Recommended 
Residential Construction 
for the Gulf Coast 

Building on Strong and Safe Foundations

FEMA 550 / July 2006 

FEMA



About the Cover

On August 29, 2005, Hurricane Katrina struck the Gulf Coast with recordbreaking storm surge 
that destroyed foundations and devastated homes from Louisiana east to Alabama. Katrina was so 
destructive that engineers assessing the carnage no longer looked for success stories (i.e., homes 
that were only moderately damaged), but rather searched for survivor homes that, while extensively 
damaged, still bore a slight resemblance to a residential building. Hurricane Katrina proved 
that, without strong foundations, homes on the coast can and will be destroyed.



Recommended 
Residential Construction
for the Gulf Coast 

Building on Strong and Safe Foundations

FEMA 550 / July 2006


FEMA



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


Acknowledgments

FEMA would like to thank the following individuals who provided information, data, review, 
and guidance during the preparation of this report.

Principal Authors

Bill Coulbourne, PE
URS Corporation

Matt Haupt, PE 
URS Corporation

Scott Sundberg, PE 
URS Corporation

David K. Low, PE
DK Low & Associates, LLC 

Jimmy Yeung, PhD, PE
Greenhorne and OMara, Inc.

John Squerciati, PE
Dewberry and Davis, LLC

Contributors and Reviewers

John Ingargiola
FEMA Headquarters

Shabbar Saifee
FEMA, Region IV

Dan Powell
FEMA, Region IV

Alan Springett
FEMA, Region IV

Keith Turi 
FEMA Headquarters

Christopher Hudson
FEMA Headquarters

Christopher P. Jones, PE

Dan Deegan, PE, CFM 
PBS&J

Ken Ford 
National Association of Homebuilders (NAHB)

Mike Hornbeck 
Gulf Construction Company, Inc.

iii



David Kriebel, PhD, PE 
U.S. Naval Academy

Jim Puglisi 
Dewberry and Davis, LLC

John Ruble 
Bayou Plantation Homes

Bob Speight, PE
URS Corporation

Naomi Chang
Greenhorne and OMara, Inc.

Deb Daly
Greenhorne and OMara, Inc.

Julie Liptak
Greenhorne and OMara, Inc.

Wanda Rizer
Design4Impact



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


Table of Contents

Acknowledgments..........................................................................................................................iii

Introduction .....................................................................................................................................ix

Chapter 1. Types of Hazards........................................................................................................1-1

1.1 High Winds.........................................................................................................................1-1

1.2 Storm Surge........................................................................................................................1-4

1.3 Flood Effects.......................................................................................................................1-6

1.3.1 Hydrostatic Forces...................................................................................................1-6

1.3.2 Hydrodynamic Forces.............................................................................................1-7

1.3.3 Waves........................................................................................................................1-8

1.3.4 Floodborne Debris................................................................................................1-10

1.3.5 Erosion and Scour.................................................................................................1-10

Chapter 2. Foundations.................................................................................................................2-1

2.1 Foundation Design Criteria...............................................................................................2-1

 



table of contents

vi

Building on strong and safe foundations

2.2 Foundation Design in Coastal Areas ................................................................................2-2

2.3 Open and Closed Foundations in Coastal Areas.............................................................2-4

2.3.1 Open Foundations..................................................................................................2-4

2.3.1.1 Piles...........................................................................................................2-4

2.3.1.2 Piers...........................................................................................................2-7

2.3.2 Closed Foundations................................................................................................2-8

2.3.2.1 Perimeter Walls........................................................................................2-9

2.3.2.2 Slab-on-Grade........................................................................................2-10

2.4 Introduction to Foundation Design and Construction ................................................2-10

2.4.1 Site Characterization............................................................................................2-10

2.4.2 Types of Foundation Construction......................................................................2-11

2.4.2.1 Piles.........................................................................................................2-11

2.4.2.2 Diagonal Bracing of Piles......................................................................2-12

2.4.2.3 Knee Bracing of Piles.............................................................................2-13

2.4.2.4 Wood-Pile-to-Wood-Girder Connections..............................................2-14

2.4.2.5 Grade Beams in Pile/Column Foundations.........................................2-15

Chapter 3. Foundation Design Loads.........................................................................................3-1 

3.1 Wind Loads........................................................................................................................3-2

3.2 Flood Loads........................................................................................................................3-3

3.2.1 Design Flood and Design Flood Elevation (DFE)................................................3-4

3.2.2 Design Stillwater Flood Depth...............................................................................3-5

3.2.3 Design Wave Height................................................................................................3-5

3.2.4 Design Flood Velocity.............................................................................................3-6

3.3 Hydrostatic Loads..............................................................................................................3-7

3.4 Wave Loads ........................................................................................................................3-8

3.4.1 Breaking Wave Loads on Vertical Piles..................................................................3-8

3.4.2 Breaking Wave Loads on Vertical Walls.................................................................3-9

3.5 Hydrodynamic Loads.......................................................................................................3-11



Table of contents

vii

3.6 Debris Impact Loads........................................................................................................3-12

3.7 Localized Scour................................................................................................................3-14

3.7.1 Localized Scour Around Vertical Piles................................................................3-15

3.7.2 Localized Scour Around Vertical Walls and Enclosures.....................................3-15

3.8 Flood Load Combinations...............................................................................................3-16

Chapter 4. Overview of Recommended Foundation Types and Construction for 
the Gulf Coast.................................................................................................................................4-1

4.1 Critical Factors Affecting Foundation Design..................................................................4-2

4.1.1 Wind Speed.............................................................................................................4-2

4.1.2 Elevation..................................................................................................................4-2

4.1.3 Construction Materials...........................................................................................4-3

4.1.3.1 Masonry Foundation Construction.........................................................4-3

4.1.3.2 Concrete Foundation Construction........................................................4-3

4.1.3.3 Field Preservative Treatment for Wood Members..................................4-4

4.1.4 Foundation Design Loads......................................................................................4-5

4.2 Recommended Foundation Types for the Gulf Coast.....................................................4-7

4.2.1 Open Foundation: Timber Pile (Case A)..............................................................4-8

4.2.2 Open Foundation: Steel Pipe Pile with Concrete Column and Grade 
Beam (Case B)........................................................................................................4-9

4.2.3 Open Foundation: Timber Pile with Concrete Column and Grade Beam 
(Case C).................................................................................................................4-11

4.2.4 Open Foundation: Concrete Column and Grade Beam with Slabs 
(Cases D and G)....................................................................................................4-12

4.2.5 Closed Foundation: Reinforced Masonry  Crawlspace (Case E).....................4-13

4.2.6 Closed Foundation: Reinforced Masonry  Stem Wall (Case F)........................4-14

Chapter 5. Foundation Selection................................................................................................5-1

5.1 Foundation Design Types..................................................................................................5-1

5.2 Foundation Design Considerations..................................................................................5-2

5.3 Cost Estimating..................................................................................................................5-4



5.4 How to Use This Manual...................................................................................................5-4

5.5 Design Examples................................................................................................................5-7

Appendices

Appendix A Foundation Designs

Appendix B Pattern Book Design

Appendix C Assumptions Used in Design

Appendix D Foundation Analysis and Design Examples 

Appendix E Cost Estimating

Appendix F Referenced Fact Sheets from FEMA 499

Appendix G FEMA Publications and Additional References

Appendix H Glossary

Appendix I Abbreviations and Acronyms



Introduction 
The purpose of this design manual is to provide recommended 
foundation designs and guidance for rebuilding homes destroyed by 
hurricanes in the Gulf Coast. In addition, the manual is intended 
to provide guidance in designing and building safer and less 
vulnerable homes to reduce the risk to life and property. 

Past storms such as Hurricanes Andrew, Hugo, and Charley, and recent storms such as Katrina and Rita continue to show the vulnerability of our built environment (see Figure 1). 
While good design and construction cannot totally eliminate risk, every storm has shown that 
sound design and construction can significantly reduce the risk to life and damage to property. 


With that in mind, FEMA has developed this manual to help the community of homebuilders, 
contractors, and local engineering professionals in rebuilding homes destroyed by Hurricanes 
Katrina and Rita, and designing and building safer and less vulnerable new homes. 

ix

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 


INTRODUCTION

 

Building on strong and safe foundations

Intent of the Manual

The intent of the manual is to provide Gulf Coast homebuilders, contractors, and local engineering 
professionals with a series of recommended foundation designs that will help create 
safer and stronger buildings along the Gulf Coast. The use of these designs is intended to cover 
many of the home styles anticipated for the construction effort. 

The foundations may differ somewhat from traditional construction techniques; however, they 
represent what are considered to be some of the better approaches to constructing strong and 
safe foundations in the hazardous areas along the Gulf Coast. The objectives used to guide the 
development of this manual are:

n To provide residential foundation designs that will require minimal engineering oversight 
n To provide foundation designs that are flexible enough to accommodate many of the homes 
identified in A Pattern Book for Gulf Coast Neighborhoods prepared for the Mississippi Governors 
Rebuilding Commission on Recovery, Rebuilding and Renewal (see Appendix B)
n To utilize model layouts so that many homes can be constructed without significant additional 
engineering efforts
The focus of this document is on the foundation of residential buildings. The assumption is 
that those who are designing and building new homes will be responsible for ensuring that the 
building itself is designed according to the latest building code (International Building Code 
[IBC], International Residential Code [IRC], and FEMA guidance) and any local requirements. 
The user of this manual is directed to other publications that also address disaster-resistant construction 
(see Appendix G). 


Figure 1. 
Damage to residential 
properties as a result 
of Hurricane Katrina's 
winds and storm surge. 
Note the building that 
was knocked off its 
foundation (circled). 



INTRODUCTION

xi

Although the foundation designs are geared to 
the coastal environment subject to storm surge, 
waves, floating debris, and high winds, several 
are suitable for supporting homes on sites protected 
by levees and floodwalls. For protected 
sites, wave loads may be less than those in an exposed 
coastal environment and, therefore, the 
designs presented in this manual may be conservative 
for such areas. 

This manual contains closed foundation designs 
for elevating homes up to 8 feet above ground 
level and open foundation designs for elevating 
homes up to 15 feet above ground level. These upper limits are a function of constructability 
limitations and overturning and stability issues for more elevated foundations. Eight-foot 
tall foundations are a practical upper limit for 8-inch thick reinforced concrete masonry unit 
(CMU) walls exposed to flood forces anticipated in non-coastal A zones. The upper limit of 15 
feet for open foundations was established by estimating the amount a home needs to be elevated 
to achieve the 2005 Advisory Base Flood Elevations (ABFEs). The ABFEs published in the 
Hurricane Recovery Maps were compared to local topographic maps for the Gulf Coast. The 
comparison revealed that approximately 80 percent of the homes damaged by Hurricane Katrina 
could be elevated to the ABFEs on foundations that are 15 feet or less in height. 

Using the Manual

The following information is needed to use this manual:

n Design wind speed and the Design Flood Elevation (DFE) at the siten The flood zone(s) at the siten Building layoutn Topographic elevation of existing building site 
n Soil conditions for the site. Soil condition assumptions used in the load calculations are intentionally 
conservative. Users are encouraged to determine soil conditions at the site to 
potentially improve the cost-effectiveness of the design. 
Most of the information can be obtained from the local building official or floodplain manager.

This document is not intended to supplant involvement from local design professionals. While 
the designs included can be used without modification (provided that the home to be elevated 
falls within the design criteria), consulting with local engineers should be considered. Local 
engineers may assist with the following:

n Incorporating local site conditions into the design
CAUTION: Although sites inside 
levees are not exposed to 
wave loads, sites immediately 
adjacent to floodwalls and levees can be 
exposed to extremely high flood velocities 
and scour if a breach occurs. Design 
professionals should be consulted before 
using these foundation designs on sites 
close to floodwalls or levees to determine 
if they are appropriate.



n Addressing and supporting unique features of the home 
n Allowing use of value engineering to produce a more efficient design
These designs have been developed to support homes with a range of dimensions, weights, and 
roof pitches. Figure 2 schematically shows the diverse range of dimensions and roof pitches. Appendix 
C contains a complete list of criteria and assumptions used in these designs. 

This manual concentrates on foundations that resist the extreme hurricane wind and flooding 
conditions found throughout the Gulf Coast. For successful, natural hazard-resistant installations, 
both the foundation and the home it supports must be properly designed and constructed 
to take all loads on the structure into the ground through the foundation. Constructing the 
home to meet all the requirements of the IBC or the IRC is a minimum requirement to producing 
hazard-resistant homes. However, any model code must contain minimum requirements 
and best practice approaches for improved resistance to natural hazards.

To gain the benefits of a best practices approach, readers are directed to publications such as 
FEMA 499, Home Builders Guide to Coastal Construction Technical Fact Sheet Series, and FEMA 55, 
Coastal Construction Manual. A more complete list of available publications is contained in Appendix 
G.


Figure 2. 
Schematic of range of 
home dimensions and 
roof pitches



Organization of the Manual

There are five chapters and seven appendices in this manual. The intent is to cover the essential 
information in the chapters and provide all the details in the appendices. Chapter 1 
provides a description of the different types of hazards that must be considered in the design 
of a residential building foundation in the Gulf Coast area. The primary issues related to designing 
foundations for residential buildings are described in Chapter 2. Chapter 3 provides 
guidance on how to determine the magnitude of the loads placed on a building by a particular 
natural hazard event or a combination of events. The different foundation types and methods 
of construction foundation for a residential building are discussed in Chapter 4. Chapter 5 and 
Appendix A present foundation designs to assist the homebuilders, contractors, and local engineering 
professionals in developing a safe and strong foundation. 

In addition to Chapters 1 through 5 and Appendix A, the following appendices are presented 
herein:

n Appendix B presents examples of how the foundation designs in this manual can be used 
with some of the houses in the publication A Pattern Book for Gulf Coast Neighborhoods.
n Appendix C provides a list of assumptions used in developing the foundation design presented 
in this manual.
n Appendix D provides detailed calculations on how to design the foundation of residential 
buildings. Two examples, one for open foundations and the other for closed foundations, 
are presented.
n Appendix E provides cost information that the homebuilders can use to estimate the cost of 
installing the foundation systems proposed in this manual.
n Appendix F includes a list of fact sheets contained in FEMA 499 that are referenced in this 
manual.
n Appendix G presents a list of references and other FEMA publications that can be of assistance 
to the users of this manual.
n Appendix H contains a glossary of terms used in the manual.
n Appendix I defines abbreviations and acronyms used in the manual.

Limitations of the Manual

This manual has been provided to assist in the reconstruction efforts after Hurricane Katrina. Builders, 
architects, or engineers using this manual assume responsibility for the resulting designs and their performance 
during a natural hazard event.

The foundation designs and analyses presented in this manual were based on the American Society of 
Civil Engineers (ASCE) 7-02 and the 2003 version of the IRC. While FEMA 550 was being developed, 
ASCE released its 2005 edition of ASCE 7 (ASCE 7-05) and the International Code Council (ICC) issued 
their 2006 editions of the IBC and IRC. The ASCE 7 revisions did not affect the load calculations 
controlling the designs and there were no substantive flood provision changes to the IRC that affect 
foundation designs in coastal areas. 



1. Types of Hazards 
This chapter discusses the following types of hazards that must 
be considered in the design of a residential building foundation for 
the Gulf Coast: high winds, storm surge, and associated flood effects, 
including hydrostatic forces, hydrodynamic forces, waves, floodborne 
debris, and erosion and scour. 

1.1 High Winds 
Hurricanes are the basis for design wind speeds for the Gulf Coast. High winds during a hurricane can create extreme positive and negative forces on a building; the net result is that wind 
forces simultaneously try to push over the building and lift it off its foundation. If the foundation is not strong enough to resist these forces, the home may slide, overturn, collapse, or incur 
substantial damage (Figure 1-1). 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 


1 TYPES OF HAZARDS

1- 

Building on strong and safe foundations

The most current design wind speeds are provided by the American Society of Civil Engineers 
(ASCE) document Minimum Design Loads for Buildings and Other Structures (ASCE 7). ASCE 7 is 
typically updated every 3 years. The 2002 edition ASCE 7-02 is referenced by the following model 
building codes: the 2003 editions of the International Building Code (IBC), the International 
Residential Code (IRC), and the NFPA 5000, Building Construction and Safety Code, published by 
the National Fire Protection Association (NFPA). 

Design wind speeds given by ASCE 7 are 3-second gust speeds, not the sustained wind speeds 
associated with the Saffir-Simpson hurricane classification scale. Figure 1-3 shows the design 
wind speeds for portions of the Gulf Coast region based on 3-second gusts (measured at 33 feet 
above the ground in Exposure C).


NOTE: Hurricanes are classified into five categories according to the Saffir-Simpson 
Scale, which uses wind speed and central pressure as the principal parameters to categorize 
storm damage potential. Hurricanes can range from Category 1 to the devastating 
Category 5 (Figure 1-2). 

Hurricanes can produce storm surge that is higher or lower than what the wind speed at landfall would 
predict. Katrinas surge was roughly that of a Category 5, although its winds at landfall were only a 
Category 3. A hurricane that is a Category 3 or above is generally considered a major hurricane.


Figure 1-1. 
Wind damage to roof 
structure and gable end 
wall from Hurricane 
Katrina (2005) (Pass 
Christian, Mississippi)



TYPES OF HAZARDS 1 

1- 

Saffir-Simpson Scale (Category/Damage)

Category 1 Hurricane  Winds 74 to 95 mph, sustained 
(91 to 116 mph, 3-second gust) 

No real damage to buildings. Damage to unanchored mobile 
homes. Some damage to poorly constructed signs. Also, some 
coastal flooding and minor pier damage. Examples: Hurricanes 
Irene (1999) and Allison (1995).

Category 2 Hurricane  Winds 96 to 110 mph, sustained 
(117 to 140 mph, 3-second gust) 

Some damage to building roofs, doors, and windows. 
Considerable damage to mobile homes. Flooding damages 
piers, and small crafts in unprotected moorings may break. 
Some trees blown down. Examples: Hurricanes Bonnie (1998), 
Georges (FL and LA 1998), and Gloria (1985).


Category 3 Hurricane  Winds 111 to 130 mph, sustained (141 
to 165 mph, 3-second gust) 

Some structural damage to small residences and utility 
buildings. Large trees blown down. Mobile homes and poorly 
built signs destroyed. Flooding near the coast destroys smaller 
structures with larger structures damaged by floating debris. 
Terrain may be flooded far inland. Examples: Hurricanes Keith 
(2000), Fran (1996), Opal (1995), Alicia (1983), Betsy (1965), 
and Katrina at landfall (2005).

Category 4 Hurricane  Winds 131 to 155 mph, sustained 
(166 to 195 mph, 3-second gust) 

More extensive curtainwall failures with some complete roof 
structure failure on small residences. Major erosion of beach 
areas. Terrain may be flooded far inland. Examples: Hurricanes 
Hugo (1989), Donna (1960), and Charley (2004).

Category 5 Hurricane  Winds greater than 155 mph, 
sustained (195 mph and greater, 3-second gust) 

Complete roof failure on many residences and industrial 
buildings. Some complete building failures with small utility 
buildings blown over or away. Flooding causes major damage 
to lower floors of all structures near the shoreline. Massive 
evacuation of residential areas may be required. Examples: 
Hurricanes Andrew (1992), Camille (1969), and the unnamed 
Labor Day storm (1935).

Note: Saffir-Simpson wind speeds (sustained 1-minute) were converted to 3-second gust wind speed utilizing the Durst Curve 
contained in ASCE 7-02, Figure C6-2.


Figure 1-2. Saffir-Simpson Scale



1.2 Storm Surge

Storm surge is water that is pushed toward the shore by the combined force of the lower 
barometric pressure and the wind-driven waves advancing to the shoreline. This advancing 
surge combines with the normal tides to create the hurricane storm tide, which in 
many areas can increase the sea level by as much as 20 to 30 feet. Figure 1-4 is a graphical depiction 
of how wind-driven waves are superimposed on the storm tide. This rise in water level can 
cause severe flooding in coastal areas, particularly when the storm tide coincides with high tides 
(see Figure 1-5). Because much of the United States densely populated Gulf Coast coastlines 
lie less than 20 feet above sea level, the danger from storm surge is great. In addition, because 
of the shape and the bathymetery of the Gulf of Mexico, storm surges along the Gulf Coast can 
be greater than anywhere else in the United States (see Figure 1-6). 


Figure 1-3. 
Design wind speed map for portions of the Gulf Coast. Contours are 3-second gust wind speeds (in miles per hour 
[meters per second]) for Exposure Category C, 33 feet height.

Source: ASCE 7-02

Figure 1-4. 
Graphical depiction of a hurricane moving ashore. In this example, a 15-foot surge added to the normal 2-foot tide 
creates a total storm tide of 17 feet.


Figure 1-5. 
Storm tide and waves 
from Hurricane Dennis 
on July 10, 2005, near 
Panacea, Florida

Source: U.S. 
Geological Survey 
(USGS) Sound Waves 
Monthly newsletter. 
Photograph 
courtesy of The 
Forgotten Coastline 
(Copyright 2005)

Figure 1-6. 
Comparison of storm surge levels along the shorelines of the Gulf Coast for Category 1, 3, and 5 storms

Source: Hurricane Katrina in the Gulf Coast MAT Report (FEMA 549) 
1.3 Flood Effects

Although coastal flooding can originate from a number of sources, Gulf Coast hurricanes 
and weaker tropical storms not categorized as hurricanes are the primary cause of flooding 
(see Figure 1-2). The flooding can lead to a variety of impacts on coastal buildings 
and their foundations: hydrostatic forces, hydrodynamic forces, waves, floodborne debris forces, 
and erosion and scour. 

1.3.1 Hydrostatic Forces

Horizontal hydrostatic forces against a structure are created when the level of standing or slowly 
moving floodwater on opposite sides of the structure are not equal. Flooding can also cause 
vertical hydrostatic forces, resulting in flotation. Rapidly rising floodwaters can also cause structures 
to float off of their foundations (see Figure 1-7). If floodwaters rise slowly enough, water 
can seep into a structure to reduce buoyancy forces. While slowly rising floodwaters reduce the 
adverse effects of buoyancy, any flooding that inundates a home can cause extreme damage.



1.3.2 Hydrodynamic Forces

Moving floodwaters create hydrodynamic forces on submerged foundations and buildings. 
These hydrodynamic forces can destroy solid walls and dislodge buildings with inadequate connections 
or load paths. Moving floodwaters can also move large quantities of sediment and 
debris that can cause additional damage. In coastal areas, moving floodwaters are usually associated 
with one or more of the following:

n Storm surge and wave runup flowing landward through breaks in sand dunes, levees, or 
across low-lying areas (see Figure 1-8)
Figure 1-7. 
Building floated 
off of foundation 
(Plaquemines Parish, 
Louisiana)

Source: Hurricane 
Katrina in the gulf 
coast (FEMA 549)
Figure 1-8. 
Aerial view of damage 
to one of the levees 
caused by Hurricane 
Katrina (photo taken 
on August 30, 2005, 
the day after the storm 
hit, New Orleans, 
Louisiana).

Source: FEMA NEWS 
PHOTO/ Jocelyn 
Augustino



n Outflow (flow in the seaward direction) of floodwaters driven into bay or upland areas by a 
stormn Strong currents along the shoreline driven by storm waves moving in an angular direction 
to the shore
High-velocity flows can be created or exacerbated by the presence of manmade or natural obstructions 
along the shoreline and by weak points formed by shore-normal (i.e., perpendicular 
to the shoreline) roads and access paths that cross dunes, bridges, or shore-normal canals, channels, 
or drainage features. For example, evidence after Hurricane Opal (1995) struck Navarre 
Beach, Florida, suggests that flow was channeled in between large, engineered buildings. The 
resulting constricted flow accelerated the storm surge and caused deep scour channels across 
the island. These channels eventually undermined pile-supported houses between large buildings 
while also washing out roads and houses farther landward (see Figure 1-9).

1.3.3 Waves

Waves can affect coastal buildings in a number of ways. The most severe damage is caused by 
breaking waves (see Figures 1-10 and 1-11). The height of these waves can vary by flood zone: 
V Zone wave heights can exceed 3 feet, while Coastal A Zone wave heights are between 1.5 
and 3 feet. The force created by waves breaking against a vertical surface is often ten or more 
times higher than the force created by high winds during a storm event. Waves are particularly 
damaging due to their cyclic nature and resulting repetitive loading. Because typical wave periods 
during hurricanes range from about 6 to 12 seconds, a structure can be exposed to 300 
to 600 waves per hour, resulting in possibly several thousand load cycles over the duration of 
the storm. 

Wave runup occurs as waves break and run up beaches, sloping surfaces, and vertical surfaces. 
Wave runup can drive large volumes of water against or around coastal buildings, creating 



Figure 1-9. 
During Hurricane Opal 
(1995), this house 
was in an area of 
channeled flow between 
large buildings. As 
a result, the house 
was undermined and 
washed into the bay 
behind a barrier island. 

Source: COastal 
Construction manual
(FEMA 55)

hydrodynamic forces (albeit smaller than breaking wave forces), drag forces from the current, 
and localized erosion and scour. Wave runup under a vertical surface (such as a wall) will create 
an upward force by the wave action due to the sudden termination of its flow. This upward 
force is much greater than the force generated as a wave moves along a sloping surface. In some 
instances, the force is large enough to destroy overhanging elements such as decks or porches. 
Another negative effect of waves is reflection or deflection, occurring when a wave is suddenly 
redirected as it impacts a building or structure.

Figure 1-10. 
Storm waves breaking 
against a seawall 
in front of a coastal 
residence at Stinson 
Beach, California 

Source: COastal 
COnStruction 
manual
(FEMA 55)
Figure 1-11. 
Storm surge and 
waves overtopping a 
coastal barrier island 
in Alabama (Hurricane 
Frederic, 1979)

Source: COastal 
COnStruction 
manual
(FEMA 55)

1.3.4 Floodborne Debris

Floodborne debris produced by coastal flood events and storms typically includes decks, steps, 
ramps, breakaway wall panels, portions of or entire houses, fuel tanks, vehicles, boats, pilings, 
fences, destroyed erosion control structures, and a variety of smaller objects (see Figure 1-12). 
In some cases, larger pieces of floodborne debris can strike buildings (e.g., shipping containers 
and barges), but the designs contained herein are not intended to withstand the loads from 
these larger debris elements. Floodborne debris is capable of destroying unreinforced masonry 
walls, light wood-frame construction, and small-diameter posts and piles (and the components 
of structures they support). Debris trapped by cross bracing, closely spaced pilings, grade beams, 
or other components is also capable of transferring flood and wave loads to the foundation of 
an elevated structure. 

1.3.5 Erosion and Scour

Erosion refers to the wearing and washing away of coastal lands, including sand and soil. It is 
part of the larger process of shoreline changes. Erosion occurs when more sediment leaves a 
shoreline area than enters from either manmade objects or natural forces. Because of the dynamic 
nature of erosion, it is one of the most complex hazards to understand and difficult to 
accurately predict at any given site along the coast. 

Short-term erosion changes can occur from storms and periods of high wave activity, lasting 
over periods ranging from a few days to a few years. Because of the variability in direction 
and magnitude, short-term erosion effects can be orders of magnitude greater than long-term 
erosion. Long-term shoreline changes occur over a period of decades or longer and tend to average 
out the short-term erosion. Both short-term and long-term changes should be considered 
in the siting and design of coastal residential construction. Refer to Chapter 7 of FEMA 55 for 
additional guidance on assessing short- and long-term erosion.

Figure 1-12. 
Pier pilings were carried 
over 2 miles by the 
storm surge and waves 
of Hurricane Opal (1995) 
before coming to rest 
against this elevated 
house in Pensacola 
Beach, Florida.

Source: COastal 
COnStruction manual
(FEMA 55)

Scour can occur when water flows at high velocities past an object embedded in or sitting on 
soil that can be eroded. Scour occurs around the object itself, such as a piling or foundation element, 
and contributes to the loss of support provided by the soil. In addition to any storm or 
flood-induced erosion that occurs in the general area, scour is generally limited to small, cone-
shaped depressions. Localized scour is capable of undermining slabs, pilings, and grade beam 
structures, and, in severe cases, can lead to structural failure (see Figure 1-13). This document 
considers these effects on the foundation size and depth of embedment requirements.


Figure 1-13. 
Extreme case of localized scour undermining a slab-on-grade house in Topsail Island, North Carolina, after 
Hurricane Fran (1996). Prior to the storm, the lot was several hundred feet from the shoreline and mapped as 
an A Zone on the FIRM. This case illustrates the need for open foundations in Coastal A Zones. 

Source: COastal COnStruction manual (FEMA 55)

2. Foundations 
This chapter discusses the primary issues related to designing 
foundations for residential buildings in coastal areas: foundation 
design criteria, National Flood Insurance Program (NFIP) requirements 
on coastal construction in A and V Zones, the performance of 
various foundation types, and foundation construction. 

2.1 Foundation Design Criteria 
Foundations on the Gulf Coast should be designed in accordance with the 2003 or 2006 edition 
of the IBC or IRC; both contain up-to-date wind provisions and are consistent with NFIP flood 
provisions. In addition, any locally adopted building ordinances must be addressed. Foundations should be designed and constructed to: 

n Properly support the elevated home and resist all loads expected to be imposed on the 
home and its foundation during a design event 

n Prevent flotation, collapse, and lateral movement of the building 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2- 



2 FOUNDATIONS

2- 

Building on strong and safe foundations

In addition, the foundation should be constructed with flood-resistant materials below the Base 
Flood Elevation (BFE).

2.2 Foundation Design in Coastal Areas

Building in a coastal environment is different from building in an inland area because:

n Storm surge, wave action, and erosion in coastal areas make coastal flooding more damaging 
than inland flooding.
n Design wind speeds are higher in coastal areas and thus require buildings and their foundations 
to be able to resist higher wind loads.
Foundations in coastal areas must be constructed such that the top of the lowest floor (in A 
Zones) or the bottom of the lowest horizontal structural members (in V Zones) of the buildings 
are elevated above the BFE, while withstanding flood forces, high winds, erosion and 
scour, and floodborne debris. Deeply embedded pile or other open foundations are required 
for V Zones because they allow waves and floodwaters to pass beneath elevated buildings. Because 
of the increased flood, wave, floodborne debris, and erosion hazards in V Zones, NFIP 
design and construction requirements are more stringent in V Zones than in A Zones.

Some coastal areas mapped as A Zones may also 
be subject to damaging waves and erosion (referred 
to as Coastal A Zones). Buildings in 
these areas that are constructed to minimum 
NFIP A Zone requirements may sustain major 
damage or be destroyed during the base flood. 
It is strongly recommended that buildings in A Zones 
subject to breaking waves and erosion be designed 
and constructed with V Zone type foundations (see 
Figure 2-1). Open foundations are often recommended 
instead of solid wall, crawlspace, slab, or 
shallow foundations, which can restrict floodwaters 
and be undermined easily. Figure 2-2 shows 
examples of building failures due to scour under 
a slab-on-grade foundation. 

NFIP Minimum Elevation 
Requirements for New 
Construction*

A Zone: Elevate top of lowest floor to or 
above BFE 

V Zone: Elevate bottom of lowest horizontal 
structural member supporting the lowest 
floor to or above BFE 

In both V and A Zones, many property owners 
have decided to elevate one full story 
above grade, even if not required, to allow 
below-building parking. See Fact Sheet No. 
2 of FEMA 499 for more information about 
NFIP minimum requirements and recommended 
best practices in A and V Zones 
(see Appendix F).

* For floodplain management purposes, new construction means structures for which the start of construction began on or 
after the effective date of the floodplain management regulation adopted by a community. Substantial improvements, repairs of 
substantial damage, and some enclosures must meet most of the same requirements as new construction.



FOUNDATIONS 2 

2- 

Figure 2-1. 
Recommended open foundation practice for buildings in A Zones, Coastal A Zones, and V Zones 

Source: COastal COnstruction manual (FEMA 55)
Figure 2-2 
Slab-on-grade foundation failure due to erosion and scour undermining and closeup of the foundation failure from 
Hurricane Dennis, 2005 (Navarre Beach, Florida).

 



2.3 Open and Closed Foundations in Coastal Areas
There are many designs that can be used to elevate buildings above the BFE: open foundations 
(pile, pier, column) and closed foundations (crawlspace, stem wall, solid wall). 
Structural fill can also be used to elevate and support stem wall, crawlspace, solid wall, slab-
on-grade, pier, and column foundations in areas not subject to damaging wave action and scour. 
Only open foundations with base members or elements (pilings or beams) located below expected 
erosion and scour are allowed in V Zones; as a best practices approach, open foundations 
are recommended, but are not NFIP required, in Coastal A Zones. Table 2-1 shows the recommended 
type of foundation depending on the coastal area. Additional information concerning 
foundation performance can be found in FEMA 499, Fact Sheet No. 11 (see Appendix F).

Table 2-1. Foundation Type Dependent on Coastal Area

Foundation Type

V Zone

Coastal A Zone

A Zone

Open

4

4

4

Closed

8

NR

4





4 = Acceptable NR = Not Recommended 8 = Not Permitted

2.3.1 Open Foundations

Open foundations are required in V Zones and recommended in Coastal A Zones. This type of 
foundation allows water to pass beneath an elevated building through the foundation and reduces 
lateral flood loads on the structure. Open foundations also have the added benefit of being less 
susceptible to damage from floodborne debris because debris is less likely to be trapped. 

2.3.1.1 Piles

Pile foundations consist of deeply placed vertical piles installed under the elevated structure. 
The piles support the elevated structure by remaining solidly placed in the soil. Because pile 
foundations are set deeply, they are inherently more tolerant to erosion and scour. Piles rely primarily 
on the friction forces that develop between the pile and the surrounding soils (to resist 
gravity and uplift forces) and the compressive strength of the soils (to resist lateral movement). 
The soils at the ends of the piles also contribute to resist gravity loads. 

Piles are typically treated wood timbers, steel pipes, or pre-cast concrete. Other materials like 
fiber reinforced polyester (FRP) are available, but are rarely used in residential construction. 
Piles can be used with or without grade beams. When used without grade beams, piles extend 
to the lowest floor of the elevated structure. Improved performance is achieved when the piles 
extend beyond the lowest floor to the roof (or an upper floor level) above. Doing so provides 
resistance to rotation (also called fixity) in the top of the pile and improves stiffness of the pile 
foundation. Occasionally, wood framing members are installed at the base of a wood piling (see 
Figure 2-3). These members are not true grade beams but rather are compression struts. They 
provide lateral support for portions of the piling near grade and reduce the potential for column 
buckling; however, due to the difficulties of constructing moment connections with wood, 
the compression struts provide very little resistance to rotation. 



Critical aspects of a pile foundation include the pile size, installation method, and embedment 
depth, bracing, and their connections to the elevated structure (see FEMA 499 Fact Sheet Nos. 
12 and 13 in Appendix F). Pile foundations with inadequate embedment will not have the structural 
capacity to resist sliding and overturning (see Figure 2-4). Inadequate embedment and 
improperly sized piles greatly increase the probability for structural collapse. However, when 
properly sized, installed, and braced with adequate embedment into the soil (with consideration 
for erosion and scour effects), a buildings pile foundation performance will allow the 
building to remain standing and intact following a design flood event (see Figure 2-5).

When used with grade beams, the piles and grade beams work in conjunction to elevate the 
structure, provide vertical and lateral support for the elevated home, and transfer loads imposed 
on the elevated home and foundation to the ground below. 


Figure 2-3. 
Compression strut at 
base of a wood piling. 
Struts provide some 
lateral support for the 
piling, but very little 
resistance to rotation.

Source: COastal 
COnStruction 
manual
(FEMA 55)
Figure 2-4. 
Near collapse due 
to insufficient pile 
embedment (Dauphin 
Island, Alabama)

Source: Hurricane 
Katrina in the Gulf 
Coast (FEMA 549)

Pile foundations with grade beams must be constructed with adequate strength to resist all lateral 
and vertical loads. Failures experienced during Hurricane Katrina often resulted from inadequate 
connections between the columns and footings or grade beams below (see Figure 2-6). Pile and 
grade beam foundations should be designed and constructed so that the grade beams act only 
to provide fixity to the foundation system and not to support the lowest elevated floor. If grade 
beams support the lowest elevated floor of the home, they become the lowest horizontal structural 
member and significantly higher flood insurance premiums would result. Also, if the grade 
beams support the structure, the structure would become vulnerable to erosion and scour. Grade 
beams must also be designed to span between adjacent piles and the piles must be capable of resisting 
both the weight of the grade beams when undermined by erosion and scour, and the loads 
imposed on them by forces acting on the structure.


Figure 2-5. 
Successful pile 
foundation following 
Hurricane Katrina 
(Dauphin Island, 
Alabama) 

Source: Hurricane 
Katrina in the Gulf 
Coast (FEMA 549)
Figure 2-6. 
Column connection 
failure (Belle Fontaine 
Point, Jackson County, 
Mississippi)

Source: Hurricane 
Katrina in the Gulf 
Coast (FEMA 549)

2.3.1.2 Piers

Piers have different design criteria in various locations around the country. As used in the Gulf 
Coast for residential construction, piers are generally placed on footings to support the elevated 
structure. Without footings, piers function as short piles and rarely have sufficient capacity 
to resist uplift and gravity loads.

The type of footing used in pier foundations greatly affects the foundations performance (see 
Figure 2-7). When exposed to lateral loads, discrete footings can rotate so piers placed on discrete 
footings are only suitable when wind and flood loads are relatively low. Piers placed on 
continuous concrete grade beams or concrete strip footings provide much greater resistance to 
lateral loads because the grade beams/footings act as an integral unit and are less prone to rotation. 
Footings and grade beams must be reinforced to resist the moment forces that develop 
at the base of the piers due to the lateral loads on the foundation and the elevated home (see 
Figure 2-8). 

Since pier foundation footings or grade beams are limited in depth of placement, they are appropriate 
only where there is limited potential for erosion or scour. The maximum estimated 
depth for long- and short-term erosion and localized scour should not extend below the bottom 
of the footing or grade beam. 

Figure 2-7. 
Performance 
comparison of pier 
foundations. Piers 
on discrete footings 
(foreground) failed 
by rotating and 
overturning while piers 
on more substantial 
footings (in this case a 
concrete mat) survived 
(Pass Christian, 
Mississippi)



2.3.2 Closed Foundations

A closed foundation is typically constructed using foundation walls, a crawlspace foundation, or 
a stem wall foundation (usually filled with compacted soil). A closed foundation does not allow 
water to pass easily through the foundation elements below the elevated building. Thus, these 
types of foundations are said to obstruct the flow. These foundations also present a large surface 
area upon which waves and flood forces act; therefore, they are prohibited in V Zones and not 
recommended for Coastal A Zones. If foundation or crawlspace walls enclose space below the 
BFE, they must be equipped with openings that allow floodwaters to flow in and out of the area 


Figure 2-8. Isometric view of an open foundation with grade beam



enclosed by the walls (see Figure 2-9 for an isometric view). The entry and exit of floodwater will 
equalize the water pressure on both sides of the wall and reduce the likelihood of the wall collapsing 
(see FEMA 499 Fact Sheet No. 15 in Appendix F). Two types of closed foundations are 
discussed in this manual, perimeter walls and slab-on-grade.

2.3.2.1 Perimeter Walls 

Perimeter walls are conventional walls (typically masonry or wood frame) that extend from the 
ground up to the elevated building. They typically bear on shallow footings. Crawlspaces and 
stem walls are two types of foundations with perimeter walls.

Crawlspaces. Crawlspace foundations are typically low masonry perimeter walls, some requiring 
interior piers supporting a floor system if the structure is wide. These foundations are usually 
supported by shallow footings and are prone to failure caused by erosion and scour.


Figure 2-9. Isometric view of a closed foundation with crawlspace



This type of foundation is characterized by a solid perimeter foundation wall around a structure 
with a continuous spread footing with reinforced masonry or concrete piers. All crawlspace 
foundation walls in the Special Flood Hazard Area (SFHA) must be equipped with flood openings. 
These openings are required to equalize the pressure on either side of the wall (see FEMA 
499 Fact Sheet Nos. 15 and 26 in Appendix F). However, even with flood vents, hydrodynamic 
and wave forces in Coastal A Zones can damage or destroy these foundations.

Stem Walls. Stem walls (i.e., a solid perimeter foundation wall on a continuous spread footing 
backfilled to the underside of the floor slab) are similar to crawlspace foundations, but the interior 
that would otherwise form the crawlspace is filled with soil or gravel that supports a floor 
slab. Stem wall foundations have been observed to perform better than crawlspace foundations 
in Coastal A Zones (but only where erosion and scour effects are minor). Flood openings are 
not required in filled stem wall foundations.

2.3.2.2 Slab-on-Grade 

A slab-on-grade foundation is concrete placed directly on-grade (to form the slab) with generally 
thickened, reinforced sections around the edges and under loadbearing walls. The slab 
itself is typically 4 inches thick where not exposed to concentrated loads and 8 to 12 inches 
thick under loadbearing walls.The thickened portions of slab-on-grade foundations are typically 
reinforced with deformed steel bars to provide structural support; the areas not thickened 
are typically reinforced with welded wire fabrics (WWF) for shrinkage control. While commonly 
used in residential structures in A Zones, slab-on-grade foundations are prone to erosion and 
prohibited in V Zones, and are not recommended for Coastal A Zones. 

Slab-on-grade foundations can be used with structural fill to elevate buildings. Fill is usually 
placed in layers called lifts with each lift compacted at the site. Because fill is susceptible to 
erosion, it is prohibited for providing structural support in V Zones. Structural fill is not recommended 
for Coastal A Zones, but may be appropriate for non-Coastal A Zones. 

2.4 Introduction to Foundation Design and Construction

This section introduces two main issues related to foundation design and construction: 
site characterization and types of foundation construction. Construction materials and 
methods (field preservation treatment, substitutions, inspection points) are addressed 
in Chapter 4.

2.4.1 Site Characterization

The foundation design chosen should be based on the characteristics that exist at the building 
site. A site characteristic study should include the following:

n The type of foundations that have been installed in the area in the past. A review of the 
latest Flood Insurance Rate Map (FIRM) is recommended to ensure that construction characteristics 
have not been changed.

n The proposed site history, which would indicate whether there are any buried materials, or 
the site has been regraded.
n How the site may have been used in the past, from a search of land records for past 
ownership.
n A Soil Investigation Report, which should include:
n Soil borings sampled from the site or taken from test pitsn A review of soil borings from the immediate area adjacent to the site 
n Information from the local office of the Natural Resource Conservation Service (formerly 
the Soil Conservation Service) and soil surveys published for each county
One of the parameters derived from a soil investigation report is the bearing capacity, which 
measures the ability of soils to support gravity loads without soil shear failure or excessive settlement. 
Measured in pounds per square foot (psf), soil bearing capacity typically ranges from 
1,000 psf for relatively weak soils to over 10,000 psf for bedrock. 

Frequently, designs are initially prepared on a presumed bearing capacity. It is then the homebuilders 
responsibility to verify actual site conditions. The actual soil bearing capacity should 
be determined. If soils are found to have higher bearing capacity, the foundation can be constructed 
as designed or the foundation can be revised to take advantage of the better soils.

Allowable load bearing values of soils given in Section 1804 of the 2003 IBC can be used when 
other data are not available. However, soils can vary significantly in bearing capacity from one 
site to the next. A geotechnical engineer should be consulted when any unusual or unknown 
soil condition is encountered.

2.4.2 Types of Foundation Construction

2.4.2.1 Piles 

A common type of pile foundation is the elevated wood pile foundation, where the piles extend 
from deep in the ground to an elevation at or above the Design Flood Elevation (DFE). 
Horizontal framing members are used to connect the piles in both directions. This grid forms a 
platform on which the house is built (see FEMA 499 Fact Sheet No. 12 in Appendix F).

The method of installation is a major consideration in the structural integrity of pile foundations. 
The ideal method is to use a pile driver. In this method, the pile is held in place with 
leads while a single-acting, double-acting diesel or air-powered hammer drives the pile into the 
ground (see Figure 2-10).

If steel piles are used, only the hammer driving method mentioned above should be used. For 
any pile driving, the authority having jurisdiction or the engineer-of-record may require that a 
driving log is kept for each pile. The log will tabulate the number of blows per foot as the driving 
progresses. This log is a key factor used in determining the pile capacity. 



Another method for driving piles is the drop hammer method. It is a lower cost alternative to 
the pile driver. A drop hammer consists of a heavy weight raised by a cable attached to a power-
driven winch and then dropped onto the pile.

A less desirable but frequently used method of inserting piles into sandy soil is jetting, which 
involves forcing a high-pressure stream of water through a pipe that advances with the pile. The 
water creates a hole in the sand as the pile is driven until the required depth is reached. Unfortunately, 
jetting loosens the soil both around the pile and the tip. This results in a lower load 
capacity due to less frictional resistance. Jetted piles are not appropriate for the design provided 
in this manual unless capacity is verified by a geotechnical engineer.

Holes for piles may be excavated by an auger if the soil has sufficient clay or silt content. Augering 
can be used by itself or in conjunction with pile driving. If the hole is full-sized, the 
pile is dropped in and the void backfilled. Alternatively, an undersized hole can be drilled and 
a pile driven into it. When the soil conditions are appropriate, the hole will stay open long 
enough to drop or drive in a pile. In general, this method may not have as much capacity as 
those methods previously mentioned. Like jetted piles, augered piles are not appropriate for 
the designs provided in this manual unless the method for compressing the soil is approved 
by a geotechnical engineer.

2.4.2.2 Diagonal Bracing of Piles

The foundation design may include diagonal bracing to stiffen the pile foundation in one or 
more directions. When installed properly, bracing lowers the point where lateral loads are applied 
to the piles. The lowering of load application points reduces the bending forces that piles 
must resist (so piles in a braced pile foundation do not need to be as strong as piles in an unbraced 
pile foundation) and also reduces lateral movement in the building. Outside pilings are 
sufficiently designed to withstand external forces, because bracing will not assist in countering 


Figure 2-10. 
Pile installation methods

Source: COastal 
COnstruction manual
(FEMA 55)

these forces. A drawback to bracing, however, is that the braces themselves can become obstructions 
to moving floodwaters and increase a foundations exposure to wave and debris impact. 

Because braces tend to be slender, they are vulnerable to compression buckling. Therefore, 
most bracing is considered tension-only bracing. Because wind and, to a lesser extent, flood 
loads can act in opposite directions, tension-only bracing must be installed in pairs. One set of 
braces resists loads from one direction while the second set resists loads from the opposite direction. 
Figure 2-11 shows how tension only bracing pairs resist lateral loads on a home. 

The braced pile design can only function when all of the following conditions are met:

n The home must be constructed with a stiff horizontal diaphragm such as a floor system 
that transfers loads to laterally braced piles.
n Solid connections, usually achieved with bolts, must be provided to transmit forces from 
the brace to the pile or floor system.
The placement of the lower bolted connection of the diagonal to the pile requires some judgment. 
If the connection is placed too high above grade, the pile length below the connection 
is not braced and the overall bracing is less strong and stiff. If the connection is placed too 
close to grade, the bolt hole is more likely to be flooded or infested with termites. Because the 
bolt hole passes through the untreated part of the pile, flooding and subsequent decay or termite 
infestation will weaken the pile at a vulnerable location. Therefore, the bolt hole should 
be treated with preservative after drilling and prior to bolt placement.

The braced wood pile designs developed for this manual use steel rods for bracing. Steel rods 
were used because:

n Steel has greater tensile strength than even wide dimensional lumber.
n There are fewer obstructions to waves and floodborne debris.
n The rod bracing can easily be tensioned with turnbuckles and can be adjusted throughout 
the life of the home.
n A balanced double shear connection is two to three times stronger than a wood to wood 
connection made with 2-inch thick dimensional lumber.
Alternative bracing should only be installed when designed by a licensed engineer.

2.4.2.3 Knee Bracing of Piles

Knee braces involve installing short diagonal braces between the upper portions of the pilings 
and the floor system of the elevated structure. The braces increase the stiffness of an elevated 
pile foundation and can be effective at resisting the lateral forces on a home. While knee braces 
do not stiffen a foundation as much as diagonal bracing, they do offer some advantages over 
diagonal braces. For example, knee braces present less obstruction to waves and debris, are 
shorter than diagonal braces, and are usually designed for both tension and compression loads. 



Unlike diagonal braces, knee braces do not reduce bending moments in the piles (they can 
actually increase bending moments) and will not reduce the diameter of the piles required to 
resist lateral loads.

The entire load path into and through the knee brace must be designed with sufficient capacity. 
The connections at each end of each knee brace must have sufficient capacity to handle both tension 
and compression and to resist axial loads in the brace. The brace itself must have sufficient 
cross-sectional area to resist compression and tensile loads. Due to the complexity of knee bracing, 
they have not been used in the foundation designs included in Appendix A of this document.

2.4.2.4 Wood-Pile-to-Wood-Girder Connections

Wood piles are often notched to provide a bearing surface for a girder. However, a notch should 
not reduce more than 50 percent of the pile cross-section (such information is typically provided 
by a designer on contract documents). For proper load transfer, the girder should bear on 
the surface of the pile notch. 


Figure 2-11. Diagonal bracing schematic



Although connections play an integral role in the design of structures, they are typically regarded 
as the weakest link. The connection between a wood pile and the elevated structure should 
be designed by an engineer (see FEMA 499 Fact Sheet No. 13 in Appendix F). 

2.4.2.5 Grade Beams in Pile/Column Foundations

Grade beams are sometimes used in conjunction with pile and column foundations to generate 
more stiffness. They generate stiffness by forcing the piles to move as a group rather than 
individually and by providing fixity (i.e., resistance to rotation) at the ends of the piles. Typically, 
they extend in both directions and are usually made of reinforced concrete. The mix design, the 
amount and placement of reinforcement, the cover, and the curing process are important parameters 
in optimizing durability. To reduce the effect of erosion and scour on foundations, grade 
beams must be designed to be self-supporting foundation elements. The supporting piers should 
be designed to carry the weight of the grade beams and resist all loads transferred to the piers.

In V Zones, grade beams must be used only for lateral support of the piles. If, during construction, 
the floor is made monolithic with the grade beams, the bottom of the beams become the 
lowest horizontal structural member. This elevation must be at or above the BFE. 

If grade beams are used with wood piles, the possibility of rot occurring must be considered 
when designing the connection between the grade beam and the pile. The connection must 
not encourage water retention. The maximum bending moment in the piles occurs at the grade 
beams, and decay caused by water retention at critical points in the piles could induce failure 
under high wind or flood forces.



Loads 
This chapter provides guidance on how to determine the magnitude 
of the loads placed on a building by a particular natural hazard event 
or a combination of events. The methods presented are intended to 
serve as the basis of a methodology for applying the calculated loads 
to the building during the design process. 

The process for determining site-specific loads from natural hazards begins with identifying the 
building codes or engineering standards in place for the selected site (e.g., the International 
Building Code 2003 (IBC 2003) or ASCE 7-02, Minimum Design Loads for Buildings and Other 
Structures), if model building codes and other building standards do not provide load determination 
and design guidance for each of the hazards identified. In such instances, supplemental 
guidance such as FEMA 55 should be sought, the loads imposed by each of the identified hazards 
should be calculated, and the load combinations appropriate for the building site should 
be determined. The load combinations used in this manual are those specified by ASCE 7-02, 
the standard referenced by the IBC 2003. Either Allowable Stress Design (ASD) or Strength 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3- 



3 FOUNDATION DESIGN LOADS

3- 

Building on strong and safe foundations

Design methods can be used to design a building. For this manual, all of the calculations, analyses, 
and load combinations presented are based on ASD. The use of Strength Design methods 
will require the designer to modify the design values presented in this manual to accommodate 
Strength Design concepts. Assumptions utilized in this document can be found in Appendix 
C.

3.1 Wind Loads

Wind loads on a building structure are calculated using the methodology presented 
in ASCE 7-02, Minimum Design Loads for Buildings and Other Structures. This document 
is the wind standard referenced by the 2003 editions of the IBC and IRC. Equations 
used to calculate wind loads are presented in Appendix D.

The most important variable in calculating wind load is the design wind speed. Design wind 
speed can be obtained from the local building official or the ASCE 7-02 wind speed map (see 
Figure 3-1). The speeds shown in this figure are 3-second gust speeds for Exposure Category 
C at a 33-foot (10-meter) height. ASCE 7-02 includes scaling factors for other exposures and 
heights. 

ASCE 7-02 specifies wind loads for structural components known as a Main Wind Force Resisting 
System (MWFRS). The foundation designs developed for this manual are based on 
MWFRS pressures calculated for Exposure Category C, the category with the highest anticipated 
wind loads for land-based structures.

ASCE 7-02 also specifies wind loads for components and cladding (C&C). Components and 
cladding are considered part of the building envelope, and ASCE 7-02 requires C&C to be designed 
to resist higher wind pressures than MWFRS. 



FOUNDATION DESIGN LOADS 3 

3- 

3.2 Flood Loads

This manual develops in more detail flood load calculations and incorporates the methodology 
presented in ASCE 7-02. Although wind loads can directly affect a structure and dictate 
the actual foundation design, the foundation is more affected by flood loads. ASCE 24 discusses 
floodproof construction. Loads developed in ASCE 24 come directly from ASCE 7-02, 
which is what the designs presented herein are based upon.

The effects of flood loads on buildings can be exacerbated by storm-induced erosion and localized 
scour, and by long-term erosion. Erosion and scour lower the ground surface around 
foundation members and can cause the loss of load-bearing capacity and resistance to lateral 
and uplift loads. Erosion and scour also increase flood depths and, therefore, increase depth 
dependent flood loads.


Figure 3-1. Wind speed (in mph) in the U.S. Gulf Coast area

Source: ASCE 7-02

3.2.1 Design Flood and Design Flood Elevation (DFE)

The design flood is defined by ASCE 7-02 as the greater of the following two flood events: 

1. Base flood, affecting those areas identified as SFHAs on the communitys FIRM, or 

2. The flood corresponding to the area designated as a flood hazard area on a communitys 
flood hazard map or otherwise legally designated.

The DFE is defined as the elevation of the design flood, including wave height and freeboard, 
relative to the datum specified on a communitys flood hazard map. Figure 3-2 shows the parameters 
that determine or are affected by flood depth.

Figure 3-2. 
Parameters that 
determine or are 
affected by flood depth

Source: COastal 
COnstruction manual
(FEMA 55)

3.2.2 Design Stillwater Flood Depth (ds)

Design stillwater flood depth (ds) is the vertical distance between the eroded ground elevation 
and the stillwater flood elevation associated with the design flood. Determining the maximum 
design stillwater flood depth over the life of a building is the single most important flood load 
calculation that will be made; nearly all other coastal flood load parameters or calculations (e.g., 
hydrostatic load, design flood velocity, hydrodynamic load, design wave height, DFE, debris impact 
load, local scour depth) depend directly or indirectly on the design stillwater flood depth. 
The design stillwater flood depth (ds) is defined as

ds = Esw  GS

Where

ds = Design stillwater flood depth (ft)

 Esw = Design stillwater flood elevation (ft) above the datum (e.g., National Geodetic Vertical 
Datum [NGVD], North American Vertical Datum [NAVD]), including wave setup 
effects

GS = Lowest eroded ground elevation above datum (ft), adjacent to building, including 
the effects of localized sour around pilings

GS is not the lowest existing pre-flood ground surface; it is the lowest ground surface that will 
result from long-term erosion and the amount of erosion expected to occur during a design 
flood, excluding local scour effects. The process for determining GS is described in Chapter 7 
of FEMA 55.

Values for Esw are not shown on a FIRM, but they are given in the Flood Insurance Study (FIS) 
report, which is produced in conjunction with the FIRM for a community. FIS reports are usually 
available from community officials, from NFIP State Coordinating Agencies, and on the web 
at the FEMA Map Service Center (http://store.msc.fema.gov). Some states have FIS reports 
available on their individual web sites.

3.2.3 Design Wave Height (Hb)

The design wave height at a coastal building site will be one of the most important design parameters. 
Therefore, unless detailed analysis shows that natural or manmade obstructions will 
protect the site during a design event, wave heights at a site will be calculated from Equation 5-2 
of ASCE 7-02 as the heights of depth-limited breaking waves (Hb), which are equivalent to 0.78 
times the design stillwater flood depth: 

Hb = 0.78ds

Note: 70 percent of the breaking wave height (0.7Hb) lies above the stillwater flood level.



3.2.4 Design Flood Velocity (V)

Estimating design flood velocities in coastal flood hazard areas is subject to considerable uncertainty. 
Little reliable historical information exists concerning the velocity of floodwaters 
during coastal flood events. The direction and velocity of floodwaters can vary significantly 
throughout a coastal flood event, approaching a site from one direction during the beginning 
of the flood event before shifting to another (or several directions). Floodwaters can inundate 
some low-lying coastal sites from both the front (e.g., ocean) and the back (e.g., bay, sound, 
river). In a similar manner, flow velocities can vary from close to zero to high velocities during 
a single flood event. For these reasons, flood velocities should be estimated conservatively by 
assuming that floodwaters can approach from the most critical direction and that flow velocities 
can be high.

For design purposes, the Commentary of ASCE7-02 suggested a range of flood velocities from:

V = ds  t (expected lower bound) 

to

V = (gds)0.5 (expected upper bound) 

Where

ds = Design stillwater flood depth

t = Time (1 second)

g = Gravitational constant (32.2 ft/sec2)

Factors that should be considered before selecting the upper- or lower-bound flood velocity for 
design include:

n Flood zonen Topography and slopen Distance from the source of floodingn Proximity to other buildings or obstructions
The upper bound should be taken as the design flood velocity if the building site is near the 
flood source, in a V Zone, in an AO Zone adjacent to a V Zone, in an A Zone subject to velocity 
flow and wave action, steeply sloping, or adjacent to other buildings or obstructions that will 
confine floodwaters and accelerate flood velocities. The lower bound is a more appropriate design 
flood velocity if the site is distant from the flood source, in an A Zone, flat or gently sloping, 
or unaffected by other buildings or obstructions. 



3.3 Hydrostatic Loads

Hydrostatic loads occur when standing or slowly moving water comes into contact with a 
building or building component. These loads can act laterally (pressure) or vertically 
(buoyancy). 

Lateral hydrostatic forces are generally not sufficient to cause deflection or displacement of 
a building or building component unless there is a substantial difference in water elevation 
on opposite sides of the building or component; therefore, the NFIP requires that floodwater 
openings be provided in vertical walls that form an enclosed space below the BFE for a building 
in an A Zone.

Lateral hydrostatic force is calculated by the following:

fstat =  . ds2

Where 

fstat = Hydrostatic force per unit width (lb/ft) resulting from flooding against vertical 
element

. = Specific weight of water (62.4 lb/ft3 for freshwater and 64 lb/ft3 for saltwater) 

Vertical hydrostatic forces during design flood conditions are not generally a concern for properly 
constructed and elevated coastal buildings. Buoyant or flotation forces on a building can be 
of concern if the actual stillwater flood depth exceeds the design stillwater flood depth. 

Vertical (buoyancy) hydrostatic force is calculated by the following:

FBuoy = . (Vol)

Where

FBuoy = vertical hydrostatic force (lb) resulting from the displacement of a given volume of 
floodwater 

Vol = volume of floodwater displaced by a submerged object (ft3) = displaced area x depth 
of flooding

Buoyant force acting on an object must be resisted by the weight of the object and any other opposing 
force (e.g., anchorage forces) resisting flotation. In the case of a building, the live load 
on floors should not be counted on to resist buoyant forces. 



3.4 Wave Loads

Calculating wave loads requires information about expected wave heights. For the purposes 
of this manual, the calculations will be limited by water depths at the site of interest. 
Wave forces can be separated into four categories:

n Non-breaking waves (can usually be computed as hydrostatic forces against walls and hydrodynamic 
forces against piles)
n Breaking waves (short duration but large magnitude forces against walls and piles) 
n Broken waves (similar to hydrodynamic forces caused by flowing or surging water)
n Uplift (often caused by wave runup, deflection, or peaking against the underside of horizontal 
surfaces)
Of these four categories, the forces from breaking waves are the largest and produce the most 
severe loads. Therefore, it is strongly recommended that the breaking wave load be used as the 
design wave load. 

Two breaking wave loading conditions are of interest in residential construction: waves breaking 
on small-diameter vertical elements below the DFE (e.g., piles, columns in the foundation of a 
building in a V Zone) and waves breaking against vertical walls below the DFE (e.g., solid foundation 
walls in A Zones, breakaway walls in V Zones). 

3.4.1 Breaking Wave Loads on Vertical Piles

The breaking wave load (Fbrkp) on a pile can be assumed to act at the stillwater flood level and 
is calculated by Equation 5-4 from ASCE 7-02:

Fbrkp = (1/2)CD.DHb2

Where

Fbrkp = Net wave force (lb)

CD = Coefficient of drag for breaking waves = 1.75 for round piles or column, and 2.25 for 
square piles or columns

. = Specific weight of water (lb/ft3) 

D = Pile or column diameter (ft) for circular section. For a square pile or column, 1.4 
times the width of the pile or column (ft).

Hb = Breaking wave height (ft)



3.4.2 Breaking Wave Loads on Vertical Walls

The net force resulting from a normally incident breaking wave (depth limited in size, with 
Hb = 0.78ds) acting on a rigid vertical wall, can be calculated by Equation 5-6 from ASCE 7-02:

Fbrkw = 1.1Cp.ds2 + 2.4.ds2

Where 

Fbrkw = net breaking wave force per unit length of structure (lb/ft) acting near the stillwater 
flood elevation

Cp = Dynamic pressure coefficient (1.6 < Cp < 3.5) (see Table 3-1)

Table 3-1. Building Category and Corresponding Dynamic Pressure Coefficient (Cp)

Building Category

Cp

I  Buildings and other structures that represent a low 
hazard to human life in the event of a failure

1.6

II  Buildings not in Category I, III, and IV

2.8

III  Buildings and other structures that represent a substantial 
hazard to human life in the event of a failure

3.2

IV  Buildings and other structures designated as essential facilities

3.5





Source: ASCE 7-02
. = Specific weight of water (lb/ft3)

ds = Design stillwater flood depth (ft) at base of building where the wave breaks

This formula assumes the following:

n The vertical wall causes a reflected or standing wave against the seaward side of the wall with 
the crest of the wave, reaching a height of 1.2ds above the design stillwater flood elevation, 
andn The space behind the vertical wall is dry, with no fluid balancing the static component of 
the wave force on the outside of the wall (see Figure 3-3).
If free-standing water exists behind the wall (see Figure 3-4), a portion of the hydrostatic component 
of the wave pressure and force disappears and the net force can be computed using 
Equation 5-7 from ASCE 7-02:

Fbrkw = 1.1Cp.ds2 + 1.9.ds2



Post-storm damage inspections show that breaking wave loads have destroyed virtually all wood-
frame or unreinforced masonry walls below the wave crest elevation; only highly engineered, 
massive structural elements are capable of withstanding breaking wave loads. Damaging wave 
pressures and loads can be generated by waves much lower than the 3-foot wave currently used 
by FEMA to distinguish between A Zones and V Zones. 


Figure 3-3. 
Normally incident 
breaking wave 
pressures against a 
vertical wall (space 
behind vertical wall is 
dry)

Source: ASCE 7-02
Figure 3-4. 
Normally incident 
breaking wave pressures 
against a vertical wall 
(stillwater level equal on 
both sides of wall)

Source: ASCE 7-02

3.5 Hydrodynamic Loads

Water flowing around a building (or a structural element or other object) imposes additional 
loads on the building. The loads (which are a function of flow velocity and 
structural geometry) include frontal impact on the upstream face, drag along the sides, 
and suction on the downstream side. This manual assumes that the velocity of the floodwaters is 
constant (i.e., steady state flow). 

One of the most difficult steps in quantifying loads imposed by moving water is determining the 
expected flood velocity. Refer to Section 3.2.4 for guidance concerning design flood velocities.

The following equation from FEMA 55 can be used to calculate the hydrodynamic load from 
flows with velocity greater than 10 ft/sec:

Fdyn = Cd .V2A

Where

Fdyn = Hydrodynamic force (lb) acting at the stillwater mid-depth (halfway between the 
stillwater elevation and the eroded ground surface)

Cd = Drag coefficient (recommended values are 2.0 for square or rectangular piles and 
1.2 for round piles)

. = Mass density of fluid (1.94 slugs/ft3 for freshwater and 1.99 slugs/ft3 for saltwater)

V = Velocity of water (ft/sec) 

A = Surface area of obstruction normal to flow (ft2)

Note that the use of this formula will provide the total force against a building of a given impacted 
surface area (A). Dividing the total force by either length or width would yield a force 
per unit length; dividing by A would yield a force per unit area. 

The drag coefficient used in the previously stated equations is a function of the shape of the 
object around which flow is directed. If the object is something other than a round, square, or 
rectangular pile, the drag coefficient can be determined using Table 3-2. 



Table 3-2. Drag Coefficient Based on Width to Depth Ratio

Width to Depth Ratio 
(w/ds or w/h)

Drag Coefficient (Cd)

1 to 12

1.25

13 to 20

1.30

21 to 32

1.40

33 to 40

1.50

41 to 80

1.75

81 to 120

1.80

>120

2.00





Note: h refers to the height of an object completely immersed in water. 

Source: FEMA 55
Flow around a building or building component will also create flow-perpendicular forces (lift 
forces). If the building component is rigid, lift forces can be assumed to be small. But if the 
building component is not rigid, lift forces can be greater than drag forces. The formula for 
lift force is similar to the formula for hydrodynamic force except that the drag coefficient 
(Cd) is replaced with the lift coefficient (Cl). For the purposes of this manual, the foundations 
of coastal residential buildings can be considered rigid, and hydrodynamic lift forces 
can therefore be ignored.

3.6 Debris Impact Loads

Debris or impact loads are imposed on a building by objects carried by moving water. The 
magnitude of these loads is very difficult to predict, yet some reasonable allowance must 
be made for them. The loads are influenced by where the building is located in the potential 
debris stream:

n Immediately adjacent to or downstream from another buildingn Downstream from large flotable objects (e.g., exposed or minimally covered storage tanks)
n Among closely spaced buildings
The following equation to calculate the magnitude of impact load is provided in the Commentary 
of ASCE 7-02:

Fi = (pWVCiCoCDCBRmax)  (2g.t)



Where

Fi = Impact force acting at the stillwater level (lb)

p = 3.14

W = Weight of debris (lb), suggest using 1,000 if no site-specific information is available

V = Velocity of object (assume equal to velocity of water) (ft/sec)

Ci = Importance coefficient (see Table C5.3 of ASCE 7-02)

Co = Orientation coefficient = 0.8

CD = Depth coefficient (see Table C5.5 and Figure C5-3 of ASCE 7-02)

CB = Blockage coefficient (see Table C5.5 and Figure 5-4 of ASCE 7-02)

Rmax= Maximum response ratio for impulsive load (see Table C5.6 of ASCE 7-02)

g = Gravitational constant (32.2 ft/sec2)

.t = Duration of impact (sec) 

When the C coefficients and Rmax are set to 1.0, the above equation reduces to

Fi = (pWV)  (2g.t)

This equation is very similar to the equation provided in ASCE 7-98 and FEMA 55. The only difference 
is the p/2 term, which results from the half-sine form of the impulse load. 

The following uncertainties must be quantified before the impact of debris loading on the 
building can be determined using the above equation:

n Size, shape, and weight (W) of the waterborne objectn Flood velocity (V)
n Velocity of the object compared to the flood velocityn Portion of the building that will be struck and most vulnerable to collapsingn Duration of the impact (t)
Once floodborne debris impact loads have been quantified, decisions must be made on how to 
apply them to the foundation and how to design foundation elements to resist them. For open 



foundations, the Coastal Construction Manual (FEMA 55) advises applying impact loading to a 
corner or critical column or piling concurrently with other flood loads (see Coastal Construction 
Manual, Table 11-6). For closed foundations (which are not recommended in Coastal A 
Zones and are not allowed in V Zones), the Coastal Construction Manual advises that the designer 
assume that one corner of the foundation will be destroyed by debris and recommends the 
foundation and the structure above be designed to contain redundancy to allow load redistribution 
to prevent collapse or localized failure. The following should be considered in determining 
debris impact loads:

Size, shape, and weight of the debris. It is recommended that, in the absence of information 
about the nature of the potential debris, a weight of 1,000 pounds be used for the debris weight 
(W). Objects of this weight could include portions of damaged buildings, utility poles, portions 
of previously embedded piles, and empty storage tanks. 

Debris velocity. Flood velocity can be approximated by one of the equations discussed in Section 
3.2.4. For the calculation of debris loads, the velocity of the waterborne object is assumed to 
be the same as the flood velocity. Note that, although this assumption may be accurate for small 
objects, it will overstate debris velocities for large objects (e.g., trees, logs, pier pilings). The 
Commentary of ASCE 7-02 provides guidance on estimating debris velocities for large debris.

Portion of building to be struck. The object is assumed to be at or near the water surface 
level when it strikes the building. Therefore, the 
object is assumed to strike the building at the 
stillwater flood level.

Duration of impact. Uncertainty about the duration 
of impact (.t) (the time from initial impact, 
through the maximum deflection caused by the 
impact, to the time the object leaves) is the most 
likely cause of error in the calculation of debris 
impact loads. ASCE 7-02 showed that measured 
impact duration (from initial impact to time of 
maximum force) from laboratory tests varied 
from 0.01 to 0.05 second. The ASCE 7-02 recommended 
value for .t is 0.03 second.

3.7 Localized Scour

Waves and currents during coastal flood conditions are capable of creating turbulence 
around foundation elements and causing localized scour. Determining potential 
scour is critical in designing coastal foundations to ensure that failure during and 
after flooding does not occur as a result of the loss in either bearing capacity or anchoring 
resistance around the posts, piles, piers, columns, footings, or walls. Localized scour determinations 
will require knowledge of the flood depth, flow conditions, soil characteristics, and 
foundation type. 


NOTE: The method for 
determining debris impact 
loads in ASCE 7-02 was 
developed for riverine impact loads 
and has not been evaluated for coastal 
debris that may impact a building over 
several wave cycles. Although these 
impact loads are very large but of short 
duration, a structural engineer should 
be consulted to determine the structural 
response to the short load duration (0.03 
second recommended).



In some locations, soil at or below the ground surface can be resistant to localized scour, and 
scour depths calculated below will be excessive. In instances where the designer believes the soil 
at a site will be scour-resistant, a geotechnical engineer should be consulted before calculated 
scour depths are reduced.

3.7.1 Localized Scour Around Vertical Piles 

The methods for calculating localized scour (Smax) in coastal areas have been largely based on 
empirical evidence gathered after storms. Much of the evidence gathered suggests that localized 
scour depths around piles and other thin vertical members are approximately equal to 1.0 
to 1.5 times the pile diameter. Figure 3-5 illustrates localized scour at a pile, with and without a 
scour-resistant terminating stratum. Currently, there is no design guidance in ASCE 7-02 on how 
to calculate scour. Localized scour around a vertical pile or similar foundation element should 
be calculated with the following formula as given in FEMA 55:

Smax = 2.0a

Where 

Smax = Maximum localized scour depth (ft)

a = Diameter of a round foundation element or the maximum diagonal cross-section dimension 
for a rectangular element (ft)

3.7.2 Localized Scour Around Vertical Walls and Enclosures 

Localized scour around vertical walls and enclosed areas (e.g., typical A Zone construction) can 
be greater than that around vertical piles, and should be estimated using Table 3-3. 

Figure 3-5. 
Scour at vertical 
foundation member 
stopped by underlying 
scour-resistant stratum

Source: COastal 
COnstruction 
manual
(FEMA 55)

Table 3-3. Local Scour Depth as a Function of Soil Type 

Soil Type

Expected Depth (% of ds)

Loose sand

80

Dense sand

50

Soft silt

50

Stiff silt

25

Soft clay

25

Stiff clay

10





Source: FEMA 55
3.8 Flood Load Combinations

Load combinations (including those for flood loads) are given in ASCE 7-02, Sections 2.3.2 and 
2.3.3 for strength design and Sections 2.4.1 and 2.4.2 for allowable stress design. 

The basic load combinations are:

Allowable Stress Design

(1) D + F

(2) D + H + F + L + T

(3) D + H + F + (Lr or S or R) 

(4) D + H + F + 0.75(L + T) + 0.75(Lr or S or R) 

(5) D + H + F + (W or 0.7E)

(6) D + H + F + 0.75(W or 0.7E) + 0.75L + 1.5Fa + 0.75(Lr or S or R) 

(7) 0.6D + W + H 

(8) 0.6D + 0.7 E + H

Strength Design

(1) 1.4 (D + F)

(2) 1.2 (D + F + T) + 1.6(L + H) + 0.5(Lr or S or R) 

(3) 1.2D + 1.6(Lr or S or R) + (L or 0.8W)

(4) 1.2D + 1.6W + L + 0.5(Lr or S or R)

(5) 1.2D + 1.0E + L + 0.2S



(6) 0.9D + 1.6W + 1.6H

(7) 0.9D + 1.0E + 1.6H

For structures located in V or Coastal A Zones:

Allowable Stress Design

Load combinations 5, 6, and 7 shall be replaced with the following:

(5) D + H + F + 1.5Fa + W

(6) D + H + F + 0.75W + 0.75L + 1.5Fa + 0.75(Lr or S or R) 

(7) 0.6D + W + H + 1.5Fa

Strength Design

Load combinations 4 and 6 given in ASCE 7-02 Section 2.3.1 shall be replaced with the following:

(4) 1.2D + 1.6W + 2.0Fa + L + 0.5(Lr or S or R)

(6) 0.9D + 1.6W + 2.0 Fa + 1.6H

Where

D = Dead Load

W = Wind Load

E = Earthquake Load

Fa = Flood Load

F = Load due to fluids with well defined pressures and maximum heights

L = Live Load

Lr = Roof Live Load

S = Snow Load

R = Rain Load

H = Lateral Earth Pressure

Flood loads were included in the load combinations to account for the strong correlation between 
flood and winds in hurricane-prone regions that run along the Gulf of Mexico and the 
Atlantic Coast.

In non-Coastal A Zones, for Allowable Stress Design, replace the 1.5Fa with 0.75Fa in load combinations 
5, 6, and 7 given above. For Strength Design, replace coefficients W and Fa in equations 
4 and 6 above with 0.8 and 1.0, respectively.



Designers should be aware that not all of the flood loads will act at certain locations or against 
certain building types. Table 3-4 provides guidance to designers for the calculation of appropriate 
flood loads in V Zones and Coastal A Zones (non-Coastal A Zone flood load combinations 
are shown for comparison).

The floodplain management regulations enacted by communities that participate in the NFIP 
prohibit the construction of solid perimeter wall foundations in V Zones, but allow such foundations 
in A Zones. Therefore, the designer should assume that breaking waves will impact piles 
in V Zones and walls in A Zones. It is generally unrealistic to assume that impact loads will occur 
on all piles at the same time as breaking wave loads; therefore, this manual recommends that 
impact loads be evaluated for strategic locations such as a building corner.

Table 3-4. Selection of Flood Load Combinations for Design

Case 1

Pile or Open Foundation in V Zone (Required)

 Fbrkp (on all piles) + Fi (on one corner or critical pile only)

or 

 Fbrkp (on front row of piles only) + Fdyn (on all piles but front row) +Fi (on one corner or critical pile only)

Case 2

Pile or Open Foundation in Coastal Z Zone (Recommended)

 Fbrkp (on all piles) + Fi (on one corner or critical pile only)

or 

 Fbrkp (on front row of piles only) + Fdyn (on all piles but front row) +Fi (on one corner or critical pile only)

Case 3

Solid (Wall) Foundation in Coastal A Zone (NOT Recommended)

 Fbrkp (on walls facing shoreline, including hydrostatic component) + Fdyn; 
assume one corner is destroyed by debris, and design in redundancy

Case 4

Solid (Wall) Foundation in Non-Coastal A Zone (Shown for Comparison)

 Fsta + Fdyn





Source: COastal COnStruction manual (FEMA 55)

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


4. Overview of 
Recommended 
Foundation Types and 
Construction for the Gulf 
Coast

Chapters 1 through 3 discussed foundation design loads and 
calculations and how these issues can be influenced by coastal 
natural hazards. This chapter will tie all of these issues together with 
a discussion of foundation types and methods of constructing 
a foundation for a residential structure. 

4- 



4 Overview of Recommended Foundation Types and Construction for the Gulf Coast

4- 

Building on strong and safe foundations

4.1 Critical Factors Affecting Foundation Design

Foundation construction types are dependent upon the following critical factors: 

n Design wind speedn Elevation height required by the BFE and local ordinancesn Flood zone 
n Soil parameters 
Soil parameters are very important but, for the purpose of creating standardized foundation designs 
in this report, soil parameters have been fixed. This section will only discuss the first three 
critical factors mentioned above. 

4.1.1 Wind Speed

A design wind speed is a factor that determines the foundation size and strength (see also Section 
1.1). The wind speed map shown in Figure 3-1 shows the design winds along most of the 
Mississippi and Louisiana Gulf Coast areas to be between 120 and 150 mph. 

To determine forces on the building and foundation, the wind speed is critical. Wind speed creates 
wind pressures that act upon the building. These pressures are proportional to the square 
of the wind speed, so a doubling of the wind speed increases the wind pressure by a factor of 
four. The pressure applied to an area of the building will develop forces that must be resisted. 
To transfer these forces from the building to the foundation, properly designed load paths are 
required. For the foundation to be properly designed, all forces including uplift, compression, 
and lateral must be taken into account.

4.1.2 Elevation

The required height of the foundation depends on three factors: the DFE, the site elevation, 
and the flood zone. The flood zone dictates whether the lowest habitable finished floor must be 
placed at the DFE or, in the case of homes in the V Zone, the bottom of the lowest horizontal 
member must be placed at the DFE. While not required by the NFIP, V Zone criteria are recommended 
for Coastal A Zones. Stated mathematically, 

H = DFE  G + Erosion

or

H = BFE  G + Erosion + Freeboard

Where

H = Required foundation height (in ft)

DFE = Design Flood Elevation

BFE = Base Flood Elevation



Overview of Recommended Foundation Types and Construction for the Gulf Coast 4 

4- 

G = Non-eroded ground elevation

Erosion = Short-term plus long-term erosion

Freeboard = Locally adopted or owner desired freeboard

The height to which a home should be elevated is one of the key factors in determining which 
pre-engineered foundation to use. Elevation height is dependent upon several factors, including 
the BFE, local ordinances requiring freeboard, and the desire of the homeowner to elevate 
the lowest horizontal structural member above the BFE (see also Chapter 2). This manual provides 
designs for closed foundations up to 8 feet above ground level and open foundations up 
to 15 feet above ground level. Custom designs can be developed for open and closed foundations 
to position the homes above those elevation levels. Foundations for homes that need to be 
elevated higher than 15 feet should be designed by a licensed professional engineer. 

4.1.3 Construction Materials

The use of flood-resistant materials below the BFE is also covered in FEMA NFIP Technical 
Bulletin 2 and FEMA 499 Fact Sheet No. 8 (see also Appendix F). This manual will cover the 
materials used in masonry and concrete foundation construction, and field preservative treatment 
for wood.

4.1.3.1 Masonry Foundation Construction

The combination of high winds, moisture, and salt-laden air creates a damaging recipe for masonry 
construction. All three can penetrate the tiniest cracks or openings in the masonry joints. 
This can corrode reinforcement, weaken the bond between the mortar and the brick, and create 
fissures in the mortar. Moisture resistance is highly influenced by the quality of the materials 
and the workmanship. 

4.1.3.2 Concrete Foundation Construction

Cast-in-place concrete elements in coastal environments should be constructed with 3 inches or 
more of concrete cover over the reinforcing bars. The concrete cover physically protects the reinforcing 
bars from corrosion. However, if salt water penetrates the concrete cover and reaches 
the reinforcing steel, the concrete alkalinity is reduced by the salt chloride, thereby corroding 
the steel. As the corrosion forms, it expands and cracks the concrete, allowing the additional 
entry of water and further corrosion. Eventually, this process weakens the concrete structural 
element and its load carrying capacity.

Alternatively, epoxy-coated reinforcing steel can be used if properly handled, stored, and placed. 
Epoxy-coated steel, however, requires more sophisticated construction techniques and more 
highly trained contractors that are not usually involved with residential construction.

Concrete mix used in coastal areas must be designed for durability. The first step in this process 
is to start with the mix design. The American Concrete Institute (ACI) 318 manual recommends 
that a maximum water-cement ratio by weight of 0.40 and a minimum compressive strength of 
4,000 pounds per square inch (psi) be used for concrete used in coastal environments. Since 



the amount of water in a concrete mix largely determines the amount that concrete will shrink 
and promote unwanted cracks, the water-cement ratio of the concrete mix is a critical parameter 
in promoting concrete durability. Adding more water to the mix to improve the workability 
increases the potential for cracking in the concrete and can severely affect its durability.

Another way to improve the durability of a concrete mix is with ideal mix proportions. Concrete 
mixes typically consist of a mixture of sand, aggregate, and cement. How these elements are 
proportioned is as critical as the water-cement ratio. The sand should be clean and free of contaminants. 
The aggregate should be washed and graded. The type of aggregate is also very important. 
Recent research has shown that certain types of gravel do not promote a tight bond with the paste. 
The builder or contractor should consult expert advice prior to specifying the concrete mix.

Addition of admixtures such as pozzolans (fly ash) is recommended for concrete construction 
along the coast. Fly ash when introduced in concrete mix has benefits such as better workability 
and increased resistance to sulfates and chlorates, thus reducing corrosion from attacking the 
steel reinforcing. 

4.1.3.3 Field Preservative Treatment for Wood Members

In order to properly connect the pile foundation to the floor framing system, making field 
cuts, notches, and boring holes are some of the activities associated with construction. Since 
pressure-preservative-treated piles, timbers, and lumber are used for many purposes in coastal 
construction, the interior, untreated parts of the wood are exposed to possible decay and infestation. 
Although treatments applied in the field are much less effective than factory treatments, 
the potential for decay can be minimized. The American Wood Preservers Association (AWPA) 
standard Care of Pressure-Treated Wood Products (AWPA 1991) describes field treatment procedures 
and field cutting restrictions for poles, piles, and sawn lumber. 

Field application of preservatives should always be done in accordance with instructions on the 
label. When detailed instructions are not provided, dip soaking for at least 3 minutes can be 
considered effective for field applications. When this is impractical, treatment may be done by 
thoroughly brushing or spraying the exposed area. It should be noted that the material is more 
absorptive at the end of a member, or end grains, than it is for the sides or side grains. To safeguard 
against decay in bored holes, the holes should be poured full of preservative. If the hole 
passes through a check (such as a shrinkage crack caused by drying), it will be necessary to brush 
the hole; otherwise, the preservative would run into the check instead of saturating the hole.

Waterborne arsenicals, pentachlorophenol, and creosote are unacceptable for field applications. 
Copper napthenate is the most widely used field treatment. Its deep green color may 
be objectionable, but the wood can be painted with alkyd paints in dark colors after extended 
drying. Zinc napthenate is a clear alternative to copper napthenate. However, it is not quite as 
effective in preventing insect infestation, and it should not be painted with latex paints. Tributyltin 
oxide (TBTO) is available, but should not be used in or near marine environments, because 
the leachates are toxic to aquatic organisms. Sodium borate is also available, but it does not 
readily penetrate dry wood and it rapidly leaches out when water is present. Therefore, sodium 
borate is not recommended.



4.1.4 Foundation Design Loads

To provide flexibility in the home designs, tension connections have been specified between the 
tops of all wood piles and the grade beams. Depending on the location of shear walls, shear wall 
openings, and the orientation of floor and roof framing, some wood piles may not experience 
tension forces. Design professionals can analyze the elevated structure to identify compression 
only pilings to reduce construction costs. For foundation design and example calculations, see 
Appendix D.

Figure 4-1 illustrates design loads acting on a column. The reactions at the base of the elevated 
structure used in the foundation designs are presented in Tables 4-1a (one-story) and 4-1b 
(two-story). These reactions are the controlling forces for the range of building weights and 
dimensions listed in Appendix A and shown in Figure 2 of the Introduction. Design reactions 
have been included for the various design wind speeds and various building elevations above 
exterior grade. ASCE 7-02 Load Combination 4 (D + 0.75L + 0.75Lr) controls for gravity loading 
and Load Combination 7 controls for uplift and lateral loads. Load Combination 7 is 0.6D + W 
+ 0.75Fa in non-Coastal A Zones and 0.6D + W + 1.5Fa in Coastal A and V Zones. Refer to Section 
3.8 for the list of flood load combinations.

Figure 4-1. 
Design loads acting on a column



Loads on the foundation elements themselves are more difficult to tabulate since they depend 
on the foundation style (open or enclosed), foundation dimensions, and foundation height. 
Table 4-2 provides reactions for the 18-inch square columns used in most of the open foundation 
designs.

Table 4-1a. Design Perimeter Wall Reactions (lb/lf) for One-Story Elevated Homes (Note: Reactions are taken at the 
base of the elevated home/top of the foundation element.)

V

120 mph

130 mph

140 mph

150 mph

(All V)

H

Horiz

Vert

Horiz

Vert

Horiz

Vert

Horiz

Vert

Gravity

5 ft

770

-175

903

-259

1,048

-350

1,203

-448

1,172

6 ft

770

-175

903

-259

1,048

-350

1,203

-448

1,172

7 ft

770

-175

903

-259

1,048

-350

1,203

-448

1,172

8 ft

804

-202

944

-291

1,095

-388

1,257

-490

1,172

10 ft

804

-202

944

-291

1,095

-388

1,257

-490

1,172

12 ft

804

-202

944

-291

1,095

-388

1,257

-490

1,172

 14 ft

832

-224

977

-317

1,133

-417

1,300

-525

1,172

15 ft

843

-226

989

-319

1,147

-419

1,317

-527

1,172





lb = pound

lf = linear foot

V = wind speed

H = height of foundation above grade

Table 4-1b. Design Perimeter Wall Reactions (lb/lf) for Two-Story Elevated Homes (Note: Reactions are taken at the 
base of the elevated home/top of the foundation element.)

V

120 mph

130 mph

140 mph

150 mph

(All V)

H

Horiz

Vert

Horiz

Vert

Horiz

Vert

Horiz

Vert

Gravity

5 ft

1,149

-145

1,348

-255

1,564

-374

1,795

-502

1,608

6 ft

1,149

-145

1,348

-255

1,564

-374

1,795

-502

1,608

7 ft

1,149

-145

1,348

-255

1,564

-374

1,795

-502

1,608

8 ft

1,182

-168

1,387

-282

1,609

-406

1,847

-539

1,608

10 ft

1,191

-171

1,397

-286

1,629

-410

1,860

-543

1,608

12 ft

1,191

-171

1,397

-286

1,620

-410

1,860

-543

1,608

14 ft

1,191

-171

1,397

-286

1,620

-410

1,860

-543

1,608

15 ft

1,210

-175

1,420

-291

1,647

-416

1,890

-550

1,608





lb = pound

lf = linear foot

V = wind speed

H = height of foundation above grade



Table 4-2. Flood Forces (in pounds) on an 18-inch Square Column

Flood Depth

Hydrodynamic

Breaking Wave

Impact

Buoyancy

5 ft

1,000

684

3,165

465

6 ft

1,440

985

3,476

577

7 ft

1,960

1,340

3,745

650

8 ft

2,560

1,750

4,004

743

10 ft

4,001

2,735

4,476

939

12 ft

5,761

3,938

4,903

1,115

14 ft

7,841

5,360

5,296

1,300

15 ft

9,002

6,155

5,482

1,394





4.2 Recommended Foundation Types for the Gulf Coast

Table 4-3 provides five open (deep and shallow) foundation types and two closed foundations 
discussed in this manual. Appendix A provides the foundation design drawings for 
the cases specified. 

Table 4-3. Recommended Foundation Types Based on Zone

Foundation

Case

V Zones

A Zones in Coastal Areas

Coastal A Zone

A Zone

Open 
Foundation 
(deep)

Timber pile

A

4

4

4

Steel pipe pile with concrete 
column and grade beam

B

4

4

4

Timber pile with concrete 
column and grade beam

C

4

4

4

Open 
Foundation 
(shallow)

Concrete column and grade 
beam

D

NR

4

4

Concrete column and grade 
beam with slab

G

NR

4

4

Closed 
Foundation 
(shallow)

Reinforced masonry 
 crawlspace

E

8

NR

4

Reinforced masonry  stem 
wall

F

8

NR

4





4 = Acceptable

NR = Not Recommended

8 = Not Permitted 



The foundation designs contained in this manual are based on soils having a bearing capacity 
of 1,500 pounds per square foot (psf). The 1,500-psf bearing capacity value corresponds to the 
presumptive value contained in the 2003 IBC for cohesive soil. Cohesive soils are fine-grained 
soils (or soils with a high clay content) with cohesive strength. These types of soils include clay, 
sandy clay, silty clay, clayey silt, silt, and sandy silt. 

The size of the perimeter footings and grade beams are generally not controlled by bearing 
capacity (uplift and lateral loads typically control footing size and grade beam dimensions). 
Refining the designs for soils with greater bearing capacities may not significantly reduce construction 
costs. However, the size of the interior pad footings for the crawlspace foundation 
(Table 4-3, E: Closed Foundation, Reinforced Masonry - Crawlspace) depends greatly on the 
soils bearing capacity. Design refinements can reduce footing sizes in areas where soils have 
greater bearing capacities. The following discussion of the foundation designs listed in Table 4-
3 is also presented in Appendix A. Figures 4-2 through 4-8 are based on Appendix A.

4.2.1 Open Foundation: Timber Pile (Case A)

This pre-engineered, timber pile foundation uses conventional, tapered, treated piles and steel 
rod bracing to support the elevated structure. No concrete, masonry, or reinforcing steel is 
needed (see Figure 4-2). Often called a stilt foundation, the driven timber pile system is suitable 
for moderate elevations if the homebuilder prefers to minimize the number of different 
construction trades used. Once the piles are driven, the wood guides and floor system are attached 
to the piles; the remainder of the house is constructed off the floor platform.

The recommended design for Case A that is presented in this manual accommodates home elevations 
up to 10 feet above grade. With customized designs and longer piles, the designs can 
be modified to achieve higher elevations. However, elevations greater than 10 feet will likely 
be prevented by pile availability, the pile strength required to resist lateral forces, and the pile 
embedment required to resist scour and erosion. A construction approach that can improve 
performance is to extend the piles above the first floor diaphragm to the second floor or roof 
diaphragm. Doing so allows the foundation and the elevated home to function more like a single, 
integrated structural frame. Extending the piles stiffens the structure, reduces stresses in the 
pilings, and reduces lateral deflections. Post disaster assessments of pile supported homes indicate 
that extending piles in this fashion improves survivability. Licensed professional engineers 
should be consulted to analyze the pile foundations and design the appropriate connections.

One drawback of the timber pile system is the exposure of the piles to floodborne debris. During 
a hurricane event, individual piles can be damaged or destroyed by large, floating debris. 
With the home in place, damaged piles are difficult to replace. Two separate ways of addressing 
this potential problem is to use piles with a diameter larger than is called for in the foundation 
design or to use a greater number of piles to increase structural redundancy. 



4.2.2 Open Foundation: Steel Pipe Pile with Concrete Column and Grade Beam 
(Case B)

This foundation incorporates open-ended steel pipe piles; this style is somewhat unique to the 
Gulf Coast region where the prevalence of steel pipe pilings used to support oil platforms has 
created local sources for these piles. Like treated wood piles, steel pipe piles are driven but have 
the advantage of greater bending strength and load carrying capacity (see Figure 4-3). The 
open steel pipe pile foundation is resistant to the effects of erosion and scour. The grade beam 
can be undermined by scour without compromising the entire foundation system.

Figure 4-2. 
Profile of Case A 
foundation type 
(see Appendix A for 
additional drawings)

for

The number of piles required depends on local soil conditions. Like other soil dependent 
foundation designs, consideration should be given to performing soil tests on the site so the 
foundation design can be optimized. With guidance from engineers, the open-ended steel pipe 
pile foundation can be designed for higher elevations. Additional piles can be driven for increased 
resistance to lateral forces, and columns can be made larger and stronger to resist the 
increased bending moments that occur where the columns join the grade beam. Because only a 
certain amount of steel can be installed to a given cross-section of concrete before the column 
sizes and the flood loads become unmanageable, a maximum elevation of 15 feet exists for the 
use of this type of foundation. 

Figure 4-3. 
Profile of Case B 
foundation type 
(see Appendix A for 
additional drawings)



4.2.3 Open Foundation: Timber Pile with Concrete Column and Grade Beam (Case C)

This foundation is similar to the steel pipe pile with concrete column and grade beam foundation 
(Case B). Elevations as high as 15 feet can be achieved for wind speeds up to 150 mph 
for both one- and two-story structures. However, because wood piles have a lower strength to 
resist the loads than steel piles, approximately twice as many timber piles are needed to resist 
loads imposed on the house and the exposed portions of the foundation (see Figure 4-4).

While treated to resist rot and damage from insects, wood piles may become vulnerable to 
damage from wood destroying organisms in areas where they are not constantly submerged by 
groundwater. If constantly submerged, there is not enough oxygen to sustain fungal growth and 
insect colonies; if only periodically submerged, the piles can have moisture levels and oxygen 
levels sufficient to sustain wood destroying organisms.Consultation with local design professionals 
in the area familiar with the use and performance of driven treated wood piles will help 
quantify this potential risk.Grade beams can be constructed at greater depths or alternative pile 
materials can be selected if wood destroying organism damage is a major concern.


Figure 4-4. 
Profile of Case C 
foundation type 
(see Appendix A for 
additional drawings)



4.2.4 Open Foundation: Concrete Column and Grade Beam with Slabs (Cases D and G) 

These open foundation types make use of a rigid mat to resist lateral forces and overturning 
moments. Frictional resistance between the grade beams and the supporting soils resist lateral 
loads while the weight of the grade beam and the above grade columns resist uplift. Case G 
(foundation with slab) contains additional reinforcement to tie the on-grade slab to the grade 
beams to provide additional weight to resist uplift (see Figure 4-5). With the integral slab, elevations 
up to 15 feet above grade are achievable. Without the slab (as for Case D), the designs as 
detailed are limited to 10-foot elevations (see Figure 4-6).

Unlike the deep driven pile foundations, both shallow grade beam foundation styles can be 
undermined by erosion and scour if exposed to waves and high flow velocities. Neither style of 
foundation should be used where anticipated erosion or scour would expose the grade beam.


Figure 4-5. 
Profile of Case G 
foundation type (see 
Appendix A for additional 
drawings)



4.2.5 Closed Foundation: Reinforced Masonry - Crawlspace (Case E)

The reinforced masonry with crawlspace type of foundation utilizes conventional construction 
similar to foundations used outside of SFHAs. Footings are cast-in-place reinforced concrete; 
walls are constructed with reinforced masonry (see Figure 4-7). The foundation designs presented 
in Appendix A permit elevated homes to be raised to 8 feet. Higher elevations are achievable 
with larger or more closely spaced reinforcing steel or with walls constructed with thicker masonry.


The required strength of a masonry wall is determined by breaking wave loads for wall heights 
3 feet or less, by non-breaking waves and hydrodynamic loads for taller walls, and by uplift for 
all walls. Perimeter footing sizes are controlled by uplift and must be relatively large for short 
foundation walls. The weight of taller walls contributes to uplift resistance and allows for smaller 
perimeter footings. Solid grouting of perimeter walls is recommended for additional weight 
and improved resistance to water infiltration. 


Figure 4-6. 
Profile of Case D 
foundation type 
(see Appendix A for 
additional drawings) 



Interior footing sizes are controlled by gravity loads and by the bearing capacity of the supporting 
soils. Since the foundation designs are based on relatively low bearing capacities, obtaining 
soils tests for the building site may allow the interior footing sizes to be reduced.

The crawlspace foundation walls incorporate NFIP required flood vents, which must allow floodwaters 
to flow into the crawlspace. In doing so, hydrostatic, hydrodynamic, and breaking wave 
loads are reduced. Crawlspace foundations are vulnerable to scour and flood forces and should 
not be used in Coastal A Zones; the NFIP prohibits their use in V Zones. 

4.2.6 Closed Foundation: Reinforced Masonry - Stem Wall (Case F)

The reinforced masonry stem walls (commonly referred to as chain walls in portions of the Gulf 
Coast) type of foundation also utilizes conventional construction to contain fill that supports 
the floor slab. They are constructed with hollow masonry block with grouted and reinforced 
cells (see Figure 4-8). Full grouting is recommended to provide increased weight, resist uplift, 
and improve longevity of the foundation. 

The amount and size of the reinforcement are controlled primarily by the lateral forces created 
by the retained soils and by surcharge loading from the floor slab and imposed live loads. 
Because the retained soils can be exposed to long duration flooding, loads from saturated soils 
should be considered in the analyses. The lateral forces on stem walls can be relatively high and 
even short cantilevered stem walls (those not laterally supported by the floor slab) need to be 
heavily reinforced. Tying the top of the stem walls into the floor slab provides lateral support 

Figure 4-7. 
Profile of Case E 
foundation type (see 
Appendix A for additional 
drawings)



for the walls and significantly reduces reinforcement requirements. Because backfill needs to be 
placed before the slab is poured, walls that will be tied to the floor slab need to be temporarily 
braced when the foundation is backfilled until the slab is poured and cured.

Figure 4-8. 
Profile of Case F 
foundation type 
(see Appendix A for 
additional drawings)


NOTE: Stem wall foundations are vulnerable to scour and should not be used in 
Coastal A Zones without a deep footing. The NFIP prohibits the use of this foundation 
type in V Zones. 



strong foundation. Foundation design types, foundation design 
considerations, cost estimating, and how to use this manual are 
discussed. 

The homebuilder, contractor, and local engineering professional can utilize the designs in this 
chapter and Appendix A to construct residential foundations in the Gulf Coast. The selection 
of appropriate foundation designs for the construction of residences is dependent upon the 

5.1 Foundation Design Types
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5- 



5 foundation selection

5- 

Building on strong and safe foundations

coastal zone, wind speed, and elevation requirements, all of which have been discussed in the 
previous chapters. The following types of foundation designs are presented in this manual:

Open Foundations

n Timber pilen Steel pipe pile with concrete column and grade beamn Timber pile with concrete column and grade beamn Concrete column and grade beamn Concrete column and grade beam with slab
Closed Foundations

n Reinforced masonry  crawlspacen Reinforced masonry  stem wall
Each of these foundation types designed for the Gulf Coast region have advantages and disadvantages 
that must be taken into account. Modifications to the details and drawings might be 
needed to incorporate specific house footprints, elevation heights, and wind speeds to a given 
foundation type. Consultation with a licensed professional engineer is encouraged prior to beginning 
construction. 

The foundation designs and materials specified in this document are based on principles and 
practices used by structural engineering professionals with years of coastal construction experience. 
This manual has been prepared to make the information easy to understand. 

Guidance on the use of the foundation designs recommended in this manual is provided in Appendix 
B. Examples of how the foundation designs in this manual can be used with some of the 
houses in the publication A Pattern Book for Gulf Coast Neighborhoods are presented in Appendix 
B. Design drawings for each of the foundation types are presented in Appendix A, and any assumptions 
used in these designs are in Appendix C.

5.2 Foundation Design Considerations

The foundation designs proposed are suitable for homes whose dimensions, weights, and 
roof pitches are within certain ranges of values. A licensed professional engineer should 
confirm the appropriateness of the foundation design of homes whose dimensions, 
weights, or roof pitches fall outside of those defined ranges. 

Most of the foundation designs are based on a 14-foot wide (maximum) by 24-foot deep (minimum) 
module (see Figure 5-1). From this basic building block, foundations for specific homes 
can be developed. For example, if a 30-foot deep by 42-foot wide home is to be constructed, 
the foundation can be designed around three 14-foot wide by 30-foot deep sections. If a 24-foot 



foundation selection 5 

5- 

deep by 50-foot wide home is desired, four 12.5-foot wide by 24-foot deep sections can be used. 
If a 22-foot deep home is desired, the foundation designs presented here should only be used 
after a licensed professional engineer determines that they are appropriate since the shallow 
depth of the building falls outside the range of assumptions used in the design.

The licensed professional engineer should also consider the following:

n Local soil conditions. The piling foundations have been developed for relatively soft subsurface 
soils. Presumptive gravity loading values of 8 tons per pile, uplift loads of 4 tons per 
pile, and lateral loads of 1 ton per pile were used in these designs. Soil testing on the site 
may determine that fewer piles are needed to support the home, and the reduced cost of 
driving fewer piles could justify the cost of soils testing and redesign. Soils test should also 
be considered to validate the assumptions made.
n Building weight. The foundations have been designed to resist uplift forces resulting from 
a relatively light structure. If the actual home is heavier (e.g., from the use of concrete 
composite siding or steel framing), it may be cost-effective to reanalyze and redesign the 
footings. This is particularly true for a home that doesnt need to be elevated more than several 
feet or has short foundation walls that can help resist uplift. 
Basic Module30' x 42' Home24' Minimum14' Maximum42'
14'14'14'
30'
28 x 50 Home50
28
12.512.512.512.5
Figure 5-1. 
Schematic of a basic 
module and two 
footprints



n Footprint complexity. By necessity, the foundations have been designed for relatively simple 
rectangular footprints. If the actual footprint of the home is relatively complex, the engineer 
may need to consider torsional wind loading, differential movement among the modules 
that make up the house, concentrated loading in the homes floor and roof diaphragms, 
and shear wall placement.
5.3 Cost Estimating

Cost information that the homebuilders can use to estimate the cost of installing the foundation 
systems proposed in this manual are presented in Appendix E. These cost estimates are from 
information provided by local contractors and are based on May 2006 prices. 

5.4 How to Use This Manual

The rest of this chapter is designed to provide the user with step by step procedures for the information 
provided in this document. 

1. Determine location of the dwelling on a general map. Identify the location relative to key 
features such as highways and bodies of water. An accurate location is essential for using flood 
and wind speed maps in subsequent steps of the design process.

2. Determine location of dwelling on the appropriate FIRM

n Determine the flood insurance risk zone from the FIRM (Select V Zone, Coastal A Zone, 
non-Coastal A Zone, or other). Refer to FEMA 255, Guide to Flood Maps, How to Use Flood 
Maps to Determine Flood Risk for a Property, for instructions. For the Gulf Coast, the FEMA Hurricane 
Katrina Flood Recovery Advisories should be used until the Gulf Coast is restudied 
and remapped. New flood maps are scheduled to be completed in 2006. 
n Determine the BFE or the interim Advisory Base Flood Elevations (ABFEs) for the location 
from the FIRM. If the dwelling is outside of floodprone areas, it only needs to be designed 
for gravity and appropriate wind loads. Seismic events are considered too rare for the Gulf 
Coast to control the design and analysis. 
FIRM Panel No. ____________________

Flood Insurance Risk Zone ____________________

Base Flood Elevation (BFE) or 
Advisory Base Flood Elevation (ABFE) ____________________



3. Identify the local building code. Several Gulf States are adopting new building codes to 
govern residential construction. Several parishes, counties, and towns in Louisiana and Mississippi 
have adopted the IBC and the IRC to govern construction. This document assumes that 
the IRC governs the design and construction requirements.

4. Identify the local freeboard requirements and DFE. Using either the local building codes, local 
floodplain ordinances, data obtained from local building officials, or personal preferences 
(only if greater than minimum requirements), determine the minimum freeboard above the 
BFE or ABFE. The DFE is the sum of the BFE or ABFE and freeboard values. 

5. Determine the required Design Wind Velocity. The IRC references ASCE 7-02 as the source 
of the wind speed information. The IRC will be used as the source of all individual and combined 
loads.

6. Establish the topographic elevation of the building site and the dwelling. Elevations can 
be obtained from official topographic maps published by the National Geodetic Survey and/or 
as established or confirmed by a surveyor.

n If the dwelling and its surrounding site are above the DFE, no flood forces need to be 
considered.
n If the desired topographic elevation is below the DFE, the dwelling must be elevated above 
the BFE or ABFE.
County/Parish/City ____________________

Building Code ____________________

Building Code Date ____________________

Base Flood Elevation (BFE) or 
Advisory Base Flood Elevation (ABFE) ______________

Freeboard + ______________

Design Flood Elevation ______________

Design Wind Velocity ______________________________

Wind Exposure Category ______________________________

Source of Topo Elevation ______________________________

Topo Elevation (Site) ______________________________



7. Determine the height of the base of the dwelling above grade. Subtract the lowest ground 
elevation at the building from the lowest elevation of the structure (i.e., bottom of lowest horizontal 
structural member).

8. Determine the general soil classification for the site. To determine the load capacity of 
the soil, the soil must first be classified according to its strength groupings. For purposes of using 
this manual, the classification system has been greatly simplified into two groups commonly 
found in coastal areas along the Gulf of Mexico States: (1) loose granular, cohesionless (having 
little or no clay content) soils and (2) soft, cohesive (principally clayey content) soils.

9. Determine the type of foundation to be used to support the structure. Depending on the 
location of the dwelling, design wind speed, and local soil conditions documented above, select 
the desired or required type of foundation. Note that more than one solution may be possible. 
Refer to Chapter 4 for the potential foundation designs that can be used within the flood zones 
determined from the FIRM maps. Drawings in Appendix A illustrate the construction details 
for each of the foundations. Refer to the drawings for further direction and information about 
the needs for each type of unit.

10. Evaluate alternate foundation type selections. The choice of foundation type may be on 
the basis of least cost or to provide a personal choice, functional, or aesthetic need at the site. 
Refer to Appendix E for guidance on preparing cost estimates. Functional needs such as provisions 
for parking, storage, or other non-habitable uses for the area beneath the living space 
should be considered in the selection of the foundation design. Aesthetic or architectural issues 
(i.e., appearance) also must be included in the evaluation process. Guidance for the architectural 
design considerations can be obtained from A Pattern Book for Gulf Coast Neighborhoods by 
the Mississippi Governors Commission on Recovery, Rebuilding and Renewal (see Appendix 
B) and from many other sources. 

As part of the final analysis, it is strongly recommended that the selection and evaluation process 
be coordinated with or reviewed by knowledgeable contractors or design professionals to 
arrive at the best solution to fulfill all of the regulatory and functional needs for the construction.


11. Select the foundation design. If the homes dimensions, height, roof pitch, and weight 
are within the ranges used to develop these designs, the foundation designs can be used as 
is. However, if the proposed structure has dimensions, height, roof pitch, or weights that fall 

Design Flood Elevation ______________________________

Topo Elevation ______________________________

Elevation Dimension ______________________________

Soil Classification ______________________________



outside of the range of values used, a licensed professional engineer should be consulted. The 
materials presented in the appendices should help reduce the engineering effort needed to develop 
a custom design. Figure 5-2 is a foundation selection decision tree for determining which 
foundation design to use based on the requirements of the home. Table 5-1 shows which foundation 
design cases can be used for the home based on height of elevation and wind velocity.

Because the designs are good for a range of buildings, they will be conservative for some applications. 
A licensed professional engineer will be able to provide value engineering and may 
produce a more efficient design that reduces construction costs. 

5.5 Design Examples

The foundation designs were developed to allow a modular approach for developing 
foundation plans. In this approach, individual rectangular foundation components can 
be assembled into non-rectangular building footprints (see Figures 5-3 through 5-5). Appendix 
D provides detailed calculations and analysis for open and closed foundation designs. 
There are, however, a few rules that must be followed when assembling the modules: 

1. The eave-to-ridge dimension of the roof is limited to 23 feet. The upper limit on roof 
height is to limit the lateral forces to those used in developing the designs.
2. Roof slopes shall not be shallower than 3:12 or steeper than 12:12. For a 12:12 roof pitch, 
this corresponds to a 42-foot deep home with a 2-foot eave overhang.
3. The tributary load depth of the roof framing shall not exceed 23 feet, including the 2-
foot maximum roof overhang. This limit is placed to restrict uplift forces on the windward 
foundation elements to those forces used in developing the design. As a practical matter, 
clear span roof trusses are rarely used on roofs over 42 feet deep; therefore, this limit should 
not be unduly restrictive. The roof framing that consists of multiple spans will require vertical 
load path continuity down through the interior bearing walls to resist uplift forces on the 
roof. Load path continuity can be achieved in interior bearing walls using many of the same 
techniques used on exterior bearing walls.
4. On the perimeter foundation wall designs (Cases E and F), foundation shear walls must 
run the full depth of the building module, and shear walls can not be spaced more than 
42 feet apart. 
5. All foundation modules shall be at least 24 feet deep and at least 24 feet long. Although 
the basic module is limited to 42 feet long, longer home dimensions can be developed, provided 
that the roof does not extend beyond the building envelope as depicted in Figure 2 of 
the Introduction.

Foundation TypesA = Timber pileB = Steel pipe pile with concrete column and grade beamC = Timber pile with concrete column and grade beamD = Concrete column and grade beamE = Reinforced masonry  crawlspaceF = Reinforced masonry  stem wallG = Concrete column and grade beam with slab
Figure 5-2.
Foundation Selection Decision Tree



Table 5-1. Foundation Design Cases Based on Height of Elevation and Wind Velocity

Wind Velocity of 120 to 150 (mph)

Height (H) 

(ft)

V Zone

Coastal A Zone*

Non-Coastal A Zone

One-Story 
Dwelling

< 4

A,B,C

A,B,C,D,G

A,B,C,D,E,F,G

5

A,B,C

A,B,C,D,G

A,B,C,D,E,G

6

A,B,C

A,B,C,D,G

A,B,C,D,E,G

7

A,B,C

A,B,C,D,G

A,B,C,D,E,G

8

A,B,C

A,B,C,D,G

A,B,C,D,E,G

9

A,B,C

A,B,C,G

A,B,C,G

10

A,B,C

A,B,C,G

A,B,C,G

11

B,C

B,C,G

B,C,G

12

B,C

B,C,G

B,C,G

13

B,C

B,C,G

B,C,G

14

B,C

B,C,G

B,C,G

15

B,C

B,C,G

B,C,G

Two-Story 
Dwelling

< 4

A,B,C

A,B,C,D,G

A,B,C,D,E,F,G

5

A,B,C

A,B,C,D,G

A,B,C,D,E,G

6

A,B,C

A,B,C,D,G

A,B,C,D,E,G

7

A,B,C

A,B,C,D,G

A,B,C,D,E,G

8

A,B,C

A,B,C,D,G

A,B,C,D,E,G

9

A,B,C

A,B,C,G

A,B,C,G

10

A,B,C

A,B,C,G

A,B,C,G

11

B,C

B,C,G

B,C,G

12

B,C

B,C,G

B,C,G

13**

B,C

B,C

B,C

14**

B,C

B,C

B,C

15**

B,C

B,C

B,C





* In the Coastal A Zone, the tops of all footings and grade beams in Cases D and G foundations must be placed below 
the maximum estimated erosion and scour depth. 

** Some foundation designs are not appropriate for two-story dwelling for a design wind speed of 150 mph. See individual 
design drawings for more details.

Foundation Types 

A = Timber pile

B = Steel pipe pile with concrete column and grade beam

C = Timber pile with concrete column and grade beam

D = Concrete column and grade beam

E = Reinforced masonry  crawlspace

F = Reinforced masonry  stem wall

G = Concrete column and grade beam with slab



Figure 5-3. 
T shaped modular 
design 
Note A: Overall building 
dimensions can exceed 
42 feet. The vertical 
dimensions from the eave 
to the ridge roof shall not 
exceed 23 feet.

Module 1Module 2Module 1Module 3Module 2Note ABuilding FootprintAlternative 1Alternative 224 - 42
24 - 42
24 - 42
24 MinimumNote A
Module 1Module 1Module 2Module 2Note A24 - 42
24 - 42
24 MinimumNote ABuilding FootprintAlternative 1Alternative 2
Figure 5-4. 
L shaped modular 
design 
Note A: Overall building 
dimensions can exceed 
42 feet. The vertical 
dimensions from the eave 
to the ridge roof shall not 
exceed 23 feet. 



Figure 5-5. 
Z shaped modular 
design 
Note A: Overall building 
dimensions can exceed 
42 feet. The vertical 
dimensions from the eave 
to the ridge roof shall not 
exceed 23 feet.

Module 1Module 1Module 2Module 2Module 3Module 3Note A24' - 42'
24' - 42'
24' - 42'
24' Minimum24' MinimumNoteABuilding FootprintAlternative 1Alternative 2

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


A. Foundation Designs

A- 



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


B. Pattern Book Design

The illustrations in this appendix are from A Pattern Book for Gulf Coast Neighborhoods prepared 
for the Mississippi Governors Rebuilding Commission on Recovery, Rebuilding and Renewal by 
Urban Design Associates (UDA) of Pittsburgh, Pennsylvania, in November 2005.

http://www.mississippirenewal.com/info/plansReports.html

B- 



pattern book design B 

B- 

TypeAffordable Housing  Doublewide Cottage
ContactLaura Anne Bossardt Welsh and Jeremy WelshContact Informationlabwelsh@gmail.comTotal Square Feet1,232Number of Bedrooms4Number of Bathrooms2TimingImmediate/Medium Term/Long TermHousing TypeMobile/Modular/Panelized/Stock PlanElevation0-410-4128'-0''
Floor Planpage 63 top7'11'11'11'11'
44' 
14'14'
Porch is open and has short 
spans. Consult with local 
engineer to determine uplift 
forces and verify suitability.
Figure B-1. 
Pattern Book for Gulf Coast Neighborhoods 
Page 63 Top



B pattern book design

B- 

Building on strong and safe foundations

Housing TypeDetached Single-FamilyContactUrban Design AssociatesContact Informationhttp://www.urbandesignassociates.com/
Total Square Feet1,311Number of Bedrooms3Number of Bathrooms2TimingMedium Term/Long TermHousing TypeStock PlanFloor PlanOptionalFireplaceOptionalDeckMaster Bedroom12422x 16Bedroom 211 x 10Bedroom 312 x 10KitchenPorchBathClPM.
BathFoyer12'8'11' 11' 11' 
45' 
page 63 bottom12'12'8'
32'
32'
Porch is open and has short spans. 
Consult with local engineer to 
determine uplift forces and verify 
suitability.
2'
Figure B-2. 
Pattern Book for Gulf Coast Neighborhoods 
Page 63 Bottom



Housing TypeDetached Single-FamilyContactUrban Design AssociatesContact Informationhttp://www.urbandesignassociates.comTotal Square Feet1,536Number of Bedrooms3Number of Bathrooms2.5TimingMedium Term/Long TermHousing TypeStock PlanFirst Floor PlanLivingRoomKitchenDining Room12 x 10800page 64 bottom8'
10'
32'
12' 12' 
24' 
10'-8''10'-8''10'-8''
32'
Porch is open and has short spans. 
Consult with local engineer to 
determine uplift forces and verify 
suitability.
Figure B-3. 
Pattern Book for Gulf Coast Neighborhoods 
Page 64 Bottom



Housing TypeDetached Single-FamilyContactUrban Design AssociatesContact Informationhttp://www.urbandesignassociates.com/
Total Square Feet1,630Number of Bedrooms4Number of Bathrooms2TimingMedium Term/Long TermHousing TypeStock PlanAlternative ElevationAlternative Elevation46'
Master Bedroom134x 16Bedroom 210 x 1010Bedroom 3/Den10 x1010page 65 bottomLiving/ Dining164x 204KitchenPorch is open and has short spans. 
Consult with local engineer to 
determine uplift forces and verify 
suitability.
11'-4''11'-4''11'-4''8'
10'-8''2'
2 @ 8'-8''
10'-8''10'-8''10'-8''
32'
2'
34'
Figure B-4. 
Pattern Book for Gulf Coast Neighborhoods 
Page 65 Bottom



Housing TypeAffordable Housing  HouseContactEric MoserContact Informationericmoser@moserdesigngroup.comTotal Square Feet2,066Number of Bedrooms4Number of Bathrooms3TimingMedium Term/Long TermHousing TypePanelized/Stock PlanElevationFirst Floor Plan13' 13' 13' 13' 
52'
11'11'11'
8'
2 @ 11'
33'
3 @ 9'- 4'' = 28'
8'3'
Porch is open and has short spans. 
Consult with local engineer to 
determine uplift forces and verify 
suitability.
page 67 bottom
Figure B-5. 
Pattern Book for Gulf Coast Neighborhoods 
Page 67 Top



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


C. Assumptions Used in 
Design 

Gulf Coast Foundation Designs

The foundation designs proposed in Appendix A are based on the following standards and 
codes:

ASCE 7-02

Minimum Design Loads for Buildings and Other Structures 
American Society of Civil Engineers (ASCE) 

ACI 530-02/ASCE 5-02/TMS 402-02

Building Code Requirements for Masonry Structures 
American Society of Civil Engineers (ASCE) 
American Concrete Institute (ACI) 
The Masonry Society (TMS) 

ACI 318-02 

Building Code Requirements for Structural Concrete 
American Concrete Institute

C- 



c ASSUMPTIONS USED IN DESIGN 

C- 

Building on strong and safe foundations

ANSI/AFPA NDS-2001 

National Design Specifications for Wood Construction 
American Forest & Paper Association (AF&PA) 
American Wood Council 

IRC-2003 

2003 International Residential Code for One- and Two-Family Dwellings 
International Code Council (ICC)

To provide flexibility for the builder, a range of dead loads and building dimensions was used 
for calculating reactions on the foundation elements. For uplift and overturning analyses, the 
structure was assumed to be relatively light and narrow, and constructed with a relatively low-
sloped roof. For sliding analyses, the home was considered relatively deep and constructed with 
a steeper roof slope. For the gravity loading analysis, a heavier structure was assumed. 

Dead Loads 

For Use in ASCE 7-02 ASD Uplift/Overturning Load Combination #7 (0.6D + W +H)

First Floor 8 psf Vinyl flooring, 5/8-inch plywood sub-floor and 2 by 8 joists 
16 inches on centers

Second Floor 10 psf First floor components plus 1 layer of -inch gypsum drywall

Wall 9 psf Wood siding, 2 by 4 studs 16 inch on centers, -inch plywood wall 
sheathing, and one layer of -inch gypsum drywall

Roof 12 psf 200 lb/sq asphalt roofing, 15 lb/sq felt, -inch plywood decking, 
2 by 4 top and bottom truss chords 24 inches on centers, -inch 
gypsum drywall ceiling finish

Dead Loads 

For Use in ASCE 7-05 ASD Gravity Load Combination #2 (D + H + F + L + T)

First Floor 16 psf Dead loads increased 8 lb/sf to account for additional finishes 
like hardwood flooring (4 lb/sf), -inch slate (7 lb/sf), or thin 
set tile (5 lb/sf)

Second Floor 18 psf

Wall 10 psf Wall weight increased to account for cement composite siding

Roof 12 psf



ASSUMPTIONS USED IN DESIGN c

C- 

Concrete 150 psf Normal weight concrete. Footings for continuous perimeter walls 
were also sized to support full height brick veneer at 40 psf. 

Masonry 115 psf Medium weight block

Grout 105 psf

Brick Veneer 40 psf

Wind Loads 

Designs provided for 120 mph, 130 mph, 140 mph, and 150 mph zones (3-second gust wind 
speeds per ASCE 7-02). Wind analysis used Method 2 for buildings of all heights. 

Exposure 

Category C Open terrain with scattered obstructions generally less than 30 
feet in height; shorelines in hurricane-prone areas

Kzt = 1 No topographic effects (i.e., no wind speedup effects from hills, 
ridges, or escarpments) 

Kd = 0.85 Wind directionality factor (for use with ASCE 7-02 load combinations)


Kz, Kh Velocity pressure coefficients for Exposure Category C 

Flood Loads 

V Zone Breaking wave load from a wave with height 78 percent of stillwater 
depth (ds) 
Flood velocity (fps) equal to (gds)1/2 up to a maximum of 10 fps 
(FEMA 55 Upper Bound)

Coastal A Zone Breaking wave load from 1 foot up to a 3 foot high wave 
Flood velocity (fps) equal to (gds)1/2 up to a maximum of 5 fps 
(FEMA 55 Upper Bound)

Non-Coastal A Zone Breaking wave load up to a 1 foot high wave 
Flood velocity (fps) equal to stillwater flood depth (ds) (in 
feet)(FEMA 55 lower bound)

Lateral Loads (on stem walls)

Lateral earth pressures from saturated soils 100 pounds per cubic foot (pcf) 

Surcharge for slab weight and first floor live load 65 pounds per square foot (psf) 



Live Loads

First Floor 40 psf

Second Floor 30 psf

Roof 20 psf

Soil Bearing Capacity

 1,500 psf Presumptive value for clay, sandy clay, silty clay, 
clayey silt, silt, and sandy silt (CI, ML, MH and CH) (2003 IRC)

Building Dimensions

Building Width 14 ft (per module)

Building Depth max 42 ft 
min 24 ft

Shear Wall Spacing max 42 ft

Floor Height 10 ft (floor to floor dimension)

Roof Pitch Ratio min 3:12 Uplift and overturning calculation 
max 12:12 Sliding calculation

Roof Overhang 2 ft



appendix demonstrates how these loads are calculated using a sample 
building and foundation. The reactions from the loads imposed on the 
example building are calculated, the loads on the foundation elements 
are determined, and the total loads are summed and applied to the 

foundation. 

There is a noteworthy difference between the approach taken for designing the foundations 
included in this manual and the analyses that a designer may undertake for an individual 
building. The analyses used for the designs in this manual were based on the worst case loading 
scenario for a range of building sizes and weights. This approach was used to provide 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST D- 



D Foundation Analysis and Design Examples 

D- 

Building on strong and safe foundations

designers and contractors with some flexibility in selecting the home footprint and characteristics 
for which these pre-engineered foundations would apply. This also makes application of the 
pre-engineered foundations simpler, reducing the number of pre-engineered foundations, and 
results in conservative designs.

For example, the designs presented were developed to resist uplift and overturning for a relatively 
light structure with a flat roof (worst case uplift and overturning) while gravity loads were 
based on a relatively heavy structure to simulate worst case gravity loads. Sliding forces were determined 
for a relatively deep home with a steep roof to simulate the largest lateral loads. The 
range of building weights and dimensions applicable to the designs are listed in Appendix C.

Since the designs are inherently conservative for some building dimensions and weights, a local 
design professional may be consulted to determine if reanalyzing to achieve a more efficient design 
is warranted. If a reanalysis is determined to be cost-effective, the sample calculations will 
aid the designer in completing that analysis. 

D.1 Sample Calculations

The sample calculations have been included to show one method of determining and calculating 
individual loads, and calculating load combinations. 

Type of Building

The sample calculation is based on a two-story home with a 28-foot by 42-foot footprint and 
a mean roof height of 26 feet above grade. The home is located on Little Bay in Harrison 
County, Mississippi, approximately 1.5 miles southwest of DeLisle (see Figure D-1). The site is 
located on the Harrison County Flood Recovery Map in an area with an Advisory Base Flood 
Elevation (ABFE) of 18 feet, located between the 1.5-foot wave contour and the 3-foot wave 
contour (Coastal A Zone). The local grade elevation is 15 feet North American Vertical Datum 
(NAVD).The calculations assume short- and long-term erosion will occur and the ground elevation 
will drop 1 foot during the life of the structure. This places the home in a Coastal A Zone 
with the flood elevation approximately 4 feet above the eroded exterior grade. Based on ASCE 
7-02, the 3-second gust design wind speed at the site is 128 miles per hour (mph) Exposure Category 
C.To reduce possible damage and for greater resistance to high winds, the home is being 
designed for a 140-mph design wind speed. 

The home has a gabled roof with a 3:12 roof pitch. The home is wood-framed, contains no brick 
or stone veneer, and has an asphalt shingled roof. It has a center wood beam supporting the first 
floor and a center load bearing wall supporting the second floor. Clear span trusses frame the 
roof and are designed to provide a 2-foot overhang. No vertical load path continuity is assumed 
to exist in the center supports, but vertical and lateral load path continuity is assumed to exist 
elsewhere in the structure.



Foundation Analysis and Design Examples D

D- 

The proposed foundation for the home is a system of steel pipe piles, a reinforced concrete 
grade beam, and concrete columns extending from the grade beam to the elevated structure. 

Methodology

1. Determine the loads based on the buildings parameters (Section D.1.1)
2. Calculate wind and flood loads using ASCE 7-02 (Section D.1.2)
3. Consider the structure as a rigid body, and use force and moment equilibrium equations to 
determine reactions at the perimeter foundation elements (Section D.2)
Figure D-1. 
Star indicates the location of the sample calculation home on Little Bay in Harrison County, Mississippi, 
approximately 1.5 miles southwest of DeLisle. Inset on the left (from the map) is enlarged. 



D.1.1 Determining Individual Loads on a Structure

Building Dimensions and Weights (pulled from the text of the example problem)

B = 42 Building width (ft) 

L = 28 Building depth (ft) 

F1 = 10 First floor height (ft)

F2 = 10 Second floor height (ft)

r = 3 3:12 roof pitch

Wovhg = 2 Width of roof overhang (ft)

Dead Loads

WrfDL = 12 Roof dead load including upper level ceiling finish (in 
pounds per square foot [psf])

W1stDL = 8 First floor dead load (psf)

W2ndDL = 10 Second floor dead load, including first floor ceiling finish (psf)

WwlDL = 9 Exterior wall weight (psf of wall area) 

Live Loads

W1stLL = 40 First floor live load (psf)

W2ndLL = 30 Second floor live load (psf)

WrfLL = 20 Roof live load (psf)

Wind Loads

Building Geometry

h/L = 1

L/B = 0.7



Site Parameters (ASCE 7-02, Chapter 6)

Kzt = 1 Topographic factor (no isolated hills, ridges, or escarpments) 

Kd = 0.85 Directionality factor (for use with ASCE 7-02, Chapter 2, 
Load Combinations)

Kh = 0.94 For simplicity, Velocity Pressure Coefficient used at the 26 foot 
mean roof height was applied at all building surfaces. 
See ASCE 7-02, Table 6-3, Case 2. 

I = 1 Importance factor (residential occupancy)

V = 140 3-second gust design wind speed (mph)

G = 0.85 Gust effect factor (rigid structure, ASCE 7-02, Section 6.5.8.1)

External Pressure Coefficients (Cp) (ASCE 7-02, Figure 6-6) 

CPwwrf = -1.0 Windward roof (side facing the wind)

CPlwrf = -0.6 Leeward roof 

CPwwl = 0.8 Windward wall 

CPlwwl = -0.5 Leeward wall (side away, or sheltered, from the wind)

CPeave = -0.8 Windward eave

Positive coefficients indicate pressures acting on the surface. Negative coefficients indicate pressures 
acting away from the surface. 

Velocity Pressure (qh) (ASCE 7-02, Section 6.5.10)

Velocity pressure at mean roof height:

qh = 0.00256 KhKzt Kd V2 I 

 = 0.00256 (0.94)(1)(0.85)(140)2(1)

qh = 40 psf 

Wind Pressures (P)

Determine external pressure coefficients for the various building surfaces. Internal pressures, 
which act on all internal surfaces, do not contribute to the foundation reactions. For sign convention, 
positive pressures act inward on a building surface and negative pressures act outward.



PwwrfV = qh GCpwwrf Windward roof

 = (40)(0.85)(-1)

PwwrfV = -34 psf

Likewise

PlwrfV = qh GCplwrf Leeward roof 

PlwrfV = -20 psf

Pwwwl = qh GCpwwwl Windward wall 

Pwwwl = 27 psf

Plwwl = qh GCplwwl Leeward wall

Plwwl = -17 psf

Pwweave = qh GCpeave Windward roof overhang 

Pwweave = -27 psf - eave 

 = -34 psf - upper surface

 = -61 psf - total

Wind Forces (F) (on a 1-foot wide section of the home)

FwwrfV = PwwrfV L/2 Windward roof vertical force

 = (-34 psf)(14 sf/lf)

 = -476 lb/lf

FlwrfV = PlwrfV L/2 Leeward roof vertical force

 = (-20 psf)(14 sf/lf)

 = -280 lb/lf 

FwwrfH = PwwrfH L/2 (r/12) Windward roof horizontal force

 = (-34 psf)(14 sf/lf)(3/12)

 = -119 lb/lf

FlwrfH = PlwrfH L/2 (r/12) Leeward roof horizontal force 

 = (-20 psf)(14 sf/lf)(3/12)

 = -70 lb/lf



Fwwwl1st = Pwwwl (F1) Windward wall on first floor

 = (27 psf)(10 sf/lf)

 = 270 lb/lf

Fwwwl2nd = Pwwwl (F2) Windward wall on second floor

 = (27 psf)(10 sf/lf)

 = 270 lb/lf

Flwwl1st = Plwwl (F1) Leeward wall on first floor

 = (-17 psf)(10 sf/lf)

 = -170 lb/lf

Flwwl2nd = Plwwl (F2) Leeward wall on second floor

 = (-17 psf)(10 sf/lf)

 = -170 lb/lf

Fwweave = Pwweavewowhg Eave vertical force (lb) 

 = -(61 psf)(2 sf/lf) horizontal projected areas is negligible so horizontal force is neglected 

 = -122 lb/lf

D.1.2 Calculating Reactions from Wind, and Live and Dead Loads

Sum overturning moments (Mwind) about the leeward corner of the home. For sign convention, 
consider overturning moments as negative. Since vertical load path continuity is assumed not to 
be present above the center support, the center support provides no resistance to overturning 
(see Figure D-2).

Mwind = (-476 lb/lf)(21 ft) + (-280 lb/lf)(7 ft) + (119 lb/lf)(21.75 ft) + 
(-70 lb/lf)(21.75 ft) + (-270 lb/lf)(5 ft) + (-270 lb/lf)(15 ft) + 
(-170 lb/lf)(5 ft) + (-170 lb/lf)(15 ft) + (-122 lb/lf)(29 ft)

 = -23,288 ft-lb/lf

Solving for the windward reaction, therefore:

Wwind = Mwind  L 

Wwind = -23,228 ft (lb/lf  28 ft)

Wwind = -830 lb/lf 



The leeward reaction is calculated by either summing vertical loads or by summing moments 
about the windward foundation wall. Leeward reaction equals -48 lb/lf. 

Lateral Wind Loads

Sum horizontal loads (Flat) on the elevated structure (Forces to the left are positive. See Figure 
D-2).

Flat = (-119 lb/lf) + (70 lb/lf) + (270 lb/lf) + (270 lb/lf) + (170 lb/lf) + (170 lb/lf)

 = 831 lb/lf

Figure D-2. Paths for 
wind, live, and dead 
loads

-20 psf 
Wind, Live and Dead Loads 
-17 psf 
4' 
M+BFELowest Horizontal 
Member 18 Sq. Concrete 
Column Pilecap 
and Driven Pile 
2' 
28' 
10' 
-34 psf 
-61 psf 
3 
12 
27 psf 
Second Floor 
First Floor 
Ground Elevation 
Eroded 
Ground Elevation 
V = 140 mph 
Roof 20 psf LL 
12 psf DL 
30 psf LL10 psf DLSecond FloorClear Span Trusses40 psf LL 
8 psf DLFirst FloorBearing Wall 
10' 

Dead Loads

In this example, dead load reactions (Wdead) are determined by summing loads over the tributary 
areas. Since the roof is framed with clear-span trusses and there is a center support in the 
home, each exterior foundation wall supports  of the roof load, all of the exterior wall load, 
and  of the first and second floor loads. This approach to analysis is somewhat conservative 
since it does not consider the entire dead load of the structure to resist overturning. Standard 
engineering practice often considers the entire weight of the structure (i.e., not just the portion 
supported by the perimeter foundation walls) available to resist overturning. The closed foundations 
in this guidance were developed considering only the tributary dead load to resist uplift. 
The open foundations were developed considering all dead loads to resist uplift.

Wdead = L/2 (wrfDL)+ L/4 (w1stDL + w2ndDL) + (F1 + F2) wwlDL 

 = [14 sf/lf (12 psf)] + [7 sf/lf (8psf + 10 psf)] + [(10 sf/lf + 10 sf/lf) 9 psf]

 = 474 lb/lf

Live Loads

Floor

Live loads (Wlive) are calculated in a similar fashion

Wlive = L/4(W1stLL + W2ndLL)

 = (7 sq ft/lf)(40 + 30) psf

 = 490 lb/lf 

Roof

Wliveroof = L/2(WrfLL)

 = (14 sq ft/lf)(20 psf)

 = 280 lb/lf

D.2 Determining Load Combinations

Combine loads as specified in Chapter 2 of ASCE 7-02. For this example, an allowable stress design 
approach was used. A strength-based design is equally valid.

Other loads (such as snow, ice, and seismic) are listed in the ASCE 7-02 Load Combinations, 
but were considered to be too rare in the Gulf Coast of the United States to be considered 
in the design. ASCE 7-02 also lists rain loads that are appropriate for the Gulf Coast region. 
Since a minimum roof slope ratio of 3:12 was assumed for the homes, rain loading was not 
considered. 



Table D-1. Design Reactions on Base of Elevated Home

ASCE 7-02 Load Combination

Vertical (lb/lf)

Horizontal (lb/lf)

#1 D

474

--

#2 D + L

964

--

#3 D + Lr

754

--

#4 D + 0.75(L) + 0.75(Lr)

{1,052}

--

#5 D + W 

-356

831

#6 D + 0.75(W) + 0.75(L) + 0.75(Lr ) 

1,016

623

#7 0.6D + W

{-546}

{831}

#8 0.6D

284

--





Where

D = Dead Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

NOTE: Critical loads are in bold and with brackets ({ }).

Flood Load Effects on a Foundation

In this example, since the foundation selected is a system of steel pipe piles, the equations used 
to calculate flood loads are based on open foundations. Some of the equations used to calculate 
flood loads will be different if the building has a closed foundation system.

Many flood calculations depend on the stillwater flooding depth (ds). While not listed on FIRMs, 
ds can be calculated from the BFE by knowing that the breaking wave height (Hb) equals 78 
percent of the stillwater depth and that 70 percent of the breaking wave exists above the stillwater 
depth (see Figure 11-3 of FEMA 55). Stated algebraically: 

BFE = GS + ds + 0.70 Hb

 = GS + ds + 0.70(0.78 ds)

 = GS + 1.55 ds 

GS = 15 ft NAVD (initial elevation)  1 ft (short- and long- term erosion)

 = 14 ft NAVD

ds = (BFE  GS)  1.55 

 = (18 feet NAVD  14 feet NAVD) 1.55



= 4 ft 1.55

 = 2.6 ft

Hydrostatic Loads

Hydrostatic loads act laterally and vertically on all submerged foundation elements. On open 
foundations, lateral hydrostatic loads cancel and do not need to be considered but vertical hydrodynamic 
forces (buoyancy) remain. The buoyancy forces reduce the effective weight of the 
foundation by the weight of the displaced water and must be considered in uplift calculations. 
For example, normal weight concrete which typically weighs 150 lb/ft3 only weighs 86 lb/ft3 
when submerged in saltwater (slightly more in freshwater). 

In this example, calculations are based on an 18-inch square normal weight concrete column 
that extends 4 feet above eroded ground elevation. The column weighs 1,350 pounds dry ((1.5 
ft)(1.5 ft)(4 ft)(150 lb/ft3). Under flood conditions, the column displaces 9 ft3 of saltwater that, 
at 64 lb/ft3, weighs 576 pounds so the column weighs only 774 pounds when submerged.

Hydrodynamic Loads

Flood Velocity

Since a Coastal A Zone is close to the flood source, flood velocity is calculated using the ASCE 
7-02 Equation C5-2:

V = (g ds)1/2 Upper bound flood velocity 

 Where 

g = Gravitational acceleration (32.2 ft/sec2)

ds = Design stillwater depth (ft)

Hence

V = [(32.2)(2.6)]1/2

 = 9.15 feet per second (fps)

Hydrodynamic Forces

A modified version of ASCE 7-02 Equation C5-4 can be used to calculate the hydrodynamic 
force on a foundation element as

Fdyn =  Cd . V2 A

Where

Fdyn = Hydrodynamic force (lb) acting on the submerged element



Cd = 2.0 Drag coefficient (equals 2.0 for a square or rectangular column)

. = 2 Mass density of salt water (slugs/cubic foot)

A = 1.5 ds Surface area of obstruction normal to flow (ft2)

For open foundation, A is the area of pier or column perpendicular to flood direction (calculated for an 
18-inch square column).

Hence

Fdyn = () (2)(2)(9.15)2(1.5)(2.6)

 = 653 lb/column

The force is assumed to act at a point ds/2 above the eroded ground surface.

The formula can also be used for loads on foundation walls. The drag coefficient, however, is 
different. For foundation walls, Cd is a function of the ratio between foundation width and foundation 
height or the ratio between foundation width and stillwater depth. For a building with 
dimensions equal to those used in this example, Cd for a closed foundation would equal 1.25 for 
full submersion (42 feet by 4 feet) or 1.3 if submersed only up to the 2.6-foot stillwater depth. 

Dynamic loads for submersion to the stillwater depth for a closed foundation are as follows:

Fdyn =  Cd . V2 A

Fdyn = () (1.3)(2)(9.15)2(1)(2.6)

 = 283 lb/lf of wall

Floodborne Debris Impacts

The loads imposed by floodborne debris were approximated using formula 11-9 contained in 
FEMA 55. 

The Commentary of ASCE 7-02 contains a more sophisticated approach for determining debris 
impact loading, which takes into account the natural period of the impacted structure, local debris 
sources, upstream obstructions that can reduce the velocity of the floodborne debris, etc. 

For ease of application and consistency, debris loads in this example have been calculated using 
the guidance contained in FEMA 55 that are based on ASCE 7-98, not the 2002 version of ASCE 
7. It is suggested that designers of coastal foundations review the later standards to determine if 
they are more appropriate to use in their particular design.

The FEMA 55 Formula 11.9 estimates debris impact loads as follows:

Fi = wV  (g . t)



Where

Fi = impact force (lb)

w = weight of the floodborne debris (lb)

V = velocity of floodborne debris (ft/sec)

g = gravitational constant = 32.2 ft/sec2

.t = impact duration (sec)

Floodborne debris velocity is assumed to equal the velocity of the moving floodwaters and acting 
at the stillwater level. For debris weight, FEMA 55 recommends using 1,000 pounds when 
no other data are available. The impact duration depends on the relative stiffness of the foundation 
and FEMA 55 contains suggested impact durations for wood foundations, steel foundations, 
and reinforced concrete foundations. For this example, the suggested impact duration of 0.1 
second was used for the reinforced concrete column foundation.

Fi = wV  gt

Fi = [1,000 lb (9.15 ft/sec)]  [(32.2 ft/sec2)(0.1 sec)]

Fi = 2,842 lb

Breaking Wave Loads 

When water is exposed to even moderate winds, waves can build quickly. When adequate wind 
speed and upstream fetch exist, floodwaters can sustain wave heights equal to 78 percent of 
their stillwater depths. Depending on wind speeds, maximum wave height for the stillwater 
depth at the site can be reached with as little as 1 to 2 miles of upwind fetch.

Breaking wave forces were calculated in this example using ASCE 7-02 formulae for wave forces 
on continuous foundation walls (ASCE 7-02 Equations 5-5 and 5-6) and on vertical pilings and 
columns (ASCE 7-02 Equation 5-4). 

The equation for vertical pilings and columns from ASCE 7-02 is

Fbrkp =  Cdb . DHb2 

Where

Fbrkp = Breaking wave force (acting at the stillwater level) (lb)

Cdb = Drag coefficient (equals 2.25 for square or rectangular piles/columns)

. = Specific weight of water (64 lb/ft3 for saltwater)

D = Pile or column diameter in ft for circular sections, or for a square pile or column, 
1.4 times the width of the pile or column (ft). For this example, since 
the column is 18-inch square, D = (1.4)(1.5ft) = 2.1 ft



Hb = Breaking wave height (0.78 ds)(ft) = (0.78)(2.6) = 2.03 ft

Note: The critical angle of a breaking wave occurs when the wave travels in a direction perpendicular 
to the surface of the column. Waves traveling at an oblique angle (a) to the surface of 
the waves are attenuated by the factor sin2a. 

Fbrkp =  Cdb . DHb2 

 =  (2.25)(64 lb/ft3)(2.1 ft)(2.03 ft)2

 = 623 lb

For closed foundations, use equations in Section 5.3.3.4.2 of ASCE 7-02 to calculate Fbrkp. FEMA 
55 contains the following two equations for calculating loads on closed foundations:

fbrkw = 1.1 Cp . ds2 + 2.41 . ds2 Case 1

and

fbrkw = 1.1 Cp . ds2 + 1.91 . ds2 Case 2

Where . and ds are the specific weights of water and design stillwater depths as before. Cp 
is the dynamic pressure coefficient that depends on the type of structure. Cp equals 2.8 for 
residential structures, 3.2 for critical and essential facilities, and 1.6 for accessory structures 
where there is a low probability of injury to human life. The term fbrkw is a distributed line 
load and equals the breaking wave load per foot of wall length where fbrkw is assumed to act 
at the stillwater elevation. 

Case 1 of Formula 11.6 represents a condition where floodwaters are not present on the interior 
of the wall being designed or analyzed. Case 1 is appropriate for foundation walls that lack flood 
vents (see Figure D-3). The less stringent Case 2 is appropriate for walls where NFIP required 
flood vents are in place to equalize hydrostatic loads and reduce forces (see Figure D-4). 

In non-Coastal A Zones, the maximum wave height is 1.5 feet. This corresponds to a stillwater 
depth (ds) of approximately 2 feet (i.e., 1.5 foot/0.78 for a depth limited wave). For closed 
foundations in coastal areas with flood vents, a 1.5-foot breaking wave creates 1,280 lbs per linear 
foot of wall and 1,400 lbs per linear foot of wall on foundations that lack flood vents. 

Wind Load on Columns

Wind loads have been calculated per ASCE 7-02, Section 6.5.13 (Wind Loads on Open Buildings 
and Other Structures). The velocity pressure (qh) calculated previously was used, although 
this is a conservative figure based on the 26-foot mean roof height. The force coefficient (Cf) 
was determined from ASCE 7-02, Figure 6-19 (chimneys, tanks, and other structures); ASCE 7-
02, Figure 6-20 (walls and solid signs) could have been used as well. 



From ASCE 7-02 Equation 6-25:

Fwind = qz G Cf Af

 = 40 psf (0.85)(1.33*)(1.5 ft)(4 ft)

 = 270 lb

 *Interpolated Cf

Wind loads on the foundation elements are not considered in combination with flood loads 
since the elements are submerged during those events.

Flood Load Combinations

Section 11.6.12 of FEMA 55 provides guidance on combining flood loads. In Coastal A Zones, 
FEMA 55 suggests two scenarios for combining flood loads. Case 1 involves analyzing breaking 
wave loads on all vertical supports and impact loading on one corner or critical support and 
Case 2 involves analyzing breaking wave loads applied to the front row of supports (row closest 
to the flood source), and hydrodynamic loads applied to all other supports and impact loads on 
one corner or critical support. 

Depending on the relative values for dynamic and breaking waves, Case 1 often controls for designing 
individual piers or columns within a home. Case 2 typically controls for the design of the 
assemblage of piers or columns working together to support a home. Because of the magnitude 
of the load, it is not always practical to design for impact loads. As an alternative, structural redundancy 
can be provided in the elevated home to allow one pier or column to be damaged by 
floodborne debris impact without causing collapse or excessive deflection.

Figure D-3. Case 1. 
Normally incident 
breaking wave 
pressures against a 
vertical wall (space 
behind vertical wall 
is dry)

Source: ASCE 7-02

For the sample calculations, Case 1 was used (see Figure D-5) with a breaking wave load of 623 
pounds applied to a non-critical column. The loads were then determined and summarized. 
Since the calculations must combine distributed loads on the elevated structure and discrete 
loads on the columns themselves, a column spacing of 7 feet is assumed in the calculations. 
For lateral loads on the structure, calculations are based on three rows of columns sharing 
lateral loads.

Figure D-4. Case 2. 
Normally incident 
breaking wave 
pressures against a 
vertical wall (stillwater 
level equal on both 
sides of wall)

Source: ASCE 7-02
Flood Loads 
BFE (4')
18'' Sq.
ColumnGround Elevation 
Eroded 
Ground Elevation 
0.7 HbHb 
0.3 Hb Fi = 2,842#
FBRKP = 623#
ds = 2.6
dsdsFSTAT=
576#
Fdyn = 653#
ds = stillwater depth (ft)
Hb = breaking wave depth (ft)
FBRKP = breaking wave load (#)
Fi = impact load (#)
FSTAT = buoyancy force for a fully 
submerged 18 Sq. 4 tall 
column
Figure D-5. 
Flood loads



Table D-2. Loads on Columns Spaced 7 Feet on Center (for three rows of columns)

ASCE 7-02 Load Combination

Vertical (lb)

Horizontal (lb)

#1 D + F

1,350 + [7(474]) = 4,668

--

#2 D + F + L

1,350 + [7(964)] = 8,098

--

#3 D + F + Lr

1,350 + [7(754)] = 6,628

--

#4 D + F + 0.75(L) + 0.75(Lr)

774 + 7(1,052) = {8,138}

--

#5 D + F + W + 1.5(Fa)

774 + [7(474 - 48)] = 3,756

[(1/3)7(831)] + [1.5(623)] 
= {2,874}

#6 D + F + 0.75(W) + 0.75(L) + 
0.75(Lr) + 1.5(Fa)

774 + 7[474 + 0.75
(-48+490+280)]
= 7,883

[(1/3)7(0.75)(831)] + [1.5(623)]
= 2,388

#7 0.6D + W + 1.5(Fa)

0.6[774 + 7(474)] + [7(-830)]
= {-3,555}

[(1/3)7(831)] + [1.5(623)] 
= {2,874}

#8 0.6D

[0.6(1,350)] + [7(306)] = 3,000

--





Where 

D = Dead Load

F = Load due to fluids with well-defined pressures and maximum heights 
(see Section D.2 for additional information)

Fa = Flood Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

Note: Critical loads are in bold with brackets ({ }).

Results

Each perimeter column needs to support the following loads:

Vertical Load = 8,138 lb

Uplift = 3,555 lb

Lateral Load = 2,874 lb

With the critical loads determined, the foundation elements and their connections to the home 
can be designed.

The following two examples are to demonstrate designs using information provided in this 
manual. The first example is based on a closed foundation; the second example is based on an 
open foundation. 



D.3 Closed Foundation Example

A structure to be supported by the closed foundation is identical to the structure analyzed in 
the example from Section D.1. The site, however, is different. For the closed foundation design, 
the structure is to be placed in a non-Coastal A Zone where breaking waves are limited to 
1.5 feet. The design stillwater depth is 2 feet, and the BFE is 3 feet above exterior grade. While 
the structure could be placed on a 3-foot foundation, the property owner requested additional 
protection from flooding and a 4-foot tall foundation is to be built. Since the home elevation is 
identical to that in the example, the loads and load combinations listed in Table D-1 are identical. 
However, since the foundation is closed, flood forces must first be analyzed.

Like the previous analysis example, flood forces consist of hydrodynamic loads, debris loads, 
and breaking wave loads. Since the home is located in a non-Coastal A Zone, it is appropriate to 
use lower bound flood velocities. This will significantly reduce hydrodynamic and debris loads. 
From FEMA 55, the following equation is used:

Vlower = ds

 = 2 ft/sec

Hydrodynamic Loads

Fdyn =  Cd . V2 A

 =  Cd . V2 (1) ds 

Fdyn = () (1.4)(2)(2)2(1)(2)

 = 11 lb/lf of wall

Where Cd of 1.4 is for a (width of wall/ds) ratio of 21 (42 ft/2 ft)

(From FEMA 55, Table 11.2) 

The hydrodynamic load can be considered to act at the mid-depth of the stillwater elevation. 
The hydrodynamic load is less than the 27 psf wind load on the windward wall. 

Debris Loads

Fi = wV  gt

Fi = [1,000 lb (2 ft/sec)]  [(32.2 ft/sec2)(0.1 sec)]

Fi = 620 lb

Due to load distribution, the impact load will be resisted by a section of the wall. Horizontal 
shear reinforcement will increase the width of the section of wall available to resist impact. For 
this example, a 3-foot section of wall is considered to be available to resist impact. The debris 
impact load becomes



Fiwall = (1/3) 620 lb

Fiwall = 210 lb/ft

Breaking Wave Loads

The home is to be constructed in a SFHA; hence, the NFIP required flood vents will be installed. 
The breaking wave load can be calculated using formulae for equalized flood depths (Case 2). 

fbrkw = 1.1 Cp . ds2 + 1.91 . ds2 

fbrkw = . ds2 (1.1 Cp + 1.91)

fbrkw = (64)(22){(1.1)(2.8) + 1.91}

fbrkw = 1,280 lb/lf 

The breaking wave load can be considered to act at the 2-foot stillwater depth (ds) above the 
base of the foundation wall.

The foundation must resist the loads applied to the elevated structure plus those on the foundation 
itself. Chapter 2 of ASCE 7-02 directs designers to include 75 percent of the flood load 
in load combinations 5, 6, and 7 for non-Coastal A Zones. Table D-1 lists the factored loads on 
the elevated structure. 

Critical loads from Table D-1 include 546 lb/lf uplift, 1,052 lb/lf gravity, and 831 lb/lf lateral 
from wind loading. The uplift load needs to be considered when designing foundation walls 
to resist wind and flood loads and when sizing footings to resist uplift; the gravity load must be 
considered when sizing footings and the lateral wind and flood loads must be considered in designing 
shear walls. 

Extending reinforcing steel from the footings to the walls allows the designer to consider the 
wall as a propped cantilever fixed at its base and pinned at the top where it connects to the 
wood-framed floor framing system. The foundation wall can also be considered simply supported 
(pinned at top and bottom). The analysis is somewhat simpler and provides conservative results.

The 1,280 lb/lf breaking wave load is the controlling flood load on the foundation. The probability 
that floodborne debris will impact the foundation simultaneously with a design breaking 
wave is low so concurrent wave and impact loading is not considered. Likewise, the dynamic 
load does not need to be considered concurrently with the breaking wave load and the 27 lb/sf 
wind load can not occur concurrently on a wall submerged by floodwaters. 

The breaking wave load is analyzed as a point load applied at the stillwater level. When subjected 
to a point load (P), a propped cantilevered beam of length (L) will produce a maximum 
moment of 0.197 (say 0.2) PL. The maximum moments occur when P is applied at a distance 
0.43L from the base. For the 4-foot tall wall, maximum moment results when the load is applied 
near the stillwater level (ds). In this example, the ASCE 7-02 required flood load of 75 percent 
of the breaking wave load will create a bending moment of



M = (0.2) fbrkw (L)

 = (0.2)(0.75)(1,280 lb/ft) (4 ft)

 = 768 ft-lb/lf or

 = 9,200 in-lb/lf

The reinforced masonry wall is analyzed as a tension-compression couple with moment arm 
jd, where d is the distance from the extreme compression fiber to the centroid of the reinforcing 
steel, and j is a factor that depends on the reinforcement ratio of the masonry wall. 
While placing reinforcing steel off center in the wall can increase the distance (d) (and reduce 
the amount of steel required), the complexity of off-center placement and the inspections required 
to verify proper placement make it disadvantageous to do so. For this design example, 
steel is considered to be placed in the center of the wall and d is taken as one half of the wall 
thickness. For initial approximation, j is taken as 0.85 and a nominal 8-inch wall with a thickness 
of 7-5/8 inches is assumed. 

Solving the moment equation is as follows:

M = T (jd)

T = M/(jd) = Tension force

 = M/(j)(t/2) (t = thickness of wall)

T = (9,200 in-lbs/lf)  {(0.85)(7.63 in)(0.5)}

 = 2,837 lb/lf

For each linear foot of wall, steel must be provided to resist 2,837 pounds of bending stress and 
546 pounds of uplift. 

Fsteel = 2,837 lbs/lf (bending) + 546 lbs/lf (uplift)

 = 3,383 lbs/lf

The American Concrete Institute (ACI) 530 allows 60 kips per square inch (ksi) steel to be stressed 
to 24 ksi so the reinforcement needed to resist breaking wave loads and uplift is as follows:

Asteel = 3,383 lbs/lf  24,000 lb/in2

 = 0.14 in2 /lf

Placing #5 bars (at 0.31 in2/bar) at 24 inches on centers will provide the required reinforcement. 
To complete the analysis, the reinforcement ratio must be calculated to determine the 
actual j factor and the stresses in the reinforcing steel need to be checked to ensure the limits 
dictated in ACI 530 are not exceeded. The wall design also needs to be checked for its ability to 
resist the lateral forces from flood and wind.



Footing Sizing

The foundation walls and footings must be sized to prevent overturning and resist the 546 lb/
lf uplift. ASCE 7-02 load combination 6 allows 60 percent of the dead load to be considered in 
resisting uplift. Medium weight 8-inch masonry cores grouted at 24 inches on center weigh 50 
lb/sf or, for a 4-foot tall wall, 200 lbs/lf. Sixty percent of the wall weight (120 lb/lf) reduces the 
amount of uplift the footing must resist to 426 lb/lf. At 90 lb/ft3 (60 percent of 150 lb/ft3 for 
normal weight concrete), the footing would need to have a cross-sectional area of 4.7 square 
feet. Grouting all cores increases the dead load to 68 lb/sf and reduces the required footing 
area to 4.25 square feet. The bearing capacity of the soils will control footing dimensions. Stronger 
soils can allow narrower footing dimensions to be constructed; weaker soils will require 
wider footing dimensions. 

The design also needs to be checked to confirm that the footings are adequate to prevent sliding 
under the simultaneous action of wind and flood forces. If marginal friction resistance 
exists, footings can be placed deeper to benefit from passive soil pressures. 

D.4 Open Foundation Example 

For this example, the calculations are based on a two-story home raised 8 feet above grade with 
an integral slab-grade beam, mat-type foundation and a 28-foot by 42-foot footprint. The home 
is sited approximately 800 feet from the shore in a Coastal A Zone with a calculated DFE of 6 
feet above the eroded exterior grade (6 inches below top of slab). The DFE was determined by 
subtracting an estimated grade elevation, shown on advisory topographic map ms-g15, from the 
ABFE elevation indicated on advisory flood map ms-g15. It is important to note, however, that 
submittal of an elevation certificate and construction plans to local building code and floodplain 
officials in many jurisdictions will require that the elevation be confirmed by a licensed 
surveyor referencing an established benchmark elevation. 

The wood-framed home has a 3:12 roof pitch with a mean roof height of 30 feet, a center wood 
beam supporting the first floor, and a center load bearing wall supporting the second floor. 
Clear span trusses frame the asphalt-shingled roof and are designed to provide a 2-foot overhang. 
This home is a relatively light structure that contains no brick or stone veneers.

The surrounding site is flat, gently sloping approximately 1 foot in 150 feet. The site and surrounding 
property have substantial vegetation, hardwood trees, concrete sidewalks, and streets. 
A four-lane highway and a massive concrete seawall run parallel to the beach and the established 
residential area where the site is located. The beach has been replenished several times in 
the last 50 years. Areas to the west of the site that have not been replenished have experienced 
beach erosion to the face of the seawall. The ASCE 7-02, 3-second gust design wind speed is 140 
mph and the site is in an Exposure Category C. 

The proposed foundation for the home incorporates a monolithic carport slab placed integrally 
with a system of grade beams along all column lines (see Figure D-6). The dimensions of the 



grade beam were selected to provide adequate bearing support for gravity loads, resistance to 
overturning and sliding, and mitigate the potential of undermining of the grade beams and slab 
due to scour action. The home is supported by concrete columns, extending from the top of 
the slab to the lowest member of the elevated structure, spaced at 14 feet on center (see Figure 
D-7). 

14'-0" Maximum3'-0"
3'-0"5'-6"
Critical Area 
of Grade Beam6" Concrete SlabGrade Beam36" Wde x 48" Deep16"x16" 
Column 
Figure D-6. 
Layout of Open Foundation Example

21 psf18 psf6'
DFEM+
Lowest HorizontalMemberGround Elevation 
(Eroded Ground Elevation)
2'
28'
10'
-36 psf65 psf31234 psfSecond FloorFirst FloorFlow ofWind and FloodGrade Beams16 SquareConcrete 
ColumnsV = 140 mphRoof12 psf DL20 psf LL30 psf LL10 psf DLSecond FloorClear Span Trusses40 psf LL 
8 psf DLFirst Floor10'
Figure D-7. 
Loading Diagram 
for Open Foundation 
Example



Lateral Wind Loads

Sum horizontal loads (Flat) on the elevated structure (forces to the left are positive)

Flat = (-126 lb/lf) + (74 lb/lf) + (280 lb/lf) + (280 lb/lf) + (180 lb/lf) + (180 lb/lf)

 = 868 lb/lf

Dead Loads

Dead load reactions (Wdead) are determined by summing loads over the tributary areas. For 
the anterior columns:

Wdead = L/2 (wrfDL)+ L/4 (w1stDL + w2ndDL) + (F1 + F2) wwlDL 

 = [14 sf/lf (12 psf)] + [7 sf/lf (8psf + 10 psf)] + [(10 sf/lf + 10 sf/lf) 9 psf]

 = 474 lb/lf 

Live Loads

Floor

Live loads (Wlive) are calculated in a similar fashion

Wlive = L/4(W1stLL + W2ndLL) 

 = (7 sq ft/lf)(40 + 30) psf 

 = 490 lb/lf 

Roof

Wliveroof = L/2(WrfLL) 

 = (14 sq ft/lf)(20 psf)

 = 280 lb/lf

A minimum roof slope of 3:12 was assumed for the homes; rain loading was not considered. 

Flood Effects

Since the foundation selected is a system of concrete columns, the equations used to calculate 
flood loads are based on open foundation. The stillwater flooding depth (ds) is as follows:

ds = DFE  1.55 

 = 6 ft  1.55 

 = 3.9 ft

Hydrostatic Loads

Calculations are based on a 16-inch square normal weight concrete column that extends 8 feet 
above the concrete slab. 



The column weighs 2,123 pounds dry ((1.33 ft)(1.33 ft)(8 ft)(150 lb/ft3). 

Under flood conditions, the column displaces 10.6 ft3 of saltwater which, at 64 lb/ft3, weighs 679 
pounds so the column weighs 1,444 pounds when submerged. 

Hydrodynamic Loads

Flood Velocity

Since a Coastal A Zone is close to the flood source, flood velocity is calculated using the ASCE 
7-02 Equation C5-2 as follows:

V = [(32.2 ft/sec2)(3.9 ft)]1/2 

 = 11.21 feet per second (fps) 

Flood Force

ASCE 7-02 Equation C5-4 is as follows: 

Fdyn =  Cd . V2 A 

 = () (2)(2)(11.21fps)2(1.33ft)(3.9ft) 

 = 1,303 lb/column

Floodborne Debris Impact

The flood debris impact can be estimated, per FEMA 55 Formula 11.9, as follows:

Fi = wV  gt 

 = [1,000 lb (11.21 ft/sec)]  [(32.2 ft/sec2)(0.1 sec)] 

 = 3,478 lb

Breaking Wave Load 

The equation for vertical pilings and columns from ASCE 7-02 is as follows:

Fbrkp =  Cdb . DHb2 

 =  (2.25)(64 lb/ft3)(1.82 ft)(3.04ft*)2 

 = 1,211 lb

Wind Load on Columns

For a load case combining both wind and flood forces, the column would be almost completely 
submerged; therefore, the wind load on the column shall not be included.

* A wave height of 3.04 ft suggests a V Zone but, in this example, the depth of water is increased by erosion which is not considered in 
mapping A Zones. The deeper water supports a bigger wave, which in this case exceeds the V Zone wave height minimum.



Calculating Reactions from Wind, Live, and Dead Loads

Sum overturning moments (Mwind) and (Mflood) about the leeward corner of the mat foundation. 
For sign convention, consider overturning moments as negative. Note in this example the 
home is slightly higher above grade and hence the wind loads are slightly higher.

Mwind = (-504 lb/lf)(21 ft) + (-294 lb/lf)(7 ft) + (126 lb/lf)(21.75 ft) + (-74 lb/lf)(21.75 
ft) + (-280 lb/lf)(13 ft) + (-280 lb/lf)(23 ft) + (-180 lb/lf)(13 ft) + (-180 lb/
lf)(23 ft) + (-130 lb/lf)(29 ft)

 = -31,841 ft-lb/lf

 The vertical components of the reaction caused by the wind overturning moment is:

R x = 31,841 lb  28 ft = +/- 1,137 lb/ft 

Mflood = 1.5[((-1,211lb)(3.9ft)) + (2(-1,303lb)(3.9ft/2)) + ((-3,478lb)(3.9ft))] = 35,053 
ft-lb/ft

The vertical component of the reaction caused by the flood overturning moment is: 

Rx = 35,053 lb  28 ft = +/- 1,252 lb outboard columns 

Load Combinations

Table D-3. Loads at Base of Columns Spaced 14 Feet on Center (for three rows of columns per bay)

ASCE 7-02 Load Combination

Vertical (lb)

Horizontal (lb)

#1 D + F

1,444 + 14(474) = 8,080

--

#2 D + F + L

1,444 + 14(964) = 14,940

--

#3 D + F + Lr

1,444 + 14(754) = 12,000

--

#4 D + F + 0.75(L) + 0.75(Lr)

8,080 + (.75)[(14)(490+280)] = 
16,165

--

#5 D + F + W + 1.5(Fa)

8,080 +/- 14(1,137) +/- 1,252 = 
25,876; -9,716 windward; leeward 

wind + (1.5)[Fdyn + Fi]
[(14(868)(1/3)] + (1.5) 
[(1,303+3,478)] = 11,222 

#6 D + F + 0.75(W) + 0.75(L) + 
0.75(Lr) + 1.5(Fa)

8,080 +/- (.75)(14)(1,137) 
+(.75)(14)([(490+280)] +/- 1,252 = 
2,348; 29,982 windward; leeward

(.75) wind + (1.5)[Fdyn + Fi]
[(0.75)(14)(868)(1/3)] + 
(1.5)[(1,303+3,478)] = 10,210

#7 0.6D + W + 1.5(Fa)

0.6 [2,123+14(474)] +/- 14(1,137) 
+/- (1.5)1,252 = -12,541; 23,051 
windward; leeward

wind + (1.5)[Fdyn + Fi]
[(14(868)(1/3)] + (1.5)
[(1,303+3,478)] = 11,222

#8 0.6D

[0.6((2,123) + 14(474))] = 5,255

--



Critical loads are in bold. 



Where 

D = Dead Load

F = Fluid (Buoyancy) Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

ww = windward

lw = leeward

Results

Each perimeter column needs to support the following loads:

Vertical load = 29,982 lb

Uplift = 12,541 lb

Lateral Load = 11,222 lb

Moment wind + fdyn = [(1/3)(14)(1,314)(8) + (1,303)(3.9/2)]  1,000 lb/kip

 = 51.6 ft-kip 

 Moment wind + fbrkp = [(1/3)(14)(1,314)(8) + (1,113)(3.9)]  1,000 lb/kip

 = 96.9 ft-kip 

 Moment wind + fdyn+ debris = 51.6 ft-kip + (3,478)(3.9)  1,000 lb/kip

 = 65.1 ft-kip

 = 13.6 ft-kip

The force is assumed to act at a point ds/2 above the eroded ground surface. For concrete design 
we use load factors per ASCE 7-02. 

Ultimate Moment wind + fdyn = (48.6)(1.2)+(2.5)(2.0) 

 = 63.4 ft-kip 

Ultimate Moment wind + fbrkp = (48.6)(1.2)+(4.3)(2.0) 

 = 66.9 ft-kip

Ultimate Moment wind + fdyn + debris = (63.4)+13.6(2) 

 = 90.6 ft-kip 



Foundation Design 

Overturning 

The overturning moment due to wind with a typical bay of 14 feet wide is as follows:

Mwind = (-31,841ft-lb/lf)(14 ft)

 = -445,774 ft-lb 

MFa (1.5) = (1.5)[(1,211lb)(3.9 ft) + (2)(1,303 lb)(3.9 ft/2)]

 = -14,707 ft-lb

Mo = -445,774 ft-lb - 14,707 ft-lb

 = -460,481 ft-lb 

In this example, it is assumed that the home and the foundation slab are reasonably symmetrical 
and uniform; therefore, it is assumed the center of gravity for the dead loads is at the center 
of the bay.

Dead Load at perimeter columns 

Dext = (474 lb/ft)(14 ft)(2 columns) 

 = 13,272 lb

Dead Load at an interior column: 

Dint = (14 ft)(14 ft)(8 psf) 

 = 1,568 lb

Dead Load of 3 columns: (3)(8 ft)(1.33 ft x 1.33 ft)(150) lb cubic ft

 = 6,368 lb 

Assume that only the grade beams are sufficiently reinforced to resist overturning (neglect 
weight of slab)

Dead Load of the grade beams (area)(depth) (density of concrete)
[(28 ft x3ft) +(3)((11 ft)(3 ft)](4 ft)(150 lb cubic ft) = 109,800 lb 

Summing the Dead Loads = 13,272+1,568+6,368+109,800 = 131,008 lb

Allowable Dead Load Moment of 60%

Md = (0.6)( 131,008 lb)(14 ft) 

 = 1,100,476 ft-lb 

Since Mot = 460,481 ft-lb is very much less than 0.6 Md = 1,100,476 ft-lb, the foundation can be 
assumed to resist overturning.



Sliding 

The maximum total lateral load of wind and flood acting on the entire typical bay is as follows:

 Lwfa = W + 1.5 Fa 

 = [(14 ft (868 lb/ ft) + 1.5(7,203 lb)] 

 = 23,375 lb

Sliding Resistance = (tanF)N + Passive Resistance at Vertical Foundation Surfaces 

F = internal angle of soil friction, assume F = 25 degrees 

N = net normal force (building weight - uplift forces)

N = (131,008) + (14 ft)[((16 ft)(-21 psf )+(14 ft)(-36 psf)+(2 ft)(-65psf)]

 = 117,428 lb

Ignore passive soil pressure 

Dead Load Sliding Resistance = (tan 25)(117,428 lb) 

 = 54,758 lb 

Since Lwfa = 23,371 lb is less than 60% of Dead Load Sliding Resistance = 54,758, the foundation 
can be assumed to resist sliding.

Soil Bearing Pressure

The simplified approach for this mat foundation assumes that only the grade beams carry loads 
to the soil, the slab between grade beams is not considered to contribute support. It is further assumed 
that the bearing pressure is uniform in the absence of wind and flood loading. The areas 
of the grade beams along the outboard column lines, in the direction of the flow of wind and 
flood, are considered the critical areas of the grade beam. The load combination table below 
indicates the bearing pressures for the ASCE 7- 02 load combinations for the critical grade beam 
area. These load combinations are calculated to ensure that downward forces of the wind and 
flood moment couple do not overstress the soil. The factored dead load moment that resists 
overturning is of a magnitude such that there is no net uplift along critical grade beams. 

Self Weight of 1 square of foot Grade Beam = (4 ft)(150 lb/cubic ft) = 650 psf 

Area of Critical Grade Beam = [(3ft)(14 ft)] + [(3 ft)(5.5 ft)]

 = 58.5 ft2

Weight of Critical Grade Beam = (58.5 ft2)(4 ft)( 150 lb/cubic ft) 

 = 35,100 lb

Critical Column Uplift = 12,541 lb (load combination 7)



Verification of Uplift Resistance = [35,100 lb(0.6)]  12,541 lb

 = 8,519 lb (positive load, no uplift) 

Presumptive Allowable Bearing Pressure = 1,500 psf

Table D-4. Foundation Bearing Pressures Typical Bay (for three rows of columns per bay)

ASCE 7-02 Load Combination

Combined Loads (lb)

Bearing Pressures (psf)

#1 D + F

8,080

8,090  58.5 + 650 = 788

#2 D + F + L

14,940

14,950  58.5 + 650 = 905

#3 D + F + Lr

12,000

12,000  58.5 + 650 = 855

#4 D + F + 0.75(L) + 0.75(Lr)

16,165

16,165  58.5 + 650 = 926

#5 D + F + W + 1.5(Fa)

28,104

28,104  58.5 + 650 = 1,130

#6 D + F + 0.75(W) + 0.75(L) + 
0.75(Lr) + 1.5(Fa)

29,982

29,982  58.5 + 650 = 1,163

#7 0.6D + W + 1.5(Fa)

23,051

23,051  58.5 + 650 = 1,044

#8 0.6D

5,255

5,255  58.5 + 650 = 740





Where 

D = Dead Load

F = Load due to fluids with well-defined pressures and maximum heights 
(See Section D.2 for additional information)

Fa = Flood Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

NOTE: The maximum bearing pressure is in bold (1,163 psf) and is less than the assumed 1,500 
psf bearing pressure.

Design of Concrete members per ACI-318-02 Code & ASCE 7-02; Sections 2.3.2 and 2.3.3-1 

Column Design 

Verify that 16-inch x 16-inch column design is adequate.

Concrete strength = 4,000 psi 



Reinforced with (4) #8 bars, grade 60 reinforcing, with 2-inch clear cover 

Note: 1,000 lbs = 1.0 kip 

Assume that the total wind load distributed through the floor uniformly to 3 columns. 

Check combined axial and bending strength:

Ultimate Moment wind + fdyn = (1.6)[(8 ft)((14 ft)(868 lb/ft)/(3))] + (2.0)[(3.9 ft/2)(1,303) 
lb)]

 = 51,849 ft-lb + 5,082 ft-lb

 = 56,931 ft-lb  1,000 lb/kip = 56.9 ft-kip 

Ultimate Moment wind + fbrkp = (51,849 ft-lb) + (2.0)[(1,211 lb)(3.9 ft)] 

 = 61,295 ft-lb  1,000 lb/kip = 61.3 ft-kip 

Ultimate Moment wind + fbrkp + debris = 61.3 ft-kip + (2.0)(3.5 kip)(3.9 ft)

 = 88,6 ft-kip 

Maximum Factored Moment = 88.6 ft-kip = 1,063 in kip 

Refer to Table D-3, conservatively assume flood load factor of 2.0 for all axial loads 

Maximum factored Axial Compression = (2.0)(30.0 kip) = 60.0 kip 

Maximum factored Axial Tension = (2.0)(12.5 kip) = 25.0 kip 

Based on a chart published by the Concrete Reinforced Steel Institute (CRSI), the maximum allowable 
moment for the column = 1,092 in kip for 0 axial load and 1,407 in kip for 102 kip axial 
load; therefore, the column is adequate.

Check Shear strength:

Critical Shear = wind + Fdyn + Fi

Ultimate Shear = Vu = [(14 ft)(.868 kip)(1/3)](1.6) + [(1.3 kip)+(3.5 kip](2.0) 

 = Vu = 16.0 kips

As the maximum unit tension stress is only 25.0 kips/16 in x16 in = .098 kip/in2 and the maximum 
axial compression stress is only 60.0 kips/16 in x 16 in = .234 kip/in2, we can conservatively 
treat the column as a flexural member or beam. The allowable shear of the concrete section 
then, per ACI-318-02 11.3.1.1, 11.3.1.3, and 11.5.5.1 with minimum shear reinforcing (tie/stirrup), 
would be as follows. 

Allowable Shear = Vc = (0.75)(16 in-2.5 in)(16 in )(2)(4,000 psi)1/2 (1/1,000) = 20.5 kips



The shear strength of the column is adequate with minimum shear reinforcement.

The minimum area of shear, Av, per ACI 318-02, 11.5.5.3 would be:

Av = (50)(width of member)(spacing of reinforcing)/yield strength 
of reinforcing 

 = (50)(16 in)(16 in)/(60,000 psi) = .21 in2

2 pieces of # 4 bar As = (2)(.2) = .40 in2 

Use of #4 bar for column ties (shear reinforcement) is adequate.

Check spacing per ACI -318-02, 7.10.4

16 diameter of vertical reinforcing bar = (16)(1 in) = 16 in 

48 diameter of column tie bar = (48)(1/2 in) = 24 in

Least horizontal dimension = 16 in 

Therefore, #4 ties at 16 inch on center are adequate. 

The column design is adequate. 

Grade Beam Design 

The size of the grade beam was configured to provide adequate bearing area, resistance to 
uplift, a reasonable measure of protection from damaging scour, and to provide a factor of redundancy 
and reserve strength should the foundation be undermined. A grade beam 36-inches 
wide and 48-inches deep was selected.

Maximum Bearing Pressure = 1,163 psf = 1.2 ksf (kip/square foot) 

Assume a combined load factor of 2.0 (for flood)

Check Shear strength:

Maximum Factored Uniform Bearing Pressure = wu = (2.0) (3.0 ft )(1.2 ksf) = 7.2 kips/ft 

Maximum Factored Shear = Vu = (7.2 kips/ft)(14 ft/2) = 50.0 kips

Allowable Shear without minimum shear reinforcing (stirrups) = Vc/2

Vc/2= (0.75)(36 in)(48 - 3.5 in)(63 psi)(1/1,000) = 75.7 kips

Use nominal #4 two leg stirrups at 24-inch on center 

Check flexural strength: Assume simple span condition

Maximum Factored Moment = Mu = (7.2 kips/ft)(14 ft)2 (1/8) = 176 ft-kip



Concrete strength = 4,000 psi 

Reinforcement grade = 60,000 psi

Try (4) #6 reinforcing bar continuous top and bottom 

As = (4)(0.44 in2) = 1.76 in2 top or bottom

total As = (2)(1.76) = 3.52 in2 

Reinforcement ratio (.) 

. = As  [(section width)(section depth- clear cover-  bar diameter)] 

. = As  [(bw)(d)] 

. = (1.76 in2)  [(36)(48 - 3 - 0.375)] 

. = 0.01096 

One method of calculating the moment strength of a rectangular beam, for a given section and 
reinforcement, is illustrated in the 2002 edition of the CRSI Design Handbook. Referencing 
page 5-3 of the handbook, the formula for calculating the moment strength can be written as 
follows: 

FMn = (F)[((As)(fy)(d))  (((As)(fy))  ((0.85)(f 'c)(width of member)(2)))]

FMn = (0.9)[((1.76)(60000)(44.63))  (((1.76)(60,000))  ((0.85)(4,000)(36)(2)))]

 = 4,241,634 in lb  12000 = 353 ft-kip

F = 0.9 

Area of reinforcing steel (As) minimum flexural 

= (0.0033)(24)(44.63) 

= 3.6 in2

or 

(1.33) (As required by analysis) = FMn is much greater than Mu

Area of steel for shrinkage and temperature required = (.0018)(48)(36) = 3.1 in2 

Total Area of steel provided = (8) #6 = (8)(0.44) = 3.52 in2 adequate 

Therefore, the grade beam design is adequate, use (4) #6 reinforcing bar continuous on the top 
and bottom with #4 stirrups at 24-inch spacing.



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


E. Cost Estimating

E- 



COST ESTIMATING E

E- 

Breakdown of Foundation Costs

Foundation Type

Average Foundation 
Costs ($)

Elevation Above Grade

Unit Costs per Square 
Foot (sf)

Open

Case A: Timber Pile

13,536

0 to 5

11

17,554

5 to 10

15

22,720

10 to 15

19

Not Evaluated

Above 15



Case B: Steel Pipe Pile with Concrete 
Column and Grade Beam

32,500

0 to 5

27

36,024

5 to 10

30

37,500

10 to 15

31

Not Evaluated

Above 15



Case C: Timber Pile with Concrete 
Column and Grade Beam

31,700

0 to 5

26

36,288

5 to 10

30

37,900

10 to 15

32

Not Evaluated

Above 15



Case D: Concrete Column and Grade 
Beam

13,500

0 to 5

11

16,860

5 to 10

14

18,500

10 to 15

15

Not Evaluated

Above 15



Case G: Concrete Column and Grade 
Beam with Slabs

18,000

0 to 5

15

21,847

5 to 10

18

24,000

10 to 15

20

Not Evaluated

Above 15

Closed

Case E: Reinforced Masonry 
- Crawlspace

12,254

0 to 4

10

14,000

4 to 8

12

Case F: Reinforced Masonry - Stem 
Wall

12,458

0 to 4

10





NOTES

1. This rough order of magnitude (ROM) cost estimate is based upon May 2006 figures for concrete, labor, equipment, 
and materials. Variations due to labor/equipment/materials shortages are anticipated and should be taken into account 
when using these costs.

2. Costs presented herein should not be construed to represent actual costs to the homebuilder, but should be utilized as 
an order of magnitude estimate only. 

3. Pile driving mobilization/demobilization can be reduced if several homes are constructed at the same time in the same 
area, thereby realizing an economy of scale. 



E COST ESTIMATING 

E- 

Building on strong and safe foundations

 4. Costs presented are based upon the general designs in this document. A 1,200 sf footprint for a single-story home at 
an assumed 130-mph wind speed, elevated to the average height for that foundation, is the basis for the estimates. 
When differences in elements of construction occur, such as number of piles or amount of concrete, an alternate cost 
is presented. The cost estimate presented represents the conservative approach to the designs in this document. If 
value engineering, different materials, or a more cost-effective design are implemented, these costs may be reduced. 

5. Costs presented herein include applicable taxes, contractor general and home office overhead, profit, and other subtier 
contract costs. 

6. Concrete costs, unless otherwise noted, include bracing, reinforcing, formwork, finishing (if necessary), and mobilization 
and demobilization of the contractor. Due to the anticipated shortage of skilled labor for concrete, variability in this 
area should be anticipated.

7. Costs experienced by the builder or contractor will be dependent upon contract agreements, local price variations in 
labor, material, equipment, and availability.

8. Costs for steel are highly variable and dependent upon supply. Variability in costs for steel should be anticipated. Costs 
for steel include materials and labor for installation.

9. Costs for block in closed foundations is based upon standard natural gray medium weight masonry block walls, including 
blocks, mortar, typical reinforcing, normal waste, and walls constructed with 8 x 8 x 16 blocks laid in running bond. 
Add for grouting cores poured by hand to 4 foot heights.



Case A: Timber Pile



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of Piles

Length 
of Piles 
Driven

Total lf to 
drive

Subtotal 

Site Prep

ls







500.00







$500

Minimum job 
charge for Driving

ls







5,000.00







$5,000

Number of Piles: 60

Over 30 to 40 
(800 lf per day)

lf

3.3

1.7

0.9

5.90

60

30

1,800

$10,620

Bolts and 
Miscellaneous

Per 
Column







15.00

60





$900

Wood Pile 
Connection to 
House

Per Pile







55.00

60





$3,300

Galvanized 
Bracing Rod and 
Turnbuckles

Per Pile







40.00

60





$2,400

Total for Piles















$22,720

Number of Piles: 42

Over 30 to 40 
(800 lf per day)

lf

3.3

1.7

0.9

5.90

42

30

1260

$7,434

Bolts and 
Miscellaneous

Per 
Column







15.00

42





$630

Wood Pile 
Connection to 
House

Per Pile







55.00

42





$2,310

Galvanized 
Bracing Rod and 
Turnbuckles

Per Pile







40.00

42





$1,680

Total for Piles















$17,554

Number of Piles: 28

Over 30 to 40 
(800 lf per day)

lf

3.3

1.7

0.9

5.90

28

30

840

$4,956

Bolts and 
Miscellaneous

Per 
Column







15.00

28





$420

Wood Pile 
Connection to 
House

Per Pile







55.00

28





$1,540

Galvanized 
Bracing Rod and 
Turnbuckles

Per Pile







40.00

28





$1,120

Total for Piles















$13,536





ls = lump sum lf = linear foot



Case B: Steel Pipe Pile/Concrete Column/Grade Beam

Site Prep

ls







500.00







$500

Minimum job 
charge for 
Driving

ls







5,000.00







$5,000

Steel Piles Driven



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of Piles

Length of 
Piles

Total lf 
to drive

Subtotal 

Steel Piles 
Driven

lf

11

3.1

0.9

15.00

28

30

840

$12,600

Bolts and 
Miscellaneous

Per 
Column







25.00

28





$700

Total for Piles

$13,300

Concrete Grade Beam



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy

Equip-
ment 
Charge



Subtotal 

Soil Excavation, 
Medium 
material, 75 cy 
per hour (57 
m3/hr)

cy

--

0.54

1.29

1.83

55

500



$601

Grade beams

cy

225

22

7.5

254.50

32





$8,144

Steel

ea







100.00

32





$3,200

Total for Grade Beams

$11,945

Concrete Columns @ 10 feet



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy/
Columns

Number 
of 
Columns



Subtotal 

18 (46 cm) 
square or round 
columns

cy

225

35

7.5

267.50

0.74

12



$2,375

Steel

Column







150.00



12



$1,800

Anchors

Column







49.55



12



$595

Angles

Column







42.45



12



$509

Subtotal for Concrete Columns













$5,279

Total for Case B

$36,024





ls = lump sum lf = linear foot cy = cubic yard ea = each



Case C: Timber Pile/Concrete Column/Grade Beam 



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number of 
Piles

Length of 
Piles

Total lf 
to Drive

Site Prep

ls

500.00







Minimum job 
charge for 
Driving

ls







5,000.00







Timber Piles Driven

Number of Wooden Piles: 42

Over 30 to 40 
(800 lf per day)

lf

3.3

1.7

0.9

5.90

42

30

1,260

Bolts and 
Miscellaneous

Per 
Column

15.00

42

Total for Piles

Concrete Grade Beam



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy

Equipment 
Charge

Soil Excavation, 
Medium 
material, 75 cy 
per hour (57 
m3/hr)

cy

--

0.54

1.29

1.83

55

500

Grade beams

cy

225

22

7.5

254.50

32

Steel

ea

100.00

32

Total for Grade Beams

Concrete Columns including Pile Caps @ 10 feet



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy/
Columns

Number of 
Columns



18 (46 cm) 
square or round 
columns

cy

225

35

7.5

267.50

0.74

12

Steel

Column

150.00

12

Anchors

Column

49.55

12

Angles

Column

42.45

Subtotal for Concrete Columns

Grand Total for Foundation Shown





ls = lump sum lf = linear foot cy = cubic yard ea = each 



Case D: Concrete Column/Grade Beam



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy

Equipment 
Charge

Subtotal 

Soil 
Excavation, 
Medium 
material, 75 cy 
per hour (57 
m3/hr)

cy

--

0.54

1.29

1.83

50

500

$592

Grade beams

cy

225

22

7.5

254.50

31

$7,890

Steel

ea

100

31

$3,100

Total for Grade Beams

$11,582

Concrete Columns @ 10 feet Elevation



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy per 
Column

Number of 
Columns

Subtotal 

18 (46 cm) 
square or 
round columns

cy

225

35

7.5

267.50

0.74

12

$2,375

Steel

Column

150.00

12

$1,800

Anchors

Column

49.55

12

$595

Angles

Column

42.45

12

$509

Subtotal for Concrete Columns

$5,279

Grand Total for Foundation Shown

$16,861





cy = cubic yard



Case G: Concrete Column/Grade Beam with Slab



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy

Equipment 
Charge

Subtotal 

Soil 
Excavation, 
Medium 
material, 75 cy 
per hour (57 
m3/hr)

cy

--

0.54

1.29

1.83

75

500

$637

Interior 
Concrete

cy

225

35

7.50

267.50

15

$4,013

Grade Beams

cy

225

35

7.50

267.50

31

$8,293

Steel

ea

100.00

31

$3,100

WWF

ea

35.00

15

$525

Total for Grade Beams

$16,568

Concrete Columns @ 10 feet Elevation



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy per 
Column

Number of 
Columns

Subtotal 

18 (46 
cm) square 
or round 
columns

cy

225

35

7.50

267.50

0.74

12

$2,375

Steel

Column

150

12

$1,800

Anchors

Column

49.55

12

$595

Angles

Column

42.45

12

$509

Subtotal for Concrete Columns

$5,279

Grand Total for Foundation Shown

$21,847





cy = cubic yard ea = each 




Case E: Reinforced Masonry

Crawlspace



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy

Equipment 
Charge

Subtotal 

Soil Excavation, 
Medium 
material, 75 cy 
per hour (57 
m3/hr)

cy

--

0.68

1.43

2.11

24

500

$551

Footings

cy

225

22

7.5

254.50

20



$5,090

Steel

cy







100.00

20



$2,000

Total for Footings (not including steel)

$5,641

Concrete Columns @ 4 feet



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy per 
Column

Number of 
Columns

Subtotal 

16 (46 cm) 
square or round 
columns piers

cy

225

35

7.5

267.50

0.40

6

$642

Steel

Column







150.00



6

$900

Anchors

Column







49.55



6

$297

Angles

Column







42.45



6

$255

Subtotal for Concrete Columns

$2,094

Concrete Walls



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of sf



Subtotal 

Concrete Block 
Walls

sf

5.23

4.53

1

10.76

420



$4,519

Grand Total for Foundation Shown (Footings + Concrete Columns + Concrete Walls) 

$12,254





cy = cubic yard sf = square foot



Case F: Reinforced Masonry Stem Wall



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of cy

Equipment 
Charge

Subtotal 

Soil 
Excavation, 
Medium 
material, 75 cy 
per hour (57 
m3/hr)

cy

--

0.54

1.29

1.83

34

500

$562

Footings

cy

225

22

7.5

254.50

20

$5,090

Steel

cy

100.00

20

$2,000

Bracing

ls

$1,500

Backfill

cy

4

0.6

1.45

6.05

130

$787

Total for Stem Wall Footings

$9,152

Concrete Walls



Unit of 
Measure

Material

Labor

Equip.

Subtotal

Number 
of sf



Subtotal 

Concrete 
Block Walls

sf

5.23

4.53

1

10.76

420

$4,519

Grand Total for Foundation Shown

$13,671





cy = cubic yard ls = lump sum sf = square foot



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


F. Referenced Fact Sheets 
from FEMA 499

Fact Sheet No. Title 

 1 Coastal Building Successes and Failures

 2 Summary of Coastal Construction Requirements and Recommendations

 4 Lowest Floor Elevation

 5 V-Zone Design and Construction Certification

 6 How Do Siting and Design Decisions Affect the Owner's Costs?

 7 Selecting a Lot and Siting the Building

 8 Coastal Building Materials

 9 Moisture Barrier Systems

 11 Foundations in Coastal Areas

 12 Pile Installation 

F- 



F REFERENCED FACT SHEETS FROM FEMA 499

F- 

Building on strong and safe foundations

 13 Wood-Pile-to-Beam Connections

 14 Reinforced Masonry Pier Construction

 15 Foundation Walls

 16 Masonry Details

 26 Shutter Alternatives

 27 Enclosures and Breakaway Walls

 29 Protecting Utilities



Coastal Building Successes 
and Failures


Technical Fact Sheet No. 1

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 1  Coastal Building Successes and Failures Home Builders Guide to Coastal Construction 08/05 

Page of 3

Purpose: To discuss how coastal construction requirements are different from those for inland construction. 
To discuss the characteristics that make for a successful coastal building.

Is Coastal Construction That Different From Inland Construction?

The short answer is yes, building in a coastal environment is different from building in an inland area:

 Flood levels, velocities, and wave action in coastal areas tend to make coastal flooding more damaging 
than inland flooding.

 Coastal erosion can undermine buildings and destroy land, roads, utilities, and infrastructure.

 Wind speeds are typically higher in coastal areas and require stronger engineered building connections and 
more closely spaced nailing of building sheathing, siding, and roof shingles.

 Wind-driven rain, corrosion, and decay are frequent concerns in coastal areas.

In general, homes in coastal areas must be 
designed and built to withstand higher loads 
and more extreme conditions. Homes in 
coastal areas will require more maintenance 
and upkeep. Because of their exposure to 
higher loads and extreme conditions, homes 
in coastal areas will cost more to design, 
construct, maintain, repair, and insure.

Building Success

In order for a coastal building to be considered 
a success, four things must occur:

 The building must be designed to withstand 
coastal forces and conditions.

 The building must be constructed as designed.

 The building must be sited so that erosion 
does not undermine the building or render it 
uninhabitable.

 The building must be maintained/repaired.

A well-built but poorly sited building can be 
undermined and will not be a success (see 
Figure 1). Even if a building is set back or 
situated farther from the coastline, it will not 
perform well (i.e., will not be a success) if it 
is incapable of resisting high winds and other 
hazards that occur at the site (see Figure 2).


Figure 1. Well-built but poorly sited building. 


Figure 2. Well-sited building that still sustained damage.



Page of 3

FS No. 1  Coastal Building Successes and Failures Home Builders Guide to Coastal Construction 08/05 

What Should Owners and Home Builders Expect From a Successful Coastal Building?

In coastal areas, a building can be considered a success only if it is capable of resisting damage 
from coastal hazards and coastal processes over a period of decades. This statement does not imply 
that a coastal residential building will remain undamaged over its intended lifetime. It means that the 
impacts of a design-level flood, storm, wind, or erosion event (or series of lesser events with combined 
impacts equivalent to a design event) will be limited to the following:

 The building foundation must remain intact and functional.

 The envelope (walls, openings, roof, and lowest floor) must remain structurally sound and capable of 
minimizing penetration by wind, rain, and debris.

 The lowest floor elevation must be sufficient to prevent floodwaters from entering the elevated 
building envelope during the design event.

 The utility connections (e.g., electricity, water, sewer, natural gas) must remain intact or be restored 
easily.

 The building must be accessible and usable following a design-level event.

 Any damage to enclosures below the Design Flood Elevation (DFE)* must not result in damage to the 
foundation, the utility connections, or the elevated portion of the building.

Recommended Practice


1

Siting  Site buildings away from 
eroding shorelines and high-hazard 
areas.

Building Form  Flat or low-sloped 
porch roofs, overhangs, and gable 
ends are subject to increased 
uplift in high winds. 
Buildings that are 
both tall and narrow 
are subject to 
overturning. Each of 
these problems can 
be overcome through 
the design process, 
but each must receive 
special attention. In 
the design process, 
chose moderate-sloped 
hip roofs (4/12 to 
6/12) if possible.

Lowest Floor Elevation  
Elevate above the DFE the bottom of the lowest horizontal structural member supporting the lowest 
floor. Add freeboard to reduce damage and lower flood insurance premiums.

Free of Obstructions  Use an open foundation. Do not obstruct the area below the elevated portion 
of the building. Avoid or minimize the use of breakaway walls. Do not install utilities or finish enclosed 
areas below the DFE (owners tend to convert these areas to habitable uses, which is prohibited under 
the National Flood Insurance Program and will lead to additional flood damage and economic loss).

Foundation  Make sure the foundation is deep enough to resist the effects of scour and erosion; 
strong enough to resist wave, current, flood, and debris forces; and capable of transferring wind and 
seismic forces on upper stories to the ground.

2

3

4

5

*The DFE is the locally mandated flood elevation, which will be equal to or higher than the Base Flood Elevation (BFE). The BFE is 
the expected elevation of flood waters and wave effects during the 100-year flood (also known as the Base Flood).



Connections  Key connections include roof sheathing, roof-to-wall, wall-to-wall, and walls-to-foundation. Be 
sure these connections are constructed according to the design. Bolts, screws, and ring-shanked nails are 
common requirements. Standard connection details and nailing should be identified on the plans.

Exterior Walls  Use structural sheathing in high-wind areas for increased wall strength. Use tighter 
nailing schedules for attaching sheathing. Care should be taken not to over-drive pneumatically driven 
nails. This can result in loss of shear capacity in shearwalls.

Windows and Glass Doors In high-wind areas, use windows and doors capable of withstanding 
increased wind pressures. In windborne debris areas, use impact-resistant glazing or shutters.

Flashing and Weather Barriers Use stronger connections and improved flashing for roofs, walls, doors, 
and windows and other openings. Properly installed secondary moisture barriers, such as housewrap or 
building paper, can reduce water intrusion from wind-driven rain.

Roof  In high-wind areas, select appropriate roof coverings and pay close attention to detailing. Avoid 
roof tiles in hurricane-prone areas.

Porch Roofs and Roof Overhangs  Design and tie down porch roofs and roof overhangs to resist uplift 
forces.

Building Materials  Use flood-resistant materials below the DFE. All exposed materials should be 
moisture- and decay-resistant. Metals should have enhanced corrosion protection.

Mechanical and Utilities  Electrical boxes, HVAC equipment, and other equipment should be elevated 
to avoid flood damage and strategically located to avoid wind damage. Utility lines and runs should be 
installed to minimize potential flood damage.

Quality Control Construction inspections and quality control are essential for building success. Even 
minor construction errors and defects can lead to major damage during high-wind or flood events. 
Keep this in mind when inspecting construction or assessing yearly maintenance needs.

Recommended practice and guidance concerning the topics listed above can be found in the documents 
referenced in these fact sheets and in many trade publications (e.g., the Journal of Light Construction, http://
www.jlconline.com).

Will the Likelihood of Success (Building 
Performance) Be Improved by Exceeding Minimum 
Requirements?

States and communities enforce regulatory requirements that 
determine where and how buildings may be sited, designed, 
and constructed. There are often economic benefits to 
exceeding the enforced requirements (see box). Designers 
and home builders can help owners evaluate their options 
and make informed decisions about whether to exceed these 
requirements.

*Note: Flood insurance premiums can be reduced up to 60 percent by exceeding minimum siting, design, and construction practices. 
See the V-Zone Risk Factor Rating Form in FEMAs Flood Insurance Manual (http://www.fema.gov/nfip/manual.shtm).

6

7

8

9

10

11

12

13

14

Benefits of Exceeding Minimum 
Requirements

 Reduced building damage during 
coastal storm events

 Reduced building maintenance

 Longer building lifetime

 Reduced insurance premiums*

 Increased reputation of builder



Summary of Coastal Construction 
Requirements and 
Recommendations


HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

Technical Fact Sheet No. 2

FS No. 2  Summary of Requirements and Recommendations Home Builders Guide to Coastal Construction 08/05

Page of 8

Purpose: To summarize National Flood Insurance Program (NFIP) regulatory requirements concerning coastal 
construction and provide recommendations for exceeding those requirements in some instances.

Key Issues

 New construction* in coastal flood hazard areas (V zones and A zones) must meet minimum NFIP and 
community requirements. Repairs, remodeling, and additions must meet community requirements and may 
also be subject to NFIP requirements.

 NFIP design and construction requirements are more stringent in V zones than in A zones, in keeping with 
the increased flood, wave, floodborne debris and erosion hazards in V zones. 

 Some coastal areas mapped as A zones may be subject to damaging waves and erosion (these areas 
are often referred to as Coastal A Zones). Buildings in these areas constructed to minimum NFIP A-
zone requirements may sustain major damage or be destroyed during the Base Flood. It is strongly 
recommended that buildings in A zones subject to breaking waves and erosion be designed and constructed 
to V-zone standards.

 Buildings constructed to minimum NFIP A-zone standards and subject solely to shallow flooding without the 
threat from breaking waves and erosion will generally sustain only minor damage during the Base Flood.

 Following the recommendations in the table below will result in lower damage to the building and reduced 
flood insurance premiums (see the V-Zone Risk Factor Rating Form in FEMA's Flood Insurance Manual 
(http://www.fema.gov/nfip/manual.shtm).

* For floodplain management purposes, new construction means structures for which the start of construction began on or after the 
effective date of a floodplain management regulation adopted by a community. Substantial improvements, repairs of substantial 
damage, and some enclosures must meet most of the same requirements as new construction.

The following tables summarize NFIP regulatory requirements and recommendations for exceeding those 
requirements for both (1) new construction and (2) repairs, remodeling, and additions.

Requirements and Recommendations for New Constructiona



FS No. 2  Summary of Requirements and Recommendations Home Builders Guide to Coastal Construction 08/05

Page of 8



Requirements and Recommendations for Repairs, Remodeling, and Additions



Notes

a Prohibited and Allowed refer to the minimum NFIP regulatory requirements; individual states 
and communities may enforce more stringent requirements that supersede those summarized 
here. Exceeding minimum NFIP requirements will provide increased flood protection and may 
result in lower flood insurance premiums.

b In these areas, buildings are subject to flooding conditions similar to, but less severe than, those 
in V zones. These areas can be subject to breaking waves = 1.5 feet high (which can destroy 
conventional wood-frame and unreinforced masonry wall construction) and erosion (which can 
undermine shallow foundations).

c In these areas, buildings are subject to flooding conditions similar to those in riverine A zones.

d Some coastal communities require open foundations in A zones.

e State or community may require freeboard or regulate to a higher elevation (e.g., Design Flood 
Elevation (DFE)).

f Some coastal communities prohibit breakaway walls and allow only open lattice or screening.

g If an area below the BFE in an A-zone building is fully enclosed by breakaway walls, the walls must 
meet the requirement for openings that allow equalization of hydrostatic pressure.

h Placement of nonstructural fill adjacent to buildings in coastal AO zones is not recommended.

i There are some differences between what is permitted under floodplain management regulations 
and what is covered by NFIP flood insurance. Building designers should be guided by floodplain 
management requirements, not by flood insurance policy provisions. For more information, see 
Section 9.3.1.1 in Chapter 9 of FEMAs Coastal Construction Manual (FEMA 55).

j Walls below BFE must be designed and constructed as breakaway walls that meet the minimum 
requirements of the NFIP regulations. For more information, see Section 6.4.3.3 in Chapter 6 of 
FEMAs Coastal Construction Manual (FEMA 55).

k Consult with authority having jurisdiction (AHJ) regarding more restrictive requirements for repairs, 
remodeling, and additions.

l NFIP requirements for new construction in V zones include those pertaining to Design and 
Construction, Flood-Resistant Materials, Siting, Foundations, Lowest Floor Elevation, Enclosures 
Below the BFE, Free of Obstructions, Utilities, and Certifications.

m NFIP requirements for new construction in A zones include those pertaining to Design and 
Construction, Flood-Resistant Materials, Siting, Foundations, Foundation Openings, Lowest Floor 
Elevation, Enclosures Below the BFE, Utilities, and Certifications.

n An addition in the form of an attached garage would not have to be elevated to or above the BFE, 
because its use (parking) would be allowed below the BFE; however, it would have to meet other 
NFIP requirements for new construction in V zones.

o An addition in the form of an attached garage would not have to be elevated to or above the BFE, 
because its use (parking) would be allowed below the BFE; however, it would have to meet other 
NFIP requirements for new construction in A zones.



Lowest Floor 

Elevation


Technical Fact Sheet No. 4

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 4  Lowest Floor Elevation Home Builders Guide to Coastal Construction 08/05 

Page of 4

Purpose: To discuss benefits of exceeding the National Flood Insurance Program (NFIP) minimum elevation 
requirements, to point out common construction practices that are violations of NFIP regulations and result in 
significantly higher flood insurance premiums, and to discuss the NFIP Elevation Certificate. 

Why Is the Lowest Floor Elevation Important?

In inland areas, experience has shown that floods damage areas of buildings not elevated above the flood 
level and destroy contents of those areas. In coastal areas, wave action causes even more damage, often 
destroying enclosed building areas below the flood level (and any building areas above the flood level that 
depend on the lower area for structural support). Once waves rise above the lowest structural member in a V 
zone or coastal A zone, the elevated portion of the building is likely to be severely damaged or destroyed.

Recommended Lowest Floor Elevations*

Because of the additional hazard associated with wave action in V zones and in A zones in coastal areas, 
it is recommended that the minimum elevation requirements of the NFIP be exceeded in these areas:

 It is recommended that the bottom of the lowest horizontal structural member of V-zone buildings be 
elevated 1 foot or more above the Base Flood Elevation (BFE), i.e., add freeboard. 

 It is recommended that the lowest horizontal structural member of A-zone buildings in coastal areas 
be elevated 1 foot or more above the BFE (i.e., add freeboard).

*NFIP minimum elevation requirements: A zone  elevate top of lowest floor to or above BFE; V zone  elevate bottom of 
lowest horizontal structural member to or above BFE. In both V and A zones, many people have decided to elevate a full story 
for below-building parking, far exceeding the elevation requirement. See Fact Sheet No. 2 for more information about NFIP 
minimum requirements in A and V zones.



FS No. 4  Lowest Floor Elevation Home Builders Guide to Coastal Construction 08/05 

Page of 4

What Does FEMA Consider the Lowest Floor?

 The lowest floor means the lowest floor of the lowest enclosed area, except for unfinished or flood-
resistant enclosures used solely for parking of vehicles, building access, or storage.

 If the lowest enclosed area is used for anything other than parking of vehicles, building access, or storage, 
the floor of that area is considered the lowest floor. This will violate NFIP requirements and drastically 
increase flood insurance premiums.

 Note that any below-BFE finished areas, including foyers, will violate NFIP requirements, sustain unreimbursable 
flood damage, and increase flood insurance premiums. 

 The floor of a basement (where basement means the floor is below grade on all sides) will always be the 
lowest floor, regardless of how the space is used.

 Walls of enclosed areas below the BFE must meet special requirements in coastal areas (see Fact Sheet No. 27). 

Construction Practices and the Lowest Floor

Setting the lowest floor at the correct elevation is critical. Failure to do so can result in a building being 
constructed below the BFE. As a result, work can be stopped, certificates of occupancy can be withheld, and 
correcting the problem can be expensive and time-consuming. 

 After piles have been installed, the intended elevation of the lowest floor should be checked before the piles 
are cut off.

 Alternatively, after piers or columns have been constructed, the intended elevation of the lowest floor should 
be checked before the lowest horizontal structural supporting members are installed.

 After the lowest horizontal structural supporting members have been installed, the elevation should be 
checked again, before any further vertical construction is carried out.

Do not modify building plans to create habitable space below the intended lowest floor. Doing so will put the 
building in violation of flood regulations and building codes.

FEMA Elevation Certificate

The NFIP requires participating communities to adopt a floodplain management ordinance that specifies 
minimum requirements for reducing flood losses. One such requirement is that communities obtain, and 
maintain a record of, the lowest floor elevations for all new and substantially improved buildings. 
The Elevation Certificate (see following pages) provides a way for a community to comply with this requirement 
and for insurers to determine flood insurance premiums.

Most communities require permit applicants to retain a surveyor, engineer, or architect to complete and 
submit the elevation certificate. Note that multiple elevation certificates may need to be submitted for the 
same building: a certificate may be required when the lowest floor level is set (and before additional vertical 
construction is carried out); a certificate will be required upon completion of all construction.

The Elevation Certificate requires that the following information be certified and signed by the surveyor/
engineer/architect and signed by the building owner:

 elevations of certain floors in the building

 lowest elevation of utility equipment/machinery

 floor slab elevation for attached garage

 adjacent grade elevations

 flood opening information (A zones)

The Elevation Certificate is available on FEMAs web site: http://www.fema.gov/nfip/elvinst.shtm



V-Zone Design 
and Construction 
Certification


Technical Fact Sheet No. 5

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 5  V-Zone Design and Construction Certification Home Builders Guide to Coastal Construction 08/05

Page of 2

Purpose: To explain the certification requirements for structural design and construction in V zones. 

Structural Design and Methods of Construction Certification

As part of the agreement for making flood insurance available in a community, the National Flood Insurance 
Program (NFIP) requires the community to adopt a floodplain management ordinance that specifies minimum 
design and construction requirements. Those requirements include a certification of the structural design and 
the methods of construction.

Specifically, NFIP regulations and local floodplain 
management ordinances require that:

1. a registered professional engineer or 
architect shall develop or review the 
structural design, specifications, and 
plans for the construction, and 

2. a registered professional engineer or 
architect shall certify that the design and 
methods of construction to be used are 
in accordance with accepted standards of 
practice for meeting the following criteria:

 the bottom of the lowest horizontal 
structural member of the lowest floor 
(excluding the pilings or columns) is elevated to or above the Base Flood Elevation (BFE); and 

 the pile or column foundation and structure attached thereto is anchored to resist flotation, collapse, 
and lateral movement due to the effects of wind and water loads acting simultaneously on all building 
components. Water loading values used shall be those associated with the Base Flood. Wind loading 
values used shall be those required by applicable 
state or local building standards.

The community, through its inspection procedures, will 
verify that the building is built in accordance with the 
certified design.

Completing the V-Zone Certification

There is no single V-zone certificate used on a nationwide 
basis. Instead, local communities and/or states have 
developed their own certification procedures and documents.

Registered engineers and architects involved in V-zone 
construction projects should check with the authority 
having jurisdiction regarding the exact nature and 
timing of required certifications.

Page 2 shows a sample certification form developed by 
one state. It is intended to show one of many possible 
ways by which a jurisdiction may require that the 
certification and supporting information be provided. In 
this instance, three certifications are included on the 
form (Lowest Floor Elevation, Design and Methods of 
Construction, Breakaway Wall Collapse).


 Lowest Floor Elevation, by a surveyor, 
engineer, or architect (see Fact Sheet No. 4)

 Breakaway Wall Collapse, by a registered 
professional engineer or architect 
(see Fact Sheet No. 27)

The Design and Methods of Construction 
certification should take into consideration 
the NFIP Free-of-Obstruction requirement for 
V zones: the space below the lowest floor must 
be free of obstructions (e.g., free of any building 
element, equipment, or other fixed objects that 
can transfer flood loads to the foundation, or that 
can cause floodwaters or waves to be deflected 
into the building), or must be constructed with 
non-supporting breakaway walls, open lattice, or 
insect screening. (See NFIP Technical Bulletin 
5-93 and Fact Sheet No. 27.) 



Page 2 of 2 FS No. 5  V-Zone Design and Construction Certification Home Builders Guide to Coastal Construction 08/05
Note: The V-zone certificate is not a substitute for and cannot be used without the NFIP Elevation 
Certificate (see Fact Sheet No. 4), which is required for flood insurance rating.

How Do Siting and Design 
Decisions Affect 
the Owners Costs? 


HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 6 
Purpose: To show the effects of planning, siting, and design decisions on coastal home costs. 

Key Issues 

 When building a coastal home, initial, operating, and long-term costs (i.e., life cycle costs) must be considered. 
 Coastal (especially oceanfront) homes cost more to design, construct, maintain, repair, and insure than inland homes. 
 Determining the risks associated with a particular building site or design is important. 
 Siting, designing, and constructing to minimum regulatory requirements do not necessarily result in the 
lowest cost to the owner over a long period of time. Exceeding minimum design requirements costs slightly 
more initially, but can save the owner money in the long run. 
Costs 

A variety of costs should be considered when planning a coastal home, not just the construction cost. Owners 
should be aware of each of the following, and consider how siting and design decisions will affect these costs: 

Initial costs include property evaluation and acquisition costs and the costs of permitting, design, and construction. 

Operating costs include costs associated with the use of the building, such as the costs of utilities and insurance*. 

Long-term costs include costs for preventive maintenance and for repair and replacement of deteriorated or 
damaged building components. 

*Note: Flood insurance premiums can be reduced up to 60 percent by exceeding minimum siting, design, and 
construction practices. See the V-Zone Risk Factor Rating Form in FEMAs Flood Insurance Manual (http:// 
www.fema.gov/nfip/manual.shtm). 

Risk 

One of the most important 
building costs to be 
considered is that resulting 
from storm and/or erosion 
damage. But how can an 
owner decide what level 
of risk is associated with 
a particular building site 
or design? One way is to 
consider the probability of a storm or erosion occurring and the potential building damage that results (see matrix). 


FS No. 6  How Do Siting and Design Decisions Affect the Owners Costs? Home Builders Guide to Coastal Construction 08/05 Page of 2 


Page of 2

FS No. 6  How Do Siting and Design Decisions Affect the Owners Costs? Home Builders Guide to Coastal Construction 08/05

Building sites or designs resulting in extreme or high risk should be avoided  the likelihood of building loss 
is great, and the long-term costs to the owner will be very high. Building sites or designs resulting in medium 
or low risk should be given preference.

Siting

Note that over a long period, poor siting decisions are rarely overcome by building design.

Design

 How much more expensive is it to build near the coast as opposed to inland areas? The table below 
suggests approximately 10 - 30 percent more.

 What about exceeding minimum design requirements in coastal areas? The table suggests that the added 
construction costs for meeting 
the practices recommended in the 
Home Builders Guide to Coastal 
Construction (beyond typical 
minimum requirements) are nominal.



Selecting a Lot and Siting 
the Building


Technical Fact Sheet No. 7

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 7  Selecting a Lot and Siting the Building Home Builders Guide to Coastal Construction 08/05

Page of 2

Purpose: To provide guidance on lot selection and siting considerations for coastal residential buildings.

Key Issues

 Purchase and siting decisions 
should be long-term decisions, 
not based on present-day 
shoreline and conditions.

 Parcel characteristics, 
infrastructure, regulations, 
environmental factors, and owner 
desires constrain siting options.

 Conformance with local/state 
shoreline setback lines does not 
mean buildings will be safe.

 Information about site conditions 
and history is available from 
several sources.

The Importance of Property 
Purchase and Siting 
Decisions

The single most common and 
costly siting mistake made by 
designers, builders, and owners is 
failing to consider future erosion 
and slope stability when an 
existing coastal home is purchased or when land is purchased and a new home is built. Purchase decisions
or siting, design, and construction decisions  based on present-day shoreline conditions often lead to future 
building failures.

Over a long period of time, owners of poorly sited coastal buildings may spend more money on erosion control 
and erosion-related building repairs than they spent on the building itself.

What Factors Constrain Siting Decisions?

Many factors affect and limit a home builders or owners ability to site coastal residential buildings, but the 
most influential is probably parcel size, followed by topography, location of roads and other infrastructure, 
regulatory constraints, and environmental constraints. 

Given the cost of coastal property, parcel sizes are often small and owners often build the largest building 
that will fit within the permissible development footprint. Buyers frequently fail to recognize that siting 
decisions in these cases have effectively been made at the time the land was platted or subdivided, and that 
shoreline erosion can render these parcels unsuitable for long-term occupation. 

In some instances, however, parcel size may be large enough to allow a hazard-resistant coastal building to 
be sited and constructed, but an owners desire to push the building as close to the shoreline as possible 
increases the likelihood that the building will be damaged or destroyed in the future. 


Siting, design, and construction should be considered together 
(see Fact Sheet No. 6), but know that poor lot selection and 
siting decisions can rarely be overcome by improved design and 
construction. Building failures (see Fact Sheet No. 1) are often the 
result of poor siting.



FS No. 7  Selecting a Lot and Siting the Building Home Builders Guide to Coastal Construction 08/05

Page of 2

Coastal Setback Lines  What Protection Do They Provide?

Many states require new buildings to be sited at or landward of coastal construction setback lines, which are 
usually based on long-term, average annual erosion rates. For example, a typical minimum 50-year setback 
line with an erosion rate of 2.5 feet/year would 
require a setback of 125 feet, typically measured 
from a reference feature such as the dune crest, 
vegetation line, or high-water line.

Building at the 125-foot setback (in this case) does 
not mean that a building will be safe from erosion 
for 50 years. 

 Storms can cause short-term erosion that far 
exceeds setbacks based on long-term averages. 

 Erosion rates vary over time, and erosion could 
surpass the setback distance in just a few years 
time. The rate variability must also be known to 
determine the probability of undermining over a 
given time period.

What Should Builders, Designers, and 
Owners Do?

 Consult local and state agencies, universities, and 
consultants for detailed, site-specific erosion and 
hazard information.

 Look for historical information on erosion and 
storm effects. How have older buildings in the area 
fared over time? Use the experience of others to 
guide siting decisions.

 Determine the owners risk tolerance, and reject 
parcels or building siting decisions that exceed 
the acceptable level of risk.

Common Siting Problems

 Building on a small lot between a road and an 
eroding shoreline is a recipe for trouble.

 Odd-shaped lots that force buildings close to 
the shoreline increase the vulnerability of the 
buildings.

 Siting a building near the edge of a bluff 
increases the likelihood of building loss, 
because of both bluff erosion and changes 
in bluff stability resulting from development 
activities (e.g., clearing vegetation, building 
construction, landscaping, changes in surface 
drainage and groundwater flow patterns).

 Siting near a tidal inlet with a dynamic 
shoreline can result in the building being 
exposed to increasing flood and erosion 
hazards over time. 

 Siting a building immediately behind an 
erosion control structure may lead to building 
damage from wave overtopping and may limit 
the owners ability to repair or maintain the 
erosion control structure. 

 Siting a new building within the footprint of a 
pre-existing building does not guarantee that 
the location is a good one.


Recommended building location on a coastal lot.

Siting should consider both long-term erosion and storm impacts.
Siting should consider site-specific experience, wherever available.



Coastal Building 

Materials


Technical Fact Sheet No. 8

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 8  Coastal Building Materials Home Builders Guide to Coastal Construction 08/05

Page of 5

Purpose: To provide guidance on the selection of building materials used for coastal construction. 

Key Issues

 The durability of a coastal home relies on the types of materials used to construct it. For more details, 
see the U.S. Department of Housing and Urban Development (HUD) report Durability by Design, A Guide for 
Residential Builders and Designers, available on the HUD User website at 
http://www.huduser.org/publications/destech/durdesign.html.

 Materials and construction methods should be resistant to flood and wind damage, driving rain, corrosion, 
moisture, and decay.

 All coastal buildings will require maintenance and repairs (more so than inland construction)  use proper 
materials and methods for repairs, additions, and other work following initial construction (see Fact Sheet No. 30).

Flood-Resistant Materials

Flooding accounts for a large percentage of the damage caused by a coastal storm. Building materials 
exposed to flooding must be resilient enough to sustain a certain amount of water exposure in order to avoid 
the need for complete replacement after the flood.

FEMA defines a flood-resistant 
material as any building 
material capable of withstanding 
direct and prolonged contact 
(i.e., at least 72 hours) with 
floodwaters without sustaining 
significant damage (i.e., requires 
more than cosmetic repair).

The following are examples of 
flood-resistant materials:

 Lumber: pressure-treated 
or naturally decay-resistant, 
including redwood, cedar, 
some oaks, and bald cypress

 Concrete: a sound, durable 
mix, and when exposed 
to saltwater or salt spray, 
made with a sulfate-resisting 
cement, with a 28-day 
compressive strength of 

Section 60.3(a)(ii) of the National Flood Insurance Program (NFIP) regulations requires that all new construction and 
substantial improvements in floodprone areas be constructed with materials below the Base Flood Elevation (BFE) 
that are resistant to flood damage. (See Fact Sheet No. 30 for a definition of substantial improvement.)


Select building materials that can endure periodic flooding.



FS No. 8  Coastal Building Materials Home Builders Guide to Coastal Construction 08/05

Page of 5

5,000 psi minimum and a water-cement ratio not higher than 0.40  consult ACI 318-02, Building Code 
Requirements for Structural Concrete and Commentary, by the American Concrete Institute International

 Masonry: reinforced and fully grouted

 Structural Steel: coated to resist corrosion

 Insulation: plastics, synthetics, and closed-cell foam, or other types approved by local building officials

This table lists examples of flood-resistant materials used in coastal homes.



Many coastal jurisdictions make available a list of approved materials that can be used in coastal environments. 
Check for locally approved flood-resistant materials. Include all proposed construction and materials in approved 
plans. For guidance on testing specific materials, refer to NES Evaluation Protocol for Determination of Flood-
Resistant Properties of Building Elements (NES, Inc.  http://www.nateval.org).

Wind-Resistant Materials

Homes in many coastal areas are often exposed to 
winds in excess of 90 mph (3-second peak gust). 
Choose building materials (e.g., roof shingles, siding, 
windows, doors, fasteners, and framing members) that 
are designed for use in high-wind areas.

Examples:

 shingles rated for high winds (see Fact Sheet No. 20)

 double-hemmed vinyl siding (see Fact Sheet No. 25)

 deformed-shank nails for sheathing attachments 
(see Fact Sheet No. 18)

 wind-resistant glazing (see Fact Sheet No. 22)

 reinforced garage doors

 tie-down connectors used throughout structure (from roof 
framing to foundation  see Fact Sheet Nos. 10 and 17)

 wider framing members (2x6 instead of 2x4)

Corrosion and Decay Resistance

Coastal environments are conducive to metal corrosion 
and moisture- and termite-related decay of other 
building materials. Metal corrosion is most pronounced 
on coastal homes (within 3,000 feet of the ocean), 
but moisture- and termite-related decay are prevalent 
throughout coastal areas.

Corrosion-Resistant Metals

Most jurisdictions require metal building hardware to 
be hot-dipped galvanized or stainless steel. Some local 
codes require protective coatings that are thicker than 
off-the-shelf products typically have. For example, 
a G90 zinc coating (0.75 mil on each face) may be 
required, which is thicker than the common G60 (0.5 
mil on each face) coating.

Recommendations

 Use hot-dipped galvanized or stainless steel hardware. 
Reinforcing steel should be protected from corrosion 
by sound materials (masonry, mortar, grout, concrete) 
and good workmanship (see Fact Sheet No. 16). Use 


Select building materials that are suitable for the 
expected wind forces.

The term "corrosion-resistant" is widely used 
but, by itself, is of little help to those specifying 
or evaluating materials for use in a coastal 
home. Every material resists corrosion to some 
extent, or conversely, every material corrodes.

The real issue is how long will a given material 
serve its intended purpose at a given home? 
The answer depends on the following:

 the material

 where it is used in the home

 whether installation techniques (e.g., drilling, 
cutting, bending) will compromise its resistance

 its degree of exposure to salt air, moisture, 
and corrosive agents

 whether maintenance required of the 
homeowner is performed

The bottom line: do not blindly specify or 
accept a product just because it is labeled 
corrosion-resistant. Evaluate the nature of 
the material, its coating type and thickness 
(if applicable), and its performance in similar 
environments before determining whether it is 
suitable for a particular application.

For guidance on the selection of metal hardware 
for use in coastal environments, consult 
an engineer with experience in corrosion protection. 
For more information about corrosion 
in coastal environments, see FEMA Technical 
Bulletin 8-96, Corrosion Protection for Metal 
Connectors in Coastal Areas for Structures 
Located in Special Flood Hazard Areas (see the 
Additional Resources section of this fact sheet).

Remember: A wind-resistant material is 
only as good as its connection. Always use 
recommended fasteners and connection 
methods.



galvanized or epoxy-coated reinforcing steel in situations where the potential for corrosion is high (see Fact 
Sheet No. 14).

 Avoid joining dissimilar metals, especially those with 
high galvanic potential (e.g., copper and steel).

 Some wood preservatives should not be used in 
direct contact with galvanized metal. Verify that wood 
treatment is suitable for use with galvanized metal, or 
use stainless steel.

 Metal-plate-connected trusses should not be exposed 
to the elements. Truss joints near vent openings 
are more susceptible to corrosion and may require 
increased corrosion protection.

Moisture Resistance

Materials resistant to moisture can greatly reduce 
maintenance and extend the life of a coastal home 
(however, by themselves, such materials cannot 
prevent all moisture damage. Proper design and 
installation of moisture barriers (see Fact Sheet No. 9) 
is also required).

Recommendations

 Control wood decay by separating wood from moisture, 
using preservative-treated wood, using naturally decay-
resistant wood, and applying protective wood finishes.

 Use proper detailing of wood joints and construction 
to eliminate standing water and reduce moisture 
absorption by the wood (e.g., avoid exposure of end 
grain cuts, which absorb moisture up to 30 times 
faster than the sides of a wood member).

 Do not use untreated wood in ground contact or high-
moisture situations. Do not use untreated wood in 
direct contact with concrete.

 Field-treat any cuts or drill holes that offer paths for 
moisture to enter wood members.

 For structural uses, employ concrete that is sound, 
dense, and durable; control cracks with welded wire 
fabric and/or reinforcing, as appropriate.

 Use masonry, mortar, and grout that conform with the 
latest building codes.

Termite Resistance

Termite damage to wood construction occurs in many 
coastal areas (attack is most frequent and severe along 
the southeastern Atlantic and Gulf of Mexico shorelines, 
in California, and in Hawaii and other tropical areas). 
Termites can be controlled by soil treatment, termite 
shields, and the use of termite-resistant materials.


Metals corrode at a much faster rate near the ocean. 
Always use well-protected hardware, such as this 
connector with thick galvanizing. (For information about 
pile-to-beam connections, see Fact Sheet No. 13).


Wood decay at the base of a wood 
post supported by concrete.



Recommendations

 Incorporate termite control methods into design in conformance with requirements of the authority having 
jurisdiction.

 Where a masonry foundation is used and anchorage to the foundation is required for uplift resistance, the 
upper block cores must usually be completely filled with grout, which may eliminate the requirement for 
termite shields (see Fact Sheet No. 14).

 Use preservative-treated wood for foundations, sills, above-foundation elements, and floor framing.

Additional Resources

FEMA. NFIP Technical Bulletin 2-93, Flood-Resistant Materials Requirements for Buildings Located in Special 
Flood Hazard Areas. (http://www.fema.gov/fima/techbul.shtm)

FEMA. NFIP Technical Bulletin 8-96, Corrosion Protection for Metal Connectors in Coastal Areas for Structures 
Located in Special Flood Hazard Areas. (http://www.fema.gov/fima/techbul.shtm)

American Concrete Institute International. (http://www.aci-int.org/general/home.asp)

American Wood-Preservers Association. (http://www.awpa.com)

International Code Council Evaluation Service, Inc. Protocol for Testing the Flood Resistance of Materials. 
(http://www.icc-es.org/index.shtml)



Moisture Barrier
Systems


Technical Fact Sheet No. 9

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 9  Moisture Barrier Systems Home Builders Guide to Coastal Construction 08/05

Page of 2

Purpose: To describe the moisture barrier system, explain how typical wall moisture barriers work, and identify 
common problems associated with moisture barrier systems.

Key Issues

 A successful moisture barrier system will 
limit water infiltration into unwanted areas 
and allow drainage and drying of wetted 
building materials. 

 Most moisture barrier systems for 
walls (e.g., siding and brick veneer) are 
redundant systems, which require at 
least two drainage planes (see page 2).

 Housewrap or building paper (asphalt-
saturated felt) will provide an adequate secondary drainage plane.

 Proper flashing and lapping of housewrap and building paper are critical to a successful moisture barrier system.

 Sealant should never be substituted for proper layering.

The purpose of the building envelope is to control the movement of water, air, thermal energy, and water vapor. 
The goal is to prevent water infiltration into the interior, limit long-term wetting of the building components, and 
control air and vapor movement through the envelope.

Locations and Causes of Common Water Intrusion Problems



FS No. 9  Moisture Barrier Systems Home Builders Guide to Coastal Construction 08/05

Page of 2

The location of water entry is often difficult to see, and the damage to substrate and structural members 
behind the exterior wall cladding frequently cannot be detected by visual inspection.

Proper Lapping Is the Key

Proper lapping of moisture barrier materials is the key to preventing water intrusion. Most water intrusion 
problems are related to the improper lapping of materials. Usually, flashing details around doors, windows, 
and penetrations are to blame. If the flashing details are right and the housewrap or building paper is properly 
installed, most moisture problems will be prevented. Capillary suction is a strong force and will move water in 
any direction. Even under conditions of light or no wind pressure, water can be wicked through seams, cracks, 
and joints upward behind the overlaps of horizontal siding. Proper lap distances and sealant help prevent 
water intrusion caused by wicking action.

How a Redundant Moisture Barrier Works



Foundations in 
Coastal Areas


Technical Fact Sheet No. 11

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 11  Foundations in Coastal Areas Home Builders Guide to Coastal Construction 08/05

Page of 3

Purpose: To describe foundation types suitable for coastal environments.

Key Issues

 Foundations in coastal areas must elevate buildings 
above the Base Flood Elevation (BFE), while 
withstanding flood forces, high winds, scour and 
erosion, and floating debris.

 Foundations used for inland construction are generally 
not suitable for coastal construction.

 Deeply embedded pile or column foundations are 
required for many coastal areas; in other coastal 
areas, they are recommended  instead of solid 
wall, crawlspace, slab, or other shallow foundations 
that can be undermined easily. ("Deeply embedded" 
means sufficient penetration into the ground to 
accommodate storm-induced scour and erosion and 
to resist all design vertical and lateral loads without 
structural damage.)

 Areas below elevated buildings in V zones must be 
free of obstructions that can transfer flood loads to the foundation and building (see Fact Sheet No. 27).

Foundation Design Criteria

All foundations for buildings in flood hazard areas must be constructed with flood-damage-resistant materials 
(see Fact Sheet No. 8) and must do two things in addition to meeting the requirements for conventional 
construction: (1) elevate the building above the BFE, and (2) prevent flotation, collapse, and lateral movement of 
the building, resulting from loads and conditions during the design flood event (in coastal areas, these loads and 
conditions include inundation by fast-moving water, breaking waves, floating debris, erosion, and high winds).

Because the most hazardous coastal areas are subject to erosion and extreme flood loads, the only practical 
way to perform these two functions is to elevate a building on a deeply embedded and open (i.e., pile or 
column) foundation. This approach resists storm-induced erosion and scour, and it minimizes the foundation 
surface area subject to lateral flood loads  it is required by the National Flood Insurance Program (NFIP) in V 
zones (even when the ground elevation lies above the BFE) and is recommended for coastal A zones. However, 
even a deeply embedded open pile foundation will not prevent eventual undermining and loss due to long-term 
erosion (see Fact Sheet No. 7).

Performance of Various Foundation Types in Coastal Areas

There are many ways to elevate buildings above the BFE: fill, slab-on-grade, crawlspace, stemwall, solid wall, pier 
(column), and pile. Not all of these are suitable for coastal areas. In fact, several of them are prohibited in V zones 
and are not recommended by the Home Builders Guide to Coastal Construction for A zones in coastal areas.

Fill  Because fill is susceptible to erosion, it is prohibited as a means of providing structural support to 
buildings in V zones and must not be used as a means of elevating buildings in any other coastal area subject to 
erosion, waves, or fast-moving water.


Storm surge and waves overtopping a barrier island 
during Hurricane Frederic.



FS No. 11  Foundations in Coastal Areas Home Builders Guide to Coastal Construction 08/05

Page of 3

Slab-on-Grade  Slab-on-grade 
foundations are also susceptible 
to erosion and are therefore 
prohibited in V zones. They 
also are not recommended 
for A zones in coastal areas. 
(Note that parking slabs are 
often permitted below elevated 
buildings, but are themselves 
susceptible to undermining and 
collapse.)

Crawlspace  Crawlspace 
foundations are prohibited in V 
zones and are not recommended 
for A zones in coastal areas. 
They are susceptible to 
erosion when the footing 
depth is inadequate to prevent 
undermining. Crawlspace walls 
are also vulnerable to wave 
attack. Where used, crawlspace 
foundations must be equipped 
with flood openings; grade elevations should be such 
that water is not trapped in the crawlspace (see Fact 
Sheet Nos. 15 and 27).

Stemwall  Stemwall foundations are similar to 
crawlspace foundations in construction, but the interior 
space that would otherwise form the crawlspace is 
often backfilled with gravel that supports a floor slab. 
Stemwall foundations have been observed to perform 
better during storms than many crawlspace and pier 
foundations. However, the building code may limit 
stemwall height to just a few feet. Flood openings 
are not required in a backfilled stemwall foundation. 
Stemwall foundations are prohibited in V zones but 
are recommended in A zones subject to limited wave 
action, as long as embedment of the wall is sufficient 
to resist erosion and scour.

Solid Foundation Walls  Solid foundation walls are prohibited by the NFIP in V zones and are not 
recommended for A zones subject to breaking waves or other large flood forces  the walls act as an 
obstruction to flood flow. Like crawlspace walls, they are susceptible to erosion when the footing depth is 
inadequate to prevent undermining. Solid walls have been used in some regions to elevate buildings one story 
in height. Where used, the walls must allow floodwaters 
to pass between or through the walls (using flood 
openings). See Fact Sheet Nos. 15 and 27.

Pier (column)  Pier foundations are recommended for 
A zones where erosion potential and flood forces are 
small. This open foundation is commonly constructed 
with reinforced and grouted masonry units atop a 
concrete footing. Shallow pier foundations are extremely 
vulnerable to erosion and overturning if the footing 
depth and size are inadequate. They are also vulnerable 
to breakage if materials and workmanship are not first 
rate. Fact Sheet No. 14 provides guidance on how to 
determine whether pier foundations are appropriate, and 
how to design and construct them.


Building failure caused by undermining of slab-on-grade foundation during
Hurricane Fran.


Failure of crawlspace foundation undermined by scour.


Pier (column) failures: footings undermined and columns 
separated from footings.



Pile  Pile foundations are recommended for V zones 
and many A zones in coastal areas. These open 
foundations are constructed with square or round, 
wood, concrete, or steel piles, driven or jetted into the 
ground, or set into augered holes. Critical aspects of a 
pile foundation include the pile size, installation method 
and embedment depth, bracing, and the connections 
to the elevated structure (see Fact Sheet Nos. 12 and 
13). Pile foundations with inadequate embedment will 
lead to building collapse. Inadequately sized piles are 
vulnerable to breakage by waves and debris.

Foundations for High-Elevation Coastal Areas

Foundation design is problematic in bluff areas that 
are vulnerable to coastal erosion but outside mapped 
flood hazard areas. Although NFIP requirements may not 
apply, the threat of undermining is not diminished.

Moreover, both shallow and deep foundations will fail 
in such situations. Long-term solutions to the problem 
may involve better siting (see Fact Sheet No. 7), moving 
the building when it is threatened, or (where permitted 
and economically feasible) controlling erosion through 
slope stabilization and structural protection.

Foundations in V Zones With Ground 
Elevations Above the BFE

In some instances, coastal areas will be mapped on 
an NFIP Flood Insurance Rate Map (FIRM) as V zones, 
but will have dunes or bluffs with ground elevations 
above the BFE shown on the FIRM. Deeply embedded 
pile or column foundations are still required in these 
areas, and solid or shallow foundations are still 
prohibited. The presence of a V-zone designation in 
these instances indicates that the dune or bluff is 
expected to erode during the base flood event and that 
V-zone wave conditions are expected after the erosion 
occurs. The presence of ground elevations above the 
BFE in a V zone should not be taken to mean that the 
area is free from Base Flood and erosion effects.


Pile failures led to collapse of floor of elevated building.


Insufficient pile embedment and failure of connections at tops 
of piles allowed elevated building to be floated 
off its foundation.

House undermined by bluff erosion. Photograph by Lesley 
Ewing. Courtesy of California Coastal Commission.



Pile
Installation


Technical Fact Sheet No. 12

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 12  Pile Installation Home Builders Guide to Coastal Construction 08/05

Page of 3

Purpose: To provide basic information about pile design and installation.

Key Issues

 Use a pile type that is appropriate for local 
conditions.

 Have piles designed by a foundation engineer for 
adequate layout, size, and length.

 Use installation methods that are appropriate for the 
conditions.

 Brace piles properly during construction.

 Make accurate field cuts, and treat all cuts and 
drilled holes to prevent decay.

 Have all pile-to-beam connections engineered, and use 
corrosion-resistant hardware. (See Fact Sheet No. 8.)

Pile Types

Treated wood piles are the most common type of pile 
used in coastal construction. They can be square 
or round in cross section. Wood piles are easily cut 
and adjusted in the field and are typically the most 
economical type. Concrete and steel can also be used 
but are less common. Concrete piles are 
more expensive, but they are stronger and 
more durable. Steel piles are rarely used, 
because of potential corrosion problems. 

Pile Size and Length

Pile size and length are determined by the 
foundation engineer. Specified bearing and 
penetration requirements must be met. 
Piles should have no less than an 8-inch tip 
diameter; minimum timber size should be 
8x8. The total length of the pile is based on 
code requirements, calculated penetration 
requirements, erosion potential, Design 
Flood Elevation (DFE), and allowance for 
cut-off and beam width (see figure at right).


Note: Misaligned piles lead to 
connection problems. See Fact Sheet 
No. 13 for information about making 
connections to misaligned piles.



FS No. 12  Pile Installation Home Builders Guide to Coastal Construction 08/05

Page of 3

Pile Layout

The pile layout is determined by the foundation engineer. Accurate placement and correction of misaligned piles is 
important. Pile placement should not result in more than 50 percent of the pile cross-section being cut for girder 
or other connections. Verify proper pile locations on drawings before construction and clarify any discrepancies. 
Layout can be done by a licensed design professional, a construction surveyor, the foundation contractor, or the 
builder. The layout process must always include establishing an elevation for the finished first floor. Construction 
of the first-floor platform should not begin until this elevation is established (see Fact Sheet No. 4).

Installation Methods

Piles can be driven, augured, or jetted into place. The 
installation method will vary with soil conditions, bearing 
requirements, equipment available, and local practice. 
One common method is to initially jet the pile to a few 
feet short of required penetration, then complete the 
installation by driving with a drop hammer.

Pile Bracing

Pile bracing is determined by the foundation engineer. 
Common bracing methods include knee and diagonal 
bracing. Bracing is often oriented perpendicular to the 
shoreline so that it is not struck broadside by waves, 
debris, and velocity flow (see figure at right). Temporary 
bracing or jacking to align piles and hold true during 
construction is the responsibility of the contractor.

Field Cutting and Drilling

A chain saw is the common tool of choice for making cuts and notches in wood piles. After making cuts, 
exposed areas should be field-treated to prevent decay. 


To avoid costly pile repairs or replacement, 
measure, locate, and double-check the required 
pile cutoff elevations before cutting off piles.



Connections

The connection of the pile to the structural members is one of the most critical connections in the structure. 
Always follow design specifications and use corrosion-resistant hardware (see Fact Sheet Nos. 8 and 13).

Verification of Pile Capacity

Generally, pile capacity for residential construction is not verified in the field. If a specified minimum pile 
penetration is provided, bearing is assumed to be acceptable for the local soil conditions. Subsurface soil 
conditions can vary from the typical assumed conditions, so verification of pile capacity may be prudent, 
particularly for expensive coastal homes. Various methods are available for predicting pile capacity. Consult a 
foundation engineer for the most appropriate method for the site.

Additional Resources

American Forest and Paper Association (AF&PA). National Design Specification for Wood Construction. (www.
afandpa.org)

American Society for Standards and Testing (ASTM). Standard Specification for Round Timber Piles, ASTM 
D25. (www.astm.org)

American Wood-Preservers Association (AWPA). All Timber Products  Preservative Treatment by Pressure 
Processes, AWPA C1-00; Lumber, Timber, Bridge Ties and Mine Ties  Preservative Treatment by Pressure 
Processes, AWPA C2-01; Piles  Preservative Treatment by Pressure Process, AWPA C3-99; and others. (www.
awpa.com)

Pile Buck, Inc. Coastal Construction. (www.pilebuck.com)



Wood-Pile-to-Beam 
Connections


Technical Fact Sheet No. 13

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 13  Wood-Pile-to-Beam Connections Home Builders Guide to Coastal Construction 08/05

Page of 5

Purpose: To illustrate typical wood-pile-to-beam connections, provide basic construction guidelines on various 
connection methods, and show pile bracing connection techniques.

NOTE: The pile-to-beam connection is one of the most critical links in the structure. This connection must 
be designed by an engineer. See Fact Sheet No. 10 for load path information. The number of bolts and 
typical bolt placement dimensions shown are for illustrative purposes only. Connection designs are not 
limited to those shown here, and not all of the information to be considered in the designs is included in 
these illustrations. Final designs are the responsibility of the engineer. 

Key Issues

 Verify pile alignment and correct, if 
necessary, before making connections.

 Carefully cut piles to ensure required 
scarf depths.

 Limit cuts to no more than 50 percent 
of pile cross-section.

 Use corrosion-resistant hardware, such 
as hot-dipped galvanized or stainless 
steel (see Fact Sheet No. 8).

 Accurately locate and drill bolt holes.

 Field-treat all 
cuts and holes to 
prevent decay.

 Use sufficient pile 
and beam sizes to 
allow proper bolt 
edge distances.

Pile-to-beam connections must:

1. provide required bearing area for beam to rest on pile

2. provide required uplift (tension) resistance

3. maintain beam in an upright position

4. be capable of resisting lateral loads (wind and seismic)

5. be constructed with durable connectors and fasteners


Note: Pile-to-beam 
connections must be 
designed by an engineer.



FS No. 13  Wood-Pile-to-Beam Connections Home Builders Guide to Coastal Construction 08/05

Page of 5


Note: Pile-to-beam 
connections must 
be designed by an 
engineer.

Problem: Misaligned piles  some piles are shifted in or out from their intended (design) locations.

Possible Solutions (see drawings on page 3 and details on page 4):

Option 1 (see page 3)  beam cannot be shifted

Option 2 (see page 3)  beam can be shifted laterally and remains square to building

Option 3 (see page 3)  beam can be shifted laterally, but does not remain square to building

Option 4 (not shown)  beam cannot be shifted, and connections shown in this fact sheet cannot be 
made; install and connect sister piles; an engineer must be consulted for this option

Option 5 (not shown)  beam cannot be shifted, and connections shown in this fact sheet cannot be 
made; remove and reinstall piles, as necessary



Note: Pile-to-beam connections must be designed by an engineer.



Connections to misaligned piles (see drawings on page 3 and details below)

1. The ability to construct the pile-to-beam connections designed by the engineer is directly dependent 
on the accuracy of pile installation and alignment.

2. Misaligned piles will require the contractor to modify pile-to-beam connections in the field.

3. Badly misaligned piles will require removal and reinstallation, sister piles, or special connections, all 
to be determined by the engineer.


Note: Pile-to-beam 
connections must 
be designed by an 
engineer.



Note: Pile-to-beam 
connections must be 
designed by an engineer.



Reinforced Masonry Pier
Construction 


Technical Fact Sheet No. 14

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 14  Reinforced Masonry Pier Construction Home Builders Guide to Coastal Construction 08/05

Page of 2

Purpose: To provide an alternative to piles in V zones and A zones in coastal areas where soil properties 
preclude pile installation, yet the need for an open foundation system still exists. Examples of appropriate 
conditions for the use of piers are where rock is at or near the surface or where the potential for erosion and 
scour is low.

Key Issues

 The footing must be designed for the soil conditions present. Pier foundations are generally not 
recommended in V zones or in A zones in coastal areas.

 The connection between the pier and its footing must be properly designed and constructed to resist 
separation of the pier from the footing and rotation to due to lateral (flood, wind, debris) forces.

 The top of the footing must be below the anticipated erosion and scour depth.

 The piers must be reinforced with steel and fully grouted.

 There must be a positive connection to the floor beam at the top of the pier.

 Special attention must be given to the application of mortar in order to prevent saltwater intrusion into the 
core, where the steel can be corroded.

Piers vs. Piles


Piers are subject to upward, downward, and horizontal loads. 
Pier reinforcement and footing size are critical to resisting 
these loads; therefore, pier and footing design must be 
verified by an engineer. 

In coastal areas, masonry pier foundations are not recommended in V zones with erodible soils, or in A zones 
subject to waves and erosion  use pile foundations in these areas.



FS No. 14  Reinforced Masonry Pier Construction Home Builders Guide to Coastal Construction 08/05

Page of 2

Pier foundations are most 
appropriate in areas where:

 erosion and scour potential 
are low,

 flood depths and lateral 
forces are low, and

 soil can help resist 
overturning of pier.

The combination of high winds 
and moist (sometimes salt-
laden) air can have a damaging 
effect on masonry construction 
by forcing moisture into 
even the smallest of cracks 
or openings in the masonry 
joints. The entry of moisture 
into reinforced masonry 
construction can lead to 
corrosion of the reinforcement 
steel and subsequent cracking 
and spalling of the masonry. 
Moisture resistance is highly 
influenced by the quality of the materials and the quality of the masonry construction at the site.

Good Masonry Practice

 Masonry units and packaged mortar and grout materials should be stored off the ground and covered.

 Masonry work in progress must be well protected.

 Mortar and grouts must be carefully batched and mixed. The 2003 International Building Code (IBC 2003) 
specifies grout proportions by volume for masonry construction.

Recommendations for Masonry Piers in Coastal Regions


The small footings on the piers in this photograph did not prevent these piers
from overturning during Hurricane Iniki.



Foundation 
Walls 


HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 15 
Purpose: To discuss the use of foundation walls in coastal buildings. 

Key Issues 

 Foundation walls include stemwalls, cripple walls, and other solid walls. 
 Foundation walls are prohibited by the National Flood Insurance Program (NFIP) in V zones.* 
 Use of foundation walls in A zones in coastal areas should be limited to locations where only shallow flooding 
occurs, and where the potential for erosion and breaking waves is low. 
 Where foundation walls are used, flood-resistant design of foundation walls must consider embedment, 
height, materials and workmanship, lateral support at the top of the wall, flood openings and ventilation 
openings, and interior grade elevation. 
Foundation Walls  When Are They Appropriate? 

Use of foundation walls  such as those in crawlspace and other solid-wall foundations  is potentially 
troublesome in coastal areas for two reasons: (1) they present an obstruction to breaking waves and fastmoving flood waters, and (2) they are typically 

FS No. 15  Foundation Walls Home Builders Guide to Coastal Construction 08/05Page 1 of 3 
constructed on shallow footings, which are 
vulnerable to erosion. For these reasons, 
their use in coastal areas should be limited 
to sites subject to shallow flooding, where 
erosion potential is low and where breaking 
waves do not occur during the Base Flood. 
The NFIP prohibits the use of foundation 
walls in V zones*. This Home Builders Guide 
to Coastal Construction recommends against 
their use in many A zones in coastal areas. 
Deeply embedded pile or column foundations 
are recommended because they present less 
of an obstruction to floodwaters and are less 
vulnerable to erosion.
* Note that the use of shearwalls below 
the Design Flood Elevation (DFE) may 
be permitted in limited circumstances 
(e.g., lateral wind/seismic loads 
cannot be resisted with a braced, open 
foundation. In such cases, minimize 
the length of shearwalls and the 
degree of obstruction to floodwaters 
and waves, orient shearwalls parallel 
to the direction of flow/waves, do not 
form enclosures). Consult the authority 
having jurisdiction for guidance 
concerning shearwalls below the DFE.

FS No. 15  Foundation Walls Home Builders Guide to Coastal Construction 08/05

Page of 3

Design Considerations for Foundation Walls

The design of foundation walls is covered by building codes and standards (e.g., Standard for Hurricane 
Resistant Residential Construction, SSTD 10, by the Southern Building Code Congress International). For flood 
design purposes, there are six additional design considerations: (1) embedment, (2) height, (3) materials and 
workmanship, (4) lateral support at the top of the wall, (5) flood openings and ventilation openings, and (6) 
interior grade elevation.

Embedment  The top of the footing should be no higher than the anticipated depth of erosion and scour 
(this basic requirement is the same as that for piers; see figure at right and Fact Sheet No. 14). If the 
required embedment cannot be achieved without extensive excavation, consider a pile foundation instead.

Height  The wall should be high 
enough to elevate the bottom of the 
floor system to or above the DFE (see 
Fact Sheet No. 4).

Materials and Workmanship 
Foundation walls can be constructed 
from many materials, but masonry, 
concrete, and wood are the most 
common. Each material can be 
specified and used in a manner to 
resist damage due to moisture and 
inundation (see Fact Sheet No. 8). 
Workmanship for flood-resistant 
foundations is crucial. Wood should 
be preservative-treated for foundation 
or marine use (aboveground or 
ground-contact treatment will not be 
sufficient). Cuts and holes should 
be field-treated. Masonry should be 
reinforced and fully grouted (see Fact Sheet No. 16 for masonry details). Concrete should be reinforced and 
composed of a high-strength, low water-to-cement ratio mix. 

Lateral Support at the Top of the Wall  Foundation walls must be designed and constructed to withstand 
all flood, wind, and seismic forces, as well as any unbalanced soil/hydrostatic loads. The walls will typically 
require lateral support from the floor system and diaphragm, and connections to the top of the walls must be 
detailed properly. Cripple walls, where used, should be firmly attached and braced.

Flood Openings and Ventilation Openings  Any area below the DFE enclosed by foundation walls must 
be equipped with openings capable of automatically equalizing the water levels inside and outside the 
enclosure. Specific flood opening requirements are included in Fact Sheet No. 27. Flood openings are not 
required for backfilled stemwall foundations supporting a slab. Air ventilation openings required by building 
codes do not generally satisfy the flood opening requirement; the air vents are typically installed near the 
top of the wall, the flood vents must be installed near the bottom, and opening areas for air flow may be 
insufficient for flood flow.

Interior Grade Elevation  Conventional practice for crawlspace construction calls for excavation of the 
crawlspace and use of the excavated soil to promote drainage away from the structure (see left-hand figure 
on page 3). This approach may be acceptable for non-floodplain areas, but in floodplains, this practice can 
result in increased lateral loads (e.g., from saturated soil) against the foundation walls and ponding in the 
crawlspace area. If the interior grade of the crawlspace is below the DFE, NFIP requirements can be met 
by ensuring that the interior grade is at or above the lowest exterior grade adjacent to the building (see 
right-hand figure on page 3). When floodwaters recede, the flood openings in the foundation walls allow 
floodwaters to automatically exit the crawlspace. FEMA may accept a crawlspace elevation up to 2 feet 
below the lowest adjacent exterior grade; however, the community must adopt specific requirements in order 
for this type of crawlspace to be constructed in a floodplain.



If a stemwall and floor slab system is used, the interior space beneath the slab should be backfilled with 
compacted gravel (or such materials as required by the building code). As long as the system can act 
monolithically, it will resist most flood forces. However, if the backfill settles or washes out, the slab will 
collapse and the wall will lose lateral support.

DFE

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 16 
Masonry Details 
FS No. 16  Masonry Details Home Builders Guide to Coastal Construction 08/05 Page of 3 
Purpose: To highlight several important details for 
masonry construction in coastal areas. 
Key Issues 
 Continuous, properly connected load paths are 
essential because of the higher vertical and lateral 
loads on coastal structures. 
 Building materials must be durable enough to 
withstand the coastal environment. 
 Masonry reinforcement requirements are more 
stringent in coastal areas. 
Load Paths 
A properly connected load path from roof to 
foundation is crucial in coastal areas (see Fact 
Sheets Nos. 10 and 17). The following details show 
important connections for a typical masonry home. 
Roof framing to masonry wall. 
Roof framing to interior masonry wall

FS No. 16  Masonry Details Home Builders Guide to Coastal Construction 08/05

Page of 3

Durability  High winds and salt-laden air can damage masonry construction. The entry of moisture into large 
cracks can lead to corrosion of the reinforcement and subsequent cracking and spalling. Moisture resistance 
is highly dependent on the materials and quality of construction.


Gable endwall connection.



Quality depends on: 

 Proper storage of material  Keep stored materials covered 
and off the ground. 
 Proper batching  Mortar and grout must be properly batched 
to yield the required strength. 
 Good workmanship  Head and bed joints must be well mortared and well tooled. Concave joints and V-joints 
provide the best moisture protection (see detail above). All block walls should be laid with full mortar coverage 
on horizontal and vertical face shells. Block should be laid using a double butter technique for spreading 
mortar head joints. This practice provides for mortar-to-mortar contact as two blocks are laid together in the 
wall and prevents hairline cracking in the head joint. 
 Protection of work in progress  Keep work in progress protected from rain. During inclement weather, the 
tops of unfinished walls should be covered at the end of the workday. The cover should extend 2 feet down 
both sides of the masonry and be securely held in place. Immediately after the completion of the walls, the 
wall cap should be installed to prevent excessive amounts of water from directly entering the masonry. 
Reinforcement: Masonry must be reinforced according to the building plans. Coastal homes will typically require more 
reinforcing than inland homes. The following figure shows typical reinforcement requirements for a coastal home. 

FS No. 16  Masonry Details Home Builders Guide to Coastal Construction 08/05Page 3 of 3 
Gable Ends: Because of their 
exposure, gable ends are more 
prone to damage than are 
hipped roofs unless the joint 
in conventional construction at 
the top of the endwall and the 
bottom of the gable is laterally 
supported for both inward and 
outward forces. The figure at 
right shows a construction 
method that uses continuous 
masonry from the floor to the 
roof diaphragm with a raked 
cast-in-place concrete bond 
beam or a cut masonry bond 
beam.
Continuous gable endwall 
reinforcement. 
Masonry reinforcement. 

Shutter

Alternatives


Technical Fact Sheet No. 26

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 26  Shutter Alternatives Home Builders Guide to Coastal Construction 08/05

Page of 5


Purpose: To provide general information 
about the installation and use of storm 
shutters in coastal areas.

Why Are Storm Shutters Needed?

Shutters are an important part of a hurricane-
resistant or storm-resistant home. They 
provide protection for glass doors and 
windows against windborne debris, which is 
often present in coastal storms. Keeping the 
building envelope intact (i.e., no window or 
door breakage) during a major windstorm is 
vital to the structural integrity of a home. If the 
envelope is breached, sudden pressurization 
of the interior can cause major structural 
damage (e.g., roof loss) and will lead to 
significant interior and contents damage from 
wind-driven rain.

Where Are Storm Shutters Required 
and Recommended?

Model building codes, which incorporate wind 
provisions from ASCE 7 (1998 edition and 
later), require that buildings within the most 
hazardous portion of the hurricane-prone 
region, called the windborne debris region 
(see page 4 of this fact sheet), either (1) be 
equipped with shutters or impact-resistant 
glazing and designed as enclosed structures, 
or (2) be designed as partially enclosed 
structures (as if the windows and doors are 
broken out). Designing a partially enclosed 
structure typically requires upgrading 
structural components and connections, but 
will not provide protection to the interior of 
the building. Designers and owners should 
assume that a total loss of the building 
interior and contents will occur in partially 
enclosed structures.

Using opening protection (e.g., shutters 
or laminated glass) is recommended in 

Plywood panels are a cost-effective means of protection.


Temporary, manufactured metal panel shutter. The shutter is installed 
in a track permanently mounted above and below the window frame. 
The shutter is placed in the track and secured with wing nuts to 
studs mounted on the track. This type of shutter is effective and 
quickly installed, and the wing nut and stud system provides a secure 
anchoring method.

Note: Many coastal homes have large and unusually shaped windows, which will require expensive, 
custom shutters. Alternatively, such windows can be fabricated with laminated (impact-resistant) glass.



Page of 5

FS No. 26  Shutter Alternatives Home Builders Guide to Coastal Construction 08/05

windborne debris regions, as opposed to designing a partially enclosed structure. The Home Builders Guide 
to Coastal Construction also recommends giving strong consideration to the use of opening protection in all 
hurricane-prone areas where the basic wind speed is 100 mph (3-second peak gust) or greater, even though 
the model building codes do not require it. Designers should check with the jurisdiction to determine whether 
state or local requirements for opening protection exceed those of the model code.

What Types of Shutters Are Available?

A wide variety of shutter types are available, from the very expensive motor-driven, roll-up type, to the less 
expensive temporary plywood panels (see photograph on page 1 of this fact sheet). Designers can refer to 
Miami-Dade County, Florida, which has established a product approval mechanism for shutters and other 
building materials to ensure they are rated for particular wind and windborne debris loads (see Additional 
Resources on page 5 of this fact sheet).

Shutter Type

Cost

Advantages

Disadvantages

Temporary plywood 
panels

Low

Inexpensive

Must be installed and taken 
down every time they are needed; 
must be adequately anchored to 
prevent blow-off; difficult to install 
on upper levels

Temporary manufactured 
panels

Low/Medium

Easily installed on 
lower levels

Must be installed and taken 
down every time they are needed; 
difficult to install on upper levels

Permanent, manual-
closing

Medium/High

Always in place
Ready to be closed

Must be closed manually from 
the outside; difficult to access on 
upper levels

Permanent, motor-driven

High

Easily opened and 
closed from the inside

Expensive





Shutter Styles

Shutter styles include colonial, Bahama, roll-up, and accordion.


Colonial shutters

Bahama shutter 



Accordion shutter

Roll-up shutter


Common methods for plywood shutter attachment to wood-frame and masonry walls. (For actual shutter design, refer to 
design drawings or see the Engineered Wood Association guidelines for constructing plywood shutters.)



Are There Special Requirements for Shutters in Coastal Areas?

ASCE 7 and the International Building Code (IBC) state that shutters (or laminated glazing) shall be tested in 
accordance with the American Society for Testing and Materials (ASTM) standards ASTM E 1886 and ASTM E 
1996 (or other approved test methods). E 1886 specifies the test procedure; E 1996 specifies missile loads. 
The IBC allows the use of wood panels (Table 1609.1.4) and prescribes the type and number of fasteners to 
be used to attach the panels. A shutter may look like it is capable of withstanding windborne missiles; unless 
it is tested, however, its missile resistance is unknown.

When installing any type of shutter, carefully follow manufacturers instructions and guidelines. Be sure to 
attach shutters to structurally adequate framing members (see shutter details on page 3 of this fact sheet). 
Avoid attaching shutters to the window frame or brick veneer face. Always use hardware not prone to corrosion 
when installing shutters.

What Are Hurricane-Prone Regions Windborne Debris Regions?

ASCE 7, the IBC, and the International Residential Code (IRC) define hurricane-prone regions as:

 the U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed is greater than 90 mph (3-
second peak gust), and

 Hawaii, Guam, Puerto Rico, the U.S. Virgin Islands, and American Samoa.

ASCE 7, the IBC, and the IRC define windborne debris regions as areas within hurricane-prone regions 
located:

 within 1 mile of the coast where the basic wind speed is equal to or greater than 110 mph (3-second peak 
gust) and in Hawaii, or

 in all areas where the basic wind speed is equal to or greater than 120 mph (3-second peak gust), including 
Guam, Puerto Rico, the U.S. Virgin Islands, and American Samoa.



Additional Resources

American Society of Civil Engineers. Minimum Design Loads for Buildings and Other Structures, ASCE 7. 
(http://www.asce.org)

International Code Council. International Building Code. 2003. (http://www.iccsafe.org)

International Code Council. International Residential Code. 2003. (http://www.iccsafe.org)

The Engineered Wood Association. Hurricane Shutter Designs Set 5 of 5. Hurricane shutter designs for wood-
frame and masonry buildings. (http://www.apawood.org)

Miami-Dade County, Florida, product testing and approval process  information available at http://www.
miamidade.gov/buildingcode/pc_home.asp



FS No. 27  Enclosures and Breakaway Walls Home Builders Guide to Coastal Construction 08/05

Page of 3

Enclosures can be divided into two types, breakaway and 
non-breakaway. 

 Breakaway enclosures are designed to fail under Base 
Flood conditions without jeopardizing the elevated 
building  any below-BFE enclosure in a V zone must be 
breakaway. Breakaway enclosures are permitted in A 
zones but must be equipped with flood openings. 

 Non-breakaway enclosures, under the NFIP, can be used 
in an A zone (they may or may not provide structural 
support to the elevated building), but they must be 
equipped with flood openings to allow the automatic 
entry and exit of floodwaters. The Home Builders Guide 
to Coastal Construction recommends their use only in 
A zone areas subject to shallow, slow-moving floodwaters 
without breaking waves.

Breakaway Walls

Breakaway walls must be designed to break 
free under the larger of the design wind load, 
the design seismic load, or 10 psf, acting 
perpendicular to the plane of the wall. If 
the loading at which the breakaway wall is 
intended to collapse exceeds 20 psf, the 
breakaway wall design must be certified. 
When certification is required, a registered 
engineer or architect must certify that 
the walls will collapse under a water load 
associated with the Base Flood and that 
the elevated portion of the building and its 
foundation will not be subject to collapse, 
displacement, or lateral movement under 
simultaneous wind and water loads. (See the 
sample certification at the bottom of page 2 
of Fact Sheet No. 5.) Utilities should not be 
attached to or pass through breakaway walls.

Flood Openings

Where permitted and used in A zones, 
foundation walls and enclosures must 
be equipped with openings that allow the 
automatic entry and exit of floodwaters.

Note the following:

 Flood openings must be provided in 
at least two of the walls forming the 
enclosure.

 The bottom of each flood opening must be 
no more than 1 foot above the adjacent 
grade outside the wall.

 Louvers, screens, or covers may be installed 
over flood openings as long as they do not interfere with the operation of the openings during a flood.

 Flood openings may be sized according to either a prescriptive method (1 square inch of flood opening per square 
foot of enclosed area) or an engineering method (which must be certified by a registered engineer or architect).

Details concerning flood openings can be found in FEMA Technical Bulletin 4-93, Openings in Foundation Walls.


Open wood lattice installed beneath 
an elevated house in a V zone.


Recommended breakaway wall construction. 



Other Considerations

Enclosures are strictly regulated because, if not constructed properly, they can transfer flood forces to the 
main structure (possibly leading to structural collapse). There are other considerations, as well:

 Owners may be tempted to convert enclosed areas below the BFE into habitable space, leading to life-
safety concerns and uninsured losses. Construction without enclosures should be encouraged. Contractors 
should not stub out utilities in enclosures; utility stub-outs make it easier for owners to finish and occupy 
the space.

 Siding used on non-breakaway portions of a building should not be extended over breakaway walls. Instead, 
a clean separation should be provided so that any siding installed on breakaway walls is structurally 
independent of siding elsewhere on the 
building. Without such a separation, the 
failure of breakaway walls can result in 
damage to siding elsewhere on the building. 

 Breakaway enclosures in V zones will result 
in substantially higher flood insurance 
premiums (especially where the enclosed 
area is 300 square feet or greater). Insect 
screening or lattice is recommended 
instead. 

 If enclosures are constructed in A zones 
with the potential for breaking waves, open 
foundations with breakaway enclosures are 
recommended in lieu of foundation walls or 
crawlspaces. If breakaway walls are used, 
they must be equipped with flood openings 
that allow flood waters to enter the enclosure 
during smaller storms. Breakaway enclosures in 
A zones will not lead to higher flood insurance 
premiums.

 Garage doors installed in below-BFE enclosures of V-zone buildings  even reinforced and high-wind-
resistant doors  must meet the performance requirement discussed in the Breakaway Walls section on 
page 2 of this fact sheet. Specifically, the doors must be designed to break free under the larger of the 
design wind load, the design seismic load, or 10 psf, acting perpendicular to the plane of the door. If the 
loading at which the door is intended to collapse is greater than 20 psf, the door must be designed and 
certified to collapse under Base Flood conditions. See the Breakaway Walls section of this fact sheet for 
information about certification requirements.


Siding on the non-breakaway portions of this elevated building was 
extended over breakaway enclosure walls and was damaged when 
breakaway walls failed under flood forces.



Enclosures and Breakaway
Walls


Technical Fact Sheet No. 27

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

Page of 3

FS No. 27  Enclosures and Breakaway Walls Home Builders Guide to Coastal Construction 08/05

Purpose: To discuss requirements and recommendations 
for enclosures and breakaway walls below the Base Flood 
Elevation (BFE). 

Key Issues

 Spaces below elevated buildings can be used only for 
building access, parking, and storage.

 Areas enclosed by solid walls below the BFE (enclosures) 
are subject to strict regulation under the National Flood 
Insurance Program (NFIP). Note that some local jurisdictions 
enforce stricter regulations for enclosures.

 Non-breakaway enclosures are prohibited in V-zone buildings. 
Breakaway enclosures in V zones must meet specific 
requirements and must be certified by a registered design 
professional

 Enclosures (breakaway and non-breakaway) in A-zone buildings 
must be built with flood-resistant materials and equipped with 
flood openings that allow water levels inside and outside to 
equalize (see Fact Sheet No. 15). 

 For V zones, enclosures below the elevated building will 
result in higher flood insurance premiums.

 Breakaway enclosure walls should be considered 
expendable, and the building owner will incur substantial 
costs when the walls are replaced.

Space Below the BFE  What Can it Be Used For?

NFIP regulations state that the area below an elevated 
building can be used only for building access, parking, 
and storage. These areas must not be finished or used for 
recreational or habitable purposes. No mechanical, electrical, 
or plumbing equipment is to be installed below the BFE. 

What Is an Enclosure?

An enclosure is formed when any space below the BFE is 
enclosed on all sides by walls or partitions. A V-zone building 
elevated on an open foundation (see Fact Sheet No. 11), 
without an enclosure or other obstructions below the BFE, 
is said to be free-of-obstructions, and enjoys favorable flood 
insurance premiums (a building is still classified free-of-
obstructions if insect screening or open wood lattice is used to 
surround space below the BFE). See FEMA Technical Bulletin 
5-93, Free of Obstruction Requirements for more information.


WARNING

 

Home builders and homeowners should 
consider the long-term effects of the 
construction of enclosures below 
elevated residential buildings and post-
construction conversion of enclosed 
space to habitable use in A zones and 
V zones. Designers and owners should 
realize that (1) enclosures and items 
within them are likely to be destroyed even 
during minor flood events, (2) enclosures, 
and most items within them, are not 
covered by flood insurance and can result 
in significant costs to the building owner, 
and (3) even the presence of properly 
constructed enclosures will increase 
flood insurance premiums for the entire 
building (the premium rate will increase 
as the enclosed area increases). 
Including enclosures in a building design 
can have significant cost implications.

This Home Builders Guide to Coastal 
Construction recommends the use of 
insect screening or open wood lattice 
instead of solid enclosures beneath 
elevated residential buildings. 


Breakaway walls that failed under the 
flood forces of Hurricane Ivan. 



Protecting Utilities


Technical Fact Sheet No. 29

HOME BUILDERS GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005

FS No. 29  Protecting Utilities Home Builders Guide to Coastal Construction 08/05

Page of 3

Purpose: To identify the special considerations that must be made when installing utility equipment in a 
coastal home.

Key Issues: Hazards, requirements, and recommendations

Special considerations must be made when installing utility systems in coastal homes. Proper placement and 
connection of utilities and mechanical equipment can significantly reduce the costs of damage caused by 
coastal storms and will enable homeowners to reoccupy their homes soon after electricity, sewer, and water 
are restored to a neighborhood.

Coastal Hazards That Damage Utility Equipment

 Standing or moving floodwaters

 Impact from floating debris in floodwaters

 Erosion and scour from floodwaters

 High winds

 Windborne missiles

Common Utility Damage in Coastal Areas

Floodwaters cause corrosion and contamination, 
short-circuiting of electronic and electrical 
equipment, and other physical damage.

Electrical  Floodwaters can corrode and short-
circuit electrical system components, possibly 
leading to electrical shock. In velocity flow 
areas, electrical panels can be torn from their 
attachments by the force of breaking waves or the 
impact of floating debris.

Water/Sewage  Water wells can be exposed 
by erosion and scour caused by floodwaters with 
velocity flow. A sewage backup can occur even without the structure flooding.

Fuel  Floodwaters can float and rupture tanks, corrode and short-circuit electronic components, and sever 
pipe connections. In extreme cases, damage to fuel systems can lead to fires.

Basic Protection Methods

The primary protection methods are elevation or component protection.

Elevation

Elevation refers to the location of a component and/or utility system above 
the Design Flood Elevation (DFE). 

Component Protection

Component protection refers to the implementation of design techniques that protect a component or group 
of components from flood damage when they are located below the DFE.


Electrical lines and box dislocated by hurricane forces.

Elevation of utilities and 
mechanical equipment is 
the preferred method of 
protection.



FS No. 29  Protecting Utilities Home Builders Guide to Coastal Construction 08/05

Page of 3

NFIP Utility Protection Requirements

The NFIP regulations [Section 60.3(a)(3)] state that:

All new construction and substantial improvements shall be constructed with electrical, heating, ventilation, 
plumbing, and air conditioning equipment and other service facilities that are designed and/or located so as 
to prevent water from entering or accumulating within the components during conditions of flooding.

Utility Protection Recommendations

Electrical

 Limit switches, wiring, and receptacles below the DFE to those items required for life safety. Substitute 
motion detectors above the DFE for below-DFE switches whenever possible. Use only ground-fault-protected 
electrical outlets below the DFE.

 Install service connections (e.g., electrical lines, panels, and meters; telephone junction boxes; cable 
junction boxes) above the DFE, on the landward side of interior piles or other vertical support members.

 Use drip loops to minimize water entry at penetrations.

 Never attach electrical components to breakaway walls.

Water/Sewage

 Attach plumbing risers on the landward side of interior piles or other vertical support members.


Recommended installation techniques for electrical and plumbing lines and other utility components. 



 When possible, install plumbing runs inside joists for protection. 

 Never attach plumbing runs to breakaway walls.

HVAC

 Install HVAC components (e.g., 
condensers, air handlers, ductwork, 
electrical components) above the DFE.

 Mount outdoor units on the leeward 
side of the building.

 Secure the unit so that it cannot move, 
vibrate, or be blown off its support.

 Protect the unit from damage by 
windborne debris.

Fuel

 Fuel tanks should be installed so 
as to prevent their loss or damage. 
This will require one of the following 
techniques: (1) elevation above the 
DFE and anchoring to prevent blowoff, 
(2) burial and anchoring to prevent 
exposure and flotation during erosion 
and flooding, (3) anchoring at ground 
level to prevent flotation during flooding and loss during scour and erosion. The first method (elevation) is 
preferred.

 Any anchoring, strapping, or other attachments must be designed and installed to resist the effects of 
corrosion and decay.

Additional Resources

American Society of Civil Engineers. Flood Resistant Design and Construction (SEI/ASCE 24-98). (http://www.
asce.org)

FEMA. NFIP Technical Bulletin 5-93, Free-Of-Obstruction Requirements for Buildings Located in Coastal High 
Hazard Areas. (http://www.fema.gov/fima/techbul.shtm)

FEMA. Protecting Building Utilities From Flood Damage. FEMA 348. November 1999. (http://www.fema.gov/
hazards/floods/lib06b.shtm)


Elevated air conditioning compressors.



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


G. FEMA Publications and 
Additional References

The American Concrete Institute (ACI). 2005. Building Code Requirements for Structural Concrete 
and Commentary, ACI 318. 01-Jan-2005.

American Forest & Paper Associations (AFPM) American Wood Council. 2005. National Design 
Specification for Wood Construction. 2005.

American Society for Testing and Materials (ASTM). 2000. Standard Test Method for High-Strain 
Dynamic Testing of Piles, ASTM D 4945. November 2000.

American Society of Civil Engineers (ASCE) 7-02. 2002. Minimum Design Loads for Buildings and 
Other Structures, ASCE 7-02. ISBN:0-7844-0624-3.

ASCE 24-05. 2006. Flood Resistant Design and Construction. ISBN: 0784408181. 01-Jan-2006.

American Wood Preservers Association (AWPA). 1991. Care of Pressure-Treated Wood Products. 

FEMA. 1984. Elevated Residential Structures, FEMA 54. March 1984.

FEMA. 1995. Guide to Flood Maps: How to Use a Flood Map to Determine Flood Risk for a Property, 
FEMA 258. May 1995.

G- 



g fema publications and additional references

G- 

Building on strong and safe foundations

FEMA. 1996. Corrosion Protection for Metal Connectors in Coastal Areas for Structures Located in Special 
Flood Hazard Areas, FEMA Technical Bulletin 8-96. August 1, 1996.

FEMA. 2000. Coastal Construction Manual, FEMA 55. June 2000.

FEMA. 2000. Design and Construction Guidance for Community Shelters, FEMA 361. July 2000.

FEMA. 2004. Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds, FEMA 
424. January 2004.

FEMA. 2004. Taking Shelter From the Storm: Building a Safe Room Inside Your House, FEMA 320. 
March 2004.

FEMA. 2005. Mitigation Assessment Team Report: Hurricane Charley in Florida, FEMA 488. April 
2005. 

FEMA. 2005. Mitigation Assessment Team Report: Hurricane Ivan in Alabama and Florida, FEMA 489. 
August 2005.

FEMA. 2005. Home Builders Guideto Coastal Construction Technical Fact Sheets,FEMA 499. August 
2005.

FEMA. 2006. Mitigation Assessment Team Report: Hurricane Katrina in the Gulf Coast, FEMA 549. 
July 2006.

FEMA. 2006. Flood Insurance Manual. http://www.fema.gov/business/nfip/manual.shtm. May 
2006.

International Building Code (IBC). 2003. 2003 International Building Code. 01-Jan-2005. 

International Residential Code (IRC). 2003. International Residential Code for One- and Two- Family 
Dwellings. 01-Mar-2003.

Mississippi Governors Rebuilding Commission on Recovery, Rebuilding and Renewal. 2005. A 
Pattern Book for Gulf Coast Neighborhoods. November 2005.

National Fire Protection Association (NFPA). 2003. NFPA 5000: Building Construction and Safety 
Code, 2003 Edition.



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


H. Glossary

3-second peak gust  The wind speed averaging time used in ASCE 7 and the IBC. 

A Zone  A Zones are the areas not listed as V Zones, but also identified on a Flood Insurance 
Rate Map (FIRM) as being subject to inundation during a 100-year flood. The associated flood 
elevation has a 1-percent chance of being equaled or exceeded in any given year. There are 
several categories of A Zones that may be identified on a FIRM with one of the following designations: 
AO, AH, A1-30, AE, and unnumbered A Zones. 

Allowable Stress Design (ASD)  A method of proportioning structural members such that elastically 
computed stresses produced in the members by nominal loads do not exceed specified 
allowable stresses (also called working stress design) (ASCE 7-02).

Base flood - A flooding having a 1 percent chance of being equaled or exceeded in any given 
year; also known as the 100-year flood.

Base Flood Elevation (BFE)  Elevation of the 1-percent flood. This elevation is the basis of the insurance 
and floodplain management requirements of the National Flood Insurance Program 
(NFIP).

Coastal A Zone  The portion of the Special Flood Hazard Area (SFHA) landward of a V Zone or 
landward of an open coast without mapped V Zones (e.g., the shorelines of the Great Lakes), 
in which the principal sources of flooding are astronomical tides, storm surges, seiches, or 
tsunamis, not riverine sources. Like the flood forces in V Zones, those in Coastal A Zones are 
highly correlated with coastal winds or coastal seismic activity. Coastal A Zones may therefore 

H-1



H Glossary

H- 

Building on strong and safe foundations

be subject to wave effects, velocity flows, erosion, scour, or combinations of these forces. During 
base flood conditions, the potential for breaking wave heights between 1.5 feet and 3.0 feet will 
exist. Coastal A Zones are not shown on present day FIRMs or mentioned in a communitys 
Flood Insurance Study (FIS) Report. 

Crawlspace foundation  Crawlspace foundations are typically low masonry perimeter walls with 
interior piers supporting a wood floor system. These foundations are usually supported by shallow 
footings and are prone to failure caused by erosion or scour.

Design flood  The design flood is often, but not always equal to the base flood for areas identified 
as Special Flood Hazard Areas (SFHAs) on a communitys FIRM.

Design Flood Elevation (DFE)  The elevation of the Design Flood, including wave height relative 
to the datum specified on a communitys Flood Hazard Map (American Society of Civil Engineers 
[ASCE 7-02]).

Design professional  A state licensed architect or engineer.

Erosion  Process by which floodwaters lower the ground surface in an area by removing upper 
layers of soil.

Exposure Category B  A wind exposure identified in ASCE 7 and the International Building 
Code (IBC) as urban and suburban areas, wooded areas, or other terrain with numerous closely 
spaced obstructions having the size of single-family dwellings or larger. 

Exposure Category C  A wind exposure identified in ASCE 7 and the IBC as open terrain with 
scattered obstructions having heights generally less than 30 feet (9.1 meters). This category includes 
flat open country, grasslands, and all water surfaces in hurricane-prone regions. 

Flood Insurance Rate Map (FIRM)  An official map of a community, on which FEMA has delineated 
both the SFHA and the risk premium zones applicable to the community. The map shows the 
extent of the base floodplain and may also display the extent of the floodway and BFEs.

Freeboard  The height added to place a structure above the base flood to reduce the potential 
for flooding.The increased elevation of a building above the minimum design flood level to 
provide additional protection for flood levels higher than the 1-percent chance flood level and 
to compensate for inherent inaccuracies in flood hazard mapping.

Hydrodynamic forces  The amount of pressure exerted by moving floodwaters on an object, such 
as a structure. Among these loads are positive frontal pressure against the structure, drag forces 
along the sides, and suction forces on the downstream side.

Hydrostatic forces  The amount of lateral pressure exerted by standing or slowly moving floodwaters 
on a horizontal or vertical surface, such as a wall or a floor slab. The water pressure 
increases with the square of the water depth.



Glossary H

H- 

Leeward  The side away, or sheltered, from the wind.

National Flood Insurance Program (NFIP)  The NFIP is a Federal program enabling property owners 
in participating communities to purchase insurance as a protection against flood losses 
in exchange for State and community floodplain management regulations that reduce future 
flood damages. Participation in the NFIP is based on an agreement between communities and 
the Federal Government. If a community adopts and enforces floodplain management regulations 
to reduce future flood risk to new construction in floodplains, the Federal Government 
will make flood insurance available within the community as a financial protection against flood 
losses. This insurance is designed to provide an insurance alternative to disaster assistance to 
reduce the escalating costs of repairing damage to buildings and their contents caused by floods. 
The program was created by Congress in 1968 with the passage of the National Flood Insurance 
Act of 1968.

National Geodetic Vertical Datum 1929 (NGVD 1929)  A vertical elevation baseline determined in 
1929 as a national standard. Used as the standard for FIRMs until 2000.

North American Vertical Datum 1988 (NAVD 1988)  A vertical elevation baseline determined in 1988 
as a more accurate national standard. The current vertical elevation standard for new FIRMs.

Scour  Erosion by moving water in discrete locations, often as a result of water impacting foundation 
elements.

Shore-normal  Perpendicular to the shoreline.

Slab-on-grade foundation  Type of foundation in which the lowest floor of the house is formed 
by a concrete slab that sits directly on the ground. 

Slug  A unit of mass in the English foot-pound-second system. One slug is the mass accelerated 
at 1 foot per second (fps) by a force of 1 pound (lb). Since the acceleration of gravity (g) in English 
units is 32.174 fps, the slug is equal to 32.174 pounds (14.593 kilograms).

Special Flood Hazard Area (SFHA)  Portion of the floodplain subject to inundation by the base 
flood.

Stem wall foundation  A type of foundation that uses masonry block and reinforced with steel 
and concrete. The wall is constructed on a concrete footing, back-filled with dirt, compacted, 
and the slab is then poured on top.

Strength Design  A method of proportioning structural members such that the computed forces 
produced in the members by the factored loads do not exceed the member design strength 
(also called load and resistance factor design) (ASCE 7-02).

V Zones  V Zones are areas identified on FIRMs as zones VE, V1-30, or V. These areas, also 
known as Coastal High Hazard Areas, are areas along the coast that have a 1 percent or greater 



annual chance of flooding from storm surge and waves greater than 3 feet in height, as well as 
being subject to significant wind forces.

Windward  The side facing the wind.



RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST


I. Abbreviations and 
Acronyms

A

ABFE Advisory Base Flood Elevation

ACI American Concrete Institute

AF&PA American Forest & Paper Association

ASCE American Society of Civil Engineers

ASD Allowable Stress Design

ASTM American Society for Testing and Materials

AWPA American Wood Preservers Association

I- 



I Abbreviations and acronyms

I- 

Building on strong and safe foundations

B

BFE Base Flood Elevation

C

C&C components and cladding

CMU concrete masonry unit

CRSI Concrete Reinforced Steel Institute

cy cubic yard

D

DFE Design Flood Elevation

DL dead load

E

ea each

F

FEMA Federal Emergency Management Agency

FIRM Flood Insurance Rate Map

FIS Flood Insurance Study

fps feet per second



Abbreviations and acronyms I

I- 

FRP fiber reinforced polyester

ft feet

G

g gravity

I

IBC International Building Code

ICC International Code Council

IRC International Residential Code

K

kip 1,000 pounds

ksi kips per square inch

L

lb pound

lb/sq pounds per square foot

lf linear foot

LL live load

ls lump sum



M

MAT Mitigation Assessment Team

mph miles per hour

MWFRS Main Wind Force Resisting System

N

NAVD North American Vertical Datum of 1988

NDS National Design Specification for Wood

NFIP National Flood Insurance Program 

NFPA National Fire Protection Association

NGVD National Geodetic Vertical Datum of 1929

NR Not Recommended

O

o.c. on center

P

pcf pounds per cubic foot

psf pounds per square foot

psi pounds per square inch



R

ROM rough order of magnitude

S 

SBC Standard Building Code

SFHA Special Flood Hazard Area

SLOSH Sea, Lake, and Overland Surges from Hurricanes

sq square foot

SWL stillwater elevation

T

TBTO tributylin oxide

TMS The Masonry Society

U

UDA Urban Design Associates

u.n.o. unless noted otherwise

USGS United States Geological Survey

W

WWF welded wire fabrics