirements for Wet Floodproofing ..................................................... 2-6

Table 2-3 Key Code Requirements for Flood-Resistant Design from IBC 2012 ........................... 2-12

Table 2-4 ASCE 24 Requirements and Limitations for Dry Floodproofing .................................. 2-14

Table 2-5 ASCE 24 Requirements and Limitations for Wet Floodproofing .................................. 2-15

Table 2-6 Drag Coefficients for Ratios of Width to Depth (w/H) and Width to Height (w/h)..... 2-28

Table 2-7 FEMA Resources on Design Guidance......................................................................... 2-34

Table 3-1 Advantages and Disadvantages of Dry Floodproofing Retrofits Compared 

to Other Flood Mitigation Retrofit Measures ................................................................. 3-2

Table 3-2 ASCE 24 Structure Categories and Minimum Floodproofing Elevation in Zone A ........ 3-4

Table 3-3 Comparison of Types of Pump Activation Switches...................................................... 3-29

Table 4-1 Class Descriptions of Flood Damage-Resistant Materials.............................................. 4-15

Equations

Equation 2-1 Flood depth.................................................................................................................. 2-19

Equation 2-2 Lateral hydrostatic forces.............................................................................................. 2-22

Equation 2-3 Submerged soil and water forces................................................................................... 2-23

Equation 2-4 Buoyancy forces ........................................................................................................... 2-25

Equation 2-5 Hydrodynamic load ..................................................................................................... 2-27

Equation 2-6 Runoff quantity in an enclosed area.............................................................................. 2-31

Equation 2-7 Runoff quantitiy from higher ground into a partially enclosed area .............................. 2-32

Equation 2-8 Minimum discharge for pump installation ................................................................... 2-33
FLOODPROOFING NON-RESIDENTIAL BUILDINGS xiii

Acronyms and 

Abbreviations

A

AA Aluminum Association 

ACI American Concrete Institute 

ADA Americans with Disabilities Act

AF&PA American Forest & Paper Association 

AHPS Advanced Hydrology Prediction Service 

AISC American Institute of Steel Construction 

ANSI American National Standards Institute 

ASCE American Society of Civil Engineers 

ASD Allowable Stress Design 

ASFPM Association of State Floodplain Managers 

ASTM ASTM International 

AWPA American Wood Protection Association 

B

BCA benefit-cost analysis 

BCR benefit-cost ratio 

BFE base flood elevation

C

CFR Code of Federal Regulations 

CMU concrete masonry unit 

D

DDF depth-damage function 

DFA Damage Frequency Assessment 

DFE design flood elevation 
xiv FLOODPROOFING NON-RESIDENTIAL BUILDINGS

ACRONYMS AND ABBREVIATIONS

E

EO Executive Order 

F

FEMA Federal Emergency Management Agency 

FIRM Flood Insurance Rate Map 

FIS Flood insurance Study 

FMA Flood Mitigation Assistance 

ft foot (feet)

ft/sec feet per second

G

gph gallons per hour 

gpm gallons per minute 

H

H&H hydrologic and hydraulic 

HMA Hazard Mitigation Assistance 

HMGP Hazard Mitigation Grant Program

HVAC heating, ventilation, and air-conditioning 

I

IBC International Building Code 

I-Codes International Code Series 

ICC Increased Cost of Compliance 

ICF Insulated Concrete Form 

IEBC International Existing Building Code 

in./hr inches per hour

IT information technology

L

lb/ft2 pounds per square foot

lb/ft3 pounds per cubic foot
FLOODPROOFING NON-RESIDENTIAL BUILDINGS xv

ACRONYMS AND ABBREVIATIONS

lb/lf pounds per linear foot

LRFD Load Resistance Factored Design

M

MEP mechanical, electrical, and plumbing 

MSB Medical School Building 

N

NFIP National Flood Insurance Program 

NFPA National Fire Protection Association

NWS National Weather Service 

P

PA Public Assistance 

PDM Program Pre-Disaster Mitigation Program 

R

Risk MAP Risk Mapping, Assessment, and Planning

S

SERRI Southeast Region Research Initiative

SFHA Special Flood Hazard Area 

SIP Structural Insulated Panels 

T

TMS The Masonry Society 

U

UL Underwriters Laboratories 

USACE U.S. Army Corps of Engineers 

U.S.C. United States Code 

FLOODPROOFING NON-RESIDENTIAL BUILDINGS 1-1

Introduction

Flooding is the most common natural hazard in the United States and results in more fatalities and higher 

losses on average than any other natural hazard. Since 2001, the average annual flood losses in the 

United States were more than $10.4 billion, and from 1978 to mid-2012, the National Flood Insurance 

Program (NFIP) paid more than $41.3 billion in flood insurance claims. 

Flood hazard mitigation can be achieved in several ways and is often different for buildings that are used for 

non-residential purposes such as business or industry, as compared to residential buildings such as homes and 

apartments. To that end, in 1986, the Federal Emergency Management Agency (FEMA) published FEMA 

102, Floodproofing for Non-Residential Structures (FEMA 1986). The publication provided guidance to 

local officials, building owners, designers, contractors and other individuals or organizations interested in 

the design and implementation of floodproofing retrofits in non-residential structures. The guidance in 

FEMA 102 covers a broad range of floodproofing techniques that can be used in new and existing nonresidential buildings to reduce or eliminate the potential for damage from flooding.

FEMA 102 is currently one of only a few documents in the FEMA Library that provides design professionals 

and community officials with guidance on floodproofing non-residential buildings. However, since its publication in 1986, floodproofing techniques and technology have evolved such that updated guidance on the 

subject is needed. 

This document, FEMA P-936, Floodproofing Non-Residential Buildings, provides current guidance on floodproofing retrofits for non-residential buildings. It is similar to FEMA 102 but has a slightly different objective, 

which is described in the following section. 

1.1 Objective and Scope

The primary objective of this publication is to provide guidance on floodproofing existing non-residential 

buildings in riverine areas and coastal areas that are not subject to wave action. Floodproofing will be most 

successful in areas subject to relatively shallow flood depths. The floodproofing concepts in this document may 

be applicable to:

■ Core areas of critical facilities

■ Buildings subject to frequent, low-level flooding for a level of protection lower than the base flood 

elevation (BFE)

■ New construction

Additionally, a portion of the document describes dry floodproofing specific to new construction. 
1-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

1 INTRODUCTION

The publication focuses primarily on dry floodproofing but provides an overview of other retrofit methods that 

can be used in conjunction with or independent of dry floodproofing, including:

■ Wet floodproofing

■ Floodwalls

■ Levees

■ Protection of utilities

■ Emergency floodproofing measures

The publication is intended to assist local government officials, engineers, architects, and property owners 

involved in the planning and implementation of floodproofing retrofits. Retrofits may be proposed voluntarily 

by the owner to reduce damage or may be necessary to meet building codes or floodplain management regulations. See Chapter 2 for information on floodplain management regulations related to the NFIP.

The following topics are not covered in detail:

■ Residential construction, including large apartment and condominium complexes with multiple 

buildings, retirement homes, and nursing homes

■ Operational considerations of floodproofing critical facilities

■ Elevation

■ Relocation

■ Wave loads and Coastal A Zones

Building location, size, construction, function, and historic preservation factors dictate which floodproofing 

measure or measures will provide the most protection. The more complex the building, the more complex it is 

to protect. Combining methods of floodproofing is sometimes the best way to provide maximum protection 

(see Section 4.5).

1.2 Definitions and Key Concepts

Floodproofing is defined as any combination of structural or nonstructural adjustments, changes, or actions 

that reduce or eliminate flood damage to a building, contents, and attendant utilities and equipment (44 

Code of Federal Regulations [CFR] §59.1 and American Society of Civil Engineers [ASCE] 24, Flood Resistant 

Design and Construction [2005]). Floodproofing can prevent damage to existing buildings and can be used to 

meet compliance requirements for new construction of non-residential buildings. 

The concepts of the floodproofing measures used in this manual are defined as follows:

■ Dry floodproofing. A combination of measures that results in a structure, including the attendant 

utilities and equipment, being watertight with all elements substantially impermeable to the entrance 

of floodwater and with structural components having the capacity to resist flood loads. 

■ Wet floodproofing. The use of flood-damage-resistant materials and construction techniques to 

minimize flood damage to areas below the flood protection level of a structure, which is intentionally 

allowed to flood. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 1-3

INTRODUCTION 1

■ Floodwall. Constructed barrier of flood-damage-resistant materials to keep water away from or out 

of a specified area. Floodwalls surround a building or area and are off-set from the exterior walls of 

the building.

■ Levee. Manmade barrier, usually an earthen embankment, designed and constructed in accordance 

with sound engineering practices to contain, control, or divert the flow of water so as to provide 

protection rom temporary flooding.

1.3 Limitations of Floodproofing and Precautionary Measures

The limitations of floodproofing and precautionary measures to consider when floodproofing include:

■ Residual risk. Residual risk is the remaining exposure to loss after all other known risks have been 

eliminated or minimized. Although residual financial risk can be minimized by purchasing flood 

insurance, building owners/managers with property in flood-prone areas should be aware that all 

risk cannot be eliminated by implementing physical measures such as floodproofing. The level of 

protection that is selected should be consistent 

with the ability to absorb the impacts of the 

residual risk. ASCE 24 and many floodplain 

management regulations incorporate 

freeboard to reduce the risk. However, the 

designer and building owner should be 

aware that floodwater levels can exceed even 

elevations that include freeboard and should 

therefore determine methods of addressing 

the residual risk, including:

■ Flood damage potential. Floodproofing does not eliminate the potential for all flood damage. For example, wet floodproofing can reduce the load on structural systems, but extended 

inundation may still compromise structural materials. 

■ Performance of building above floodproofing design level. The areas above the protection 

levels of both dry and wet floodproofing are still at risk of damage from higher-than-expected 

floodwater levels, contamination, toxic materials near or inside the building, and mold from 

higher-than-normal humidity. 

Terminology

n Passive/active measures. Floodproofing measures are either passive or active depending on whether they require human intervention. Passive measures do not require human intervention and are 

recommended whenever possible. Active (or emergency) measures require human intervention and 

are effective only if there is enough warning time to mobilize the labor and equipment necessary to 

implement them and to safely evacuate. 

n Substantially impermeable. According to the U.S. Army Corps of Engineers (USACE), a wall is considered substantially impermeable if it limits water accumulation to 4 inches in a 24 hour period. In 

addition, sump pumps are required to control any seepage and flood-resistant materials must be used 

in all areas where sepage is likely to occur. This standard is the minimum requirement; lower seepage 

rates are possible and strongly encouraged by FEMA, particularly in new construction (USACE 1995).

Terminology

Freeboard is any additional height above 

the BFE used as a measure of safety in setting the minimum elevation of a building or 

floodproofing measure applied to a building.
1-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

1 INTRODUCTION

■ Space below the floodproofing design level. Floodproofing retrofits are implemented to prevent 

damage to existing buildings and are not intended to create usable space below the flood protection 

level. 

■ Occupation of floodproofed buildings. Floodproofed buildings are not meant to be occupied 

during a flood. Flood warning time should be adequate and evacuation plans should be developed 

to ensure that occupants are not stranded in the building during a flood. Dry floodproofing actually 

increases the risk to occupants if floodwaters rise higher than the floodproofing design level because 

severe structural damage can occur. Further, the interior of the building will likely be subject to 

inundation, which may occur rapidly.

1.4 Assumptions

The guidance on floodproofing existing buildings in this publication is based on the following assumptions:

■ The building does not have any unresolvable issues related to strength or materials that preclude dry 

floodproofing.

■ Flood characteristics (e.g., depth, duration, velocity) on the building site are well defined and are 

reasonably predictable.

■ Dry floodproofing is most likely to be successful for buildings subject to flooding depths, including 

freeboard, that do not exceed three feet, although it is recognized that floodproofing to a greater 

depth is feasible and may be appropriate, depending on the project.

■ The building is in a riverine flood hazard area or in coastal areas subject to flood conditions without 

waves.

■ Flood protection measures will be implemented to the flood protection level (or local regulatory flood 

elevation if compliance is required) not exceeding a height of three feet. FEMA strongly encourages 

flood retrofits to provide protection to the flood protection level or BFE plus one foot, whichever 

is higher, in accordance with International Building Code (IBC [2012]) and ASCE 24. Lower flood 

protection is sometimes appropriate, but the insurance implications should be considered. Building 

owners and design professionals should meet with a local building official to discuss the selected 

retrofit measure and the flood protection level.

All designs should be prepared or verified by a registered design professional before being implemented. 

1.5 Evaluation of Floodproofing Options

The owner and designer should evaluate all possible methods of flood hazard mitigation before implementing mitigation options on a building. If relocating or elevating a building is not feasible or cost-effective, 

floodproofing may be an appropriate alternative. Table 1-1 presents important points to consider for various 

floodproofing measures, including dry floodproofing, wet floodproofing, floodwalls, and levees. These points 

of consideration are based either on established standards in ASCE 24, on regulatory documents, or on best 

practice guidance. Italic text indicates a consideration that is based on best practice guidance. The building and 

site characteristics may not be compatible with certain floodproofing measures, so the unique characteristics 

for each project should be taken into account. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 1-5

INTRODUCTION 1

Table 1-1. Consideration of Floodproofing Measures for Non-Residential Buildings

Type of Mitigation Building or Site Attribute Issues for Consideration

Dry Floodproofing

Building strength • The superstructure and foundation should be able to adequately 

resist flood-related forces (hydrostatic, hydrodynamic, buoyancy, 

soil and debris impact) and the non-flood-related forces (e.g., 

wind, seismic) that are expected at the site. The superstructure 

and foundation should be evaluated by a registered design professional.

• If the structure is not capable of resisting the expected forces, 

additional retrofits to the structure may be necessary before 

floodproofing work begins.

Warning time Warning time may be required to activate or deploy a given 

floodproofing measure before floodwaters begin to impact the site. 

Adequate warning time estimates should include time for evacuation, 

notification of key personnel, travel time to the site if key personnel 

are not located on site, implementation of the measure, and 

evacuation of key personnel.

Flood characteristics Dry floodproofing is not recommended where flooding is expected 

to persist for a long period (longer than 12 hours). Prolonged contact 

with floodwaters increases the chance of seepage and structural 

failure in floodproofed buildings. Additionally, frequent flooding can 

adversely affect the building’s structural integrity over time. 

Level of protection Dry floodproofing is most likely to be successful in cases where 

flood depths do not exceed three feet, although floodproofing to a 

greater flood depth may be possible. If NFIP compliance is required, 

building code requirements or local regulations govern the level of 

protection.

Building location 

(Coastal A Zone and 

Zone V)

Dry floodproofing is not permitted:

• In Zone V under NFIP

• In Coastal A Zone or Zone V per ASCE 24

• In Zone V if the community enforces building codes based on the 

IBC

Operational 

considerations

Dry floodproofing measures require periodic inspection and 

maintenance plans to ensure that they are kept in working order.

Seepage considerations Measures to remove water that will infiltrate the building are 

necessary for a dry floodproofing measure to be successful.

Utilities • Alternate power may be required to operate sump pumps if normal power sources are unavailable during a flooding event.

• Underground utilities may need to be effectively sealed to prevent backflow of floodwaters into the building.

• Electrical utilities below the flood protection level must be protected against floodwaters.

Substantial 

Improvement/Damage

Dry floodproofing is permitted under the NFIP compliance regulations 

for buildings that are undergoing Substantial Improvement or 

have incurred Substantial Damage only if the buildings are nonresidential. It is not permitted for residential buildings with Substantial 

Improvement/Damage or new construction. However, it is permissible 

for non-Substantial Improvement/Damage retrofit of residential 

buildings. It is not recommended for wood-frame construction or for 

areas where flood levels are greater than two to three feet. 
1-6 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

1 INTRODUCTION

Type of Mitigation Building or Site Attribute Issues for Consideration

Wet Floodproofing

Building strength • The superstructure and foundation should be able to adequately 

resist flood-related forces other than hydrostatic load (i.e., hydrodynamic, buoyancy, soil and debris impact) and the non-floodrelated forces (e.g., wind, seismic) that are expected at the site. 

The superstructure and foundation should be evaluated by a 

registered design professional.

• If the building is not capable of resisting the expected forces, additional retrofits to the building may be necessary.

Warning time Warning time may be required to activate or deploy a given 

floodproofing measure before the floodwaters begin to impact 

the site. Adequate warning time estimates should include time for 

evacuation, notification of necessary individuals, travel time to the 

site if key personnel are not located on site, implementation of the 

measure, evacuation of key personnel. 

Flood-damage-resistant 

materials

Any materials used below the BFE in wet floodproofing measures 

must be flood-damage resistant.

Operational 

considerations 

Wet floodproofing mitigation measures require periodic inspection 

and maintenance plans to ensure they are kept in working order.

Utilities Utilities below the flood protection level must be designed, 

constructed, and installed to prevent floodwaters, including any 

backflow through the system, from entering or accumulating within 

the components. They should also be designed to prevent damage 

to the system as a result of factors such as buoyancy and corrosion.

Floodwalls/Levees

Level of protection Floodwalls, levees, and other flood protective works should not be 

considered as protective of buildings during the design flood unless 

these works are shown on a community’s flood hazard map as 

providing protection.

Warning time Warning time may be required to activate or deploy a given 

floodproofing measure before the floodwaters begin to impact 

the site. Adequate warning time estimates should include time for 

evacuation, notification of key personnel, travel time to the site if key 

personnel are not located on site, implementation of the measure, 

and evacuation of key personnel. 

Substantial 

Improvement/Damage 

Accredited levees result in removal of the Special Flood Hazard 

Area (SFHA) designation in the areas they protect. However, small 

levees protecting a single or limited number of buildings are generally 

not accredited, and their construction does not satisfy Substantial 

Improvement/Damage requirements or bring new buildings into 

compliance. 

To meet 44 CFR §65.10 requirements for levee accreditation, 

operations and maintenance must be under the jurisdiction of an 

approved government agency.

Utilities • Underground utilities should be considered in the design of 

floodwalls to prevent backflow of floodwaters into the building.

• If a levee or floodwall is breached, the resulting flow may be high 

velocity, possibly causing scour and dislocation. 

• Underground utilities may threaten the stability of the levee itself, 

if they run underneath the structure.

Table 1-1. Consideration of Floodproofing Measures for Non-Residential Buildings (continued)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 1-7

INTRODUCTION 1

Type of Mitigation Building or Site Attribute Issues for Consideration

Floodwalls/Levees 

(continued)

Seepage potential and 

local/internal drainage 

• The longer the duration (i.e., the longer floodwaters are in contact 

with the floodwall), the greater the potential for seepage, and the 

greater the need for seepage control measures such as backfill, 

cutoff walls, or pumps.

• Local drainage systems should be designed to minimize the 

rainfall runoff of floodwaters within the protected area.

• The soil type surrounding the building is a key consideration in 

floodwall design. The soil mineralogy and deposition can vary 

widely in coastal deposits. This variability affects both permeability and strength properties, and should be carefully evaluated. Seepage potential is lower for less permeable soils, which 

reduces the required floodwall drainage design flow volume 

and rate. However, less permeable soils must be checked for 

adequate stability and strength to resist static and dynamic flood 

forces.

Floodwall openings Floodwalls with fewer/smaller openings are simpler to design and 

require less warning time to install protective floodwall closures, but 

can limit site access. 

Location and 

topography 

Levees require a significant amount of surrounding vacant land and 

are not typically suitable for densely developed communities.

If the natural topography is such that only one or two sides of a 

building need to be protected, a levee may be feasible.

Regulatory requirements Federal, State, and local laws and regulations should be reviewed 

to determine whether floodwall or levee construction is permissible, 

restricted, or prohibited. For example, certain criteria restrict floodwall 

or levee construction within FEMA-designated floodways. Additionally, 

when floodprone property is acquired via a FEMA mitigation grant 

program, deed restrictions on land use prohibit most development, 

including the construction of levees, on the property.

1.6 Icons

Throughout this manual, the following icons are used, indicating: 

Special Note: Significant or interesting information

Terminology: Definition or explanation of pertinent terms 

Cross Reference: Reference to another relevant part of the text or another source of information 

Equation: Use of a mathematical equation 

Warning: Special cautions need to be exercised

Table 1-1. Consideration of Floodproofing Measures for Non-Residential Buildings (continued)
1-8 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

1 INTRODUCTION

1.7 Organization

The information in this manual is organized as follows:

■ Chapter 1: Introduction – Definition of floodproofing, limitations and assumptions in floodproofing 

non-residential buildings, and an evaluation of floodproofing measures.

■ Chapter 2: Design Considerations for Floodproofing – Factors that influence the decision to 

implement a floodproofing measure.

■ Chapter 3: Dry Floodproofing Measures – General design considerations for dry floodproofing, 

as well as a discussion of the types of dry floodproofing measures.

■ Chapter 4: Other Floodproofing Measures – Floodwalls, levees; floodproofing utilities, wet 

floodproofing, and emergency floodproofing; pros and cons of each measure; other factors to consider 

when selecting a floodproofing measure; and how to combine floodproofing measures.

■ Appendix A: FEMA Assistance – Overview of FEMA’s Hazard Mitigation Assistance grant 

programs.

■ Appendix B: Understanding the FEMA Benefit-Cost Process – Importance of the BenefitCost Analysis (BCA) in FEMA assistance, data required to run a BCA module, and resources with 

additional information.

■ Appendix C: Checklist for Vulnerability of Flood-prone Sites and Buildings – A tool that can 

be used to help assess site-specific flood hazards and building vulnerability.

■ Appendix D: References – Cited references. 

■ Appendix E: Resources – Resources with additional information, including vulnerability and 

maintenance checklists.

■ Appendix F: FEMA Region Contact Informattion – Mailing addresses and phone numbers for 

the FEMA Regions.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-1

T he most effective flood mitigation methods are relocation and elevation, but when these methods are 

not feasible or cost-effective, floodproofing may be an appropriate alternative. Some emergency measures can be accomplished without expert construction assistance, and many can be used for low-level 

or nuisance flooding while significantly reducing losses from these types of events. 

The development of a floodproofing strategy should include considerations of a number of factors that will 

influence the design of the floodproofing measure or measures. This chapter contains a discussion of these factors, which are: 

■ Design requirements. Regulatory 

requirements, building codes, design 

standards, and other guidance documents 

(Section 2.1)

■ Design loads and site characteristics. 

Hydrostatic loads, hydrodynamic loads, 

wave loads, impact loads from flood-borne 

debris, internal drainage, and site drainage 

(Section 2.2)

■ Flood characteristics. Flood elevations, 

duration of flooding, rate of floodwater rise 

and fall, flood frequency (Section 2.3)

■ Site factors. Flood hazard boundaries, 

erosion and scour, and geotechnical 

considerations (Section 2.4)

■ Functional, operational, and economic 

factors. Functional use requirements of the 

building, occupant safety, flood warning 

time, flood emergency operations plans, 

inspection and maintenance plans, and 

BCAs (Section 2.5)

■ Vulnerability assessments. All-hazards vulnerability assessments, structural condition assessments 

of the building, and utility assessments (Section 2.6)

Design Considerations in 

Floodproofing

Cross Reference

Have questions about the NFIP?

See FEMA F-084, Answers to Questions 

about the NFIP (FEMA 2011b) at: http://

www.fema.gov/media-library/assets/documents/272. This document is intended 

to acquaint the public with the NFIP. It is 

designed for readers who do not need 

a detailed history or technical or legal 

explanations but who do need a basic 

understanding of the program and the 

answers to some frequently asked questions. For legal definitions, see the NFIP 

Flood Insurance Manual (FEMA 2013), 

and National Flood Insurance Program 

Regulations (FEMA 2009a).
2-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

2.1 Regulatory Requirements, Building Codes, Design Standards, 

and Guidance Documents 

Floodproofing may be proposed voluntarily by building owners or may be necessary to meet floodplain management regulations or building codes. This section contains a discussion of the floodplain management 

regulations and building codes that can affect the type and design of floodproofing measures.

2.1.1 National Flood Insurance Program

Communities that participate in the NFIP are required to adopt and enforce local regulations for development 

in mapped Special Flood Hazard Areas (SFHAs) to reduce the risk of flooding (see 44 CFR Parts 59 and 60). 

However, communities are encouraged to adopt requirements that exceed Federal regulations. Homeowners, 

renters, and business owners, as well as communities that own buildings in participating communities are eligible for NFIP flood insurance coverage.

With the inclusion of NFIP-consistent provisions in the International Code Series (I-Codes), communities that have adopted the I-Codes have two ways of enforcing NFIP flood-resistant design and construction requirements for buildings and structures: 

■ Using the I-Codes with NFIP-consistent provisions intact and IBC Appendix G; or 

■ Using the I-Codes with NFIP-consistent provisions intact and local floodplain management 

regulations that include requirements comparable to those in Appendix G.

These tools are designed to work together to result in buildings and structures, and all other development, that 

are resistant to flood loads and flood damage.

If a participating community has not adopted the I-Codes or if the NFIP-consistent provisions of the codes 

are not intact, the community must adopt local floodplain management regulations that include detailed and 

specific requirements for buildings and structures. 

Consensus standards are incorporated into building codes by 

reference; ASCE 7, Minimum 

Design Loads for Buildings and 

Other Structures (2010), and ASCE 

24 are two consensus standards 

that are consistent with NFIP 

regulations. See Section 2.1.7 for 

more information on consensus 

standards. Figure 2-1 shows how 

building design is regulated by the 

NFIP regulations and building 

codes. 

*NFIP-consistent administrative provisions, community-specific adoption of Flood 

Insurance Studies and maps, and technical requirements for development outside the 

scope of the building code (and higher standards, in some communities)

Figure 2-1. Satisfying NFIP requirements through building codes
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-3

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

The requirements in 44 CFR Part 60 apply to all development, which the NFIP broadly defines to include 

buildings and structures, site work, roads and bridges, 

and other activities. The regulations require buildings 

to be designed and constructed to resist flood damage, 

which is achieved primarily through elevation. Dry 

floodproofing can be used to fulfill the requirements for 

non-residential buildings in SFHAs that are not subject to high velocity wave action. Some requirements 

apply to existing buildings when the cost of repairing 

or improving a building in an SFHA equals or exceeds 

50 percent of the building’s market value. The NFIP 

requires that new and Substantially Improved buildings 

be constructed in ways that minimize or prevent flood 

damage. As with new non-residential buildings, existing 

non-residential buildings may be brought into compliance by elevating them on compliant foundations or, if 

determined to be feasible, by implementing dry floodproofing measures.

The NFIP’s performance requirements are identical for 

new construction and for Substantial Improvement 

or repair of Substantial Damage of existing buildings. 

Some of the key requirements are:

■ Buildings shall be designed and adequately 

anchored to prevent flotation, collapse, or 

lateral movement resulting from hydrodynamic 

and hydrostatic loads, including the effects of 

buoyancy (44 CFR §60.3(a)(3)(i)).

■ Building materials used below the BFE shall 

be resistant to flood damage (44 CFR §60.3(a)

(3)(ii)). 

■ Buildings shall be constructed by methods and 

practices that minimize flood damage (44 CFR 

§60.3(a)(3)(iii)).

■ Buildings shall be constructed with electrical, 

heating, ventilation, plumbing, and airconditioning equipment and other service 

facilities that are designed and/or located so as 

to prevent water from entering or accumulating 

within the components (44 CFR §60.3(a)(3)

(iv)). 

Terminology

“Substantial Damage” is damage of any 

origin sustained by a structure whereby the 

cost of restoring the structure to its beforedamage condition would equal or exceed 

50 percent of the market value of the structure before the damage occurred (FEMA 

2010c).

“Substantial Improvement” is any repair, 

reconstruction, rehabilitation, addition, 

or improvement of a building, the cost of 

which equals or exceeds 50 percent of 

the market value of the building before 

the improvement or repair is started (certain historic structures may be excluded) 

(FEMA 2010c).

Substantially Impermeable: FEMA uses 

USACE’s definition of substantially impermeable from Flood Proofing Regulations 

(USACE 1995). This document states that 

a substantially impermeable wall “shall 

not permit the accumulation of more than 

4 inches of water depth during a 24-hour 

period and, sump pumps shall be required 

to control this seepage.” 

Special Note

The NFIP establishes minimum criteria and design performance requirements 

that communities participating in the NFIP 

must enforce for structures in SFHAs. The 

criteria specify how a structure should be 

constructed in order to minimize or reduce 

the potential for flood damage. A primary 

requirement is that buildings shall be elevated to or above the BFE. Depending on 

flood zone, non-residential buildings may 

be protected with specifically designed 

and certified dry floodproofing measures 

that are watertight below and protect to the 

BFE. See Section 2.1.2 for information on 

the Floodproofing Certificate.
2-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

■ New and replacement water supply systems 

shall be designed to minimize or eliminate 

infiltration of flood waters into the systems (44 

CFR §60.3(a)(5)). 

■ New and replacement sanitary sewage systems 

shall be designed to minimize or eliminate the 

infiltration of discharges from the systems into 

floodwaters (44 CFR §60.3(a)(6)(i)).

■ All new construction and Substantial 

Improvement of non-residential structures 

within Zones A1–30, AE, and AH on the 

community’s Flood Insurance Rate Map 

(FIRM) must (i) have the lowest floor 

(including basement) elevated to or above the 

base flood level or, (ii) together with attendant 

utility and sanitary facilities, be designed so that below the base flood level the structure is watertight 

with walls substantially impermeable to the passage of water and with structural components having 

the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy (44 CFR 

§60.3(c)(3)).

■ Within any Zone AO on the community’s FIRM, all new construction and Substantial Improvement 

of nonresidential structures must (i) have the lowest floor (including basement) elevated above the 

highest adjacent grade at least as high as the depth number specified in feet on the community’s 

FIRM (at least 2 feet if no depth number is specified), or (ii) together with attendant utility and 

sanitary facilities be completely floodproofed to that level to meet the floodproofing standards 

specified in 44 §60.3(c)(3)(ii) and 60.3(c)(8).

When dry floodproofing measures are proposed for 

non-residential buildings, communities that participate 

in the NFIP require applicants to provide certification that registered professional engineers or architects 

have developed or reviewed the structural design, specifications, and plans for proposed dry floodproofing 

measures. In addition, the dry floodproofing design 

and proposed methods of construction are to be certified as being in accordance with accepted standards of 

practice (see Section 2.1.2). The standards of practice 

require that the building, together with attendant utility 

and sanitary facilities, be designed so that it is watertight 

below the BFE, with walls substantially impermeable 

to the passage of water and with structural components 

Special Note

This publication specifies that in order for 

dry floodproofing to achieve a favorable 

NFIP insurance rating, it must extend to the 

BFE + 1 foot of freeboard. For new construction or Substantial Improvement/Damage, 

it must extend to the BFE. However, the 

owner may choose to protect an existing 

building from lesser events of shallower, 

more frequent flooding using dry floodproofing measures provided Substantial 

Improvement/Damage is not triggered. 

Special Note

The NFIP does not strictly prohibit hazardous materials from areas subject to 

flooding, but requiring such materials to 

be protected from floodwaters, is an effective way to reduce or eliminate the chance 

of damage associated with the release of 

harmful materials. FEMA 480, Floodplain 

Management Requirements, A Study 

Guide and Desk Reference for Local 

Officials, provides a list of potential contaminants that may be of concern (FEMA 

2005).
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-5

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

that are capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy associated with the 

design flood event.

Although NFIP regulations require non-residential 

buildings to be watertight and protected only to the BFE 

for floodplain management purposes (to meet NFIP 

regulations), protection to a higher level is necessary for 

dry floodproofing measures to be considered for NFIP 

flood insurance rating purposes. Because of the additional risk associated with dry floodproofed buildings, 

to receive an insurance rating based on 1-percentannual-chance (100-year) flood protection, a building 

must be dry floodproofed to an elevation at least 1 foot 

above the BFE. Insurance premiums will be lower if dry 

floodproofing extends higher than the BFE + 1 foot. 

Dry floodproofed buildings with active floodproofing 

measures and requiring human intervention are subject 

to higher insurance premiums than dry floodproofed 

buildings with completely passive floodproofing measures that do not require human intervention.

Wet floodproofing also has implications for NFIP flood insurance rating purposes. NFIP floodplain management regulations restrict the use of space below the BFE to parking of vehicles, building access, and storage. 

Although floodwalls or levees can be used to keep floodwaters away from buildings, implementing these 

measures will not affect a building’s flood insurance rating unless the flood control structure is accredited in 

accordance NFIP requirements (44 CFR §65.10) and provides protection from at least the 1-percent-annualchance (100-year) flood. In addition, floodwalls or levees as a retrofit measure will not bring the building into 

compliance with NFIP requirements for Substantial Improvement/Damage.

Tables 2-1 and 2-2 provide other requirements for dry and wet floodproofing based on the NFIP. 

Table 2-1. NFIP General Requirements for Dry Floodproofing

NFIP General Requirements for Dry Floodproofing References

For new construction and Substantial Improvement/Damage, permitted only in nonresidential buildings in special flood hazard areas not subject to high velocity wave action 

(i.e., permitted in Zone A).

44 CFR §60.3(c)(3)

44 CFR §60.3(c)(8)

44 CFR §60.3(c)(4)

Technical Bulletin 3 

(FEMA 1993a)

Must be designed so the structure is watertight below the BFE with walls substantially 

impermeable to the passage of floodwater.(a)

Attendant utility and sanitary facilities must be completely floodproofed to below the BFE.(a)

A registered design professional must develop and/or review structural designs, 

specifications, and plans and certify that the design and methods of construction are in 

accordance with accepted standards of practice.

Not permitted in Coastal High Hazard Areas (Zone V).

(a) Dry floodproofed properties are eligible for insurance only if floodproofing extends to 1 foot above the BFE; 44 CFR §60.3(c)(3) requires 

floodproofing to the BFE.

Special Note

A building that is valued at $150,000 and 

located in a zone A can have differing 

insurance premiums based on the level of 

floodproofing. If the building is floodproofed 

to 1 foot above the BFE, the annual premium would be approximately $1380. If 

the same building is floodproofed to 2 feet 

above the BFE, the annual premium would 

be approximately $540. The increase in 

floodproofing design level would result in 

a 61 percent savings in annual insurance 

premiums that would be passed onto the 

building owner. 
2-6 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Table 2-2. NFIP General Requirements for Wet Floodproofing 

NFIP General Wet Floodproofing Requirements References

Permitted only for attached garages or parking, access, and storage areas below 

the BFE 

44 CFR §60.3(a)(3)

44 CFR §60.3(c)(5)

44 CFR §60.6(a)

44 CFR §60.6(a)(7) 

Technical Bulletin 7 (FEMA 1993b)

Some historic structures, accessory structures, structures functionally dependent 

on proximity to water, and agricultural buildings may be wet floodproofed 

Portions of the structure below the BFE must be constructed of flood-resistant 

materials

Must be designed to allow for automatic entry and exit of floodwaters

2.1.2 Floodproofing Certificate for 

Non-Residential Buildings in Zone A

When dry floodproofing is used to comply with local 

regulations or building code requirements, the NFIP 

and model building codes require the submission of a 

certificate stating that the design satisfies all applicable requirements. Strictly speaking, certification is not 

required for retrofit measures that are not required to 

meet the minimum requirements; however, FEMA recommends that communities require it for all retrofit dry 

floodproofing projects. The recommended form to use 

for this purpose is the FEMA Floodproofing Certificate 

for Non-Residential Structures (FEMA Form 086-

0-34) (FEMA 2012b). This form is required for the 

floodproofing measures to be recognized for NFIP 

flood insurance purposes. It is important to note that 

this certificate is not an “as-built” certification; it is used 

by the designer only to certify the design. Certification 

of design is not required for wet floodproofing. For 

floodwalls and levees, a certificate is required only if the 

mitigation results in a change to the FIRM.

The design certification is required for the following 

types of buildings in Zone A:

■ Dry floodproofed non-residential structures 

(no residential uses)

■ Dry floodproofed portions of mixed-use 

buildings that have all residential uses located 

above the floodproofing design elevation

The certificate is submitted as part of the permit application and has the following three sections: 

Special Note

Design professionals need to be aware of 

several requirements not explicitly noted 

on current floodproofing certificates, specifically, they must:

n Provide interior drainage (pumps) to 

control seepage into building

n Provide a continuous source of electricity to operate any necessary 

floodproofing components

n Use flood-resistant materials in areas 

where seepage is expected to occur

n Conduct planning, including developing 

a flood emergency operations plan and 

an inspection and maintenance plan

To ensure better documentation and to 

demonstrate the importance of implementing active measures, FEMA suggests that 

local officials require a photograph of the 

building to be submitted with the certificate. 

If there are openings on the floodproofed 

portion of the building, the photograph 

should be taken with opening protection 

fully installed/in place.

Further, the designer should sign off on 

the floodproofing certificate stating that 

he or she has reviewed the emergency 

operations plan AND inspection and maintenance plan and that they are adequate. 

Finally, additional technical documentation, such as design drawings and material 

specifications, may be required for insurance purposes.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-7

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

■ Section I. FIRM information, including community number, map panel number, date of the FIRM 

index, flood zone, and BFE.

■ Section II. Floodproofing information. The designer is required to identify the floodproofing design 

elevation and the height of the floodproofing measures above the lowest adjacent grade. 

■ Section III. Certification by the design professional licensed in the State where the project is located. 

The designer signs to certify that the dry floodproofed area of the building, together with attendant 

utilities and sanitary facilities, will be watertight to the floodproofed design elevation indicated, with 

walls that are substantially impermeable to the passage of water. The designer is also required to 

certify that all structural components are capable of resisting hydrostatic and hydrodynamic flood 

forces, including the effects of buoyancy, and anticipated debris impact forces. 

The designer provides copies of the completed certificate to the building owner who submits it with the permit 

application to his/her insurance agent/company and the community official. Communities are required to 

maintain copies of design certifications as part of their commitment to the NFIP.

2.1.3 Floodproofing Historic Buildings

The NFIP gives special consideration to the unique value of designated historic buildings and structures. 

Provided such structures retain their designations, communities do not have to require them to be brought 

into compliance if the structures will be Substantially Improved or have been Substantially Damaged. The 

NFIP definition of “historic structures” includes structures that are (1) listed or preliminarily determined to 

be eligible for listing in the National Register of Historic Places, (2) certified or preliminarily determined by 

the Secretary of the Department of Interior as contributing to the historical significance of a registered historic district or a district preliminarily determined to qualify as a registered historic district, or (3) designated 

as a historic site under a State or local historic preservation program that is approved by the Secretary of the 

Department of Interior. The definition does not include structures that are merely old, those that residents 

refer to as historic, or those that happen to be located in historic districts. Section 4.5.3 includes a case study 

involving the application of floodproofing to historic buildings.

When voluntary retrofit floodproofing measures are applied to historic buildings, the measures should be 

designed to mitigate or reduce the flood risk while preserving the building’s historic integrity. Consultation 

with the State Historic Preservation Officer and a design professional (engineer or architect), preferably one 

experienced in rehabilitating historic structures, is necessary. Ideally, any retrofit floodproofing measure applied 

to a historic building and/or its site will not affect the property’s designation. If a structure does not retain its 

historic designation, it is subject to the basic NFIP requirements for Substantial Improvement/Damage.

Retrofit floodproofing measures for historic buildings need not be comprehensive to provide at least some 

degree of protection. The techniques listed below may have minimal impact on the historically significant features of the structure (FEMA 2008b):

■ Elevating electrical and mechanical systems and utilities

■ Relocating contents 

■ Creating positive drainage, where the grade allows water to drain away from the building

■ Using flood damage-resistant materials 
2-8 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

■ Filling in basements or wet floodproofing basements

■ Installing small floodwalls to protect openings such as window wells

2.1.4 National Policies for Federal Actions in Floodplains 

When Federal assistance is provided for the planning, 

design, and construction of buildings or for the repair 

of existing buildings located in SFHAs (and within the 

0.2-percent-annual-chance [500-year] floodplain if the 

activity funded is a “critical action” or critical facility), 

the funding agency is required to address additional 

considerations.

Executive Order (EO) 11988, Floodplain Management, 

requires Federal agencies to follow a decision-making 

process to avoid, to the extent possible, the short- and 

long-term adverse impacts associated with the occupancy 

and modification of floodplains and to avoid supporting 

floodplain development directly or indirectly whenever 

there is a practicable alternative. If there is no practicable 

alternative, the Federal agency must take steps to minimize any adverse impacts on people’s lives, property, and 

the floodplain’s natural and beneficial functions. EO 

11988 applies directly to Federal agencies and indirectly 

to tribes, States, and local governments through Federal 

actions and requirements. 

FEMA’s regulations in 44 CFR Part 9 set forth the 

agency’s policy, procedure, and responsibilities for 

implementation and enforcement of EO 11988 and 

also EO 11990, Protection of Wetlands. Other Federal 

agencies have similar regulations or policies that satisfy 

the requirements of the order. 

As defined in 44 CFR §9.4, a critical action is an action 

for which even a slight chance of flooding is too great. 

The minimum floodplain of concern for critical actions 

is the 0.2-percent-annual-chance (500-year) floodplain. 

Critical actions include actions that create or extend the 

useful life of structures or facilities such as those that 

produce, use, or store highly volatile, flammable, explosive, toxic or water reactive materials; hospitals, nursing 

homes, and housing for the elderly; emergency operation centers, data storage centers; utility systems and 

power generating plants. 

Warning

Although 44 CFR Part 9 implementation 

rules addresses “critical actions” in SFHAs 

(actions for which even a slight chance of 

flooding is too great), sometimes relocating 

a critical action (building) is a better option 

than elevating or floodproofing 

Special Note

44 CFR §9.11(d)(1) states that FEMA, as 

part of its implementation of the Disaster 

Relief Act of 1974, tshall apply certain minimization provisions. Specifically, FEMA 

funding shall not be used to support new 

construction or Substantial Improvement in 

a floodway, and no new construction in a 

coastal high hazard area, except for (i) a 

functionally dependent use or (ii) a structure or facility which facilitates an open 

space use.

44 CFR §59.1 defines the regulatory floodway as the channel of a river or other 

watercourse and the adjacent land areas 

that must be reserved in order to discharge 

the base flood without cumulatively increasing the water surface elevation more than a 

designated height.

44 CFR §59.1 defines the coastal high 

hazard area as an area of special flood 

hazard extending from offshore to the 

inland limit of a primary frontal dune along 

an open coast and any other area subject 

to high velocity wave action from storms or 

seismic sources.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-9

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Critical actions should be given special consideration when developing regulatory alternatives and floodplain 

management plans. Under EO 11988 and 44 CFR Part 9, critical actions are required to avoid the 0.2 percent-annual-chance (500-year) floodplain or to elevate or protect structures and essential components to the 

0.2-percent-annual-chance (500-year) flood level. Critical actions should not occur in a floodplain, if possible. 

The 8-step decision-making process called for in EO 11988 is further developed and clarified in 44 CFR 

§9.6(b). FEMA uses the decision-making process illustrated in Figure 2-2 to satisfy the requirements. 

Figure 2-2. FEMA’s 8-step decision-making process for compliance with Executive Order (EO) 11998 and 44 CFR Part 9
2-10 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

2.1.5 Local Floodplain Management Regulations 

To participate in the NFIP, communities are required to adopt and enforce local floodplain management 

regulations that meet or exceed the minimum requirements established in 44 CFR Parts 59 and 60. 

Until the advent of model building codes that included flood provisions deemed consistent with NFIP 

requirements for buildings (see Section 2.1.1), communities adopted stand-alone floodplain management 

regulations or ordinances that included administrative, land use, and building requirements.

Some States have requirements that exceed the minimum NFIP requirements, and many communities adopt 

higher standards to achieve a greater level of protection and public safety. The most common higher standards 

are: 

■ Requirement to protect to a higher elevation 

than the minimum requirement (freeboard)

■ A cumulative Substantial Improvement in 

which the improvements and repairs are tallied 

over a certain period of time (e.g., 5 or 10 

years). The effect of a cumulative improvement 

provision is that more existing buildings are 

required to be brought into compliance with 

the requirements for new construction

■ Prohibition of new construction in the floodway, SFHA, or conservation zones

■ Prohibition of the use of building materials and practices that have proven to be ineffective in flooding

■ Restrictions on the use and type of construction fill material

2.1.6 Model Building Codes 

Many States and communities regulate the construction of buildings by adopting and enforcing building 

codes based on model building codes. Building codes have minimum requirements on issues such as structural 

design, materials, fire safety, number and location of exits, natural hazard mitigation, sanitary facilities, light 

and ventilation, environmental control, fire protection, and energy conservation. Building codes apply to the 

construction of new buildings and structures and to existing buildings and structures, including alteration, 

relocation, enlargement, replacement, repair, and change of occupancy. 

The I-Codes and the National Fire Protection Association (NFPA) Building Construction and Safety Code 

(NFPA 5000 [2012]) were the first model codes to include comprehensive provisions for flood hazards. The 

flood provisions were incorporated into building codes in the early 2000s. Both codes are consistent with the 

minimum provisions of the NFIP that pertain to the design and construction of buildings and other structures. 

The IBC and International Existing Building Code (IEBC [2012]) are pertinent to this manual because they 

address the primary requirements for design and construction of non-residential buildings and because of their 

widespread use in the United States. The IBC contains flood provisions, and the IEBC references the flood 

provisions of the IBC for all repairs, additions, and alterations to existing buildings in flood hazard areas that 

are proposed to be Substantially Improved or that have sustained Substantial Damage.

Warning

For any building that is proposed for dry 

floodproofing, always determine whether 

the community where the building is located has adopted higher standards.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-11

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

The IBC incorporates by reference a number of standards 

developed through a formal or accredited consensus 

process. The standards that are related to flood-resistant design are ASCE 7, Minimum Design Loads for 

Buildings and Other Structures, and ASCE 24, Flood 

Resistant Design and Construction. The IBC addresses 

flood loads and flood-resistant construction primarily 

in Section 1612. FEMA has determined that the flood 

provisions of the I-Codes are consistent with NFIP 

requirements for buildings and structures. The family of 

I-Codes addresses all of the key building requirements 

of the NFIP. Communities that enforce building codes 

based on the I-Codes should coordinate their floodplain 

management ordinances with the codes to minimize 

duplication and conflicts and to ensure that all requirements are addressed, including requirements for development other than buildings and structures. 

Some key code requirements from the 2012 IBC are described in Table 2-3 (previous editions of the IBC have 

the same or similar requirements). 

A dry floodproofing retrofit project may trigger several sections of a community’s building code that must be 

considered during the design. The designer or engineer should be cognizant of codes that may be triggered 

when considering flood mitigation projects (see code trigger example on page 2-13).

Cross Reference

The International Code Council’s family of 

building codes can be purchased at http://

www.iccsafe.org/. The I-Codes are NOT 

available for free (although some States 

have made them available through separate copyright agreements). Excerpts of the 

flood provisions of the I-Codes are posted 

on the FEMA Building Science Web site: 

http://www.fema.gov/building-science.
2-12 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Table 2-3. Key Code Requirements for Flood-Resistant Design from IBC 2012

IBC 2012 Section(a) Requirement Comments

110.3.3 [Required 

Inspections] Lowest 

Floor Elevation

In flood hazard areas, upon placement of the lowest 

floor, including the basement, and prior to further 

vertical construction, the elevation certificate required 

in Section 1612.5 shall be submitted to the building 

official.

Requires submission of elevation 

certificate once lowest floor has 

been constructed, before further 

vertical construction.

1403.6 [Exterior Walls] 

Flood Resistance

For buildings in flood hazard areas as established in 

Section 1612.3, exterior walls extending below the 

elevation required by Section 1612 shall be constructed 

with flood-damage-resistant materials. Wood shall 

be pressure-preservative treated in accordance 

with AWPA-U1-12, Use Category System: User 

Specification for Treated Wood (AWPA 2012) for the 

species, product, and end use using a preservative 

listed in Section 4 of AWPA U1 or decay-resistant 

heartwood of redwood, black locust, or cedar.

Requires buildings in flood hazard 

areas to use flood-damage-resistant 

materials on exterior walls below 

the required elevation. 

1605.2.1 [Structural 

Design] Load 

Combinations (using 

strength design or 

load and resistance 

factor design) and 

Other Loads.

Where flood loads, Fa, are to be considered in the 

design, the load combinations of Section 2.3.3 of 

ASCE 7 shall be used. Where self-straining loads, T, 

are considered in design, their structural effects in 

combination with other loads shall be determined in 

accordance with Section 2.4.4 of ASCE 7. Where an 

ice-sensitive structure is subjected to loads due to 

atmospheric icing, the load combinations of Section 

2.3.4 of ASCE 7 shall be considered. 

Requires buildings designed for 

flood hazard areas to be designed 

to resist flood loads, along with 

other loads. 

1605.3.1.2 [Structural 

Design] Load 

Combinations (using 

allowable stress 

design) and Other 

Loads. 

Where flood loads, Fa, are to be considered in design, 

the load combinations of Section 2.4.2 of ASCE 7 shall 

be used. Where self-straining loads, T, are considered 

in design, their structural effects in combination with 

other loads shall be determined in accordance with 

Section 2.4.4 of ASCE 7. Where an ice-sensitive 

structure is subjected to loads due to atmospheric 

icing, the load combinations of Section 2.3.4 of ASCE 7 

shall be considered.

Requires buildings designed for 

flood hazard areas to be designed 

to resist flood loads, along with 

other loads.

1612.1 [Structural 

Design] Flood Loads

Within flood hazard areas as established in Section 

1612.3, all new construction of buildings, structures 

and portions of buildings and structures, including 

Substantial Improvement and restoration of Substantial 

Damage to buildings and structures, shall be designed 

and constructed to resist the effects of flood hazards 

and flood loads. For buildings that are located in more 

than one flood hazard area, the provisions associated 

with the most restrictive flood hazard area shall apply.

Requires all new buildings, 

Substantial Improvement, and 

repair of Substantial Damage to 

be designed to resist the most 

restrictive flood hazard applicable to 

the location. 

1612.4 [Structural 

Design] Flood Loads

The design and construction of buildings and 

structures located in flood hazard areas, including flood 

hazard areas subject to high-velocity wave action, shall 

be in accordance with Chapter 5 of ASCE 7 and with 

ASCE 24.

References ASCE 7 and ASCE 24 

for the specific requirements for the 

design and construction of buildings 

in flood hazard areas.

International Building Code (IBC), American Society of Civil Engineers (ASCE), American Wood Protection Association (AWPA)

(a) Flood-resistant provisions of the I-Codes can be found at http://www.fema.gov/building-science/building-code-resources.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-13

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

2.1.7 Consensus Standards 

The consensus standards relevant to flood-resistant 

design are ASCE 7 and ASCE 24. The requirements in 

these standards are consistent with the minimum NFIP 

requirements. 

ASCE 7 outlines methods to determine design loads 

and load combinations in flood hazard areas, including hydrostatic loads, hydrodynamic loads, wave loads, 

and debris impact loads. To compute the loads and 

load combinations, the designer must identify site-specific characteristics, including flood depths, velocities, 

waves, and the likelihood that debris impacts need to 

be considered. 

ASCE 24 addresses design and construction requirements for buildings in flood hazard areas, including 

floodways, coastal high hazard areas, and other highrisk flood hazard areas such as alluvial fans, flash flood 

areas, mudslide areas, erosion-prone areas, and highvelocity areas. ASCE 24 sets forth requirements for 

elevation, foundation designs, enclosures below elevated 

buildings, materials, dry and wet floodproofing, utility 

Code Trigger Example

An example of a requirement that could be triggered by a floodproofing retrofit project is means of 

egress. The IEBC has criteria on means of egress that may be relevant depending on the level of alteration. Level 2 alterations “include the reconfiguration of space, the addition or elimination of any door or 

window, the reconfiguration or extension of any system, or the installation of any additional equipment.” 

Under the IEBC, in a Level 2 alteration, the requirements for both Level 1 and Level 2 alterations need 

to be followed. The requirements may involve finish, structural, accessibility/egress, fire-resistance, and 

other requirements. For example, a Level 2 alteration may trigger means of egress requirements that 

include:

n Minimum number of exits in the work area, as required by the IBC (some buildings are required to 

have only one exit if certain criteria are met

n Fire escapes requirements such as unobstructed access

n New fire escape requirements

n Mezzanine egress requirements

n Requirements for openings in corridor walls

n Means of egress lighting, exit signs, handrails, and guard

Warning

ASCE 24 addresses design and construction requirements for buildings in 

coastal high-hazard areas (Zone V), 

Coastal A Zones, and high-flood-velocity areas but limits the applications of dry 

floodproofing in these areas because of 

increased hydrodynamic and wave loads.

Cross Reference

ASCE standards are available for purchase 

at: http://www.asce.org/codes-standards/. 

Highlights of ASCE 24 are posted on the 

FEMA Building Science Web page: http://

www.fema.gov/building-science. 
2-14 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

installations, building access, and miscellaneous structures (e.g., decks, porches, patios, garages, chimneys and 

fireplaces, pools, above- and below-ground storage tanks). 

ASCE 24, Section 6.2 and Commentary 6.2, Dry Floodproofing, specify design and construction requirements for dry floodproofing when used for the construction of new buildings or when existing buildings are 

proposed to be Substantially Improved (including repair of Substantial Damage). Table 2-4 provides a list of 

general requirements and limitations for dry floodproofing. ASCE 24 promulgates the standards of practice 

and should be used for floodproofing retrofits, even if the work does not constitute a Substantial Improvement. 

Table 2-4. ASCE 24 Requirements and Limitations for Dry Floodproofing

ASCE 24 

Section Dry Floodproofing Requirements and Limitations

Minimum 

Elevation of 

Floodproofing 

(Table 6-1)

Specifies the minimum elevation of dry floodproofing relative to the base flood elevation (BFE) 

or design flood elevation (DFE) as a function of structure/risk category and limits use of dry 

floodproofing to flood hazard areas outside of high risk flood hazard areas.

Limitations 

(Section 6.2.1)

Dry floodproofing of buildings is not permitted in:

• Coastal High Hazard Areas (Zone V) 

• Coastal A Zones

• Other High Risk Flood Areas where the following are known to occur: alluvial fan flooding, flash 

floods, mudslides, ice jams, high velocity flows, or erosion

• Areas where flood velocities adjacent to buildings is greater than 5 feet per second during the 

design flood

Requirements 

(Section 6.2.2)

Buildings shall be designed and constructed:

• So that any area below the applicable elevation specified in Table 6-1 is flood resistant with 

walls that are substantially impermeable to the passage of water

• To resist all flood related loads resulting from flooding to the elevation listed in Table 6-1, 

including hydrostatic, hydrodynamic, and other flood related loads, including the effects of 

buoyancy

• To have soil or fill adjacent to the structure compacted and protected against erosion and scour 

in accordance with ASCE 24, Section 2.4

• To have at least one door satisfying building code requirements as an exit door or primary 

means of escape above the applicable elevation specified in Table 6-1

Human 

Intervention 

(Section 6.2.3)

Buildings proposed to be dry floodproofed that require human intervention to activate or implement 

measures prior to flooding shall be permitted only if all of the following conditions are satisfied: 

• Minimum of 12-hour warning time, unless community operates a flood warning system 

and implements an emergency plan to ensure safe evacuation and the community can 

provide a minimum warning time to allow the implementation of measures requiring human 

implementation

• Removable shields or covers for openings must be designed to resist flood loads specified in 

Section 1.6

• Flood emergency plan must be approved by the authority having jurisdiction, shall specify 

certain information critical to implementation, and shall be posted in at least two locations 

within structure
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-15

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Section 6.3 and Commentary 6.3, Wet Floodproofing, in ASCE 24 specify design and construction requirements for wet floodproofing measures. Table 2-5 provides a list of general requirements for wet floodproofing. 

ASCE 24 Section 6.3 and Commentary 6.3 should be reviewed for more information on these requirements. 

Table 2-5. ASCE 24 Requirements and Limitations for Wet Floodproofing

ASCE 24 

Section Wet Floodproofing Requirements and Limitations

Limitations on use 

(Section 6.3.1)

• Wet floodproofing of enclosed areas below elevations listed in Table 6-1 shall be limited to: 

Category I structures (from Table 1-1, includes certain agricultural structures, certain temporary 

facilities, and minor storage facilities)

• Enclosures used solely for parking, building access or storage

• Structures that are functionally dependent on close proximity to water 

• Agricultural structures not included in Category I structures that cannot be located elsewhere 

and that are used solely for agricultural purposes

Requirements 

(Section 6.3.2)

Wet floodproofing shall be accomplished by:

• Use of techniques that minimize damage to the structure associated with flood loads

• Meeting the requirements for enclosures (Section 2.6 or Section 4.6) depending on the flood 

hazard area

• Installation of utilities, including plumbing fixtures, in conformance with the requirements of 

Section 7 (Utilities)

2.1.8 Additional Federal Guidance Documents

Two important Federal guidance documents on floodproofing are:

■ NFIP Technical Bulletin 3-93, NonResidential Floodproofing: Requirements and 

Certification for Buildings Located in Special 

Flood Hazard Areas in Accordance with the 

National Flood Insurance Program (FEMA 

1993a)

■ USACE’s Flood Proofing Regulations 

(EP 1165-2-314), a technical model for 

floodproofing-related regulations but not a 

regulation (USACE 1995)

FEMA’s Technical Bulletins provide guidance on 

complying with the minimum requirements of existing NFIP regulations on limited topics including 

non-residential floodproofing, wet floodproofing, 

flood damage-resistant materials, and elevators. The 

NFIP Technical Bulletin 3-93 provides step-by-step 

guidance on:

Terminology

Regulations and building codes establish the 

requirements that must be met. Guidance is additional information that may be useful to code 

officials and others who are responsible for interpreting, enforcing, and complying with regulations 

and codes. Guidance can also provide recommendations that are beyond the minimum requirements 

of building codes, standards or regulations.

Cross Reference

FEMA’s Technical Bulletins are available at: http://

www.fema.gov/national-flood-insurance-program-2/

nfip-technical-bulletins.

USACE’s Flood Proofing Regulations is available at:

http://publications.usace.army.mil/publications/engpamphlets/EP_1165-2-314/toc.htm.
2-16 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

■ NFIP regulations that apply to the design of floodproofing for non-residential buildings

■ Planning considerations (e.g., warning time, flood characteristics)

■ Minimum engineering considerations and equations for calculating flood forces

■ Preparing the Floodproofing Certificate for Non-Residential Structures (see Section 2.1.2) 

USACE’s Flood Proofing Regulations was among the earliest documents to provide an administrative and 

technical model for code design and enforcement and to present detailed information on implementing floodproofing techniques. It has served as the framework for the preparation of numerous other floodproofing 

publications. Flood Proofing Regulations pertains to riverine flooding and does not address wave action, corrosion, or erosion associated with coastal flooding, debris impact, mudslides, or high-density fluid problems.

2.2 Design Loads and Site Characteristics 

Floodproofing measures must ensure that buildings will be designed and constructed to resist flotation, collapse, and lateral movement associated with flooding. The loads and conditions discussed in this section 

include but are not limited to: 

■ Flood-related hazards such as hydrostatic 

and hydrodynamic loads, flood-borne debris 

impact loads, and internal and site drainage 

considerations

■ Site-specific soil and geotechnical 

considerations such as soil pressure, bearing 

capacity, land subsidence, erosion, scour, and 

shrink-swell potential

This section provides an overview of how these forces 

can act on a building. See FEMA P-259, Engineering 

Principles and Practices for Retrofitting Flood-Prone 

Residential Structures (FEMA 2012a) for more information on flood-related loads and conditions.

2.2.1 Identifying the Base Flood Elevation 

Determining the expected BFE is critical to understanding the site-specific flood risk. The flood zone and estimated BFE of a project area are identified using a FIRM panel. Flood hazard area boundaries on many FIRMs 

are delineated for the 1- and 0.2-percent-annual-chance (100-year and 500-year) flood. 

Figure 2-3 shows the location of a subject building on a FIRM. The area with blue dots is the 1-percent-annualchance (100-year) flood hazard area. The area with black dots is the 0.2-percent-annual-chance (500-year) 

flood hazard area. After the building is located on the FIRM, the flood profiles in the relevant Flood Insurance 

Study (FIS) should be used to verify the BFE and to determine the flood elevations for other modeled flood 

recurrence intervals. 

Cross Reference

For areas in which BFEs have not been 

established, designers can refer to FEMA 

265 Zone A Manual: Managing Floodplain 

Development in Approximate Zone A Areas

(FEMA 1995) (http://www.fema.gov/medialibrary/assets/documents/7273). This guide 

provides information on obtaining and developing BFEs.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-17

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Figure 2-3. Building and stream location on a FIRM 

Some FIRMs do not show the 0.2-percent-annual-chance (500-year) flood hazard area, and many FIRMs do 

not provide detailed information about predicted flood elevations along every body of water, especially smaller 

streams and tributaries. When existing data are insufficient, additional statistical methods and engineering 

analyses are necessary to determine the flood-prone areas and the appropriate characteristics of flooding. If a 

proposed or existing site has been affected or has the potential to be affected by flooding, a site-specific topographic survey is critical to delineate the land below the flood elevation. If detailed flood elevation information 

is not available, a floodplain study may be required to identify the important flood characteristics and data 

required for sound design.

2.2.2 Design Flood Elevation

The I-Codes, ASCE 7, and ASCE 24 define the design flood elevation (DFE) as “elevation of the design flood, 

including wave height, relative to the datum specified on the community’s flood hazard map.” The design flood 

is the “greater of the following two flood events: (1) the base flood, affecting those areas identified as SFHAs 

on the community’s FIRM or (2) the flood corresponding to the area designated as a flood hazard area on a 
2-18 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

community’s flood hazard map or otherwise legally designated.” Some communities use the DFE to refer to 

the BFE plus locally required additional height (usually referred to as “freeboard”). 

The I-Codes and ASCE 24 specify the elevation of buildings or the elevation of floodproofing measures based 

on the Occupancy/Risk Category of the building. All buildings are required to be assigned a category, which 

is then used in ASCE 24 to determine the level of protection. The more important the building, as indicated 

by the assigned category, the higher the level of protection. 

2.2.3 Determining the Flood Depth

The first step in determining the flood depth for a site 

is to identify the DFE that is specified by the building code or the floodplain management regulations 

that are enforced by the governing authority. The most 

common flood elevation used for design is the BFE. 

ASCE 24 requires some height of freeboard above the 

BFE, the amount of which is determined by the building occupancy. Local regulations and requirements 

should be compared to ASCE 24, and the most restrictive condition should be followed. 

Terminology 

Base flood elevation (BFE) – The elevation of the base flood relative to the datum specified on a 

community’s FIRM. The base flood has a 1-percent chance of being equaled or exceeded in any given 

year (commonly called the 100-year flood). BFEs are shown on FIRMs for many SFHAs. The BFE is 

the NFIP’s minimum elevation to which the lowest floor of a building must be elevated or floodproofed 

(Zone A). In Zone V, the bottom of the lowest horizontal structural member must be elevated to or above 

the BFE; floodproofing is not permitted in Zone V. Many SFHAs are shown on FIRMs without BFEs; in 

these areas, community officials and permit applicants are required to obtain and use information from 

other sources, or must estimate or develop BFEs at specific locations.

Freeboard – An added margin of safety, expressed in feet above a specific flood elevation, usually the 

BFE. In States and communities that require freeboard, buildings are required to be elevated or floodproofed to the higher elevation. For example, if a community adopts a 2-foot freeboard, non-residential 

buildings are required to be elevated or floodproofed to 2 feet above the BFE.

Design flood elevation (DFE) – The elevation of the design flood relative to the datum specified on 

the community’s FIRM. The design flood is associated with the greater of the area subject to the base 

flood or the area designated as a flood hazard area on a community flood map or otherwise designated. 

The I-Codes, ASCE 7, and ASCE 24 use the term DFE. In most communities, the DFE is identical to 

the BFE. Communities may designate a design flood (or DFE) in order to regulate based on a flood of 

record, to account for future increases in flood levels based on upland development, or to incorporate 

freeboard.

Cross Reference

The FEMA publication, Managing 

Floodplain Development through the NFIP, 

IS-9 (FEMA 2007a), provides guidance on 

determining flood elevations through flood 

profiles in the FIS. The document can be 

downloaded here: http://www.fema.gov/

media-library/assets/documents/6029.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-19

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

If NFIP compliance is not required (the building does not have to meet the requirements of Substantial 

Improvement/Damage), then the flood depth is based on the flood protection level selected by the owner or 

designer. On the other hand, if the building must be brought into compliance with the requirements of NFIP, 

the flood depth is equal to the BFE/DFE. 

The second step is to determine the expected elevation 

of the ground at the site. The expected ground elevation must account for any erosion, scour, subsidence, 

or other ground-eroding conditions that occur over 

time. Erosion is possible even in low-velocity flooding 

areas and can increase future flood hazards by lowering ground levels. Land subsidence is the lowering of 

the ground as a result of water, oil, gas extraction, soil 

consolidation, decomposition of organic material, and 

tectonic movement. The lowest expected ground elevation is determined by considering subsidence and 

erosion during flood conditions. 

In this publication, the flood depth (H) is defined as the difference between the flood protection level and the 

lowest eroded ground surface elevation (GS) adjacent to the building (see Equation 2-1). Because these data 

are usually obtained from different sources, determining whether they are based on the same datum is important. If not, standard datum corrections must be applied. 

H = DFE – GS

where:

H = flood depth (ft)

DFE = flood protection level or design flood elevation (ft) 

GS = lowest eroded ground surface elevation adjacent to the building (ft)

Equation 2-1. Flood depth

Determining the flood depth associated with the flood protection level is most important for load calculations. Nearly every other flood load parameter or calculation (e.g., hydrostatic load, hydrodynamic load, debris 

impact load, local scour depth) depends directly or indirectly on the flood depth. The flood depth is shown in 

Figure 2-4. For new construction or Substantial Improvement, if NFIP compliance is required, the flood protection level should be equal to the BFE/DFE.

Special Note

Subsidence effects can be estimated by 

lowering all existing ground elevations at 

the site by the product of the subsidence 

rate times the building lifetime. For example, if subsidence occurs at a rate of 0.05 

foot/year and the building lifetime is 50 

years, the profile should be lowered 2.5 

feet.
2-20 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

2.2.4 Determining Hydrostatic Loads

Hydrostatic pressures occur when floodwaters come into contact with a foundation, building, or building 

element. These pressures are always perpendicular to the building surface and increase linearly with depth or 

“head” of water below the surface of the water. Hydrostatic pressures can cause severe deflection or displacement of buildings or building components if water levels on opposite sides of the component (or inside and 

outside the building) are substantially different. Figure 2-5 shows equal and unequal hydrostatic pressures 

applied to the exterior of a building. Dry floodproofing results in unequal hydrostatic forces that must be 

accounted for in the floodproofing design. 

Figure 2-4. Flood depth
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-21

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Figure 2-5. Equal (A) and unequal (B) hydrostatic pressures applied to the exterior elements of a building; (B) 

shows the building protected by dry floodproofing methods applied

The sum of the pressures over the surface under consideration represents the load acting on that surface. For 

structural analysis, hydrostatic forces are defined to act:

■ Vertically upward on the underside of any submerged members such as floor slabs, walls, and footings

■ Laterally on perimeter walls, piers, and similar vertical surfaces

The basic equation for analyzing the lateral force from hydrostatic pressures from the flood depth to the lowest 

eroded ground surface elevation adjacent to the building is illustrated in Equation 2-2.
2-22 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

 fsta = 1⁄2PhH= 1⁄2 γ

w H 2 

where:

f

sta = hydrostatic force from flood depth (lb/lf) acting at a distance H/3 above ground

Ph = hydrostatic pressure due to standing water at a depth of H (lb/ft2), (Ph = γw H) 

γw = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) 

H = flood depth (ft)

Equation 2-2. Lateral hydrostatic forces

The resultant hydrostatic force f

sta acts at a point two-thirds of the distance down from the water surface or onethird the distance up from the bottom of the flooded or submerged surface.

If any portion of the building is below grade, saturated soil pressures must be included in the design load calculations. Saturated soil pressures include pressure from both the soil and water acting on the structure’s wall and 

are applied from the lowest adjacent grade of the building to the bottom of the flooded or submerged surface. 

Since the lateral hydrostatic force equation already calculates standing water pressures from the, bottom of the 

flooded or submerged surface a differential soil force equation must be used so that hydrostatic pressures are 

not accounted for twice in the load calculations. 

The differential soil forces (fdif) equation is calculated by subtracting the unit weight of water from the equivalent fluid weight of the saturated soil (a combination of the unit weight of water and the effective saturated 

weight of soil based on a conversion from lateral earth pressure derived from shear strength properties). The 

equivalent fluid weights of the submerged soil and water can be found in various design manuals, including 

Table 4-3 in FEMA P-259 (FEMA 2012a). 

When a structure is subject to hydrostatic forces from both saturated soil and standing water, the resultant 

cumulative lateral force is the sum of the lateral water hydrostatic force and the differential soil force. The basic 

equation for computing f

dif is illustrated in Equation 2-3. Although the differential soil force equation is not 

specifically site dependent, the equation is considered a more conservative approach for floodproofing design. 

Expansive or swelling soils may significantly increase lateral earth pressures and foundation heave pressures, 

and need to be evaluated separately and added to these cumulative forces. See Section 2.4.3 for discussion of 

procedures to evaluate these geotechnical behaviors.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-23

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

 fdif = 1⁄2(S – γ

w ) D 2 

where:

f

dif = differential soil/water force acting at a distance D/3 from the point under 

consideration (lb/lf) 

S = equivalent fluid weight of submerged soil and water (lb/ft3) (shown in Table 4-3 of 

FEMA 259)

D = depth of saturated soil from adjacent grade to the (bottom of the flooded or 

submerged surface ft) 

γw = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater)

Equation 2-3. Submerged soil and water forces

Figure 2-6 shows a building subject to hydrostatic forces from saturated soil and water. 

f

dif acts at a point D/3 where D is the distance 

from the adjacent grade to the bottom of the 

flooded or submerged surface.
2-24 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Figure 2-6. Hydrostatic forces acting on a foundation wall 

In a basement, vertical hydrostatic pressure acts on the bases of the foundation walls and on the concrete floor 

slab. The total vertical hydrostatic force that acts on the structure is the volume of floodwater displaced by the 

submerged structure multiplied by the specific weight of water.

Vertical hydrostatic forces on a structure, also known as buoyant forces, must be resisted by the weight of 

the building itself. When a building is too light to resist buoyancy, other opposing forces, such as those from 

ground or soil anchors, must be added. Buoyant or flotation forces on a building can be of great concern 

when the elevation of floodwaters on the exterior of a building exceeds the elevation of floodwaters inside the 

building. 

When a below-grade foundation or crawl space is backfilled with compacted structural fill that supports the 

floor slab, unbalanced lateral and vertical loads against the walls and foundation slab will be reduced. This is 

one way to help counteract the buoyancy forces during flooding. 

The basic equation for analyzing buoyancy forces is shown in Equation 2-4. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-25

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

 Fbuoy = γ

w (Vol)

where:

Fbuoy = vertical hydrostatic force resulting from the displacement of a given volume of 

floodwater (lb) 

γw = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater)

Vol = volume of floodwater displaced by a submerged object (ft3) 

Equation 2-4. Buoyancy forces

As noted in Equation 2-4, the specific weight of freshwater is 62.4 pounds per cubic foot (lb/ft3), while the specific weight of saltwater is slightly higher at 64 lb/ft3

. Both fresh and saltwater are relatively dense, so buoyant 

forces can be extreme. For example, the buoyant forces on a 24-by-36-foot foundation with 4 feet of freshwater 

flooding can be as high as 214,272 pounds (24 ft x 36 ft x 4 ft x 62 lb/ft3). Approximately 250,000 pounds of 

buoyant force will exceed the weight of all but the heaviest structures. It is assumed that the foundation walls 

and slab are substantially impermeable to the passage of water. Buildings with substantially impermeable basement walls and floor that have sump pumps to remove water that enters the basement can experience increased 

buoyant forces. When substantially impermeable buildings with below-grade areas are exposed to flooding, 

they can actually float on the floodwaters they displace. 

The computation of hydrostatic forces is vital to the successful design of floodwalls, sealants, closures, shields, 

foundation walls, slabs, and a variety of other dry floodproofing measures. Computation of these forces is illustrated in Sections 4.1.2.2 through 4.1.2.6 of FEMA P-259.

2.2.5 Determining Hydrodynamic Forces

Water flowing around a building, structural elements, 

and other submerged objects imposes loads on submerged building elements. These loads are known as 

hydrodynamic loads (see Figure 2-7). Hydrodynamic 

loads are a function of flow velocity and structural 

geometry and include frontal impact on the upstream 

face, drag along the sides, and suction on the downstream side. One of the most difficult steps in 

quantifying loads imposed by moving water is determining the expected floodwater velocity. 

Special Note

Sources of data for determining expected 

flood velocity include hydraulic calculations, 

historical measurements, Risk Mapping, 

Assessment, and Planning (Risk MAP) 

velocity data grids, and rules of thumb. If 

no data exist for flood flow velocity for a 

site, contact an experienced hydrologist or 

hydraulic engineer for estimates.
2-26 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Figure 2-7. Hydrodynamic and impact loads

For the purpose of this publication, floodwater velocity is assumed to be 5 feet per second (ft/sec) or less. 

ASCE 24, which is incorporated by reference in the 

IBC, states that dry floodproofing should be limited to 

areas where flood velocities are less than or equal to 5 ft/

sec during the design flood. The velocity of floodwater 

is also assumed to be constant (i.e., steady-state flow). 

Hydrodynamic loads can be calculated using Equation 

25.

Equation 2-5 provides the total hydrodynamic force 

against a building of a given surface area, A. Dividing 

the total force by either length or width yields a force 

per linear unit; dividing by surface area, A, yields a force 

per unit area.

Special Note

The 5 ft/sec velocity restriction for floodproofing is not a requirement of the NFIP 

but is used in USACE’s Flood Proofing 

Regulations (1995) in the design of structures exposed to water loads from stagnant 

or flowing waters. Although effective dry 

floodproofing can be designed for higher 

velocities, this is a reasonable existing limit 

that addresses safety of dry floodproofed 

structures during a flood. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-27

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

 Fdyn = Cd r A

where:

Fdyn = horizontal drag force (lb) 

Cd = drag coefficient (taken from Table 

2-6) 

r = mass density of fluid (1.94 slugs/ft3 

for fresh water and 1.99 slugs/ft3 for 

saltwater)

V = velocity of floodwater (ft/sec) 

A = surface area of obstruction normal 

to flow (ft2) = (w)(H) if the object is 

completely immersed

Equation 2-5. Hydrodynamic load

The drag coefficient used in Equation 2-5 can be found in the Shore Protection Manual, Volume 2 (USACE 

1984). Additional guidance is provided in Section 5.4.3 of ASCE 7. The drag coefficient is a function of the 

shape of the object around which flow is directed. When an object is something other than a round, square, or 

rectangular pile, the coefficient is determined by one of the following ratios (see Table 2-6): 

1. The ratio of the width of the object (w) to the height of the object (h) if the object is completely 

immersed in water, or

2. The ratio of the width of the object (w) to the flood depth of the water (H) if the object is not fully 

immersed

V2

2

Fdyn acts at a point H/2, half way 

between the water elevation and the 

eroded ground surface
2-28 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Table 2-6. Drag Coefficients for Ratios of Width to Depth (w/H) and Width to Height (w/h)

Width to Height Ratio (w/H or w/h) Drag Coefficient (Cd)

1–12 1.25

13–20 1.3

21–32 1.4

33–40 1.5

41–80 1.75

81–120 1.8

>120 2.0

Source: Shore Protection Manual, Volume 2 (USACE 1984)

Flow around a building or building element also creates flow-perpendicular forces (lift forces). When a building element is rigid, lift forces can be assumed to be small. When the element is not rigid, lift forces can be 

greater than drag forces. The equation for lift force is the same as that for hydrodynamic force except that the 

drag coefficient (Cd ) is replaced with the lift coefficient (Cl). In this publication, the foundations of buildings 

in low-velocity riverine areas are considered rigid, and since hydrodynamic lift forces for rigid foundations are 

assumed to be small, they can be ignored.

2.2.6 Determining Impact Loads

Debris impact loads are imposed on a building by objects 

carried by moving water. The magnitude of these loads 

is difficult to predict, but a reasonable allowance must 

be made for them in the design of floodproofing measures. Factors that affect debris impact load include size, 

shape, and weight of the waterborne object; flood velocity; velocity of the waterborne object compared to the 

flood velocity; duration of the impact; portion of the 

building to be struck; depth of flooding; and blockage 

upstream of structure. Detailed guidance, including an 

equation for calculating debris loads, first appeared in 

ASCE 7 Commentary; guidance can also be found in 

Section 4.1.2.9 in FEMA P-259 (FEMA 2012a) and 

Section 8.5.10 of FEMA P-55 (FEMA 2011c). Figure 

2-8 depicts normal impact loads for a structure. 

2.2.7 Interior Drain Systems

When floodwater surrounds a building or saturates surrounding soils, it has a high probability of seeping 

into the building through the exterior walls, foundations, and slabs. Interior drain systems for buildings are 

designed to keep water from accumulating in those interior below-grade areas. These systems do not require 

the soil to be excavated from around the exterior below-grade walls to install underdrains. 

Figure 2-8. Frontal impact from debris
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-29

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Sump pumps are perhaps the most familiar method of dewatering below-grade areas. The sump is generally 

constructed so that its bottom is well below the base of the floor slab. Water in the areas adjacent to belowgrade walls and floor migrate along the lines of least resistance, which should be 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 structure to follow. To achieve this, pipe segments are inserted and sometimes drilled through the below-grade wall and into the fill behind, purposefully allowing the interior to flood. 

Gravel is placed around the pipe segments on the exterior of the foundation wall to filter the surrounding soil, 

not allowing it to enter the interior of the building. The pipe segments are then connected to larger diameter 

pipes running along a gravel-filled trench or cove area into the floor slab and into one or more sumps (see 

Figure 2-9). 

Interior drain systems can be overwhelmed by a quickly rising water table and are subject to potential power 

outages.

Figure 2-9. Typical interior drain systems

In selecting a sump pump for use in floodproofing, 

the designer should consider the advantages of each 

pump type and make a selection based on requirements 

determined from the investigation of the building. 

Considerations include pump capacity (gpm [gallons 

per minute]), pump head (vertical height that the water 

is lifted), and electrical power required to operate the 

pump. Section 3.7 provides more detail on internal 

drainage systems design. 

Warning

Drilling holes around the interior floor slab 

and installing interior drains under the floor 

slab should be done in small segments. 

Cutting and replacing the perimeter of the 

interior floor slab in sections will prevent the 

foundation wall from rotating inward toward 

the interior of the building.
2-30 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

2.2.8 Determining Site Drainage for Floodwalls and Levees 

A floodwall is a freestanding, permanent, engineered structure designed to prevent encroachment of floodwaters. Levees are constructed with compacted soil. Levees are more common than floodwalls as flood protection 

for a single building or a limited number of buildings, but given the cost of levees compared to other flood 

mitigation measures and the amount of land they require, they are less common for a single building than 

many of the other floodproofing measures discussed in this publication. Nevertheless, a properly designed and 

constructed floodwall or levee can be effective as a barrier to inundation.

The drainage system for the area enclosed by a floodwall or levee must accommodate the precipitation runoff 

from the 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 (see Figure 2-10). Drainage systems may include pumps and holding ponds depending on the topography and layout of the site. 

Figure 2-10. Rectangular area enclosed by a 

floodwall or levee

To determine the amount of precipitation that can collect in the contained area, the rainfall intensity, in inches 

per hour, must be determined for a particular location. 

This value is multiplied by the enclosed area, Aa (in 

square feet), a terrain runoff coefficient (c), and a conversion factor of 0.01. The answer is given in gpm. See 

Equation 2-6. 

When determining rainfall intensity, it is recommended 

to consult with water resource specialists and hydrologists. Overdesigning site drainage is a relatively easy way 

to provide added protection, however an under-designed 

system will cause increased damage to a particular site. 

Warning

The rational equation is used to compute 

the amount of precipitation runoff from a 

given area. It has limited applicability and 

should only be used for areas that are 

200 acres or less. Some other constraints 

include: 

n The method should only be used for 

areas where rainfall is distributed 

uniformly. 

n The method does not account for storage in the drainage area.

n Rainfall intensity is assumed to be uniform throughout the duration of the 

storm.

Special Note

The terrain runoff coefficient, c, is used to 

model the runoff characteristics of different 

land uses. Use the value for the predominant land use in the subject area or develop 

a weighted average for areas with multiple 

land uses. The most common coefficients 

are 0.70 for residential areas, 0.90 for commercial areas, and 0.40 for undeveloped 

land.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-31

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

 Qa = 0.01cirAa

where:

Qa = runoff from the enclosed area (gpm) 

0.01 = factor converting the answer to gpm 

c = most suitable terrain runoff 

coefficient 

i

r = intensity of rainfall (in./hr)

Aa = area enclosed by the floodwall or 

levee (ft2) 

Equation 2-6. Runoff quantity in an enclosed area

Some levees and floodwalls extend only partially around a property and tie into higher ground (see Figure 

2-11). In such cases, the amount of precipitation that can flow downhill as runoff into the protected area, Aa, 

must be included. To calculate this value, the area discharging to the area partially enclosed by the floodwall or 

levee, Ab, should be estimated. This value is then multiplied by the previously determined rainfall intensity, i

r , 

by the most suitable terrain runoff coefficient, and by 0.01. See Equation 2-7.

When determining the minimum discharge size for pumps 

in enclosed areas, the designer 

should consider the impacts of 

the lag time between when the 

peak discharge is experienced in 

the enclosed area and the outfall 

to which it drains (i.e., inside and 

outside the enclosed area) and the 

storage capacity in the enclosed 

area after the gravity discharge 

system closes. If the designer is 

not familiar with storm lag time and 

the computation of storage in an 

enclosed area, the designer should 

consult an experienced hydrologist 

or hydraulic engineer.
2-32 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

 Qb = 0.01cirAb

where:

Qb = runoff from additional contributing area (gpm) 

0.01 = factor converting the answer to gpm

c = most suitable terrain runoff coefficient 

i

r = intensity of rainfall (in./hr)

Ab = area discharging to the area partially enclosed by the floodwall or 

levee (ft2) 

Equation 2-7. Runoff quantity from higher ground into a partially enclosed area

Seepage under or through the floodwall and levee along with the natural capillarity of the soil layer contribute 

to water inside the protected area. The water level inside the floodwall or levee increases as the depth of flooding outside the floodproofing structure increases and may compromise the effectiveness of the floodwall or 

levee for long-duration events if not addressed. The estimated seepage flow rates from the floodwall or levee 

vary depending on the site conditions and should be calculated by a geotechnical engineer or designer. Seepage 

rates may vary greatly with factors such as the depth of retained water and soil type.

The values for inflow in the enclosed area, runoff from uphill areas draining into the enclosure, and seepage 

through or under the floodwall/levee should be summed to estimate the minimum discharge size, Qsp, in gpm. 

See Equation 2-8.

Figure 2-11. Rectangular area partially enclosed by a 

floodwall or levee
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-33

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Qsp = Qa + Qb + Qc 

where:

Qsp = minimum discharge for pump installation (gpm)

Qa = discharge from an enclosed area (from Equation 2-6) (gpm)

Qb = discharge from higher ground to partially enclosed area (from Equation 2-7) (gpm) 

Qc = discharge from seepage through a floodwall or levee (gpm) 

Equation 2-8. Minimum discharge for pump installation

Important considerations in determining the minimum discharge size of a pump are the storage available in 

the enclosed area and the lag time between when the peak discharge is experienced in the enclosed area and 

the outfall to which it drains. Pumps continue to operate during flooding events (assuming power is constant 

or backup power is available), but gravity drains close when the floodwater elevation outside the enclosed area 

exceeds the elevation of the drain pipe/flap gate.

2.2.9 Understanding the All-Hazards Approach

In addition to flooding, a building might be subject to other hazards such as earthquakes, high winds, or tornadoes. The registered design professional should incorporate an all-hazards approach when selecting and 

designing floodproofing measures to avoid increasing the vulnerability of the structure, envelope, and systems 

to damage from other hazards. A mitigation measure that is appropriate for flooding, such as elevating a heavy 

chiller unit, may subject the building to greater seismic forces during earthquakes and increase vulnerability to 

damage unless the seismic hazard is accurately accounted for in the design.

Table 2-7 lists some FEMA resources with design guidance on mitigating damage to new and existing nonresidential construction for multiple hazards.
2-34 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Table 2-7. FEMA Resources on Design Guidance

Hazard Resource

Seismic • FEMA 232, Homebuilders’ Guide to Earthquake Resistant Design and Construction (2006)

• FEMA P-420, Engineering Guideline for Incremental Seismic Rehabilitation (2009)

• FEMA 454, Designing for Earthquakes: A Manual for Architects (2006)

• FEMA 547, Techniques for the Seismic Rehabilitation of Existing Buildings (2007)

• FEMA P-749, Earthquake-Resistant Design Concepts (2010)

• FEMA P-750, NEHRP Recommended Seismic Provisions for New Buildings (2009)

Tornadoes • FEMA P-320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small 

Business, Third Edition (2008)

• FEMA P-361, Design and Construction Guidance for Community Safe Rooms (2008)

High Winds • FEMA P-55, Coastal Construction Manual (2011)

• Protect Your Property from High Winds (2011); eight flyers

Multi-Hazard • FEMA P-424, Design Guide for School Safety in Earthquakes, Floods, and High Winds (2010)

• FEMA 543, Design Guide for Improving Critical Facility Safety from Flooding and High Winds

(2007)

• FEMA 577, Design Guide for Improving Hospital Safety in Earthquakes, Floods and High Winds 

(2007)

2.3 Other Flood Characteristics

Other flood characteristics of a site must be considered 

when determining whether dry floodproofing measures 

are best suited for a site. Flood characteristics that must 

also be considered include the duration of flooding, 

rate of floodwater rise and fall, and flood frequency. 

These flood characteristics not only indicate the 

expected nature of flooding in a given area, they can 

also be used to anticipate the performance of dry 

floodproofing measures based on the potential hazards 

associated with each flood characteristic.

2.3.1 Duration of Flooding

Duration is the measure of how long water remains 

above normal levels. The duration of riverine flooding is primarily a function of watershed size and the 

longitudinal slope of the valley (slope influences how 

fast water drains). Small watersheds are more likely to 

experience a rapid rise and fall of floodwaters. Larger, 

shallow, basin-like watersheds adjacent to large rivers 

may be flooded for weeks or months. 

Special Note

NFIP Technical Bulletin 2, Flood DamageResistant Materials Requirements (FEMA 

2008a), defines a “flood [damage]-resistant 

material” as “any building product [material, component or system] capable of 

withstanding direct and prolonged contact 

with floodwaters without sustaining significant damage.” “Prolonged contact” means 

at least 72 hours, and “significant damage” 

means any damage requiring more than 

cosmetic repair. 

An NFIP requirement is “building materials 

used below the BFE shall be resistant to 

flood damage (44 CFR §60.3(a)(3)(ii)).”
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-35

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Prolonged contact with floodwaters may make some mitigation measures, including dry floodproofing, 

inappropriate because of the increased chance of seepage and potential structural failure. Long periods of 

inundation are more likely to cause greater damage to structural members and finishes than short periods of 

flooding. Increased durations also result in a higher probability of floodwater accumulation and ultimately 

affects pump design for interior drainage. Designers should consider the duration of flooding when determining the applicability of selected building materials, pump design, and flood mitigation measures. 

2.3.2 Rate of Floodwater Rise and Fall

Steep topography and locations with small drainage areas may experience flash flooding, an event in 

which floodwater can rise very quickly with little or 

no warning. High-velocity water flows usually accompany flash floods and preclude certain types of flood 

mitigation measures, especially those requiring human 

intervention. 

If a building is susceptible to flash floods, insufficient 

warning time may make the timely installation of 

shields on windows, doors, and floodwalls and the activation of pump systems and backup energy sources impossible. Temporarily relocating movable contents to a 

higher level may also be impractical. Floodproofing is not appropriate for sites in flash flood areas because of 

the potentially short warning time. Active floodproofing measures (those requiring human intervention) may 

be effective if a building is not subject to flash flooding and the area has adequate flood warning systems.

Rapid rates of the rise and fall of floodwater can also lead to unequal hydrostatic pressures on a building. The 

probability of unequal hydrostatic pressures increases when building exteriors are designed to be watertight.

2.3.3 Flood Frequency

Flood frequency analyses define the probability that 

a flood of a specific size will be equaled or exceeded 

in any given year. A flood elevation with a 1-percentannual-chance flood of being equaled or exceeded in 

a given year is referred to as the “base flood,” commonly called the 100-year flood. Figure 2-12 illustrates 

the relationship between flood recurrence intervals 

and the probability of the event occurring within a 

given period. The probability that a base flood will 

be equaled or exceeded is 26 percent during a 30-year 

period. During a 70-year period (the potential useful 

life of many buildings), the probability increases to 50 

percent. Although the base flood serves as the basis for 

NFIP insurance rates and regulatory floodplain management requirements, the relative frequency of any 

Special Note

Although buildings are required to be 

protected only to the BFE for floodplain 

management purposes (to meet the NFIP 

regulations), protection to a higher level is 

necessary for the floodproofing measures 

to be considered for flood insurance rating 

purposes. It is possible to protect buildings 

from lesser flood events using dry floodproofing measures, but doing so will not 

bring buildings into compliance with the 

NFIP.

Warning

ASCE 24 does not permit the use of dry 

floodproofing for buildings in high-risk 

flood hazard areas. These include alluvial 

fan, flash flood, mudslide, erosion-prone, 

high-velocity, wave action, and ice jam and 

debris-prone areas. 
2-36 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

given flood (e.g., 2-year or 10-year) serves as a useful reference point when selecting a retrofitting option and 

evaluating cost effectiveness. 

2.3.4 Future Conditions

Designers should use past events and trends as an indication of the nature and severity of effects likely to occur 

during those forecast events. Information about past events at the site of interest and at similar sites should be 

considered. This historical information should be combined with knowledge about the site and local conditions to estimate future hazard effects on the site.

2.4 Site Factors

Site characteristics such as flood hazard boundaries, vulnerability to erosion or local scour, and geotechnical 

considerations play a critical role in determining applicable floodproofing measures.

2.4.1 Flood Hazard Boundaries

As discussed in Section 2.2.1, the boundaries of flood hazard areas are delineated on FIRMs, which are 

developed based on data described in FISs. Designers may use data from FIRMs and FISs to determine the 

boundaries of the various flood hazard areas, flood depth, flood elevation, and flood frequency for a given site. 

Figure 2-12. 

Relationship between 

flood recurrence 

intervals and the 

probability of an event 

occurring within a 

given period
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-37

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

In addition to the aforementioned flood characteristics that can affect buildings, site location in relation to 

the floodplain is also an important factor when considering dry floodproofing. Designers should note whether 

buildings are in or near the floodway, on the floodway fringe, near road crossings or other obstructions because 

these may divert floodwaters toward the site. 

2.4.2 Erosion

Erosion refers to the wearing or washing away of land and can occur in riverine as well as in coastal environments. Erosion is difficult to predict and is capable of threatening existing structures by lowering ground 

elevations, causing instability and failure in embankments, and transporting sediments landward or downstream. Erosion may also increase flood forces by increasing water depths. Erosion may be caused by natural 

actions such as flood-inducing storms and may be exacerbated by human actions such as constructing flood 

diversion or flood protection structures, dredging channels, damming rivers, and altering surface vegetation.

Riverine erosion affects the stability of stream banks and adjacent structures through the interaction of multiple geophysical and geotechnical factors. Variables that affect the stability (or erodibility) of stream banks 

include:

■ Slope

■ Critical height

■ Inclination

■ Cohesive strength of the soil in the slope

■ Level and variation of groundwater in the slope

■ Degree of stabilization of the surface of the slope

■ Level and variation in level of water on the toe of the slope

■ Distance of the structure in question from the shoulder of the stream bank

■ Shear strength of the soil

■ Frequency of rise and fall of the surface of the stream

Consideration of siting and the erodibility of land is critical when planning floodproofing projects because 

moving floodwater can undermine foundations and cause building, floodwall, and levee failure. Shallow 

foundation systems generally do not provide sufficient protection against soil erosion without some type of 

additional protection or armoring measure of below-grade elements. The local office of the Natural Resources 

Conservation Service has information concerning the erodibility of the soils native to a specific site, and community officials may have knowledge of local soil types and know whether erosion has occurred during past 

floods. 

The analysis of erosion impacts to stream banks and nearby structures is a detailed effort that is usually accompanied by detailed geotechnical investigations. 
2-38 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

2.4.3 Geotechnical Considerations

Site-specific soil properties are important factors in the design of any surface intended to resist flood loads. The 

properties include: 

■ Saturated soil forces

■ Allowable bearing capacity

■ Potential for scour

■ Land subsidence

■ Frost zone location

■ Permeability

■ Shrink-swell potential

The computation of lateral soil forces and determination of soil-bearing capacity are critical in the design of 

dry floodproofed foundations and walls. These forces and related geotechnical behaviors include a consideration of the frost depth, potential expansive or collapsible soils, or potential scour and erosion, and play an 

important role in selecting an acceptable foundation. Likewise, the permeability and compaction behavior of 

soils are key factors in selecting borrow materials for backfill, levee, or floodwall construction. For more information on these geotechnical issues, see Chapter 4 of FEMA P259 (2012a).

Site investigations for soils include surface and subsurface investigations. Surface investigations can identify 

the potential for landslides and evidence of areas affected by erosion or scour, determine accessibility for 

equipment needed for subsurface testing and construction, and help identify the suitability of a particular 

foundation type based on the performance of existing structures. Subsurface exploration provides invaluable 

data on soils below grade. The data are both qualitative (e.g., soil classification) and quantitative (e.g., bearing capacity). Subsurface exploration is complex and site-dependent. For example, testing for expansive soil 

requires assessing samples at various depths for plasticity, expansion index, and swell pressure to determine 

resulting swell forces under saturation conditions. Consultation with a geotechnical engineer familiar with the 

site is strongly recommended. 

2.5 Functional, Operational, and Economic Factors 

The functional, operational, and economic factors that should be considered when determining the appropriate floodproofing method for a building are:

■ Functional use requirements of the building (how the flood-prone portions of the building are used)

■ Occupant safety

■ Flood warning time

■ Flood emergency operations plan

■ Inspection and maintenance plan

■ Economic factors
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DESIGN CONSIDERATIONS IN FLOODPROOFING 2

2.5.1 Functional Use Requirements of the Building

The functions of non-residential buildings and whether active floodproofing measures (those requiring human 

intervention) can be used affect the types of floodproofing measures that are appropriate. For example, if a 

doorway that may be vulnerable to flooding is used by personnel and for freight delivery, permanently filling in 

the doorway is not feasible. Likewise, if extended interruption of function would be detrimental, floodproofing is not feasible because personnel should not occupy a building that is affected by floodwaters. Relocation 

may be a better option in this situation. 

The current and future use of buildings must be evaluated carefully when deciding to what degree access can 

be limited, determining how long the facilities can be closed during floods, and assessing whether the effects 

of events exceeding the design flood can be tolerated.

Use requirements that should be considered when deciding whether floodproofing is a good option for nonresidential buildings include but are not limited to:

■ Access requirements

■ Level and duration of business interruption that can be tolerated

■ Ability to accommodate flood damage repair

■ Ability to maintain dry floodproofing measures once implemented

Critical and essential facilities such as emergency operation centers, hospitals, and nursing homes may be 

floodproofed even if they are unoccupied during a flood event. Communities have an interest in protecting the 

contents of these facilities to minimize the downtime of such buildings and to ensure post-flood functionality. 

The protection and usage of critical and essential facilities may be vital to ensure an immediate response to the 

flood event and a rapid recovery. 

2.5.2 Occupant Safety

The relationship of floodproofing options to occupant 

safety must be evaluated in the pre-design phase. Safe 

access to and egress from floodproofed buildings is a 

critical factor in the determination of whether floodproofing measures that depend on human intervention 

are appropriate. 

If a floodproofed building is likely to be completely 

surrounded by floodwaters, provisions must be made 

for the evacuation of all occupants before the building 

is isolated. Evacuation is essential because it is possible that floods may exceed the design capacity of the 

floodproofing measures, which could result in extreme 

danger to any occupants who remain at the site. For 

events larger than the design event, specific additional 

emergency procedures should be developed. 

Special Note

NWS river forecast centers can be accessed here: http://water.weather.gov/ahps/

rfc/rfc.php.

The Advanced Hydrology Prediction Service (AHPS) offers data such as:  

n Flood forecast levels

n Probabilities of a river exceeding minor, 

moderate, or major flooding

n Chances of a river exceeding a certain 

level, volume, and flow of water 

n Maps of areas surrounding the forecast 

point likely to be flooded
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2 DESIGN CONSIDERATIONS IN FLOODPROOFING

If the proposed floodproofing measure is active (requires human intervention), all roads that provide access 

to the building should remain passable long enough for the floodproofing measures to be installed and for all 

personnel to safely evacuate the site. 

2.5.3 Flood Warning Time

Some floodproofing methods require adequate warning to be successful. The length of warning time required 

varies from a few hours to several days depending on the complexity of the floodproofing method. For flood 

warnings to be effective, they must be issued promptly, and the forecasts that inform the flood warnings must 

be accurate. 

A flood forecasting system should be able to determine 

when a flood is imminent and predict when specific 

areas will be flooded. Determining when and at what 

elevation the flood will crest may also be necessary. 

States and communities may have flood warning systems in place. Building owners should contact their 

local emergency management agency to determine any 

active flood warning systems in place.

River-flood forecasts are also prepared by National 

Weather Service (NWS) river-forecast centers and disseminated to the public by NWS offices. However, 

many non-residential buildings are located on smaller 

streams that are not included in a major forecasting 

network. In these areas, interested property owners 

can work with appropriate local and State agencies to 

develop an adequate flood forecasting system.

During periods of flooding, the NWS river-forecast 

centers issue forecasts of the height of the flood crest, 

the date and time when the river is expected to overflow its banks, and the date and time the flow in the 

river is expected to recede to within its banks. The U.S. 

Geological Survey and the NWS work together during 

a flood to collect and use the most up-to-date data and 

to update forecasts as new information is acquired. The 

NWS is also responsible for issuing flood and flash 

flood watches and warnings. The NWS conveys the 

data to other Federal agencies and to State and local 

agencies for use in flood management and disaster 

mitigation. 

State and local emergency management officials use the flood data to make informed decisions on how and 

when to evacuate their communities. Building owners and operators should follow the guidance of State 

Terminology

A flood watch indicates potential for 

flooding.

A flood warning means that flooding is 

imminent. 

Special Note

When removable shields are to be used, 

flood emergency plans must include: 

n Storage location for the shields

n Method of installation

n Conditions that activate installation

n Maintenance of shields and attachment 

devices

n Periodic practice of installing shields

n Testing sump pumps and other drainage measures

n Inspecting necessary material and 

equipment to activate floodproofing

Source: ASCE 24-05, Section 6.2.3
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DESIGN CONSIDERATIONS IN FLOODPROOFING 2

and local emergency management agencies, local weather reports, the NWS, or a local flood warning system 

regarding when to evacuate. The typical flood warning time should be considered when selecting a floodproofing measure.

2.5.4 Flood Emergency Operations Plan

Flood emergency operations plans are highly recommended for floodproofing methods. 

Plans should contain information on how floodproofing measures will work during and after the flooding 

event. For example, equipment such as sump pumps that require electricity will need to maintain power 

throughout the duration of the flood event. Maintaining power may require installing a generator and developing an operations plan for the generator to function during and after the flood event until power is restored. 

Maintaining power can be complicated by the fact that dry floodproofed areas should not be occupied during 

the flood event. Fueling and generator maintenance may require the generator to be located in an area above 

the desired level of flood protection. 

Preparation of plans is the responsibility of the building owner or operator. The design professional certifying 

the floodproofing project is solely responsible for how the measures resist flood loads and make the building 

watertight but should be consulted on the maintenance, testing, and inspection schedule of the project. 

A flood emergency operations plan should do the following: 

■ Establish a chain of command and assign responsibilities to each person involved in the installation 

and maintenance of the floodproofing measures. This will range from the authority to activate 

personnel through the duration of the event and restoration of the building to normal operations. 

The assigned personnel should not be assigned additional overlapping emergency duties to make 

sure that the floodproofing measures are installed in a timely manner and maintained. The chain of 

command should also take into account where assigned personnel live and their ability to access the 

site in an emergency. If key personnel are not available, a plan for succession of command and/or 

delegation of authority should also be covered. 

■ Delineate notification procedures for all personnel involved in the floodproofing operation. This 

includes details on making sure personnel can get to the building and enter areas of the building 

necessary to install the floodproofing measures. These areas include the floodproofed portion of the 

building and any storage facilities that house the flood shields and pumps. 

■ Assign personnel duties and include a description of the locations of floodproofing measures, 

installation procedures, and repair procedures. Instructions for each location should be posted close 

to the location.

■ Include evacuation instructions for all personnel who normally occupy the building, and for 

the personnel who have installed the measures, what to do after the floodproofing measures are 

accomplished. Evacuation routes should be posted in the floodproofed areas. Any doors necessary 

to exit the floodproofed area should be marked and should not be possible to lock in a manner that 

prevents egress from the floodproofed area.
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2 DESIGN CONSIDERATIONS IN FLOODPROOFING

■ Include a periodic drill and training program to make sure personnel clearly understand the procedures 

and timeliness by which they need to accomplish floodproofing measures and complete evacuation. 

Drills should be conducted at least once a year and coordinated with community officials. 

■ Include a schedule for regular evaluation and update of the flood emergency operations plan to 

reflect changes in personnel and procedures.

At a minimum, the plan should be posted in two clearly marked locations, but it is recommended that either 

the entire plan or relevant sections be posted close to every location where flood shields are to be installed. 

Requirements for the flood emergency operations plan are in FEMA’s NFIP Technical Bulletin 3-93 (FEMA 

1993a). 

Although flood emergency operations plans are not required for wet floodproofing and floodwalls/levee mitigation measures, plans should be considered a best practice to ensure the effectiveness of all flood mitigation 

measures.

2.5.5 Inspection and Maintenance Plan

An inspection and maintenance plan should cover both 

the maintenance of the floodproofing measures and 

periodic inspections of the components. Inspections 

should cover the entire floodproofing system, including the walls, floor slab, openings, flood shields, valves, 

drainage system, and any pump system. A list of repairs 

should be developed after each inspection and implemented as required. Maintenance procedures should 

not rely on the annual inspection for identification but 

should be part of routine operations of the building’s 

facility maintenance staff. Inspection and maintenance 

items include but are not limited to:

■ Wall systems, for cracks in the structural system or waterproofing coatings. Repair of cracks should 

be addressed immediately because ignoring them could result in significant structural damage to the 

building during a flood event.

■ Entire floor slab, to make sure settlement or other cracks have not appeared. Additionally, it is 

important to make sure the floor slab is able to provide drainage for any water that may leak into 

the building.

■ Openings, to clear debris trapped in the supports for flood shields, damage to permanently mounted 

hardware or gaskets, which would prevent proper operation of a flood shield.

■ Flood shields, for damage to attached gaskets, proper labels identifying the proper location, and 

damage to the actual shield, which might prevent it from performing properly. The inspection should 

include an inventory of shields and all the hardware required to properly install them.

■ Backflow valves or shutoff valves, to make sure they can properly operate and are clear of debris.

■ Drainage system and pump systems, to make sure there is no damage to piping or debris that would 

prevent the pipes from draining properly. Sump pits should be inspected and cleared of any sediment 

Special Note

Some communities require annual inspections of dry floodproofed buildings, 

especially if human intervention is required. 

Annual inspections lead to an increased 

awareness and effectiveness of floodproofing systems and also reduce concerns 

about liability. 
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DESIGN CONSIDERATIONS IN FLOODPROOFING 2

that may have built up. Switches and sump pumps should be inspected and tested to make sure they 

will run properly. If a generator is necessary for operation of the sump pump, it should be tested 

periodically to verify it will start and run during a flood event.

■ An inventory of flood emergency equipment, supplies, and required tools to ensure that all required 

items are available in the event of a flood. The inventory should include a listing of the tools and 

where they are stored. 

2.5.6 Economic Factors 

When floodproofing has been determined to be feasible considering regulatory requirements and the physical 

characteristics of the site and building, the most cost-effective floodproofing option can be identified. A BCA 

can be used to validate cost-effectiveness. BCA is a way to estimate the future benefits of a mitigation project 

and compare the benefits to the cost. The result of the analysis is a benefit-cost ratio (BCR), which is derived 

by dividing the project’s net benefits by the project cost. 

In a cost-effective project, the total cost of floodproofing (installation, operation, and maintenance) is less than 

the value of physical flood damage, lost earnings, and other economic impacts that are likely to occur if the 

structure is not floodproofed. The BCR is a numerical expression of the cost-effectiveness of a project. A project is considered cost-effective when the BCR is 1.0 or greater, indicating the benefits of a prospective hazard 

mitigation project are sufficient to justify the costs.

Benefits are defined as avoided damage, and a BCA estimate may not account for all of the potential benefits. 

Therefore, a BCR of less than 1.0 should not automatically remove dry floodproofing from consideration. 

The BCA described in Appendix B is used by FEMA to evaluate cost-effectiveness of projects under mitigation grant programs.

2.6 Building Vulnerability Assessments

For a building to remain functional during and following a natural hazard event, it must be undamaged, have 

sustained limited damage that does not prevent the 

building from functioning, or have sustained damage 

that can be readily repaired. Determining how well 

a building can withstand a natural hazard requires a 

building vulnerability assessment. 

A vulnerability assessment can identify weaknesses 

in a building’s structure, envelope, and electrical and 

mechanical systems. The assessment can determine 

which natural hazards the building can withstand as 

is and which mitigation opportunities are available to 

make the building more hazard resistant. 

Cross Reference

FEMA P-424, Design Guide for Improving 

School Safety in Earthquakes, Flood and 

High Winds (FEMA 2010a), contains checklists that can be used to assess a building’s 

vulnerability to these natural hazards. The 

manual is geared to schools, but the guidance is also appropriate for other facilities. 

The flood checklist in FEMA P-424 is provided in Appendix C. 
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2 DESIGN CONSIDERATIONS IN FLOODPROOFING

2.6.1 All-Hazards Vulnerability Assessment

The overall success of a building can only be achieved by identifying and managing natural hazard vulnerabilities. When mitigation measures for a flooding hazard are considered, an understanding of the other hazards, 

including frequency of occurrence of those other hazards, is important if the building is expected to perform 

as required by the owner. If other hazards are present that are likely to cause significant damage to the building 

and flooding is a relatively minor hazard, floodproofing alone may not be the best option.

The following should be completed and the results considered before the decision about floodproofing or other 

types of mitigation is made: 

■ Obtain the most up-to-date published hazard 

data to assess the vulnerability of the subject 

site

■ Conduct or update a detailed risk assessment 

if there is reason to believe the physical 

site conditions have changed significantly 

since the hazard data were published or the 

published hazard data are not representative 

of the subject site

■ Review or revise an existing risk assessment 

if there is reason to believe the physical site 

conditions will change significantly over the 

expected life of the building

■ Ask the designer to review options that will 

mitigate the effects of any identified hazards 

in addition to the flooding risk after a risk 

assessment has been completed

2.6.2 Structural Condition Assessment 

Assessing a building’s vulnerability to flood involves 

identifying structural components that could fail when 

exposed to flood forces and structural components 

that could degrade or deteriorate when inundated 

with floodwaters. Structural degradation is much 

more of a problem in residential construction where 

wood framing is more prevalent than in non-residential construction. Structural degradation in commercial 

or industrial facilities is typically much less of a concern because the structures are usually built with steel, 

masonry, concrete, or other materials that offer inherent resistance to damage from floodwater inundation. 

Interior and exterior finishes in commercial and 

industrial buildings, however, may be vulnerable to 

Special Note

In structural engineering, there are two 

approaches in design and analyses: ASD 

(Allowable Stress Design) and LRFD 

(Load Resistance Factor Design). ASD is 

the older approach but is still widely used 

in wood, steel, and masonry design. LRFD 

is the newer approach. It is used almost 

exclusively in concrete design and frequently in steel design. Provisions for LRFD 

have been recently added to codes and 

standards governing wood and masonry 

design. 

In ASD, service loads are applied to a 

structure, and the resulting stresses that 

the service loads create are calculated. 

The calculated stresses are compared 

with the maximum allowable stress for 

each component in the structure. Allowable 

stresses are determined by applying factors of safety to ultimate stress (typically 

stress at failure). If the calculated stresses 

from service loads are less than the allowable stresses, the design is acceptable. 

In LRFD, the service loads are increased 

by load factors, and the ultimate strength of 

a structure is reduced by resistance factors. 

If the factored loads are less than the factored strengths, the design is acceptable. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-45

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

degradation from floodwater inundation because they are not often constructed with flood damage-resistant 

materials.

Assessing a building in two stages is recommended. First, a preliminary assessment is completed to help determine the overall feasibility of flood mitigation. The preliminary assessment is often based only on a visual 

examination of the building and, when available, a review of construction drawings. The depth of floodproofing desired can also be determined in the preliminary assessment. 

If the preliminary assessment suggests that flood mitigation is possible, the next stage is to perform additional 

site and drawing reviews and conduct testing and analyses to confirm that flood mitigation is feasible. A 

detailed assessment requires accurate drawings of the building or, if drawings are not available, invasive testing 

to determine the structural aspects and condition of the building. Soil tests to determine the type and permeability of soils onsite may also needed.

The loads for the proposed dry floodproofed area must then be determined. Load determination is discussed 

in Sections 2.2.4 through 2.2.6. When the loads are determined, the next step is to evaluate all portions of 

the building to assess its ability to withstand flood loads created by dry floodproofing without floatation, collapse, or lateral movement. All building components below the flood level may be exposed to flood loads, 

and portions of the building above the flood level can be exposed to flood loads (particularly buoyant forces) 

that translate through the building’s structure. At a minimum, foundation walls, the connections between the 

foundation walls, and the floor slab below and structure above, and the floor slabs themselves should be evaluated. Figure 2-13 shows the major building components that are often exposed to flood loads. 

Identifying structural vulnerabilities to floods involves quantifying the loads a flood will apply to a structure 

and the resistance the structure has to resist the loads. For a building’s structure to withstand a flood, its structural components must be adequate to resist the applied flood loads without being overstressed (Allowable 

Stress Design [ASD]) or without the ultimate strength of the structural components being exceeded when 

exposed to factored flood loads in Load Resistance Factored Design (LRFD).

Figure 2-13. Basic 

building components 

exposed to flood loads
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2 DESIGN CONSIDERATIONS IN FLOODPROOFING

The walls should be inspected to verify that they are vertically plumb and that no bowing exists. An out-ofplumb wall can result from excessive pressure at the top or bottom of the wall. A bowed wall can result from 

excessive bending in the wall. 

Concrete and masonry walls should also be checked for staining, which can result from corrosion in the reinforcing steel. If steel has extensive corrosion, its tensile strength or the strength of the bond from the steel to the 

concrete or masonry can be reduced, and the strength of the wall can be compromised. Staining can also result 

from water being in frequent contact with the walls, which may suggest that the soils are permeable enough to 

allow even short-duration floodwaters to expose the walls to hydrostatic loads. 

Bowing, lateral movement, corrosion, staining, and evidence of frequent water entry all may indicate that the 

building is not an ideal candidate for dry floodproofing. 

Once the preliminary assessment confirms that the foundation walls are free of evidence of existing structural 

problems, a determination must be made regarding the feasibility of strengthening them to resist flood loads 

from a design event. Except when a design flood will produce only a low level of flooding (about 2 feet), some 

wall strengthening will likely be required. The feasibility of ensuring the walls can be made to resist flood loads 

is typically done during subsequent evaluations when the details of the wall construction (thickness, height, 

reinforcement, and connection details) are known. 

Walls can be strengthened with steel beams or grouting (concrete masonry unit [CMU] walls) or by overlaying fiber-reinforced polymers or carbon fiber strapping systems composed of sheets or strips that form a grid 

across the wall. How the wall system will be floodproofed is important to consider before selecting a system 

to improve the wall strength. If the waterproofing or sealant is to be applied on the same wall face as the wallstrengthening retrofit, the two measures need to be compatible. 

Floor slabs should be evaluated in a manner similar to the wall system. As-built drawings are a good place to 

begin evaluating the slab, but it is likely that some field investigations will need to be done in order to ascertain the true properties of the slab. The initial evaluation should include any deficiencies in the floor slab that 

need to be addressed before correcting the floor slab to resist buoyancy forces. Issues such as settlement in 

the concrete slab may present retrofitting challenges if not properly corrected (see Figure 2-14). The reason 

for cracking in the slab is important to identify. Cracks may occur from soil expansion, soil contraction, or 

washing out of soils. Soils can wash out if underdrain lines were not properly installed when the building was 

constructed. On large commercial slabs where equipment such as forklifts are used, joints in the concrete slab 

should be checked to ensure that the slab has not rocked and created a void below the joints.

When the floor slab has been evaluated, the soil under the slab should be assessed to determine whether it may 

present problems under flood conditions. Some soils have low permeability and are slow to become saturated 

by floodwaters while highly permeable soils may become saturated quickly and need to be drained. Highly 

permeable soils may require installing underdrain lines, which should be sized for flood conditions. 
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DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Per NFIP requirements, dry floodproofing measures 

must be designed to meet the minimum requirements 

of being substantially impermeable, and these requirements assume there is no sump pump. For additional 

protection, the NFIP requires the installation of a sump 

pump when dry floodproofing is used as a retrofit technique, despite substantially impermeable requirements. 

See Section 3.7 for information on internal drainage 

systems. Whether or not underdrain lines are installed, 

the slab should be examined to determine the thickness and size and location of the slab reinforcing steel. 

This examination may require some destructive testing 

because slab reinforcing steel is usually small diameter 

wire mesh, which is difficult to detect.

Unless designed to support heavy equipment, slabs generally cannot resist hydrostatic forces if water is allowed 

to accumulate beneath them because floor slabs are typically designed to resist dead loads applied from above 

when they are continuously supported by soils below. Most soil supported slabs, if reinforced, have reinforcement designed primarily for controlling thermal and shrinkage cracks. Reinforcement for controlling 

shrinkage and thermal effects alone is inadequate to enable the slabs to function as beams exposed to negative 

(upward) bending from buoyancy. If the reinforcing steel is too low to provide uplift resistance in the slab section, the slab will need to be retrofitted. If the slab is imagined as a beam, the reinforcing steel should be placed 

on the opposite side of the beam from the applied load or in the side of the slab in tension. Slabs supported 

by soils also lack positive connections that prevent the slabs from being lifted because they rely only on their 

self-weight to avoid being displaced vertically. 

Figure 2-14. Significant 

differential settlement 

in the foundation 

causing slab failure

Special Note

Even in buildings that are designed to be 

substantially impermeable, sump pumps 

are required to control seepage, and 

flood damage-resistant materials, which 

are described in FEMA Technical Bulletin 

2, Flood Damage-Resistant Materials 

Requirements (FEMA 2008a), must be 

used in all areas where seepage is likely 

to occur.
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2 DESIGN CONSIDERATIONS IN FLOODPROOFING

Although concrete can be added to thicken slabs (and increase their resistance to uplift strictly by increasing their weight), it is typically impractical to mitigate slabs to resist buoyant forces. If water can accumulate 

under a floor slab and installing underfloor drains cannot alleviate hydrostatic pressures acting to lift the slab, 

the building may not be a candidate for dry floodproofing. The only other mitigation technique that could be 

used to resist buoyancy on a concrete slab is to install soil anchors through the slab into the soil beneath the 

slab to provide upward resistance.

In addition, buoyant forces acting on submerged materials reduce their effective dead load and ability to resist 

uplift and overturning moments. Therefore, before dry floodproofing projects are undertaken, the overall stability of a building needs to be checked to ensure that buoyant forces will not make the building unstable. 

The load combinations contained in Chapter 2 of ASCE 7 should be used to evaluate the stability of the dry 

floodproofed building.

The deficiencies in the slab and the normal use of the floodproofed area are important considerations in selecting a retrofitting measure. If the area requires equipment to drive across the slab or maintenance crews to work 

in the area, maintaining a flat, unobstructed slab may be important. Similarly, maintaining the existing ceiling 

height may justify other retrofitting considerations.

The condition assessment should not only determine the ability of structural components to withstand flood 

loads, but also their impermeability. For example, basement walls between adjacent buildings should be evaluated for flood load resistance and impermeability. This is especially important in an urban environment or 

in buildings constructed in phases; otherwise, the source of flooding may become the adjacent building. 

Structural components, window wells, ventilation openings, and utilities (discussed in the subsequent section) 

can each be floodwater points of entry if not properly assessed and mitigated. 

2.6.3 Vulnerability Assessments for Electrical and Mechanical Utilities and Systems

Utility and system assessments can determine how well the utilities that serve a facility and the major mechanical, electrical, and plumbing (MEP) systems in a facility can resist natural hazards. Although utilities and MEP 

systems can be damaged by high winds, seismic events, and winter storms, this discussion is focused on their 

vulnerability to flooding. In a discussion of system vulnerabilities, it is beneficial to distinguish utilities from 

systems components. Utilities are generally external to the building, while most mechanical and electrical systems are internal. Although utilities themselves can be vulnerable to flooding, this document focuses primarily 

on the vulnerability of buildings associated with utilities when they acts as conduits and allow floodwaters to 

enter a building. 

Utilities can be electrical or mechanical. Electrical utilities typically include power, communication (both copper-based and fiber-optic), and occasionally hard-wired annunciation systems such as fire alarm loops. This 

document focuses on electrical power utilities. Mechanical utilities include domestic water service, water service for fire suppression, steam service, and utilities to collect and dispose of sanitary sewer and storm sewer. 

In many municipalities, fossil fuels, namely natural gas, are also brought to buildings. Utilities can be private 

or municipal and can be part of a campus, which is the case when a group of buildings are supplied by a central plant. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-49

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

Electrical utilities are often described as “dry utilities,” and mechanical utilities are often described as “wet 

utilities.”

Electrical systems include power distribution, controls, lighting, fire alarm, telephone, and IT (information 

technology). Mechanical systems include heating, ventilation, and air conditioning (HVAC); domestic water 

systems; drain, waste, and vent systems; smoke control systems; fuel storage and distribution systems; and fire 

suppression systems. Figure 2-15 shows common locations of these systems in buildings.

2.6.3.1 Utilities General

Utilities often enter a building below grade. In areas where groundwater levels are high and in areas vulnerable 

to flooding, all utility penetrations are potential sources of water entry. 

In assessing the vulnerability of water entry through utilities, consider the following questions:

■ The sealing of penetrations: When utilities enter the building, are the spaces around the conduits and 

pipes properly sealed to prevent water entry? 

■ The sealing of conduits: When conduits enter a building, are the spaces between cables within the 

conduits sealed to prevent water entry?

■ Backflow prevention: For wet utilities, are measures in place to prevent floodwaters from entering the 

building through piping systems?

■ Utility trenches: Are utility trenches provided with submarine doors or other methods that will 

prevent floodwaters from migrating between buildings?

2.6.3.2 Electrical Utilities

Electrical utilities may be overhead or underground. Overhead utilities are inherently resistant to damage from 

a design flood unless they are located below the DFE. When designed for submerged installations, the buried 

portions of underground electrical utilities are also generally resistant to flood damage, but above-ground components of underground electrical utilities such as below-grade electrical vaults, pad-mounted transformers, 

pad-mounted switchgear, and electrical substations can be damaged by floods when located below the DFE.

Figure 2-15. Typical 

systems in buildings
2-50 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

2 DESIGN CONSIDERATIONS IN FLOODPROOFING

The following list summarizes the components of electrical utilities that may be damaged by flood inundation 

when located below the DFE. These components should be considered when assessing flood vulnerabilities 

associated with electric utilities.

■ Electrical substations

■ Pad-mounted transformers and other pad-mounted equipment (switchgear)

■ Live-front electrical equipment (i.e., equipment with exposed energized terminations) in underground 

manholes

■ Cable terminations and splices not designed for submerged conditions

■ Underground transformer vaults

■ Meter centers

■ Electrical service equipment (switchboards in larger facilities, service panels in smaller facilities)

■ Network interface devices for communication utilities

■ Fire alarm master boxes below the DFE

2.6.3.3 Mechanical Utilities

Pressurized mechanical utilities such as domestic water services, fire suppression service, and fossil fuel services 

are generally resistant to flooding. Some vulnerability to floodwater inundation may exist in above-ground 

equipment such as pressure regulators and utility meters for natural gas lines. Occasionally pressurized systems 

rely on electrically driven pumps to maintain system pressure. These systems can become vulnerable to floodwater contamination if power is lost to electrically driven pumps. When system pressure is lost, pressurized 

systems are often assumed to be contaminated, and “boil water before use” orders are given until the system 

pressures can be restored and the systems can be decontaminated or disinfected.

Non-pressurized mechanical utilities such as gravity-draining sanitary sewers and gravity-draining storm 

sewers generally are not damaged by slow-moving or riverine flooding. However, they can become conduits 

that allow floodwaters to flow into a facility. Backflow prevention devices can reduce the potential for floodwaters entering facilities through non-pressurized utilities. These devices, which are essentially check valves that 

allow flows only in one direction, require periodic maintenance and testing to ensure they are functional and 

will not obstruct normal flows. 

2.6.3.4 Electrical Systems

Nearly all electrical systems in a facility below the DFE are vulnerable to flooding. Electrical wiring, communication equipment, fire alarm and security systems, and other electrical equipment are inherently vulnerable to 

inundation unless specifically designed for submerged applications, and few electrical devices used in buildings 

are designed to be submerged. Conduit systems should not be considered watertight, and although the exterior 

sheaths of some electrical cables can resist water infiltration, they should not be considered 100 percent effective unless designed and installed for submerged applications. Sump pumps, underwater lighting fixtures, and 

some sensing devices or transducers are possible exceptions, but these devices account for only a small percentage of the electrical equipment in a typical facility.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 2-51

DESIGN CONSIDERATIONS IN FLOODPROOFING 2

2.6.3.5 Mechanical Systems

The vulnerability of mechanical systems to damage from flooding varies greatly. Pressurized piping such as 

domestic water systems, chilled water piping systems, and hot water piping systems can generally be exposed 

to flood inundation without significant damage. When flooding is saltwater flooding or when floodwaters are 

corrosive, piping systems may need to be cleaned to prevent degradation. In pressurized systems, pumps and 

controls can be damaged from floodwaters unless designed for submerged use.

Pipe insulation, particularly insulation that is not closed-cell foam, typically needs to be replaced after inundation. Any pipe insulation below the DFE should be considered vulnerable to flooding unless it is closed-cell 

foam.

Forced-air distribution systems are particularly vulnerable to flood damage. The ducts are designed for air pressures that are typically measured in inches or fractions of inches of water column and cannot resist hydrostatic 

pressures from even small depths of floodwaters. Also, duct systems are rarely watertight, and floodwaters can 

enter ducts, saturate internal insulation, contaminate duct systems, and lead to the formation of molds and 

mildews that can significantly affect air quality. When contaminated, it is often more practical to remove and 

replace submerged ducts system than to try to clean them particularly with insulated duct systems. Any ducts 

below the DFE should be considered vulnerable to flooding.

Floodwaters may also enter exhaust vents that remove stale air from a building’s interior and intake vents that 

provide fresh make-up air. Water can flow into clothes dryer vents and bathroom or kitchen exhaust vents if 

the floodwater is higher than the exit locations on the building.

Boilers, chillers, domestic water heater, booster pumps, and HVAC controls are rarely designed for submerged 

installation and will be damaged by floodwater inundation.

Fuel distribution and storage systems can be vulnerable to flooding. Although fuel distribution piping is a 

closed pressurized system that is able to resist relatively high external and internal pressures, fuel tanks are 

much less so and can be damaged by floodwaters. Fuel tanks are typically designed to resist only internal pressures that result from the weight of the fuel stored within them and from filling operations. Tanks, unless 

specifically designed for submerged conditions, can fail when exposed to the external pressures that result from 

floodwater inundation. Tank failures can result from crushing pressures, which increase with the depth of 

inundation, and from anchorage failures, which increase with the amount of floodwater displaced by the tank. 

During Hurricane Sandy, many tanks located below grade were damaged when floodwaters filled basements. 

All tanks below the DFE should be considered vulnerable unless they are designed to resist crushing pressures 

and anchored to resist buoyancy. 

In addition, fuel tanks are often located on the lowest floor of a building and pumps are installed to pump 

fuel to equipment, such as emergency generators, located on upper floors. When pumps are located below the 

DFE, they can be vulnerable to flooding. During vulnerability assessments, fuel pumps located below the DFE 

along with their power and control wiring should be considered vulnerable unless designed for submerged use.

FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-1

T he purpose of dry floodproofing a building is to 

make it watertight to floods of limited duration 

(a few hours) and depth (typically less than 3 

feet). Dry floodproofing reduces the potential for flood 

damage by reducing the probability that the building 

interior will be inundated. It can be an appropriate alternative for flood mitigation when relocating or elevating 

buildings is not cost-effective or technically feasible.

The minimum performance requirement for dry floodproofing measures is a space that is protected by walls 

that are substantially impermeable and resistant to flood 

loads. As noted in Section 1, a substantially impermeable 

wall should limit water accumulation to a maximum 

accumulation of 4 inches in a 24-hour period with a sump pump to control seepage (USACE 1995). However, 

the minimum performance requirement can be exceeded with proper planning, design, and materials. 

Incorporating flood damage-resistant materials into the dry floodproofing design up to the height of the dry 

floodproofing measure is recommended. Additionally, building systems such as walls and foundations may 

need to be strengthened to withstand direct flood forces and the loads imposed by floodproofing measures 

(e.g., shields, watertight doors), which are used to temporarily seal openings. 

An effective dry floodproofing retrofit requires the following:

■ Detailed site evaluation (see Section 3.1.2)

■ Detailed building evaluation (see Sections 2.6.2 and 2.6.3)

■ Careful evaluation of all of the dry floodproofing measures (see Sections 3.2 through 3.7), including 

a consideration of residual risk (see Section 1.3)

■ Design by a qualified registered design professional

■ Verification/testing that the constructed systems provide the desired floodproofing effectiveness

■ Floodproofing Certificate for Non-Residential Structures for the dry floodproofing design (see 

Section 2.1.2)

■ A plan for deploying any active dry floodproofing measures that require human intervention (see 

Section 2.5.4) 

■ Sufficient warning time to deploy active dry floodproofing measures and vacate the building

■ Operations and maintenance plan (see Section 3.8)

Dry Floodproofing 

Measures

Special Note

FEMA strongly encourages that flood retrofits provide protection to the DFE (the 

community’s regulatory DFE). However, 

in some situations, lower flood-protection 

levels may be appropriate. Owners and 

design professionals should meet with a 

local building official to discuss the selected retrofit measure and the elevation to 

which it will protect the building. 
3-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

Chapter 3 begins with a discussion of the design considerations for dry floodproofing projects followed by a 

discussion of the types of dry floodproofing measures, as follows:

■ Continuous impermeable walls. Sealing the building’s exterior walls using technologies that 

include impermeable waterproof membranes and potentially strengthening those walls

■ Flood resistance in interior core areas. Critical core components and areas can be made flood 

resistant when dry floodproofing the entire building footprint is not needed or possible 

■ Sealants for openings. Protection of the building depends on sealing openings, such as doors, 

windows, and utility penetrations, and sealing walls and slabs, which are rarely designed to be 

watertight or resist flood loads

■ Flood shields for openings in exterior walls. Watertight structural systems that close the openings 

in a building’s exterior walls to the entry of water

■ Backflow valves. Prevent floodwater flow into the building because of blockages in the sewage 

system 

■ Internal drainage systems. Primary method of removing water that may seep through small fissures 

and pathways in the protection system 

Table 3-1 compares dry floodproofing retrofit measures to other flood mitigation retrofit measures. 

Table 3-1. Advantages and Disadvantages of Dry Floodproofing Retrofits Compared to Other Flood Mitigation 

Retrofit Measures

Advantages Disadvantages

• May be less costly than other retrofitting methods

• Does not require the land that may be needed for 

levees and floodwalls

• May be fundable under FEMA mitigation grant 

programs

• May be used to bring Substantial Improvement/

Damage non-residential structures into compliance 

with the community’s floodplain management 

regulations and codes

• Can be used to protect against more frequent flooding 

even if it is not cost-effective to floodproof to the BFE/

DFE

• Active dry floodproofing measures require human 

intervention and adequate warning

• Does not always minimize the potential damage from 

high-velocity flood flow or wave action

• Requires ongoing maintenance

• Flood shields may not be aesthetically pleasing (see 

Section 3.5)

• Potential failure of the structure’s walls and/or property 

damage if the flood event is greater than the level of 

protection to which the dry floodproofing measure was 

designed

3.1 Design Considerations for Dry Floodproofing Projects

Chapter 2 covers several planning and design issues that must be considered in a dry floodproofing project, 

including flood warning time, structural evaluation, and flood hazard evaluation. Because of the importance 

of these topics in relation to dry floodproofing, they are briefly revisited in Section 3.1.

3.1.1 Flood Warning Time

Installing active dry floodproofing measures, which require human intervention, takes time and requires 

sufficient warning. Active dry floodproofing measures are therefore not appropriate if the warning time is 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-3

DRY FLOODPROOFING MEASURES 3

insufficient. For example, dry floodproofing is not appropriate in areas where floodwaters are known to rapidly 

rise, such as where flash flooding is common, because the rapid rise in water gives little or no warning time to 

install active measures. See Section 2.5.3 for additional information regarding flood warning time. 

Building owners should rely on the community flood warning system unless there is easy access to NWS flood 

predictions (such as estimates of stream gage heights) and the owner knows how to compare that information 

to the building elevation. A plan based on the warning time provided by community flood warning system can 

be developed to ensure that there will be sufficient time for:

■ Personnel responsible for installing dry floodproofing measures to travel to the building and install 

the measures

■ Proper activation of all necessary floodproofing measures, which can include installing flood gates 

and shields, activating sump pumps, and closing manual valves

■ Evacuation of the building and evacuation of personnel responsible for installing the floodproofing 

measures before the onset of flooding

The amount of time needed to install the measures depends on available personnel and the number of steps in 

the installation. See Sections 2.5.4 and 3.8 for more information on what the plan should include.

3.1.2 Site and Building Evaluation

The site and building need to be evaluated to determine whether dry floodproofing is appropriate. The site 

investigation will determine if the existing building can be cost-effectively retrofitted by looking at flood conditions needed to calculate the flood loads, such as depth of flooding and flood velocity. The site investigation 

will also determine whether the existing soil conditions and any existing fill under or around the building 

could resist scour and erosion during a design flood event. 

The building should be evaluated by a structural engineer to determine whether the exterior wall and floor 

systems can resist the forces generated by the design flood event. Flood loads can cause wall systems to fail, 

possibly resulting in structural damage that is more severe than damage from inundation. A primary design 

consideration in dry floodproofing is therefore the determination of the ability of the foundation, floor system, 

and exterior walls to withstand the forces generated by the design flood event. If the building strength is found 

to be inadequate, decisions must be made about how to achieve the desired level of performance. Options 

include strengthening the existing wall systems or other types of mitigation (e.g., elevation, acquisition, mitigation reconstruction). The costs and obstacles associated with retrofitting an existing building to resist flood 

loads may indicate that other floodproofing measures are more appropriate. See Sections 2.4 through 2.6 for 

additional factors related to the site and building evaluation.

3.1.3 Building Standards and Codes

Section 2.1 covers a range of dry floodproofing regulatory requirements that vary based on which codes are in 

place in the project’s jurisdiction. For example, some, but not all, jurisdictions require dry floodproofing to be 

designed and constructed in compliance with ASCE 24. Although most of the ASCE 24 requirements outlined 

in Chapter 2 were developed for new construction and may be required only for Substantial Improvement/

Damage, ASCE 24 requirements should be considered in all dry floodproofing projects. 
3-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

ASCE 24 should be relied on to determine the flood protection level and elements of a properly constructed 

dry floodproofed building. Utilities should meet the requirements in Section 7 of ASCE 24 to place utilities 

outside the dry floodproofed area either above a specified elevation or to be designed to resist flood loads to 

prevent the intrusion of floodwaters.

If required, Section 6 of ASCE 24, which provides minimum floodproofing elevations (see Table 3-2) can be 

used for determining the flood protection level of the dry floodproofing retrofits. Any critical core components 

or other building areas not protected by the dry floodproofing measure should be elevated to the applicable 

elevation specified in ASCE 24.

Table 3-2. ASCE 24 Structure Categories and Minimum Floodproofing Elevation in Zone A

ASCE Structure Category(a) Minimum Floodproofing Elevation (Zone A)

I, II, and III BFE + 1 foot or DFE, whichever is higher

IV BFE + 2 feet or DFE, whichever is higher

Source: ASCE 24-05

(a) See Section 1.6 for information on the ASCE structure categories

When evaluating building systems, designers should refer to the requirements in the NFIP, building codes, and 

consensus standards (see Section 2.1) and other resources. For concrete and masonry walls, design professionals 

typically turn to American Concrete Institute (ACI) 318-08, Building Code Requirements for Structural Concrete 

and Commentary (ACI 2008), or ACI 530-11/ASCE 5-11/ The Masonry Society (TMS) 402-11, Building 

Code Requirements and Specifications for Masonry Structures (ACI/ASCE/TMS 2011). For wood-framed structures, designers may use American National Standards Institute / American Forest & Paper Association (ANSI/

AF&PA) NDS2005, National Design Standard for Wood Construction (ANSI/AF&PA 2005). 

If all the regulatory requirements discussed above and in 

Section 2.1 can be met and the retrofit is determined to 

be feasible, the designer should then consider the construction materials and products necessary to complete 

the project. The designer should specify the products 

and reference a standard the products must meet in 

order to provide a measure of certainty that both the 

constructed and purchased products will result in the 

desired level of protection. FM 2510, Approval Standard 

for Flood Abatement Equipment, was developed to certify 

certain products that provide floodproofing for conditions up to 3 feet of water. 

The presence of an FM Approvals product certification/seal certifies that the product meets the requirements 

of FM 2510. However, compliance with FM 2510 for specific products does not, by itself, imply compliance 

with the design requirements in ASCE 24, nor does use of the products mean that the dry floodproofed area 

will be ASCE 24 or NFIP compliant. The designer should compare the specification requirements in ASCE 

24 and FM 2510 to ensure that FM 2510-certified products are applicable for use on any given project. Some 

of the primary requirements that should be evaluated when selecting a product are as follows:

Special Note

FM 2510, Approval Standard for Flood 

Abatement Equipment, can serve as a 

product standard for temporary flood barriers, opening barrier abatement equipment, 

backflow preventer flood abatement equipment, and sump pump flood abatement 

equipment. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-5

DRY FLOODPROOFING MEASURES 3

■ Hydrostatic loads

■ Hydrodynamic loads

■ Wave loads

■ Buoyancy requirements

■ Debris impact loads

■ Leakage

■ Installation requirements

■ Requirements related to material exposure

3.1.4 Verification and Testing of Systems

An often overlooked part of the design process deciding on a testing method for the effectiveness of the dry 

floodproofing. During the construction phase of the project, as wall systems are being retrofitted and installed, 

it is important to test them to verify that they can resist hydrostatic loads and the components are indeed 

waterproof. While some projects may protect such valuable resources that large-scale testing is cost-effective, 

in other situations, the testing of individual components such as flood shields protecting doors may be all that 

is necessary. Large-scale tests have entailed constructing large barriers around the outside of buildings and 

the area immediately around the building being flooded for a few hours. Smaller-scale tests may only require 

small barriers or forms to be constructed around individual components and those areas filled with water. The 

main reason for any type of test is ensure the designed hydrostatic load is achieved. The area must be filled 

with water to the designed flood protection level to develop the necessary hydrostatic load. Testing allows leaks 

to be identified under a controlled process and addressed prior to the completion of construction. However, 

designers and owners should bear in mind that these tests will only test the system for hydrostatic loads for a 

specific duration. Other loading factors such as buoyancy loads or the impacts of long duration flooding may 

be difficult or impossible to test.

3.2 Continuous Impermeable Walls

A continuous impermeable wall is substantially impermeable to the passage of water, and the structural components of the wall are capable of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy. 

Two resources for dry floodproofing building wall assemblies to create continuous impermeable walls are Flood 

Proofing Tests: Tests of Materials and Systems for Flood Proofing Structures (USACE 1988) and the Southeast 

Region Research Initiative’s (SERRI) Floodproof Construction: Working for Coastal Communities (ORNL 2011), 

referred to as the SERRI Report. 

The designer should review the USACE report (which recommends dry floodproofing in many cases up to 

3 feet) to determine whether the recommendations are consistent with the walls in the retrofit project. The 

USACE report contains information on tested systems and observed deflections. The SERRI Report focuses 

on new construction but may provide the designer with some ideas of building assemblies that proved to be 

impermeable in that research. 

After the primary wall system and foundation have been strengthened to resist flood loads (if necessary), the 

building must be sealed and other portions of the building (e.g., windows, doors, utility points of entry) 
3-6 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

must be evaluated to determine how best to prevent 

floodwaters from entering the enclosed area. The three 

categories of measures that can contribute to making 

the primary wall system impermeable are protecting 

openings (closing, sealing, or shielding), waterproofing 

the walls, and using a flood wrapping system.

In some instances, it may be more cost-effective or less 

invasive to building occupants during the retrofit process to construct a continuous impermeable wall on the 

outside of the existing wall system. Some wall systems, 

such as steel stud wall systems, may be too difficult to 

make impermeable, and in those instances a new wall 

system may be constructed along the perimeter of the 

existing wall to provide protection. In these instances, 

the load path to the foundation may be a primary concern for the designer.

3.2.1 Openings

The designer and owner should consider permanently closing any openings in the building’s exterior if doing 

so would be inconsequential to functional use. Although filling in openings may affect the original or normal 

use of the building, filled openings limit the number of areas that require human intervention before a flood 

event. Openings similar to the one shown in Figure 3-1 must be evaluated individually in order to properly 

tie in the retrofit to the existing wall system and prevent a potential weak spot. Filled openings should be constructed so they match the full thickness of the wall system and are anchored properly into the surrounding 

wall system. 

Permanently filling openings can be used in conjunction with deployable flood shields, which protect the 

remaining openings in exterior walls. Flood shields are used to temporarily seal openings from incoming floodwaters (see Section 3.5 for more information on flood shields). 

Special Note

The SERRI Report describes several 

wall assemblies including sealed CMU 

walls, cavity walls, unsealed CMU walls, 

Insulated Concrete Form Walls, metal stud 

walls, Structural Insulated Panel walls, 

sheet membranes over CMU walls, and 

a waterproof coating on a CMU wall. The 

report is available at: http://www.serri.org/

publications/Pages/Reports.aspx.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-7

DRY FLOODPROOFING MEASURES 3

Figure 3-1. Filled window opening

3.2.2 Wall Systems

The decision to use sealants to waterproof a wall should include a consideration of the structural soundness 

of the building, including the walls and floor slab, and the building’s ability to resist flood and flood-related 

loads. The structural systems should be evaluated when any type of dry floodproofing is under consideration. 

The level of waterproofing that a wall system needs is highly dependent on the type of system. Systems such 

as poured concrete may require minimal waterproofing, while systems such as CMU may require filling cells 

with a flowable grout mix that contains a water-resistant additive. Retrofitting a CMU wall by grouting the 

cells requires creating openings at the top and bottom of the wall to ensure that the grout fills all the cells 

completely. Grout can be obstructed by mortar between courses of block or by debris left in the cell during 

construction of the wall. Drilled observation holes in the bottom course of a CMU block wall can be used to 

verify that grout flows through the entire wall and to inspect the connection between the wall and the floor 

slab to determine to what extent the connection can be relied on for shear load capacity.

Although Structural Insulated Panel (SIP) wall systems have been waterproofed successfully, waterproofing 

an existing SIP wall system is not recommended. This wall system can be waterproofed sufficiently to prevent 

almost all water from intruding, but the panel-to-slab anchors may be difficult to improve without installing 

vertical braces on the outside of the panels, and the panels may not be able to resist the buoyant forces.

Insulated Concrete Form (ICF) systems require minimal waterproofing. In addition, ICF systems have significant structural capacity and are likely to require little if any structural retrofits to withstand flood loads, 

but the slab-to-wall connection should be checked. The detailing of the exterior finish may require some 

thought depending on how the exterior of the ICF system is finished. The construction of the exterior face of 

an ICF building may make it difficult to prevent water from getting behind the exterior veneer, so drainage is 

important.

Previous

window opening
3-8 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

Creating a waterproof barrier in a section of wall to make it impermeable may require the use of sealants. 

Sealants include compounds that are applied directly to the exterior surface of the building to seal exterior 

walls and floors and typically fall into two categories (see Figure 3-2):

■ Positive-side sealant. Applied to the wall exterior where the sealant acts as a barrier between 

floodwaters and the wall

■ Negative-side sealant. Applied to the interior of a wall or floor where the water pushes against the 

sealant after it has passed through the wall or slab

Figure 3-2. Application of a waterproof membrane on the exterior (positive side) of a wall (left) and fiberreinforced polymer wrap applied to the interior (negative side) of a wall (right)

Above-ground walls can be sealed using either category of sealant because interior and exterior sides are both 

typically accessible while below-ground walls and floor slabs almost always require negative-side sealants. 

Positive-side sealants also include wrap-style adhered membranes and spray-applied sealants, both of which 

can be applied to the exterior wall or foundation at or below the ground. Products such as elastomeric waterproofing material and self-adhering membrane sheets have been successfully used to prevent water intrusion 

for more than 24 hours. Temporary positive-side sealants called “flood wraps” can be attached to the wall 

above-grade during flooding. See Section 4.4.3 for more information on flood wrapping systems.

Negative-side sealants that are applied to a concrete slab or wall must be bonded directly to the slab or wall 

to prevent the sealant from pulling away from the surface. Negative-side sealants on slabs must be formulated 

and installed to withstand floor-related wear and must be applied across expansion joints common in concrete 

floor systems. 

When the determination has been made that the building and foundation system can withstand the expected 

flood-related forces, selecting a sealant system is relatively straightforward. The decision centers on the compatibility of the sealant product with the expected duration and depth of flooding and the construction 

materials in the building. Materials such as brick veneers have been used in low-flood-height applications 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-9

DRY FLOODPROOFING MEASURES 3

of dry floodproofing, but Building Code Requirements and Specifications for Masonry Structures (ACI/ASCE/

TMS 2011), does not allow brick veneers to be included as part of the lateral load resistant system. The sealant 

should be selected using the decision process shown in Figure 3-3. 

Figure 3-3. Decision process for selecting type of sealant 

Even with sealants, a dry floodproofed building still requires a well-developed internal drainage system to 

collect the inevitable leaks and seepage that will develop (see Section 3.7). Many dry floodproofing systems 

still experience some water infiltration, and the owner will need a dewatering system capable of removing the 

water. Such a system may require establishing drains around footings and slabs (Figure 3-4) to direct seepage to 

a central collection point where it can be removed by a sump pump. Additionally, dry-floodproofed buildings 

usually need backflow devices and other measures designed to eliminate backwater flooding through waste and 

wastewater system components. 

A particular area of concern in dry floodproofing non-residential buildings is the presence of adjacent buildings with shared walls or narrow gaps between walls. Although the only viable option for a shared wall may be 

to use a negative-side sealant, the shared wall may make dry floodproofing infeasible. 

Adjacent walls also present a design challenge. Even if both buildings are to be dry floodproofed, it may not be 

possible to floodproof all areas of the adjacent walls. Sealants and filler material used to bridge these gaps have 

been used to protect these areas for short durations. If these areas are exposed to flooding for extended periods, 

water may migrate under the building foundations and flood the areas. The condition of adjacent buildings 

should be thoroughly investigated to ensure that the selected floodproofing measures will be effective. 
3-10 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

Figure 3-4. Internal drain in a dry floodproofed retail building 

3.3 Flood Resistance of Interior Core Areas

Critical core components and areas can be made flood resistant even if dry floodproofing the entire building 

footprint is not needed or possible because of building occupancy type, geometry, function, or cost. Typical 

critical core areas contain utilities such as electrical distribution and switching areas, emergency generators, 

emergency fuel supplies, and other mission-critical components that cannot be moved or elevated. In many 

large complexes or campuses of buildings such as museums, universities, and large businesses, the utilities may 

be housed in a central building and linked to the other buildings via tunnels. Although the main utility building may not be at risk of flooding during a particular event, utility tunnels are often subject to more frequent 

flooding. The tunnels may need to be protected from floodwaters by watertight doors. Figure 3-5 is an example 

of a watertight door that would prevent flooding of a utility room.

An important consideration in making a core area watertight is that floodwater levels may be higher than 

the height of typical dry floodproofing measures that protect the entire building, and additional anchorage 

may be needed to make sure the area does not become buoyant. Both the floor system and existing walls 

should be carefully studied and evaluated (see Section 3.1.2). Because these areas are typically designed to be 

fully resistant to high flood loads, additional anchoring or securing of the core area may be required to resist 

buoyancy forces.

Core areas can be made watertight by building infillwalls or retrofitting existing interior walls. Waterproofed 

walls may be constructed of cast-in-place concrete with sufficient detailing to make sure the walls are tied to 

the floor slab. Fully grouted reinforced CMU walls can also be used to construct the interior walls. CMU walls 

may require additional waterproofing to be considered fully impermeable. Special detailing should be done at 

the joint between the floor slab and wall because this is a common location for leaks. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-11

DRY FLOODPROOFING MEASURES 3

If access doors or hatches are necessary below the flood protection level, a hinged door is recommended so the 

area can be sealed quickly. Doors or hatches above the flood protection level may allow continuous access even 

during flood events, but require stairs or ladders. Although stairs or ladders may allow maintenance personnel 

to access the area during an event, they may limit the ability to move items in and out of the area. A pump 

system is still required in these areas to address any unidentified leaks. 

3.4 Shields for Openings

Dry floodproofing of wall systems is a complex undertaking because openings such as doors, windows, and 

utility connections are rarely designed to be watertight or to resist flood loads. When openings that must 

be maintained below the flood protection level are evaluated, a primary consideration should be the wall or 

foundation system’s ability to resist the loads. Any system of flood doors, panels, or shields will depend on the 

transfer of the flood loads from the shields to the wall such that the load path is maintained. If the walls or 

foundation are structurally insufficient to carry these loads, they must be reinforced to maintain the load path 

(see Section 3.2.2).

Penetrations through walls for utilities have much narrower openings than those of doors or windows, so sealants are usually sufficient for preventing water intrusion at utility connections. However, if utility openings are 

not properly sealed from floodwaters, water can enter the building through these openings. Protecting water 

line penetrations properly and sealing electrical conduits can often minimize flood damage.

Figure 3-5. Watertight 

door used to protect 

mechanical rooms

subject to flooding
3-12 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

3.4.1 Doors 

During flood conditions, doors typically present the largest openings requiring protection from water intrusion into the building. Most door openings vary from 3-foot-wide exterior doors to 16-foot-wide garage-type

roll-up doors or cargo doors. Flood shields for doors (see Figure 3-6) must span these widths. The permanency 

of the shield may be dictated by the normal use of the opening, warning time available to install the shield, and 

the use of the door as a means of egress from the building. Emergency plans should identify the personnel who 

have been designated to close or install flood shields before a flood event and instructions on how to install the 

shields. Issues related to properly sealing the shield are discussed in Section 3.5.

3.4.2 Windows

Basement windows can be the first entry point for floodwaters. Window height can range from small basement 

windows that are 1 to 2 feet tall to full height windows. Removing a window and incorporating the opening 

into the wall system may be easier than retrofitting a window with watertight flood shields (see Section 3.2.1). 

The decision of whether to eliminate the window may depend on the following:

■ Use of the window (e.g., provides light, means of egress, architectural feature)

■ Location of the window on the building

■ The ease with which the opening can be filled in and incorporated into the wall system 

Basement windows may be good candidates for elimination, whereas windows higher on the building may 

only need to be shielded partially rather than eliminated. In areas where the flood protection level is higher 

Figure 3-6. Equipment 

room with watertight 

door (source: Presray 

Corporation) 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-13

DRY FLOODPROOFING MEASURES 3

than the elevation of the window, products such as submarine glass systems have been successfully used to 

replace standard windows. Replacing standard windows with submarine glass systems will render them inoperable, but the glass will still allow natural light into the area. If windows are used below the flood protection 

level, anchorage of the window frame, and attachment of mullions to the frame and the seals between the 

window and the frame must be considered because they are common places that fail or leak. Due to the loading requirements many of these window systems require oversized mullions in order to adequately distribute 

the loads.

3.4.3 Utility Connections

Where a utility enters the building or connects to the building’s utility system usually depends on the type of 

utility. Overhead electrical lines may be attached near the roof system while buried water, electrical, gas, communications and sanitary line connections, and building penetrations are typically near or below the ground. 

Floodwater can enter the building where the utility line penetrates the building through the wall or floor or 

directly through a line such as an electrical or sewer line. Gaps in the opening around the utility line should 

be filled with an expansive foam to create a waterproof seal. Sealants that are used to seal openings in walls or 

floors should be able to withstand being submerged for the anticipated duration of flooding. 

Testing the waterproof seal may be difficult, but it should be done to make sure the seal is completely watertight 

for the expected hydrostatic pressures. Ideally, the floodproofing measure will only need to resist hydrostatic 

pressures as waters rise, but any utility that penetrates the building should be evaluated to determine whether 

the anchorage needs to be improved to prevent buoyancy forces, hydrodynamic loads, erosion, or scour from 

damaging the utility line or to prevent the line from damaging the seal around the wall penetration.

Nonresidential buildings may have ventilation shafts, exhaust fans, and louvered openings that should be 

protected with specially fitted flood shields. Placing the flood shields may require shutting down parts of the 

building or interrupting some of the building’s critical utilities or mechanical systems. It may be feasible and 

cost-effective to reroute ventilation shafts, exhaust fans, or other utility openings above the flood protection 

level to avoid having to shut down some operations during a flood.

Older buildings may have openings into the basement that were used as coal chutes. As furnaces were updated 

for natural gas or electricity, these openings were sealed to prevent the loss of heat or animals from entering 

through them. The conventional methods used to fill in these opening were likely not designed to resist flood 

loads and rarely result in a waterproof covering or watertight seal. Attention is necessary to make sure they are 

sealed properly and do not present a weakness in the floodproofing system. 

Even areas without wall penetrations, such as utility chases on exterior walls, can be subject to water infiltration. These areas may have electrical lines, plumbing, gas, communication, or ductwork running through 

them. Maintenance access points below the flood protection level can allow the infiltration of floodwaters that 

goes unnoticed and result in significant water entering the building. 
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3.5 Flood Shields for Openings in Exterior Walls 

Flood shields or panels are watertight structural systems that bridge the openings in walls to prevent the entry 

of floodwaters. Flood shields work in tandem with waterproof barriers to resist water penetration. 

Although flood shields are most often temporary measures, they can also be used as a permanent floodproofing measure (e.g., hinged plate or door, mini-floodwall at a subgrade opening). Flood shields transfer 

flood-induced forces into the adjacent structural components and, like sealants, can overstress the structural 

capabilities of the building. Most flood shields are mounted against the exterior of the opening, allowing rising 

floodwaters to further compress the gaskets and seals between the flood shield and the wall system or frame of 

the opening. A number of vendors make special doors for permanent installation and drop-in panels or barriers that are designed to be watertight and installed as needed for flood protection.

For shallow and short-duration flooding, panel-style flood shields of sturdy material can be constructed to fit 

doorways and other openings to minimize the entry of floodwaters. Shields will only be watertight if a flexible gasket or sealant is provided and the mounting hardware is designed to apply even pressure on the gasket 

around the opening. Personnel must know where the materials are stored and be trained in their deployment 

(see Section 3.8). 

3.5.1 Types of Flood Shields

The type of shield that is used depends on the size of the opening that needs to be protected and the duration 

of flooding. Examples of flood shields are shown in Figures 3-7 through 3-9.

Figure 3-7. Door opening protected 

from low-level flooding by a flood 

shield 
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DRY FLOODPROOFING MEASURES 3

Figure 3-8. Window 

protected from lowlevel flooding by a flood 

shield and wall sealant 

Figure 3-9. Aluminum 

flood shield used for 

flooding less than 3 

feet deep 
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3 DRY FLOODPROOFING MEASURES

As noted above, longer and larger flood shields, such as for vehicle entrances, are normally constructed of steel 

plate or heavy aluminum plate. Because of the weight of the shield, it is usually best for the shield to be hinged 

so that it can swing into place (see Figure 3-10). Hinging can be along the bottom so the shield lies flat when 

not in use, or it can be placed along one side so the shield can fold back out of the way. Shields hinged on the 

bottom must fold into a recess so the surface of the entrance is smooth. Shields that fold into a recess require a 

design to make the shields and recess able to withstand the weight of the traffic over them. In addition, belowgrade recesses can fill with water and debris, which increases maintenance and hinders rapid deployment.

Hinged and sliding flood shields (see Figure 3-10) only require the user to unlock and rotate or slide the flood 

shield and lock it into place. These flood shields may include pedestrian doors that are full-height doors with 

complex latching mechanisms for higher flood heights or lower half-door systems. Although hinged flood 

shields require human intervention, they can often be deployed by one person. Room must be available for the 

systems to swing or slide either beside or above the door when not in use. 

Heavy flood shields for larger openings may require electrical or mechanical systems to move them into place. 

Designs should include a consideration of the fact that power may not be available following the event and 

that access through the opening may be necessary to restore power. 

Passive (automatic) flood shields (see Figure 3-10) may be preferred to active flood shields, which require 

human intervention. Passive flood shields allow openings to be used until floodwaters reach a certain height. 

Rising floodwaters use a ballast system to push the flood shield closed. Ballast systems can be used in dry 

floodproofing and floodwalls when large shields are difficult to install quickly. Passive flood shield systems may 

require room under the opening to allow the flood shield to be stored when it is not in use.

Flood shields that must be moved into position prior to a flood event require the most time critical and labor 

intensive human intervention of any dry floodproofing measure. Although shield systems may be the most aesthetically pleasing, more than one person may be needed to carry and install them. A plan is needed to ensure 

that they will be installed efficiently, and the installers may need to have extensive training on proper installation (see Section 3.8).
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DRY FLOODPROOFING MEASURES 3

Figure 3-10. Types of 

flood shields 
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3 DRY FLOODPROOFING MEASURES

3.5.2 Flood Shield Materials

Considerations such as the size of the opening to be protected, the normal use of the openings, who will install 

the flood shields, and how quickly after the floodwaters recede the openings need to be available are important 

in determining the material to be used and also how the flood shield will be attached to the structure.

Steel, aluminum, and, in limited applications, marine-grade plywood are some of the materials that are used 

to fabricate shields, depending on loads. 

For normal sized openings such as entrance doors, aluminum is probably the most common material. It is 

lightweight, allowing for easy fabrication and transport, and is resistant to corrosion. However, aluminum can 

buckle under large hydrostatic pressures, so additional reinforcement may be required. Shields designed for 

long-duration flooding are typically steel or aluminum.

For smaller openings such as windows with short-duration shallow flooding, marine-grade plywood is also 

commonly used. However, plywood is subject to warping if not properly stored. In addition, it will collapse 

under relatively low flood forces and usually requires significant reinforcement, which is usually some type 

of wood frame. Plywood flood shields are limited to short spans and low water heights. In addition, most 

plywood deteriorates when exposed to high moisture. Therefore, plywood flood shields should be examined 

periodically and replaced as necessary.

Longer and larger flood shields, such as for vehicle entrances, must be able to withstand significant flood forces 

and should therefore be constructed of a substantial material. This material is normally steel plate, which is 

protected against rust and corrosion. Heavy aluminum plate may also be used, although it will likely need to 

be reinforced. 

3.5.3 Gasket and Seals

When leaks do occur into a dry floodproofed area, gaskets and seals are often the primary source. Flood shields 

depend on a variety of gasket and seal materials and configurations to prevent water intrusion. Pneumatic seals 

have been used successfully on some systems, but they rely on maintaining air pressure to prevent water from 

leaking past them. In long-duration flooding, it may not be possible to refill or maintain pneumatic seals. 

Self-sealing compression seals are more reliable and can be used in conjunction with pneumatic seals for a 

redundant configuration, which provides more protection. 

Seals and gaskets can be monitored during a flood event by moisture monitors (e.g., water sensor, camera) 

inside the flood shield, and maintenance personnel can be notified of any leaks.

Seals and gaskets are subject to cracking or rot and need to be repaired or replaced periodically to be an 

effective watertight seal under flood conditions. Storage of flood shields and components outside can cause 

premature deterioration of seals and gasket materials.
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3.5.4 Plate-Style Flood Shields

When it has been determined that the building can withstand the expected flood and flood-related forces, 

selecting a flood shield system is relatively straightforward. The decision hinges on the selected material’s compatibility with the existing construction materials, and its ability to be constructed such that it can withstand 

the duration and depth of the expected flooding. Flood shields for standard size openings are available for purchase, but some openings may require flood shields to be designed for the opening. 

The selection and design of a panel, or plate-style, flood shield should follow the process shown in Figure 

3-11. If additional structural retrofitting is required to transfer loads from the flood shield to the wall system, 

the retrofit should be implemented in accordance with the guidance in Section 3.1. Similar steps are followed 

when a flood shield is purchased, but the manufacturer will provide most or all of the necessary design values.

Figure 3-11. Selection/design of plate-style flood shields 
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3 DRY FLOODPROOFING MEASURES

The process for selecting and designing plate-style flood shields is as follows:

Step 1. Determine the flood and flood-related loads. Loads calculated in Chapter 2 should be used to 

determine the flood loads acting on the shield. The height of the flood protection level (the depth as 

it relates to the panel) and the related flood loads calculated per linear foot should be applied over 

the entire width of the area to be protected by the shield. 

Step 2. Select the plate shield material. Material selection is driven by the size of the opening and duration 

of flooding. Factors to consider are:

a. Flood duration: Select steel or aluminum materials for long-duration flooding and consider 

marine grade plywood materials for short-duration, shallow flooding.

b. Size of opening: Select steel and aluminum materials with stiffeners for larger openings and 

shored marine grade plywood with appropriate bracing for small openings.

c. Installation: Should be quick and require minimal effort to minimize personnel needs. 

Step 3. Determine panel stresses. The designer should check the flood shield panel either as a plate or a 

horizontal/vertical span across the opening, as follows:

a. Using end conditions and attachments to determine how the panel will work, calculate stresses 

based on bending of the plate. In larger shield applications, also compute the end shear. b. 

Compare these stresses to the allowable stresses from a material design value source.

c. Address shields that have a free end at the top or other unusual configuration on a case-by-case 

basis.

d. Adjust the plate thickness to select the most economical section. If the shield does not work for 

larger thicknesses, add stiffeners.

e. Refer to the American Institute of Steel Construction (AISC) 325, Steel Construction Manual, 

for steel plate design (AISC 2011); the Aluminum Association’s (AA’s) Aluminum Design Manual 

for aluminum design (AA 2010); the ANSI/AF&PA National Design Specification for Wood 

Construction for plywood design (ANSI/AF&PA 2005); and applicable codes and standards. 

Step 4A. Check deflections. A shield that is acceptable for stresses may not be acceptable for deflection. 

Deflection may be controlled by using alternative plate materials. Check deflections as follows:

a. Calculate deflections for the shield and evaluate on the basis of connections and sealants.

b. If the stresses are such that the loads will permanently deflect the shield or cause leakage around 

the gasket material, the deflection should be considered unacceptable and stiffeners should be 

added.

c. Refer to the AISC 325 for steel plate design (AISC 2011), the Aluminum Design Manual 

(AA 2010) for aluminum design, the ANSI/AF&PA National Design Specification for Wood 

Construction for plywood design (ANSI/AF&PA 2005), and applicable codes and standards.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-21

DRY FLOODPROOFING MEASURES 3

Step 4B. Design stiffeners as required. Plate overstress or deflection may be solved by using stiffeners. 

Design the stiffening as follows:

a. Select the section to be used as a stiffener. Angles may be used for steel or aluminum shields and 

wood stock for plywood shields.

b. Calculate the stresses and deflection based on the composite section of stiffener and plate.

c. Calculate the horizontal shear between the sections, and design the connections to carry this 

load.

d. Keep plate connections and frame in mind when detailing stiffeners.

e. Refer to the AISC 325 for steel plate design (AISC 2011), the Aluminum Design Manual,

(AA 2010) for aluminum design, the ANSI/AF&PA National Design Specification for Wood 

Construction for plywood design (ANSI/AF&PA 2005), and applicable codes and standards.

Step 5A. Design the connections and hardware. 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 (e.g., hinged, free top, bolted, latching dogs).

b. Consider ease of installation and aesthetics. Any hardware that can be permanently attached to 

walls systems or the shields will eliminate the potential to lose hardware.

c. Design the connection to operate in conjunction with gasket or sealant to prevent leakage.

d. Design the connection to be capable of resisting live loads in the direction opposite of surges.

e. Refer to the AISC 325 for steel plate design (AISC 2011), the Aluminum Design Manual 

(AA 2010) for aluminum design, the ANSI/AF&PA National Design Specification for Wood 

Construction for plywood design (ANSI/AF&PA 2005), and applicable codes and standards.

Step 5B. Select the gasket or waterproofing. 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 or waterproofing required. Gasket/waterproofing must be able to 

withstand expected forces and able to function during climatic extremes.

b. Consider ease of installation and ability to work with plate/connections as a single unit.

c. Refer to the manufacturer’s literature and check against duration/depth of flooding, the applicability to selected building materials, and storage requirements. Some gasket materials can be 

damaged by extended exposure to sunlight or other weather conditions. Vulnerability to sunlight or weather may affect the selection of the gasket or waterproofing material.

Step 6. Check adjacent walls, lintels, sills, and top/bottom connections. Resistance of structural components adjacent to the shield such as walls, lintels, sills, and top/bottom connections should be 

checked against maximum loading conditions. Different methods of attachment may load the 
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3 DRY FLOODPROOFING MEASURES

adjacent wall differently. These support areas will be depended on to maintain the load path from 

the shield and to the wall system.

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. Connections, if used, should 

be evaluated for shear resistance and ability to transfer loads to the horizontal diaphragm above. 

When removable shields are used, a flood emergency plan should be developed and posted in at least 

two conspicuous locations in the building. The plan should specify, at a minimum, the following:

■ Storage location(s) of the shields and hardware (storage in outside locations can cause 

premature deterioration of gaskets and waterproofing materials)

■ Methods of installation

■ Conditions activating installation

■ Maintenance of shields and attachment devices (check for deterioration)

■ Cleaning of any permanently mounted channels or gaskets

■ Periodic shield installation practice 

■ Testing of backflow valves

■ Testing sump pumps and other measures associated with the internal drainage collection 

system

■ Inspecting material and equipment required to implement the dry floodproofing measure

A maintenance plan is an important part of a floodproofing system that includes flood shields. Flood shields, 

hinges, hoists, latches, channels, and seals should be inspected periodically for damage. Typically, the time 

between the flood warning and the flood event is not sufficient to repair any damage to shields or seals. See 

Section 3.8 for more information on operations and maintenance plans.

3.5.5 Case Study: Retrofit Dry Floodproofed Building, New Castle, DE

A machine shop located in northern Delaware was badly damaged by flooding in 2003 and 2004. 

Although the owner received several hundred thousand dollars in claim payments from the NFIP, the 

time required to recover meant significant loss of business. Despite wanting to relocate his business, 

the owner was unable to find an alternative site outside of the SFHA because the surrounding area is 

so densely developed. Instead, he worked with the New Castle Conservation District and the State of 

Delaware to pursue a mitigation grant from FEMA. 

Without any guarantee of Federal assistance, the owner paid to have a structural engineer evaluate the 

building to determine whether it was feasible to retrofit. The engineer computed flood loads, evaluated 

options, and developed a retrofit floodproofing solution. The engineer also prepared a probable cost 

estimate. Federal grant funds were awarded to the State of Delaware, and to the District as a subgrant 

applicant, which worked with the owner to construct the floodproofing measures. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-23

DRY FLOODPROOFING MEASURES 3

A key aspect of the project’s feasibility was the fact that stream gages are installed throughout the upper 

watershed, including one placed in Pennsylvania by the State of Delaware. The gages are part of a warning system that transmits text messages and pages to property owners and businesses throughout the 

flood-prone lower reach of Red Clay Creek. Because of the short warning time, business owners who 

implement floodproofing measures that require human intervention agree to deploy those measures 

when buildings are vacant, such as overnight and on weekends.

The structural engineer determined that the machine shop’s concrete masonry walls that form the main 

part of the building and the metal walls that form the rear portion would not resist anticipated flood 

loads, prompting design of supplementary walls. The main part of the shop building has two exit doors 

and a garage door at the front that were retrofit with drop-in aluminum panels with inflatable gaskets 

(see Figure 3-12). The exit door at the back of the building was protected with a permanent, hinged 

aluminum panel (see Figure 3-13). 

The Delaware Department of Natural Resources and Environmental Control, as the State agency 

administering the Federal grant, required submission of an emergency operation plan that specified 

how flood threats are monitored and identified which personnel are responsible for specific actions. A 

flood in 2007 affected the area, but the machine shop was not damaged.

Figure 3-12. Front of retrofit dry floodproofed 

building where drop-in flood shields protect 

doors 

Figure 3-13. Rear of retrofit dry floodproofed 

building with permanently installed flood shield
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3 DRY FLOODPROOFING MEASURES

3.6 Backflow Valves

A backflow valve is similar to a check valve used in water systems (see Figure 3-14). It has an internal hinged 

plate that opens in the normal direction of flow, and if flow is reversed, the hinged plate closes over the inlet 

to cover the pipe opening. The valve generally has corrosion-resistant internal parts and a cast-iron body with 

a removable cover for access. Valves are available in sizes from 2 to 8 inches in diameter.

Backflow valves can help prevent water flowing from the 

exterior to the interior of the building through the sanitary sewer and/or water drainage systems and should be 

considered for sanitary sewer drainage systems with fixtures below the flood protection level. Combined sewers 

(sanitary and storm) may present the greatest need for 

backflow valves because the valves can prevent both a 

health and a flooding hazard. However, the effectiveness 

of a backflow valve can be reduced if its internal mechanism is fouled by soil or debris. Periodic maintenance 

and testing is required to maintain functionality. 

Some manufacturers add a shear gate mechanism that can be manually operated to close the drain line when 

backflow conditions are anticipated. The valve remains open during normal use. When manually operated 

backflow valves are used, the time necessary to close the valves should be factored into the emergency operations plan. A second type of backflow valve is a ball float check valve (see Figure 3-15) 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 

often built into floor drains or traps in newer construction. 

Figure 3-14. Backflow 

valve 

Special Note

Alternatives to backflow valves include retrofitting sewer lines and standpipes so that 

they are overhead or to install a gate valve 

which must be closed manually.
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DRY FLOODPROOFING MEASURES 3

Advanced backflow valve systems have ejector pump attachments to pump sewage around the backflow valve, 

forcing it into the sewer system during flooding. This system is useful for maintaining normal operation of 

sanitary and drainage system components during a flood. 

Detailed information must be obtained about the existing building and the location of sanitary and drain lines 

to determine whether using backflow valves is feasible. Once the design data are collected, the designer should 

follow the process shown in Figure 3-16 to develop a preliminary concept for the installation of the backflow 

valve. 

The elements of the backflow valve selection process are as follows: 

Step 1. Determine relationship of drains to flood protection level. If any drain or pipe fixture is below 

the flood protection level, backflow valves should be installed. If all drains and fixtures are above the 

flood protection level, backflow valves are not necessary. 

Figure 3-15. Floor drain 

with a backflow valve 

with a ball float check 

valve 

Figure 3-16. Backflow 

valve selection process 
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3 DRY FLOODPROOFING MEASURES

Step 2. Confirm regulations on backflow valves. Based on information collected during the field investigation, confirm the local code or governing regulations allow the use and installation of backflow 

valves.

Step 3. Determine the layout of drains that serve the affected fixtures. Sketch the floor plan of the building showing the location of all plumbing fixtures, appliances, floor drains, and drain piping below 

the flood protection level. 

Step 4. Determine pipe sizes on affected drains. Obtain the size of drainage lines below the flood protection level from the field investigation or construction drawings. 

Step 5. Determine type, size, and location for valves. Determine type, size, and location of backflow 

valves required, paying attention to any special conditions related to installation. Factors to be considered are: 

■ Clearance for access and maintenance

■ Cutting and patching of concrete floors

■ Indicating on the floor plan sketch the tentative location(s) of the backflow valve(s) to 

verify they do not conflict with other utility lines or equipment

At this point, the designer should confirm the preliminary design with the owner, discussing the following items: 

■ Verify that proposed locations of backflow valves are feasible

■ Verify existing conditions at location of proposed backflow valves

■ Confirm the size and location of needed backflow valves

■ Confirm special considerations regarding existing conditions affecting design and installation of backflow valves

Step 6. Prepare details and specifications. The final plans and specifications should include the following 

items: 

■ Floor plan or site plan with location of backflow valves

■ Details, notes, and schedules: 

■ Backflow valve detail

■ Wall, floor, and wall penetration details

■ Installation notes

■ Equipment notes (or schedule)

■ Specifications governing the installation of: 

■ Pipes and fittings

■ Insulation

■ Hangers and supports

■ Valves
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DRY FLOODPROOFING MEASURES 3

The designer should coordinate the backflow valve plans with any other floodproofing retrofit measures that may be proposed for the same building.

3.7 Internal Drainage 

Internal drainage systems serve two primary functions in dry floodproofing projects. First, they remove water 

that has seeped through small openings in the sealant system or through the gaskets of shields that are protecting openings. Additionally, internal drain systems may be used to remove water collected from underdrain 

systems in the below-grade walls and floors of the building. See Section 2.2.7 for additional information.

3.7.1 Sump Pumps

Other than the piping system, sump pumps are the most common piece of equipment in an internal drainage 

system (see Figure 3-17). In dry floodproofing applications, sump pumps are used to prevent accumulation of 

water in the building and handle the inevitable small leaks that occur around shields and sealed openings and 

the leaks from the buildup of hydrostatic pressure against walls. Sump pumps may be used with other floodproofing methods to protect areas around mechanical equipment and other systems that may be located in 

lower building levels that are subject to flooding. If the building has excessive seepage or a significant inflow 

of water from below the floor slab, or it is totally inundated by overtopping, the pumping capacity of sump 

pumps will likely be exceeded.

Before designing a sump pump system, the designer should verify that electrical power will be available for the 

pump system during and after a flood event. A generator may be required. When sizing the generator system, 

the designer should account for the pump’s electrical load on startup. An electrical engineer should be consulted to make sure the generator is sized properly. Additionally the designer should consider whether the fuel 

source for the generator can be relied on during a flood event. 

Figure 3-17. Typical 

sump detail 
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Sump pump and pit systems are constructed so that the bottom of the pit is below the base of the floor slab. 

Water in the areas adjacent to the walls and floor migrate toward the pit along the lines of least water flow resistance. If the pit is located properly, water will flow toward and into the sump pit. 

To remove water that has seeped into the dry floodproofed area, the floor slab should be sloped toward 

the sump pit(s). The slope will reduce the potential for water to accumulate before it reaches the sump pit. 

Placement of any equipment, storage items, or other potential obstructions should be considered so drainage 

is not impeded.

A path of reduced resistance may need to be constructed for water that has collected in the backfill material 

next to and adjacent to the building so that it can travel to the sump pit. Short pipe segments are inserted into 

holes drilled through the foundation walls into the backfill adjacent to the foundation wall. These pipe segments are connected to larger diameter pipes running along a gravel-filled trench or cove area in the basement 

floor that leads to one or more sumps. Although a sump system is effective in areas with low water tables, it 

may be overwhelmed by high water tables.

Two commonly used types of sump pumps are the submersible and pedestal. The submersible type has a watertight motor connected directly to the pump casing and is installed at the bottom of the sump. Pedestal sump 

pumps have an open motor supported on a pipe column with the pump at its base and a long shaft inside the 

column connecting the motor to the pump impeller. 

Submersible pumps are preferred for smaller applications because they continue to operate if the water level 

exceeds the height of the pump. In larger or commercial applications, a pedestal floor-mounted pump is preferred. Larger pumps require greater maintenance because of the larger volume of water they are designed to 

move. Larger pumps must therefore be mounted above the water collection pit for accessibility.

When selecting a sump pump for floodproofing applications, the designer should consider the advantages of 

each pump type and select a pump based on the requirements of the building. Considerations are as follows:

■ Pump capacity (gallons per minute or gallons per hour)

■ Pump head (vertical height the water is lifted)

■ Frictional resistance of fluid flow in the discharge piping system

■ Electrical power required (small non-residential buildings are usually powered by 120/240 volt, 

single-phase AC, but larger buildings may have three-phase systems with higher voltages)

■ Type of pump activation switch system

The pump activation switch is an important component of the sump pump system. Many pumps use one of 

four types of switches: diaphragm, vertical action float, tethered float, or electronic free float. Although all of 

these switches are viable, the strengths and reliability of each one must be understood. Table 3-3 provides a 

comparison of the pump activation switch types. 
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DRY FLOODPROOFING MEASURES 3

Table 3-3. Comparison of Types of Pump Activation Switches

Float Switch Type Description Strengths Considerations

Diaphragm switch Activated by water 

pressure

Well suited for most pit 

situations; works well in 

small sump pits

Most expensive; not 

always the most reliable: 

not adjustable

Vertical action float 

switch

Attached to a vertical 

rod, which activates the 

switch as it rises along 

with the water level

Inexpensive; relatively 

reliable

Not ideal for a deep 

sump pit because there 

may not be sufficient 

adjustment for the pit 

depth

Tethered float switch Works similar to the 

vertical action float but is 

tethered by a line instead 

of a vertical rod

Inexpensive Subject to operational 

problems; easily shut 

off by trapped debris; 

requires space in the 

sump pit

Electronic float free 

switch

Uses a wire that senses 

contact with water; may 

include an audible alarm

Few moving parts to fail Relatively expensive

If a pump system is to be depended on for dry floodproofing, the pump(s) must be periodically checked to 

ensure that they are working properly. One of the most common causes of failure is the malfunction of the 

switch. The owner must be familiar with the proper procedure for replacing the switch. Although the switch 

can be an inexpensive part, the malfunction of a switch can negate the effectiveness of other floodproofing 

measures. Other common problems are an improperly working float (tells the sump pump when to operate), 

blocked intake, and blocked impeller. Although not directly connected to the pump, the discharge system 

should incorporate a check valve to make sure that backflow does not occur along the discharge pipe. Check 

valves should be inspected periodically for proper operation, and owners should be aware that debris in the 

discharge pipe can prevent proper operation. Sump pumps should be incorporated into the operations and 

maintenance plan for the building along with other floodproofing measures.

Larger buildings and critical facilities require large internal drainage systems, which may be significantly different from small systems. Large systems require more careful design, layout, and significantly higher power 

requirements. Many large systems require three-phase electric motors and are applicable only where the feed 

to the building is 3-phase. 

Pumping systems typically fall into two categories: a constant speed pump or a variable speed pump. A constant speed pump may be the only viable option when the project is under cost constraints because a constant 

speed pump is less expensive than a variable speed pump. 

During a flooding event, the slow rise of floodwaters may result in low flows of water into the water collection 

pit. A constant speed sump pump will likely cycle on and off several times to empty the water collection pit 

until the flood protection level is reached, when the pump will likely need to accommodate a more constant 

flow of water into the collection pit. 

A variable speed sump pump can be adjusted to address the variability in the flow rates into the collection 

pit. The more consistent operation of a variable speed pump will likely reduce the size of the generator system 
3-30 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

needed to compensate for the startup electrical draw required for the pump system. A large commercial application using large constant speed sump pumps could require either the installation of a larger generator system 

or reductions in the number of other types of equipment that can be run on a smaller generator system.

Once the sump pump type is determined, the design should follow the procedure shown in Figure 3-18.

Step 1. Determine the rate of drainage. This is covered in Section 2.2.7, Internal Building Drainage.

Step 2. Determine the location for the sump pump. Consider the following:

■ Verify there is adequate room for the sump.

■ Assess whether the subfloor conditions (i.e., structural footings) would interfere with the 

sump pump installation.

■ If penetration of the floor is not recommended, consider using a submersible pump design 

for use on any flat surface.

■ If other floodproofing measures are being considered, such as placing a flood barrier 

around heating equipment or plumbing appliances, locate the sump pump or provide piping to it to keep a protected area dewatered. Sketch a preliminary location for the sump 

pump, discharge piping, and electrical receptacle for the pump.

■ Coordinate the sump pump location with the design of the drainage collection system.

Step 3. Determine the location for the discharge. Check with local officials about the discharge of clear 

water wastes. In most jurisdictions, it is not acceptable to connect to a sanitary drainage system, nor 

may it be desirable because of the potential for backflow under flood conditions. If allowable, the 

desirable location for the discharge is a point above the flood protection level at some distance away 

from the building. The discharge point should be far enough away from the building that water does 

Figure 3-18. Sump 

pump design process 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-31

DRY FLOODPROOFING MEASURES 3

not infiltrate back into the building. From the information obtained during the field investigation, 

tentatively lay out the route of the discharge piping and locate the point of discharge.

Step 4. Select the discharge piping route.

■ Minimize the length of pipe between sump and discharge point

■ Avoid utility and structural interferences along the route

■ Attach the discharge pipe to the structure as required by code

■ Protect the discharge point against erosion and install a downspout discharge block under 

the sump pump pipe discharge

Step 5. Select the pump size. Sump pumps for non-residential use generally have motors from 1/6 to 3/4 

horsepower and pumping capacities from 8 to 60 gpm. In selecting a pump, the designer needs to 

estimate the rate of flow of floodwater that will infiltrate into the space (gpm or gallons per hour 

[gph]). Additionally, the total dynamic head for the sump discharge must be determined. The total 

dynamic head equals the vertical distance from the pump to the point of discharge plus the frictional 

resistance to flow through the piping, the fittings, and the transitions. The head loss from pipe friction can be obtained from hydraulic engineering data books and depends on the pipe material and 

pipe length.

Other pump size considerations may be:

■ Physical size of the sump pump given the area available to place the 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. Size the electrical components.

■ Obtain horsepower and full load amperage rating

■ Select a ground fault interrupter circuit, as required by code

■ Size minimum circuit ampacity and maximum fuse size

■ Size maximum circuit breaker size

■ Obtain recommended fuse size or circuit breaker size from manufacturer and compare to 

above maximum and minimum National Electrical Code sizes

At this point, the designer should prepare a floor plan sketch showing the location of the sump 

pump, routing of the discharge line, location of the discharge point, and the preliminary specifications for the sump pump, sump pit, piping, and appurtenances and confirm the preliminary design 

with the owner or facility management, covering the following items:

■ Verify that the proposed location of the sump pump and pit is feasible

■ Verify electrical availability for the sump pump
3-32 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

■ Verify existing conditions along the proposed routing of discharge piping and at the discharge pipe termination

■ Confirm selection and size of the sump pump

■ Confirm size and location of the sump pit

■ Confirm special considerations regarding existing conditions affecting design and installation of the sump pump and sump pit

Step 7. Prepare details and specifications.

Prepare final plans showing:

■ Floor plan with locations of sump and backflow valves

■ Routing of discharge pipe and location of discharge point

■ Sump pump detail

■ Wall, floor, and wall penetration details:

■ Sump construction details

■ Installation notes 

■ Equipment notes (or schedule) 

■ Specifications (on drawing or as a specifications booklet):

■ Pipe and fittings 

■ Insulation 

■ Hangers and supports 

■ Valves (including backwater valves) 

■ Sump pumps

■ Coordinate plans with the work of others on additional floodproofing measures that 

may be proposed at the same building

3.7.2 Pressure Relief Systems

If flooding exceeds the level of protection and water fills the building, pumping out an area before the floodwater has receded can cause the walls to collapse if hydrostatic pressure from the floodwater exceeds the structural 

resistance of the foundation walls and the floor slab. Incorporating a pressure relief system is recommended to 

avoid structural damage to the building.

Pressure relief systems are similar to wet floodproofing measures in that they allow floodwaters into an area 

rather than risking damage by hydrostatic pressures. The systems allow for some level of dry floodproofing and 

then release the hydrostatic pressure if water levels exceed a specific height. A pressure relief system provides an 

added degree of protection against structural failure of a new building or for an existing structure that cannot 

be modified to reduce uplift pressures. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-33

DRY FLOODPROOFING MEASURES 3

Installing some type of pressure relief system is generally desirable. For floor systems that are not thick enough 

or sufficiently reinforced to resist buoyancy forces, the system may be a series of relief valves equally spaced 

across the floor slab. If floodwaters begin to collect in the soil under the slab, the relief valves will allow the 

water to percolate through the floor slab, eliminating the buoyancy forces. Dry floodproofing protection will 

not be achieved, but this is preferable to losing the structure.

3.8 Flood Emergency Operations Plan and Inspection and 

Maintenance Plan 

All dry floodproofed buildings must maintain a Flood Emergency Operations Plan and an Inspection and 

Maintenance Plan. The complexity of these plans depends largely on whether the dry floodproofing measures 

are passive or active and how much human intervention the active measures require. If ASCE 24 is required to 

be followed for the retrofit design, these plans will need to be approved by the Authority Having Jurisdiction. 

Both the Flood Emergency Operations Plan and the Inspection and Maintenance Plan should be drafted and 

submitted as part of the building permit application. More information on the minimum requirements for 

operations, maintenance, and inspection plans is available in Sections 2.5.4 and 2.5.5. The following paragraphs describe in more detail the typical components of a dry floodproofing measure that would be inspected 

and what common failures an inspector might see.

When performing routine inspections of dry floodproofing measures, gaskets and attachment hardware should 

be evaluated to determine whether they are still in good condition. Missing or deteriorated gaskets (see Figure 

3.19) should be replaced with materials that are designed for use with the dry floodproofing shields. Shields 

and anchorage hardware should be installed at least annually to verify that all necessary hardware is available. 

A recommended practice is for owners to test their dry floodproofing components when renewing their flood 

policy each year. Emergency power sources and sump pumps should also be tested to verify that they are also 

in good working order. Sump pumps should be tested using the emergency power source rather than using the 

normal power source. Some dry floodproofing measures incorporate the use of leak detectors, which should 

also be tested. An inspection of the exterior of the building is also necessary to verify that no additional penetrations have been made below the DFE to which the dry floodproofing measure protects. Plumbing, electrical, 

mechanical, communications, or other penetrations can be installed over time and render the dry floodproofing ineffective if not properly sealed. Although sealing these penetrations is the building owner’s responsibility, 

the design professional should make it clear to the building owner that failure to maintain the dry floodproofing measures can result in either greater water intrusion than the sump pump system was designed for or, in a 

worst case scenario, water infiltration to a degree that renders the dry floodproofing measures useless. 
3-34 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

3.9 Dry Floodproofing in New Construction

Although this chapter focuses on retrofitting existing 

buildings, similar methods are used for designing and 

constructing new buildings that are dry floodproofed. 

Depending on which codes are locally enforced, ASCE 

24 will likely be the required standard for flood-resistant 

design and construction of a new building and is recommended as a standard of practice even if not required. 

ASCE 24 will be used to establish the elevation of the 

floodproofing measure, and ASCE 7 will be followed for 

the design loads that should be considered. 

Being able to design the layout of the site and building is a benefit of new construction that can avoid many 

of the design challenges in a retrofit project. If permitted by floodplain management regulations, the site can 

be graded to reduce portions of the building that need to be dry floodproofed. Additionally, laying out the 

building to minimize or eliminate openings and points of egress below the required elevation will reduce construction details and the human intervention that may be necessary to prevent the intrusion of floodwaters. 

Higher ceiling heights can allow windows to be located above the required elevation and still allow sunlight to 

reach the lower floors, which can create flexibility in the use of the lower floors. Mechanical systems and electrical systems can also be located on higher floors, eliminating the need to protect them during a flood event.

Careful consideration should be given to the placement of critical building systems (including, but not limited to, MEP components, gas installations, communications systems, and fire suppression equipment) that 

are essential to the functionality of a building. Flood damage to critical building systems can cause the building to be closed for weeks or months, resulting in building loss of function similar to structural damage. There 

Special Note

New construction must comply with the 

locally enforced BFE/DFE and/or IBC 

(ASCE 24 by reference).

Figure 3-19. A 

deteriorated flood 

shield gasket (see red 

circle) that must be 

replaced for the shield 

to seal and function 

properly (Ocean City, 

NJ)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-35

DRY FLOODPROOFING MEASURES 3

is substantial residual risk associated with relying on dry floodproofing measures to protect critical building 

systems. Designers should relocate the systems above the DFE or, at a minimum, provide additional protective measures. For example, a building may be designed with an emergency connection for temporary heat or 

power in case the primary source is compromised. Aside from the residential use limitation, there are very few 

restrictions on occupancy categories of dry floodproofed areas. Designers must consider flood damage implications to areas below the DFE as well as the impacts to building inhabitants because other parts of the building 

may need to be occupied immediately following the flood event. 

In some cases, critical building systems, such as fuel tanks for emergency power, are required by building 

codes to be placed on the lowest floor (including basement). This location, while ideal for reducing the risk of 

fire associated with large volumes of flammable liquids, may be the most vulnerable to flooding. As a result, 

elevating the system above the flood level may not be feasible, but it may be possible to protect it by placing 

it in a dry floodproofed enclosure (see Section 3.3). These enclosures, often considered vaults, are typically 

constructed of reinforced concrete because its inherent mass helps counteract buoyancy and, with proper 

reinforcement, concrete can be constructed to resist hydrostatic pressures (see Figure 3-20). Because rooms 

containing building systems require access and ventilation, they should be equipped with specially designed, 

impermeable doors and ventilation equipment (see Figure 3-21). Also, because barriers used for dry floodproofing are rarely 100 percent watertight, a system to prevent seepage and infiltration is required. Sump 

pumps powered by emergency power sources are recommended. Note, these enclosures are not intended to be 

occupied when flooding is imminent. 

A large building area with a floor slab deep below the flood protection level can experience significant buoyancy loads. A retrofitted building must rely on its dead load and any foundation connections from the original 

design to resist buoyancy, but the foundation of a new building can be designed to resist buoyancy. Deep foundations or large, robust foundation elements can be necessary to achieve the required resistance.

Figure 3-20. Dry 

floodproofed fuel 

pump room adjacent 

to generator fuel tank 

vault
3-36 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

Figure 3-21. Door to 

a dry floodproofed 

generator fuel tank 

vault servicing multiple 

generators in a highrise building

Walls and floor slabs are subject to the loads described earlier in Section 2.2, but the cost of constructing walls 

and slabs sufficient to resist these loads can be minimized in new construction. Floor slabs can be properly 

reinforced and sufficiently thick to prevent buoyancy forces from cracking them. Additionally, sufficient waterproofing can be applied to the slab and joints during construction to eliminate or minimize the potential for 

water intrusion and seepage. Perimeter and underdrain systems can be drained to a location outside the main 

building to eliminate the need for sump pits, which is another location where water can infiltrate the building.

Floor slabs and walls can be detailed to allow a sufficient connection between them in order to maintain the 

load path. The connection can be further detailed to minimize the potential for water migrating through the 

wall-to-slab connection. The wall-to-slab connection is often an area of weakness for water intrusion in dry 

floodproofing projects. 

Walls can be floodproofed by minimizing cold joints and properly detailing them to minimize pathways for 

water intrusion. Excavation for below-grade walls will allow for the proper application of a waterproofing 

membrane or coating. The designer may have a wider selection of products to choose from because of accessibility to the walls. Wall penetrations can be located above the required elevation or detailed and tested to 

prevent water intrusion.

The SERRI Report referenced in Section 3.2 suggests that simple wall systems can be successful and that dry 

floodproofing increases the cost of construction by 15 percent. Although cast-in-place concrete walls are commonly limited to industrial structures, wall assemblies may be appropriate for many other non-residential 

and commercial buildings requiring dry floodproofing measures. The SERRI Report indicates that if detailed 

properly, an ICF system and metal SIPs are capable of being substantially impermeable. A CMU block wall 

with filled cells and an exterior membrane (see Figure 3-22) was also successful in meeting the requirements 

for substantially impermeable buildings. The SERRI Report indicates that multi-layered polymer sealants 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-37

DRY FLOODPROOFING MEASURES 3

and liquid-applied asphaltic membranes are both successful. Prior to using these systems, the designer should 

review the SERRI Report to evaluate the appropriateness of a particular wall system and to evaluate the construction details under which the systems were found to be substantially impermeable.

Doors, windows, and other openings below the required elevation should be detailed to eliminate the need for 

flood shields if possible, but at a minimum, permanently installed flood shields should be incorporated. New 

construction allows for more passive flood shields than in retrofits because the shields and shield supports can 

be incorporated into the design. Windows that cannot be situated above the required elevation should use 

materials such as submarine glass systems and seals that eliminate the need for a flood shield. Door frames and 

window mullions are particular areas of concern, and field testing to verify proper installation is important. 

Door and window frame anchorage should also be carefully checked and verified during installation. If flood 

shields are required, see Section 3.5.

Figure 3-22. Cross 

section of the test 

mock-up used for 

the SERRI tests 

of a substantially 

impermeable CMU wall 

system (SERRI Report) 

– Not intended for 

design purposes
3-38 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

Plumbing systems and mechanical systems should be run inside the building as much as possible in new construction. Properly waterproofing wall penetrations is often a challenging process. If lines running into the 

building are located above the required elevation, many of the common points of water entry during flood 

events can be eliminated. If plumbing and mechanical systems are located in utility chases along interior walls, 

the potential for water intrusion through an unnoticed leak in a chase can be eliminated. Utility chases along 

exterior walls may need to be grouted after utilities are routed to prevent the potential for water intrusion. 

Moving lines above the required elevation will also allow backflow valves to be located above floodwaters.

A Flood Emergency Operations Plan and a Maintenance and Operations Plan should be drafted (see Sections 

2.5.4, 2.5.5, and 3.8). These plans need to meet the same requirements as a retrofit project, but the amount of 

human intervention required to successfully implement the plan should be lower.

The final step in designing a dry floodproofing project is to provide a Floodproofing Certificate for NonResidential Structures, which needs to meet the requirements discussed in Section 2.1.2.

3.10 Case Study: University of Texas Perimeter Wall and Dry 

Floodproofing Project

In 2001, Tropical Storm Allison left the Medical School Building (MSB) at the Texas Medical Center 

in Houston, TX, with a flooded first floor and basement and losses of more than $205 million. The 

first floor and basement housed mechanical equipment, gross anatomy classrooms, the morgue, and 

research laboratories. 

To reduce the potential for future flooding, the first floor and basement were dry floodproofed to the 

0.2-percent-annual-chance (500-year) flood elevation plus 1 foot. The floodproofing did not affect 

the function of the spaces. The flood elevation requirements resulted in large portions of the first floor 

having to resist flood loads for depths of 7 feet. The project also needed to be designed to minimize the 

impacts to existing trees and landscaping to be aesthetically pleasing with measures unobtrusively incorporated into the building and landscaping. Additionally, operations at the MSB needed to continue 

during construction, which required dividing the project into 11 phases. 

The total project cost was approximately $12 million. The floodproofing included:

■ Reinforcing or replacing existing concrete walls and constructing sections of new concrete 

floodwalls

■ Installing flood doors at key locations to maintain points of egress (see Figure 3-23) 

■ Retrofitting windows with aquarium (submarine) glass and creating a floodproof window system

■ Installing isolation (backflow) valves on sanitary water system and sewer lines

■ Retrofitting the basement to resist flood loads and buoyancy

■ Replacing exterior stairways below the level of flood protection 

■ Waterproofing connections between buildings
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 3-39

DRY FLOODPROOFING MEASURES 3

Because some sections of the original first floor walls were curtain walls, they could not be properly 

retrofitted to resist the flood loads. The curtain walls were replaced with reinforced concrete walls. One 

area of the main building required that the concrete walls be constructed offset from the building to 

maintain the continuity of the wall system.

Nine flood doors were added to maintain points of egress. Some of the flood doors have dual inflatable 

gaskets to provide redundant protection. The flood door seal pressures and closure bolts are monitored 

from a remote and secure location during a storm event and are on an independently powered building automation system.

Retrofitting windows was a particular challenge because of the flood elevation requirements. Aquarium 

(submarine) glass was used to allow natural light to enter the first floor. The retrofit consisted of replacing the conventional window wall system with laminated glass panels and oversized mullions to resist 

flood loads. 

Plumbing systems (sanitary water systems and sewer lines) were protected with isolation valves that act 

as backflow prevention devices. Loss of power tips the devices and prevents potential floodwaters from 

entering the building. 

Ross Sterling Avenue, a public street that passes under the MSB, provides access to other areas of the 

medical center (see Figure 3-24). Local authorities would not allow floodgates to be placed across the 

road, so the road was raised to create a berm that provides protection to the level of the base flood. 

Because Ross Sterling Avenue passes under the second floor of the building, all penetrations through 

the walls were waterproofed, and the mechanical chases were grouted to seal the area between the chase 

and the ductwork and pipes inside the chase. The waterproofed areas allow Ross Sterling Avenue to 

flood without compromising the building. 

In the portion of the basement that is under Ross Sterling Avenue, the existing pan joist system of 

the basemtent ceiling was strengthened with fiber-reinforced polymer materials to minimize space 

consumption relative to existing and future equipment. Because of the potential buoyancy forces 

acting on the basement slab, some areas were retrofitted with beams and tie-down plates, and some 

equipment required additional anchoring. All existing expansion joints and wall cracks were filled 

Figure 3-23. Flood doors incorporated into 

the existing building façade (source: Walter P. 

Moore)
3-40 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

3 DRY FLOODPROOFING MEASURES

with a urethane grout to allow some movement in the walls without compromising the floodproofing 

measures. To maintain continuity of operation during a flood event, the MEP equipment room was 

further floodproofed as a backup measure in case the dry floodproofed exterior walls fail. Portions of the 

equipment room were located over the basement, and the floor systems of these areas were upgraded to 

resist buoyancy forces.

Areas of particular concern were sections of the stairwell that originally had doors to exit at grade, but 

were below the flood protection level. The doors were walled in, and eight new doors and elevated platforms were constructed from the emergency stair landing between floors to maintain points of egress 

above the flood protection level (see Figure 3-25). 

Connections between buildings presented a considerable design challenge because there were limited 

options for floodproofing. In some areas, the tight spaces between buildings were filled with expansion 

joint material, which was then waterproofed to prevent floodwater infiltration.

Figure 3-25. Three sets of stairs that provide building 

egress during the design flood event, but still allow normal 

use of the building (source: Walter P. Moore)

Figure 3-24. Ross Sterling Avenue was raised 

to protect the MSB to the level of the base flood 

(source: Walter P. Moore)
FLOODPROOFING NON-RESIDENTIAL BUILSINGS 4-1

Other Flood Protection 

Measures

Chapters 1, 2, and 3 focus on dry floodproofing, but other flood protection measures are also available 

to protect existing non-residential buildings from flooding. This chapter describes several other flood 

protection measures and the factors that should be considered when selecting one of these measures or 

a combination of measures. 

■ The flood protection measures that are discussed in this chapter are:

■ Permanent floodwalls and levees, which create a barrier between the building and floodwaters

■ Wet floodproofing, which allows floodwaters to enter the building while using various techniques to 

minimize flood damage and protect critical systems and contents

■ Floodproofing measures for electrical and mechanical utility systems that are difficult to dry 

floodproof

■ Emergency measures for temporary protection (sandbags, temporary flood barriers, and flood 

wrapping systems)

As with the dry floodproofing measures discussed in the previous chapters, the flood protection measures in 

this chapter should be evaluated by a registered design professional to determine the design flood forces and 

which measures would be most effective. 

4.1 Floodwalls and Levees 

Permanent floodwalls and levees are constructed barriers 

that provide flood protection to one or more buildings. Unlike the dry floodproofing measures described 

in Chapter 3, which provide structural protection for 

shallow flood depths, floodwalls and levees can provide 

effective flood protection to buildings that experience 

flood levels of 4 feet or greater. However, if a floodwall 

or levee is breached or overtopped, then the barriers provide no flood protection. 

4.1.1 Floodwalls

A floodwall is a freestanding, permanent, engineered 

structure designed to prevent encroachment of floodwaters. Floodwalls, which are typically constructed of 

reinforced concrete or masonry, provide a barrier against 

Warning

Floodwalls and levees are not permitted to 

address Substantial Improvement/Damage 

and do not bring new buildings into compliance with NFIP regulations unless 

they are accredited per 44 CFR § 65.10. 

Furthermore, the floodwalls and levees 

described in this chapter do not affect NFIP 

flood insurance rates or mandatory purchase requirements.

Additionally, NFIP regulations do not 

permit encroachments such as floodwalls 

and levees in a regulatory floodway unless 

hydrologic and hydraulic analyses demonstrate that the proposed floodwall or levee 

would not result in any increase in flood 

levels in the community during the base 

flood (44 CFR § 60.3(d)(3)).
4-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

inundation, protect structures from hydrostatic and hydrodynamic loads, and may deflect flood-borne debris 

and ice away from the building. When located in an area where ASCE 7 is referenced by adopted codes, floodwalls must be designed to resist ASCE 7 load combinations. Figure 4-1 shows a masonry floodwall. 

Floodwalls are normally placed some distance from the building to avoid having to make structural modifications to the building. Depending on the site topography, floodwalls may protect only the low side of the site 

(and must tie into high ground), or they may surround the site. Floodwalls that surround a site have openings that provide access to the site. The openings must be closed before the onset of a flood, which is done by 

installing engineered closure structures (see Figure 4-1). Site access is affected while the closure structures are 

in place. 

When a building is protected by a floodwall, underground utilities that serve the building and run under the 

floodwall must be considered so the utilities do not become conduits that allow floodwaters to pass through or 

under the floodwall and into the building. See Section 4.1.1.2.

The following sections contain information on the most common types of floodwalls, the building and site 

characteristics to be considered when designing a floodwall, and the floodwall design process.

4.1.1.1 Types of Floodwalls

The most common types of floodwalls are gravity, cantilever, buttress, and counterfort (see Figure 4-2). 

Figure 4-1. Typical 

masonry floodwall with 

engineered closures, 

which protected the 

Oak Grove Lutheran 

School in Fargo, ND, 

from flooding in 2001 

(source: Flood Control 

America, LLC)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-3

OTHER FLOOD PROTECTION MEASURES 4

4.1.1.1.1 Gravity Floodwalls

As the name implies, a gravity floodwall depends on its weight for structural stability. Structural stability is 

attained by effective positioning of the mass of the wall at its base, rather than by the weight of the retained 

materials (water or soil) on top of the wall foundations. A gravity floodwall resists overturning primarily 

because of the dead weight of the construction material (concrete or masonry); it is simply too heavy to be 

overturned by a lateral flood load. 

Compared to the other types of floodwalls that are discussed, gravity floodwalls are relatively easy and straightforward to construct. However, the primary disadvantage of gravity floodwalls is that they require massive 

amounts of material compared to the other floodwall types. As the height of a gravity floodwall increases 

and the amount of required material increases, the more cost-effective the other types of floodwalls become. 

Gravity walls are therefore most appropriate for low walls or lightly loaded walls. In addition, the sheer weight 

of the floodwalls required to resist flood forces can overload the bearing capacity of the supporting soils, which 

Figure 4-2. Gravity, 

cantilever, buttress, and 

counterfort floodwalls 
4-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

can make gravity floodwalls inappropriate when walls need to be relatively tall and the bearing soils are relatively weak. 

4.1.1.1.2 Cantilever Floodwalls

Cantilever floodwalls are the most common type of floodwall because they are economical to design and 

construct. They use cantilever action to retain the mass behind the wall. Cantilever floodwalls are usually constructed of reinforced concrete or concrete block with steel reinforcing bars embedded in the concrete core of 

the wall (see Figure 4-3). 

Figure 4-3. Concrete cantilever floodwall reinforcement 

Stability is achieved partially from the weight of the soil on the heel portion of the base and from the weight 

of the wall itself balanced by the lateral forces and overturning moments (see Figure 4-4). The footing is often 

constructed with a “key” to increase sliding resistance (see Figure 4-3). 

Because a cantilever floodwall often also serves as a cantilever retaining wall, the floodwall must be designed 

to resist the load combinations in ASCE 7 or the loads in other accepted engineering standards. The design 

should take into account buoyancy effects that reduce the submerged weight of the floodwall and the reduced 

bearing capacity of the soils that support the wall. Backfill may be placed along the side of the wall exposed to 

flooding to keep water away from the wall during flooding conditions.

Similar to the gravity floodwall, as the flood elevation increases and the required materials and cost of the cantilevered floodwall increase, the more cost-effective the alternative types of floodwalls may become. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-5

OTHER FLOOD PROTECTION MEASURES 4

4.1.1.1.3 Buttress and Counterfort Floodwalls

The only difference between a buttress and counterfort floodwall is that the transverse support wall is on opposite sides (see Figure 4-2). In a buttressed floodwall, the transverse support wall is on the heel side, opposite 

the retained materials, and in a counterfort wall, the transverse support wall is on the toe side. Counterfort 

floodwalls are more widely used than buttressed floodwalls because their transverse support walls are hidden 

under the retained material (water or soil), whereas buttress floodwalls occupy what could otherwise be usable 

space in front of the wall.

A counterfort floodwall is similar to a cantilever floodwall except that a counterfort can be used when the cantilever would be long or when very high pressures would be exerted behind the wall. Counterfort walls include 

intermediate transverse support bracing designed and built at intervals along the wall to allow for a more economical wall design. Counterfort walls are generally cost-effective for walls higher than 20 feet.

4.1.1.2 Building and Site Considerations in Floodwall Design

Designing a floodwall requires detailed information about the existing building and site. Key information 

includes: 

■ Surveyed lowest point of entry

■ Topographic and utilities survey

■ Identified flood hazards

■ Soil type

■ Local building requirements

■ Owner preferences

Figure 4-4. Stability of 

a cantilever floodwall
4-6 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

After this information has been collected, the designer must assess the existing building and site conditions, 

as follows:

■ Existing building foundation conditions. Existing building foundation conditions may affect the 

floodwall design directly. For example, evidence of seepage or cracking in foundation walls may 

indicate the need to relieve hydrostatic pressure on the foundation as part of the floodwall design.

■ Soil type. The type of soil surrounding the existing building is a key consideration in floodwall 

design. In general, the more cohesive soils (e.g., silty sands, clays) have lower permeability and 

reduced seepage potential, and can simplify floodwall drainage design. Less cohesive soils, such as 

clean sands or gravels, tend to have higher permeability and increased seepage potential, which must 

be accounted for in the drainage design. More cohesive soils tend to have lower bearing capacity and 

frictional resistance that may require larger floodwall footings than those on less cohesive soils.

■ Potential for seepage under the floodwall.

A floodwall may not reduce the hydrostatic 

pressures against a below-grade foundation. 

Seepage under the floodwall and the natural 

capillary action of the soil layer may result in 

a water level inside the floodwall that is equal 

to or above grade. The water level inside the 

floodwall increases as the depth of flooding 

outside the floodwall increases and may 

compromise floodwall effectiveness for longduration events if not addressed. 

■ The potential for seepage under the floodwall 

can be relieved by installing a foundation 

drainage system (drainage tile and sump pump) at the footing level and/or by extending the distance 

from the foundation to the floodwall. Seepage pressures can also be decreased by placing backfill 

against the floodwall to extend the point where floodwaters submerge the soil or by installing a 

sheet pile or cement curtain cutoff wall below the floodwall foundation surrounding the existing 

structure. Computing the proper spacing between the structure and floodwall foundation, backfill 

soils, or cutoff walls required to address seepage pressure is complex and should be done by an 

experienced geotechnical engineer.

■ Number and size of floodwall openings. The number and size of floodwall openings have a 

direct impact not only on the floodwall design but also on the operation of the existing building. 

Floodwalls with fewer and smaller openings are simpler to design and require less warning time to 

protect with floodwall closures, but the reduced number of openings can limit site access, hampering 

the ability of the existing building to function efficiently. Designers can consider passive floodwall 

opening systems that minimize the need for human intervention. Designers must therefore discuss 

the floodwall openings and access/egress issues with owners to understand the needs and level of 

disruption to be expected to facility operations.

■ Utility penetrations through or under the floodwall. Utilities that penetrate the floodwall or run 

under the floodwall may become conduits that allow floodwaters to enter the area protected by the 

floodwall. Utilities should be sealed, and because sealing is rarely 100 percent effective, provisions to 

collect and dispose of seepage that flows through underground utilities should be installed.

Warning

Flood duration is a critical consideration 

in the design of floodwall seepage control 

measures. The longer the duration (i.e., 

the longer floodwaters are in contact with 

the floodwall), the greater the potential for 

seepage and the greater the need for seepage control measures such as backfill or 

cutoff walls.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-7

OTHER FLOOD PROTECTION MEASURES 4

Best Practice – Floodwall System with Passive Floodgates

Protects Two Hospitals

Lourdes Hospital in Binghamton, NY, is in the 100-year floodplain of the Susquehanna River. Flooding 

in 2006 forced the hospital to close for 2 weeks and caused $20 million in damage (FEMA 2011a). 

Relocating the hospital was not feasible, but it was determined that a floodwall system would provide 

the necessary protection. The system was constructed for an estimated $7 million using funds from 

FEMA and New York State. The floodwall, which protects the hospital to a 500-year flood elevation, 

consists of a concrete T-wall and passive floodgates at each of the 11 entry points. The gates automatically deploy during a flood, triggered by the hydrostatic pressure of the rising floodwaters. When the 

floodwaters recede, the gates lower to their original open position. The floodwall was completed in 2010.

In 2011, Tropical Storm Lee swept through Binghamton depositing 7.5 inches of rain in a single day. The 

Susquehanna River crested at 25.7 feet before receding (NOAA 2011). Despite the record rainfall, the 

hospital remained fully operational and experienced no flooding (see Figures 4-5 and 4-6).

Columbus Regional Hospital in Columbus, IN, was closed for 6 months in 2008 because of flooding. 

The flooding forced the evacuation of 157 patients, knocked out primary and emergency electrical systems, and caused $180 million in damage (Columbus Regional Hospital 2012). Relocating the hospital 

was not feasible because of cost. FEMA and the hospital staff determined that a floodwall would be the 

best way to provide flood protection. Construction began in June 2011 and was completed in April 2012. 

The floodwall was funded by the FEMA Public Assistance Program, 406 Mitigation Program. The encircling 2,400-foot floodwall is 2 feet higher than the 100-year flood elevation and incorporates 15 passive 

floodgates (FEMA 2012c). The hospital has also strengthened its Flood Emergency Response Plan. 

Hospital officials are more involved with community management now and remain aware of weather 

conditions (see Figures 4-7 and 4-8).

Figure 4-5. Floodwall successfully safeguards Lourdes 

Hospital from Tropical Storm Lee flooding (source: 

FloodBreak)

Figure 4-6 Aerial view showing effective protection of 

Lourdes Hospital from flooding as a result of Tropical 

Storm Lee
4-8 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.1.1.3 Floodwall Design Process

Floodwall design depends primarily on the type of flooding expected at the building site. High water levels 

and velocities can exert significant hydrostatic and hydrodynamic forces that must be accounted for in the 

floodwall design. 

The design of any type of floodwall must address the following three concerns: 

■ Ability of the wall to resist external loads and hold back floodwater

■ Sufficiency of floodwall closure strength and stiffness to resist the calculated stresses

■ Ability of surrounding soils to resist scour and erosion

Most non-residential floodwalls are engineered to flood depths of 6 or 7 feet above existing grade. A minimum 

of 1 foot of freeboard above the flood protection level is recommended. Tall floodwalls (taller than 10 feet) can 

be expensive to construct and maintain and may require additional land for grading and drainage.

Designers should follow the eight-step process shown in Figure 4-9 and develop specifications for appurtenances such as drainage systems, waterproof materials to stop seepage and leakage, and miscellaneous details 

to meet site and owner preferences. 

Important issues to be considered in the eight-step floodwall design process are as follows:

■ When determining the wall height and footing depth based on site and design flood conditions (Step 

1 in Figure 4-9), remember to include freeboard where appropriate and when required by local codes 

or regulations.

■ Use load combinations specified by ASCE 7 to calculate lateral and vertical forces acting on the wall 

(Step 3 in Figure 4-9).

■ If the calculated factors of safety against sliding, overturning, or bearing capacity failure of the wall 

are insufficient (Steps 4, 5, and 7 in Figure 4-9), revise wall dimensions and repeat analyses based on 

the corrected dimensions.

Figure 4-7. Floodwaters surround Columbus Regional 

Hospital in 2008

Figure 4-8 Columbus Regional Hospital schematic of 

floodwall plan
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-9

OTHER FLOOD PROTECTION MEASURES 4

The floodwall design process is iterative—the initial design is based on experience and successful designs, 

checked against design loads and conditions, and revised as necessary until all requirements are satisfied by the 

design.

Figure 4-9. Floodwall design process
4-10 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.1.2 Levees

Unlike floodwalls, levees are not made of manmade materials but rather compacted soil. Levees are more 

commonly used to protect large areas such as agricultural facilities. However, given their relative cost and the 

amount of land required, levees are a less common flood-mitigation measure than many of the other flood 

protection options presented in this manual. The following sections provide basic details on levee construction 

considerations and design.

4.1.2.1 Building and Site Considerations in Levee Design

Designing a levee requires collecting information about 

the existing building(s) to be protected and the surrounding site, including the surveyed lowest point of 

entry, topographic and utilities surveys, flood hazard 

identification, soil type, local building requirements, 

and owner preferences. After this information has been 

collected, the designer must assess whether certain conditions exist before a levee can be considered a viable 

floodproofing option. The key conditions to consider before proceeding are listed below.

■ Property area. Levees typically require a significant amount of vacant land surrounding the area to 

be protected and are not suitable for densely developed areas. 

■ Topography. A significant portion of the cost associated with the construction of a levee hinges 

on the amount of fill material needed. If the natural topography around the area to be protected is 

such that only one or two sides of the area need to be protected, a levee may be more feasible and 

economical.

■ Suitable soil availability. Relatively impermeable soils that will support the levee foundation and 

act as suitable impervious fill materials must be readily available to address concerns of stability 

and seepage. ASTM International (ASTM) defines impermeable soils (e.g., high-plasticity clays, 

low-plasticity clays, clayey sands) in ASTM D2487, Standard Practice for Classification of Soils for 

Engineering Purposes (Unified Soil Classification System) (ASTM 2011).

■ Regulatory requirements. Relevant Federal and State laws and regulations and local ordinances 

must be reviewed. Coordination with Federal, State, and local officials may be necessary to determine 

whether levee construction is permissible, restricted, or prohibited. Also, NFIP regulations restrict 

levee construction in a FEMA-designated floodway, which is the main portion of a stream or 

watercourse that conveys flow during the base flood.

■ Flood depth and velocity. Levees become increasingly more expensive to design and construct 

as flood depths exceed 7 feet because of material costs and space requirements. Additionally, if 

flood velocities exceed 8 feet per second (ft/sec), the increased cost of protecting against the scour 

potential may require considering a different retrofit measure. Finally, flood depths and velocities 

should be checked to ensure that the levee will not result in increased flood hazards upstream. In 

many cases, the local floodplain regulations may require an analysis of the proposed modification to 

the floodplain.

Special Note

For more information on levee design and 

construction, see Chapter 5F of FEMA 

P-259. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-11

OTHER FLOOD PROTECTION MEASURES 4

■ Seepage potential. Seepage under a levee and the natural capillary action of the soil layer may 

result in a water level inside the levee that is equal to or above grade and may compromise the 

levee effectiveness. This condition can be relieved by using an impervious core that extends to the 

bottom of the inspection trench, installing a drainage toe, and/or extending the distance from the 

foundation to the levee. 

4.1.2.2 Basic Levee Design Parameters

The basic parameters described below help to control 

levee design costs while providing a conservative design 

in general accordance with the USACE guidance. The 

parameters pertain to the design and construction of 

localized levees for a maximum flood depth of 7 feet. 

Slope stability analysis and calculation of seepage rates 

are not addressed. The recommended side slopes are 

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 

in ASTM D698, Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort

(ASTM 2012), should be adequate to ensure stability of such low levees without the need for laboratory or 

field testing or extensive calculations.

The basic parameters for crest width and levee side slopes are defined below and illustrated in Figure 4-10. In 

combination with the toe drainage trench and the cutoff effect provided by backfilling of the inspection trench 

(Section 4.1.2.3), these parameters should provide sufficient control of seepage and may not require complex 

analyses.

■ Maximum settled levee height of 8 to 10 feet.

Recommended as the practical limit of levees 

that protect one or more individual structures 

based on available space and material costs.

■ Minimum levee crest width of 10 to 12 feet.

Recommended to minimize seepage concerns 

and allow for ease of construction, vehicle 

access, and maintenance.

■ Levee floodwater side slope of 1 vertical to 

2.5 horizontal. Recommended to minimize 

the erosion and scour potential, provide 

adequate stability under all conditions 

(including rapid drawdown situations), and 

facilitate maintenance.

■ Levee land side slope. May vary based on the levee material. If the material is clayey, a land side 

slope of 1 vertical to 3 horizontal is acceptable. If the levee material is sandy, a flatter slope of 1 

vertical to 5 horizontal is recommended to provide a lower seepage gradient.

Warning

The design parameters for a typical nonresidential levee as shown in Figure 4-6 

are based on guidance from the USACE 

and other sources and are intended to be 

conservative. Alternate parameters for a 

specific site may be developed by a geotechnical engineer qualified in levee design.

Warning

Duration of flooding is a critical consideration in the design of levee seepage 

control measures. The longer the duration 

of flooding (i.e., the longer floodwaters are 

in contact with the levee), the greater the 

potential for seepage, and the greater the 

need for seepage control measures such 

as cutoffs, drainage toes, and impervious 

cores.
4-12 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

■ 1 foot of freeboard. Recommended to provide a margin of safety against overtopping and to allow 

for the effects of wave and wind action. Wave and wind forces create an additional threat by raising 

the height of the floodwaters.

Figure 4-10. Levee design parameters for a typical non-residential levee

In addition to these design parameters, considerations must be made for the maintenance of the levee. 

Maintenance must be completed on a regular basis. The maintenance program should include:

■ A collection or sand trench on the inward or landward toe of the levee to collect any seepage that may 

occur and to act as a place to collect interior rainfall runoff. See Figure 4-8 above.

■ A levee meant to be in place permanently should include an inspection/cutoff trench. This trench 

serves many purposes, including tying the levee structure into natural ground; as a means of 

identifying various utility lines that may be passing underneath the levee and need relocating; as a 

means of identifying burrowing animal passages; and, when backfilled with an impervious soil, as a 

means of stopping seepage underneath the levee.

■ Drainage and runoff inside the levee must be taken into consideration. The above sand drainage toe 

facilitates the collection of interior runoff. When directed into sumps along the toe of the levee, the 

collected runoff can be pumped out of the protected area.

■ Burrowing animals often favor levee embankments as a place for their dens and borrows. Some of 

the worst offenders are muskrats and woodchucks or ground hogs. These burrows afford a ready 

means for floodwaters to pass through the levee structure. Such burrowing will eventually lead to a 

weakening of the levee and possible failure.

■ Trees and large shrubs should not be allowed to grow on a levee. If they are removed or die at a later 

time, their root systems decay and provide weak areas in the levee that can also lead to failure.

■ Utility lines, such as electrical conduits or sewers, should not pass through a levee. Seepage along the 

exterior side of these lines can lead to what is known as “piping,” where fine soil particles are washed 

away in the interior of the levee. As this process continues, larger and larger particles are dislodged, 

again leading to potential levee failure.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-13

OTHER FLOOD PROTECTION MEASURES 4

■ The flood or water side of the levee should be protected with the appropriate size of rip-rap if flood 

velocities are sufficiently high to warrant it. Check with a qualified local engineer to determine the 

need and size of rip-rap.

■ Barriers such as levees may not be permitted by regulatory agencies because of their potential adverse 

impact on flood stages. They should be designed and planned by a qualified engineer.

■ If water overtops a levee, it will likely fail at that point unless heavily armored. Keep in mind that 

once a levee begins to fail, the area meant to be protected will flood quickly.

■ Constructing behind a levee system creates residual risk as a result of the potential of failure of the 

levee structure.

4.1.2.3 Levee Design Process

Designing levees involves sizing the levee properly and developing the specifications for appurtenances such as 

drainage systems, impervious fill materials to minimize seepage and leakage, and miscellaneous details to meet 

site and owner preferences. The six-step process outlined in Figure 4-11 provides a simplified approach to levee 

design. Note that because of the importance of the soil characteristics of the levee foundation, the excavation 

of an inspection trench is required. The minimum dimensions of the inspection trench are shown in Figure 

4-9. The inspection trench is required to run the length of and be located beneath the center of the levee, and 

provides the designer with information that will dictate the subsequent steps in the design process.

Figure 4-11. Basic levee design process
4-14 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.2 Wet Floodproofing Measures

Unlike dry floodproofing, permanent floodwalls and levees, and emergency floodproofing measures (see 

Section 4.4), wet floodproofing involves modifying a building to allow floodwaters to enter it in order to minimize damage to the building. Wet floodproofing involves the following:

Using flood damage-resistant materials below the DFE throughout the building

■ Raising utilities and important contents to or 

above the flood protection level

■ Installing and configuring electrical and 

mechanical systems to minimize disruptions 

and facilitate repairs

■ Installing flood openings or other methods to 

equalize the hydrostatic pressure exerted by 

floodwaters

■ Installing pumps to gradually remove 

floodwater from basement areas after the flood

The following subsections provide details on the most common wet floodproofing measures. More information is available in NFIP Technical Bulletin 7-93, Wet Floodproofing Requirements (FEMA 1993b).

4.2.1 Flood Damage-Resistant Materials

Using flood damage-resistant materials can help reduce flood damage and facilitate cleanup to allow buildings 

to restore service as quickly as possible. Interior building elements such as wall finishes, floors, ceilings, roofs, 

and building envelope openings can suffer significant damage from inundation by floodwaters, which can lead 

to failure or unsanitary conditions. The exterior cladding of a building subject to flooding should be nonporous, resistant to chemical corrosion or debris deposits, and conducive to easy cleaning. Interior finishes 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 damage-resistant materials to 

minimize damage during and after inundation.

A detailed list of appropriate flood damage-resistant materials can be found in NFIP Technical Bulletin 2, Flood 

Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with 

the National Flood Insurance Program (FEMA 2008a). Technical Bulletin 2 classifies flood damage-resistance of 

materials as acceptable or unacceptable based on cleanability and water resistance (see Table 4-1).

Warning

NFIP regulations do not permit wet floodproofing to be used to bring a Substantial 

Improvement/Damage structure into 

compliance unless the area to be wet floodproofed is used solely for parking, building 

access, or storage (44 CFR § 60.3(c)(5)).
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-15

OTHER FLOOD PROTECTION MEASURES 4

Table 4-1. Class Descriptions of Flood Damage-Resistant Materials

NFIP Class Class Description

Acceptable

5

Highly resistant to floodwater(a) damage, including damage caused by moving water.(b) These 

materials can survive wetting and drying and may be successfully cleaned after a flood to render them 

free of most harmful pollutants.(c) Materials in this class are permitted for partially enclosed or outside 

uses with essentially unmitigated flood exposure.

4

Resistant to floodwater(a) damage from wetting and drying but less durable when exposed to moving 

water.(b) These materials can survive wetting and drying and may be successfully cleaned after a 

flood to render them free of most harmful pollutants.(c) Materials in this class may be exposed to and/

or submerged in floodwaters in interior spaces and do not require special waterproofing protection.

Unacceptable

3

Resistant to clean water(d) damage but not floodwater damage. Materials in this class may be 

submerged in clean water during periods of flooding. These materials can survive wetting and drying 

but may not be able to be successfully cleaned after floods to render them free of most(c) harmful 

pollutants.

2

Not resistant to clean water(d) damage. Materials in this class are used in predominantly dry spaces 

that may be subject to occasional water vapor and/or slight seepage. These materials cannot survive 

the wetting and drying associated with floods.

1 

Not resistant to clean water(d) damage or moisture damage. Materials in this class are used in 

spaces with conditions of complete dryness. These materials cannot survive the wetting and drying 

associated with floods.

Source: NFIP Technical Bulletin 2 (FEMA 2008a)

(a) Floodwater is assumed to be considered “black” water; black water contains pollutants such as sewage, chemicals, heavy metals, or 

other toxic substances that are potentially hazardous to humans. 

(b) Moving water is defined as water moving at low velocities of 5 feet per second (ft/sec) or less. Water moving at velocities greater than 

5 ft/sec may cause structural damage to building materials. 

(c) Some materials can be successfully cleaned of most of the pollutants typically found in floodwater. However, some individual pollutants 

such as heating oil can be extremely difficult to remove from uncoated concrete. These materials are flood damage-resistant except 

when exposed to individual pollutants that cannot be successfully cleaned.

(d) Clean water includes potable water as well as “gray” water; gray water is wastewater collected from normal uses (e.g., laundry, 

bathing, food preparation).

Table 2 in Technical Bulletin 2 can be used as a guide for selecting structural building components (framing 

and some sheathing) and non-structural building components (coverings finishes, insulation, cabinets, doors, 

partitions, and windows) to use below the expected flood level. Some combinations of acceptable materials 

may result in unacceptable conditions; the manufacturer’s specifications should always be reviewed. 

Technical Bulletin 2 also contains criteria for selecting flood damage-resistant connectors. Generally, the performance requirements in Technical Bulletin 2 suggest that masonry or concrete construction is best suited for 

flood damage resistance. Wood structures may be acceptable if constructed of solid structural (2x4) lumber 

with exterior-grade plywood sheathing or if the wood has been pressure treated or is naturally decay-resistant. 

Steel structures may be acceptable if the steel is galvanized or protected with rust-retardant paint.
4-16 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.2.2 Protection of Vulnerable Equipment and Contents

Protecting vulnerable equipment and contents by placing them above the DFE is a simple, inexpensive, and 

effective way to reduce flood damage. This type of protection is particularly effective for non-residential buildings where the value of equipment or contents exceeds the value of the building. All critical records, files, 

documents, computer servers, high-value equipment, or stock should be located on an upper floor whenever 

possible. If this is not practicable, vulnerable equipment and contents may be elevated above the DFE using 

racks, shelves, and/or pedestals that are installed to resist lateral movement from flood forces.

If permanently elevating equipment and contents is not feasible, these items should be positioned so they 

can be relocated above the DFE or removed in the event of a flood. If heavy equipment is to be lifted or 

moved, overhead hoists may be needed. For facilities with smaller equipment or stock that is to be removed 

or when a hoist cannot be provided, aisles should be designed to accommodate forklifts or similar transportation equipment. The material to be relocated should be placed on pallets or equipped with lifting eyes or bars. 

To facilitate removal of manufacturing equipment, quick disconnects should be installed on all electric and 

hydraulic lines. Emergency planning measures for relocated equipment should include provisions for a safe, 

reliable form of transportation to deliver materials from the existing structure to a nearby storage location outside of the flood hazard area.

Best Practice – Wet Floodproofing Retrofits to Beach Front Restaurant

The Duval Beach Club is on the beach in Key West, FL. After the club suffered flood damage in 

Hurricanes Rita and Wilma, the owner decided to mitigate against future flood damage by implementing wet floodproofing retrofits (see figure 4-12). The retrofits consisted of:

n Elevating the electrical system by running 

wiring along the top of the walls, down to 

each outlet

n Locating outlets 42 inches above the floor

n Fitting appliances with quick disconnections

n Installing furniture so it could be removed 

quickly

n Adding breakaway walls parallel to the 

ocean

n Attaching hurricane clips to the roof to make 

a continuous load path from the roof to the 

floor slab

n Using non-absorbent materials and coatings throughout the building

Cleanup after a storm now involves shoveling out the sand and cleaning and resanitizing surfaces 

and fixtures. Now the time from cleanup to opening is measured in days, not weeks or months (FEMA 

2007b).

Figure 4-12. The Duval Beach Club after wet 

floodproofing retrofits
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-17

OTHER FLOOD PROTECTION MEASURES 4

4.2.3 Flood Openings for Equalization

When structures that are constructed on extended solid foundation walls or that have other enclosures below 

the DFE, the foundation walls must have openings that permit the automatic entry and exit of floodwater 

from the enclosure areas (see Figure 4-13). 

Figure 4-13. Typical openings in walls of enclosures

Flood openings allow floodwaters to reach equal levels on both sides of the walls and reduce the potential 

for damage from hydrostatic pressure. NFIP regulations require these openings in all new construction and 

Substantial Improvements of existing buildings in SFHAs. Additionally, this guide recommends retrofitting 

existing buildings that were constructed before the community joined the NFIP with flood openings for enclosures below the DFE. 

The minimum NFIP criteria for the design of these openings are in 44 CFR § 60.3(c)(5) and are as follows: 

■ A minimum of two openings must be provided 

on different sides of each enclosed area.

■ Openings must have a total net area of not 

less than 1 square inch for every square foot of 

enclosed area subject to flooding; this criterion 

is not required if openings are engineered and 

certified.

■ The bottom of all openings must be no higher 

than 1 foot above exterior or interior grade. 

Special Note

For more information on the regulations 

and design guidelines for flood openings, see FEMA NFIP Technical Bulletin 1, 

Openings in Foundation Walls and Walls of 

Enclosures (FEMA 2008d). 
4-18 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

■ Openings may be equipped with screens, louvers, or other coverings or devices, provided these 

components permit the automatic entry and exit of floodwater and do not reduce the net open area 

to less than the required open area. 

It is important to minimize the likelihood that flood openings will be obstructed during a flood event. If openings are obstructed by drywall or other wall coverings, then the openings may not function as intended, which 

can result in significant damage. Figure 4-14 shows a non-residential building with properly installed flood 

openings.

4.3 Floodproofing Electrical and Mechanical Utilities and Systems 

Fully sealing all mechanical and electrical utilities is not 

possible. Also, many mechanical and electrical system 

components cannot operate when inundated and 

cannot resist the buoyant forces caused by submersion. 

Consequently, as a rule, the portions of mechanical 

and electrical utilities and systems in areas vulnerable 

to flooding cannot readily be made flood resistant;1

they can only be elevated above flood levels or placed 

in areas that have been dry-floodproofed. Unless placed 

in dry-floodproofed areas or elevated, pad-mounted 

transformers, switchgear, transformers in underground 

vaults, HVAC equipment, HVAC ducts, pumps and 

emergency generators, and tanks not designed for submerged operation will remain vulnerable to damage 

from a design flood or weaker flood events when they 

are located below the level of flooding. 

Figure 4-14. 

Non-residential 

structure retrofitted 

with flood openings 

following Hurricane 

Katrina (New Orleans, 

LA, 2008)

Special Note

The NFIP allows dry floodproofing in non-residential buildings. However, in new construction, 

Substantial Improvements, and in the restoration 

of Substantially Damaged buildings, mechanical and electrical equipment should be 

elevated instead of being located in dry-floodproofed areas. Elevation provides greater 

protection than dry floodproofing, particularly in 

events that produce floods that exceed the level 

of protection provided by the dry floodproofing. 

For existing structures, it is often not practical to 

elevate all equipment that is vulnerable to flooding. In those instances, a combination of dry 

floodproofing and wet floodproofing is appropriate. Areas containing centralized mechanical 

and electrical equipment can be dry floodproofed 

to protect the equipment from flood damage. 

Remote mechanical and electrical equipment 

can be wet floodproofed to minimize disruption 

of utilities and to minimize restoration times. 

1 Some electrical equipment is designed to operate under water and 

can be floodproofed. However, electrical equipment for submerged 

use is expensive, not readily available, and impractical for many 

electrical components and devices.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-19

OTHER FLOOD PROTECTION MEASURES 4

Figure 4-15 shows an electrical control panel at a water treatment plant that was destroyed when floodwaters 

inundated approximately two-thirds of it. Most of the equipment in the panel was destroyed.

Figure 4-16 shows the main electrical service switchboard that was submerged by floodwaters. The submersion 

prevented power from being supplied to the facility even after floodwaters receded. After floodwaters receded, 

submerged electrical equipment was either repaired or replaced, but was not elevated. Flood risks were not 

mitigated. 

Figure 4-15. Equipment in an electrical 

control panel that was mostly destroyed when 

approximately two-thirds of the height of panel 

was inundated by floodwaters (Columbus 

Junction, IA, 2008)

Figure 4-16. Main electrical service switchboard 

inundated by floodwaters that rose to the red 

mark on the doorframe (Cedar Rapids, IA, 2008)
4-20 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

When elevated, electrical equipment can survive even extreme events. Figures 4-17 and 4-18 show electrical 

equipment that was located above the floodwaters and therefore not damaged during Hurricane Ike. 

Figure 4-17. 

Undamaged secondary 

switchgear located 

at the University of 

Texas Medical Branch. 

The switchgear had 

been constructed on 

an upper floor that 

remained above flood 

levels. The switchgear 

was not damaged 

during Hurricane Ike 

(Galveston, TX, 2008).

Figure 4-18. Emergency 

generator elevated 

above flood levels 

at the University 

of Texas Medical 

Branch, Hurricane 

Ike (Galveston, TX, 

2008). The secondary 

switchgear shown in 

Figure 4-12 is located 

in the room to the left 

at approximately the 

same elevation as the 

emergency generator. 

The red line shows the 

location of the base of 

the generator.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-21

OTHER FLOOD PROTECTION MEASURES 4

The proper placement of components and equipment to minimize the flood vulnerability of electrical and 

mechanical utilities is discussed in the following subsections.

4.3.1 Electrical Utilities and Systems

The characteristics of the flood hazard at a building must be considered when decisions are made about the 

location of electrical utilities and systems. Some components are inherently resistant to flood damage, but 

others are inherently vulnerable and should be placed above the DFE.

Standard pad-mounted transformers and medium voltage switchgear (see Figure 4-19) will be damaged or 

destroyed if flooded. For flood resistance, these components must be placed above the DFE. 

Occasionally, some utility components, namely pad-mounted transformers, cannot be elevated because of a 

distance restriction between the transformer and the building’s electrical service equipment (secondary services 

must be kept short to limit voltage drop). If the transformer cannot be elevated, a submersible transformer can 

be considered. 

Figure 4-19. Pad-mounted transformer (left) and 15 kilovolt switchgear (right), both vulnerable to damage 

when inundated with floodwaters (Cedar Rapids, IA, 2008)

Electrical service equipment should be located above the DFE, which often requires placing the equipment 

on an upper floor of a flood-prone building and feeding power downward to the vulnerable lower floors. The 

electrical equipment that is placed in areas of the building that are vulnerable to flooding should be minimized, 

but any such equipment should be supplied from separate and dedicated electrical feeders. That arrangement 

will allow damaged equipment to be electrically isolated from undamaged equipment in order to minimize 

electrical interruptions. 

For simplicity, branch circuit panelboard(s) can be placed on every flood-prone level of a building, and all electrical devices in that area can be fed from the area panelboard to allow the vulnerable portion of the electrical 

system to be isolated by turning off a minimum number of circuit breakers. 
4-22 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

Electrical wiring in flood-prone areas should be installed so that it can be easily replaced or cleaned and reused. 

Cable systems cannot be cleaned if floodwaters have entered the exterior sheaths of the cables, but when the 

cable systems are accessible, they are relatively easy to replace (see Figure 4-20).

Conductors placed in conduits are more labor intensive to install than cabling systems, but often portions of 

conduit and conductor systems can be cleaned as reused. Conduits inundated with flooding may be cleaned, 

provided the floodwaters are not corrosive or otherwise damaging and the conduits are routed and installed 

(sloped to drain and with no low points within them) to prevent water from accumulating inside them. When 

the inundated conductors have been removed and the conduits have been cleaned, new insulated conductors 

can readily be installed. Conductors should be replaced after flooding unless it can be confirmed that they have 

not been damaged from inundation (see Figure 4-21).

Figure 4-20. Electrical cable (left) and an example of an electrical installation using cables (right) 

Figure 4-21. Example 

of installation using 

electrical conduits and 

insulated conductors
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-23

OTHER FLOOD PROTECTION MEASURES 4

Since the severity of a flood cannot readily be predicted, wiring should be installed so the smallest possible portion of the system will be rendered inoperative from any given flood. For example, because of the low elevation 

of wiring for receptacles, this wiring should be separate from the wiring that supplies lighting fixtures. Where 

possible, all electrical equipment in flood-prone portions of a building should be placed as high as practical. 

As with electrical service equipment, communication service equipment should be elevated above the DFE, 

and communication wiring should be routed and installed in such a way that damage and service interruptions 

resulting from inundation will be minimized. Providing connectors that can isolate damaged communication 

wiring from wiring routed above floodwaters will allow portions of the communication system to be placed 

back in service and used while flood-damaged portions of the wiring are replaced. Installing communication 

wiring that is vulnerable to flooding in conduits can greatly facilitate cable replacement even when conduits 

are not required to satisfy codes and standards.

4.3.2 Mechanical Utilities and Systems

The approach to limiting damage to mechanical utilities and systems is the same as electrical utilities and systems. All equipment that is vulnerable to flooding should be elevated above the DFE and when that is not 

possible, located in dry-floodproofed areas. Equipment that must be placed in areas prone to flooding should 

be designed to (1) minimize disruptions to the portions of the mechanical systems that are above the floodwaters and (2) facilitate removal and replacement of flood-damaged mechanical equipment.

Large central mechanical units such as chillers, particularly air-cooled chillers, boilers, and pumps, should be 

placed above the DFE. For existing installations, the area where central mechanical units are located should be 

dry floodproofed if elevation is not practical. Evaporator towers can be placed below the DFE if they can be 

readily cleaned or if the evaporative media are replaced after being in contact with floodwaters. HVAC controls, many of which must be placed near the mechanical equipment they serve, should be placed as high as 

possible and installed in a way that facilitates their replacement if they are damaged by floodwaters. Central 

processing units that provide supervisory control can and should be installed above the DFE. 

As with electrical panelboards, dedicated air handling units should be installed to serve flood-prone areas. Air 

handling units vulnerable to flood damage should have independent supplies, returns, and ventilation ducts 

that prevent cross contamination of conditioned air between areas damaged by floodwaters and those above 

the floodwaters. Isolation valves should be installed to allow damaged HVAC components to be replaced without requiring draining or disrupting chilled water or hot water distribution systems. In addition, domestic 

water lines supplying fixtures in flood-prone levels should be isolated from domestic water lines serving upper 

floors. 

Exhaust vents and fresh air make-up vents should be relocated above the DFE. If relocation is not possible, 

flood shields may need to be installed to prevent water entry. 

To prevent floodwaters from entering non-pressurized mechanical systems, check valves should be installed 

where allowed by code and local regulations. All check valves should be installed so they can be maintained 

and tested periodically.
4-24 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

Fuel tanks in areas vulnerable to flooding should be designed to resist the crushing pressures that exist at their 

flood depth and anchored to resist buoyant forces that result from inundation. ASCE 24 requires that tanks be 

designed and anchored to resist 1.5 times the potential flood forces acting on a tank when it is empty. 

Where possible, piping that needs to be insulated should be run above the DFE. Where piping must be 

installed below the DFE, flood-resistant insulation must be used. Piping should be installed in a fashion that 

facilitates insulation replacement.

4.4 Emergency Measures

Emergency measures are temporary measures that are implemented between the flood warning and the flood 

event to protect the building from floodwaters. Sandbags, temporary flood barriers, and flood wrapping systems are common emergency flood protection measures and are described in the following subsections.

4.4.1 Sandbags

The use of sandbags has changed little over time. Temporary walls constructed of sandbags can be used to protect structures from flooding or provide additional height to existing levee systems when floodwaters reach 

critical levels. Typical sandbags are constructed of plastic or treated burlap bags approximately 14 inches wide 

and 24 inches long and are filled with sand or other fine-grained soils. 

The various USACE districts have prepared guidance on the proper use and placement of sandbags to provide 

temporary protection of structures from flooding (see Figure 4-22). However, unless emergency placement is 

planned well in advance under the direction of trained personnel, most sandbag barriers are not constructed in 

accordance with proper practices, leading to leakage and failures. Because of the intensive effort and amount of 

time required to provide protection even from relatively shallow water, sandbag walls are not a reliable protection measure. To be effective, sandbags and sand should be stockpiled and checked regularly to ensure that the 

sandbags have not deteriorated. Sand and/or filled sandbags stored unprotected out of doors in cold weather 

climates may freeze and be rendered unusable.

The disadvantages of sandbags are high disposal costs and a tendency to absorb pollutants from contaminated 

floodwaters, which necessitates their disposal as hazardous waste. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-25

OTHER FLOOD PROTECTION MEASURES 4

Figure 4-22. Techniques for proper placement of sandbags (source: USACE St. Paul District) 

4.4.2 Temporary Flood Barriers

A number of vendors make temporary flood barriers that can be assembled relatively easily, moved into place, 

anchored, and filled with water (see Figure 4-23) or sand (see Figure 4-24). The barriers must be sized for the 

site. Training and annual drills are important so personnel know how to deploy the barriers. Proper storage, 

including cleaning after deployment, is necessary to protect the materials over long periods.

The Association of State Floodplain Managers (ASFPM) Non-Structural Floodproofing Committee worked 

with the USACE’s National Non-Structural Flood Proofing Committee and Underwriters Laboratories (UL) 

to establish a testing/certification program for temporary flood barriers. ASFPM, UL, and USACE initiated 

program development, and FM Approvals (a division of FM Global) developed an approval system for recognizing temporary barriers as flood abatement equipment for their policyholders. In 2006, FM Approvals 

published FM Standard 2510, Approval Standard for Flood Abatement Equipment (FM Approvals 2006). The 

current FM Approvals test protocols are for self-supporting, temporary barriers designed to protect against riverine flood depths up to 3 feet; however, the laboratory set-up can be adapted easily to allow for testing panel 

closures and demountable barriers. These barriers are not tested for coastal flooding applications, where the 

presence of saltwater may hinder their performance. Because saltwater is denser than freshwater, a barrier filled 

with freshwater in a coastal location may float instead of providing protection against flooding. 
4-26 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.4.3 Flood Wrapping Systems

Flood wrapping systems are temporary emergency measures. They consist of plastic or other synthetic waterproof sheeting material that is used to seal a building to prevent water intrusion during the flood duration. 

Wrapping systems present different challenges from impervious wall systems: they need to be anchored, stored, 

and repaired. 

Flood wraps benefit from barrier reinforcement such as sandbags or plywood walls and should generally be 

able to withstand the pressure of 3 feet of water for a limited period. Wrapping systems rely on the existing 

walls, which may need to be strengthened to resist flood loads, but they also need to bridge openings such as 

doors and windows, which typically require some type of temporary reinforcement to support the portion of 

the wrapping system that spans the openings. The area of openings and the flood protection level should be 

considered when selecting the wrapping material. When using flood wrapping material, refer to the manufacturer’s specifications for depth of flooding limitations, reinforcement requirements, and applicability with 

Figure 4-24. Gravelfilled containers that 

formed a barrier to 

protect the 

University of Iowa 

(2008)

Figure 4-23. Threefoot-high water-filled 

temporary barrier 

protecting a structure 

in Tunica, MS (source: 

Hydrological Solutions, 

Inc.)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-27

OTHER FLOOD PROTECTION MEASURES 4

existing construction materials at the openings. Figure 4-25 illustrates a span across a doorway where the wrap 

is deflecting due to flood loads. These situations should be avoided because the stress of the wrap deflecting 

could cause it to tear and leak.

Figure 4-26 shows plastic sheeting attached to a brick-faced wall. Weep holes and wick drains work both ways 

to allow moisture to pass from high to low pressure. Weep holes and flashing should therefore be above the 

DFE, and the veneer below that level should be fully grouted. Wrapping systems should be selected using the 

decision process shown in Figure 4-27.

Figure 4-25. Plan 

view of wall section 

showing the 

deflection of a wrap 

at a doorway 

Figure 4-26. Plastic 

sheeting attached to a 

brick-faced wall to seal 

it from water intrusion

Wall

Deflection of wrap Wrap

Door

Wall

Design flood

elevation Attach to building

6 mil. polyethylene placed

loosely on wall

Brick veneer

Sand bags

Loose

sand

Grade

6 ̋ to 8 ̋

8 ̋ to 10 ̋

Monolithic slab

and footing

Maximum

height = 3 ft

CMU

wall

4 ̋ PVC perforated pipe

(drain to sump with

backup power source)
4-28 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

Figure 4-27. Decision process for the selection and design of a flood wrapping system 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-29

OTHER FLOOD PROTECTION MEASURES 4

Wrap systems require secure connections at both the 

top and bottom of the wrap. The actual loads imposed 

vertically on the wrap are difficult to determine because 

they can vary depending on the quality of the installation. Since the intent of flood wrapping systems is 

to provide floodproofing and not structural support, 

voids left from poor construction may force the wrap 

to carry the weight of the water and should be avoided. 

The following should be considered when selecting the method to attach the wrap to the building:

■ The wall attachment system should uniformly support the wrap. Small spacing between the 

connections and a member with some rigidity on the outside of the wrap can provide the needed 

support.

■ The existing wall construction can vary widely. Part of the connection may need to be a permanent 

part of the wall.

Anchoring wrap into the grade at the base of a wall is the most important link in the wrap system (see Figure 

4-24). The following recommendations should be followed during selection and design of a grade connection 

method:

■ A drain line connected to a sump pump should be located between the wrap and the building to 

remove any water that leaks through the wrap or seeps through the soil under the at-grade anchor.

■ The end of the wrap should be buried at least below the topsoil layer. Additional ballast may be 

needed (e.g., sandbags, stone) to prevent wrap movement in a saturated or frozen soil condition.

■ The product literature for the wrap material and applicable codes and standards should be reviewed 

and followed.

Before the final selection of a wrapping system, the following issues should be addressed by the manufacturer 

and the instructions should be provided to the owner:

■ Based on the type of building the wrapping system will be applied to, any issues with chemicals used 

or stored onsite that could damage the wrapping system should be identified. It is also important for 

the designer or owner to evaluate adjacent properties to make sure that any potential chemicals that 

could damage the wrapping system during a flood have been identified.

■ The manufacturer should provide guidance on how to repair the wrapping system and approximately 

how much additional wrapping material is required for each repair. It is also important to know 

whether the wrapping material can be repaired once it has gotten wet or whether it must be dry.

4.5 Combination of Floodproofing Measures

Some non-residential buildings and site conditions require multiple floodproofing measures for adequate protection. A single floodproofing measure may provide only limited protection or protect only a portion of a 

single building or group of buildings. In these situations, combining floodproofing measures may be appropriate. Combining floodproofing measures is discussed in the following subsections. 

Special Note

Wrap systems may be affected by 

freeze-thaw cycles. Careful evaluation of 

performance in frozen climates is advisable 

and installation in accordance with manufacturer instructions is recommended.
4-30 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.5.1 Wet and Dry Floodproofing Techniques

Many non-residential buildings can benefit from using a combination of the wet floodproofing measures 

described in Section 4.2 and the dry floodproofing measures described in Chapter 3. Combining measures is 

particularly useful when one or more of the following building or site conditions exist:

■ Multi-story or split-level buildings where different measures can be applied to different foundation 

types at different elevations

■ Large factories, warehouses, and other industrial facilities constructed of a variety of materials that 

respond better to multiple floodproofing measures

■ Groups of buildings on the same site but at different elevations

Figure 4-28 shows a commercial building that was mitigated by raising the interior first floor using flood damage-resistant materials and flood shields and by reinforcing walls.

Retrofitting an entire large building or multiple buildings with dry floodproofing is a complex and expensive 

undertaking that requires analysis and design to protect the buildings against flooding from numerous points 

of entry of various sizes. Consequently, limiting dry floodproofing measures to the most critical elements or 

operations of a facility that cannot be elevated may be more technically feasible and cost effective. Building 

managers and owners can then focus on elevating other critical areas and wet floodproofing other lower-level 

areas that are less critical. This situation may apply to flood-prone hospitals, schools, fire and police stations, 

Figure 4-28. 

Commercial structure 

in Darlington, WI, 

mitigated using a 

combination of wet 

and dry floodproofing 

techniques 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-31

OTHER FLOOD PROTECTION MEASURES 4

emergency operations centers, communication and data centers, essential government buildings, and other 

critical facilities that serve the community or affect the safety, health, or welfare of a large population. 

Elevating critical equipment and operations often involves relocating them to upper floors; in many facilities, 

space must be created on those upper floors to house the relocated equipment and operations. Creating that 

space often requires moving less critical equipment and operations to areas that are more vulnerable to flooding. Identifying what equipment and operations can be relocated can be straightforward, as shown in Figure 

4-29, or can be complex. For the building in Figure 4-29, a non-critical break room was moved to a lower floor 

to create space for a critical control room needed for plant operations. 

In complex situations, identifying what non-critical (or less-critical) equipment and operations can be more 

exposed to flooding requires long-term planning because exposing any equipment to flooding can affect the 

facility’s ability to respond to and recover from a flood event. For example, in a health care facility, food service, 

laundry operations, and the facility’s electrical service and distribution equipment are all required for the facility to function. However, unlike the food service and laundry operations, which can be provided by off-site 

suppliers, the electrical service and distribution equipment must be protected. So for installations where laundry or food service equipment are located on higher floors, those operations can be relocated to lower floors to 

free up space for essential electrical service and distribution equipment.

To improve the building performance of such facilities, vulnerability assessments that take a holistic view of 

critical equipment, critical systems, and critical functions should be completed to identify vulnerabilities and 

identify possible flood mitigation measures. Those flood mitigation measures should be incorporated whenever damaged facilities are repaired or reconstructed. Refer to the Midwest Flood MAT Recovery Advisory, 

Design Considerations for Improving Critical Facility Functionality during Flood Events, in Appendix D of FEMA 

P-765 (FEMA 2009b) for additional details. 

Figure 4-29. A noncritical break room, 

originally located on 

an upper floor was 

relocated to create 

space for the critical 

control room 
4-32 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

4 OTHER FLOOD PROTECTION MEASURES

4.5.2 Other Combinations

In addition to a combination of wet and dry floodproofing, the following combinations may increase mitigation effectiveness:

■ Dry floodproofing and floodwalls/levees. May be applicable to buildings with multi-level 

foundations that are suitable for dry floodproofing and the site slopes down toward the flooding 

source or a building where one side is less suitable for dry floodproofing (see Chapter 3 and Section 

4.1)

■ Dry floodproofing and floodproofing utilities. May be applicable to a complex of buildings or 

utility facilities where some structures are suitable for dry floodproofing but others are not (see 

Chapter 3 and Section 4.3)

■ Dry floodproofing and emergency measures. May be applicable to buildings or facilities that are 

suitable for dry floodproofing but contain many large openings that can be protected with emergency 

measures (see Chapter 3 and Section 4.4)

■ Wet floodproofing and emergency measures. May be applicable for building spaces that are 

suitable for wet floodproofing where there is a need to protect a portion of key building systems or 

equipment with emergency measures (see Section 4.2 and Section 4.4)

4.5.3 Case Study: Application to Historic Buildings

Darlington, WI, provides an example of how multiple floodproofing measures can be successfully implemented in historic structures to allow architectural and cultural resources to withstand future flooding. 

In response to historic floods and devastation from the 1993 Midwest Flood (see Figure 4-30), the city 

of Darlington developed a 10-year progressive mitigation plan to preserve the downtown business area 

along Main Street while maintaining its designation as a historic district (FEMA 2008c).

To increase the level of flood protection for some commercial structures along Main Street, existing 

basements were aba ndoned and filled with sand and gravel or concrete, and interior first floors were 

elevated (see Figure 4-31).

A hardware store on Main Street was mitigated by raising the interior first floor using a poured monolithic concrete slab and installing flood damage-resistant materials in areas below the DFE (see Figure 

Figure 4-30. Flooding of businesses in 

historic downtown Darlington, WI, Midwest 

Flood (1993) (source: Wisconsin Emergency 

Management)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS 4-33

OTHER FLOOD PROTECTION MEASURES 4

4-32). The mitigation project also included an interior ramp for Americans with Disabilities Act (ADA) 

compliance (see Figure 4-33) as well as floodproofing of mechanical and electrical equipment.

After the floodproofing measures were implemented in the businesses on Main Street, the historic downtown district successfully withstood severe flooding in 2007 and 2008. 

Figure 4-31. Businesses along Main Street 

in Darlington, WI, mitigated with an elevated 

interior first floor

Figure 4-32. Hardware store on 

Main Street in Darlington, WI, 

(left) mitigated with a raised 

interior first floor and flood 

damage-resistant materials 

(right) 

Figure 4-33. Hardware store on Main Street 

in Darlington, WI, showing ramp to elevated 

interior first floor for ADA compliance

FLOODPROOFING NON-RESIDENTIAL BUILDINGS A-1

F EMA assistance is available to help property owners implement flood retrofitting projects. The sources 

of the assistance are the Increased Cost of Compliance (ICC) coverage in Standard Flood Insurance 

Policies from the National Flood Insurance Program (NFIP) (see Section A.1), FEMA’s Hazard 

Mitigation Assistance (HMA) Programs (see Section A.2), and Section 406 Hazard Mitigation funding under 

the Public Assistance Program (see Section A.3). Resources on FEMA funding are listed in Section A.4.

A.1 Increased Cost of Compliance Coverage

Property owners who have Standard Flood Insurance Policies for buildings in Special Flood Hazard Areas 

(SFHAs) are eligible to receive up to $30,000 (as of May 2011) to bring the building into compliance with 

State or local floodplain laws or ordinances and building code requirements. The building must have substantial or repetitive flood damage to be eligible for ICC funds. ICC coverage can be used for elevating, relocating, 

demolishing, or floodproofing a non-residential building. 

ICC claims are adjusted separately from flood damage 

claims filed under the Standard Flood Insurance Policy. 

ICC coverage is provided in all new and renewed 

Standard Flood Insurance Policies in the NFIP. 

An ICC claim may be paid if the property is determined to be Substantially Damaged by a State or local 

official or a repetitive loss property, which are defined 

as follows:

■ Substantially Damaged. The cost of repairing flood damage equals or exceeds 50 percent of the 

building’s pre-damage market value.

■ A repetitive loss property. At least two losses in 10 years have occurred in which the cost of repair, 

on average, equaled or exceeded 25 percent of the building’s market value at the time of each flood.

Additionally, the State or community must have a cumulative Substantial Damage provision or repetitive loss 

provision in its floodplain management law or ordinance being enforced against the structure to be eligible for 

an ICC claim payment.

FEMA Assistance

Special Note

For more information on ICC coverage, 

see FEMA P-301, NFIP Increased Cost 

Compliance (ICC) Coverage (FEMA 2003).
A-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

A FEMA ASSISTANCE

A.2 FEMA’s Hazard Mitigation Assistance Programs

FEMA’s HMA Programs present a critical opportunity to reduce the risk to individuals and property from 

natural hazards while simultaneously reducing reliance on Federal disaster funds. The programs are authorized 

by Section 404 of the Robert T. Stafford Disaster Relief and Emergency Assistance Act of 1988, as amended 

(Title 42, United States Code [U.S.C.] 5170c), Section 203 of the Stafford Act, 42 U.S.C. 5133 and Section 

1366 of the National Flood Insurance Act of 1968, as amended (42 U.S.C. 4104c). All programs are subject 

to changes in statutory requirements and amounts of authorized assistance. 

All mitigation projects must be cost-effective, 

cost reasonable and technically feasible and meet 

Environmental Planning and Historic Preservation 

requirements in accordance with HMA Program 

requirements. States, territories, federally recognized 

Indian tribal governments, and communities are eligible and encouraged to take advantage of funding 

provided by the following HMA Programs in both the 

pre- and post-disaster time frames:

■ Hazard Mitigation Grant Program (HMGP). Provides grants for long-term hazard mitigation 

measures after a major disaster declaration in a given State. The purpose of HMGP is to reduce 

the loss of life and property as a result of natural disasters and to enable the implementation of 

mitigation measures during the recovery from a disaster.

■ Pre-Disaster Mitigation (PDM) Program. Provides nationally competitive grants for hazard 

mitigation planning and implementing mitigation projects before a disaster event. Funding the plans 

and projects reduces the risk to people and property and the reliance on funding that is authorized 

after a Presidential disaster declaration to rebuild. 

■ Flood Mitigation Assistance (FMA) Program. Provides grants for certain flood mitigation projects 

to reduce or eliminate flood risk to buildings, manufactured homes, and other buildings that are 

currently NFIP insured. The National Flood Insurance Fund (NFIF) provides the funding for the 

FMA program.

HMGP is available, when authorized under a Presidential major disaster declaration, in the areas of the State 

requested by the Governor. The PDM and FMA programs are subject to the availability of appropriation funding, as well as any program-specific directive or restriction made with respect to such funds. 

Table A-1 is a summary of the flood mitigation projects in non-residential buildings that are eligible for funding under HMA Programs. 

Special Note

For more information on FEMA Hazard 

Mitigation Assistance programs, see https://

www.fema.gov/hazard-mitigation-assistance. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS A-3

FEMA ASSISTANCE A

Table A-1. Flood Mitigation Projects in Non-Residential Buildings Eligible for Funding Under HMA Programs 

Eligible Activities HMA Program

HMGP PDM FMA

Property acquisition and building demolition 3 3 3

Property acquisition and building relocation 3 3 3

Building elevation 3 3 3

Dry floodproofing non-residential building 3 3 3

Source: FEMA (2010c)

Note: HMGP and PDM are authorized under the Robert T. Stafford Disaster Relief and Emergency Assistance Act. FMA and PDM are authorized under the 

National Flood Insurance Act.

FMA = Flood Mitigation Assistance HMGP = Hazard Mitigation Grant Program

HMA = Hazard Mitigation Assistance PDM = Pre-Disaster Mitigation

Figure A-1 shows the process for FEMA grant applications and approvals. The process is divided into five 

stages, starting with mitigation planning and ending with project closeout. The process requires coordination 

among FEMA, the State, and the local government. The coordination is represented by the three rings in the 

figure. Regardless of which HMA Program the funds will come from, the FEMA grants cycle process includes 

the five stages shown in Figure A-1 and described in Sections A.2.1 through A.2.5.

Figure A-1. HMA grants cycle process and the roles and responsibilities of FEMA and State and local governments 
A-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

A FEMA ASSISTANCE

A.2.1 Stage 1: Mitigation Planning

All project grant applications require a State or tribal multi-hazard mitigation plan. The plan must describe 

the process for identifying the hazard risks in a community and the actions that will help reduce the risks. 

Non-residential flood mitigation projects that are proposed for FEMA funding under HMA Programs must 

be consistent with the State’s or tribe’s mitigation plan. The mitigation planning process requires public participation and the identification of measures to reduce risks and is therefore a good opportunity for property 

owners to address concerns about flood hazards. More information is available at http://www.fema.gov/

hazard-mitigation-planning-overview.

A.2.2 Stage 2: Program Funding

HMA Programs enable hazard mitigation measures to be implemented before, during, and after disasters. 

Funding depends on the availability of appropriation funding or is based on disaster recovery expenditures, 

as well as any directive or restriction made with respect to such funds. HMGP funding depends on Federal 

assistance provided for disaster recovery following a Presidential disaster declaration in a State, and PDM and 

FMA funding may be authorized annually by Congress. 

When the application period opens, the State notifies local governments of the availability of funds and relays 

information about the application process, project requirements, and eligibility criteria for the local government. Table A-2 shows the cost-share requirements for the HMA Programs. Property owners should work with 

their local governments to express interest in participating in a flood mitigation project; the local government 

can then submit a subapplication to the State and request HMA funding. In general, the community applying 

for the grant must participate in the NFIP. Eligible subapplicants include State agencies, Indian tribal governments, local governments and communities, and private non-profit organizations.

Table A-3 lists the eligibility of subapplicants for HMA Program grant funding.

Table A-2. Cost-Share Requirements for the HMA Program Grants

HMA Program Subcategory Federal/Non-Federal Share(a)

HMGP All subapplicants 75/25

PDM

All subapplicants 75/25

Subgrantee is small impoverished community 90/10

Tribal Grantee is small impoverished community 90/10

FMA All subapplicants Up to 100/0 for certain properties

(a) Ratios are as of February 2010. Refer to the current fiscal year’s HMA Unified Guidance for current ratios 

when referencing this table. The current version of the HMA Unified Guidance is available at http://www.fema.gov/

hazard-mitigation-assistance.

FMA = Flood Mitigation Assistance HMGP = Hazard Mitigation Grant Program

HMA = Hazard Mitigation Assistance PDM = Pre-Disaster Mitigation
FLOODPROOFING NON-RESIDENTIAL BUILDINGS A-5

FEMA ASSISTANCE A

Table A-3. Eligiility of Subapplicants for HMA Program Grants

Subapplicant HMA Programs(a)

HMGP PDM FMA

State agencies Yes Yes Yes

Tribal governments Yes Yes Yes

Local governments/communities Yes Yes Yes

Private non-profit organizations Yes No No

(a) Private properties may be included on an HMA Program application if the application is submitted by an eligible 

Applicant.

FMA = Flood Mitigation Assistance HMGP = Hazard Mitigation Grant Program

HMA = Hazard Mitigation Assistance PDM = Pre-Disaster Mitigation

A.2.3 Stage 3: Application Development

Businesses cannot apply for HMA funds, so the non-residential property owner must work with the local government to develop a project subapplication on behalf of the owner. Local governments may submit a retrofit 

project for a property as an individual subapplication or combine it with other projects as part of an aggregate 

subapplication (subject to program restrictions). Aggregating benefit and cost values is allowed for multiple 

buildings if they are all vulnerable to damage from similar hazard conditions. See the current version of the 

HMA Unified Guidance (periodically updated) for information on aggregating projects in one subapplication.

Key elements for non-residential flood mitigation applications are:

■ Identification of the property to be mitigated.

■ Identification of key project personnel and roles, such as design professional and contractor.

■ Selection of an eligible project (see Table A-1).

■ Inspection of the building by a registered design professional to verify that the project can 

be implemented if possible; if not done at this stage; it must be done during Stage 4, Project 

Implementation (see Section A.2.4).

■ Development of a project cost estimate and work schedule.

■ Benefit-Cost Analysis (BCA) using FEMA’s BCA software (see Appendix B for additional 

information); if the benefit-cost ratio (BCR) is 1.0 or more, the project is cost-effective. FEMA 

requires a BCR of 1.0 or greater for funding.

■ Verification that properties in designated SFHAs will obtain flood insurance and that the insurance 

will be recorded on the property deed.

The local government submits the subapplication to the State. The State then selects projects based on its priorities and submits applications to FEMA for review. FEMA reviews the projects for eligibility, completeness, 

engineering feasibility, cost-effectiveness, cost reasonableness, and environmental and historic preservation 

documentation. The review process also confirms that all hazard mitigation activities adhere to all relevant 

statutes; regulations; program requirements, including other applicable Federal, State, tribal, and local laws; 

implementing regulations; and Executive Orders, all of which are detailed in the grant program guidance. 
A-6 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

A FEMA ASSISTANCE

The most current version of the guidance can be found at the FEMA HMA website (http://www.fema.gov/

hazard-mitigation-assistance). 

Once FEMA approves a project and awards the grant, the State distributes the funds to the local government, 

which distributes it to individuals as appropriate. No construction activities should begin until after the money 

has been awarded because HMA funding is not available for activities initiated or completed prior to award 

or final approval.

A.2.4 Stage 4: Project Implementation

After the State has awarded the funds to the local government, the next stage is project implementation. HMA 

projects must be completed within a specified period of time (the period of performance), which is normally 

not more than 36 months. During the period of performance, the local government must maintain a record 

of work and expenditures for the quarterly reports that the State submits to FEMA.

Because the final design may not be completed prior to award, once the project is awarded, the design must be 

finalized by a registered design professional with some exceptions. If the scope of work or cost estimate changes 

as a result of completing the final design, the HMA Unified Guidance should be consulted for direction on 

scope of work modifications. If there is already a final design when the grant is awarded, the subgrantee can 

proceed with the appropriate contracting procurement procedures to secure the services of a contractor to execute the requirements in the design and grant documents. 

Some grant projects do not require the services of a design professional. In these circumstances, once the grant 

is awarded, the subgrantee can proceed with appropriate contracting procurement procedures to secure the 

services of a contractor to execute the requirements in the contract documents necessary to perform the work 

in the approved grant. 

To summarize, the basic steps in implementing an approved HMA mitigation flood retrofit grant project are:

1. If a design was not developed before Stage 3, secure a registered design professional to design, 

inspect, and sign off on a mitigation retrofit solution within the bounds of the approved grant.

2. If a design solution was developed before Stage 3 or if a registered design professional is not needed 

because of the nature of the work, secure the services of a contractor to execute the work in the 

approved grant.

3. Monitor the work being performed to ensure that all grant requirements are being met.

4. Inspect the finished project and verify that all grant requirements have been met. Work with the 

designer / contractor to resolve any issues of concern and work with the State in closing out the 

grant after all requirements have been met.

A.2.5 Stage 5: Project Closeout

When the grant project has been completed, a registered design professional (preferably the same one as above) 

should conduct a final inspection and verify in writing that the project he or she designed/signed off on was 

implemented as intended in the approved grant. If a contractor was the only professional who performed the 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS A-7

FEMA ASSISTANCE A

work, the contractor should verify in writing that he or she performed the work as outlined in the contract 

and the grant. It is crucial for the subgrantee to ensure that the grant requirements have been met through any 

contracts the subgrantee has have with design professionals or contractors because the subgrantee is ultimately 

responsible for meeting the grant requirements. Poorly written contracts can result in work that complies with 

the contract but is noncompliant with the grant requirements. The written verification of the work performed 

along with other project documentation demonstrating grant compliance will help facilitate a smooth, efficient project closeout.

After obtaining project verification from the designer/contractor, the subgrantee then submits the grant project 

documentation to the State. The State verifies that the work was completed in accordance with the approved 

grant documentation, including the grant scope of work, and performs the closeout procedures. If the property is in an SFHA, the local government must provide documentation of flood insurance for the property and 

a copy of the recorded deed amendment. The HMA Unified Guidance contains a description of all closeout 

requirements that must be addressed.

A.3 The Public Assistance Program and Section 406 Hazard 

Mitigation Funding

The Public Assistance (PA) Program is a grant program authorized by the Robert T. Stafford Disaster 

and Emergency Assistance Act (the Stafford Act) to 

make funding available for response and recovery 

efforts after the President has declared a disaster or 

emergency. 

After the declaration is made, FEMA determines 

which locations are eligible for assistance under which 

categories of work. Eligible disaster-related work, 

which is either emergency or permanent work, is 

divided into seven categories, as listed below. The first 

two categories are emergency work, and the other categories are permanent work.

■ Category A: Debris Removal (Emergency Work)

■ Category B: Emergency Protective Measures (Emergency Work)

■ Category C: Roads and Bridges (Permanent Work)

■ Category D: Water Control Facilities (Permanent Work)

■ Category E: Buildings and Equipment (Permanent Work)

■ Category F: Utilities (Permanent Work)

■ Category G: Parks, Recreational Facilities and Other Items (Permanent Work)

Entities that are eligible to apply for PA funding are limited to State agencies, local governments, private 

nonprofit organizations (which must meet stringent requirements to be determined eligible), and federally 

recognized Indian tribes or authorized tribal organizations and Alaskan Native village organizations. 

Special Note

More information on the Stafford Act and 

Section 406 is available at:

h ttp://www.fema.gov/public-assis -

tance-local-state-tribal-and-non-profit/

hazard-mitigation-funding-under-section-406-0.
A-8 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

A FEMA ASSISTANCE

Under the PA Program, the FEMA/State cost share is usually 75 percent/25 percent, although the cost share 

is subject to change based on the severity of the disaster. Applicants are reimbursed for eligible costs under 

the categories of work that FEMA has determined eligible for reimbursement under that specific disaster 

declaration.

The PA Program has a required focus on restoring damaged infrastructure to its pre-disaster function and 

capacity. Section 406 of the Stafford Act allows funding of mitigation measures that go beyond restoring a 

facility to its pre-disaster condition and is applied only to the damaged element of the facility. Mitigation 

measures must be cost-effective, cost reasonable, technically feasible and meet Environmental Planning and 

Historic Preservation requirements in accordance with Federal laws, regulations, and Executive Orders and 

must reduce the risk of damage from future similar events to be eligible for Section 406 funding.

Only projects involving permanent work are eligible for Section 406 hazard mitigation funding. Hazard mitigation measures under Section 406 are considered part of the total eligible cost of the repair, restoration, 

reconstruction, or relocation of a facility. Funding under Section 406 is not applicable to alternate or improved 

projects if a new replacement facility is involved. Upgrades to meet applicable codes and standards are also not 

eligible under Section 406 funding because they are not mitigation measures and may be an eligible part of 

restoration work under the PA Program. Examples of eligible Section 406 mitigation measures are:

■ Relocation of facilities from hazardous locations

■ Slope stabilization to protect facilities

■ Protection from high winds

■ Floodproofing of buildings

■ Flood protection of bridges and culverts

■ Seismic protection

■ Protection of utilities

Hazard mitigation measures submitted under Section 406 are reviewed by FEMA to ensure eligibility, technical feasibility, environmental and historical compliance, and cost effectiveness. When the project has passed all 

reviews, FEMA obligates the funds, and the State ensures that the funds are distributed to PA Program applicants in accordance with State laws.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS A-9

FEMA ASSISTANCE A

A.4 FEMA Assistance Resources

Benefit-Cost Analysis http://www.fema.gov/benefit-cost-analysis

Building Science Helpline Telephone: (866) 927-2104 

E-mail: FEMA-BuildingscienceHelp@fema.dhs.gov

Environmental Planning and Historic 

Preservation

http://www.fema.gov/environmental-planning-and-historic-preservationprogram

Flood Mitigation Assistance Program http://www.fema.gov/flood-mitigation-assistance-program

Hazard Mitigation Grant Program http://www.fema.gov/hazard-mitigation-grant-program

Hazard Mitigation Assistance policies http://www.fema.gov/hazard-mitigation-assistance-policy

HMA Helpline Telephone: (866) 222-3580

E-mail: hmagrantshelpline@dhs.gov

HMA overview; includes link to the 

current HMA Unified Guidance http://www.fema.gov/hazard-mitigation-assistance

Increased Cost of Compliance; 

includes a link to FEMA 301, 

NFIP Increased Cost Compliance 

Coverage (FEMA 2003)

http://www.fema.gov/national-flood-insurance-program-2/increased-costcompliance-coverage

http://www.fema.gov/media-library/assets/documents/1973

Mitigation Planning http://www.fema.gov/hazard-mitigation-planning-overview

Pre-Disaster Mitigation Program http://www.fema.gov/pre-disaster-mitigation-grant-program

Understanding the FEMA 

Benefit-Cost Process

T he purpose of this appendix is to provide basic 

guidance on using the Federal Emergency 

Management Agency’s (FEMA’s) Benefit-Cost 

Analysis (BCA) Tool (Version 4.5.5 [FEMA 2009a]) 

to complete a BCA when considering floodproofing a 

non-residential building.

The FEMA BCA Tool is used to determine the cost 

effectiveness of proposed mitigation projects submitted for assistance under FEMA’s Hazard Mitigation 

Assistance grant programs. The software is used to estimate the economic consequences of a natural disaster 

(flood, hurricane, tornado, earthquake, or wildfire) with and without the proposed mitigation. 

For flood events, loss is estimated using depth-damage functions (DDFs), which are used to predict inundation 

impacts to the building, contents, and use of the building. DDFs relate flood depths to predicted percentages 

of damage to a building exposed to inundation at a given recurrence interval. The estimated avoided damage 

(loss) from the mitigation project is the benefit.

The flood recurrence interval is typically based on flood hazard data from a FEMA Flood Insurance Study 

(FIS) and/or hydrologic and hydraulic (H&H) study. When available flood hazard data are limited, the recurrence interval may be provided based on data collected after an event to determine the recurrence interval or 

by use of the unknown frequency calculator built into the Damage Frequency Assessment (DFA) module in 

the FEMA BCA Tool.

Anticipated damage to non-residential buildings varies based on the type of building, building attributes, and 

in some instances, location. 

Determining the cost effectiveness of a floodproofing project can be done using either the Flood module or 

DFA module, both of which are part of the BCA Tool. The Flood module relies on flood hazard data, building 

characteristics, and DDFs, and the DFA module relies on historical or expected damage along with a recurrence interval associated with the damage. The DFA module is used more often for floodproofing because it 

generally requires less data collection and may better represent the complexity of some floodproofing projects. 

The data needed for the BCA Tool Flood module and BCA Tool DFA module are listed in Table B-1.

FLOODPROOFING NON-RESIDENTIAL BUILDINGS B-1

Special Note

Property owners considering a floodproofing retrofit may use the BCA Tool during 

their decision-making process. A BCA is 

required only when applying for FEMA mitigation grant assistance.
B UNDERSTANDING THE FEMA BENEFIT-COST PROCESS

Table B-1. Data Requirements of the BCA Tool Flood Module and the BCA Tool Damage DFA Module

Item/Description BCA Tool Flood 

Module BCA Tool DFA

Scope of Work: Work activities, deliverables, and timelines associated 

with a project. For a dry floodproofing project, the scope of work typically 

includes the problem description, proposed solution, description of existing 

conditions, and work schedule.

Required Required

Project Useful Life: Estimated number of years the mitigation will be 

effective; typically based on the type of mitigation measure.

Required Required

Project costs: Cost estimate based on all anticipated project costs. Project 

costs typically include:

• Labor

• Materials

• Engineering and design

• Project management

• Construction engineering and inspection

• Permitting

• Estimated annual maintenance costs

Required Required

Flood hazard data: Data indicating the source and frequency of flooding 

at the project location. Commonly based on an FIS or H&H study indicating 

the source of flooding and on 10-, 50-, 100-, and 500-year flood hazard 

data 

Required N/A

Size of building: Total enclosed square footage of the building(s) being 

protected.

Required N/A

Building replacement value: Cost per square foot to build a comparable 

structure(s)

Required N/A

Primary use of building(a) Required N/A

Building contents value: Description of contents, their value, and how the 

value was assessed

Required N/A

Displacement cost: Estimated cost of displacement while damage is 

repaired

Required N/A

Type of service(s) provided by non-residential building (e.g., 

government, library, education, medical, shelter, administrative, warehouse/

storage)

Required N/A

B-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS
UNDERSTANDING THE FEMA BENEFIT-COST PROCESS B

Item/Description BCA Tool Flood 

Module BCA Tool DFA

Basis for damage: Explanation of how pre-mitigation damage was derived 

(historical or expected damages) and how post-mitigation damage was 

estimated (explanation of project level of effectiveness). Post-mitigation 

damage is expected except in acquisition projects. Damage is an 

approximation of damage if floodwaters exceed the height of the mitigation 

measure. 

• Damage should include:

• Building

• Contents

• Displacement and/or loss of function

Other (possibe reduction in emergency temporary protective measures 

such as sandbags)

Damage is often estimated by applying a DDF; see Section 2.1.4.7, Using 

the BCA Full Data Flood Module to Maximize Benefits in the DFA Module, 

in Supplement to the Benefit=-Cost Analysis Reference Guide (FEMA 

2011d).

N/A Required

(a) For example, retail, hotel, fast food, non-fast food, hospital, medical office, protective services, correctional facility, recreation, religious facilities, schools, 

service station, office, convenience store, grocery store, apartment, industrial, or warehouse 

BCA = Benefit-Cost Analysis FEMA = Federal Emergency Management Agency

DDF = depth-damage function FIS = Flood Insurance Study

DFA = Damage Frequency Assessment H&H = hydrologic and hydraulic

Loss of function is the direct economic impact that occurs when physical damage is severe enough to 

interrupt the function or normal use of a building. Loss of function is often overlooked in floodproofing 

project BCAs. Loss of function is generally the largest percentage of benefit for mitigation projects for nonresidential buildings. 

Typically, loss-of-function damage is calculated using the annual net income of a business or the annual operating budget for a public service (e.g., school, library) to estimate a value of service per day for the function of 

the building. The value of service per day is multiplied by the estimated number of days a building is expected 

to be closed based on the depth of flooding (the estimated number of days is typically included in a DDF and 

varies by building and occupancy type). It is important to consider whether displacement benefits1 are already 

being accounted for in the BCA; if so, displacement and loss of function cannot both be included in the BCA 

if the function or service is being provided at a temporary facility (an exception is if partial displacement and 

loss of function are combined). The two components of risk, magnitude of potential loss and probability of 

loss, are important to consider when determining the cost effectiveness of a proposed mitigation project. Most 

floodproofing projects help reduce the risk of flood damage, especially in frequently occurring (high probability) floods. The greater the effectiveness of the floodproofing project to reduce or eliminate that flood risk for 

high probability flooding, the more likely the project will be cost effective (see Table B-2).

1 The displacement benefit is the reduction of time from pre-mitigation to post-mitigation that the occupants of a building need to 

relocate. Moving to another location includes rental expenses for the new building and costs associated with moving building contents 

and setting up in a new location.

Table B-1. Data Requirements of the BCA Tool Flood Module and the BCA Tool Damage DFA Module (continued)

FLOODPROOFING NON-RESIDENTIAL BUILDINGS B-3
B UNDERSTANDING THE FEMA BENEFIT-COST PROCESS

Table B-2. Likelihood of Cost Effectiveness of Floodproofing Project

Magnitude of 

Potential Loss ($)

Probability of Loss

Low Medium High

Low Unlikely Unlikely Likely

Medium Unlikely Likely Highly Likely

High Likely Likely Highly Likely

B-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS
FLOODPROOFING NON-RESIDENTIAL BUILDINGS C-1

Checklist for Vulnerability 

of Flood-Prone Sites and 

Buildings

T he Checklist for Vulnerability of Flood-Prone Sites and Building can be used to assess site-specific flood 

hazards and building vulnerability. The checklist presented here is an amended version of the checklist 

that was developed for FEMA P-424, Design Guide for Improving School Safety in Earthquakes, Floods, 

and High Winds (FEMA 2010a). The checklist is organized by specialty area, and each section can be assigned 

to a subject matter expert in that specialty for greater accuracy and completeness of the assessment. The results 

should be integrated into a master vulnerability assessment to guide the design process and choice of appropriate mitigation measures. 

Checklist for Vulnerability of Flood-Prone Sites and Buildings

Vulnerability Considerations Guidance Observations

Siting Conditions

Is the site near a body of water 

(with or without a mapped flood 

hazard area)? 

Is the site in a flood hazard area 

shown on the community’s map 

(FIRM or other adopted map)? 

If so, what is the flood zone?

Is the site affected by a 

regulatory floodway?

All bodies of water are subject to flooding, but 

not all have been designated as a floodplain on 

FIRMs. 

Flood hazard maps are usually available for review 

in local planning and permit offices. Electronic 

versions of the FIRMs may be available online at 

http://www.fema.gov. Paper maps can be ordered 

by calling (800) 358-9616.

Development in floodways, where floodwaters are 

typically faster and deeper, must be supported by 

engineering analyses that demonstrate no rise in 

flood levels. 

Floodwalls and levees are not permitted in 

floodways per NFIP regulations.

Is the site in a storm surge 

inundation zone (or tsunami 

inundation area)?

In coastal communities, even sites at some 

distance inland from the shoreline can be 

exposed to extreme storm surge flooding. Storm 

surge maps may be available at State or local 

emergency management offices. 

ASCE 24, Flood Resistant Design and 

Construction, and NFIP regulations do not allow 

dry floodproofing in Coastal High Hazard Areas. 

Further, ASCE 24 does not allow dry floodproofing 

in Coastal A Zones or in High Risk Flood Hazard 

Areas.
C-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

C CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS

Vulnerability Considerations Guidance Observations

What is the DFE (or does an 

analysis have to be done to 

determine the DFE)? What 

is the minimum protection 

level required by regulatory 

authorities?

Does the FIS or other study 

have information about the 500-

year flood hazard area?

Has FEMA issued post-disaster 

advisory flood elevations and 

maps?

What are the expected 

depths of flooding at the 

site (determined using 

flood elevations and ground 

elevations)?

Refer to the FIS for flood profiles and data tables. 

Site-specific analyses should be performed by 

qualified engineers. 

Check with regulatory authorities to determine the 

required level of protection.

If a major flood event has affected the community, 

FEMA may have issued new flood hazard 

information, especially if areas not shown on 

the FIRMs have been affected. Sometimes 

these maps are adopted and replace the FIRMs; 

sometimes the new data are advisory only.

Has the site been affected by 

past flood events? What is the 

flood of record? 

Records of actual flooding augment studies that 

predict flooding, especially if historical events 

resulted in deeper or more widespread flooding. 

Information may be available from local planning, 

emergency management, and public works 

agencies, State agencies, the U.S. Army Corps of 

Engineers, or the Natural Resources Conservation 

Service.

The flood of record is often a lower probability 

event (with higher flood elevations) than the 100-

year flood.

What is the expected velocity of 

floodwaters on the site?

Velocity is a factor in computing loads associated 

with hydrodynamic forces, including drag on 

building surfaces. Approximations of velocity may 

be interpolated from data in the FIS Floodway 

Data Table if the waterway was studied using 

detailed methods, application of approximation 

methods based on continuity, local observations 

and sources, or site-specific studies. 

ASCE 24 limits dry floodproofing to areas where 

flood velocities are less than or equal to 5 feet per 

second.

Are waves expected to affect 

the site?

Waves can exert considerable dynamic forces 

on buildings and contribute to erosion and scour. 

Wind-driven waves occur in areas subject to 

coastal flooding and where unobstructed winds 

affect wide floodplains (large lakes and major 

rivers). In riverine floodplains with high velocities, 

standing waves may occur.

ASCE 24 and NFIP regulations do not allow 

floodproofing in Coastal High Hazard Areas. 

ASCE 24 also does not allow dry floodproofing in 

Coastal A Zones.

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS C-3

CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS C

Vulnerability Considerations Guidance Observations

Is there information on how 

quickly floodwaters may affect 

the site?

What is the expected duration 

of flooding?

Warning time is a key factor in the safe and 

orderly evacuation of critical facilities. Certain 

protective measures may require adequate 

warning so that actions can be taken by skilled 

personnel.

For dry floodproofing, ASCE 24 specifies minimum 

warning times when human intervention is 

necessary based on whether the community has 

a warning system and emergency plan. 

Duration has bearing on the stability of earthen 

fills, access to a site and emergency response, 

and durability of materials that come into contact 

with water. Records of actual flooding are the best 

indicator of duration because most floodplain 

analyses do not include an examination of 

duration. 

Is there a history of floodrelated debris problems or 

erosion on the site?

Floodproofing design should account for 

deposition of debris and sediment, as well as 

the potential for erosion-related movement of the 

shoreline or waterway as appropriate. Buildings 

exposed to debris impact or undermining by scour 

and erosion should be designed to account for 

these conditions. 

Is the site in an area predicted 

to flood if a levee or floodwall 

fails or is overtopped? 

Is the site in an area predicted 

to be inundated if an upstream 

dam failed?

Flood protection works may be distant from the 

sites being assessed and not readily observable. 

Although, failure or overtopping is a low-probability 

event, it can cause unexpected and catastrophic 

damage because the protected lands are not 

regulated as flood hazard areas.

The effects of an upstream dam failure are not 

shown on the FIRMs or most flood hazard maps 

prepared locally. Although dam failure is generally 

considered an unlikely event, the potential threat 

should be evaluated because of the catastrophic 

consequences. (Owners of certain dams should 

have emergency action plans for notifying and 

evacuating vulnerable populations and critical 

facilities.)

Does the surrounding 

topography contribute to the 

flooding at the site? Is there a 

history of local surface drainage 

problems due to inadequate site 

drainage?

If areas with poor local drainage and frequent 

flooding cannot be avoided, filling, re-grading, and 

installation of storm drainage facilities may be 

required.

Given the nature of anticipated 

flooding and soils, is scour 

around and under the 

foundation likely?

Scour-prone sites should be avoided, in part 

because of likely long-term maintenance 

requirements. Flooding that is high velocity or 

accompanied by waves is more likely to cause 

scour, especially on fills, or where local soils are 

unconsolidated and subject to erosion.

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
C-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

C CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS

Vulnerability Considerations Guidance Observations

Has water from other sources 

entered the building (e.g., 

high groundwater, water main 

breaks, sewer backup)? Is there 

a history of water intrusion 

through floor slabs or wallfloor connections? Are there 

underground utility systems or 

areaways that can contribute to 

basement flooding? Are there 

stormwater sewer manholes 

upslope of window areas 

or openings that allow local 

drainage to enter the basement/

lower floor areas? 

These questions pertain to existing facilities that 

may be impaired by water from sources other than 

the primary source of flooding. The entire building 

envelope, including below-grade areas, should be 

examined to identify potential water damage.

Is at least one access road 

to the site/building passable 

during flood events? 

Are at-grade parking lots 

located in flood-prone areas?

Are below-grade parking areas 

susceptible to flooding?

The longer the duration of the flood, the more 

important access is. For the safety of occupants, 

most critical facilities should not be occupied 

during flood events.

Areas where vehicles could be affected should 

have signage to warn users, including bus drivers, 

of the flooding risk. Emergency response plans 

should include instructions on notifying car 

owners.

Architectural

Are any critical building 

functions occupying space 

below the elevation of the 500-

year flood or the DFE?

Can critical functions be 

relocated to upper levels that 

are above predicted flood 

elevations?

If critical functions cannot be 

relocated, is floodproofing 

feasible?

If critical functions must 

continue during a flood 

event, have power, supplies, 

and access issues been 

addressed?

New critical facilities in flood hazard areas should 

not have any functions occupying flood-prone 

spaces other than parking, building access, and 

limited storage. 

Existing facilities in floodplains should be 

examined carefully to identify the best options for 

protecting functionality and the structure itself.

Are any critical contents (files, 

computers, servers, equipment, 

or data) on levels of the facility 

below the flood elevations? 

Are critical records maintained 

offsite?

Existing facilities that are located in flood hazard 

areas may require continued use of flood-prone 

space. However, the potential for flooding should 

be recognized and steps taken to minimize loss 

of expensive equipment and irreplaceable data. 

If critical contents cannot be permanently located 

on higher floors, a flood response plan should 

take into account the time and attention needed to 

move such contents safely.

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS C-5

CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS C

Vulnerability Considerations Guidance Observations

Structural Systems

What is the construction type 

and foundation type and what is 

the load-bearing capacity?

Has the foundation been 

designed to resist hydrostatic 

and hydrodynamic flood loads?

If siting in a floodplain is unavoidable, new 

facilities should be designed to account for all 

loads and load combinations, including flood 

loads. Building components may need to be 

strengthened to withstand flood forces and the 

loads imposed by dry floodproofing components. 

If the building has below-grade 

areas (basements), are the 

lower floor slabs subject to 

cracking and uplift?

Below-grade spaces and their contents are the 

most vulnerable to flooding and local drainage 

problems. Rapid pump-out of below-grade spaces 

can unbalance forces if the surrounding soil is 

saturated, leading to structural failure. If belowgrade spaces are intended to be dry floodproofed, 

the design must account for buoyant forces.

Building spaces below the design flood level can 

be dry floodproofed, but higher flood levels can 

overtop the protection measures and result in 

severe damage. Dry floodproofing creates large 

unbalanced forces that can jeopardize walls and 

foundations that are not designed to resist the 

hydrostatic and hydrodynamic loads.

Are any portions of the building 

below the DFE?

Has the building been damaged 

in previous floods?

For existing buildings, it is important to determine 

which portions are vulnerable in order to evaluate 

floodproofing options. If flood depths are expected 

to exceed 2 or 3 feet, dry floodproofing may not be 

feasible. Alternatives include modifying the use of 

flood-prone areas.

If the building is elevated on 

a crawlspace or on an open 

foundation, are there any 

enclosed areas?

New buildings may have enclosures below the 

DFE if the use of the enclosures is limited to 

crawlspace, parking, building access, and limited 

storage. In addition, the enclosures must have 

flood openings to allow inflow and outflow of 

floodwaters to minimize differential hydrostatic 

pressure. 

Existing buildings that are elevated and have 

enclosures below the flood elevation can be 

retrofit with flood openings.

For an existing building with 

high-value uses below the 

flood elevation, is the building 

suitable for elevation in-place, 

or could it be relocated to 

higher ground? 

Elevating a building provides better protection 

than dry floodproofing. Depending on the type and 

soundness of the foundation, even large buildings 

can be elevated on a new foundation or moved to 

a site outside the floodplain.

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
C-6 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

C CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS

Vulnerability Considerations Guidance Observations

Building Envelope

Are there existing floodproofing 

measures below the expected 

flood elevation? What is the 

nature of the measures and 

what condition are they in? Is 

there an annual inspection and 

maintenance plan?

Is there an action plan to 

implement floodproofing 

measures when flooding is 

predicted? Do the building 

operators/occupants know what 

to do when a flood warning is 

issued?

Floodproofing measures are only as good as 

their design and condition, especially if many 

years have passed since initial installation. 

Floodproofing measures that require human 

intervention are entirely dependent on the 

adequacy of advance warning and the availability 

and ability of personnel to install the measures 

properly. 

For existing buildings, what 

types of openings penetrate 

the building envelope below 

the 500-year flood elevation or 

the DFE (e.g., doors, windows, 

cracks, vent openings, 

plumbing fixtures, floor drains)?

For dry floodproofing to be effective, every 

opening must be identified and either permanently 

seal or covered with special barriers to resist 

infiltration. Sewage backflow can enter through 

unprotected plumbing fixtures.

Are flood-resistant materials 

used for structural and 

nonstructural components and 

finishes below the 500-year 

elevation or DFE?

Flood-resistant materials are capable of 

withstanding direct and prolonged contact with 

floodwaters without sustaining damage that 

requires more than cosmetic repair. Contact is 

considered to be prolonged if it is 72 hours or 

longer in freshwater flooding areas, or 12 hours or 

longer in areas subject to coastal flooding.

Utility Systems

Is the potable water supply 

for the facility protected from 

flooding? If served by a well, is 

the wellhead protected? 

Operators of critical facilities that depend on 

freshwater for continued functionality should learn 

about the vulnerability of the local water supply 

system and the utility owner’s plans for recovery of 

service in the event of a flood.

Is the wastewater service for 

the building protected from 

flooding? 

Are any manholes below 

the DFE? Is infiltration of 

floodwaters into sewer lines a 

problem? If the site is served by 

an onsite system that is located 

in a flood-prone area, have 

backflow valves been installed? 

Most waste lines exit buildings at the lowest 

elevation. Even buildings that are outside the 

floodplain can be affected by sewage backups 

during floods. 

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS C-7

CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS C

Vulnerability Considerations Guidance Observations

Are there any aboveground 

or underground tanks on the 

site in flood hazard areas? Are 

they installed and anchored to 

resist flotation during the design 

flood? Are tank openings and 

vents elevated above the 

500-year elevation or DFE, or 

are they otherwise protected 

to prevent entry of floodwater 

or release of product during a 

flood event?

Dislodged tanks become floating debris 

that poses special hazards during recovery. 

Lost product causes environmental damage. 

Functionality may be impaired if tanks for heating 

fuel, propane, or fuel for emergency generators 

are lost or damaged. 

Mechanical Systems

Are air handlers, HVAC 

systems, ductwork, and other 

mechanical equipment and 

systems located above the 500-

year elevation or DFE? Are the 

vents and inlets located above 

the flood level or sealed to 

prevent entry of floodwater?

In existing buildings, utility equipment that is 

critical for functionality should be relocated to 

higher floors or elevated additions. 

Plumbing and Gas Systems

Are plumbing fixtures and gasfired equipment (e.g., meters, 

pilot-light devices/burners) 

located above the 500-year 

elevation or DFE?

In existing buildings, utility equipment that is 

critical for functionality should be relocated to 

higher floors or elevated additions.

Is plumbing and gas piping 

that extends below flood levels 

installed to minimize damage?

Piping that is exposed could be affected by debris.

Electrical Systems

Are electrical systems, including 

backup power generators, 

panels, and primary service 

equipment, located above the 

500-year elevation or DFE? 

Are electrical stand-by 

equipment and generators 

equipped with circuits to turn off 

power?

Are the switches and wiring 

required for safety (minimal 

lighting, door openers) below 

the flood level designed for use 

in damp locations?

In existing buildings, utility equipment that is 

critical for functionality should be relocated to 

higher floors or elevated additions.

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
C-8 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

C CHECKLIST FOR VULNERABILITY OF FLOOD-PRONE SITES AND BUILDINGS

Vulnerability Considerations Guidance Observations

Fire Alarm Systems

Is the fire alarm system located 

above the 500-year elevation 

or DFE?

In existing buildings, utility equipment that is 

critical for functionality should be relocated to 

higher floors or elevated additions.

Communications and IT Systems

Are the communication/IT 

systems located above the 500-

year elevation or DFE? 

In existing buildings, communications and 

IT systems critical for functionality should be 

relocated to higher floors or elevated additions.

ASCE American Society of Civil Engineers

DFE design flood elevation

FEMA Federal Emergency Management Agency

FIRM Flood Insurance Rate Map

HVAC heating, ventilation, and air conditioning

IT information technology

NFIP National Flood Insurance Program

Checklist for Vulnerability of Flood-Prone Sites and Buildings (continued)
FLOODPROOFING NON-RESIDENTIAL BUILDINGS D-1

References

AA (Aluminum Association). 2010. Aluminum Design Manual. 

ACI (American Concrete Institute). 2008. Building Code Requirements for Structural Concrete and 

Commentary. ACI 318-08.

ACI/American Society of Civil Engineers (ASCE) / The Masonry Society (TMS). 2011. Building Code 

Requirements and Specifications for Masonry Structures. ACI 530-11/ASCE 5-11/TMS 402-11.

AISC (American Institute of Steel Construction). 2011. Steel Construction Manual (14th ed.). AISC 32511.

ANSI (American National Standards Institute) / AF&PA (American Forest & Paper Association). 2005. 

National Design Specification for Wood Construction. NDS-2005.

ASCE (American Society of Civil Engineers). 2005. Flood Resistant Design and Construction. 

ASCE Standard 24.

ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE/SEI Standard 7-10.

ASTM (ASTM International). 2011. Standard Practice for Classification of Soils for Engineering Purposes 

(Unified Soil Classification System). ASTM D2487-11.

ASTM. 2012. Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort. 

ASTM D698-12.

AWPA (American Wood Protection Association). 2012. Use Category System: User Specification for Treated 

Wood. AWPA-U1-12.

Columbus Regional Hospital. 2012. “About Us.” Available at http://www.crh.org/about-us/default.aspx. 

Accessed August 12, 2012.

FEMA (Federal Emergency Management Agency). 1986. Floodproofing Non-Residential Structures. 

FEMA 102. Available at http://www.fema.gov/media-library/assets/documents/15599.

FEMA. 1993a. Non-Residential Floodproofing Requirements and Certification for Buildings Located in Special 

Flood Hazard Areas in Accordance with the NFIP. NFIP Technical Bulletin 3-93 (FIATB3). Available at 

http://www.fema.gov/media-library/assets/documents/3473.
D-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

D REFERENCES

FEMA. 1993b. Wet Floodproofing Requirements. NFIP Technical Bulletin 7-93 (FIA-TB-7). Available at http://

www.fema.gov/media-library/assets/documents/3503.

FEMA. 1995. Zone A Manual: Managing Floodplain Development in Approximate Zone A Areas. FEMA 265. 

Available at: http://www.fema.gov/media-library/assets/documents/7273. 

FEMA. 2003. NFIP Increased Cost Compliance (ICC) Coverage: Guidance for State and Local Officials. FEMA 

301. Available at http://www.fema.gov/media-library/assets/documents/1973. 

FEMA. 2005. Floodplain Management Requirements, A Study Guide and Desk Reference for Local Officials. 

FEMA 480. Available at http://www.fema.gov/media-library/assets/documents/902. 

FEMA 2007a. Managing Floodplain Development through the National Flood Insurance Program. IS-9. Available 

at http://www.fema.gov/media-library/assets/documents/6029.

FEMA. 2007b. Wet Floodproofing Reduces Damage to Popular Beach Restaurant. Available at https://www.llis.

dhs.gov/content/wet-floodproofing-reduces-damage-popular-beach-restaurant?mitssId=3025. Accessed April 

18, 2012.

FEMA. 2008a. Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard 

Areas in Accordance with the National Flood Insurance Program. NFIP Technical Bulletin 2. Available at http://

www.fema.gov/media-library/assets/documents/2655. 

FEMA. 2008b. Historic Structures. NFIP Floodplain Management Bulletin P-467-2. Available at http://www.

fema.gov/media-library/assets/documents/13411.

FEMA. 2008c. Multiple Mitigation Measures Give Darlington an Elevating Experience: Mitigation Best Practice 

Story. Available at https://www.llis.dhs.gov/content/multiple-mitigation-measures-give-darlington-elevatingexperience. Accessed April 19, 2012.

FEMA. 2008d. Openings in Foundation Walls and Walls of Enclosures. NFIP Technical Bulletin 1. Available at 

http://www.fema.gov/media-library/assets/documents/2644.

FEMA. 2009a. Benefit-Cost Analysis Tool. Version 4.5.5. Available at http://www.fema.gov/media-library/

assets/documents/22970. Accessed April 12, 2012.

FEMA. 2009b. Design Considerations for Improving Critical Facility Functionality during Flood Events. FEMA 

P-765. Available at http://www.fema.gov/media-library/assets/documents/17329. 

FEMA. 2009c. National Flood Insurance Program Regulations. FEMA F-775. Available at http://www.fema.

gov/media-library/assets/documents/18184. 

FEMA. 2010a. Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds (Second 

Edition). Risk Management Series FEMA P-424. Available at http://www.fema.gov/media-library/assets/

documents/5264.
FLOODPROOFING NON-RESIDENTIAL BUILDINGS D-3

REFERENCES D

FEMA. 2010c. Substantial Improvement/Substantial Damage Desk Reference. FEMA P-758. Available at http://

www.fema.gov/media-library/assets/documents/18562. 

FEMA. 2011a. Advanced Mitigation Planning Allows Hospital to Stay Dry During Tropical Storm: Mitigation 

Best Practice Story. Available at https://www.llis.dhs.gov/content/advanced-mitigation-planning-allows-hospital-stay-dry-during-tropical-storm?mitssId=8850. Accessed April 18, 2012.

FEMA. 2011b. Answers to Questions About the NFIP. FEMA F-084. Available at http://www.fema.gov/

media-library/assets/documents/272.

FEMA. 2011c. Coastal Construction Manual: Principles and Practices of Planning, Siting, Designing, Construction, 

and Maintaining Residential Buildings in Coastal Areas (Fourth Edition). FEMA P-55. Available at http://www.

fema.gov/media-library/assets/documents/3293. 

FEMA. 2011d. Supplement to the Benefit-Cost Analysis Reference Guide. Available at http://sema.dps.mo.gov/

docs/programs/Logistics,%20Resources,%20Mitigation%20&%20Floodplain/mitigation/BCA_Reference_

Guide_Supplement%20June%202011.pdf. Accessed April 19, 2012.

FEMA. 2012a. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures (Third 

Edition). FEMA P-259. Available at http://www.fema.gov/media-library/assets/documents/3001.

FEMA. 2012b. Floodproofing Certificate for Non-Residential Structures. FEMA Form 086-0-34 (7/12). Available 

at http://www.fema.gov/media-library/assets/documents/2748. Accessed May 21, 2013.

FEMA. 2012c. Floodwall with Passive Floodgates Signals Commitment to Patients and Community: Mitigation 

Best Practice Story. Available at https://www.llis.dhs.gov/content/floodwall-passive-floodgates-signals-commitment-patients-and-community?mitssId=9311. Accessed April 17, 2012. 

FEMA. 2013. National Flood Insurance Program Flood Insurance Manual. Available at http://www.fema.gov/

flood-insurance-manual.

FM Approvals. 2006. Approval Standard for Flood Abatement Equipment. FM Approvals Class Number 2510. 

Available at http://www.fmglobal.com/assets/pdf/fmapprovals/2510.pdf. Accessed April 17, 2012. 

IBC. 2012. International Building Code. Published by the International Code Council. 

IEBC. 2012. International Existing Building Code. Published by the International Code Council. 

NFPA (National Fire Protection Association). 2012. Building Construction and Safety Code. NFPA 5000.

NOAA (National Oceanic and Atmospheric Administration). 2011, September 19. “Record Rains and Floods 

in the Northeast.” Climate Watch Magazine. Available at http://www.climatewatch.noaa.gov/image/2011/

record-rains-floods-in-the-northeast. Accessed August 12, 2012.
D-4 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

D REFERENCES

ORNL (Oakridge National Laboratory). 2011. Floodproof Construction: Working for Coastal Communities. 

SERRI (Southeast Region Research Initiative) Report 80024. Available at http://www.serri.org/publications/Documents/MSU%20Project%2080024%20-%20Final%20Report%20for%20Phase%201%20

(Floodproof%20Construction)%20-%2026%20September%202011%20(Perkes).pdf. Accessed August 9, 

2012.

USACE (U.S. Army Corps of Engineers). 1984. Shore Protection Manual, Volume 2.

USACE. 1988. Flood Proofing Tests: Tests of Materials and Systems for Flood Proofing Structures. National Flood 

Proofing Committee. Available at http://archive.org/details/shoreprotectionm02unit. Accessed August 13, 

2012.

USACE. 1995. Flood Proofing Regulations. Engineering Pamphlet EP 1165-2-314. Available at http://publications.usace.army.mil/publications/eng-pamphlets/EP_1165-2-314/toc.htm. 
FLOODPROOFING NON-RESIDENTIAL BUILDINGS E-1

Resources

FEMA Hazard Mitigation Assistance (HMA) Programs

Benefit-Cost Analysis http://www.fema.gov/benefit-cost-analysis

Benefit-Cost Analysis Helpline http://www.bchelpline.com/

Environmental Planning and 

Historic Preservation

http://www.fema.gov/environmental-planning-and-historic-preservation-program

Flood Mitigation Assistance 

Program

http://www.fema.gov/flood-mitigation-assistance-program

Hazard Mitigation Assistance 

Overview

http://www.fema.gov/hazard-mitigation-assistance 

Hazard Mitigation Assistance 

Helpline

Telephone: (866) 222-3580

E-mail: hmagrantshelpline@dhs.gov

Hazard Mitigation Assistance 

policies

http://www.fema.gov/hazard-mitigation-assistance-policy

Hazard Mitigation Grant Program http://www.fema.gov/hazard-mitigation-grant-program

Increased Cost of Compliance 

coverage

http://www.fema.gov/national-flood-insurance-program-2/increased-costcompliance-coverage

Pre-Disaster Mitigation Program http://www.fema.gov/pre-disaster-mitigation-grant-program 

Repetitive Flood Claims Program http://www.fema.gov/repetitive-flood-claims-program

FEMA Building Science Publications and Other Resources

Community Rating System http://www.fema.gov/national-flood-insurance-program/community-rating-system

Community Rating System 

Resource Center

http://training.fema.gov/EMIWeb/CRS/

FEMA Building Science Branch http://www.fema.gov/building-science 

FEMA Library http://www.fema.gov/library/index.jsp

FEMA P-787, Catalog of FEMA 

Flood and Wind Publications, and 

Training Courses

http://www.fema.gov/media-library/assets/documents/12909

Flood Insurance Studies http://www.fema.gov/national-flood-insurance-program-2/flood-insurance-study-fis 

Flood Insurance Rate Maps http://www.fema.gov/national-flood-insurance-program-2/flood-insurance-ratemap-firm 

Information and Guidance on 

Building Safer

http://www.fema.gov/safer-stronger-protected-homes-communities

Map Service Center http://msc.fema.gov/

Mitigation http://www.fema.gov/what-mitigation 

Mitigation Assessment Team 

Reports

http://www.fema.gov/fema-mitigation-assessment-team-reports 
E-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

E RESOURCES

FEMA Building Science Publications and Other Resources (continued)

National Flood Insurance Program http://www.fema.gov/national-flood-insurance-program

National Flood Insurance Program 

Technical Bulletins

http://www.fema.gov/national-flood-insurance-program-2/nfip-technical-bulletins 

National Preparedness Directorate 

National Training and Education

http://www.training.fema.gov/

Building Codes and Standards

The Aluminum Association http://www.aluminum.org

American Concrete Institute http://www.concrete.org

American Institute of Steel 

Construction

http://www.aisc.org

American Society of Civil 

Engineers Publications

http://www.asce.org/PPLContent.aspx?id=2147483667

American Society for Testing and 

Materials

http://www.astm.org

The Engineered Wood Association http://www.apawood.org

International Code Council: Codes 

and Standards

http://www.iccsafe.org/cs/

National Fire Protection 

Association

http://www.nfpa.org/categoryList.asp?categoryID=124&URL=Codes%20&%20

Standards

Other Resources

Flood Mitigation News http://www.floodmitigation.com/

FloodSafe California, Urban Levee 

Design Criteria

http://www.water.ca.gov/floodsafe/leveedesign/

International Association of 

Structural Movers

www.iasm.org

National Oceanic and Atmospheric 

Administration’s National Weather 

Service 

http://www.nws.noaa.gov/

Natural Resource Conservation 

Service

http://www.nrcs.usda.gov/programs/

Natural Resource Conservation 

Service Soils website

http://soils.usda.gov/

Natural Resource Conservation 

Service Technical Resource 

Library

http://www.nrcs.usda.gov/technical/

National Weather Service 

Precipitation Frequency Studies

http://www.nws.noaa.gov/oh/hdsc/currentpf.htm

Susquehanna Flood Forecast and 

Warning System

http://www.susquehannafloodforecasting.org/current-conditions.html#riverforecasts

U.S. Army Corps of Engineers 

Library

http://140.194.76.129/publications/

U.S. Army Corps of Engineers, 

Design and Construction of 

Levees (EM 1110-2-1913)

http://www.mde.state.md.us/programs/Water/DamSafety/TechnicalReferences/

Documents/www.mde.state.md.us/assets/document/damsafety/COE/Levees%20

Design%20Construction.pdf

U.S. Department of Housing and 

Urban Development

http://portal.hud.gov/portal/page/portal/HUD
FLOODPROOFING NON-RESIDENTIAL BUILDINGS E-3

RESOURCES E

State and Regional Contacts

Association of State Floodplain 

Managers

http://www.floods.org/

Association of State Floodplain 

Managers Levee Information and 

Resources

http://www.floods.org/index.asp?menuID=400

Federal Emergency Management 

Agency 

http://www.fema.gov/fire-management-assistance-grants-regional-contacts 

National Flood Insurance Program http://www.fema.gov/national-flood-insurance-program/national-flood-insuranceprogram-regional-offices 

State Hazard Mitigation Officers http://www.fema.gov/state-hazard-mitigation-officers 

State Historic Preservation Offices http://www.nps.gov/nr/shpolist.htm

U.S. Army Corps of Engineers http://www.usace.army.mil/

FLOODPROOFING NON-RESIDENTIAL BUILDINGSS F-1

FEMA Region Contact 

Information

Figure F-1. FEMA Regions and location of Regional Offices
F-2 FLOODPROOFING NON-RESIDENTIAL BUILDINGS

F FEMA REGION CONTACT INFORMATION

Table F-1. FEMA Region Contact Information

FEMA Region States and Territories Address Telephone

Headquarters Federal Emergency Management Agency

500 C Street, S.W.

Washington, D.C. 20472

800.621.3362

Region I Connecticut, Maine, 

Massachusetts, New 

Hampshire, Rhode Island, 

Vermont

Federal Emergency Management Agency

99 High Street, 5th Floor

Boston, MA 02110

617.956.7506

Alternate: 

877.336.2734

Region II New Jersey, New York, 

Puerto Rico, U.S. Virgin 

Islands

Federal Emergency Management Agency

26 Federal Plaza

New York, NY 10278-0002

Region II Caribbean Address

Federal Emergency Management Agency

Caribbean Division

P.O. Box 70105

San Juan, Puerto Rico 00936-8105

212.680.3600

Region III Delaware, District of 

Columbia, Maryland, 

Pennsylvania, Virginia, 

West Virginia

Federal Emergency Management Agency

615 Chestnut Street

Philadelphia, PA 19106-4404

215.931.5500

Region IV Alabama, Florida, 

Georgia, Kentucky, 

Mississippi, North 

Carolina, South Carolina, 

Tennessee

Federal Emergency Management Agency

3003 Chamblee Tucker Road

Atlanta, GA 30341

770.220.5200

Region V Illinois, Indiana, Michigan, 

Minnesota, Ohio, 

Wisconsin

Federal Emergency Management Agency

536 South Clark Street, 6th Floor

Chicago, IL 60605

312.408.5500

Region VI Arkansas, Louisiana, 

New Mexico, Oklahoma, 

Texas

Federal Emergency Management Agency

FRC 800 North Loop 288

Denton, TX 76209-3698

940.898.5104

Region VII Iowa, Kansas, Missouri, 

Nebraska

Federal Emergency Management Agency

9221 Ward Parkway, Suite 300

Kansas City, MO 64114-3372

816.283.7061

Region VIII Colorado, Montana, 

South Dakota, Utah, 

Wyoming

Federal Emergency Management Agency

Denver Federal Center

Building 710, Box 25267

Denver, CO 80225-0267

Region IX Arizona, California, 

Guam, Hawaii, Nevada, 

Commonwealth of 

Northern Mariana Islands, 

Republic of the Marshall 

Islands, Federated States 

of Micronesia, American 

Samoa

Federal Emergency Management Agency

1111 Broadway, Suite 1200

Oakland, CA 94607-4052

510.627.7100

Pacific Area Office: 

808.851.7900

Region X Alaska, Idaho, Oregon, 

Washington

Federal Emergency Management Agency

Federal Regional Center

130 228th Street, Southwest

Bothell, WA 98201-8627

425.487.4600