Recommended 

Residential Construction 

for Coastal Areas

Building on Strong and Safe Foundations

FEMA P-550, Second Edition/December 2009 

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 Coastal Areas 

Building on Strong and Safe Foundations

FEMA P-550, Second Edition / December 2009

FEMA

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS iii

Preface

Since the publication of the First Edition of FEMA 550 in July 2006, several advances have been 

made in nationally adopted codes and standards. Two editions of the International Residential Code® (the 2006 IRC® and the 2009 IRC) and the International Building Code® (the 2006 

IBC® and the 2009 IBC) have been published and the long awaited International Code Council 

(ICC) 600 Standard for Residential Construction in High Wind Areas (a successor to the legacy standard SSTD-10) has been issued.

To keep pace with developing codes and standards and to improve its guidance, FEMA is issuing 

this Second Edition of FEMA 550. In addition to being renamed to more accurately reflect its 

applicability, the Second Edition of FEMA 550 contains a new foundation style Case H, which incorporates an elevated concrete beam for improved structural efficiency. The Second Edition of 

FEMA 550 has also been updated for consistency with the 2006 and 2009 editions of the IRC and 

IBC, and the 2005 Edition of ASCE 7 Minimum Design Loads for Buildings and Other Structures.

made in nationally adopted codes and standards. Two editions of the International Residen

tial Code

IBC and the 2009 IBC) have been published and the long awaited International Code Council 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS v

Acknowledgments

FEMA would like to thank the following individuals who provided information, data, review, 

and guidance in developing the Second Edition of this publication.

In addition, FEMA would like to acknowledge the members of the project team for the First Edition of the publication. (Note: all affiliations were current as of July 2006.)

FEMA

John Ingargiola

FEMA Headquarters

Consultants

Dave Conrad

PBSJ

Deb Daly

Greenhorne & O'Mara, Inc.

Julie Liptak

Greenhorne & O'Mara, Inc.

David K. Low, PE

DK Low & Associates, LLC

Kelly Park

Greenhorne & O'Mara, Inc.

Scott Sundberg

Category X Coastal Consulting

Scott Tezak

URS Corporation

Jimmy Yeung, PhD, PE

Greenhorne & O’Mara, Inc.

and guidance in de
vi Building on strong and safe foundations

acknowledgments

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 

PBSJ

Ken Ford 

National Association of Homebuilders (NAHB)

Mike Hornbeck 

Gulf Construction Company, Inc.

David Kriebel, PhD, PE 

U.S. Naval Academy

Jim Puglisi 

Dewberry & Davis, LLC

John Ruble 

Bayou Plantation Homes

Bob Speight, PE

URS Corporation

Deb Daly

Greenhorne & O’Mara, Inc.

Julie Liptak

Greenhorne & O’Mara, Inc.

Wanda Rizer

Design4Impact

Naomi Chang Zajic

Greenhorne & O’Mara, Inc.

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 & O’Mara, Inc.

John Squerciati, PE

Dewberry & Davis, LLC
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS vii

Table of Contents

Preface...............................................................................................................................................iii

Acknowledgments.............................................................................................................................v

Introduction ......................................................................................................................................xv

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

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

1.2 Storm Surge........................................................................................................................ 1-5

1.3 Flood Effects....................................................................................................................... 1-5

1.3.1 Hydrostatic Forces...................................................................................................1-7

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

2.3 Foundation Styles in Coastal Areas................................................................................... 2-4

2.3.1 Open Foundations..................................................................................................2-5

2.3.1.1 Piles..............................................................................................................2-5

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

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

2.3.2.1 Perimeter Walls...........................................................................................2-8

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

2.4 Introduction to Foundation Design and Construction ................................................ 2-11

2.4.1 Site Characterization............................................................................................2-11

2.4.2 Types of Foundation Construction......................................................................2-12

2.4.2.1 Piles............................................................................................................2-12

2.4.2.2 Diagonal Bracing of Piles.........................................................................2-13

2.4.2.3 Knee Bracing of Piles................................................................................2-14

2.4.2.4 Wood-Pile-to-Wood-Girder Connections.................................................2-15

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........................................................................................................................ 3-2

3.2.1 Design Flood and DFE............................................................................................3-2

3.2.2 Design Stillwater Flood Depth (ds)........................................................................3-4

3.2.3 Design Wave Height (Hb).......................................................................................3-5

3.2.4 Design Flood Velocity (V)......................................................................................3-5

3.3 Hydrostatic Loads.............................................................................................................. 3-6

3.4 Wave Loads ........................................................................................................................ 3-7

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

3.4.2 Breaking Wave Loads on Vertical Walls.................................................................3-8

3.5 Hydrodynamic Loads......................................................................................................... 3-9

3.6 Debris Impact Loads........................................................................................................ 3-12
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS ix

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3.7 Erosion and Localized Scour.......................................................................................... 3-14

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

3.7.2 Localized Scour Around Vertical Walls and Enclosures.....................................3-19

3.8 Flood Load Combinations............................................................................................... 3-19

Chapter 4. Overview of Recommended Foundation Types and Construction for 

Coastal Areas.................................................................................................................................. 4-1

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

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

4.1.2 Elevation..................................................................................................................4-3

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

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

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

4.1.3.3 Field Preservative Treatment for Wood Members....................................4-5

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

4.1.5 Foundation Design Loads and Analyses................................................................4-8

4.2 Recommended Foundation Types for Coastal Areas..................................................... 4-14

4.2.1 Open/Deep Foundation: Timber Pile (Case A).................................................4-15

4.2.2 Open/Deep Foundation: Steel Pipe Pile with Concrete Column and

Grade Beam (Case B)...........................................................................................4-17

4.2.3 Open/Deep Foundation: Timber Pile with Concrete Column and

Grade Beam (Case C)...........................................................................................4-17

4.2.4 Open/Deep Foundation: Timber Pile with Concrete Grade and Elevated

Beams and Concrete Columns (Case H)............................................................4-19

4.2.5 Open/Shallow Foundation: Concrete Column and Grade Beam with Slabs

(Cases D and G)....................................................................................................4-21

4.2.6 Closed/Shallow Foundation: Reinforced Masonry – Crawlspace (Case E)......4-21

4.2.7 Closed/Shallow Foundation: Reinforced Masonry – Stem Wall (Case F).........4-23

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
x Building on strong and safe foundations

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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 Pertinent Coastal Construction Information

Appendix G FEMA Publications and Additional References

Appendix H Glossary

Appendix I Abbreviations and Acronyms

Tables

Chapter 2

Table 2-1. Foundation Type Dependent on Coastal Area..................................................... 2-5

Chapter 3

Table 3-1. Building Category and Corresponding Dynamic Pressure Coefficient (Cp)...... 3-9

Table 3-2. Drag Coefficient Based on Width to Depth Ratio............................................. 3-11

Table 3-3. Example Foundation Adequacy Calculations for a Two-Story Home

Supported on Square Timber Piles.................................................................... 3-17

Table 3-4. Local Scour Depth as a Function of Soil Type .................................................. 3-19

Table 3-5. Selection of Flood Load Combinations for Design........................................... 3-21

Chapter 4

Table 4-1a. Design Perimeter Wall Reactions (lb/lf) for One-Story Elevated Homes ......... 4-7

Table 4-1b. Design Perimeter Wall Reactions (lb/lf) for Two-Story Elevated Homes.......... 4-7
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS xi

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Table 4-2. Flood Forces (in pounds) on an 18-Inch Square Column.................................. 4-7

Table 4-3. Wind Reactions Used to Develop Case H Foundations....................................... 4-8

Table 4-4. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for

10-Foot Tall 3-Bay Foundations........................................................................... 4-10

Table 4-5. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for

15-Foot Tall 3-Bay Foundations........................................................................... 4-11

Table 4-6. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for

10-Foot Tall 6-Bay Foundations .......................................................................... 4-12

Table 4-7. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for

15-Foot Tall 6-Bay Foundations .......................................................................... 4-12

Table 4-8. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for

10-Foot Tall 9-Bay Foundations .......................................................................... 4-13

Table 4-9. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for

15-Foot Tall 9-Bay Foundations .......................................................................... 4-14

Table 4-10. Recommended Foundation Types Based on Zone ........................................... 4-15

Chapter 5

Table 5-1a. Foundation Design Cases for One-Story Homes Based on Height of

Elevation and Wind Velocity............................................................................... 5-10

Table 5-1b. Foundation Design Cases for Two-Story Homes Based on Height of

Elevation and Wind Velocity............................................................................... 5-11

Figures

Introduction

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 ..........xvi

Figure 2. Schematic range of home dimensions and roof pitches used as the basis for

the foundation designs presented in this manual..............................................xviii

Chapter 1

Figure 1-1. Wind damage to roof structure and gable end wall from Hurricane Katrina

(2005) (Pass Christian, Mississippi)...................................................................... 1-2

Figure 1-2. Saffir-Simpson Scale............................................................................................... 1-3
xii Building on strong and safe foundations

table of contents

Figure 1-3. Wind speeds (in mph) for the entire U.S............................................................ 1-4

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....... 1-5

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

Florida..................................................................................................................... 1-6

Figure 1-6. Comparison of storm surge levels along the shorelines of the Gulf Coast for

Category 1, 3, and 5 storms................................................................................... 1-6

Figure 1-7. Building floated off of its foundation (Plaquemines Parish, Louisiana)........... 1-7

Figure 1-8. Aerial view of damage to one of the levees caused by Hurricane Katrina.......... 1-8

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. ................................................................... 1-8

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

Stinson Beach, California. .................................................................................... 1-9

Figure 1-11. Storm surge and waves overtopping a coastal barrier island in Alabama

(Hurricane Frederic, 1979)................................................................................... 1-9

Figure 1-12. Pier piles were carried over 2 miles by the storm surge and waves of

Hurricane Opal (1995) before coming to rest in Pensacola Beach, Florida... 1-10

Figure 1-13. Extreme case of localized scour undermining a slab-on-grade house in

Topsail Island, North Carolina, after Hurricane Fran (1996)........................... 1-11

Chapter 2

Figure 2-1. Recommended open foundation practice for buildings in A zones, Coastal

A zones, and V zones............................................................................................. 2-3

Figure 2-2 Slab-on-grade foundation failure due to erosion and scour undermining

from Hurricane Dennis, 2005 (Navarre Beach, Florida).................................... 2-3

Figure 2-3. Compression strut at base of a wood pile. Struts provide some lateral support

for the pile, but very little resistance to rotation.................................................. 2-6

Figure 2-4. Near collapse due to insufficient pile embedment (Dauphin Island,

Alabama)................................................................................................................ 2-6

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

Alabama). .............................................................................................................. 2-6
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS xiii

Table of contents

Figure 2-6. Column connection failure (Belle Fontaine Point, Jackson County,

Mississippi)............................................................................................................. 2-7

Figure 2-7. Performance comparison of pier foundations. Piers on discrete footings

failed while piers on more substantial footings survived (Pass Christian,

Mississippi)............................................................................................................. 2-8

Figure 2-8. Isometric view of an open foundation with grade beam..................................... 2-9

Figure 2-9. Isometric view of a closed foundation with crawlspace..................................... 2-10

Figure 2-10. Pile installation methods..................................................................................... 2-12

Figure 2-11. Diagonal bracing schematic................................................................................ 2-14

Chapter 3

Figure 3-1. Wind speeds (in mph) for the entire U.S. .......................................................... 3-3

Figure 3-2. Parameters that determine or are affected by flood depth................................. 3-4

Figure 3-3. Normally incident breaking wave pressures against a vertical wall (space

behind vertical wall is dry).................................................................................. 3-10

Figure 3-4. Normally incident breaking wave pressures against a vertical wall (stillwater

level equal on both sides of wall)........................................................................ 3-10

Figure 3-5. Distinguishing between coastal erosion and scour. A building may be subject

to either or both, depending on the building location, soil characteristics,

and flood conditions............................................................................................ 3-14

Figure 3-6. Scour at vertical foundation member stopped by underlying scour-resistant

stratum.................................................................................................................. 3-16

Chapter 4

Figure 4-1. The BFE, freeboard, erosion, and ground elevation determine the

foundation height required.................................................................................. 4-3

Figure 4-2. Design loads acting on a column.......................................................................... 4-6

Figure 4-3. Shear panel reactions for the 3- and 6-bay models. Reactions for the 9-bay

model were similar to those of the 6-bay............................................................ 4-10

Figure 4-4. Profile of Case A foundation type....................................................................... 4-16

Figure 4-5. Profile of Case B foundation type....................................................................... 4-18

Figure 4-6. Profile of Case C foundation type....................................................................... 4-19
xiv Building on strong and safe foundations

table of contents

Figure 4-7. Profile of Case H foundation type...................................................................... 4-20

Figure 4-8. Profile of Case G foundation type....................................................................... 4-22

Figure 4-9. Profile of Case D foundation type. ..................................................................... 4-23

Figure 4-10. Profile of Case F foundation type....................................................................... 4-24

Figure 4-11. Profile of Case E foundation type...................................................................... 4-24

Chapter 5

Figure 5-1. Schematic of a basic module and two footprints................................................. 5-3

Figure 5-2. Foundation selection decision tree....................................................................... 5-8

Figure 5-3. “T” shaped modular design................................................................................. 5-12

Figure 5-4. “L” shaped modular design ................................................................................ 5-12

Figure 5-5. “Z” shaped modular design ................................................................................ 5-13 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS xv

Introduction 

The purpose of this design manual is to provide recommended 

foundation designs and guidance for rebuilding homes destroyed by 

hurricanes in coastal areas. 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, Charley, Katrina, and Rita, and recent events 

such as Hurricane Ike continue to show the vulnerability of our “built environment” (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, the Federal Emergency Management Agency (FEMA) has developed this 

manual to help the community of homebuilders, contractors, and local engineering professionals in rebuilding homes destroyed by hurricanes, and designing and building safer and less 

vulnerable new homes.
xvi

INTRODUCTION

BUILDING ON STRONG AND SAFE FOUNDATIONS

Intent of the Manual

The intent of the manual is to provide homebuilders, contractors, and engineering professionals with a series of recommended foundation designs that will help create safer and stronger 

buildings in coastal areas. The designs are intended to help support rebuilding efforts after 

coastal areas have been damaged by floods, high winds, or other natural hazards.

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 hazardous coastal areas. The objectives used to guide the development of 

this manual are:

O To provide residential foundation designs that will require minimal engineering oversight 

O 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 Governor’s Rebuilding Commission on Recovery, Rebuilding, and Renewal (see Appendix B)

O To utilize "model" layouts so that many homes can be constructed without significant additional engineering efforts

The focus of this document is on the foundations 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).

SOURCE: HURRICANE 

KATRINA MAT PHOTO 
xvii

INTRODUCTION

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 

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 or in riverine areas subjected to high-velocity flows. Design professionals 

can be contacted to ensure the foundation designs provided in this manual are suitable for 

specific sites.

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) as determined in response 

to Hurricanes Katrina and Rita. The ABFEs published in the Hurricane Recovery Maps were 

compared to local topographic maps for the Gulf Coast. The comparison revealed that providing foundation designs up to 15 feet tall would allow over 80 percent of the homes damaged 

by Hurricane Katrina to be protected from flood events reflected in the ABFEs and in the Hurricane Recovery Maps. Many homes can be elevated to the BFE on foundations that are 4 feet 

tall or less. 

This updated edition of FEMA 550 introduces the Case H foundation, which is an open/deep 

foundation developed for use in coastal high hazard areas (V zones). It is also appropriate to use 

the Case H foundation in Coastal A and non-coastal A zones. Case H foundations incorporate 

elevated reinforced concrete beams that provide three important benefits. One, the elevated 

beams work in conjunction with the reinforced concrete columns and grade beams to produce 

a structural frame that is more efficient at resisting lateral loads than the grade beams and cantilevered columns used in other FEMA 550 open foundations. The increased efficiency allows 

foundations to be constructed with smaller columns that are less exposed to flood forces.

The second benefit is that the elevated reinforced concrete beams provide a continuous foundation that can support many homes constructed to prescriptive designs from codes and standards 

such as the IRC, the American Forest and Paper Association’s (AF&PA’s) Wood Frame Construction Manual for One- and Two-Family Dwellings (WFCM), and the International Code Council’s 

(ICC’s) Standard for Residential Construction in High Wind Regions (ICC-600).

The third benefit that Case H foundations provide is the ability to support relatively narrow 

(14-foot wide) homes. It is anticipated that Case H foundations can be used for several styles of 

modular homes.

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.
xviii

INTRODUCTION

Building on strong and safe foundations

Using the Manual

The following information is needed to use this manual:

n Design wind speed and the Design Flood Elevation (DFE) at the site

n The flood zone(s) at the site

n Building layout

n 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

n Addressing and supporting unique features of the home

n Confirming the suitability of the designs for a specific home on a specific site

n Allowing use of value engineering to produce a more efficient design

These "prescriptive" 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 

Figure 2. 

Schematic range of 

home dimensions and 

roof pitches used as the 

basis for the foundation 

designs presented in 

this manual.
xix

INTRODUCTION

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 

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 in many coastal areas. 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. Designing and constructing the home to meet all the requirements of the IBC or the IRC is the minimum action 

necessary to producing hazard-resistant homes. However, any model code must contain minimum requirements. FEMA supports the use of best practice approaches for improved resistance 

to natural hazards.

The foundations presented in this manual have been designed to resist the flood, wind, and 

gravity loads specified in Appendix C and load combinations specified in the American Society 

of Civil Engineers’ (ASCE’s) Minimum Design Loads for Buildings and Other Structures (ASCE 7-05). 

Although the designs provide significant resistance to gravity, lateral, and uplift loads, they have 

not been specifically designed for seismic events. In coastal areas where seismic risks exist, design professionals should confirm that the foundation designs presented herein are adequate 

to resist seismic loads on site.

To gain the benefits of a “best practices” approach, readers are directed to publications such as 

FEMA 499, Home Builder’s 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. 

Organization of the Manual

There are five chapters and nine 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 a coastal 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 safe and strong foundations. 

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 homes 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.
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INTRODUCTION

Building on strong and safe foundations

Limitations of the Manual

This manual has been provided to assist in reconstruction efforts after coastal areas have been damaged by floods, high winds, or other natural hazards. 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 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 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. 

This Second Edition of FEMA 550 is consistent with the 2009 editions of the IBC and IRC.

n Appendix D presents detailed calculations on how to design the foundation of residential 

buildings. Two examples, one for open foundations and the other for closed foundations, 

are included.

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 fact sheets contained in FEMA 499 (Home Builder’s Guide to Coastal 

Construction Technical Fact Sheet Series) and a recovery advisory contained in FEMA P-757 

(Hurricane Ike in Texas and Louisiana: Mitigation Assessment Team Report, Building Performance 

Observations, Recommendations, and Technical Guidance) that are pertinent to construction in 

coastal areas.

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 this manual.

n Appendix I defines abbreviations and acronyms used in this manual.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 1-1

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 

coastal areas: 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 and typhoons are the basis for design wind speeds for many portions of the U.S. and 

its territories. 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). 
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

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 2009 editions of the International Building Code® (IBC®) and the 

International Residential Code® (IRC®). 

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 1-2). 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. While Hurricane Katrina’s storm surge was roughly that of a Category 5, 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).

Source: Hurricane 

Katrina MAT photo
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 1-

TYPES OF HAZARDS 1

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 7-05, Figure C6-2.

Figure 1-2. 	 Saffir-Simpson Scale.

Source: Hurricane Katrina in the GULF COAST (FEMA 549)

Saffir-Simpson Scale (Category/Damage)
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

Figure 1-3. Wind speeds (in mph) for the entire U.S.Sour

ce: ASCE 7-05
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 1-

TYPES OF HAZARDS 1

1.2	 Storm Surge

S

torm 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 (Figure 1-5). Because much of the United States’ densely populated coastlines lie less than 20 feet 

above sea level, the danger from storm surge is great. This is particularly true along the Gulf of 

Mexico where the shape and bathymetry of the Gulf contribute to storm surge levels that can 

exceed most other areas in the U.S. (Figure 1-6).

1.3	 Flood Effects

Although coastal flooding can originate from a number of sources, hurricanes and weaker 

tropical storms not categorized as hurricanes are the primary cause of flooding (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. 

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.
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

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 (FEMA 549) 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 1-

TYPES OF HAZARDS 1

1.3.1	 Hydrostatic Forces

Horizontal hydrostatic forces against a structure are created when the level of standing or slowly 

moving floodwaters 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 (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 (Figure 1-8)

n Outflow (flow in the seaward direction) of floodwaters driven into bay or upland areas by a 

storm

n 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 

Figure 1-7. 

Building floated off

of its foundation

(Plaquemines Parish,

Louisiana).

Source: Hurricane 

Katrina in the gulf

coast (FEMA 549)
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

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 (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 (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 

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

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)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 1-

TYPES OF HAZARDS 1

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 

hydrodynamic forces (although 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 carports, 

decks, porches, or awnings. 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)
1-10 Building on strong and safe foundations

1 TYPES OF HAZARDS

1.3.4	 Floodborne Debris

Floodborne debris produced by coastal flood events and storms typically includes carports, 

decks, porches, awnings, steps, ramps, breakaway wall panels, portions of or entire houses, fuel 

tanks, vehicles, boats, piles, fences, destroyed erosion control structures, and a variety of smaller objects (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 piles, 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 coastal areas. 

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 (storm-induced) 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, Coastal Construction Manual for additional guidance on assessing short- and long-term 

erosion.

Figure 1-12.

Pier piles were carried

over 2 miles by the

storm surge and waves

of Hurricane Opal (1995)

before coming to rest

near this elevated house

in Pensacola Beach,

Florida.

Source: COastal

COnStruction manual

(FEMA 55)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 1-11

TYPES OF HAZARDS 1

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 pile 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, piles, and grade beam structures, 

and, in severe cases, can lead to structural failure (Figure 1-13). This document considers these 

effects on the foundation size and depth of embedment requirements.

FEMA 55 contains guidance on predicting scour, much of which is based on conditions observed after numerous coastal storms. FEMA 55 suggests that scour depths around individual 

plies be estimated at two times the pile diameter for circular piles and two times the diagonal 

dimension for square or rectangular piles. 

In some storms (e.g., Hurricane Ike, which struck the Texas coast in October 2008), observed 

scour depths exceed those suggested in FEMA 55. Because erosion and scour reduce the resistance of the pile (by reducing its embedment) and increases stresses within the pile (by 

increasing the bending moment within the pile that the lateral forces create), they can readily 

cause failure of a coastal foundation. To help prevent failure, erosion and scour depths should 

be approximated conservatively. After Hurricane Ike, FEMA developed eight Hurricane Ike Recovery Advisories (RAs). One of the RAs, Erosion, Scour, and Foundation Design, discusses erosion 

and scour and their effects on coastal homes with pile foundations and is presented in Appendix F. All of the Hurricane Ike RAs are available at http://www.fema.gov/library/viewRecord.

do?id=3539.

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)

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-

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 in coastal areas should be designed in accordance with the 2006 or 2009 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, or lateral movement of the building 
2- Building on strong and safe foundations

2 FOUNDATIONS

n Function after being exposed to the anticipated levels of erosion and scour that may occur 

over the life of the building.

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”). A Coastal A zone 

is also known as the Limit of Moderate Wave Action (LiMWA), which is the landward extent of 

coastal areas designated Zone AE where waves 

higher than 1.5 feet can exist during a design 

flood. 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 

(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 erosion and 

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. Fact 

Sheet No. 2 of FEMA 499 contains information about NFIP 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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-

FOUNDATIONS 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).

Source: HURRICANE DENNIS MAT PHOTO
2- Building on strong and safe foundations

2 FOUNDATIONS

2.3 Foundation Styles in Coastal Areas

S

everal styles of foundations can be used to elevate homes. In discussing foundation styles, it 

is beneficial to categorize them as open, closed, shallow, or deep. 

As the name implies, open foundations generally consist of piles, piers, or columns and 

present minimal obstructions to moving floodwaters. With open foundations, moving floodwaters, breaking waves, and smaller pieces of floodborne debris should meet relatively few 

obstructions and hopefully be able to pass under the home without imparting large flood loads 

on the foundation. Open foundations have the added benefit of disrupting flood flows less than 

larger obstructions. This can help to reduce scour around foundation elements.

On the other hand, closed foundations typically consist of continuous foundation walls (constructed of masonry, concrete, or treated wood) that can enclose crawlspaces or, as in the case 

of stem walls, areas of retained soils. Closed foundation walls create large obstructions to moving floodwaters and large flood forces can be imparted on them by breaking waves, floodborne 

debris, and the hydrodynamic loads associated with moving water. Closed foundations are also 

more vulnerable to scour than open foundations.

The terms shallow and deep signify the relative depth of the soils on which the homes are 

founded. Shallow foundations are set on soils that are relatively close to the surface of the 

surrounding grade, generally within 3 feet of the finished grade. In cold climates, shallow foundations may need to be extended 4 feet or more below grade to set the foundation beneath the 

design frost depth. Shallow foundations can consist of discrete concrete pad footings, strip footings, or a matrix of strip footings placed to create a mat foundation. Mat foundations have the 

added benefit of better resisting uplift and overturning forces than foundations consisting of 

discrete pad footings.

Deep foundations are designed to be supported on much deeper soils or rock. These foundations frequently are used where soils near the surface have relatively weak bearing capacities 

(typically 700 pounds per square foot [psf] or less), when soils near the surface contain expansive clays (also called shrink/swell soils because they shrink when dry and swell when wet) or 

where surface soils are vulnerable to being removed by erosion or scour.

Although typical foundation styles vary geographically, deep foundations for residential construction in coastal areas generally consist of driven treated timber piles or treated square piles. 

Driven concrete piles are common in other areas. 

Only open foundations with base members or elements (piles 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 in coastal areas can be found in FEMA 499, Fact Sheet No. 11 (see Appendix F).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-

FOUNDATIONS 2

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. As previously 

mentioned, 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 pile 

(Figure 2-3). These members are not true grade beams but rather are compression struts. They 

provide lateral support for portions of the pile 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 (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 building’s pile foundation performance will allow the 

building to remain standing and intact following a design flood event (Figure 2-5).
2- Building on strong and safe foundations

2 FOUNDATIONS

Figure 2-5. 

Successful pile 

foundation following 

Hurricane Katrina 

(Dauphin Island, 

Alabama). 

Source: Hurricane 

Katrina in the Gulf 

Coast (FEMA 549)

Figure 2-3. 

Compression strut at 

base of a wood pile. 

Struts provide some 

lateral support for 

the pile, 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)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-

FOUNDATIONS 2

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. 

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 (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.

2.3.1.2 Piers

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 foundation’s performance (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 (Figure 

2-8). 

Figure 2-6. 

Column connection 

failure (Belle Fontaine 

Point, Jackson County, 

Mississippi).

Source: Hurricane 

Katrina in the Gulf 

Coast (FEMA 549)
2- Building on strong and safe foundations

2 FOUNDATIONS

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.

 

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 

Base Flood Elevation (BFE), they must be equipped with openings that allow floodwaters to flow 

in and out of the area enclosed by the walls (Figure 2-9 presents an isometric view). The entry 

and exit of floodwaters 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.

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).

Source: HURRICANE 

KATRINA MAT PHOTO
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-

FOUNDATIONS 2

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

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.

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.
2-10 Building on strong and safe foundations

2 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 (WWFs) for shrinkage control. While commonly 

used in residential structures in A zones, slab-on-grade foundations are prone to erosion, prohibited in V zones, and 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 

Figure 2-9. Isometric view of a closed foundation with crawlspace.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-11

FOUNDATIONS 2

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

T

his section introduces two main issues related to foundation design and construction: 

site characterization and types of foundation construction. Construction materials and 

methods 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 

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 if 

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 pits

n 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 (NRCS) 

(formerly the Soil Conservation Service [SCS]) 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 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 homebuilder’s 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 1806 of the 2009 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.
2-12 Building on strong and safe foundations

2 FOUNDATIONS

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 (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 powerdriven winch and then dropped onto the pile.

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 

Figure 2-10. 

Pile installation 

methods.

Source: COastal 

COnstruction 

manual

(FEMA 55)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-13

FOUNDATIONS 2

the designs provided in this manual unless the method for compressing the soil is approved 

by a geotechnical engineer.

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 designs provided in this manual unless capacity is verified 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 piles are 

sufficiently designed to withstand external forces, because bracing will not assist in countering 

these forces. A drawback to bracing, however, is that the braces themselves can become obstructions to moving floodwaters and increase a foundation’s 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.
2-14 Building on strong and safe foundations

2 FOUNDATIONS

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 piles 

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. Although knee 

braces do not stiffen a foundation as much as diagonal bracing, they do offer some advantages 

Figure 2-11. Diagonal bracing schematic.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 2-15

FOUNDATIONS 2

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 herein.

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. 

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 a licensed 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.

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-1

3. Foundation Design

 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 2009 (IBC 2009) or ASCE 7-05, 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 these 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 

7-05, the standard referenced by the IBC 2009. Either allowable stress design (ASD) or strength 
3- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 to accommodate strength design concepts. 

Assumptions utilized in this manual can be found in Appendix C.

3.1	 Wind Loads

Wind loads on a building structure are calculated using the methodology presented in 

ASCE 7-05. 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 7-05 wind speed map (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 7-05 includes scaling factors for other exposures and 

heights. 

ASCE 7-05 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 7-05 also specifies wind loads for components and cladding (C&C). Components and 

cladding are considered part of the building envelope, and ASCE 7-05 requires C&C to be designed to resist higher wind pressures than a MWFRS. 

3.2	 Flood Loads

T

his manual develops in more detail flood load calculations and incorporates the methodology presented in ASCE 7-05. Although wind loads can directly affect a structure and dictate 

the actual foundation design, the foundation is more affected by flood loads. ASCE 24-05 

discusses floodproof construction. Loads developed in ASCE 24-05 come directly from ASCE 7-

05, 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.

3.2.1	 Design Flood and DFE

The design flood is defined by ASCE 7-05 as the greater of the following two flood events: 

1. Base flood, affecting those areas identified as SFHAs on the community’s FIRM, or 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-

FOUNDATION DESIGN LOADS 3 Figure 3-1. 	 Wind speeds (in mph) for the entire U.S. Source: ASCE 7-05
3- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 

Figure 3-2.

Parameters that

determine or are

affected by flood

depth.

Source: COastal 

COnstruction 

manual

(FEMA 55)

2. The flood corresponding to the area designated as a flood hazard area on a community’s 

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 community’s flood hazard map. Figure 3-2 shows the parameters that determine or are affected by flood depth.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-

FOUNDATION DESIGN LOADS 3

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 piles

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 7-05 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 
3- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 ASCE 7-05 suggested a range of flood velocities from:

V = ds ÷ t (expected lower bound) 

to

V = (gds)0.5 (expected upper bound) 

Where

V = Average velocity of water in ft/s

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 zone

n Topography and slope

n Distance from the source of flooding

n 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). 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-

FOUNDATION DESIGN LOADS 3

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 = 1⁄2 γ ds

2

Where 

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

element

γ = 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 = γ (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)
3- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 7-05:

Fbrkp = (1/2)CDγDHb

2

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

γ = 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 7-05:

Fbrkw = 1.1Cpγds

2 + 2.4γds2

Where 

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

flood elevation
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-

FOUNDATION DESIGN LOADS 3

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, or 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

γ = 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, 

and

n 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 (Figure 3-3).

If free-standing water exists behind the wall (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 7-05:

Fbrkw = 1.1Cpγds

2 + 1.9γds2

Post-storm damage inspections show that breaking wave loads have virtually destroyed 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 and V zones. 

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, 
3-10 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

Figure 3-4.

Normally incident

breaking wave

pressures against a

vertical wall (stillwater

level equal on both

sides of wall).

Source: ASCE 7-05

Figure 3-3.

Normally incident

breaking wave

pressures against a

vertical wall (space

behind vertical wall is

dry).

Source: ASCE 7-05

and suction on the downstream side. This manual assumes that the velocity of the floodwaters 

is constant (i.e., steady state flow). 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-11

FOUNDATION DESIGN LOADS 3

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 = 1⁄2Cd ρV2A

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)

ρ = 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: COASTAL CONSTRUCTION MANUAL (FEMA 55)
3-12 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 building

n Downstream from large floatable 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 7-05:

Fi = (πWVbCICOCDCBRmax) ÷ (2g∆t)

Where

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

π = 3.14

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

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

CI = Importance coefficient (see Table C5-1 of ASCE 7-05)

CO = Orientation coefficient = 0.8

CD = Depth coefficient (see Table C5-2 and Figure C5-1 of ASCE 7-05)

CB = Blockage coefficient (see Table C5-3 and Figure C5-2 of ASCE 7-05)

Rmax= Maximum response ratio for impulsive load (see Table C5-4 of ASCE 7-05)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-13

FOUNDATION DESIGN LOADS 3

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 = (πWV) ÷ (2g∆t)

This equation is very similar to the equation provided in ASCE 7-98 and FEMA 55. The only difference is the π/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 object

n Flood velocity (V)

n Velocity of the object compared to the flood velocity

n Portion of the building that will be struck and most vulnerable to collapsing

n 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 pile concurrently with other flood loads (see FEMA 55, Table 11-6). 

For closed foundations (which are not recommended in Coastal A zones and are not allowed 

in V zones), FEMA 55 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 piles). The Commentary of ASCE 7-05 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.
3-14 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 7-05 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 7-05 recommended value for ∆t is 0.03 second.

3.7 	 Erosion and Localized Scour

E

rosion is defined by Section 1-2 of ASCE 24-

05 as the "wearing away of the land surface 

by detachment and movement of soil and 

rock fragments, during a flood or storm or over 

a period of years, through the action of wind, water, or other geological processes." Section 7.5 

of FEMA 55 describes erosion as “the wearing or 

washing away of coastal lands.” Since the exact 

configuration of the soil loss is important for foundation design purposes, a more specific definition is used in this document (see the text box above and Figure 3-5).

Waves and currents during coastal flood conditions are capable of creating turbulence around 

foundation elements and causing localized scour, and the moving floodwaters can cause 

generalized erosion. Determining potential for localized scour and generalized erosion 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 

NOTE: The method for 

determining debris impact 

loads in ASCE 7-05 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).

Erosion refers to a general lowering of 

the ground surface over a wide area.

Scour refers to a localized loss of soil, 

often around a foundation element.

Figure 3-5. Distinguishing between coastal erosion and scour. A building may be subject to either or both,

depending on the building location, soil characteristics, and flood conditions.

Original

Ground

Erosion Scour Erosion

and Scour

Original

Ground
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-15

FOUNDATION DESIGN LOADS 3

the posts, piles, piers, columns, footings, or walls. Localized scour and generalized erosion 

determinations will require knowledge of the flood depth, flow conditions, soil characteristics, 

and foundation type. 

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 3-6 illustrates localized scour at a pile, with and without 

a scour-resistant terminating stratum. Currently, there is no design guidance in ASCE 7-05 on 

how to calculate scour. FEMA 55 suggests that localized scour around a foundation element be 

calculated by the following equation: 

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)

However, recent storms (e.g., Hurricane Ike, 

which struck the Texas coast in October 2008) 

have produced localized scour that exceeded the 

suggested depths. Because scour, coupled with 

erosion, can cause foundation systems to fail, a 

more conservative approach should be considered. Foundation systems should be analyzed for 

their ability to resist scour depths of 3 to 4 times 

pile diameters in addition to anticipated erosion 

levels. This guidance is more conservative than 

what has been recommended in FEMA 55, FEMA 

499, and other publications.

Erosion and scour can have several adverse impacts on coastal foundations:

n Erosion and scour can reduce the embedment of the foundation into the soil, causing 

shallow foundations to collapse and making buildings on deep foundations more 

susceptible to settlement, lateral movement, or overturning from lateral loads.

NOTE: Resisting higher 

bending moments brought 

about by erosion and scour 

may necessitate a larger 

cross-section or decreased pile spacing 

(i.e., more piles) or, in some cases, use 

of a different pile material (e.g., concrete 

or steel instead of wood). Resisting 

increased lateral flood loads brought about 

by erosion (and possibly by linear scour) 

would necessitate a similar approach. 

However, designers should remember 

that increasing the number of piles or 

increasing the pile diameter will, in turn, 

also increase lateral flood loads on the 

foundation.

Resisting increased unbraced lengths

brought about by erosion and scour 

will require deeper embedment of the 

foundation into the ground.
3-16 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

n Erosion and scour can increase the unbraced length of pile foundations, increase the bending moment to which they are subjected, and overstress piles.

n Erosion over a large area between a foundation and a flood source can expose the foundation to increased lateral flood loads (i.e., greater stillwater depths, possible higher wave 

heights, and higher flow velocities).

n Local scour around individual piles will not generally expose foundations to greater flood 

loads, but scour across a building site may do so.

To illustrate these points, calculations were made to examine the effects of erosion and scour on 

foundation design for a simple case – a 32-foot x 32-foot two-story home (10-foot story height), 

situated away from the shoreline and elevated 8 feet above grade on 25 square timber piles 

(spaced 8 feet apart), on medium dense sand. The home was subjected to a design wind event 

with a 130-mph (3-second gust speed) wind speed and a 4-foot stillwater depth above the uneroded grade, with storm surge and broken waves passing under the elevated building. Lateral wind 

and flood loads were calculated in accordance with ASCE. For simplicity, the piles were analyzed under lateral wind and flood loads only; dead, live, and wind uplift loads were neglected. 

If dead, live, and wind uplift loads were included in the analysis, deeper pile embedment and 

possibly larger piles may be needed. 

Three different timber pile sizes (8-, 10-, and 12-inch square) were evaluated using pre-storm 

embedment depths of 10-, 15-, and 20-feet, and five different erosion and scour conditions (erosion = 0 or 1 foot; scour ranges from 2.0 times the pile diameter to 4.0 times the pile diameter). 

The results of the analysis are shown in Table 3-3. A shaded cell indicates the combination of pile 

size, pre-storm embedment, and erosion and scour would not provide the bending resistance 

and/or embedment required to resist the lateral loads imposed on them. The reason(s) for a 

foundation failure is indicated in each shaded cell, using “P” for pile failure due to bending and 

overstress within the pile and “E” for an embedment failure from the pile/soil interaction. An 

Figure 3-6.

Scour at vertical

foundation member

stopped by underlying

scour-resistant

stratum.

Source: COastal 

COnstruction 

manual

(FEMA 55)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-17

FOUNDATION DESIGN LOADS 3

unshaded cell with “OK” indicates bending and foundation embedment criteria would both be 

satisfied by the particular pile size/pile embedment/erosion and scour combination. 

Table 3-3. Example Foundation Adequacy Calculations for a Two-Story Home Supported on Square Timber Piles

(and situated away from the shoreline, with storm surge passing under the home, a 130-mph wind zone, and soil

is medium dense sand)

Pile Embedment Before

Erosion and Scour

Erosion and Scour

Conditions

Pile Diameter, a Pile Diameter, a Pile Diameter, a

8 inch 10 inch 12 inch

10 feet

Erosion = 0, 

Scour = 0 P, E E OK

Erosion = 1 foot, 

Scour = 2.0 a P, E E E

Erosion = 1 foot, 

Scour = 2.5 a P, E E E

Erosion = 1 foot, 

Scour = 3.0 a P, E E E

Erosion = 1 foot, 

Scour = 4.0 a P, E P, E E

15 feet

Erosion = 0, 

Scour = 0 P OK OK

Erosion = 1 foot, 

Scour = 2.0 a P OK OK

Erosion = 1 foot, 

Scour = 2.5 a P OK OK

Erosion = 1 foot, 

Scour = 3.0 a P OK OK

Erosion = 1 foot, 

Scour = 4.0 a P, E P, E E

20 feet

Erosion = 0, 

Scour = 0 P OK OK

Erosion = 1 foot, 

Scour = 2.0 a P OK OK

Erosion = 1 foot, 

Scour = 2.5 a P OK OK

Erosion = 1 foot, 

Scour = 3.0 a P OK OK

Erosion = 1 foot, 

Scour = 4.0 a P P OK

P = pile failure due to bending and overstress within the pile

E = embedment failure from the pile/soil interaction

OK = bending and foundation embedment criteria both satisfied by the particular pile size/pile embedment/erosion and 

scour combination 
3-18 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

A review of Table 3-3 shows several key points:

n Increasing pile embedment will not offset foundation inadequacy (bending failure) resulting from too small a pile cross-section or too weak a pile material.

n Increasing cross-section (or material strength) will not compensate for inadequate pile 

embedment.

n Given the building and foundation configuration used in the example, the 8-inch square 

pile is not strong enough to resist the lateral loads resulting from the 130-mph design wind 

speed under any of the erosion and scour conditions evaluated, even if there is no erosion 

or scour. Homes supported by 8-inch square timber piles, with embedment depths of 10 feet 

or less, will likely fail in large numbers when subjected to design or near design loads and 

conditions. Homes supported by deeper 8-inch piles may still be lost during a design event 

due to pile (bending failures).

n The 10-inch square pile is strong enough to resist bending under all but the most severe 

erosion and scour conditions analyzed.

n The 12-inch pile is the only pile size evaluated that satisfies bending requirements under all 

erosion and scour conditions analyzed. This pile works with 10 feet of embedment under 

the no erosion and scour condition. However, introducing as little as 1 foot of erosion and 

scour equal to twice the pile diameter was enough to render the foundation too shallow.

n Fifteen feet of pile embedment is adequate for both 10- and 12-inch piles subject to 1 foot of 

erosion and scour up to three times the pile diameter. However, when the scour is increased 

to four times the pile diameter (frequently 

observed following Hurricane Ike), 15 feet of 

embedment is inadequate for both piles. In 

general terms, approximately 11 feet of embedment is required in this example home to 

resist the loads and conditions after erosion 

and scour are imposed.

n The 12-inch pile with 20 feet of embedment 

was the only foundation that worked under 

all erosion and scour conditions analyzed. 

This pile design may be justified for the 

example home analyzed when expected erosion and scour conditions are unknown or 

uncertain.

These analyses were based on only 1 foot of erosion, which historically is a relatively small 

amount. Many storms like Hurricanes Isabel, Ivan, and Ike caused much more extensive erosion. In some areas, these storms stripped away several feet of soil.

A foot of erosion is more damaging than a foot of scour. While scour reduces pile embedment 

and increases stresses within the pile, erosion reduces embedment, increases stresses, and, since 

it increases stillwater depths, it also increases the flood loads that the foundation must resist. 

CAUTION: The results in Table 

3-3 should not be used in lieu of 

building- and site-specific engineering analyses and foundation design. The 

table is intended for illustrative purposes only 

and is based upon certain assumptions and 

simplifications, and for the combinations of 

building characteristics, soil conditions, and 

wind and flood conditions described above. 

Registered design professionals should be 

consulted for foundation designs.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-19

FOUNDATION DESIGN LOADS 3

Table 3-3 suggests that increasing embedment beyond 15 feet is not necessary for 10- and 12-

inch piles. This is only the case for relatively small amounts of erosion (like the 1 foot of erosion 

in the example). If erosion depths are greater, pile embedment must be increased. 

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 3-4. 

Table 3-4. 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: COASTAL CONSTRUCTION MANUAL (FEMA 55) 

3.8	 Flood Load Combinations

L

oad combinations (including those for flood loads) are given in ASCE 7-05, 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
3-20 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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 7-05 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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 3-21

FOUNDATION DESIGN LOADS 3

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 ASD, 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 3-5 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 3-5. 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 A 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 COASTAL AREAS 4-

4.	Overview of

Recommended

Foundation Types and

Construction for Coastal

Areas

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- Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

4.1	 Critical Factors Affecting Foundation Design

Foundation construction types are dependent upon the following critical factors: 

n Design wind speed

n Elevation height required by the BFE and local ordinances

n Flood zone 

n Soil parameters 

Soil parameters, like bearing capacities, shear coefficients, and subgrade moduli, are important 

in designing efficient and effective foundations. But, for the purpose of creating the standardized foundation concepts for use in a variety of sites, some soil parameters have been assumed 

(as in the case of bearing capacity for shallow foundations) and others have been stipulated (as 

those required to produce specific performance – as in the case for deep driven piles). Assumptions used in developing the foundations are listed in Appendix C, where stipulations on pile 

capacity are also listed in the individual drawings.

4.1.1	 Wind Speed

The basic wind speed determines the wind velocity used in establishing wind loads for a building. It can also have a significant influence on the size and strength of foundations that support 

homes. Contemporary codes and standards like the IRC, IBC, and ASCE 7 specify basic wind 

speeds as 3-second gust wind speeds. Earlier versions of codes and standards specified wind 

speeds with different averaging periods. One example is the fastest mile wind speed that was 

specified in the 1988 (and earlier) versions of ASCE 7 and in pre-2000 versions of most model 

building codes.

The wind speed map shown in Figure 3-1 illustrates that the basic (3-second gust) wind speeds 

along most of the Gulf of Mexico, the Atlantic coast, and coastal Alaska range between 120 and 

150 mph. The basic wind speed for most of the Pacific coast is 85 mph. Several areas in the Pacific Northwest are designated as special wind regions and wind speeds are dictated locally. The 

design wind speeds for many of the U.S. territories and protectorates are tabulated in ASCE 7.

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.

Although wind loads are important in the design of a building, in coastal areas flood loads often 

have a much greater effect on the design of the foundation itself.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

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. Figure 4-1 illustrates how the BFE, freeboard, erosion, 

and the ground elevation determine the foundation height required. 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

G = Non-eroded ground elevation

Erosion = Short-term plus long-term erosion

Freeboard = 2009 IRC required in SFHAs, 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 

Figure 4-1.

The BFE, freeboard,

erosion, and ground

elevation determine

the foundation height

required.
4- Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

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, Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard 

Areas in accordance with the National Flood Insurance Program and FEMA 499, Fact Sheet No. 8 (see 

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 than are 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. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

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) 

AWPA M4-08 Standard for the Care of Preservative-Treated Wood Products (AWPA 2008) 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 piles to reduce construction costs. For foundation design and example calculations, see 

Appendix D.
4- Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

Figure 4-2 illustrates design loads acting on a column. The reactions at the base of the elevated 

structure used in most of 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 7-05 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.

Loads on the foundation elements themselves are more difficult to tabulate because 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.

Figure 4-2.

Design loads acting on

a column.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

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 H = height of foundation above grade

lf = linear foot Horiz = horizontal

V = wind speed Vert = vertical

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

b = pound H = height of foundation above grade

lf = linear foot Horiz = horizontal

V = wind speed Vert = vertical

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
4- Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

Flood Depth Hydrodynamic Breaking Wave Impact Buoyancy

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

4.1.5	 Foundation Design Loads and Analyses

Load analyses used to develop Case H foundations are similar to the analyses completed for the 

original FEMA 550 designs. Live loads used were those specified by the IRC and the original 

and augmented foundations were developed to support a range of dead loads. Wind and flood 

loads were calculated per ASCE 7, Minimum Design Loads for Buildings and Other Structures (the 

Case H design loads were calculated using ASCE 7-05; loads used in the original designs were 

calulated using ASCE 7-02, which are consistent with the 2005 edition). Design assumptions are 

listed in Appendix C.

Some noteworthy differences exist. Wind loads used in the original FEMA 550 designs were the 

worst case loads for a home that varied in width from 24 feet to 42 feet and in roof slope from 

3:12 to 12:12. The foundation reactions for the original designs are listed in Table 4-1b. In the 

Case H designs, separate wind loads were determined based on the number of stories (one or 

two) and the building width (14 feet for the 3-bay designs, 28 feet for the 6-bay designs, and 42

feet for the 9-bay designs). The more precise matching of wind loads to building widths and 

heights provide greater design efficiencies.

Wind loads used to develop the Case H foundations are listed in Table 4-3. 

Table 4-3. Wind Reactions Used to Develop Case H Foundations

Two-Story

3-Bay 6-Bay 9-Bay

ww

(p/lf)

lw

(p/lf)

lat

(p/lf)

ww

(p/lf)

lw

(p/lf)

lat

(p/lf)

ww

(p/lf)

lw

(p/lf)

lat

(p/lf)

120 mph -710 320 420 -640 -50 510 -730 -270 610

130 mph -840 380 490 -750 -60 600 -860 -310 710

140 mph -970 440 570 -870 -70 700 -1,000 -360 830

150 mph -1,100 500 650 -1,000 -80 800 -1,140 -410 950

Table 4-2. Flood Forces (in pounds) on an 18-Inch Square Column (continued)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

One-Story

3-Bay 6-Bay 9-Bay

ww

(p/lf)

lw

(p/lf)

lat

(p/lf)

ww

(p/lf)

lw

(p/lf)

lat

(p/lf)

ww

(p/lf)

lw

(p/lf)

lat

(p/lf)

120 mph -340 -20 240 -440 -200 320 -580 -340 410

130 mph -400 -20 280 -510 -230 380 -680 -400 480

140 mph -470 -30 320 -600 -270 440 -790 -460 560

150 mph -540 -30 370 -690 -310 500 -900 -530 640

ww = vertical forces on windward edge of foundation 

lw = vertical forces on leeward edge of foundation 

lat = horizontal forces on windward and leeward edges of foundation

1. (+) loads act upward; (-) pressures act downward. 

2. Lateral loads are applied to both windward and leeward foundation elements.

To account for shear panel reactions from segmented shear walls, the analyses of foundations 

supporting one-story homes included 6.72 kip quarter span point loads for the 3-bay design 

(point loads were applied at mid-span for the 6- and 9-bay models, Figure 4-3). The loads correspond to 10-foot tall wood framed shear panels constructed with 7/16-inch blocked wood 

structural panels fastened with 8d common nails 6 inches on center (o.c.). Foundations supporting two-story homes were analyzed with 13.44 kip shear panel reactions or twice that of the 

one-story home. The foundations will also support homes constructed with perforated shear 

walls.

Another difference in design methodology was required due to the nature of structural frames. 

In the original designs, the concrete columns were considered statically determinant and analyzed as such. The structural frames created by the concrete grade beams, concrete columns, 

and elevated beams, however, are not statically determinant and computer modeling was warranted. To analyze the frame action developed by those structural elements, computer models 

using RISA© structural software were created. Design loads were applied to the frames and critical shears and moments were tabulated for the grade beams, columns, and elevated beams. 

Critical axial forces were also tabulated for the columns. 

Tables 4-4 through 4-9 summarize the critical shears, moments, and axial loads of the computer 

models used to develop the Case H foundations. 

Table 4-3. Wind Reactions Used to Develop Case H Foundations (continued)
4-10 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

Table 4-4. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 10-Foot Tall 3-Bay Foundations

10-Foot Foundation 3-Bay One-Story 3-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Moment + 24 25 27 30 33 38 44 51

Column Moment - 37 40 43 47 51 57 63 69

Column Shear Bottom 9 9 10 10 11 12 13 14

Column Shear Top 5 6 6 8 8 9 11 12

Figure 4-3.

Shear panel reactions for the 3- and 6-bay

models. Reactions for the 9-bay model were

similar to those of the 6-bay.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-11

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

10-Foot Foundation 3-Bay One-Story 3-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Axial Maximum 24 24 24 25 46 48 49 50

Axial Minimum 8 8 7 7 1.6 1.2 0.5 0.3

Elevated Beam

Moment +

22 24 26 29 39 43 46 47

Elevated Beam

Moment - 21 23 25 27 41 44 48 51

Elevated Beam Shear

at Column 3 3 3 3 4 4 3 3

Elevated Beam Shear

at Mid-Span 7 7 8 8 13 14 15 15

Grade Beam Moment + 30 30 30 31 41 42 44 46

Grade Beam Moment - 18 18 19 20 26 28 30 32

Grade Beam Shear at

Column 9 9 9 9 10 10 10 10

Grade Beam Shear at

Mid-Span 4 4 4 4 5 5 6 6

1. (+) loads act upward; (-) pressures act downward.

Table 4-5. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 15-Foot Tall 3-Bay Foundations

15-Foot Foundation 3-Bay One-Story 3-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Moment + 53 57 62 67 73 81 90 98

Column Moment - 79 84 88 95 104 112 122 132

Column Shear Bottom 13 13 14 15 15 17 18 19

Column Shear Top 6 6 7 8 9 10 11 12

Axial Maximum 27 27 27 28 46 48 50 53

Axial Minimum 7 7 6 6 12 1 -0.3 -1.6

Elevated Beam

Moment +

51 55 59 65 67 79 87 95

Elevated Beam

Moment - 39 46 50 55 63 68 78 86

Elevated Beam Shear

at Column 4 5 5 6 3 4 5 6

Elevated Beam Shear

at Mid-Span 11 12 13 13 19 20 21 22

Grade Beam Moment + 30 30 30 29 36 37 39 41

Grade Beam Moment - 21 21 21 21 26 27 29 31

Table 4-4. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 10-Foot Tall 3-Bay Foundations

(continued)
4-12 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

15-Foot Foundation 3-Bay One-Story 3-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Grade Beam Shear at

Column 9 9 9 9 10 10 9 10

Grade Beam Shear at

Mid-Span 4 4 4 4 5 5 4 5

1. (+) loads act upward; (-) pressures act downward.

Table 4-6. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 10-Foot Tall 6-Bay Foundations

10-Foot Foundation 6-Bay One-Story 6-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Moment + 56 59 62 65 77 84 90 97

Column Moment - 74 78 81 85 69 75 81 88

Column Shear Bottom 19 20 21 21 17 18 19 20

Column Shear Top 8 9 10 11 14 15 17 19

Axial Maximum 32 32 30 30 47 47 46 46

Axial Minimum 8 8 7 6 10 9 9 8

Elevated Beam

Moment +

29 31 32 33 42 44 46 48

Elevated Beam

Moment - 23 23 23 23 42 42 43 43

Elevated Beam Shear

at Column 9 9 9 9 14 14 14 15

Elevated Beam Shear

at Mid-Span 3 3 3 3 7 7 7 8

Grade Beam Moment + 71 73 77 80 60 64 69 74

Grade Beam Moment - 53 75 79 83 55 61 67 73

Grade Beam Shear at

Column 13 13 14 14 11 12 12 14

Grade Beam Shear at

Mid-Span 10 11 11 11 8 9 10 11

1. (+) loads act upward; (-) pressures act downward.

Table 4-7. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 15-Foot Tall 6-Bay Foundations

15 Foot Foundation 6-Bay One-Story 6-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Moment + 81 87 92 98 118 127 137 140

Column Moment - 100 105 111 118 129 139 150 157

Column Shear Bottom 15 16 17 18 20 21 22 24

Table 4-5. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 15-Foot Tall 3-Bay Foundations

(continued)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-13

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

15 Foot Foundation 6-Bay One-Story 6-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Shear Top 9 10 11 11 13 14 16 18

Axial Maximum 37 37 32 33 48 48 48 45

Axial Minimum -1 -2 -4 -5 1 -1 -1 -1

Elevated Beam

Moment +

43 46 49 52 62 66 71 75

Elevated Beam

Moment - 23 22 24 27 44 44 44 41

Elevated Beam Shear

at Column 11 11 12 12 16 16 17 18

Elevated Beam Shear

at Mid-Span 2 2 1 2 4 5 3 3

Grade Beam Moment + 99 104 109 114 119 127 136 140

Grade Beam Moment - 107 114 121 129 128 138 150 155

Grade Beam Shear at

Column 19 20 21 21 22 23 20 19

Grade Beam Shear at

Mid-Span 15 16 16 18 18 19 18 15

1. (+) loads act upward; (-) pressures act downward.

Table 4-8. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 10-Foot Tall 9-Bay Foundations

10-Foot Foundation 9-Bay One-Story 9-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Moment + 21 23 26 29 24 28 32 36

Column Moment - 40 43 47 50 52 56 61 63

Column Shear Bottom 9 9 10 10 10 11 12 13

Column Shear Top 4 5 6 7 6 7 9 10

Axial Maximum 32 47

Axial Minimum 8 10

Elevated Beam Moment + 29 29 29 29 47 47 47 47

Elevated Beam Moment - 15 15 15 15 25 25 25 25

Elevated Beam Shear at

Column 11 11 11 11 18 18 18 18

Elevated Beam Shear at

Mid-Span 12 12 12 12 20 20 20 20

Grade Beam Moment + 45 48 51 54 55 58 63 68

Grade Beam Moment - 44 47 50 54 56 60 66 71

Table 4-7. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 15-Foot Tall 6-Bay Foundations

(continued)
4-14 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

10-Foot Foundation 9-Bay One-Story 9-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Grade Beam Shear at

Column 9 10 10 10 10 11 12 13

Grade Beam Shear at

Mid-Span 7 7 8 7 7 8 8 9

1. (+) loads act upward; (-) pressures act downward.

Table 4-9. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 15-Foot Tall 9-Bay Foundations

15 Foot Foundation 9-Bay One-Story 9-Bay Two-Story

120 mph 130 mph 140 mph 150 mph 120 mph 130 mph 140 mph 150 mph

Column Moment + 49 54 59 98 51 65 73 81

Column Moment - 80 86 92 118 100 106 115 124

Column Shear Bottom 12 13 14 18 14 15 16 17

Column Shear Top 6 6 7 11 7 8 10 11

Axial Maximum 34 39 34 34 49 49 49 49

Axial Minimum 6 6 6 6 9 8 8 8

Elevated Beam

Moment +

29 29 29 29 48 48 48 48

Elevated Beam

Moment - 16 16 16 13 26 26 26 26

Elevated Beam Shear

at Column 15 12 12 12 20 20 20 20

Elevated Beam Shear

at Mid-Span 2 1 1 1 2 2 2 2

Grade Beam Moment

+

95 100 105 114 111 117 125 133

Grade Beam Moment - 103 109 116 128 123 132 141 151

Grade Beam Shear at

Column 19 19 20 22 21 22 23 25

Grade Beam Shear at

Mid-Span 14 15 16 18 17 18 19 21

1. (+) loads act upward; (-) pressures act downward.

4.2	 Recommended Foundation Types for Coastal Areas

T

able 4-10 provides six 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 4-8. Design Moments (K-ft), Axial Loads (in kips), and Shears (in kips) for 10-Foot Tall 9-Bay Foundations

(continued)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-15

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

Table 4-10. Recommended Foundation Types Based on Zone

Foundation Case V Zones

A Zones in Coastal Areas

Coastal A Zone A Zone

Open Foundation (deep)

Braced 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

Timber pile with concrete 

grade and elevated beams 

and concrete columns

H 4 4 4

Open

Foundation

(shallow)Concrete column and grade 

beam D NR 4 4

Concrete column and grade 

beam with integral 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 Section 1806 of the 2009 IBC. The presumptive bearing capacity is for clay, sandy clay, silty clay, clayey silt, and sandy silt (CL, ML, MH, and CH soils). 

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 4-10, Case E) depends greatly on the soil’s 

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 

4-10 is also presented in Appendix A. Figures 4-4 through 4-10 are based on Appendix A.

4.2.1	 Open/Deep 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 4-4). Often called a “stilt” foundation, the driven timber pile system is 
4-16 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

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 home 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 erosion and scour. A construction approach that can improve 

performance is to extend the piles above the first floor diaphragm to the second floor or roof 

Figure 4-4.

Profile of Case A

foundation type

(see Appendix A for

additional drawings).

for
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-17

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

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 piles, 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/Deep 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 piles 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 4-5). 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.

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. 

4.2.3	 Open/Deep 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 home and the exposed portions of the foundation (Figure 4-6).

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 
4-18 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

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 4-5.

Profile of Case B

foundation type

(see Appendix A for

additional drawings).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-19

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

4.2.4	 Open/Deep Foundation: Timber Pile with Concrete Grade and Elevated Beams

and Concrete Columns (Case H)

Case H foundation designs augment designs contained in the first edition of FEMA 550. They 

incorporate elevated reinforced beams into the V zone timber pile foundation design. The elevated beams provide two important benefits:

The elevated beams, columns, and grade beams function as structural frames that resist lateral loads. The frame action allows smaller concrete columns to be used. Smaller 

columns reduce the flood loads imposed on the foundation and provide more efficient 

designs.

The elevated beams provide attachment points for homes constructed per prescriptive 

codes and standards like ANSI/AF&PA Wood Frame Construction Manual, American Iron 

and Steel Institute (AISI) Standard for Cold-Formed Steel Framing – Prescriptive Method for One 

and Two Family Dwellings, SSTD10-99 Standard for Hurricane Resistant Residential Construction, and ICC-600 Standard for Residential Construction in High Wind Regions.

.

.

Figure 4-6.

Profile of Case C

foundation type

(see Appendix A for

additional drawings).
4-20 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

Case H designs include a 3-bay design suitable for homes as narrow as 14 feet. Designs for foundation heights of 10 and 15 feet are provided.

As previously stated, the Case H designs are more precise and foundation strengths more closely 

match design loads. In addition, the structural frame action provided by the grade beams, columns, and elevated beams allow smaller columns to be constructed. One drawback of the design, 

however, is that constructing elevated concrete beams is more complicated than constructing 

grade beams and reinforced columns; therefore, more knowledgeable and experienced contractors would be needed (Figure 4-7).

Sections were designed with an emphasis on strength, ductility, and constructability. To simplify detailing and construction, axial and shear reinforcement were made consistent through 

each section. Section properties throughout each member were selected to resist the maximum 

forces (positive and negative moments, axial loads, and shears) that exist within the elements 

(grade beams, columns, or elevated beams). To simplify forming, the dimensions of the 

#3 Stirrups

@ 12" on center u.n.c. (Typ.)

Tension Connection

Ground Level

Column Dowel

Height “H”

Bottom of Lowest

Horizontal Member

Concrete Column

1'-0" 1'-0"

2'-0"

2'-6" 6"

Figure 4-7.

Profile of Case H

foundation type

(see Appendix A for

additional drawings).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-21

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

elevated beams matched the columns into which they frame. The designs were based on a belief 

that the potential increase in concrete costs would be more than offset by the savings in labor 

costs in constructing simple forms. Design professionals using the guidance contained in this 

manual may find it beneficial to vary from this approach.

The approach used to design and detail the Case H foundation system was to develop easily scalable column and beam systems. The size allows for the use of variable amounts of steel while 

keeping rebar congestion to a minimum. A 16-inch wide system to allow for the economical use 

of structural form panels with minimal waste was selected. The consistent column and elevated 

beam sizes also allow for reuse of the concrete forms between columns and beams. The member 

size and aspect ratio (member shape factor) allow for high lateral capacities.

The continuous bars in the beams provide a tie around the entire structure, imparting redundancy should an element fail, as well as the ability for the system to bridge over failed elements 

below. This redundancy improves the foundation performance, especially with impact from 

floodborne debris that exceeds design loads. 

4.2.5 	 Open/Shallow 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 (Figure 4-8). 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 (Figure 4-9).

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.

4.2.6	 Closed/Shallow 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 (Figure 4-10). 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 
4-22 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

smaller perimeter footings. Solid grouting of perimeter walls is recommended for additional 

weight and improved resistance to water infiltration. 

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. 

Figure 4-8.

Profile of Case G

foundation type

(see Appendix A for

additional drawings).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-23

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

4.2.7	 Closed/Shallow 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 (Figure 4-11). 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 

for the walls and significantly reduces reinforcement requirements. Because backfill needs to be 

Figure 4-9.

Profile of Case D

foundation type

(see Appendix A for

additional drawings).
4-24 Building on strong and safe foundations

4 Overview of Recommended Foundation Types and Construction for COASTAL AREAS

Figure 4-11.

Profile of Case E

foundation type

(see Appendix A for

additional drawings).

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 4-10.

Profile of Case F

foundation type

(see Appendix A for

additional drawings).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 4-25

Overview of Recommended Foundation Types and Construction for COASTAL AREAS 4

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. 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-1

5. Foundation Selection

This chapter provides foundation designs, along with the use 

of the drawings in Appendix A, to assist the homebuilder, contractor, 

and local engineering professional in developing a safe and 

strong foundation. Foundation design types, foundation design 

considerations, cost estimating, and details on how to use this 

manual are presented.

5.1 Foundation Design Types

The homebuilder, contractor, and local engineering professional can utilize the designs in this 

chapter and Appendix A to construct residential foundations in coastal areas. The selection 

of appropriate foundation designs for the construction of residences is dependent upon the 
5- Building on strong and safe foundations

5 foundation selection

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/Deep Foundations

n Braced timber pile (Case A)

n Steel pipe pile with concrete column and grade beam (Case B)

n Timber pile with concrete column and grade beam (Case C)

n Timber pile with concrete grade and elevated beams and concrete columns (Case H)

Open/Shallow Foundations

n Concrete column and grade beam (Case D)

n Concrete column and grade beam with slab (Case G)

Closed/Shallow Foundations

n Reinforced masonry – crawlspace (Case E)

n Reinforced masonry – stem wall (Case F)

Each of these foundation types designed for coastal areas have advantages and disadvantages 

that must be taken into account. Modifications to the details and drawings might be needed to 

incorporate specific home 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 herein is provided in Appendix 

B. Examples of how the foundation designs can be used with some of the homes 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

T

he foundation designs proposed are suitable for homes with dimensions, weights, and roof 

pitches within certain ranges of values. A licensed professional engineer should confirm 

the appropriateness of the foundation design of homes with dimensions, weights, or roof 

pitches that fall outside of those defined ranges. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-

foundation selection 5

Most of the foundation designs are based on a 14-foot wide (maximum) by 24-foot deep (minimum) “module” (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 

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.

Figure 5-1.

Schematic of a basic

module and two

footprints.

The licensed professional engineer should also consider the following:

n Local soil conditions. The pile foundations have been developed for relatively soft subsurface soils. For driven treated lumber piles, the presumptive allowable working load values 

of 7 tons per pile gravity, 4.65 tons per pile uplift, and 2 tons per pile lateral were used. For 

steel pipe piles, the presumptive allowable working load piles were greater (10 tons per pile 

for gravity loading, 6.7 tons per pile for uplift, and 4 tons per pile for lateral loading). Soil 

testing on the site should also be considered to validate the assumptions made.

In some areas of the coastal U.S. (e.g., portions of Louisiana), soils may exist that will 

not provide the presumptive pile values. In those areas, aspects of the FEMA 550 deep 
5- Building on strong and safe foundations

5 foundation selection

foundation designs are still valid, but geotechnical engineers will need to be involved in portions of the design to determine required pile parameters. In poor soils, additional piles 

may need to be installed or long piles may need to be driven; however, the portions of the 

designs from the grade beams upward should remain valid.

The FEMA 550 shallow foundations are based on a presumptive bearing capacity of 1,500 

psf. This value is consistent with the presumptive bearing capacity of Section 1806 of the 

2009 IBC for clay, sandy clays, clayey silts, and sandy silts (CL, ML, MH, and CH soils). In 

areas where soils will not provide this presumed bearing capacity, the shallow FEMA 550 designs should not be used until their ability to support the required loads can be confirmed 

by design professionals.

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 doesn’t need to be elevated more than several feet 

or has short foundation walls that can help resist uplift. 

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 home, concentrated loading in the home’s floor and roof diaphragms, 

and shear wall placement.

5.3	 Cost Estimating

C

ost information that 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 based on May 2006 prices from information provided by local contractors for the First 

Edition of this manual. 

5.4 	 How to Use This Manual

T

he rest of this chapter is designed to provide the user with step by step procedures for the 

information contained in this manual. 

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 258, Guide to Flood Maps, How to Use Flood 

Maps to Determine Flood Risk for a Property, for instructions. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-

foundation selection 5

n Determine the BFE or the interim Advisory Base Flood Elevations (ABFEs) for the location 

from the FIRM. If the dwelling is outside of flood-prone areas, flood loads do not need to 

be considered. 

3. Identify the local building code. Several states and municipalities in coastal areas are adopting new building codes to govern residential construction. This manual 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 2006 and 2009 IRCs reference ASCE 

7-05 as the source of the wind speed information. 

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 (NGS) 

and/or as established or confirmed by a surveyor.

FIRM Panel No. ____________________

Flood Insurance Risk Zone ____________________

Base Flood Elevation (BFE) or 

Advisory Base Flood Elevation (ABFE) ____________________

County/Parish/City ____________________

Building Code ____________________

Building Code Date ____________________

Base Flood Elevation (BFE) or 

Advisory Base Flood Elevation (ABFE) ______________

Freeboard + ______________

Design Flood Elevation (DFE) ______________

Design Wind Velocity ______________________________

Wind Exposure Category ______________________________
5- Building on strong and safe foundations

5 foundation selection

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.

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. For shallow foundations, confirm 

that the soils on site have a minimum bearing capacity of 1,500 psf. If soils lack that minimum capacity, contact a geotechnical engineer and/or a structural engineer to confirm that the FEMA 

550 foundation solutions are appropriate.

For deep foundations, confirm that the presumptive pile capacities (for gravity loads, uplift 

loads, and lateral loads) are achievable. If soils present on site will not support the presumed 

pile capacities, contact a geotechnical engineer and/or a structural engineer to determine appropriate pile plans.

9. Estimate erosion and scour. Estimate accumulated erosion and episodic scour over the 

life of the structure. Use accumulated erosion to determine eroded grade elevation and use accumulated erosion and episodic scour to determine the foundation depth required to ensure 

shallow foundations will not be undermined. 

10. 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 

Design Flood Elevation (DFE) ______________________________

Topo Elevation ______________________________

Elevation Dimension ______________________________

Soil Classification ______________________________

Source of Topo Elevation ______________________________

Topo Elevation (Site) ______________________________
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-

foundation selection 5

each of the foundations. Refer to the drawings for further direction and information about the 

needs for each type of unit.

11. 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 Governor’s 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.

12. Select the foundation design. If the home’s 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 

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. Tables 5-1a and 5-1b show 

which foundation design cases can be used for one- and two-story homes, respectively, 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

T

he 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.
5- Building on strong and safe foundations

5 foundation selection

Braced timber pile

Figure 5-2.

Foundation selection decision tree.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-

foundation selection 5
5-10 Building on strong and safe foundations

5 foundation selection

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.

Table 5-1a. Foundation Design Cases for One-Story Homes 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,H A,B,C,D,G,H A,B,C,D,E,F,G,H

5 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

6 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

7 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

8 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

9 A,B,C,H A,B,C,G,H A,B,C,G,H

10 A,B,C,H A,B,C,G,H A,B,C,G,H

11 B,C,H B,C,G,H B,C,G,H

12 B,C,H B,C,G,H B,C,G,H

13 B,C,H B,C,G,H B,C,G,H

14 B,C,H B,C,G,H B,C,G,H

15 B,C,H B,C,G,H B,C,G,H

* 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. 

Foundation Types

A = Braced 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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-11

foundation selection 5

F = Reinforced masonry – stem wall

G = Concrete column and grade beam with integral slab

H = Timber pile with concrete grade and elevated beams and concrete columns

Table 5-1b. Foundation Design Cases for Two-Story Homes 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

Two-Story Dwelling

< 4 A,B,C,H A,B,C,D,G,H A,B,C,D,E,F,G,H

5 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

6 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

7 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

8 A,B,C,H A,B,C,D,G,H A,B,C,D,E,G,H

9 A,B,C,H A,B,C,G,H A,B,C,G,H

10 A,B,C,H A,B,C,G,H A,B,C,G,H

11 B,C,H B,C,G,H B,C,G,H

12 B,C,H B,C,G,H B,C,G,H

13** B,C,H B,C,H B,C,H

14** B,C,H B,C,H B,C,H

15** B,C,H B,C,H B,C,H

* 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 homes for a design wind speed of 150 mph. See individual 

design drawings for more details.

Foundation Types

A = Braced 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 integral slab

H = Timber pile with concrete grade and elevated beams and concrete columns
5-12 Building on strong and safe foundations

5 foundation selection

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.

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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS 5-13

foundation selection 5

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.

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS A-

A.	Foundation Designs

This appendix contains the Case A through Case G drawings originally developed for the July 

2006 edition of FEMA 550 and the new Case H drawings developed for this Second Edition of 

FEMA 550.

Case H drawings did not appear in the First Edition of FEMA 550. The drawings developed for 

the Case H designs vary in style and format from the original FEMA 550 designs for Cases A 

through G. Because of the differences in style and format, and the fact that thousands of copies 

of the July 2006 edition of FEMA 550 have been distributed, the Case H drawings are presented 

as standalone drawings. Separate title sheets and general notes for the Case H drawings are presented that are not intended to be used with the original drawings for Cases A through G.



























































RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS B-

B. Pattern Book Design

The illustrations in this appendix are from A Pattern Book for Gulf Coast Neighborhoods prepared 

for the Mississippi Governor’s Rebuilding Commission on Recovery, Rebuilding, and Renewal 

by Urban Design Associates (UDA) of Pittsburgh, Pennsylvania, in November 2005.

http://www.mississippirenewal.com/documents/Rep_PatternBook.pdf

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS B-

pattern book design B

Figure B-1. 

Pattern Book for Gulf Coast Neighborhoods 

Page 63 Top
B- Building on strong and safe foundations

B pattern book design

Figure B-2. 

Pattern Book for Gulf Coast Neighborhoods 

Page 63 Bottom

Housing Type Detached Single-Family

Contact Urban Design Associates

Contact Information http://www.urbandesignassociates.com/

Total Square Feet 1,311

Number of Bedrooms 3

Number of Bathrooms 2

Timing Medium Term/Long Term

Housing Type Stock Plan Floor Plan

Optional

Fireplace

Optional

Deck

Master Bedroom

124x 16

Bedroom 2

11 x 10

Bedroom 3

12 x 10

Kitchen

Porch

Bath

Cl

P M.

Bath

Foyer

' 12 11' 11' 11' 8'

45' 

page 63 bottom

12' 12'

32'

8'

32'

Porch is open and has short spans. Consult with local engineer to determine uplift forces and verify suitability.

2'
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS Bpattern book design B

Figure B-3. 

Pattern Book for Gulf Coast Neighborhoods 

Page 64 Bottom
B- Building on strong and safe foundations

B pattern book design

Figure B-4. 

Pattern Book for Gulf Coast Neighborhoods 

Page 65 Bottom
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS B-

pattern book design B

Figure B-5. 

Pattern Book for Gulf Coast Neighborhoods 

Page 67 Top

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS C-

C. Assumptions Used in 

Design 

Coastal Areas Foundation Designs

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

codes:

ASCE 7-05

Minimum Design Loads for Buildings and Other Structures 

American Society of Civil Engineers (ASCE) 

ASCE 24 

Flood Resistant Design and Construction

American Society of Civil Engineers (ASCE)

ACI 318-02

Building Code Requirements for Structural Concrete 

American Concrete Institute (ACI)
C- Building on strong and safe foundations

c ASSUMPTIONS USED IN DESIGN 

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

Building Code Requirements for Masonry Structures 

American Concrete Institute (ACI) 

American Society of Civil Engineers (ASCE) 

The Masonry Society (TMS) 

ANSI/AF&PA NDS-2005

National Design Specifications for Wood Construction 

American Forest & Paper Association (AF&PA) 

American National Standards Institute

American National Standards Institute (ANSI)

American Wood Council (AWC) 

IRC-2003 

2003 International Residential Code for One- and Two-Family Dwellings 

International Code Council (ICC)

FEMA 550 has been checked and found to be consistent with both the 2006 and the 2009 IRC.

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 lowsloped 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 7-05 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 1⁄2-inch gypsum drywall

Wall 9 psf Wood siding, 2 by 4 studs 16 inches on centers, 1⁄2-inch plywood 

wall sheathing, and one layer of 1⁄2-inch gypsum drywall

Roof 12 psf 200 lb/sq asphalt roofing, 15 lb/sq felt, 1⁄2-inch plywood decking, 

2 by 4 top and bottom truss chords 24 inches on centers, 1⁄2-inch 

gypsum drywall ceiling finish

Dead Loads 

For Use in ASCE 7-05 ASD Gravity Load Combination #2 (D + H + F + L + T)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS C-

ASSUMPTIONS USED IN DESIGN c

First Floor 16 psf Dead loads increased 8 lb/sf to account for additional finishes 

like hardwood flooring (4 lb/sf), 1⁄2-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

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 7-05). 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 11⁄2 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)
C- Building on strong and safe foundations

c ASSUMPTIONS USED IN DESIGN 

Non-Coastal A zone Breaking wave load up to a 11⁄2-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 0 psf

Soil Bearing Capacity

1,500 psf presumptive value for clay, sandy clay, silty clay, clayey silt, and sandy silt (CL, ML, MH, 

and CH soils) (2009 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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-

D.	Foundation Analysis

	 and Design Examples

Chapter 3 described the types of loads considered in this manual. This 

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 
D- Building on strong and safe foundations

D Foundation Analysis and Design Examples 

designers and contractors with some flexibility in selecting the home footprint and characteristics for which these pre-engineered foundations would apply. This also simplifies application 

of the pre-engineered foundations, 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 7-05, 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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS DFoundation Analysis and Design Examples 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 building’s parameters (Section D.1.1)

2. Calculate wind and flood loads using ASCE 7-05 (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- Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS DFoundation Analysis and Design Examples D

Site Parameters (ASCE 7-05, Chapter 6)

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

Kd = 0.85 Directionality factor (for use with ASCE 7-05, 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 7-05, Table 6-3, Cases 1 and 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 7-05, Section 6.5.8.1)

External Pressure Coefficients (Cp) (ASCE 7-05, 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 7-05, 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.
D- Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS DFoundation Analysis and Design Examples D

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 
D- Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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

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 1⁄2 of the roof load, all of the exterior wall load, 

Figure D-2. Paths for

wind, live, and dead

loads.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS DFoundation Analysis and Design Examples D

and 1⁄4 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 (8 psf + 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 7-05. 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 7-05 Load Combinations, 

but were considered to be too rare in the Gulf Coast of the United States to be considered 

in the design. ASCE 7-05 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 lists foundation wall reactions for each load case. Critical reactions that 

contain the foundation design are highlighted.
D-10 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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

ASCE 7-05 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 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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-11

Foundation Analysis and Design Examples D

= 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 

7-05 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 7-05 Equation C5-4 can be used to calculate the hydrodynamic 

force on a foundation element as

Fdyn = 1⁄2 Cd ρ V2 A

Where

Fdyn = Hydrodynamic force (lb) acting on the submerged element
D-12 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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

ρ = 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 = (1⁄2) (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 = 1⁄2 Cd ρ V2 A

Fdyn = (1⁄2) (1.3)(2)(9.15)2(1)(2.6)

= 283 lb/lf of wall

Floodborne Debris Impacts

In this example, the loads imposed by floodborne debris were approximated using formula 11-

9 contained in FEMA 55. 

The Commentary of ASCE 7-05 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. 

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 Δ t)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-13

Foundation Analysis and Design Examples D

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

Δt = 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 ÷ gΔt

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 7-05 formulae for wave forces 

on continuous foundation walls (ASCE 7-05 Equations 5-5 and 5-6) and on vertical piles and 

columns (ASCE 7-05 Equation 5-4). 

The equation for vertical piles and columns from ASCE 7-05 is

Fbrkp = 1⁄2 Cdb γ DHb

2

Where

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

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

γ = 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 inches square, D = (1.4)(1.5 ft) = 2.1 ft.
D-14 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 (α) to the surface of 

the waves are attenuated by the factor sin2α. 

Fbrkp = 1⁄2 Cdb γ DHb

2 

= 1⁄2 (2.25)(64 lb/ft3)(2.1 ft)(2.03 ft)2

= 623 lb

For closed foundations, use equations in Section 5.4.4.2 of ASCE 7-05 to calculate Fbrkp. FEMA 

55 contains the following two equations for calculating loads on closed foundations:

Fbrkw = 1.1 Cp ρ ds

2 + 2.4 γ ds2 Case 1

and

Fbrkw = 1.1 Cp ρ ds

2 + 1.9 γ ds2 Case 2

Where γ 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 whereFbrkw 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 7-05, Section 6.5.13 (Wind Loads on Open Buildings 

and with Monoslope, Pitched, or Troughed Roofs). 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 7-05, Figure 6-21 (chimneys, tanks, rooftop 

equipment, and similar structures); ASCE 7-05, Figure 6-20 (walls and solid signs) could have 

been used as well. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-15

Foundation Analysis and Design Examples D

From ASCE 7-05 Equation 6-28:

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 7-05
D-16 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 (Table D-2).

Figure D-4. Case 2.

Normally incident

breaking wave

pressures against a

vertical wall (stillwater

level equal on both

sides of wall).

Source: ASCE 7-05

Figure D-5.

Flood loads.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-17

Foundation Analysis and Design Examples D

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

ASCE 7-05 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-18 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 = 1⁄2 Cd ρ V2 A

= 1⁄2 Cd ρ V2 (1) ds

Fdyn = (1⁄2) (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:
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-19

Foundation Analysis and Design Examples D

Fiwall = (1/3) 620 lb

Fiwall = 210 lb/ft

Breaking Wave Loads

The home is to be constructed in an 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 γ ds

2 + 1.91 γ ds2 

Fbrkw = γ ds

2 (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 7-05 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 7-05 required flood load of 75 percent 

of the breaking wave load will create a bending moment of:
D-20 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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-lb/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 lb/lf (bending) + 546 lb/lf (uplift)

= 3,383 lb/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 lb/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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-21

Foundation Analysis and Design Examples D

Footing Sizing

The foundation walls and footings must be sized to prevent overturning and resist the 546 lb/

lf uplift. ASCE 7-05 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 lb/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. Subtracting the elevation 

of the site (determined from a topographic map or preferably from a survey) from the ABFE 

and adding estimated erosion (in feet) determines that the floodwaters during a design event 

(including wave effects and runup) will extend 6 feet above the eroded exterior grade. 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 7-05, 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 
D-22 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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). 

Figure D-6.

Layout of Open Foundation Example.

14'-0" Maximum

3'-0"

5'-6" 3'-0"

Critical Area 

of Grade Beam

6" Concrete Slab

Grade Beam

36" Wde x 48" Deep

16"x16" 

Column 

Figure D-7.

Loading Diagram for Open

Foundation Example.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-23

Foundation Analysis and Design Examples D

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 (8 psf + 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. 
D-24 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 

7-05 Equation C5-2 as follows:

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

= 11.21 feet per second (fps) 

Flood Force

ASCE 7-05 Equation C5-4 is as follows: 

Fdyn = 1⁄2 Cd ρ V2 A 

= (1⁄2) (2)(2)(11.21 fps)2(1.33 ft)(3.9 ft) 

= 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 piles and columns from ASCE 7-05 is as follows:

Fbrkp = 1⁄2 Cdb γ DHb

2 

= 1⁄2 (2.25)(64 lb/ft3)(1.82 ft)(3.04 ft*)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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-25

Foundation Analysis and Design Examples D

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

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 summarizes loads on the open foundation example. Loads are listed for the eight 

load combinations and critical loads are highlighted.

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

ASCE 7-05 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 + (0.75)[(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 +/- (0.75)(14)(1,137) 

+(0.75)(14)([(490+280)] +/- 

1,252 = 2,348; 29,982 windward; 

leeward

(0.75) 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. 
D-26 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 debris = (3,478)(3.9) ÷ 1,000 lb/kip

= 13.6 ft-kip 

Moment wind + fdyn+ debris = 51.6 ft-kip + 13.6 ft-kip

= 65.1 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 7-05. 

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 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-27

Foundation Analysis and Design Examples D

Foundation Design 

Overturning 

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

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

= -445,774 ft-lb 

MFa (1.5) = (1.5)[(1,211 lb)(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 x 3 ft) + (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 percent

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.
D-28 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 = (tanΦ)N + Passive Resistance at Vertical Foundation Surfaces 

Φ = internal angle of soil friction, assume Φ = 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)(-65 psf)]

= 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 percent 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- 05 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. Table 

D-4 presents foundation bearing pressures for typical bays. 

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)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-29

Foundation Analysis and Design Examples D

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 for Typical Bays (for three rows of columns per bay)

ASCE 7-05 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 and ASCE 7-05; 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 
D-30 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

Reinforced with (4) #8 bars, grade 60 reinforcing, with 21⁄2-inch clear cover 

Note: 1,000 lb = 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)(0.868 kip)(1/3)](1.6) + [(1.3 kip)+(3.5 kip](2.0) 

= Vu = 16.0 kip

As the maximum unit tension stress is only 25.0 kip/16 in x 16 in = 0.098 kip/in2 and the 

maximum axial compression stress is only 60.0 kip/16 in x 16 in = 0.234 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 kip
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS D-31

Foundation Analysis and Design Examples D

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) = 0.21 in2

2 pieces of #4 bar As = (2)(0.2) = 0.40 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 inches 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 kip/ft 

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

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 kip

Use nominal #4 two leg stirrups at 24 inches on center 

Check flexural strength: Assume simple span condition

Maximum Factored Moment = Mu = (7.2 kip/ft)(14 ft)2 (1/8) = 176 ft-kip
D-32 Building on strong and safe foundations

D Foundation Analysis and Design Examples 

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 (ρ) 

ρ = As ÷ [(section width)(section depth- clear cover- 1⁄2 bar diameter)] 

ρ = As ÷ [(bw)(d)] 

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

ρ = 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: 

ΦMn = (Φ)[((As)(fy)(d)) – (((As)(fy)) ÷ ((0.85)(f 'c)(width of member)(2)))]

ΦMn = (0.9)[((1.76)(60,000)(44.63)) – (((1.76)(60,000)) ÷ ((0.85)(4,000)(36)(2)))]

= 4,241,634 in lb ÷ 12,000 = 353 ft-kip

Φ = 0.9 

Area of reinforcing steel (As) minimum flexural 

= (0.0033)(24)(44.63) 

= 3.6 in2

or 

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

Area of steel for shrinkage and temperature required = (0.0018)(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 COASTAL AREAS E-

E. Cost Estimating

The cost data provided in Appendix E were developed in 2006 for the First Edition of FEMA 

550 for select communities along the Gulf of Mexico. The applicability or accuracy of the data 

to other coastal areas has not been investigated. Although relative costs between foundation systems may apply in other coastal regions, users of the manual should verify current actual costs 

for any given location.
E- Building on strong and safe foundations

E COST ESTIMATING 

Breakdown of Foundation Costs

Foundation Type Average Foundation 

Costs ($) Elevation Above Grade Unit Costs per Square Foot (sf)

Open

Case A: Braced 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 Integral Slab

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. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS E-

COST ESTIMATING E

 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.
E- Building on strong and safe foundations

E COST ESTIMATING 

Case A: Braced 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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS ECOST ESTIMATING E

Case B: Steel Pipe Pile with Concrete Column and 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

Equipment 

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
E- Building on strong and safe foundations

E COST ESTIMATING 

Case C: Timber Pile with Concrete Column and 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 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS E-

COST ESTIMATING E

Case D: Concrete Column and 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 ea = each
E- Building on strong and safe foundations

E COST ESTIMATING 

Case G: Concrete Column and Grade Beam with Integral 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 WWF = welded wire fabric
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS E-

COST ESTIMATING E

Case E: Reinforced Masonry – Crawlspace

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) $7,641

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) $14,254

cy = cubic yard sf = square foot
E-10 Building on strong and safe foundations

E COST ESTIMATING 

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 COASTAL AREAS F-

F.	Pertinent Coastal

Construction Information 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
F- Building on strong and safe foundations

F Pertinent coastal construction information

12	 Pile Installation	

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

All of the FEMA 499 Fact Sheets listed above can be viewed, downloaded, or printed. Go to

http://www.fema.gov/library/viewRecord.do?id=1570 and click on the Resource File for the

Fact Sheet(s) of interest.

FEMA P-757 Recovery Advisory	

	 Erosion, Scour, and Foundation Design

The above Recovery Advisory can be viewed, downloaded, or printed. Go to http://www.fema.

gov/library/viewRecord.do?id=3577 and click on Appendix D, pages 20-23.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS G-

G.	FEMA Publications and

	 Additional References

The American Concrete Institute (ACI). 2005. Building Code Requirements for Structural Concrete 

and Commentary, ACI 318. 

American Forest & Paper Association’s (AF&PA) American Wood Council (AWC). 2005. National Design Specification for Wood Construction. ANSI/AF&PA NDS 2005.

American Forest & Paper Association. 2008. Wood Frame Construction Manual (WFCM) for Oneand Two-Family Dwellings.

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) 7-05. 2005. Minimum Design Loads for Buildings and 

Other Structures, ASCE 7-05. ISBN: 0784408092.

ASCE 24-05. 2006. Flood Resistant Design and Construction. ISBN: 0784408181.

American Wood Preservers’ Association (AWPA). 1991. Care of Pressure-Treated Wood Products. 

American Wood Preservers’ Association. 2008. AWPA M4-08 Standard for the Care of PreservativeTreated Wood Products.

Concrete Reinforcing Steel Institute (CRSI). 2002. CRSI Design Handbook.
G- Building on strong and safe foundations

g fema publications and additional references

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.

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. 2004. Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds, FEMA 

424. January 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’ Guide to 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.

FEMA. 2008. NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements for Buildings 

Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program. August 

2008

FEMA. 2009. Hurricane Ike MAT Recovery Advisories: Enclosures and Breakaway Walls and Erosion, 

Scour, and Foundation Design. FEMA P-757. April 2009.

International Building Code (IBC). 2009 International Building Code. 2009.

International Code Council (ICC). Standard for Residential Construction in High Wind Regions 

(ICC-600). November 2006.

International Residential Code (IRC). 2009 International Residential Code for One- and Two-Family 

Dwellings. 2009.

Mississippi Governor’s 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 COASTAL AREAS H-1

H.	Glossary

3-second peak gust – The wind speed averaging time used in ASCE 7 and the IBC. 

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).

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. 

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 
H- Building on strong and safe foundations

H Glossary

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 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 community’s 

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 SFHAs on a community’s FIRM.

Design Flood Elevation (DFE) – The elevation of the design flood, including wave height relative to 

the datum specified on a community’s Flood Hazard Map.

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. 

Fixity – Resistance to flotation; stable or immovable.

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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS HGlossary H

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.

Leeward – The side away, or sheltered, from the wind.

Limit of Moderate Wave Action (LiMWA) – The landward extent of coastal areas designated Zone 

AE where waves higher than 1.5 feet can exist during a design flood (also known as the Coastal 

A zone).

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 risks 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.
H- Building on strong and safe foundations

H Glossary

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).

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.

Wave trough – The lowest part of the wave between crests.

Windward – The side facing the wind.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS I-

I.	 Abbreviations and 	 	 	 	 	

	 Acronyms

A

ABFE Advisory Base Flood Elevation

ACI American Concrete Institute

AF&PA American Forest & Paper Association

AISI American Iron and Steel Institute

AL Alabama

ANSI American National Standards Institute

ASCE American Society of Civil Engineers

ASD allowable stress design

ASTM American Society for Testing and Materials
I- Building on strong and safe foundations

I Abbreviations and acronyms

AWC American Wood Council

AWPA American Wood Preservers’ Association

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

E

ea each

F

FEMA Federal Emergency Management Agency

FIRM Flood Insurance Rate Map

FIS Flood Insurance Study

FL Florida
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS I-

Abbreviations and acronyms I

fps feet per second

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

LA Louisiana

lb/sq pounds per square foot

lf linear foot

LiMWA Limit of Moderate Wave Action

ls lump sum
I- Building on strong and safe foundations

I Abbreviations and acronyms

M

MAT Mitigation Assessment Team

mph miles per hour

m/s meters per second

MS Mississippi

MWFRS main wind force resisting system

N

NAVD North American Vertical Datum

NDS National Design Specification

NFIP National Flood Insurance Program 

NFPA National Fire Protection Association

NGS National Geodetic Survey 

NGVD National Geodetic Vertical Datum

NR Not Recommended

NRCS National Resource Conservation Service

O

o.c. on center

P

PCA Portland Cement Association
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR COASTAL AREAS I-

Abbreviations and acronyms I

pcf pounds per cubic foot

p/lf pounds per linear foot

psf pounds per square foot

psi pounds per square inch

R

RA Recovery Advisory

RISA Rapid Interactive Structure Analysis

ROM rough order of magnitude

S 

SBC Standard Building Code

SCS	 Soil Conservation Service

SEI	 Structural Engineering Institute

SFHA	 Special Flood Hazard Area

SLOSH	 Sea, Lake, and Overland Surges from Hurricanes

sq	 square foot

SWL stillwater level

T

TBTO tributylin oxide

TMS The Masonry Society

TX Texas
I- Building on strong and safe foundations

I Abbreviations and acronyms

U

UDA Urban Design Associates

u.n.o.	 unless noted otherwise

USGS United States Geological Survey

W

WCFM Wood Frame Construction Manual for One- and Two-Family Dwellings 

WWF welded wire fabric