Recommended 

Residential Construction 

for the Gulf Coast 

Building on Strong and Safe Foundations

FEMA 550 / July 2006 

FEMA
About the Cover

On August 29, 2005, Hurricane Katrina struck the Gulf Coast with recordbreaking storm surge 

that destroyed foundations and devastated homes from Louisiana east to Alabama. Katrina was so 

destructive that engineers assessing the carnage no longer looked for “success stories” (i.e., homes 

that were only moderately damaged), but rather searched for “survivor” homes that, while extensively damaged, still bore a slight resemblance to a residential building. Hurricane Katrina proved 

that, without strong foundations, homes on the coast can and will be destroyed.
Recommended 

Residential Construction

for the Gulf Coast 

Building on Strong and Safe Foundations

FEMA 550 / July 2006

FEMA

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST iii

Acknowledgments

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

and guidance during the preparation of this report.

Principal Authors

Bill Coulbourne, PE

URS Corporation

Matt Haupt, PE 

URS Corporation

Scott Sundberg, PE 

URS Corporation

David K. Low, PE

DK Low & Associates, LLC 

Jimmy Yeung, PhD, PE

Greenhorne and O’Mara, Inc.

John Squerciati, PE

Dewberry and Davis, LLC

Contributors and Reviewers

John Ingargiola

FEMA Headquarters

Shabbar Saifee

FEMA, Region IV

Dan Powell

FEMA, Region IV

Alan Springett

FEMA, Region IV

Keith Turi 

FEMA Headquarters

Christopher Hudson

FEMA Headquarters

Christopher P. Jones, PE

Dan Deegan, PE, CFM 

PBS&J

Ken Ford 

National Association of Homebuilders (NAHB)

Mike Hornbeck 

Gulf Construction Company, Inc.
David Kriebel, PhD, PE 

U.S. Naval Academy

Jim Puglisi 

Dewberry and Davis, LLC

John Ruble 

Bayou Plantation Homes

Bob Speight, PE

URS Corporation

Naomi Chang

Greenhorne and O’Mara, Inc.

Deb Daly

Greenhorne and O’Mara, Inc.

Julie Liptak

Greenhorne and O’Mara, Inc.

Wanda Rizer

Design4Impact
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 

Table of Contents

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

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

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

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

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

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

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

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

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

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

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

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

2.1 Foundation Design Criteria............................................................................................... 2-1
vi Building on strong and safe foundations

table of contents

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

3.5 Hydrodynamic Loads....................................................................................................... 3-11
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST vii

Table of contents

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

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

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

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

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

Chapter 4. Overview of Recommended Foundation Types and Construction for 

the Gulf Coast.................................................................................................................................. 4-1

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

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

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

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

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

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

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

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

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

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

4.2.2 Open Foundation: Steel Pipe Pile with Concrete Column and Grade

Beam (Case B)........................................................................................................4-9

4.2.3 Open Foundation: Timber Pile with Concrete Column and Grade Beam

(Case C).................................................................................................................4-11

4.2.4 Open Foundation: Concrete Column and Grade Beam with Slabs

(Cases D and G)....................................................................................................4-12

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

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

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

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

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

5.3 Cost Estimating.................................................................................................................. 5-4
viii Building on strong and safe foundations

table of contents

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

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

Appendices

Appendix A Foundation Designs

Appendix B Pattern Book Design

Appendix C Assumptions Used in Design

Appendix D Foundation Analysis and Design Examples

Appendix E Cost Estimating

Appendix F Referenced Fact Sheets from FEMA 499

Appendix G FEMA Publications and Additional References

Appendix H Glossary

Appendix I Abbreviations and Acronyms
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 

the Gulf Coast: high winds, storm surge, and associated flood effects, 

including hydrostatic forces, hydrodynamic forces, waves, floodborne 

debris, and erosion and scour.

1.1	 High Winds

Hurricanes are the basis for design wind speeds for the Gulf Coast. High winds during a hurricane can create extreme positive and negative forces on a building; the net result is that wind 

forces simultaneously try to push over the building and lift it off its foundation. If the foundation is not strong enough to resist these forces, the home may slide, overturn, collapse, or incur 

substantial damage (Figure 1-1). 
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

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. Katrina’s surge was roughly that of a Category 5, although its winds at landfall were only a 

Category 3. A hurricane that is a Category 3 or above is generally considered a major hurricane.

Figure 1-1. 

Wind damage to roof

structure and gable end

wall from Hurricane

Katrina (2005) (Pass

Christian, Mississippi)

The most current design wind speeds are provided by the American Society of Civil Engineers 

(ASCE) document Minimum Design Loads for Buildings and Other Structures (ASCE 7). ASCE 7 is 

typically updated every 3 years. The 2002 edition ASCE 7-02 is referenced by the following model building codes: the 2003 editions of the International Building Code (IBC), the International 

Residential Code (IRC), and the NFPA 5000, Building Construction and Safety Code, published by 

the National Fire Protection Association (NFPA). 

Design wind speeds given by ASCE 7 are 3-second gust speeds, not the sustained wind speeds 

associated with the Saffir-Simpson hurricane classification scale. Figure 1-3 shows the design 

wind speeds for portions of the Gulf Coast region based on 3-second gusts (measured at 33 feet 

above the ground in Exposure C).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 7-02, Figure C6-2.

Figure 1-2. 	 Saffir-Simpson Scale

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

1 TYPES OF HAZARDS

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 

(see Figure 1-5). Because much of the United States’ densely populated Gulf Coast coastlines 

lie less than 20 feet above sea level, the danger from storm surge is great. In addition, because 

of the shape and the bathymetery of the Gulf of Mexico, storm surges along the Gulf Coast can 

be greater than anywhere else in the United States (see Figure 1-6). 

Figure 1-3. 

Design wind speed map for portions of the Gulf Coast. Contours are 3-second gust wind speeds (in miles per hour

[meters per second]) for Exposure Category C, 33 feet height.

Source: ASCE 7-02
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 1-

TYPES OF HAZARDS 1

Figure 1-4.

Graphical depiction of a hurricane moving ashore. In this example, a 15-foot surge added to the normal 2-foot tide

creates a total storm tide of 17 feet.

Figure 1-5.

Storm tide and waves

from Hurricane Dennis

on July 10, 2005, near

Panacea, Florida

Source: U.S. 

Geological Survey 

(USGS) Sound Waves

Monthly newsletter. 

Photograph

courtesy of The 

Forgotten Coastline

(Copyright 2005)
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

Figure 1-6.

Comparison of storm surge levels along the shorelines of the Gulf Coast for Category 1, 3, and 5 storms

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

1.3	 Flood Effects

Although coastal flooding can originate from a number of sources, Gulf Coast hurricanes 

and weaker tropical storms not categorized as hurricanes are the primary cause of flooding (see Figure 1-2). The flooding can lead to a variety of impacts on coastal buildings 

and their foundations: hydrostatic forces, hydrodynamic forces, waves, floodborne debris forces, and erosion and scour. 

1.3.1	 Hydrostatic Forces

Horizontal hydrostatic forces against a structure are created when the level of standing or slowly moving floodwater on opposite sides of the structure are not equal. Flooding can also cause 

vertical hydrostatic forces, resulting in flotation. Rapidly rising floodwaters can also cause structures to float off of their foundations (see Figure 1-7). If floodwaters rise slowly enough, water 

can seep into a structure to reduce buoyancy forces. While slowly rising floodwaters reduce the 

adverse effects of buoyancy, any flooding that inundates a home can cause extreme damage.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 1-

TYPES OF HAZARDS 1

1.3.2	 Hydrodynamic Forces

Moving floodwaters create hydrodynamic forces on submerged foundations and buildings. 

These hydrodynamic forces can destroy solid walls and dislodge buildings with inadequate connections or load paths. Moving floodwaters can also move large quantities of sediment and 

debris that can cause additional damage. In coastal areas, moving floodwaters are usually associated with one or more of the following:

n Storm surge and wave runup flowing landward through breaks in sand dunes, levees, or 

across low-lying areas (see Figure 1-8)

Figure 1-7. 

Building floated

off of foundation

(Plaquemines Parish,

Louisiana)

Source: Hurricane 

Katrina in the gulf

coast (FEMA 549)

Figure 1-8.

Aerial view of damage

to one of the levees

caused by Hurricane

Katrina (photo taken

on August 30, 2005,

the day after the storm

hit, New Orleans,

Louisiana).

Source: FEMA NEWS 

PHOTO/ Jocelyn

Augustino
1- Building on strong and safe foundations

1 TYPES OF HAZARDS

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 

resulting constricted flow accelerated the storm surge and caused deep scour channels across 

the island. These channels eventually undermined pile-supported houses between large buildings while also washing out roads and houses farther landward (see Figure 1-9).

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)

1.3.3	 Waves

Waves can affect coastal buildings in a number of ways. The most severe damage is caused by 

breaking waves (see Figures 1-10 and 1-11). The height of these waves can vary by flood zone: 

V Zone wave heights can exceed 3 feet, while Coastal A Zone wave heights are between 1.5 

and 3 feet. The force created by waves breaking against a vertical surface is often ten or more 

times higher than the force created by high winds during a storm event. Waves are particularly 

damaging due to their cyclic nature and resulting repetitive loading. Because typical wave periods during hurricanes range from about 6 to 12 seconds, a structure can be exposed to 300 

to 600 waves per hour, resulting in possibly several thousand load cycles over the duration of 

the storm. 

Wave runup occurs as waves break and run up beaches, sloping surfaces, and vertical surfaces. Wave runup can drive large volumes of water against or around coastal buildings, creating 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 1-

TYPES OF HAZARDS 1

hydrodynamic forces (albeit smaller than breaking wave forces), drag forces from the current, 

and localized erosion and scour. Wave runup under a vertical surface (such as a wall) will create an upward force by the wave action due to the sudden termination of its flow. This upward 

force is much greater than the force generated as a wave moves along a sloping surface. In some 

instances, the force is large enough to destroy overhanging elements such as decks or porches. 

Another negative effect of waves is reflection or deflection, occurring when a wave is suddenly 

redirected as it impacts a building or structure.

Figure 1-10.

Storm waves breaking

against a seawall

in front of a coastal

residence at Stinson

Beach, California

Source: COastal 

COnStruction 

manual

(FEMA 55)

Figure 1-11.

Storm surge and

waves overtopping a

coastal barrier island

in Alabama (Hurricane

Frederic, 1979)

Source: COastal 

COnStruction 

manual

(FEMA 55)
1-10 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 decks, steps, 

ramps, breakaway wall panels, portions of or entire houses, fuel tanks, vehicles, boats, pilings, 

fences, destroyed erosion control structures, and a variety of smaller objects (see Figure 1-12). 

In some cases, larger pieces of floodborne debris can strike buildings (e.g., shipping containers and barges), but the designs contained herein are not intended to withstand the loads from 

these larger debris elements. Floodborne debris is capable of destroying unreinforced masonry 

walls, light wood-frame construction, and small-diameter posts and piles (and the components 

of structures they support). Debris trapped by cross bracing, closely spaced pilings, grade beams, 

or other components is also capable of transferring flood and wave loads to the foundation of 

an elevated structure. 

Figure 1-12.

Pier pilings were carried

over 2 miles by the

storm surge and waves

of Hurricane Opal (1995)

before coming to rest

against this elevated

house in Pensacola

Beach, Florida.

Source: COastal 

COnStruction manual

(FEMA 55)

1.3.5	 Erosion and Scour

Erosion refers to the wearing and washing away of coastal lands, including sand and soil. It is 

part of the larger process of shoreline changes. Erosion occurs when more sediment leaves a 

shoreline area than enters from either manmade objects or natural forces. Because of the dynamic nature of erosion, it is one of the most complex hazards to understand and difficult to 

accurately predict at any given site along the coast. 

Short-term erosion changes can occur from storms and periods of high wave activity, lasting 

over periods ranging from a few days to a few years. Because of the variability in direction 

and magnitude, short-term erosion effects can be orders of magnitude greater than long-term 

erosion. Long-term shoreline changes occur over a period of decades or longer and tend to average out the short-term erosion. Both short-term and long-term changes should be considered 

in the siting and design of coastal residential construction. Refer to Chapter 7 of FEMA 55 for 

additional guidance on assessing short- and long-term erosion.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 1-11

TYPES OF HAZARDS 1

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)

Scour can occur when water flows at high velocities past an object embedded in or sitting on 

soil that can be eroded. Scour occurs around the object itself, such as a piling or foundation element, and contributes to the loss of support provided by the soil. In addition to any storm or 

flood-induced erosion that occurs in the general area, scour is generally limited to small, coneshaped depressions. Localized scour is capable of undermining slabs, pilings, and grade beam 

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

considers these effects on the foundation size and depth of embedment requirements.

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 on the Gulf Coast should be designed in accordance with the 2003 or 2006 edition 

of the IBC or IRC; both contain up-to-date wind provisions and are consistent with NFIP flood 

provisions. In addition, any locally adopted building ordinances must be addressed. Foundations should be designed and constructed to: 

n Properly support the elevated home and resist all loads expected to be imposed on the 

home and its foundation during a design event 

n Prevent flotation, collapse, and lateral movement of the building 
2- Building on strong and safe foundations

2 FOUNDATIONS

NFIP Minimum Elevation 

Requirements for New 

Construction*

A Zone: Elevate top of lowest floor to or 

above BFE 

V Zone: Elevate bottom of lowest horizontal 

structural member supporting the lowest 

floor to or above BFE 

In both V and A Zones, many property owners have decided to elevate one full story 

above grade, even if not required, to allow 

below-building parking. See Fact Sheet No. 

2 of FEMA 499 for more information about 

NFIP minimum requirements and recommended best practices in A and V Zones 

(see Appendix F).

* For floodplain management purposes, “new construction” means structures for which the start of construction began on or 

after the effective date of the floodplain management regulation adopted by a community. Substantial improvements, repairs of 

substantial damage, and some enclosures must meet most of the same requirements as new construction.

In addition, the foundation should be constructed with flood-resistant materials below the Base 

Flood Elevation (BFE).

2.2 Foundation Design in Coastal Areas

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

n Storm surge, wave action, and erosion in coastal areas make coastal flooding more damaging than inland flooding.

n Design wind speeds are higher in coastal areas and thus require buildings and their foundations to be able to resist higher wind loads.

Foundations in coastal areas must be constructed such that the top of the lowest floor (in A 

Zones) or the bottom of the lowest horizontal structural members (in V Zones) of the buildings are elevated above the BFE, while withstanding flood forces, high winds, erosion and 

scour, and floodborne debris. Deeply embedded pile or other open foundations are required 

for V Zones because they allow waves and floodwaters to pass beneath elevated buildings. Because of the increased flood, wave, floodborne debris, and erosion hazards in V Zones, NFIP 

design and construction requirements are more stringent in V Zones than in A Zones.

Some coastal areas mapped as A Zones may also 

be subject to damaging waves and erosion (referred to as “Coastal A Zones”). Buildings in 

these areas that are constructed to minimum 

NFIP A Zone requirements may sustain major 

damage or be destroyed during the base flood. 

It is strongly recommended that buildings in A Zones 

subject to breaking waves and erosion be designed 

and constructed with V Zone type foundations (see 

Figure 2-1). Open foundations are often recommended instead of solid wall, crawlspace, slab, or 

shallow foundations, which can restrict floodwaters and be undermined easily. Figure 2-2 shows 

examples of building failures due to scour under 

a slab-on-grade foundation. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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).
2- Building on strong and safe foundations

2 FOUNDATIONS

2.3 Open and Closed Foundations in Coastal Areas

T

here are many designs that can be used to elevate buildings above the BFE: open foundations (pile, pier, column) and closed foundations (crawlspace, stem wall, solid wall). 

Structural fill can also be used to elevate and support stem wall, crawlspace, solid wall, slabon-grade, pier, and column foundations in areas not subject to damaging wave action and scour. 

Only open foundations with base members or elements (pilings or beams) located below expected erosion and scour are allowed in V Zones; as a “best practices” approach, open foundations 

are recommended, but are not NFIP required, in Coastal A Zones. Table 2-1 shows the recommended type of foundation depending on the coastal area. Additional information concerning 

foundation performance can be found in FEMA 499, Fact Sheet No. 11 (see Appendix F).

Table 2-1. Foundation Type Dependent on Coastal Area

Foundation Type V Zone Coastal A Zone A Zone

Open 4 4 4

Closed 8 NR 4

4 = Acceptable NR = Not Recommended 8 = Not Permitted

2.3.1 Open Foundations

Open foundations are required in V Zones and recommended in Coastal A Zones. This type of 

foundation allows water to pass beneath an elevated building through the foundation and reduces 

lateral flood loads on the structure. Open foundations also have the added benefit of being less 

susceptible to damage from floodborne debris because debris is less likely to be trapped. 

2.3.1.1 Piles

Pile foundations consist of deeply placed vertical piles installed under the elevated structure. 

The piles support the elevated structure by remaining solidly placed in the soil. Because pile 

foundations are set deeply, they are inherently more tolerant to erosion and scour. Piles rely primarily on the friction forces that develop between the pile and the surrounding soils (to resist 

gravity and uplift forces) and the compressive strength of the soils (to resist lateral movement). 

The soils at the ends of the piles also contribute to resist gravity loads. 

Piles are typically treated wood timbers, steel pipes, or pre-cast concrete. Other materials like 

fiber reinforced polyester (FRP) are available, but are rarely used in residential construction. 

Piles can be used with or without grade beams. When used without grade beams, piles extend 

to the lowest floor of the elevated structure. Improved performance is achieved when the piles 

extend beyond the lowest floor to the roof (or an upper floor level) above. Doing so provides 

resistance to rotation (also called “fixity”) in the top of the pile and improves stiffness of the pile 

foundation. Occasionally, wood framing members are installed at the base of a wood piling (see 

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

provide lateral support for portions of the piling near grade and reduce the potential for column buckling; however, due to the difficulties of constructing moment connections with wood, 

the compression struts provide very little resistance to rotation. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2-

FOUNDATIONS 2

Figure 2-3. 

Compression strut at 

base of a wood piling. 

Struts provide some 

lateral support for the 

piling, but very little 

resistance to rotation.

Source: COastal 

COnStruction 

manual

(FEMA 55)

Critical aspects of a pile foundation include the pile size, installation method, and embedment 

depth, bracing, and their connections to the elevated structure (see FEMA 499 Fact Sheet Nos. 

12 and 13 in Appendix F). Pile foundations with inadequate embedment will not have the structural capacity to resist sliding and overturning (see Figure 2-4). Inadequate embedment and 

improperly sized piles greatly increase the probability for structural collapse. However, when 

properly sized, installed, and braced with adequate embedment into the soil (with consideration for erosion and scour effects), a building’s pile foundation performance will allow the 

building to remain standing and intact following a design flood event (see Figure 2-5).

Figure 2-4. 

Near collapse due 

to insufficient pile 

embedment (Dauphin 

Island, Alabama)

Source: Hurricane 

Katrina in the Gulf 

Coast (FEMA 549)

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. 
2- Building on strong and safe foundations

2 FOUNDATIONS

Pile foundations with grade beams must be constructed with adequate strength to resist all lateral 

and vertical loads. Failures experienced during Hurricane Katrina often resulted from inadequate 

connections between the columns and footings or grade beams below (see Figure 2-6). Pile and 

grade beam foundations should be designed and constructed so that the grade beams act only 

to provide fixity to the foundation system and not to support the lowest elevated floor. If grade 

beams support the lowest elevated floor of the home, they become the lowest horizontal structural member and significantly higher flood insurance premiums would result. Also, if the grade 

beams support the structure, the structure would become vulnerable to erosion and scour. Grade 

beams must also be designed to span between adjacent piles and the piles must be capable of resisting both the weight of the grade beams when undermined by erosion and scour, and the loads 

imposed on them by forces acting on the structure.

Figure 2-5. 

Successful pile 

foundation following 

Hurricane Katrina 

(Dauphin Island, 

Alabama) 

Source: Hurricane 

Katrina in the Gulf 

Coast (FEMA 549)

Figure 2-6. 

Column connection 

failure (Belle Fontaine 

Point, Jackson County, 

Mississippi)

Source: Hurricane 

Katrina in the Gulf 

Coast (FEMA 549)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2-

FOUNDATIONS 2

2.3.1.2 Piers

Piers have different design criteria in various locations around the country. As used in the Gulf 

Coast for residential construction, piers are generally placed on footings to support the elevated structure. Without footings, piers function as short piles and rarely have sufficient capacity 

to resist uplift and gravity loads.

The type of footing used in pier foundations greatly affects the foundation’s performance (see 

Figure 2-7). When exposed to lateral loads, discrete footings can rotate so piers placed on discrete footings are only suitable when wind and flood loads are relatively low. Piers placed on 

continuous concrete grade beams or concrete strip footings provide much greater resistance to 

lateral loads because the grade beams/footings act as an integral unit and are less prone to rotation. Footings and grade beams must be reinforced to resist the moment forces that develop 

at the base of the piers due to the lateral loads on the foundation and the elevated home (see 

Figure 2-8). 

Since pier foundation footings or grade beams are limited in depth of placement, they are appropriate only where there is limited potential for erosion or scour. The maximum estimated 

depth for long- and short-term erosion and localized scour should not extend below the bottom 

of the footing or grade beam. 

Figure 2-7. 

Performance 

comparison of pier 

foundations. Piers 

on discrete footings 

(foreground) failed 

by rotating and 

overturning while piers 

on more substantial 

footings (in this case a 

concrete mat) survived 

(Pass Christian, 

Mississippi)
2- Building on strong and safe foundations

2 FOUNDATIONS

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

BFE, they must be equipped with openings that allow floodwaters to flow in and out of the area 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2-

FOUNDATIONS 2

enclosed by the walls (see Figure 2-9 for an isometric view). The entry and exit of floodwater will 

equalize the water pressure on both sides of the wall and reduce the likelihood of the wall collapsing (see FEMA 499 Fact Sheet No. 15 in Appendix F). Two types of closed foundations are 

discussed in this manual, perimeter walls and slab-on-grade.

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

2.3.2.1 Perimeter Walls 

Perimeter walls are conventional walls (typically masonry or wood frame) that extend from the 

ground up to the elevated building. They typically bear on shallow footings. Crawlspaces and 

stem walls are two types of foundations with perimeter walls.

Crawlspaces. Crawlspace foundations are typically low masonry perimeter walls, some requiring interior piers supporting a floor system if the structure is wide. These foundations are usually 

supported by shallow footings and are prone to failure caused by erosion and scour.
2-10 Building on strong and safe foundations

2 FOUNDATIONS

This type of foundation is characterized by a solid perimeter foundation wall around a structure with a continuous spread footing with reinforced masonry or concrete piers. All crawlspace 

foundation walls in the Special Flood Hazard Area (SFHA) must be equipped with flood openings. These openings are required to equalize the pressure on either side of the wall (see FEMA 

499 Fact Sheet Nos. 15 and 26 in Appendix F). However, even with flood vents, hydrodynamic 

and wave forces in Coastal A Zones can damage or destroy these foundations.

Stem Walls. Stem walls (i.e., a solid perimeter foundation wall on a continuous spread footing 

backfilled to the underside of the floor slab) are similar to crawlspace foundations, but the interior that would otherwise form the crawlspace is filled with soil or gravel that supports a floor 

slab. Stem wall foundations have been observed to perform better than crawlspace foundations 

in Coastal A Zones (but only where erosion and scour effects are minor). Flood openings are 

not required in filled stem wall foundations.

2.3.2.2 Slab-on-Grade 

A slab-on-grade foundation is concrete placed directly on-grade (to form the slab) with generally thickened, reinforced sections around the edges and under loadbearing walls. The slab 

itself is typically 4 inches thick where not exposed to concentrated loads and 8 to 12 inches 

thick under loadbearing walls. The thickened portions of slab-on-grade foundations are typically reinforced with deformed steel bars to provide structural support; the areas not thickened 

are typically reinforced with welded wire fabrics (WWF) for shrinkage control. While commonly 

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

prohibited in V Zones, and are not recommended for Coastal A Zones. 

Slab-on-grade foundations can be used with structural fill to elevate buildings. Fill is usually 

placed in layers called “lifts” with each lift compacted at the site. Because fill is susceptible to 

erosion, it is prohibited for providing structural support in V Zones. Structural fill is not recommended for Coastal A Zones, but may be appropriate for non-Coastal A Zones. 

2.4 Introduction to Foundation Design and Construction

T

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

site characterization and types of foundation construction. Construction materials and 

methods (field preservation treatment, substitutions, inspection points) are addressed 

in Chapter 4.

2.4.1 Site Characterization

The foundation design chosen should be based on the characteristics that exist at the building 

site. A site characteristic study should include the following:

n The type of foundations that have been installed in the area in the past. A review of the 

latest Flood Insurance Rate Map (FIRM) is recommended to ensure that construction characteristics have not been changed.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2-11

FOUNDATIONS 2

n The proposed site history, which would indicate whether there are any buried materials, or 

the site has been regraded.

n How the site may have been used in the past, from a search of land records for past 

ownership.

n A Soil Investigation Report, which should include:

n Soil borings sampled from the site or taken from test 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 (formerly the Soil Conservation Service) and soil surveys published for each county

One of the parameters derived from a soil investigation report is the bearing capacity, which 

measures the ability of soils to support gravity loads without soil shear failure or excessive settlement. Measured in pounds per square foot (psf), soil bearing capacity typically ranges from 

1,000 psf for relatively weak soils to over 10,000 psf for bedrock. 

Frequently, designs are initially prepared on a presumed bearing capacity. It is then the 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 1804 of the 2003 IBC can be used when 

other data are not available. However, soils can vary significantly in bearing capacity from one 

site to the next. A geotechnical engineer should be consulted when any unusual or unknown 

soil condition is encountered.

2.4.2 Types of Foundation Construction

2.4.2.1 Piles 

A common type of pile foundation is the elevated wood pile foundation, where the piles extend from deep in the ground to an elevation at or above the Design Flood Elevation (DFE). 

Horizontal framing members are used to connect the piles in both directions. This grid forms a 

platform on which the house is built (see FEMA 499 Fact Sheet No. 12 in Appendix F).

The method of installation is a major consideration in the structural integrity of pile foundations. The ideal method is to use a pile driver. In this method, the pile is held in place with 

leads while a single-acting, double-acting diesel or air-powered hammer drives the pile into the 

ground (see Figure 2-10).

If steel piles are used, only the hammer driving method mentioned above should be used. For 

any pile driving, the authority having jurisdiction or the engineer-of-record may require that a 

driving log is kept for each pile. The log will tabulate the number of blows per foot as the driving progresses. This log is a key factor used in determining the pile capacity. 
2-12 Building on strong and safe foundations

2 FOUNDATIONS

Figure 2-10. 

Pile installation methods

Source: COastal 

COnstruction manual

(FEMA 55)

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.

A less desirable but frequently used method of inserting piles into sandy soil is “jetting,” which 

involves forcing a high-pressure stream of water through a pipe that advances with the pile. The 

water creates a hole in the sand as the pile is driven until the required depth is reached. Unfortunately, jetting loosens the soil both around the pile and the tip. This results in a lower load 

capacity due to less frictional resistance. Jetted piles are not appropriate for the design provided 

in this manual unless capacity is verified by a geotechnical engineer.

Holes for piles may be excavated by an auger if the soil has sufficient clay or silt content. Augering can be used by itself or in conjunction with pile driving. If the hole is full-sized, the 

pile is dropped in and the void backfilled. Alternatively, an undersized hole can be drilled and 

a pile driven into it. When the soil conditions are appropriate, the hole will stay open long 

enough to drop or drive in a pile. In general, this method may not have as much capacity as 

those methods previously mentioned. Like jetted piles, augered piles are not appropriate for 

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

by a geotechnical engineer.

2.4.2.2 Diagonal Bracing of Piles

The foundation design may include diagonal bracing to stiffen the pile foundation in one or 

more directions. When installed properly, bracing lowers the point where lateral loads are applied to the piles. The lowering of load application points reduces the bending forces that piles 

must resist (so piles in a braced pile foundation do not need to be as strong as piles in an unbraced pile foundation) and also reduces lateral movement in the building. Outside pilings are 

sufficiently designed to withstand external forces, because bracing will not assist in countering 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2-13

FOUNDATIONS 2

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.

n There are fewer obstructions to waves and floodborne debris.

n The rod bracing can easily be tensioned with turnbuckles and can be adjusted throughout 

the life of the home.

n A balanced double shear connection is two to three times stronger than a wood to wood 

connection made with 2-inch thick dimensional lumber.

Alternative bracing should only be installed when designed by a licensed engineer.

2.4.2.3 Knee Bracing of Piles

Knee braces involve installing short diagonal braces between the upper portions of the pilings 

and the floor system of the elevated structure. The braces increase the stiffness of an elevated 

pile foundation and can be effective at resisting the lateral forces on a home. While knee braces 

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

diagonal braces. For example, knee braces present less obstruction to waves and debris, are 

shorter than diagonal braces, and are usually designed for both tension and compression loads. 
2-14 Building on strong and safe foundations

2 FOUNDATIONS

Unlike diagonal braces, knee braces do not reduce bending moments in the piles (they can 

actually increase bending moments) and will not reduce the diameter of the piles required to 

resist lateral loads.

The entire load path into and through the knee brace must be designed with sufficient capacity. 

The connections at each end of each knee brace must have sufficient capacity to handle both tension and compression and to resist axial loads in the brace. The brace itself must have sufficient 

cross-sectional area to resist compression and tensile loads. Due to the complexity of knee bracing, 

they have not been used in the foundation designs included in Appendix A of this document.

Figure 2-11. Diagonal bracing schematic

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. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 2-15

FOUNDATIONS 2

Although connections play an integral role in the design of structures, they are typically regarded as the weakest link. The connection between a wood pile and the elevated structure should 

be designed by an engineer (see FEMA 499 Fact Sheet No. 13 in Appendix F). 

2.4.2.5 Grade Beams in Pile/Column Foundations

Grade beams are sometimes used in conjunction with pile and column foundations to generate more stiffness. They generate stiffness by forcing the piles to move as a group rather than 

individually and by providing fixity (i.e., resistance to rotation) at the ends of the piles. Typically, 

they extend in both directions and are usually made of reinforced concrete. The mix design, the 

amount and placement of reinforcement, the cover, and the curing process are important parameters in optimizing durability. To reduce the effect of erosion and scour on foundations, grade 

beams must be designed to be self-supporting foundation elements. The supporting piers should 

be designed to carry the weight of the grade beams and resist all loads transferred to the piers.

In V Zones, grade beams must be used only for lateral support of the piles. If, during construction, the floor is made monolithic with the grade beams, the bottom of the beams become the 

lowest horizontal structural member. This elevation must be at or above the BFE. 

If grade beams are used with wood piles, the possibility of rot occurring must be considered 

when designing the connection between the grade beam and the pile. The connection must 

not encourage water retention. The maximum bending moment in the piles occurs at the grade 

beams, and decay caused by water retention at critical points in the piles could induce failure 

under high wind or flood forces.

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-

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 2003 (IBC 2003) or ASCE 7-02, Minimum Design Loads for Buildings and Other 

Structures), if model building codes and other building standards do not provide load determination and design guidance for each of the hazards identified. In such instances, supplemental 

guidance such as FEMA 55 should be sought, the loads imposed by each of the identified hazards should be calculated, and the load combinations appropriate for the building site should 

be determined. The load combinations used in this manual are those specified by ASCE 7-02, 

the standard referenced by the IBC 2003. Either Allowable Stress Design (ASD) or Strength 
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 presented in this manual to accommodate 

Strength Design concepts. Assumptions utilized in this document can be found in Appendix 

C.

3.1	 Wind Loads

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

in ASCE 7-02, Minimum Design Loads for Buildings and Other Structures. This document 

is the wind standard referenced by the 2003 editions of the IBC and IRC. Equations 

used to calculate wind loads are presented in Appendix D.

The most important variable in calculating wind load is the design wind speed. Design wind 

speed can be obtained from the local building official or the ASCE 7-02 wind speed map (see 

Figure 3-1). The speeds shown in this figure are 3-second gust speeds for Exposure Category 

C at a 33-foot (10-meter) height. ASCE 7-02 includes scaling factors for other exposures and 

heights. 

ASCE 7-02 specifies wind loads for structural components known as a Main Wind Force Resisting System (MWFRS). The foundation designs developed for this manual are based on 

MWFRS pressures calculated for Exposure Category C, the category with the highest anticipated wind loads for land-based structures.

ASCE 7-02 also specifies wind loads for components and cladding (C&C). Components and 

cladding are considered part of the building envelope, and ASCE 7-02 requires C&C to be designed to resist higher wind pressures than MWFRS. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-

FOUNDATION DESIGN LOADS 3

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

Source: ASCE 7-02

3.2 Flood Loads

T

his manual develops in more detail flood load calculations and incorporates the methodology presented in ASCE 7-02. Although wind loads can directly affect a structure and dictate 

the actual foundation design, the foundation is more affected by flood loads. ASCE 24 discusses floodproof construction. Loads developed in ASCE 24 come directly from ASCE 7-02, 

which is what the designs presented herein are based upon.

The effects of flood loads on buildings can be exacerbated by storm-induced erosion and localized scour, and by long-term erosion. Erosion and scour lower the ground surface around 

foundation members and can cause the loss of load-bearing capacity and resistance to lateral 

and uplift loads. Erosion and scour also increase flood depths and, therefore, increase depth 

dependent flood loads.
3- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

Figure 3-2.

Parameters that

determine or are

affected by flood depth

Source: COastal 

COnstruction manual

(FEMA 55)

3.2.1	 Design Flood and Design Flood Elevation (DFE)

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

1. Base flood, affecting those areas identified as SFHAs on the community’s FIRM, or 

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 THE GULF COAST 3-

FOUNDATION DESIGN LOADS 3

3.2.2	 Design Stillwater Flood Depth (ds)

Design stillwater flood depth (ds) is the vertical distance between the eroded ground elevation 

and the stillwater flood elevation associated with the design flood. Determining the maximum 

design stillwater flood depth over the life of a building is the single most important flood load 

calculation that will be made; nearly all other coastal flood load parameters or calculations (e.g., 

hydrostatic load, design flood velocity, hydrodynamic load, design wave height, DFE, debris impact load, local scour depth) depend directly or indirectly on the design stillwater flood depth. 

The design stillwater flood depth (ds) is defined as

ds = Esw – GS

Where

ds = Design stillwater flood depth (ft)

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

effects

GS = Lowest eroded ground elevation above datum (ft), adjacent to building, including 

the effects of localized sour around pilings

GS is not the lowest existing pre-flood ground surface; it is the lowest ground surface that will 

result from long-term erosion and the amount of erosion expected to occur during a design 

flood, excluding local scour effects. The process for determining GS is described in Chapter 7 

of FEMA 55.

Values for Esw are not shown on a FIRM, but they are given in the Flood Insurance Study (FIS) 

report, which is produced in conjunction with the FIRM for a community. FIS reports are usually available from community officials, from NFIP State Coordinating Agencies, and on the web 

at the FEMA Map Service Center (http://store.msc.fema.gov). Some states have FIS reports 

available on their individual web sites.

3.2.3	 Design Wave Height (Hb)

The design wave height at a coastal building site will be one of the most important design parameters. Therefore, unless detailed analysis shows that natural or manmade obstructions will 

protect the site during a design event, wave heights at a site will be calculated from Equation 5-2 

of ASCE 7-02 as the heights of depth-limited breaking waves (Hb), which are equivalent to 0.78 

times the design stillwater flood depth: 

Hb = 0.78ds

Note: 70 percent of the breaking wave height (0.7Hb) lies above the stillwater flood level.
3- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

3.2.4	 Design Flood Velocity (V)

Estimating design flood velocities in coastal flood hazard areas is subject to considerable uncertainty. Little reliable historical information exists concerning the velocity of floodwaters 

during coastal flood events. The direction and velocity of floodwaters can vary significantly 

throughout a coastal flood event, approaching a site from one direction during the beginning 

of the flood event before shifting to another (or several directions). Floodwaters can inundate 

some low-lying coastal sites from both the front (e.g., ocean) and the back (e.g., bay, sound, 

river). In a similar manner, flow velocities can vary from close to zero to high velocities during 

a single flood event. For these reasons, flood velocities should be estimated conservatively by 

assuming that floodwaters can approach from the most critical direction and that flow velocities can be high.

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

V = ds ÷ t (expected lower bound) 

to

V = (gds)0.5 (expected upper bound) 

Where

ds = Design stillwater flood depth

t = Time (1 second)

g = Gravitational constant (32.2 ft/sec2)

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

design include:

n Flood 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. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-

FOUNDATION DESIGN LOADS 3

3.3	 Hydrostatic Loads

Hydrostatic loads occur when standing or slowly moving water comes into contact with a 

building or building component. These loads can act laterally (pressure) or vertically 

(buoyancy). 

Lateral hydrostatic forces are generally not sufficient to cause deflection or displacement of 

a building or building component unless there is a substantial difference in water elevation 

on opposite sides of the building or component; therefore, the NFIP requires that floodwater 

openings be provided in vertical walls that form an enclosed space below the BFE for a building 

in an A Zone.

Lateral hydrostatic force is calculated by the following:

fstat = 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- Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

3.4	 Wave Loads

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

n Non-breaking waves (can usually be computed as hydrostatic forces against walls and hydrodynamic forces against piles)

n Breaking waves (short duration but large magnitude forces against walls and piles) 

n Broken waves (similar to hydrodynamic forces caused by flowing or surging water)

n Uplift (often caused by wave runup, deflection, or peaking against the underside of horizontal surfaces)

Of these four categories, the forces from breaking waves are the largest and produce the most 

severe loads. Therefore, it is strongly recommended that the breaking wave load be used as the 

design wave load. 

Two breaking wave loading conditions are of interest in residential construction: waves breaking 

on small-diameter vertical elements below the DFE (e.g., piles, columns in the foundation of a 

building in a V Zone) and waves breaking against vertical walls below the DFE (e.g., solid foundation walls in A Zones, breakaway walls in V Zones). 

3.4.1	 Breaking Wave Loads on Vertical Piles

The breaking wave load (Fbrkp) on a pile can be assumed to act at the stillwater flood level and 

is calculated by Equation 5-4 from ASCE 7-02:

Fbrkp = (1/2)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)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-

FOUNDATION DESIGN LOADS 3

3.4.2	 Breaking Wave Loads on Vertical Walls

The net force resulting from a normally incident breaking wave (depth limited in size, with 

Hb = 0.78ds) acting on a rigid vertical wall, can be calculated by Equation 5-6 from ASCE 7-02:

Fbrkw = 1.1Cpγds

2 + 2.4γds2

Where 

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

flood elevation

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

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

Building Category Cp

I – Buildings and other structures that represent a low 

hazard to human life in the event of a failure 1.6

II – Buildings not in Category I, III, and IV 2.8

III – Buildings and other structures that represent a substantial 

hazard to human life in the event of a failure 3.2

IV – Buildings and other structures designated as essential facilities 3.5

Source: ASCE 7-02

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 (see Figure 3-3).

If free-standing water exists behind the wall (see Figure 3-4), a portion of the hydrostatic component of the wave pressure and force disappears and the net force can be computed using 

Equation 5-7 from ASCE 7-02:

Fbrkw = 1.1Cpγds

2 + 1.9γds2
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 7-02

Figure 3-3.

Normally incident

breaking wave

pressures against a

vertical wall (space

behind vertical wall is

dry)

Source: ASCE 7-02

Post-storm damage inspections show that breaking wave loads have destroyed virtually all woodframe or unreinforced masonry walls below the wave crest elevation; only highly engineered, 

massive structural elements are capable of withstanding breaking wave loads. Damaging wave 

pressures and loads can be generated by waves much lower than the 3-foot wave currently used 

by FEMA to distinguish between A Zones and V Zones. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-11

FOUNDATION DESIGN LOADS 3

3.5	 Hydrodynamic Loads

Water flowing around a building (or a structural element or other object) imposes additional loads on the building. The loads (which are a function of flow velocity and structural geometry) include frontal impact on the upstream face, drag along the sides, 

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

constant (i.e., steady state flow). 

One of the most difficult steps in quantifying loads imposed by moving water is determining the 

expected flood velocity. Refer to Section 3.2.4 for guidance concerning design flood velocities.

The following equation from FEMA 55 can be used to calculate the hydrodynamic load from 

flows with velocity greater than 10 ft/sec:

Fdyn = 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. 
3-12 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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

Width to Depth Ratio

(w/ds or w/h) Drag Coefficient (Cd)

1 to 12 1.25

13 to 20 1.30

21 to 32 1.40

33 to 40 1.50

41 to 80 1.75

81 to 120 1.80

>120 2.00

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

Source: FEMA 55

Flow around a building or building component will also create flow-perpendicular forces (lift 

forces). If the building component is rigid, lift forces can be assumed to be small. But if the 

building component is not rigid, lift forces can be greater than drag forces. The formula for 

lift force is similar to the formula for hydrodynamic force except that the drag coefficient 

(Cd) is replaced with the lift coefficient (Cl). For the purposes of this manual, the foundations of coastal residential buildings can be considered rigid, and hydrodynamic lift forces 

can therefore be ignored.

3.6	 Debris Impact Loads

Debris or impact loads are imposed on a building by objects carried by moving water. The 

magnitude of these loads is very difficult to predict, yet some reasonable allowance must 

be made for them. The loads are influenced by where the building is located in the potential debris stream:

n Immediately adjacent to or downstream from another building

n Downstream from large flotable objects (e.g., exposed or minimally covered storage tanks)

n Among closely spaced buildings

The following equation to calculate the magnitude of impact load is provided in the Commentary 

of ASCE 7-02:

Fi = (πWVCiCoCDCBRmax) ÷ (2g∆t)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-13

FOUNDATION DESIGN LOADS 3

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

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

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

Co = Orientation coefficient = 0.8

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

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

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

g = Gravitational constant (32.2 ft/sec2)

∆t = Duration of impact (sec) 

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

Fi = (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 
3-14 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

foundations, the Coastal Construction Manual (FEMA 55) advises applying impact loading to a 

corner or critical column or piling concurrently with other flood loads (see Coastal Construction Manual, Table 11-6). For closed foundations (which are not recommended in Coastal A 

Zones and are not allowed in V Zones), the Coastal Construction Manual advises that the designer assume that one corner of the foundation will be destroyed by debris and recommends the 

foundation and the structure above be designed to contain redundancy to allow load redistribution to prevent collapse or localized failure. The following should be considered in determining 

debris impact loads:

Size, shape, and weight of the debris. It is recommended that, in the absence of information 

about the nature of the potential debris, a weight of 1,000 pounds be used for the debris weight 

(W). Objects of this weight could include portions of damaged buildings, utility poles, portions 

of previously embedded piles, and empty storage tanks. 

Debris velocity. Flood velocity can be approximated by one of the equations discussed in Section 3.2.4. For the calculation of debris loads, the velocity of the waterborne object is assumed to 

be the same as the flood velocity. Note that, although this assumption may be accurate for small 

objects, it will overstate debris velocities for large objects (e.g., trees, logs, pier pilings). The 

Commentary of ASCE 7-02 provides guidance on estimating debris velocities for large debris.

Portion of building to be struck. The object is assumed to be at or near the water surface 

level when it strikes the building. Therefore, the 

object is assumed to strike the building at the 

stillwater flood level.

Duration of impact. Uncertainty about the duration of impact (∆t) (the time from initial impact, 

through the maximum deflection caused by the 

impact, to the time the object leaves) is the most 

likely cause of error in the calculation of debris 

impact loads. ASCE 7-02 showed that measured 

impact duration (from initial impact to time of 

maximum force) from laboratory tests varied 

from 0.01 to 0.05 second. The ASCE 7-02 recommended value for ∆t is 0.03 second.

3.7 	 Localized Scour

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

around foundation elements and causing localized scour. Determining potential 

scour is critical in designing coastal foundations to ensure that failure during and 

after flooding does not occur as a result of the loss in either bearing capacity or anchoring 

resistance around the posts, piles, piers, columns, footings, or walls. Localized scour determinations will require knowledge of the flood depth, flow conditions, soil characteristics, and 

foundation type. 

NOTE: The method for 

determining debris impact 

loads in ASCE 7-02 was 

developed for riverine impact loads 

and has not been evaluated for coastal 

debris that may impact a building over 

several wave cycles. Although these 

impact loads are very large but of short 

duration, a structural engineer should 

be consulted to determine the structural 

response to the short load duration (0.03 

second recommended).
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-15

FOUNDATION DESIGN LOADS 3

In some locations, soil at or below the ground surface can be resistant to localized scour, and 

scour depths calculated below will be excessive. In instances where the designer believes the soil 

at a site will be scour-resistant, a geotechnical engineer should be consulted before calculated 

scour depths are reduced.

3.7.1	 Localized Scour Around Vertical Piles

The methods for calculating localized scour (Smax) in coastal areas have been largely based on 

empirical evidence gathered after storms. Much of the evidence gathered suggests that localized scour depths around piles and other thin vertical members are approximately equal to 1.0 

to 1.5 times the pile diameter. Figure 3-5 illustrates localized scour at a pile, with and without a 

scour-resistant terminating stratum. Currently, there is no design guidance in ASCE 7-02 on how 

to calculate scour. Localized scour around a vertical pile or similar foundation element should 

be calculated with the following formula as given in FEMA 55:

Smax = 2.0a

Where 

Smax = Maximum localized scour depth (ft)

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

Figure 3-5.

Scour at vertical

foundation member

stopped by underlying

scour-resistant stratum

Source: COastal 

COnstruction 

manual

(FEMA 55)

3.7.2	 Localized Scour Around Vertical Walls and Enclosures

Localized scour around vertical walls and enclosed areas (e.g., typical A Zone construction) can 

be greater than that around vertical piles, and should be estimated using Table 3-3. 
3-16 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

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

Soil Type Expected Depth (% of ds)

Loose sand 80

Dense sand 50

Soft silt 50

Stiff silt 25

Soft clay 25

Stiff clay 10

Source: FEMA 55

3.8	 Flood Load Combinations

Load combinations (including those for flood loads) are given in ASCE 7-02, Sections 2.3.2 and 

2.3.3 for strength design and Sections 2.4.1 and 2.4.2 for allowable stress design. 

The basic load combinations are:

Allowable Stress Design

(1) D + F

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

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

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

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

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

(7) 0.6D + W + H 

(8) 0.6D + 0.7 E + H

Strength Design

(1) 1.4 (D + F)

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

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

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

(5) 1.2D + 1.0E + L + 0.2S
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 3-17

FOUNDATION DESIGN LOADS 3

(6) 0.9D + 1.6W + 1.6H

(7) 0.9D + 1.0E + 1.6H

For structures located in V or Coastal A Zones:

Allowable Stress Design

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

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

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

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

Strength Design

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

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

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

Where

D = Dead Load

W = Wind Load

E = Earthquake Load

Fa = Flood Load

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

L = Live Load

Lr = Roof Live Load

S = Snow Load

R = Rain Load

H = Lateral Earth Pressure

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

Atlantic Coast.

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

4 and 6 above with 0.8 and 1.0, respectively.
3-18 Building on strong and safe foundations

3 FOUNDATION DESIGN LOADS

Designers should be aware that not all of the flood loads will act at certain locations or against 

certain building types. Table 3-4 provides guidance to designers for the calculation of appropriate flood loads in V Zones and Coastal A Zones (non-Coastal A Zone flood load combinations 

are shown for comparison).

The floodplain management regulations enacted by communities that participate in the NFIP 

prohibit the construction of solid perimeter wall foundations in V Zones, but allow such foundations in A Zones. Therefore, the designer should assume that breaking waves will impact piles 

in V Zones and walls in A Zones. It is generally unrealistic to assume that impact loads will occur 

on all piles at the same time as breaking wave loads; therefore, this manual recommends that 

impact loads be evaluated for strategic locations such as a building corner.

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

Case 1 Pile or Open Foundation in V Zone (Required)

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

or 

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

Case 2 Pile or Open Foundation in Coastal Z Zone (Recommended)

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

or 

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

Case 3 Solid (Wall) Foundation in Coastal A Zone (NOT Recommended)

 Fbrkp (on walls facing shoreline, including hydrostatic component) + Fdyn;

 assume one corner is destroyed by debris, and design in redundancy

Case 4 Solid (Wall) Foundation in Non-Coastal A Zone (Shown for Comparison)

 Fsta + Fdyn

Source: COastal COnStruction manual (FEMA 55)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-

4.	Overview of

Recommended

Foundation Types and

Construction for the Gulf

Coast

Chapters 1 through 3 discussed foundation design loads and 

calculations and how these issues can be influenced by coastal 

natural hazards. This chapter will tie all of these issues together with 

a discussion of foundation types and methods of constructing 

a foundation for a residential structure. 
4- Building on strong and safe foundations

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

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 are very important but, for the purpose of creating standardized foundation designs in this report, soil parameters have been fixed. This section will only discuss the first three 

critical factors mentioned above. 

4.1.1	 Wind Speed

A design wind speed is a factor that determines the foundation size and strength (see also Section 1.1). The wind speed map shown in Figure 3-1 shows the design winds along most of the 

Mississippi and Louisiana Gulf Coast areas to be between 120 and 150 mph. 

To determine forces on the building and foundation, the wind speed is critical. Wind speed creates wind pressures that act upon the building. These pressures are proportional to the square 

of the wind speed, so a doubling of the wind speed increases the wind pressure by a factor of 

four. The pressure applied to an area of the building will develop forces that must be resisted. 

To transfer these forces from the building to the foundation, properly designed load paths are 

required. For the foundation to be properly designed, all forces including uplift, compression, 

and lateral must be taken into account.

4.1.2	 Elevation

The required height of the foundation depends on three factors: the DFE, the site elevation, 

and the flood zone. The flood zone dictates whether the lowest habitable finished floor must be 

placed at the DFE or, in the case of homes in the V Zone, the bottom of the lowest horizontal 

member must be placed at the DFE. While not required by the NFIP, V Zone criteria are recommended for Coastal A Zones. Stated mathematically, 

H = DFE – G + Erosion

or

H = BFE – G + Erosion + Freeboard

Where

H = Required foundation height (in ft)

DFE = Design Flood Elevation

BFE = Base Flood Elevation
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-

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

G = Non-eroded ground elevation

Erosion = Short-term plus long-term erosion

Freeboard = Locally adopted or owner desired freeboard

The height to which a home should be elevated is one of the key factors in determining which 

pre-engineered foundation to use. Elevation height is dependent upon several factors, including the BFE, local ordinances requiring freeboard, and the desire of the homeowner to elevate 

the lowest horizontal structural member above the BFE (see also Chapter 2). This manual provides designs for closed foundations up to 8 feet above ground level and open foundations up 

to 15 feet above ground level. Custom designs can be developed for open and closed foundations to position the homes above those elevation levels. Foundations for homes that need to be 

elevated higher than 15 feet should be designed by a licensed professional engineer. 

4.1.3	 Construction Materials

The use of flood-resistant materials below the BFE is also covered in FEMA NFIP Technical 

Bulletin 2 and FEMA 499 Fact Sheet No. 8 (see also Appendix F). This manual will cover the 

materials used in masonry and concrete foundation construction, and field preservative treatment for wood.

4.1.3.1 Masonry Foundation Construction

The combination of high winds, moisture, and salt-laden air creates a damaging recipe for masonry construction. All three can penetrate the tiniest cracks or openings in the masonry joints. 

This can corrode reinforcement, weaken the bond between the mortar and the brick, and create fissures in the mortar. Moisture resistance is highly influenced by the quality of the materials 

and the workmanship. 

4.1.3.2	 Concrete Foundation Construction

Cast-in-place concrete elements in coastal environments should be constructed with 3 inches or 

more of concrete cover over the reinforcing bars. The concrete cover physically protects the reinforcing bars from corrosion. However, if salt water penetrates the concrete cover and reaches 

the reinforcing steel, the concrete alkalinity is reduced by the salt chloride, thereby corroding 

the steel. As the corrosion forms, it expands and cracks the concrete, allowing the additional 

entry of water and further corrosion. Eventually, this process weakens the concrete structural 

element and its load carrying capacity.

Alternatively, epoxy-coated reinforcing steel can be used if properly handled, stored, and placed. 

Epoxy-coated steel, however, requires more sophisticated construction techniques and more 

highly trained contractors that are not usually involved with residential construction.

Concrete mix used in coastal areas must be designed for durability. The first step in this process 

is to start with the mix design. The American Concrete Institute (ACI) 318 manual recommends 

that a maximum water-cement ratio by weight of 0.40 and a minimum compressive strength of 

4,000 pounds per square inch (psi) be used for concrete used in coastal environments. Since 
4- Building on strong and safe foundations

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

the amount of water in a concrete mix largely determines the amount that concrete will shrink 

and promote unwanted cracks, the water-cement ratio of the concrete mix is a critical parameter in promoting concrete durability. Adding more water to the mix to improve the workability 

increases the potential for cracking in the concrete and can severely affect its durability.

Another way to improve the durability of a concrete mix is with ideal mix proportions. Concrete mixes typically consist of a mixture of sand, aggregate, and cement. How these elements are 

proportioned is as critical as the water-cement ratio. The sand should be clean and free of contaminants. The aggregate should be washed and graded. The type of aggregate is also very important. 

Recent research has shown that certain types of gravel do not promote a tight bond with the paste. 

The builder or contractor should consult expert advice prior to specifying the concrete mix.

Addition of admixtures such as pozzolans (fly ash) is recommended for concrete construction 

along the coast. Fly ash when introduced in concrete mix has benefits such as better workability 

and increased resistance to sulfates and chlorates, thus reducing corrosion from attacking the 

steel reinforcing. 

4.1.3.3	 Field Preservative Treatment for Wood Members

In order to properly connect the pile foundation to the floor framing system, making field 

cuts, notches, and boring holes are some of the activities associated with construction. Since 

pressure-preservative-treated piles, timbers, and lumber are used for many purposes in coastal 

construction, the interior, untreated parts of the wood are exposed to possible decay and infestation. Although treatments applied in the field are much less effective than factory treatments, 

the potential for decay can be minimized. The American Wood Preservers’ Association (AWPA) 

standard Care of Pressure-Treated Wood Products (AWPA 1991) describes field treatment procedures 

and field cutting restrictions for poles, piles, and sawn lumber. 

Field application of preservatives should always be done in accordance with instructions on the 

label. When detailed instructions are not provided, dip soaking for at least 3 minutes can be 

considered effective for field applications. When this is impractical, treatment may be done by 

thoroughly brushing or spraying the exposed area. It should be noted that the material is more 

absorptive at the end of a member, or end grains, than it is for the sides or side grains. To safeguard against decay in bored holes, the holes should be poured full of preservative. If the hole 

passes through a check (such as a shrinkage crack caused by drying), it will be necessary to brush 

the hole; otherwise, the preservative would run into the check instead of saturating the hole.

Waterborne arsenicals, pentachlorophenol, and creosote are unacceptable for field applications. Copper napthenate is the most widely used field treatment. Its deep green color may 

be objectionable, but the wood can be painted with alkyd paints in dark colors after extended 

drying. Zinc napthenate is a clear alternative to copper napthenate. However, it is not quite as 

effective in preventing insect infestation, and it should not be painted with latex paints. Tributyltin oxide (TBTO) is available, but should not be used in or near marine environments, because 

the leachates are toxic to aquatic organisms. Sodium borate is also available, but it does not 

readily penetrate dry wood and it rapidly leaches out when water is present. Therefore, sodium 

borate is not recommended.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-

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

4.1.4	 Foundation Design Loads

To provide flexibility in the home designs, tension connections have been specified between the 

tops of all wood piles and the grade beams. Depending on the location of shear walls, shear wall 

openings, and the orientation of floor and roof framing, some wood piles may not experience 

tension forces. Design professionals can analyze the elevated structure to identify compression 

only pilings to reduce construction costs. For foundation design and example calculations, see 

Appendix D.

Figure 4-1 illustrates design loads acting on a column. The reactions at the base of the elevated structure used in the foundation designs are presented in Tables 4-1a (one-story) and 4-1b 

(two-story). These reactions are the controlling forces for the range of building weights and 

dimensions listed in Appendix A and shown in Figure 2 of the Introduction. Design reactions 

have been included for the various design wind speeds and various building elevations above 

exterior grade. ASCE 7-02 Load Combination 4 (D + 0.75L + 0.75Lr) controls for gravity loading 

and Load Combination 7 controls for uplift and lateral loads. Load Combination 7 is 0.6D + W 

+ 0.75Fa in non-Coastal A Zones and 0.6D + W + 1.5Fa in Coastal A and V Zones. Refer to Section 

3.8 for the list of flood load combinations.

Figure 4-1.

Design loads acting on a column
4- Building on strong and safe foundations

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

Loads on the foundation elements themselves are more difficult to tabulate since they depend 

on the foundation style (open or enclosed), foundation dimensions, and foundation height. 

Table 4-2 provides reactions for the 18-inch square columns used in most of the open foundation designs.

Table 4-1a. Design Perimeter Wall Reactions (lb/lf) for One-Story Elevated Homes (Note: Reactions are taken at the

base of the elevated home/top of the foundation element.)

V 120 mph 130 mph 140 mph 150 mph (All V)

H Horiz Vert Horiz Vert Horiz Vert Horiz Vert Gravity

5 ft 770 -175 903 -259 1,048 -350 1,203 -448 1,172

6 ft 770 -175 903 -259 1,048 -350 1,203 -448 1,172

7 ft 770 -175 903 -259 1,048 -350 1,203 -448 1,172

8 ft 804 -202 944 -291 1,095 -388 1,257 -490 1,172

10 ft 804 -202 944 -291 1,095 -388 1,257 -490 1,172

12 ft 804 -202 944 -291 1,095 -388 1,257 -490 1,172

 14 ft 832 -224 977 -317 1,133 -417 1,300 -525 1,172

15 ft 843 -226 989 -319 1,147 -419 1,317 -527 1,172

lb = pound

lf = linear foot

V = wind speed

H = height of foundation above grade

Table 4-1b. Design Perimeter Wall Reactions (lb/lf) for Two-Story Elevated Homes (Note: Reactions are taken at the

base of the elevated home/top of the foundation element.)

V 120 mph 130 mph 140 mph 150 mph (All V)

H Horiz Vert Horiz Vert Horiz Vert Horiz Vert Gravity

5 ft 1,149 -145 1,348 -255 1,564 -374 1,795 -502 1,608

6 ft 1,149 -145 1,348 -255 1,564 -374 1,795 -502 1,608

7 ft 1,149 -145 1,348 -255 1,564 -374 1,795 -502 1,608

8 ft 1,182 -168 1,387 -282 1,609 -406 1,847 -539 1,608

10 ft 1,191 -171 1,397 -286 1,629 -410 1,860 -543 1,608

12 ft 1,191 -171 1,397 -286 1,620 -410 1,860 -543 1,608

14 ft 1,191 -171 1,397 -286 1,620 -410 1,860 -543 1,608

15 ft 1,210 -175 1,420 -291 1,647 -416 1,890 -550 1,608

lb = pound

lf = linear foot

V = wind speed

H = height of foundation above grade
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-

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

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

Flood Depth Hydrodynamic Breaking Wave Impact Buoyancy

5 ft 1,000 684 3,165 465

6 ft 1,440 985 3,476 577

7 ft 1,960 1,340 3,745 650

8 ft 2,560 1,750 4,004 743

10 ft 4,001 2,735 4,476 939

12 ft 5,761 3,938 4,903 1,115

14 ft 7,841 5,360 5,296 1,300

15 ft 9,002 6,155 5,482 1,394

4.2	 Recommended Foundation Types for the Gulf Coast

T

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

the cases specified. 

Table 4-3. Recommended Foundation Types Based on Zone

Foundation Case V Zones

A Zones in Coastal Areas

Coastal A Zone A Zone

Open Foundation

(deep)

Timber pile A 4 4 4

Steel pipe pile with concrete 

column and grade beam B 4 4 4

Timber pile with concrete 

column and grade beam C 4 4 4

Open

Foundation

(shallow)Concrete column and grade 

beam D NR 4 4

Concrete column and grade 

beam with slab G NR 4 4

Closed

Foundation

(shallow)Reinforced masonry 

– crawlspace E 8 NR 4

Reinforced masonry – stem 

wall F 8 NR 4

4 = Acceptable

NR = Not Recommended

8 = Not Permitted 
4- Building on strong and safe foundations

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

The foundation designs contained in this manual are based on soils having a bearing capacity 

of 1,500 pounds per square foot (psf). The 1,500-psf bearing capacity value corresponds to the 

presumptive value contained in the 2003 IBC for cohesive soil. Cohesive soils are fine-grained 

soils (or soils with a high clay content) with cohesive strength. These types of soils include clay, 

sandy clay, silty clay, clayey silt, silt, and sandy silt. 

The size of the perimeter footings and grade beams are generally not controlled by bearing 

capacity (uplift and lateral loads typically control footing size and grade beam dimensions). 

Refining the designs for soils with greater bearing capacities may not significantly reduce construction costs. However, the size of the interior pad footings for the crawlspace foundation 

(Table 4-3, E: Closed Foundation, Reinforced Masonry - Crawlspace) depends greatly on the 

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-

3 is also presented in Appendix A. Figures 4-2 through 4-8 are based on Appendix A.

4.2.1	 Open Foundation: Timber Pile (Case A)

This pre-engineered, timber pile foundation uses conventional, tapered, treated piles and steel 

rod bracing to support the elevated structure. No concrete, masonry, or reinforcing steel is 

needed (see Figure 4-2). Often called a “stilt” foundation, the driven timber pile system is suitable for moderate elevations if the homebuilder prefers to minimize the number of different 

construction trades used. Once the piles are driven, the wood guides and floor system are attached to the piles; the remainder of the house is constructed off the floor platform.

The recommended design for Case A that is presented in this manual accommodates home elevations up to 10 feet above grade. With customized designs and longer piles, the designs can 

be modified to achieve higher elevations. However, elevations greater than 10 feet will likely 

be prevented by pile availability, the pile strength required to resist lateral forces, and the pile 

embedment required to resist scour and erosion. A construction approach that can improve 

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

diaphragm. Doing so allows the foundation and the elevated home to function more like a single, integrated structural frame. Extending the piles stiffens the structure, reduces stresses in the 

pilings, and reduces lateral deflections. Post disaster assessments of pile supported homes indicate that extending piles in this fashion improves survivability. Licensed professional engineers 

should be consulted to analyze the pile foundations and design the appropriate connections.

One drawback of the timber pile system is the exposure of the piles to floodborne debris. During a hurricane event, individual piles can be damaged or destroyed by large, floating debris. 

With the home in place, damaged piles are difficult to replace. Two separate ways of addressing 

this potential problem is to use piles with a diameter larger than is called for in the foundation 

design or to use a greater number of piles to increase structural redundancy. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-

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

4.2.2	 Open Foundation: Steel Pipe Pile with Concrete Column and Grade Beam

(Case B)

This foundation incorporates open-ended steel pipe piles; this style is somewhat unique to the 

Gulf Coast region where the prevalence of steel pipe pilings used to support oil platforms has 

created local sources for these piles. Like treated wood piles, steel pipe piles are driven but have 

the advantage of greater bending strength and load carrying capacity (see Figure 4-3). The 

open steel pipe pile foundation is resistant to the effects of erosion and scour. The grade beam 

can be undermined by scour without compromising the entire foundation system.

Figure 4-2.

Profile of Case A

foundation type

(see Appendix A for

additional drawings)

for
4-10 Building on strong and safe foundations

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

The number of piles required depends on local soil conditions. Like other soil dependent 

foundation designs, consideration should be given to performing soil tests on the site so the 

foundation design can be optimized. With guidance from engineers, the open-ended steel pipe 

pile foundation can be designed for higher elevations. Additional piles can be driven for increased resistance to lateral forces, and columns can be made larger and stronger to resist the 

increased bending moments that occur where the columns join the grade beam. Because only a 

certain amount of steel can be installed to a given cross-section of concrete before the column 

sizes and the flood loads become unmanageable, a maximum elevation of 15 feet exists for the 

use of this type of foundation. 

Figure 4-3.

Profile of Case B

foundation type

(see Appendix A for

additional drawings)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-11

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

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

This foundation is similar to the steel pipe pile with concrete column and grade beam foundation (Case B). Elevations as high as 15 feet can be achieved for wind speeds up to 150 mph 

for both one- and two-story structures. However, because wood piles have a lower strength to 

resist the loads than steel piles, approximately twice as many timber piles are needed to resist 

loads imposed on the house and the exposed portions of the foundation (see Figure 4-4).

While treated to resist rot and damage from insects, wood piles may become vulnerable to 

damage from wood destroying organisms in areas where they are not constantly submerged by 

groundwater. If constantly submerged, there is not enough oxygen to sustain fungal growth and 

insect colonies; if only periodically submerged, the piles can have moisture levels and oxygen 

levels sufficient to sustain wood destroying organisms. Consultation with local design professionals in the area familiar with the use and performance of driven treated wood piles will help 

quantify this potential risk. Grade beams can be constructed at greater depths or alternative pile 

materials can be selected if wood destroying organism damage is a major concern.

Figure 4-4.

Profile of Case C

foundation type

(see Appendix A for

additional drawings)
4-12 Building on strong and safe foundations

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

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

These open foundation types make use of a rigid mat to resist lateral forces and overturning 

moments. Frictional resistance between the grade beams and the supporting soils resist lateral 

loads while the weight of the grade beam and the above grade columns resist uplift. Case G 

(foundation with slab) contains additional reinforcement to tie the on-grade slab to the grade 

beams to provide additional weight to resist uplift (see Figure 4-5). With the integral slab, elevations up to 15 feet above grade are achievable. Without the slab (as for Case D), the designs as 

detailed are limited to 10-foot elevations (see Figure 4-6).

Unlike the deep driven pile foundations, both shallow grade beam foundation styles can be 

undermined by erosion and scour if exposed to waves and high flow velocities. Neither style of 

foundation should be used where anticipated erosion or scour would expose the grade beam.

Figure 4-5.

Profile of Case G

foundation type (see

Appendix A for additional

drawings)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-13

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

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

The reinforced masonry with crawlspace type of foundation utilizes conventional construction 

similar to foundations used outside of SFHAs. Footings are cast-in-place reinforced concrete; 

walls are constructed with reinforced masonry (see Figure 4-7). The foundation designs presented in Appendix A permit elevated homes to be raised to 8 feet. Higher elevations are achievable 

with larger or more closely spaced reinforcing steel or with walls constructed with thicker masonry.

The required strength of a masonry wall is determined by breaking wave loads for wall heights 

3 feet or less, by non-breaking waves and hydrodynamic loads for taller walls, and by uplift for 

all walls. Perimeter footing sizes are controlled by uplift and must be relatively large for short 

foundation walls. The weight of taller walls contributes to uplift resistance and allows for smaller perimeter footings. Solid grouting of perimeter walls is recommended for additional weight 

and improved resistance to water infiltration. 

Figure 4-6.

Profile of Case D

foundation type

(see Appendix A for

additional drawings)
4-14 Building on strong and safe foundations

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

Interior footing sizes are controlled by gravity loads and by the bearing capacity of the supporting soils. Since the foundation designs are based on relatively low bearing capacities, obtaining 

soils tests for the building site may allow the interior footing sizes to be reduced.

The crawlspace foundation walls incorporate NFIP required flood vents, which must allow floodwaters to flow into the crawlspace. In doing so, hydrostatic, hydrodynamic, and breaking wave 

loads are reduced. Crawlspace foundations are vulnerable to scour and flood forces and should 

not be used in Coastal A Zones; the NFIP prohibits their use in V Zones. 

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

The reinforced masonry stem walls (commonly referred to as chain walls in portions of the Gulf 

Coast) type of foundation also utilizes conventional construction to contain fill that supports 

the floor slab. They are constructed with hollow masonry block with grouted and reinforced 

cells (see Figure 4-8). Full grouting is recommended to provide increased weight, resist uplift, 

and improve longevity of the foundation. 

The amount and size of the reinforcement are controlled primarily by the lateral forces created by the retained soils and by surcharge loading from the floor slab and imposed live loads. 

Because the retained soils can be exposed to long duration flooding, loads from saturated soils 

should be considered in the analyses. The lateral forces on stem walls can be relatively high and 

even short cantilevered stem walls (those not laterally supported by the floor slab) need to be 

heavily reinforced. Tying the top of the stem walls into the floor slab provides lateral support 

Figure 4-7.

Profile of Case E

foundation type (see

Appendix A for additional

drawings)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 4-15

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

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

placed before the slab is poured, walls that will be tied to the floor slab need to be temporarily 

braced when the foundation is backfilled until the slab is poured and cured.

Figure 4-8.

Profile of Case F

foundation type

(see Appendix A for

additional drawings)

NOTE: Stem wall foundations are vulnerable to scour and should not be used in 

Coastal A Zones without a deep footing. The NFIP prohibits the use of this foundation 

type in V Zones. 

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5-

5.	Foundation Selection

This chapter presents 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 how to use this manual are 

discussed.

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 the Gulf Coast. 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 Foundations

n Timber pile

n Steel pipe pile with concrete column and grade beam

n Timber pile with concrete column and grade beam

n Concrete column and grade beam

n Concrete column and grade beam with slab

Closed Foundations

n Reinforced masonry – crawlspace

n Reinforced masonry – stem wall

Each of these foundation types designed for the Gulf Coast region have advantages and disadvantages that must be taken into account. Modifications to the details and drawings might be 

needed to incorporate specific house footprints, elevation heights, and wind speeds to a given 

foundation type. Consultation with a licensed professional engineer is encouraged prior to beginning construction. 

The foundation designs and materials specified in this document are based on principles and 

practices used by structural engineering professionals with years of coastal construction experience. This manual has been prepared to make the information easy to understand. 

Guidance on the use of the foundation designs recommended in this manual is provided in Appendix B. Examples of how the foundation designs in this manual can be used with some of the 

houses in the publication A Pattern Book for Gulf Coast Neighborhoods are presented in Appendix 

B. Design drawings for each of the foundation types are presented in Appendix A, and any assumptions used in these designs are in Appendix C.

5.2	 Foundation Design Considerations

T

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

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

confirm the appropriateness of the foundation design of homes whose dimensions, 

weights, or roof pitches fall outside of those defined ranges. 

Most of the foundation designs are based on a 14-foot wide (maximum) by 24-foot deep (minimum) “module” (see Figure 5-1). From this basic building block, foundations for specific homes 

can be developed. For example, if a 30-foot deep by 42-foot wide home is to be constructed, 

the foundation can be designed around three 14-foot wide by 30-foot deep sections. If a 24-foot 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5-

foundation selection 5

deep by 50-foot wide home is desired, four 12.5-foot wide by 24-foot deep sections can be used. 

If a 22-foot deep home is desired, the foundation designs presented here should only be used 

after a licensed professional engineer determines that they are appropriate since the shallow 

depth of the building falls outside the range of assumptions used in the design.

Basic Module

30' x 42' Home

24' Minimum

14' Maximum

42'

14' 14' 14'

30'

28’ x 50’ Home

50’

28’

12.5’ 12.5’ 12.5’ 12.5’

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 piling foundations have been developed for relatively soft subsurface soils. Presumptive gravity loading values of 8 tons per pile, uplift loads of 4 tons per 

pile, and lateral loads of 1 ton per pile were used in these designs. Soil testing on the site 

may determine that fewer piles are needed to support the home, and the reduced cost of 

driving fewer piles could justify the cost of soils testing and redesign. Soils test should also 

be considered to validate the assumptions made.

n Building weight. The foundations have been designed to resist uplift forces resulting from 

a relatively light structure. If the actual home is heavier (e.g., from the use of concrete 

composite siding or steel framing), it may be cost-effective to reanalyze and redesign the 

footings. This is particularly true for a home that doesn’t need to be elevated more than several feet or has short foundation walls that can help resist uplift. 
5- Building on strong and safe foundations

5 foundation selection

n	 Footprint complexity. By necessity, the foundations have been designed for relatively simple 

rectangular footprints. If the actual footprint of the home is relatively complex, the engineer 

may need to consider torsional wind loading, differential movement among the “modules” 

that make up the house, concentrated loading in the home’s floor and roof diaphragms, 

and shear wall placement.

5.3	 Cost Estimating

Cost information that the homebuilders can use to estimate the cost of installing the foundation 

systems proposed in this manual are presented in Appendix E. These cost estimates are from 

information provided by local contractors and are based on May 2006 prices. 

5.4 	 How to Use This Manual

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

1. Determine location of the dwelling on a general map. Identify the location relative to key 

features such as highways and bodies of water. An accurate location is essential for using flood 

and wind speed maps in subsequent steps of the design process.

2. Determine location of dwelling on the appropriate FIRM

n Determine the flood insurance risk zone from the FIRM (Select V Zone, Coastal A Zone, 

non-Coastal A Zone, or other). Refer to FEMA 255, Guide to Flood Maps, How to Use Flood 

Maps to Determine Flood Risk for a Property, for instructions. For the Gulf Coast, the FEMA Hurricane Katrina Flood Recovery Advisories should be used until the Gulf Coast is restudied 

and remapped. New flood maps are scheduled to be completed in 2006. 

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

from the FIRM. If the dwelling is outside of floodprone areas, it only needs to be designed 

for gravity and appropriate wind loads. Seismic events are considered too rare for the Gulf 

Coast to control the design and analysis. 

FIRM Panel No. ____________________

Flood Insurance Risk Zone ____________________

Base Flood Elevation (BFE) or 

Advisory Base Flood Elevation (ABFE) ____________________
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5-

foundation selection 5

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.

County/Parish/City ____________________

Building Code ____________________

Building Code Date ____________________

Base Flood Elevation (BFE) or 

Advisory Base Flood Elevation (ABFE) ______________

Freeboard + ______________

Design Flood Elevation ______________

Design Wind Velocity ______________________________

Wind Exposure Category ______________________________

5. Determine the required Design Wind Velocity. The IRC references ASCE 7-02 as the source 

of the wind speed information. The IRC will be used as the source of all individual and combined loads.

6. Establish the topographic elevation of the building site and the dwelling. Elevations can 

be obtained from official topographic maps published by the National Geodetic Survey and/or 

as established or confirmed by a surveyor.

n If the dwelling and its surrounding site are above the DFE, no flood forces need to be 

considered.

n If the desired topographic elevation is below the DFE, the dwelling must be elevated above 

the BFE or ABFE.

Source of Topo Elevation ______________________________

Topo Elevation (Site) ______________________________

3. Identify the local building code. Several Gulf States are adopting new building codes to 

govern residential construction. Several parishes, counties, and towns in Louisiana and Mississippi have adopted the IBC and the IRC to govern construction. This document assumes that 

the IRC governs the design and construction requirements.
5- Building on strong and safe foundations

5 foundation selection

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).

Design Flood Elevation ______________________________

Topo Elevation ______________________________

Elevation Dimension ______________________________

Soil Classification ______________________________

8. Determine the general soil classification for the site. To determine the load capacity of 

the soil, the soil must first be classified according to its strength groupings. For purposes of using this manual, the classification system has been greatly simplified into two groups commonly 

found in coastal areas along the Gulf of Mexico States: (1) loose granular, cohesionless (having 

little or no clay content) soils and (2) soft, cohesive (principally clayey content) soils.

9. Determine the type of foundation to be used to support the structure. Depending on the 

location of the dwelling, design wind speed, and local soil conditions documented above, select 

the desired or required type of foundation. Note that more than one solution may be possible. 

Refer to Chapter 4 for the potential foundation designs that can be used within the flood zones 

determined from the FIRM maps. Drawings in Appendix A illustrate the construction details 

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

the needs for each type of unit.

10. Evaluate alternate foundation type selections. The choice of foundation type may be on 

the basis of least cost or to provide a personal choice, functional, or aesthetic need at the site. 

Refer to Appendix E for guidance on preparing cost estimates. Functional needs such as provisions for parking, storage, or other non-habitable uses for the area beneath the living space 

should be considered in the selection of the foundation design. Aesthetic or architectural issues 

(i.e., appearance) also must be included in the evaluation process. Guidance for the architectural design considerations can be obtained from A Pattern Book for Gulf Coast Neighborhoods by 

the Mississippi 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.

11. 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 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5-

foundation selection 5

outside of the range of values used, a licensed professional engineer should be consulted. The 

materials presented in the appendices should help reduce the engineering effort needed to develop a custom design. Figure 5-2 is a foundation selection decision tree for determining which 

foundation design to use based on the requirements of the home. Table 5-1 shows which foundation design cases can be used for the home based on height of elevation and wind velocity.

Because the designs are good for a range of buildings, they will be conservative for some applications. A licensed professional engineer will be able to provide value engineering and may 

produce a more efficient design that reduces construction costs. 

5.5	 Design Examples

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.

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.
5- Building on strong and safe foundations

5 foundation selection

Foundation Types

A = Timber pile

B = Steel pipe pile with concrete column and grade beam

C = Timber pile with concrete column and grade beam

D = Concrete column and grade beam

E = Reinforced masonry – crawlspace

F = Reinforced masonry – stem wall

G = Concrete column and grade beam with slab

Figure 5-2.

Foundation Selection Decision Tree
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5-

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

5 foundation selection

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

Wind Velocity of 120 to 150 (mph)

Height (H)

(ft)

V Zone Coastal A Zone* Non-Coastal A Zone

One-Story Dwelling

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

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

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

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

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

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

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

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

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

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

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

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

Two-Story Dwelling

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

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

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

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

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

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

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

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

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

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

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

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

* In the Coastal A Zone, the tops of all footings and grade beams in Cases D and G foundations must be placed below 

the maximum estimated erosion and scour depth. 

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

design drawings for more details.

Foundation Types

A = Timber pile

B = Steel pipe pile with concrete column and grade beam

C = Timber pile with concrete column and grade beam

D = Concrete column and grade beam

E = Reinforced masonry – crawlspace

F = Reinforced masonry – stem wall

G = Concrete column and grade beam with slab
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 5-11

foundation selection 5

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.

Module 1

Module 2

Module 1 Module 2 Module 3

Note A

Building Footprint

Alternative 1 Alternative 2

24’ - 42’

24’ - 42’

24’ - 42’

24’ Minimum

Note A

Module 1 Module 1

Module 2

Module 2

Note A

24’ - 42’

24’ - 42’

24’ Minimum

Note A

Building Footprint

Alternative 1 Alternative 2
5-12 Building on strong and safe foundations

5 foundation selection

Figure 5-5.

“Z” shaped modular

design

Note A: Overall building

dimensions can exceed

42 feet. The vertical

dimensions from the eave

to the ridge roof shall not

exceed 23 feet.

Module 1

Module 1

Module 2 Module 2

Module 3

Module 3

Note A

24' − 42'

24' − 42'

24' − 42'

24' Minimum

24' Minimum

Note

A

Building Footprint

Alternative 1 Alternative 2
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST A-

A.	Foundation Designs
































RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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/info/plansReports.html

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST B-

pattern book design B

Housing Type Affordable Housing – “Doublewide Cottage”

Contact Laura Anne Bossardt Welsh and Jeremy Welsh

Contact Information labwelsh@gmail.com

Total Square Feet 1,232

Number of Bedrooms 4

Number of Bathrooms 2

Timing Immediate/Medium Term/Long Term

Housing Type Mobile/Modular/Panelized/Stock Plan

Elevation

0- 41 0- 41

28'-0''

Floor Plan

page 63 to

p

11' 11' 11' 11' 7'

44' 

14' 14'

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

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 THE GULF COAST Bpattern book design B

Figure B-3. 

Pattern Book for Gulf Coast Neighborhoods 

Page 64 Bottom

Housing Type Detached Single-Family

Contact Urban Design Associates

Contact Information http://www.urbandesignassociates.co

m

Total Square Feet 1,536

Number of Bedrooms 3

Number of Bathrooms 2.5

Timing Medium Term/Long Term

Housing Type Stock Plan

First Floor Plan

Living Room

Kitchen

Dining Roo

m

12 x 108

page 64 bottom

8'

10'32'

12' 12' 

24' 

10'-8'' 10'-8'' 10'-8''

32'

Porch is open and has short spans. Consult with local engineer to determine uplift forces and verify suitability.
B- Building on strong and safe foundations

B pattern book design

Figure B-4. 

Pattern Book for Gulf Coast Neighborhoods 

Page 65 Bottom

Housing Type Detached Single-Family

Contact Urban Design Associates

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

Total Square Feet 1,630

Number of Bedrooms 4

Number of Bathrooms 2

Timing Medium Term/Long Term

Housing Type Stock Plan

Alternative Elevation

Alternative Elevation

' 64

Master Bedroom

134 x 16

Bedroom 2

10 x 10 10

Bedroom 3/Den

10 x10 10

page 65 bottom

Living/ Dining

164 x 20 4

Kitchen

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

11'-4'' 11'-4'' 11'-4'' 8' 10'-8'' 2'

2 @ 8'-8''

10'-8'' 10'-8'' 10'-8''

32'

2'

34'
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST B-

pattern book design B

Figure B-5. 

Pattern Book for Gulf Coast Neighborhoods 

Page 67 Top

Housing Type Affordable Housing – House

Contact Eric Moser

Contact Information ericmoser@moserdesigngroup.co

m

Total Square Feet 2,066

Number of Bedrooms 4

Number of Bathrooms 3

Timing Medium Term/Long Term

Housing Type Panelized/Stock Plan

Elevation

First Floor Plan

13' 13' 13' 13' 

 52'

11' 11' 11'

8'

2 @ 11'

33'

3 @ 9'- 4'' = 28'

8' 3'

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

page 67 bottom

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST C-

C. Assumptions Used in 

Design 

Gulf Coast Foundation Designs

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

codes:

ASCE 7-02

Minimum Design Loads for Buildings and Other Structures 

American Society of Civil Engineers (ASCE) 

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

Building Code Requirements for Masonry Structures 

American Society of Civil Engineers (ASCE) 

American Concrete Institute (ACI) 

The Masonry Society (TMS) 

ACI 318-02 

Building Code Requirements for Structural Concrete 

American Concrete Institute
C- Building on strong and safe foundations

c ASSUMPTIONS USED IN DESIGN 

ANSI/AFPA NDS-2001

National Design Specifications for Wood Construction 

American Forest & Paper Association (AF&PA) 

American Wood Council 

IRC-2003 

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

International Code Council (ICC)

To provide flexibility for the builder, a range of dead loads and building dimensions was used 

for calculating reactions on the foundation elements. For uplift and overturning analyses, the 

structure was assumed to be relatively light and narrow, and constructed with a relatively 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 7-02 ASD Uplift/Overturning Load Combination #7 (0.6D + W +H)

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

16 inches on centers

Second Floor 10 psf First floor components plus 1 layer of 1⁄2-inch gypsum drywall

Wall 9 psf Wood siding, 2 by 4 studs 16 inch 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)

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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST C-

ASSUMPTIONS USED IN DESIGN c

Concrete 150 psf Normal weight concrete. Footings for continuous perimeter walls 

were also sized to support full height brick veneer at 40 psf. 

Masonry 115 psf Medium weight block

Grout 105 psf

Brick Veneer 40 psf

Wind Loads 

Designs provided for 120 mph, 130 mph, 140 mph, and 150 mph zones (3-second gust wind 

speeds per ASCE 7-02). Wind analysis used Method 2 for buildings of all heights. 

Exposure 

Category C Open terrain with scattered obstructions generally less than 30 

feet in height; shorelines in hurricane-prone areas

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

ridges, or escarpments) 

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

Kz, Kh Velocity pressure coefficients for Exposure Category C 

Flood Loads 

V Zone Breaking wave load from a wave with height 78 percent of stillwater depth (ds

) 

Flood velocity (fps) equal to (gds)1/2 up to a maximum of 10 fps 

(FEMA 55 Upper Bound)

Coastal A Zone Breaking wave load from 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)

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) 
C- Building on strong and safe foundations

c ASSUMPTIONS USED IN DESIGN 

Live Loads

First Floor 40 psf

Second Floor 30 psf

Roof 0 psf

Soil Bearing Capacity

,500 psf Presumptive value for clay, sandy clay, silty clay, 

clayey silt, silt, and sandy silt (CI, ML, MH and CH) (2003 IRC)

Building Dimensions

Building Width 14 ft (per module)

Building Depth max 42 ft 

min 24 ft

Shear Wall Spacing max 42 ft

Floor Height 10 ft (floor to floor dimension)

Roof Pitch Ratio min 3:12 Uplift and overturning calculation 

max 12:12 Sliding calculation

Roof Overhang 2 ft
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 makes application of the 

pre-engineered foundations simpler, reducing the number of pre-engineered foundations, and 

results in conservative designs.

For example, the designs presented were developed to resist uplift and overturning for a relatively light structure with a flat roof (worst case uplift and overturning) while gravity loads were 

based on a relatively heavy structure to simulate worst case gravity loads. Sliding forces were determined for a relatively deep home with a steep roof to simulate the largest lateral loads. The 

range of building weights and dimensions applicable to the designs are listed in Appendix C.

Since the designs are inherently conservative for some building dimensions and weights, a local 

design professional may be consulted to determine if reanalyzing to achieve a more efficient design is warranted. If a reanalysis is determined to be cost-effective, the sample calculations will 

aid the designer in completing that analysis. 

D.1	 Sample Calculations

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

Type of Building

The sample calculation is based on a two-story home with a 28-foot by 42-foot footprint and 

a mean roof height of 26 feet above grade. The home is located on Little Bay in Harrison 

County, Mississippi, approximately 1.5 miles southwest of DeLisle (see Figure D-1). The site is 

located on the Harrison County Flood Recovery Map in an area with an Advisory Base Flood 

Elevation (ABFE) of 18 feet, located between the 1.5-foot wave contour and the 3-foot wave 

contour (Coastal A Zone). The local grade elevation is 15 feet North American Vertical Datum 

(NAVD). The calculations assume short- and long-term erosion will occur and the ground elevation will drop 1 foot during the life of the structure. This places the home in a Coastal A Zone 

with the flood elevation approximately 4 feet above the eroded exterior grade. Based on ASCE 

7-02, the 3-second gust design wind speed at the site is 128 miles per hour (mph) Exposure Category C. To reduce possible damage and for greater resistance to high winds, the home is being 

designed for a 140-mph design wind speed. 

The home has a gabled roof with a 3:12 roof pitch. The home is wood-framed, contains no brick 

or stone veneer, and has an asphalt shingled roof. It has a center wood beam supporting the first 

floor and a center load bearing wall supporting the second floor. Clear span trusses frame the 

roof and are designed to provide a 2-foot overhang. No vertical load path continuity is assumed 

to exist in the center supports, but vertical and lateral load path continuity is assumed to exist 

elsewhere in the structure.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 7-02 (Section D.1.2)

3. Consider the structure as a rigid body, and use force and moment equilibrium equations to 

determine reactions at the perimeter foundation elements (Section D.2)

Figure D-1.

Star indicates the location of the sample calculation home on Little Bay in Harrison County, Mississippi,

approximately 1.5 miles southwest of DeLisle. Inset on the left (from the map) is enlarged. 
D- 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 THE GULF COAST DFoundation Analysis and Design Examples D

Site Parameters (ASCE 7-02, Chapter 6)

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

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

Load Combinations)

Kh = 0.94 For simplicity, Velocity Pressure Coefficient used at the 26 foot 

mean roof height was applied at all building surfaces. 

See ASCE 7-02, Table 6-3, Case 2. 

I = 1 Importance factor (residential occupancy)

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

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

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

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

CPlwrf = -0.6 Leeward roof 

CPwwl = 0.8 Windward wall 

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

CPeave = -0.8 Windward eave

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

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

Velocity pressure at mean roof height:

qh = 0.00256 KhKzt Kd V2 I 

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

qh = 40 psf 

Wind Pressures (P)

Determine external pressure coefficients for the various building surfaces. Internal pressures, 

which act on all internal surfaces, do not contribute to the foundation reactions. For sign convention, positive pressures act inward on a building surface and negative pressures act outward.
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 THE GULF COAST 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

Figure D-2. Paths for

wind, live, and dead

loads

-20 psf 

Wind, Live and Dead Loads

-17 psf 

4' 

M+ BFE

Lowest Horizontal 

18” Sq. Concrete Member 

Column Pilecap

and Driven Pile 

2' 

28'

10' 

-34 psf 

-61 psf 

3 

12 

27 psf 

Second Floor 

First Floor 

Ground Elevation 

Eroded

Ground Elevation 

V = 140 mph 

Roof 20 psf LL 

12 psf DL

30 psf LL

10 psf DL

Second Floor

Clear Span Trusses

40 psf LL

 8 psf DL

First Floor

Bearing Wall 

10' 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST DFoundation Analysis and Design Examples D

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, 

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 (8psf + 10 psf)] + [(10 sf/lf + 10 sf/lf) 9 psf]

= 474 lb/lf

Live Loads

Floor

Live loads (Wlive) are calculated in a similar fashion

Wlive = L/4(W1stLL + W2ndLL)

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

= 490 lb/lf

Roof

Wliveroof = L/2(WrfLL)

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

= 280 lb/lf

D.2	 Determining Load Combinations

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

Other loads (such as snow, ice, and seismic) are listed in the ASCE 7-02 Load Combinations, 

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

in the design. ASCE 7-02 also lists rain loads that are appropriate for the Gulf Coast region. 

Since a minimum roof slope ratio of 3:12 was assumed for the homes, rain loading was not 

considered. 
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 7-02 Load Combination Vertical (lb/lf) Horizontal (lb/lf)

#1 D 474 --

#2 D + L 964 --

#3 D + Lr 754 --

#4 D + 0.75(L) + 0.75(Lr) {1,052} --

#5 D + W -356 831

#6 D + 0.75(W) + 0.75(L) + 0.75(Lr ) 1,016 623

#7 0.6D + W {-546} {831}

#8 0.6D 284 --

Where

D = Dead Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

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

Flood Load Effects on a Foundation

In this example, since the foundation selected is a system of steel pipe piles, the equations used 

to calculate flood loads are based on open foundations. Some of the equations used to calculate 

flood loads will be different if the building has a closed foundation system.

Many flood calculations depend on the stillwater flooding depth (ds). While not listed on FIRMs, 

ds can be calculated from the BFE by knowing that the breaking wave height (Hb) equals 78 

percent of the stillwater depth and that 70 percent of the breaking wave exists above the stillwater depth (see Figure 11-3 of FEMA 55). Stated algebraically: 

BFE = GS + ds + 0.70 Hb

= GS + ds + 0.70(0.78 ds)

= GS + 1.55 ds

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

= 14 ft NAVD

ds = (BFE – GS) ÷ 1.55 

= (18 feet NAVD – 14 feet NAVD)÷ 1.55
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 

7-02 Equation C5-2:

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

 Where 

g = Gravitational acceleration (32.2 ft/sec2)

ds = Design stillwater depth (ft)

Hence

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

= 9.15 feet per second (fps)

Hydrodynamic Forces

A modified version of ASCE 7-02 Equation C5-4 can be used to calculate the hydrodynamic 

force on a foundation element as

Fdyn = 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

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

FEMA 55. 

The Commentary of ASCE 7-02 contains a more sophisticated approach for determining debris 

impact loading, which takes into account the natural period of the impacted structure, local debris sources, upstream obstructions that can reduce the velocity of the floodborne debris, etc. 

For ease of application and consistency, debris loads in this example have been calculated using 

the guidance contained in FEMA 55 that are based on ASCE 7-98, not the 2002 version of ASCE 

7. It is suggested that designers of coastal foundations review the later standards to determine if 

they are more appropriate to use in their particular design.

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

Fi = wV ÷ (g Δ t)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 ÷ gt

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

Fi = 2,842 lb

Breaking Wave Loads

When water is exposed to even moderate winds, waves can build quickly. When adequate wind 

speed and upstream fetch exist, floodwaters can sustain wave heights equal to 78 percent of 

their stillwater depths. Depending on wind speeds, maximum wave height for the stillwater 

depth at the site can be reached with as little as 1 to 2 miles of upwind fetch.

Breaking wave forces were calculated in this example using ASCE 7-02 formulae for wave forces 

on continuous foundation walls (ASCE 7-02 Equations 5-5 and 5-6) and on vertical pilings and 

columns (ASCE 7-02 Equation 5-4). 

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

Fbrkp = 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-inch square, D = (1.4)(1.5ft) = 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 5.3.3.4.2 of ASCE 7-02 to calculate Fbrkp. FEMA 

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

fbrkw = 1.1 Cp ρ ds

2 + 2.41 γ ds2 Case 1

and

fbrkw = 1.1 Cp ρ ds

2 + 1.91 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 where fbrkw is assumed to act 

at the stillwater elevation. 

Case 1 of Formula 11.6 represents a condition where floodwaters are not present on the interior 

of the wall being designed or analyzed. Case 1 is appropriate for foundation walls that lack flood 

vents (see Figure D-3). The less stringent Case 2 is appropriate for walls where NFIP required 

flood vents are in place to equalize hydrostatic loads and reduce forces (see Figure D-4). 

In non-Coastal A Zones, the maximum wave height is 1.5 feet. This corresponds to a stillwater depth (ds) of approximately 2 feet (i.e., 1.5 foot/0.78 for a depth limited wave). For closed 

foundations in coastal areas with flood vents, a 1.5-foot breaking wave creates 1,280 lbs per linear foot of wall and 1,400 lbs per linear foot of wall on foundations that lack flood vents. 

Wind Load on Columns

Wind loads have been calculated per ASCE 7-02, Section 6.5.13 (Wind Loads on Open Buildings and Other Structures). The velocity pressure (qh) calculated previously was used, although 

this is a conservative figure based on the 26-foot mean roof height. The force coefficient (Cf) 

was determined from ASCE 7-02, Figure 6-19 (chimneys, tanks, and other structures); ASCE 7-

02, Figure 6-20 (walls and solid signs) could have been used as well. 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST D-15

Foundation Analysis and Design Examples D

From ASCE 7-02 Equation 6-25:

Fwind = qz G Cf Af

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

= 270 lb

 *Interpolated Cf

Wind loads on the foundation elements are not considered in combination with flood loads 

since the elements are submerged during those events.

Flood Load Combinations

Section 11.6.12 of FEMA 55 provides guidance on combining flood loads. In Coastal A Zones, 

FEMA 55 suggests two scenarios for combining flood loads. Case 1 involves analyzing breaking 

wave loads on all vertical supports and impact loading on one corner or critical support and 

Case 2 involves analyzing breaking wave loads applied to the front row of supports (row closest 

to the flood source), and hydrodynamic loads applied to all other supports and impact loads on 

one corner or critical support. 

Depending on the relative values for dynamic and breaking waves, Case 1 often controls for designing individual piers or columns within a home. Case 2 typically controls for the design of the 

assemblage of piers or columns working together to support a home. Because of the magnitude 

of the load, it is not always practical to design for impact loads. As an alternative, structural redundancy can be provided in the elevated home to allow one pier or column to be damaged by 

floodborne debris impact without causing collapse or excessive deflection.

Figure D-3. Case 1.

Normally incident

breaking wave

pressures against a

vertical wall (space

behind vertical wall

is dry)

Source: ASCE 7-02
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.

Figure D-4. Case 2.

Normally incident

breaking wave

pressures against a

vertical wall (stillwater

level equal on both

sides of wall)

Source: ASCE 7-02

Figure D-5.

Flood loads Flood Loads 

BFE (4')

18'' Sq.

Column

Ground Elevation 

Eroded

Ground Elevation 

0.7 Hb Hb 

Fi = 2,842# 0.3 Hb 

FBRKP = 623#

ds = 2.6’

1⁄2ds

ds

FSTAT=

576#

Fdyn = 653#

ds = stillwater depth (ft)

Hb = breaking wave depth (ft)

FBRKP = breaking wave load (#)

Fi = impact load (#)

FSTAT = buoyancy force for a fully

submerged 18” Sq. 4’ tall 

column
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 7-02 Load Combination Vertical (lb) Horizontal (lb)

#1 D + F 1,350 + [7(474]) = 4,668 --

#2 D + F + L 1,350 + [7(964)] = 8,098 --

#3 D + F + Lr 1,350 + [7(754)] = 6,628 --

#4 D + F + 0.75(L) + 0.75(Lr) 774 + 7(1,052) = {8,138} --

#5 D + F + W + 1.5(Fa) 774 + [7(474 - 48)] = 3,756 [(1/3)7(831)] + [1.5(623)] 

= {2,874}

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

0.75(Lr) + 1.5(Fa)

774 + 7[474 + 0.75

(-48+490+280)]

= 7,883

[(1/3)7(0.75)(831)] + [1.5(623)]

= 2,388

#7 0.6D + W + 1.5(Fa) 0.6[774 + 7(474)] + [7(-830)]

= {-3,555}

[(1/3)7(831)] + [1.5(623)] 

= {2,874}

#8 0.6D [0.6(1,350)] + [7(306)] = 3,000 --

Where 

D = Dead Load

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

(see Section D.2 for additional information)

Fa = Flood Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

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

Results

Each perimeter column needs to support the following loads:

Vertical Load = 8,138 lb

Uplift = 3,555 lb

Lateral Load = 2,874 lb

With the critical loads determined, the foundation elements and their connections to the home 

can be designed.

The following two examples are to demonstrate designs using information provided in this 

manual. The first example is based on a closed foundation; the second example is based on an 

open foundation. 
D-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 THE GULF COAST 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 a SFHA; hence, the NFIP required flood vents will be installed. 

The breaking wave load can be calculated using formulae for equalized flood depths (Case 2). 

fbrkw = 1.1 Cp 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 7-02 directs designers to include 75 percent of the flood load 

in load combinations 5, 6, and 7 for non-Coastal A Zones. Table D-1 lists the factored loads on 

the elevated structure. 

Critical loads from Table D-1 include 546 lb/lf uplift, 1,052 lb/lf gravity, and 831 lb/lf lateral 

from wind loading. The uplift load needs to be considered when designing foundation walls 

to resist wind and flood loads and when sizing footings to resist uplift; the gravity load must be 

considered when sizing footings and the lateral wind and flood loads must be considered in designing shear walls. 

Extending reinforcing steel from the footings to the walls allows the designer to consider the 

wall as a propped cantilever fixed at its base and pinned at the top where it connects to the 

wood-framed floor framing system. The foundation wall can also be considered simply supported 

(pinned at top and bottom). The analysis is somewhat simpler and provides conservative results.

The 1,280 lb/lf breaking wave load is the controlling flood load on the foundation. The probability that floodborne debris will impact the foundation simultaneously with a design breaking 

wave is low so concurrent wave and impact loading is not considered. Likewise, the dynamic 

load does not need to be considered concurrently with the breaking wave load and the 27 lb/sf 

wind load can not occur concurrently on a wall submerged by floodwaters. 

The breaking wave load is analyzed as a point load applied at the stillwater level. When subjected to a point load (P), a propped cantilevered beam of length (L) will produce a maximum 

moment of 0.197 (say 0.2) PL. The maximum moments occur when “P” is applied at a distance 

0.43L from the base. For the 4-foot tall wall, maximum moment results when the load is applied 

near the stillwater level (ds). In this example, the ASCE 7-02 required flood load of 75 percent 

of the breaking wave load will create a bending moment of
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-lbs/lf) ÷ {(0.85)(7.63 in)(0.5)}

= 2,837 lb/lf

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

546 pounds of uplift. 

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

= 3,383 lbs/lf

The American Concrete Institute (ACI) 530 allows 60 kips per square inch (ksi) steel to be stressed 

to 24 ksi so the reinforcement needed to resist breaking wave loads and uplift is as follows:

Asteel = 3,383 lbs/lf ÷ 24,000 lb/in2

 = 0.14 in2 /lf

Placing #5 bars (at 0.31 in2/bar) at 24 inches on centers will provide the required reinforcement. To complete the analysis, the reinforcement ratio must be calculated to determine the 

actual “j” factor and the stresses in the reinforcing steel need to be checked to ensure the limits 

dictated in ACI 530 are not exceeded. The wall design also needs to be checked for its ability to 

resist the lateral forces from flood and wind.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 7-02 load combination 6 allows 60 percent of the dead load to be considered in 

resisting uplift. Medium weight 8-inch masonry cores grouted at 24 inches on center weigh 50 

lb/sf or, for a 4-foot tall wall, 200 lbs/lf. Sixty percent of the wall weight (120 lb/lf) reduces the 

amount of uplift the footing must resist to 426 lb/lf. At 90 lb/ft3 (60 percent of 150 lb/ft3 for 

normal weight concrete), the footing would need to have a cross-sectional area of 4.7 square 

feet. Grouting all cores increases the dead load to 68 lb/sf and reduces the required footing 

area to 4.25 square feet. The bearing capacity of the soils will control footing dimensions. Stronger soils can allow narrower footing dimensions to be constructed; weaker soils will require 

wider footing dimensions. 

The design also needs to be checked to confirm that the footings are adequate to prevent sliding under the simultaneous action of wind and flood forces. If marginal friction resistance 

exists, footings can be placed deeper to benefit from passive soil pressures. 

D.4	 Open Foundation Example

For this example, the calculations are based on a two-story home raised 8 feet above grade with 

an integral slab-grade beam, mat-type foundation and a 28-foot by 42-foot footprint. The home 

is sited approximately 800 feet from the shore in a Coastal A Zone with a calculated DFE of 6 

feet above the eroded exterior grade (6 inches below top of slab). The DFE was determined by 

subtracting an estimated grade elevation, shown on advisory topographic map ms-g15, from the 

ABFE elevation indicated on advisory flood map ms-g15. It is important to note, however, that 

submittal of an elevation certificate and construction plans to local building code and floodplain officials in many jurisdictions will require that the elevation be confirmed by a licensed 

surveyor referencing an established benchmark elevation. 

The wood-framed home has a 3:12 roof pitch with a mean roof height of 30 feet, a center wood 

beam supporting the first floor, and a center load bearing wall supporting the second floor. 

Clear span trusses frame the asphalt-shingled roof and are designed to provide a 2-foot overhang. This home is a relatively light structure that contains no brick or stone veneers.

The surrounding site is flat, gently sloping approximately 1 foot in 150 feet. The site and surrounding property have substantial vegetation, hardwood trees, concrete sidewalks, and streets. 

A four-lane highway and a massive concrete seawall run parallel to the beach and the established residential area where the site is located. The beach has been replenished several times in 

the last 50 years. Areas to the west of the site that have not been replenished have experienced 

beach erosion to the face of the seawall. The ASCE 7-02, 3-second gust design wind speed is 140 

mph and the site is in an Exposure Category C. 

The proposed foundation for the home incorporates a monolithic carport slab placed integrally 

with a system of grade beams along all column lines (see Figure D-6). The dimensions of the 
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

21 psf

18 psf

6'

DFE

M+

Lowest Horizontal

Member

Ground Elevation 

(Eroded Ground Elevation)

2'

28'

10'

-36 psf

65 psf

3

12

34 psf

Second Floor

First Floor

Flow of

Wind and Flood

Grade Beams

16” Square

Concrete 

Columns

V = 140 mph

Roof 12 psf DL

20 psf LL

30 psf LL

10 psf DL

Second Floor

Clear Span Trusses

40 psf LL

 8 psf DL

First Floor

10'
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 (8psf + 10 psf)] + [(10 sf/lf + 10 sf/lf) 9 psf]

= 474 lb/lf

Live Loads

Floor

Live loads (Wlive) are calculated in a similar fashion

Wlive = L/4(W1stLL + W2ndLL) 

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

= 490 lb/lf

Roof

Wliveroof = L/2(WrfLL) 

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

= 280 lb/lf

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

Flood Effects

Since the foundation selected is a system of concrete columns, the equations used to calculate 

flood loads are based on open foundation. The stillwater flooding depth (ds) is as follows:

ds = DFE ÷ 1.55 

= 6 ft ÷ 1.55 

= 3.9 ft

Hydrostatic Loads

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

above the concrete slab. 
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 

7-02 Equation C5-2 as follows:

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

= 11.21 feet per second (fps) 

Flood Force

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

Fdyn = 1⁄2 Cd ρ V2 A 

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

= 1,303 lb/column

Floodborne Debris Impact

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

Fi = wV ÷ gt 

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

= 3,478 lb

Breaking Wave Load

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

Fbrkp = 1⁄2 Cdb γ DHb

2 

= 1⁄2 (2.25)(64 lb/ft3)(1.82 ft)(3.04ft*)2

= 1,211 lb

Wind Load on Columns

For a load case combining both wind and flood forces, the column would be almost completely 

submerged; therefore, the wind load on the column shall not be included.

* A wave height of 3.04 ft suggests a V Zone but, in this example, the depth of water is increased by erosion which is not considered in 

mapping A Zones. The deeper water supports a bigger wave, which in this case exceeds the V Zone wave height minimum.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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[((-1,211lb)(3.9ft)) + (2(-1,303lb)(3.9ft/2)) + ((-3,478lb)(3.9ft))] = 35,053 

ft-lb/ft

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

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

Load Combinations

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

ASCE 7-02 Load Combination Vertical (lb) Horizontal (lb)

#1 D + F 1,444 + 14(474) = 8,080 --

#2 D + F + L 1,444 + 14(964) = 14,940 --

#3 D + F + Lr 1,444 + 14(754) = 12,000 --

#4 D + F + 0.75(L) + 0.75(Lr) 8,080 + (.75)[(14)(490+280)] = 

16,165 --

#5 D + F + W + 1.5(Fa) 8,080 +/- 14(1,137) +/- 1,252 = 

25,876; -9,716 windward; leeward 

wind + (1.5)[Fdyn + Fi]

[(14(868)(1/3)] + (1.5) 

[(1,303+3,478)] = 11,222 

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

0.75(Lr) + 1.5(Fa)

8,080 +/- (.75)(14)(1,137) 

+(.75)(14)([(490+280)] +/- 1,252 = 

2,348; 29,982 windward; leeward

(.75) wind + (1.5)[Fdyn + Fi]

[(0.75)(14)(868)(1/3)] + 

(1.5)[(1,303+3,478)] = 10,210

#7 0.6D + W + 1.5(Fa) 0.6 [2,123+14(474)] +/- 14(1,137) 

+/- (1.5)1,252 = -12,541; 23,051 

windward; leeward

wind + (1.5)[Fdyn + Fi]

[(14(868)(1/3)] + (1.5)

[(1,303+3,478)] = 11,222

#8 0.6D [0.6((2,123) + 14(474))] = 5,255 --

Critical loads are in bold. 
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 wind + fdyn+ debris = 51.6 ft-kip + (3,478)(3.9) ÷ 1,000 lb/kip

= 65.1 ft-kip

= 13.6 ft-kip

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

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

 = 63.4 ft-kip 

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

 = 66.9 ft-kip

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

 = 90.6 ft-kip 
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 = (-31,841ft-lb/lf)(14 ft)

= -445,774 ft-lb 

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

= -14,707 ft-lb

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

= -460,481 ft-lb 

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

of the bay.

Dead Load at perimeter columns 

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

= 13,272 lb

Dead Load at an interior column: 

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

= 1,568 lb

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

= 6,368 lb 

Assume that only the grade beams are sufficiently reinforced to resist overturning (neglect 

weight of slab)

Dead Load of the grade beams (area)(depth) (density of concrete)

[(28 ft x3ft) +(3)((11 ft)(3 ft)](4 ft)(150 lb cubic ft) = 109,800 lb 

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

Allowable Dead Load Moment of 60%

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

= 1,100,476 ft-lb 

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

assumed to resist overturning.
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)(-65psf)]

= 117,428 lb

Ignore passive soil pressure 

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

= 54,758 lb 

Since Lwfa = 23,371 lb is less than 60% of Dead Load Sliding Resistance = 54,758, the foundation 

can be assumed to resist sliding.

Soil Bearing Pressure

The simplified approach for this mat foundation assumes that only the grade beams carry loads 

to the soil, the slab between grade beams is not considered to contribute support. It is further assumed that the bearing pressure is uniform in the absence of wind and flood loading. The areas 

of the grade beams along the outboard column lines, in the direction of the flow of wind and 

flood, are considered the “critical areas” of the grade beam. The load combination table below 

indicates the bearing pressures for the ASCE 7- 02 load combinations for the critical grade beam 

area. These load combinations are calculated to ensure that downward forces of the wind and 

flood moment couple do not overstress the soil. The factored dead load moment that resists 

overturning is of a magnitude such that there is no net uplift along critical grade beams. 

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

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

= 58.5 ft2

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

= 35,100 lb

Critical Column Uplift = 12,541 lb (load combination 7)
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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 Typical Bay (for three rows of columns per bay)

ASCE 7-02 Load Combination Combined Loads (lb) Bearing Pressures (psf)

#1 D + F 8,080 8,090 ÷ 58.5 + 650 = 788

#2 D + F + L 14,940 14,950 ÷ 58.5 + 650 = 905

#3 D + F + Lr 12,000 12,000 ÷ 58.5 + 650 = 855

#4 D + F + 0.75(L) + 0.75(Lr) 16,165 16,165 ÷ 58.5 + 650 = 926

#5 D + F + W + 1.5(Fa) 28,104 28,104 ÷ 58.5 + 650 = 1,130

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

0.75(Lr) + 1.5(Fa) 29,982 29,982 ÷ 58.5 + 650 = 1,163

#7 0.6D + W + 1.5(Fa) 23,051 23,051 ÷ 58.5 + 650 = 1,044

#8 0.6D 5,255 5,255 ÷ 58.5 + 650 = 740

Where 

D = Dead Load

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

(See Section D.2 for additional information)

Fa = Flood Load

L = Live Load

Lr = Roof Live Load

W = Wind Load

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

psf bearing pressure.

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

Column Design 

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

Concrete strength = 4,000 psi 
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 lbs = 1.0 kip 

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

Check combined axial and bending strength:

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

 lb)]

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

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

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

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

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

 = 88,6 ft-kip 

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

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

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

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

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

load; therefore, the column is adequate.

Check Shear strength:

Critical Shear = wind + Fdyn + Fi

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

= Vu = 16.0 kips

As the maximum unit tension stress is only 25.0 kips/16 in x16 in = .098 kip/in2 and the maximum axial compression stress is only 60.0 kips/16 in x 16 in = .234 kip/in2, we can conservatively 

treat the column as a flexural member or beam. The allowable shear of the concrete section 

then, per ACI-318-02 11.3.1.1, 11.3.1.3, and 11.5.5.1 with minimum shear reinforcing (tie/stirrup), would be as follows. 

Allowable Shear = Vc = (0.75)(16 in-2.5 in)(16 in )(2)(4,000 psi)1/2 (1/1,000) = 20.5 kips
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST 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) = .21 in2

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

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

Check spacing per ACI -318-02, 7.10.4

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

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

Least horizontal dimension = 16 in 

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

The column design is adequate. 

Grade Beam Design 

The size of the grade beam was configured to provide adequate bearing area, resistance to 

uplift, a reasonable measure of protection from damaging scour, and to provide a factor of redundancy and reserve strength should the foundation be undermined. A grade beam 36-inches 

wide and 48-inches deep was selected.

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

Assume a combined load factor of 2.0 (for flood)

Check Shear strength:

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

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

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

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

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

Check flexural strength: Assume simple span condition

Maximum Factored Moment = Mu = (7.2 kips/ft)(14 ft)2 (1/8) = 176 ft-kip
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)(60000)(44.63)) – (((1.76)(60,000)) ÷ ((0.85)(4,000)(36)(2)))]

= 4,241,634 in lb ÷ 12000 = 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 = (.0018)(48)(36) = 3.1 in2

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

Therefore, the grade beam design is adequate, use (4) #6 reinforcing bar continuous on the top 

and bottom with #4 stirrups at 24-inch spacing.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST E-

E. Cost Estimating

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST E-

COST ESTIMATING E

Breakdown of Foundation Costs

Foundation Type Average Foundation 

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

Open

Case A: Timber Pile

13,536 0 to 5 11

17,554 5 to 10 15

22,720 10 to 15 19

Not Evaluated Above 15

Case B: Steel Pipe Pile with Concrete 

Column and Grade Beam

32,500 0 to 5 27

36,024 5 to 10 30

37,500 10 to 15 31

Not Evaluated Above 15

Case C: Timber Pile with Concrete 

Column and Grade Beam

31,700 0 to 5 26

36,288 5 to 10 30

37,900 10 to 15 32

Not Evaluated Above 15

Case D: Concrete Column and Grade 

Beam

13,500 0 to 5 11

16,860 5 to 10 14

18,500 10 to 15 15

Not Evaluated Above 15

Case G: Concrete Column and Grade 

Beam with Slabs

18,000 0 to 5 15

21,847 5 to 10 18

24,000 10 to 15 20

Not Evaluated Above 15

Closed

Case E: Reinforced Masonry 

- Crawlspace

12,254 0 to 4 10

14,000 4 to 8 12

Case F: Reinforced Masonry - Stem 

Wall 12,458 0 to 4 10

NOTES

1. This rough order of magnitude (ROM) cost estimate is based upon May 2006 figures for concrete, labor, equipment, 

and materials. Variations due to labor/equipment/materials shortages are anticipated and should be taken into account 

when using these costs.

2. Costs presented herein should not be construed to represent actual costs to the homebuilder, but should be utilized as 

an order of magnitude estimate only. 

3. Pile driving mobilization/demobilization can be reduced if several homes are constructed at the same time in the same 

area, thereby realizing an economy of scale. 
E- Building on strong and safe foundations

E COST ESTIMATING 

 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.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST E-

COST ESTIMATING E

Case A: Timber Pile

Unit of 

Measure Material Labor Equip. Subtotal Number of Piles

Length 

of Piles 

Driven

Total lf to 

drive Subtotal 

Site Prep ls 500.00 — — — $500

Minimum job 

charge for Driving ls — — — 5,000.00 — — — $5,000

Number of Piles: 60

Over 30’ to 40’ 

(800 lf per day) lf 3.3 1.7 0.9 5.90 60 30 1,800 $10,620

Bolts and 

Miscellaneous

Per 

Column 15.00 60 $900

Wood Pile 

Connection to 

House

Per Pile 55.00 60 $3,300

Galvanized 

Bracing Rod and 

Turnbuckles

Per Pile 40.00 60 $2,400

Total for Piles $22,720

Number of Piles: 42

Over 30’ to 40’ 

(800 lf per day) lf 3.3 1.7 0.9 5.90 42 30 1260 $7,434

Bolts and 

Miscellaneous

Per 

Column 15.00 42 $630

Wood Pile 

Connection to 

House

Per Pile 55.00 42 $2,310

Galvanized 

Bracing Rod and 

Turnbuckles

Per Pile 40.00 42 $1,680

Total for Piles $17,554

Number of Piles: 28

Over 30’ to 40’ 

(800 lf per day) lf 3.3 1.7 0.9 5.90 28 30 840 $4,956

Bolts and 

Miscellaneous

Per 

Column 15.00 28 $420

Wood Pile 

Connection to 

House

Per Pile 55.00 28 $1,540

Galvanized 

Bracing Rod and 

Turnbuckles

Per Pile 40.00 28 $1,120

Total for Piles $13,536

ls = lump sum lf = linear foot
E- Building on strong and safe foundations

E COST ESTIMATING 

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

Site Prep ls 500.00 — — — $500

Minimum job 

charge for 

Driving

ls — — — 5,000.00 — — — $5,000

Steel Piles Driven

Unit of 

Measure Material Labor Equip. Subtotal Number of Piles

Length of 

Piles

Total lf 

to drive Subtotal 

Steel Piles 

Driven lf 11 3.1 0.9 15.00 28 30 840 $12,600

Bolts and 

Miscellaneous

Per 

Column 25.00 28 $700

Total for Piles $13,300

Concrete Grade Beam

Unit of 

Measure Material Labor Equip. Subtotal Number of cy

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
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST E-

COST ESTIMATING E

Case C: Timber Pile/Concrete Column/Grade Beam 

Unit of 

Measure Material Labor Equip. Subtotal Number of Piles

Length of 

Piles

Total lf 

to Drive

Site Prep ls 500.00 — — —

Minimum job 

charge for 

Driving

ls — — — 5,000.00 — — —

Timber Piles Driven

Number of Wooden Piles: 42

Over 30’ to 40’ 

(800 lf per day) lf 3.3 1.7 0.9 5.90 42 30 1,260

Bolts and 

Miscellaneous

Per 

Column 15.00 42

Total for Piles

Concrete Grade Beam

Unit of 

Measure Material Labor Equip. Subtotal Number of cy

Equipment 

Charge

Soil Excavation, 

Medium 

material, 75 cy 

per hour (57 

m3/hr)

cy -- 0.54 1.29 1.83 55 500

Grade beams cy 225 22 7.5 254.50 32

Steel ea 100.00 32

Total for Grade Beams

Concrete Columns including Pile Caps @ 10 feet

Unit of 

Measure Material Labor Equip. Subtotal

Number 

of cy/

Columns

Number of 

Columns

18” (46 cm) 

square or round 

columns

cy 225 35 7.5 267.50 0.74 12

Steel Column 150.00 12

Anchors Column 49.55 12

Angles Column 42.45

Subtotal for Concrete Columns

Grand Total for Foundation Shown

ls = lump sum lf = linear foot cy = cubic yard ea = each 
E- Building on strong and safe foundations

E COST ESTIMATING 

Case D: Concrete Column/Grade Beam

Unit of 

Measure Material Labor Equip. Subtotal Number of cy

Equipment 

Charge Subtotal 

Soil 

Excavation, 

Medium 

material, 75 cy 

per hour (57 

m3/hr)

cy -- 0.54 1.29 1.83 50 500 $592

Grade beams cy 225 22 7.5 254.50 31 $7,890

Steel ea 100 31 $3,100

Total for Grade Beams $11,582

Concrete Columns @ 10 feet Elevation

Unit of 

Measure Material Labor Equip. Subtotal

Number 

of cy per 

Column

Number of 

Columns Subtotal 

18” (46 cm) 

square or 

round columns

cy 225 35 7.5 267.50 0.74 12 $2,375

Steel Column 150.00 12 $1,800

Anchors Column 49.55 12 $595

Angles Column 42.45 12 $509

Subtotal for Concrete Columns $5,279

Grand Total for Foundation Shown $16,861

cy = cubic yard
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST E-

COST ESTIMATING E

Case G: Concrete Column/Grade Beam with Slab

Unit of 

Measure Material Labor Equip. Subtotal Number of cy

Equipment 

Charge Subtotal 

Soil 

Excavation, 

Medium 

material, 75 cy 

per hour (57 

m3/hr)

cy -- 0.54 1.29 1.83 75 500 $637

Interior 

Concrete cy 225 35 7.50 267.50 15 $4,013

Grade Beams cy 225 35 7.50 267.50 31 $8,293

Steel ea 100.00 31 $3,100

WWF ea 35.00 15 $525

Total for Grade Beams $16,568

Concrete Columns @ 10 feet Elevation

Unit of 

Measure Material Labor Equip. Subtotal

Number 

of cy per 

Column

Number of 

Columns Subtotal 

18” (46 

cm) square 

or round 

columns

cy 225 35 7.50 267.50 0.74 12 $2,375

Steel Column 150 12 $1,800

Anchors Column 49.55 12 $595

Angles Column 42.45 12 $509

Subtotal for Concrete Columns $5,279

Grand Total for Foundation Shown $21,847

cy = cubic yard ea = each 
E-10 Building on strong and safe foundations

E COST ESTIMATING 

Case E: Reinforced Masonry

Crawlspace

Unit of 

Measure Material Labor Equip. Subtotal Number of cy

Equipment 

Charge Subtotal 

Soil Excavation, 

Medium 

material, 75 cy 

per hour (57 

m3/hr)

cy -- 0.68 1.43 2.11 24 500 $551

Footings cy 225 22 7.5 254.50 20 $5,090

Steel cy 100.00 20 $2,000

Total for Footings (not including steel) $5,641

Concrete Columns @ 4 feet

Unit of 

Measure Material Labor Equip. Subtotal

Number 

of cy per 

Column

Number of 

Columns Subtotal 

16” (46 cm) 

square or round 

columns piers

cy 225 35 7.5 267.50 0.40 6 $642

Steel Column 150.00 6 $900

Anchors Column 49.55 6 $297

Angles Column 42.45 6 $255

Subtotal for Concrete Columns $2,094

Concrete Walls

Unit of 

Measure Material Labor Equip. Subtotal Number of sf Subtotal 

Concrete Block 

Walls sf 5.23 4.53 1 10.76 420 $4,519

Grand Total for Foundation Shown (Footings + Concrete Columns + Concrete Walls) $12,254

cy = cubic yard sf = square foot
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST E-11

COST ESTIMATING E

Case F: Reinforced Masonry Stem Wall

Unit of 

Measure Material Labor Equip. Subtotal Number of cy

Equipment 

Charge Subtotal 

Soil 

Excavation, 

Medium 

material, 75 cy 

per hour (57 

m3/hr)

cy -- 0.54 1.29 1.83 34 500 $562

Footings cy 225 22 7.5 254.50 20 $5,090

Steel cy 100.00 20 $2,000

Bracing ls $1,500

Backfill cy 4 0.6 1.45 6.05 130 $787

Total for Stem Wall Footings $9,152

Concrete Walls

Unit of 

Measure Material Labor Equip. Subtotal

Number 

of sf Subtotal 

Concrete 

Block Walls sf 5.23 4.53 1 10.76 420 $4,519

Grand Total for Foundation Shown $13,671

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

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST F-

F.	Referenced Fact Sheets 	 	

	 from FEMA 499

Fact Sheet No.	 Title

1		 Coastal Building Successes and Failures

	 2		 Summary of Coastal Construction Requirements and Recommendations

	 4		 Lowest Floor Elevation

	 5		 V-Zone Design and Construction Certification

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

	 7		 Selecting a Lot and Siting the Building

	 8		 Coastal Building Materials

	 9		 Moisture Barrier Systems

11	 Foundations in Coastal Areas

12	 Pile Installation	
F- Building on strong and safe foundations

F REFERENCED FACT SHEETS FROM FEMA 499

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
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 1

Coastal Building Successes 

and Failures

FS No. 1 – Coastal Building Successes and Failures Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Purpose: To discuss how coastal construction requirements are different from those for inland construction.

To discuss the characteristics that make for a successful coastal building.

Is Coastal Construction That Different From Inland Construction?

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

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

than inland flooding.

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

• Wind speeds are typically higher in coastal areas and require stronger engineered building connections and

more closely spaced nailing of building sheathing, siding, and roof shingles.

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

In general, homes in coastal areas must be

designed and built to withstand higher loads

and more extreme conditions. Homes in

coastal areas will require more maintenance

and upkeep. Because of their exposure to

higher loads and extreme conditions, homes

in coastal areas will cost more to design,

construct, maintain, repair, and insure.

Building Success

In order for a coastal building to be considered

a “success,” four things must occur:

•	The building must be designed to withstand

coastal forces and conditions.

•	The building must be constructed as designed.

•	The building must be sited so that erosion

does not undermine the building or render it

uninhabitable.

•	The building must be maintained/repaired.

A well-built but poorly sited building can be

undermined and will not be a success (see

Figure 1). Even if a building is set back or

situated farther from the coastline, it will not

perform well (i.e., will not be a success) if it

is incapable of resisting high winds and other

hazards that occur at the site (see Figure 2).

Figure 1. Well-built but poorly sited building. 

Figure 2. Well-sited building that still sustained damage.
FS No. 1 – Coastal Building Successes and Failures Home Builder’s Guide to Coastal Construction	 08/05 Page  of 3

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

In coastal areas, a building can be considered a success only if it is capable of resisting damage 

from coastal hazards and coastal processes over a period of decades. This statement does not imply

that a coastal residential building will remain undamaged over its intended lifetime. It means that the

impacts of a design-level flood, storm, wind, or erosion event (or series of lesser events with combined

impacts equivalent to a design event) will be limited to the following:

•	The building foundation must remain intact and functional.

•	The envelope (walls, openings, roof, and lowest floor) must remain structurally sound and capable of

minimizing penetration by wind, rain, and debris.

•	The lowest floor elevation must be sufficient to prevent floodwaters from entering the elevated

building envelope during the design event.

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

easily.

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

•	Any damage to enclosures below the Design Flood Elevation (DFE)* must not result in damage to the

foundation, the utility connections, or the elevated portion of the building.

Siting – Site buildings away from

eroding shorelines and high-hazard

areas.

Building Form – Flat or low-sloped

porch roofs, overhangs, and gable

ends are subject to increased

uplift in high winds.

Buildings that are

both tall and narrow

are subject to

overturning. Each of

these problems can

be overcome through

the design process,

but each must receive

special attention. In

the design process,

chose moderate-sloped

hip roofs (4/12 to

6/12) if possible.

Lowest Floor Elevation – 

Elevate above the DFE the bottom of the lowest horizontal structural member supporting the lowest

floor. Add “freeboard” to reduce damage and lower flood insurance premiums.

Free of Obstructions – Use an open foundation. Do not obstruct the area below the elevated portion

of the building. Avoid or minimize the use of breakaway walls. Do not install utilities or finish enclosed

areas below the DFE (owners tend to convert these areas to habitable uses, which is prohibited under

the National Flood Insurance Program and will lead to additional flood damage and economic loss).

Foundation – Make sure the foundation is deep enough to resist the effects of scour and erosion;

strong enough to resist wave, current, flood, and debris forces; and capable of transferring wind and

seismic forces on upper stories to the ground.

1

2

3

4

5

Recommended Practice

*The DFE is the locally mandated flood elevation, which will be equal to or higher than the Base Flood Elevation (BFE). The BFE is

the expected elevation of flood waters and wave effects during the 100-year flood (also known as the Base Flood).
FS No. 1 – Coastal Building Successes and Failures Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Connections – Key connections include roof sheathing, roof-to-wall, wall-to-wall, and walls-to-foundation. Be

sure these connections are constructed according to the design. Bolts, screws, and ring-shanked nails are

common requirements. Standard connection details and nailing should be identified on the plans.

Exterior Walls – Use structural sheathing in high-wind areas for increased wall strength. Use tighter

nailing schedules for attaching sheathing. Care should be taken not to over-drive pneumatically driven

nails. This can result in loss of shear capacity in shearwalls.

Windows and Glass Doors – In high-wind areas, use windows and doors capable of withstanding

increased wind pressures. In windborne debris areas, use impact-resistant glazing or shutters.

Flashing and Weather Barriers – Use stronger connections and improved flashing for roofs, walls, doors,

and windows and other openings. Properly installed secondary moisture barriers, such as housewrap or

building paper, can reduce water intrusion from wind-driven rain.

Roof – In high-wind areas, select appropriate roof coverings and pay close attention to detailing. Avoid

roof tiles in hurricane-prone areas.

Porch Roofs and Roof Overhangs – Design and tie down porch roofs and roof overhangs to resist uplift

forces.

Building Materials – Use flood-resistant materials below the DFE. All exposed materials should be

moisture- and decay-resistant. Metals should have enhanced corrosion protection.

Mechanical and Utilities – Electrical boxes, HVAC equipment, and other equipment should be elevated

to avoid flood damage and strategically located to avoid wind damage. Utility lines and runs should be

installed to minimize potential flood damage.

Quality Control – Construction inspections and quality control are essential for building success. Even

“minor” construction errors and defects can lead to major damage during high-wind or flood events.

Keep this in mind when inspecting construction or assessing yearly maintenance needs.

Recommended practice and guidance concerning the topics listed above can be found in the documents

referenced in these fact sheets and in many trade publications (e.g., the Journal of Light Construction, http://

www.jlconline.com).

Will the Likelihood of Success (Building 

Performance) Be Improved by Exceeding Minimum 

Requirements?

States and communities enforce regulatory requirements that

determine where and how buildings may be sited, designed,

and constructed. There are often economic benefits to

exceeding the enforced requirements (see box). Designers

and home builders can help owners evaluate their options

and make informed decisions about whether to exceed these

requirements.

*Note: Flood insurance premiums can be reduced up to 60 percent by exceeding minimum siting, design, and construction practices.

See the V-Zone Risk Factor Rating Form in FEMA’s Flood Insurance Manual (http://www.fema.gov/nfip/manual.shtm).

Benefits of Exceeding Minimum 

Requirements

•	Reduced building damage during

coastal storm events

•	Reduced building maintenance

•	Longer building lifetime

•	Reduced insurance premiums*

•	Increased reputation of builder

6

7

8

9

10

12

13

14

11

Summary of Coastal Construction 

Requirements and 

Recommendations

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 2

FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page  of 8

Purpose: To summarize National Flood Insurance Program (NFIP) regulatory requirements concerning coastal

construction and provide recommendations for exceeding those requirements in some instances.

Key Issues

•	New construction* in coastal flood hazard areas (V zones and A zones) must meet minimum NFIP and

community requirements. Repairs, remodeling, and additions must meet community requirements and may

also be subject to NFIP requirements.

•	NFIP design and construction requirements are more stringent in V zones than in A zones, in keeping with

the increased flood, wave, floodborne debris and erosion hazards in V zones.	

•	Some coastal areas mapped as A zones may be subject to damaging waves and erosion (these areas

are often referred to as Coastal A Zones). Buildings in these areas constructed to minimum NFIP Azone requirements may sustain major damage or be destroyed during the Base Flood. It is strongly 

recommended that buildings in A zones subject to breaking waves and erosion be designed and constructed 

to V-zone standards.

•	Buildings constructed to minimum NFIP A-zone standards and subject solely to shallow flooding without the

threat from breaking waves and erosion will generally sustain only minor damage during the Base Flood.

•	Following the recommendations in the table below will result in lower damage to the building and reduced

flood insurance premiums (see the V-Zone Risk Factor Rating Form in FEMA's Flood Insurance Manual

(http://www.fema.gov/nfip/manual.shtm).

* For floodplain management purposes, new construction means structures for which the start of construction began on or after the

effective date of a floodplain management regulation adopted by a community. Substantial improvements, repairs of substantial

damage, and some enclosures must meet most of the same requirements as new construction.

The following tables summarize NFIP regulatory requirements and recommendations for exceeding those

requirements for both (1) new construction and (2) repairs, remodeling, and additions.

Requirements and Recommendations for New Constructiona
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page of 8
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page  of 8
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page  of 8
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page  of 8

Requirements and Recommendations for Repairs, Remodeling, and Additions
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page  of 8
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page  of 8
FS No. 2 – Summary of Requirements and Recommendations	 Home Builder’s Guide to Coastal Construction 08/05 Page of 8

Notes

a	 “Prohibited” and “Allowed” refer to the minimum NFIP regulatory requirements; individual states

and communities may enforce more stringent requirements that supersede those summarized

here. Exceeding minimum NFIP requirements will provide increased flood protection and may 

result in lower flood insurance premiums.

b	 In these areas, buildings are subject to flooding conditions similar to, but less severe than, those

in V zones. These areas can be subject to breaking waves ≥ 1.5 feet high (which can destroy

conventional wood-frame and unreinforced masonry wall construction) and erosion (which can

undermine shallow foundations).

c	 In these areas, buildings are subject to flooding conditions similar to those in riverine A zones.

d	 Some coastal communities require open foundations in A zones.

e	 State or community may require freeboard or regulate to a higher elevation (e.g., Design Flood

Elevation (DFE)).

f	 Some coastal communities prohibit breakaway walls and allow only open lattice or screening.

g	 If an area below the BFE in an A-zone building is fully enclosed by breakaway walls, the walls must

meet the requirement for openings that allow equalization of hydrostatic pressure.

h	 Placement of nonstructural fill adjacent to buildings in coastal AO zones is not recommended.

i	 There are some differences between what is permitted under floodplain management regulations 

and what is covered by NFIP flood insurance. Building designers should be guided by floodplain

management requirements, not by flood insurance policy provisions. For more information, see

Section 9.3.1.1 in Chapter 9 of FEMA’s Coastal Construction Manual (FEMA 55).

j	 Walls below BFE must be designed and constructed as breakaway walls that meet the minimum

requirements of the NFIP regulations. For more information, see Section 6.4.3.3 in Chapter 6 of

FEMA’s Coastal Construction Manual (FEMA 55).

k	 Consult with authority having jurisdiction (AHJ) regarding more restrictive requirements for repairs,

remodeling, and additions.

l NFIP requirements for new construction in V zones include those pertaining to Design and

Construction, Flood-Resistant Materials, Siting, Foundations, Lowest Floor Elevation, Enclosures

Below the BFE, Free of Obstructions, Utilities, and Certifications.

m NFIP requirements for new construction in A zones include those pertaining to Design and

Construction, Flood-Resistant Materials, Siting, Foundations, Foundation Openings, Lowest Floor

Elevation, Enclosures Below the BFE, Utilities, and Certifications.

n 	 An addition in the form of an attached garage would not have to be elevated to or above the BFE,

because its use (parking) would be allowed below the BFE; however, it would have to meet other

NFIP requirements for new construction in V zones.

o 	 An addition in the form of an attached garage would not have to be elevated to or above the BFE,

because its use (parking) would be allowed below the BFE; however, it would have to meet other

NFIP requirements for new construction in A zones.
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 4

Lowest Floor 

Elevation

FS No. 4 – Lowest Floor Elevation Home Builder’s Guide to Coastal Construction	 08/05 Page  of 4

Purpose: To discuss benefits of exceeding the National Flood Insurance Program (NFIP) minimum elevation

requirements, to point out common construction practices that are violations of NFIP regulations and result in

significantly higher flood insurance premiums, and to discuss the NFIP Elevation Certificate.

Why Is the Lowest Floor Elevation Important?

In inland areas, experience has shown that floods damage areas of buildings not elevated above the flood

level and destroy contents of those areas. In coastal areas, wave action causes even more damage, often

destroying enclosed building areas below the flood level (and any building areas above the flood level that 

depend on the lower area for structural support). Once waves rise above the lowest structural member in a V 

zone or coastal A zone, the elevated portion of the building is likely to be severely damaged or destroyed.

Recommended Lowest Floor Elevations*

Because of the additional hazard associated with wave action in V zones and in A zones in coastal areas,

it is recommended that the minimum elevation requirements of the NFIP be exceeded in these areas:

•	It is recommended that the bottom of the lowest horizontal structural member of V-zone buildings be 

elevated 1 foot or more above the Base Flood Elevation (BFE), i.e., add freeboard.

•	It is recommended that the lowest horizontal structural member of A-zone buildings in coastal areas 

be elevated 1 foot or more above the BFE (i.e., add freeboard).

*NFIP minimum elevation requirements: A zone – elevate top of lowest floor to or above BFE; V zone – elevate bottom of

lowest horizontal structural member to or above BFE. In both V and A zones, many people have decided to elevate a full story 

for below-building parking, far exceeding the elevation requirement. See Fact Sheet No. 2 for more information about NFIP

minimum requirements in A and V zones.
FS No. 4 – Lowest Floor Elevation Home Builder’s Guide to Coastal Construction	 08/05 Page  of 4

What Does FEMA Consider the Lowest Floor?

•	The “lowest floor” means the lowest floor of the lowest enclosed area, except for unfinished or floodresistant enclosures used solely for parking of vehicles, building access, or storage.

•	If the lowest enclosed area is used for anything other than parking of vehicles, building access, or storage,

the floor of that area is considered the lowest floor. This will violate NFIP requirements and drastically

increase flood insurance premiums.

•	Note that any below-BFE finished areas, including foyers, will violate NFIP requirements, sustain unreimbursable

flood damage, and increase flood insurance premiums.

•	The floor of a basement (where “basement” means the floor is below grade on all sides) will always be the

lowest floor, regardless of how the space is used.

•	Walls of enclosed areas below the BFE must meet special requirements in coastal areas (see Fact Sheet No. 27).

Construction Practices and the Lowest Floor

Setting the lowest floor at the correct elevation is critical. Failure to do so can result in a building being

constructed below the BFE. As a result, work can be stopped, certificates of occupancy can be withheld, and

correcting the problem can be expensive and time-consuming.

•	After piles have been installed, the intended elevation of the lowest floor should be checked before the piles

are cut off.

•	Alternatively, after piers or columns have been constructed, the intended elevation of the lowest floor should

be checked before the lowest horizontal structural supporting members are installed.

•	After the lowest horizontal structural supporting members have been installed, the elevation should be

checked again, before any further vertical construction is carried out.

Do not modify building plans to create habitable space below the intended lowest floor. Doing so will put the

building in violation of flood regulations and building codes.

FEMA Elevation Certificate

The NFIP requires participating communities to adopt a floodplain management ordinance that specifies

minimum requirements for reducing flood losses. One such requirement is that communities obtain, and 

maintain a record of, the lowest floor elevations for all new and substantially improved buildings.

The Elevation Certificate (see following pages) provides a way for a community to comply with this requirement

and for insurers to determine flood insurance premiums.

Most communities require permit applicants to retain a surveyor, engineer, or architect to complete and

submit the elevation certificate. Note that multiple elevation certificates may need to be submitted for the 

same building: a certificate may be required when the lowest floor level is set (and before additional vertical

construction is carried out); a certificate will be required upon completion of all construction.

The Elevation Certificate requires that the following information be certified and signed by the surveyor/

engineer/architect and signed by the building owner:

•	elevations of certain floors in the building

•	lowest elevation of utility equipment/machinery

•	floor slab elevation for attached garage

•	adjacent grade elevations

•	flood opening information (A zones)

The Elevation Certificate is available on FEMA’s web site: http://www.fema.gov/nfip/elvinst.shtm


HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 5

V-Zone Design 

and Construction 

Certification

FS No. 5 – V-Zone Design and Construction Certification	 Home Builder’s Guide to Coastal Construction	 08/05 Page  of 2

Purpose: To explain the certification requirements for structural design and construction in V zones.

Structural Design and Methods of Construction Certification

As part of the agreement for making flood insurance available in a community, the National Flood Insurance

Program (NFIP) requires the community to adopt a floodplain management ordinance that specifies minimum

design and construction requirements. Those requirements include a certification of the structural design and 

the methods of construction.

Specifically, NFIP regulations and local floodplain

management ordinances require that:

1. a registered professional engineer or 

architect shall develop or review the

structural design, specifications, and 

plans for the construction, and

2. a registered professional engineer or 

architect shall certify that the design and 

methods of construction to be used are

in accordance with accepted standards of

practice for meeting the following criteria:

•	the bottom of the lowest horizontal 

structural member of the lowest floor

(excluding the pilings or columns) is elevated to or above the Base Flood Elevation (BFE); and

•	the pile or column foundation and structure attached thereto is anchored to resist flotation, collapse, 

and lateral movement due to the effects of wind and water loads acting simultaneously on all building

components. Water loading values used shall be those associated with the Base Flood. Wind loading

values used shall be those required by applicable

state or local building standards.

The community, through its inspection procedures, will

verify that the building is built in accordance with the

certified design.

Completing the V-Zone Certification

There is no single V-zone certificate used on a nationwide

basis. Instead, local communities and/or states have

developed their own certification procedures and documents.

Registered engineers and architects involved in V-zone

construction projects should check with the authority 

having jurisdiction regarding the exact nature and 

timing of required certifications.

Page 2 shows a sample certification form developed by

one state. It is intended to show one of many possible

ways by which a jurisdiction may require that the

certification and supporting information be provided. In

this instance, three certifications are included on the

form (Lowest Floor Elevation, Design and Methods of

Construction, Breakaway Wall Collapse).

•	Lowest Floor Elevation, by a surveyor,

engineer, or architect (see Fact Sheet No. 4)

•	Breakaway Wall Collapse, by a registered

professional engineer or architect

(see Fact Sheet No. 27)

The Design and Methods of Construction 

certification should take into consideration 

the NFIP Free-of-Obstruction requirement for 

V zones: the space below the lowest floor must 

be free of obstructions (e.g., free of any building 

element, equipment, or other fixed objects that 

can transfer flood loads to the foundation, or that 

can cause floodwaters or waves to be deflected 

into the building), or must be constructed with 

non-supporting breakaway walls, open lattice, or 

insect screening. (See NFIP Technical Bulletin 

5-93 and Fact Sheet No. 27.)
FS No. 5 – V-Zone Design and Construction Certification	 Home Builder’s Guide to Coastal Construction	 08/05 Page of 2

Note: The V-zone certificate is not a substitute for and cannot be used without the NFIP Elevation

Certificate (see Fact Sheet No. 4), which is required for flood insurance rating.
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 6

How Do Siting and Design 

Decisions Affect

the Owner’s Costs?

FS No. 6 – How Do Siting and Design Decisions Affect the Owner’s Costs? Home Builder’s Guide to Coastal Construction	 08/05 Page  of 2

Purpose: To show the effects of planning, siting, and design decisions on coastal home costs. 

Key Issues

•	When building a coastal home, initial, operating, and long-term costs (i.e., life cycle costs) must be considered.

•	Coastal (especially oceanfront) homes cost more to design, construct, maintain, repair, and insure than inland homes.

•	Determining the risks associated with a particular building site or design is important.

•	Siting, designing, and constructing to minimum regulatory requirements do not necessarily result in the

lowest cost to the owner over a long period of time. Exceeding minimum design requirements costs slightly

more initially, but can save the owner money in the long run.

Costs

A variety of costs should be considered when planning a coastal home, not just the construction cost. Owners

should be aware of each of the following, and consider how siting and design decisions will affect these costs:

Initial costs include property evaluation and acquisition costs and the costs of permitting, design, and construction.

Operating costs include costs associated with the use of the building, such as the costs of utilities and insurance*.

Long-term costs include costs for preventive maintenance and for repair and replacement of deteriorated or

damaged building components.

*Note: Flood insurance premiums can be reduced up to 60 percent by exceeding minimum siting, design, and

construction practices. See the V-Zone Risk Factor Rating Form in FEMA’s Flood Insurance Manual (http://

www.fema.gov/nfip/manual.shtm).

Risk

One of the most important

building costs to be

considered is that resulting

from storm and/or erosion

damage. But how can an

owner decide what level

of risk is associated with

a particular building site

or design? One way is to

consider the probability of a storm or erosion occurring and the potential building damage that results (see matrix).
FS No. 6 – How Do Siting and Design Decisions Affect the Owner’s Costs? Home Builder’s Guide to Coastal Construction	 08/05 Page of 2

Building sites or designs resulting in extreme or high risk should be avoided — the likelihood of building loss

is great, and the long-term costs to the owner will be very high. Building sites or designs resulting in medium

or low risk should be given preference.

Siting

Note that over a long period, poor siting decisions are rarely overcome by building design.

Design

•	How much more expensive is it to build near the coast as opposed to inland areas? The table below

suggests approximately 10 - 30 percent more.

•	What about exceeding minimum design requirements in coastal areas? The table suggests that the added

construction costs for meeting

the practices recommended in the

Home Builder’s Guide to Coastal 

Construction (beyond typical

minimum requirements) are nominal.
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 7

Selecting a Lot and Siting 

the Building

FS No. 7 – Selecting a Lot and Siting the Building Home Builder’s Guide to Coastal Construction	 08/05 Page  of 2

Purpose: To provide guidance on lot selection and siting considerations for coastal residential buildings.

Key Issues

•	Purchase and siting decisions

should be long-term decisions,

not based on present-day

shoreline and conditions.

•	Parcel characteristics,

infrastructure, regulations,

environmental factors, and owner

desires constrain siting options.

•	Conformance with local/state

shoreline setback lines does not

mean buildings will be “safe.”

•	Information about site conditions

and history is available from

several sources.

The Importance of Property 

Purchase and Siting 

Decisions

The single most common and 

costly siting mistake made by 

designers, builders, and owners is 

failing to consider future erosion 

and slope stability when an

existing coastal home is purchased or when land is purchased and a new home is built. Purchase decisions—

or siting, design, and construction decisions — based on present-day shoreline conditions often lead to future

building failures.

Over a long period of time, owners of poorly sited coastal buildings may spend more money on erosion control

and erosion-related building repairs than they spent on the building itself.

What Factors Constrain Siting Decisions?

Many factors affect and limit a home builder’s or owner’s ability to site coastal residential buildings, but the

most influential is probably parcel size, followed by topography, location of roads and other infrastructure,

regulatory constraints, and environmental constraints. 

Given the cost of coastal property, parcel sizes are often small and owners often build the largest building

that will fit within the permissible development footprint. Buyers frequently fail to recognize that siting

decisions in these cases have effectively been made at the time the land was platted or subdivided, and that

shoreline erosion can render these parcels unsuitable for long-term occupation.

In some instances, however, parcel size may be large enough to allow a hazard-resistant coastal building to

be sited and constructed, but an owner’s desire to push the building as close to the shoreline as possible

increases the likelihood that the building will be damaged or destroyed in the future.

Siting, design, and construction should be considered together

(see Fact Sheet No. 6), but know that poor lot selection and

siting decisions can rarely be overcome by improved design and

construction. Building failures (see Fact Sheet No. 1) are often the

result of poor siting.
FS No. 7 – Selecting a Lot and Siting the Building Home Builder’s Guide to Coastal Construction	 08/05 Page of 2

Coastal Setback Lines – What Protection Do They Provide?

Many states require new buildings to be sited at or landward of coastal construction setback lines, which are

usually based on long-term, average annual erosion rates. For example, a typical minimum 50-year setback

line with an erosion rate of 2.5 feet/year would

require a setback of 125 feet, typically measured

from a reference feature such as the dune crest,

vegetation line, or high-water line.

Building at the 125-foot setback (in this case) does

not mean that a building will be “safe” from erosion

for 50 years. 

•	Storms can cause short-term erosion that far

exceeds setbacks based on long-term averages. 

•	Erosion rates vary over time, and erosion could

surpass the setback distance in just a few years’

time. The rate variability must also be known to

determine the probability of undermining over a

given time period.

What Should Builders, Designers, and 

Owners Do?

•	Consult local and state agencies, universities, and

consultants for detailed, site-specific erosion and

hazard information.

•	Look for historical information on erosion and

storm effects. How have older buildings in the area

fared over time? Use the experience of others to

guide siting decisions.

•	Determine the owner’s risk tolerance, and reject

parcels or building siting decisions that exceed

the acceptable level of risk.

Common Siting Problems

•	Building on a small lot between a road and an 

eroding shoreline is a recipe for trouble.

• Odd-shaped lots that force buildings close to

the shoreline increase the vulnerability of the

buildings.

•	Siting a building near the edge of a bluff 

increases the likelihood of building loss,

because of both bluff erosion and changes

in bluff stability resulting from development

activities (e.g., clearing vegetation, building

construction, landscaping, changes in surface

drainage and groundwater flow patterns).

•	Siting near a tidal inlet with a dynamic

shoreline can result in the building being

exposed to increasing flood and erosion

hazards over time.

•	Siting a building immediately behind an 

erosion control structure may lead to building

damage from wave overtopping and may limit

the owner’s ability to repair or maintain the

erosion control structure.

•	Siting a new building within the footprint of a

pre-existing building does not guarantee that

the location is a good one.

Siting should consider both long-term erosion and storm impacts.

Siting should consider site-specific experience, wherever available.

Recommended building location on a coastal lot.
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 8

Coastal Building 

Materials

FS No. 8 – Coastal Building Materials Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

Purpose: To provide guidance on the selection of building materials used for coastal construction.

Key Issues

•	The durability of a coastal home relies on the types of materials used to construct it. For more details,

see the U.S. Department of Housing and Urban Development (HUD) report Durability by Design, A Guide for 

Residential Builders and Designers, available on the HUD User website at

http://www.huduser.org/publications/destech/durdesign.html.

•	Materials and construction methods should be resistant to flood and wind damage, driving rain, corrosion, 

moisture, and decay.

•	All coastal buildings will require maintenance and repairs (more so than inland construction) — use proper

materials and methods for repairs, additions, and other work following initial construction (see Fact Sheet No. 30).

Flood-Resistant Materials

Flooding accounts for a large percentage of the damage caused by a coastal storm. Building materials

exposed to flooding must be resilient enough to sustain a certain amount of water exposure in order to avoid

the need for complete replacement after the flood.

FEMA defines a flood-resistant

material as any building 

material capable of withstanding 

direct and prolonged contact 

(i.e., at least 72 hours) with 

floodwaters without sustaining 

significant damage (i.e., requires 

more than cosmetic repair).

The following are examples of

flood-resistant materials:

• Lumber: pressure-treated

or naturally decay-resistant,

including redwood, cedar,

some oaks, and bald cypress

• Concrete: a sound, durable

mix, and when exposed

to saltwater or salt spray,

made with a sulfate-resisting

cement, with a 28-day

compressive strength of Select building materials that can endure periodic flooding.

Section 60.3(a)(ii) of the National Flood Insurance Program (NFIP) regulations requires that all new construction and

substantial improvements in floodprone areas be constructed with materials below the Base Flood Elevation (BFE)

that are resistant to flood damage. (See Fact Sheet No. 30 for a definition of “substantial improvement.”)
FS No. 8 – Coastal Building Materials Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

5,000 psi minimum and a water-cement ratio not higher than 0.40 – consult ACI 318-02, Building Code 

Requirements for Structural Concrete and Commentary, by the American Concrete Institute International

• Masonry: reinforced and fully grouted

• Structural Steel: coated to resist corrosion

• Insulation: plastics, synthetics, and closed-cell foam, or other types approved by local building officials

This table lists examples of flood-resistant materials used in coastal homes.
FS No. 8 – Coastal Building Materials Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

Many coastal jurisdictions make available a list of approved materials that can be used in coastal environments.

Check for locally approved flood-resistant materials. Include all proposed construction and materials in approved

plans. For guidance on testing specific materials, refer to NES Evaluation Protocol for Determination of FloodResistant Properties of Building Elements (NES, Inc. – http://www.nateval.org).

Wind-Resistant Materials

Homes in many coastal areas are often exposed to

winds in excess of 90 mph (3-second peak gust).

Choose building materials (e.g., roof shingles, siding,

windows, doors, fasteners, and framing members) that

are designed for use in high-wind areas.

Examples:

•	shingles rated for high winds (see Fact Sheet No. 20)

•	double-hemmed vinyl siding (see Fact Sheet No. 25)

•	deformed-shank nails for sheathing attachments

(see Fact Sheet No. 18)

•	wind-resistant glazing (see Fact Sheet No. 22)

•	reinforced garage doors

•	tie-down connectors used throughout structure (from roof

framing to foundation — see Fact Sheet Nos. 10 and 17)

•	wider framing members (2x6 instead of 2x4)

Corrosion and Decay Resistance

Coastal environments are conducive to metal corrosion

and moisture- and termite-related decay of other

building materials. Metal corrosion is most pronounced

on coastal homes (within 3,000 feet of the ocean),

but moisture- and termite-related decay are prevalent

throughout coastal areas.

Corrosion-Resistant Metals

Most jurisdictions require metal building hardware to

be hot-dipped galvanized or stainless steel. Some local

codes require protective coatings that are thicker than

“off-the-shelf” products typically have. For example,

a G90 zinc coating (0.75 mil on each face) may be

required, which is thicker than the common G60 (0.5

mil on each face) coating.

Recommendations

•	Use hot-dipped galvanized or stainless steel hardware.

Reinforcing steel should be protected from corrosion

by sound materials (masonry, mortar, grout, concrete)

and good workmanship (see Fact Sheet No. 16). Use

Select building materials that are suitable for the 

expected wind forces.

The term "corrosion-resistant" is widely used

but, by itself, is of little help to those specifying

or evaluating materials for use in a coastal

home. Every material resists corrosion to some

extent, or conversely, every material corrodes.

The real issue is how long will a given material 

serve its intended purpose at a given home?

The answer depends on the following:

•	the material

•	where it is used in the home

•	whether installation techniques (e.g., drilling,

cutting, bending) will compromise its resistance

•	its degree of exposure to salt air, moisture,

and corrosive agents

•	whether maintenance required of the

homeowner is performed

The bottom line: do not blindly specify or 

accept a product just because it is labeled 

corrosion-resistant. Evaluate the nature of

the material, its coating type and thickness

(if applicable), and its performance in similar

environments before determining whether it is

suitable for a particular application.

For guidance on the selection of metal hardware for use in coastal environments, consult

an engineer with experience in corrosion protection. For more information about corrosion

in coastal environments, see FEMA Technical

Bulletin 8-96, Corrosion Protection for Metal 

Connectors in Coastal Areas for Structures 

Located in Special Flood Hazard Areas (see the

Additional Resources section of this fact sheet).

Remember: A wind-resistant material is

only as good as its connection. Always use

recommended fasteners and connection

methods.
FS No. 8 – Coastal Building Materials Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

galvanized or epoxy-coated reinforcing steel in situations where the potential for corrosion is high (see Fact

Sheet No. 14).

•	Avoid joining dissimilar metals, especially those with

high galvanic potential (e.g., copper and steel).

•	Some wood preservatives should not be used in

direct contact with galvanized metal. Verify that wood

treatment is suitable for use with galvanized metal, or

use stainless steel.

•	Metal-plate-connected trusses should not be exposed

to the elements. Truss joints near vent openings

are more susceptible to corrosion and may require

increased corrosion protection.

Moisture Resistance

Materials resistant to moisture can greatly reduce

maintenance and extend the life of a coastal home

(however, by themselves, such materials cannot

prevent all moisture damage. Proper design and

installation of moisture barriers (see Fact Sheet No. 9)

is also required).

Recommendations

•	Control wood decay by separating wood from moisture,

using preservative-treated wood, using naturally decayresistant wood, and applying protective wood finishes.

•	Use proper detailing of wood joints and construction

to eliminate standing water and reduce moisture

absorption by the wood (e.g., avoid exposure of end

grain cuts, which absorb moisture up to 30 times

faster than the sides of a wood member).

•	Do not use untreated wood in ground contact or highmoisture situations. Do not use untreated wood in

direct contact with concrete.

•	Field-treat any cuts or drill holes that offer paths for

moisture to enter wood members.

•	For structural uses, employ concrete that is sound,

dense, and durable; control cracks with welded wire

fabric and/or reinforcing, as appropriate.

•	Use masonry, mortar, and grout that conform with the

latest building codes.

Termite Resistance

Termite damage to wood construction occurs in many

coastal areas (attack is most frequent and severe along

the southeastern Atlantic and Gulf of Mexico shorelines,

in California, and in Hawaii and other tropical areas).

Termites can be controlled by soil treatment, termite

shields, and the use of termite-resistant materials.

Wood decay at the base of a wood 

post supported by concrete.

Metals corrode at a much faster rate near the ocean. 

Always use well-protected hardware, such as this 

connector with thick galvanizing. (For information about 

pile-to-beam connections, see Fact Sheet No. 13).
FS No. 8 – Coastal Building Materials Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Recommendations

•	Incorporate termite control methods into design in conformance with requirements of the authority having

jurisdiction.

•	Where a masonry foundation is used and anchorage to the foundation is required for uplift resistance, the

upper block cores must usually be completely filled with grout, which may eliminate the requirement for

termite shields (see Fact Sheet No. 14).

•	Use preservative-treated wood for foundations, sills, above-foundation elements, and floor framing.

Additional Resources

FEMA. NFIP Technical Bulletin 2-93, Flood-Resistant Materials Requirements for Buildings Located in Special 

Flood Hazard Areas. (http://www.fema.gov/fima/techbul.shtm)

FEMA. NFIP Technical Bulletin 8-96, Corrosion Protection for Metal Connectors in Coastal Areas for Structures 

Located in Special Flood Hazard Areas. (http://www.fema.gov/fima/techbul.shtm)

American Concrete Institute International. (http://www.aci-int.org/general/home.asp)

American Wood-Preservers’ Association. (http://www.awpa.com)

International Code Council Evaluation Service, Inc. Protocol for Testing the Flood Resistance of Materials.

(http://www.icc-es.org/index.shtml)

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 9

Moisture Barrier

Systems

FS No. 9 – Moisture Barrier Systems Home Builder’s Guide to Coastal Construction	 08/05 Page  of 2

Purpose: To describe the moisture barrier system, explain how typical wall moisture barriers work, and identify

common problems associated with moisture barrier systems.

Key Issues

•	A successful moisture barrier system will

limit water infiltration into unwanted areas

and allow drainage and drying of wetted

building materials.

•	Most moisture barrier systems for

walls (e.g., siding and brick veneer) are

“redundant” systems, which require at

least two drainage planes (see page 2).

•	Housewrap or building paper (asphaltsaturated felt) will provide an adequate secondary drainage plane.

•	Proper flashing and lapping of housewrap and building paper are critical to a successful moisture barrier system.

•	Sealant should never be substituted for proper layering.

The purpose of the building envelope is to control the movement of water, air, thermal energy, and water vapor.

The goal is to prevent water infiltration into the interior, limit long-term wetting of the building components, and

control air and vapor movement through the envelope.

Locations and Causes of Common Water Intrusion Problems
FS No. 9 – Moisture Barrier Systems Home Builder’s Guide to Coastal Construction	 08/05 Page of 2

The location of water entry is often difficult to see, and the damage to substrate and structural members

behind the exterior wall cladding frequently cannot be detected by visual inspection.

Proper Lapping Is the Key...

Proper lapping of moisture barrier materials is the key to preventing water intrusion. Most water intrusion

problems are related to the improper lapping of materials. Usually, flashing details around doors, windows,

and penetrations are to blame. If the flashing details are right and the housewrap or building paper is properly

installed, most moisture problems will be prevented. Capillary suction is a strong force and will move water in

any direction. Even under conditions of light or no wind pressure, water can be wicked through seams, cracks,

and joints upward behind the overlaps of horizontal siding. Proper lap distances and sealant help prevent

water intrusion caused by wicking action.

How a Redundant Moisture Barrier Works
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 11

Foundations in 

Coastal Areas

FS No. 11 – Foundations in Coastal Areas Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Purpose: To describe foundation types suitable for coastal environments.

Key Issues

•	Foundations in coastal areas must elevate buildings

above the Base Flood Elevation (BFE), while

withstanding flood forces, high winds, scour and

erosion, and floating debris.

•	Foundations used for inland construction are generally

not suitable for coastal construction.

•	Deeply embedded pile or column foundations are

required for many coastal areas; in other coastal

areas, they are recommended – instead of solid

wall, crawlspace, slab, or other shallow foundations

that can be undermined easily. ("Deeply embedded"

means sufficient penetration into the ground to

accommodate storm-induced scour and erosion and

to resist all design vertical and lateral loads without

structural damage.)

•	Areas below elevated buildings in V zones must be

“free of obstructions” that can transfer flood loads to the foundation and building (see Fact Sheet No. 27).

Foundation Design Criteria

All foundations for buildings in flood hazard areas must be constructed with flood-damage-resistant materials

(see Fact Sheet No. 8) and must do two things in addition to meeting the requirements for conventional

construction: (1) elevate the building above the BFE, and (2) prevent flotation, collapse, and lateral movement of

the building, resulting from loads and conditions during the design flood event (in coastal areas, these loads and

conditions include inundation by fast-moving water, breaking waves, floating debris, erosion, and high winds).

Because the most hazardous coastal areas are subject to erosion and extreme flood loads, the only practical 

way to perform these two functions is to elevate a building on a deeply embedded and “open” (i.e., pile or 

column) foundation. This approach resists storm-induced erosion and scour, and it minimizes the foundation

surface area subject to lateral flood loads – it is required by the National Flood Insurance Program (NFIP) in V

zones (even when the ground elevation lies above the BFE) and is recommended for coastal A zones. However,

even a deeply embedded open pile foundation will not prevent eventual undermining and loss due to long-term

erosion (see Fact Sheet No. 7).

Performance of Various Foundation Types in Coastal Areas

There are many ways to elevate buildings above the BFE: fill, slab-on-grade, crawlspace, stemwall, solid wall, pier

(column), and pile. Not all of these are suitable for coastal areas. In fact, several of them are prohibited in V zones

and are not recommended by the Home Builder’s Guide to Coastal Construction for A zones in coastal areas.

Fill – Because fill is susceptible to erosion, it is prohibited as a means of providing structural support to 

buildings in V zones and must not be used as a means of elevating buildings in any other coastal area subject to 

erosion, waves, or fast-moving water.

Storm surge and waves overtopping a barrier island 

during Hurricane Frederic.
FS No. 11 – Foundations in Coastal Areas Home Builder’s Guide to Coastal Construction	 08/05 Page  of 3

Slab-on-Grade – Slab-on-grade

foundations are also susceptible

to erosion and are therefore

prohibited in V zones. They

also are not recommended

for A zones in coastal areas.

(Note that parking slabs are

often permitted below elevated

buildings, but are themselves

susceptible to undermining and

collapse.)

Crawlspace – Crawlspace

foundations are prohibited in V 

zones and are not recommended 

for A zones in coastal areas.

They are susceptible to

erosion when the footing

depth is inadequate to prevent

undermining. Crawlspace walls

are also vulnerable to wave

attack. Where used, crawlspace

foundations must be equipped

with flood openings; grade elevations should be such

that water is not trapped in the crawlspace (see Fact

Sheet Nos. 15 and 27).

Stemwall – Stemwall foundations are similar to

crawlspace foundations in construction, but the interior

space that would otherwise form the crawlspace is

often backfilled with gravel that supports a floor slab.

Stemwall foundations have been observed to perform

better during storms than many crawlspace and pier

foundations. However, the building code may limit

stemwall height to just a few feet. Flood openings

are not required in a backfilled stemwall foundation.

Stemwall foundations are prohibited in V zones but

are recommended in A zones subject to limited wave 

action, as long as embedment of the wall is sufficient

to resist erosion and scour.

Solid Foundation Walls – Solid foundation walls are prohibited by the NFIP in V zones and are not

recommended for A zones subject to breaking waves or other large flood forces – the walls act as an

obstruction to flood flow. Like crawlspace walls, they are susceptible to erosion when the footing depth is

inadequate to prevent undermining. Solid walls have been used in some regions to elevate buildings one story

in height. Where used, the walls must allow floodwaters

to pass between or through the walls (using flood

openings). See Fact Sheet Nos. 15 and 27.

Pier (column) – Pier foundations are recommended for 

A zones where erosion potential and flood forces are 

small. This open foundation is commonly constructed

with reinforced and grouted masonry units atop a

concrete footing. Shallow pier foundations are extremely

vulnerable to erosion and overturning if the footing

depth and size are inadequate. They are also vulnerable

to breakage if materials and workmanship are not first

rate. Fact Sheet No. 14 provides guidance on how to

determine whether pier foundations are appropriate, and

how to design and construct them.

Building failure caused by undermining of slab-on-grade foundation during

Hurricane Fran.

Failure of crawlspace foundation undermined by scour.

Pier (column) failures: footings undermined and columns 

separated from footings.
FS No. 11 – Foundations in Coastal Areas Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Pile – Pile foundations are recommended for V zones 

and many A zones in coastal areas. These open

foundations are constructed with square or round,

wood, concrete, or steel piles, driven or jetted into the

ground, or set into augered holes. Critical aspects of a

pile foundation include the pile size, installation method

and embedment depth, bracing, and the connections

to the elevated structure (see Fact Sheet Nos. 12 and

13). Pile foundations with inadequate embedment will

lead to building collapse. Inadequately sized piles are

vulnerable to breakage by waves and debris.

Foundations for High-Elevation Coastal Areas

Foundation design is problematic in bluff areas that

are vulnerable to coastal erosion but outside mapped

flood hazard areas. Although NFIP requirements may not

apply, the threat of undermining is not diminished.

Moreover, both shallow and deep foundations will fail

in such situations. Long-term solutions to the problem

may involve better siting (see Fact Sheet No. 7), moving

the building when it is threatened, or (where permitted

and economically feasible) controlling erosion through

slope stabilization and structural protection.

Foundations in V Zones With Ground 

Elevations Above the BFE

In some instances, coastal areas will be mapped on

an NFIP Flood Insurance Rate Map (FIRM) as V zones,

but will have dunes or bluffs with ground elevations

above the BFE shown on the FIRM. Deeply embedded 

pile or column foundations are still required in these 

areas, and solid or shallow foundations are still 

prohibited. The presence of a V-zone designation in

these instances indicates that the dune or bluff is

expected to erode during the base flood event and that

V-zone wave conditions are expected after the erosion

occurs. The presence of ground elevations above the

BFE in a V zone should not be taken to mean that the

area is free from Base Flood and erosion effects.

Pile failures led to collapse of floor of elevated building.

Insufficient pile embedment and failure of connections at tops 

of piles allowed elevated building to be floated 

off its foundation.

House undermined by bluff erosion. Photograph by Lesley 

Ewing. Courtesy of California Coastal Commission.

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 12

Pile

Installation

FS No. 12 – Pile Installation Home Builder’s Guide to Coastal Construction	 08/05 Page 1 of 3

Purpose: To provide basic information about pile design and installation.

Key Issues

•	Use a pile type that is appropriate for local

conditions.

•	Have piles designed by a foundation engineer for

adequate layout, size, and length.

•	Use installation methods that are appropriate for the

conditions.

•	Brace piles properly during construction.

•	Make accurate field cuts, and treat all cuts and

drilled holes to prevent decay.

•	Have all pile-to-beam connections engineered, and use

corrosion-resistant hardware. (See Fact Sheet No. 8.)

Pile Types

Treated wood piles are the most common type of pile

used in coastal construction. They can be square

or round in cross section. Wood piles are easily cut

and adjusted in the field and are typically the most

economical type. Concrete and steel can also be used

but are less common. Concrete piles are

more expensive, but they are stronger and

more durable. Steel piles are rarely used,

because of potential corrosion problems.

Pile Size and Length

Pile size and length are determined by the

foundation engineer. Specified bearing and

penetration requirements must be met.

Piles should have no less than an 8-inch tip

diameter; minimum timber size should be

8x8. The total length of the pile is based on

code requirements, calculated penetration

requirements, erosion potential, Design

Flood Elevation (DFE), and allowance for

cut-off and beam width (see figure at right).

Note: Misaligned piles lead to

connection problems. See Fact Sheet

No. 13 for information about making

connections to misaligned piles.
FS No. 12 – Pile Installation Home Builder’s Guide to Coastal Construction	 08/05 Page 2 of 3

Pile Layout

The pile layout is determined by the foundation engineer. Accurate placement and correction of misaligned piles is

important. Pile placement should not result in more than 50 percent of the pile cross-section being cut for girder

or other connections. Verify proper pile locations on drawings before construction and clarify any discrepancies.

Layout can be done by a licensed design professional, a construction surveyor, the foundation contractor, or the

builder. The layout process must always include establishing an elevation for the finished first floor. Construction

of the first-floor platform should not begin until this elevation is established (see Fact Sheet No. 4).

Installation Methods

Piles can be driven, augured, or jetted into place. The

installation method will vary with soil conditions, bearing

requirements, equipment available, and local practice.

One common method is to initially jet the pile to a few

feet short of required penetration, then complete the

installation by driving with a drop hammer.

Pile Bracing

Pile bracing is determined by the foundation engineer.

Common bracing methods include knee and diagonal

bracing. Bracing is often oriented perpendicular to the

shoreline so that it is not struck broadside by waves,

debris, and velocity flow (see figure at right). Temporary

bracing or jacking to align piles and hold true during

construction is the responsibility of the contractor.

To avoid costly pile repairs or replacement,

measure, locate, and double-check the required

pile cutoff elevations before cutting off piles.

Field Cutting and Drilling

A chain saw is the common tool of choice for making cuts and notches in wood piles. After making cuts,

exposed areas should be field-treated to prevent decay.
FS No. 12 – Pile Installation Home Builder’s Guide to Coastal Construction	 08/05 Page 3 of 3

Connections

The connection of the pile to the structural members is one of the most critical connections in the structure.

Always follow design specifications and use corrosion-resistant hardware (see Fact Sheet Nos. 8 and 13).

Verification of Pile Capacity

Generally, pile capacity for residential construction is not verified in the field. If a specified minimum pile

penetration is provided, bearing is assumed to be acceptable for the local soil conditions. Subsurface soil

conditions can vary from the typical assumed conditions, so verification of pile capacity may be prudent,

particularly for expensive coastal homes. Various methods are available for predicting pile capacity. Consult a

foundation engineer for the most appropriate method for the site.

Additional Resources

American Forest and Paper Association (AF&PA). National Design Specification for Wood Construction. (www.

afandpa.org)

American Society for Standards and Testing (ASTM). Standard Specification for Round Timber Piles, ASTM

D25. (www.astm.org)

American Wood-Preservers Association (AWPA). All Timber Products – Preservative Treatment by Pressure 

Processes, AWPA C1-00; Lumber, Timber, Bridge Ties and Mine Ties – Preservative Treatment by Pressure 

Processes, AWPA C2-01; Piles – Preservative Treatment by Pressure Process, AWPA C3-99; and others. (www.

awpa.com)

Pile Buck, Inc. Coastal Construction. (www.pilebuck.com)

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 13

Wood-Pile-to-Beam 

Connections

FS No. 13 – Wood-Pile-to-Beam Connections Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Purpose: To illustrate typical wood-pile-to-beam connections, provide basic construction guidelines on various

connection methods, and show pile bracing connection techniques.

NOTE: The pile-to-beam connection is one of the most critical links in the structure. This connection must 

be designed by an engineer. See Fact Sheet No. 10 for “load path” information. The number of bolts and

typical bolt placement dimensions shown are for illustrative purposes only. Connection designs are not

limited to those shown here, and not all of the information to be considered in the designs is included in

these illustrations. Final designs are the responsibility of the engineer. 

Key Issues

•	Verify pile alignment and correct, if

necessary, before making connections.

•	Carefully cut piles to ensure required

scarf depths.

•	Limit cuts to no more than 50 percent

of pile cross-section.

•	Use corrosion-resistant hardware, such

as hot-dipped galvanized or stainless

steel (see Fact Sheet No. 8).

•	Accurately locate and drill bolt holes.

•	Field-treat all

cuts and holes to

prevent decay.

•	Use sufficient pile

and beam sizes to

allow proper bolt

edge distances.

Pile-to-beam connections must:

1.	provide required bearing area for beam to rest on pile

2.	provide required uplift (tension) resistance

3.	maintain beam in an upright position

4.	be capable of resisting lateral loads (wind and seismic)

5.	be constructed with durable connectors and fasteners

Note: Pile-to-beam

connections must be

designed by an engineer.
FS No. 13 – Wood-Pile-to-Beam Connections Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

Problem: Misaligned piles – some piles are shifted in or out from their intended (design) locations.

Possible Solutions (see drawings on page 3 and details on page 4):

Option 1 (see page 3) – beam cannot be shifted

Option 2 (see page 3) – beam can be shifted laterally and remains square to building

Option 3 (see page 3) – beam can be shifted laterally, but does not remain square to building

Option 4 (not shown) – beam cannot be shifted, and connections shown in this fact sheet cannot be

made; install and connect sister piles; an engineer must be consulted for this option

Option 5 (not shown) – beam cannot be shifted, and connections shown in this fact sheet cannot be

made; remove and reinstall piles, as necessary

Note: Pile-to-beam

connections must

be designed by an

engineer.
FS No. 13 – Wood-Pile-to-Beam Connections Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Note: Pile-to-beam connections must be designed by an engineer.
FS No. 13 – Wood-Pile-to-Beam Connections Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Connections to misaligned piles (see drawings on page 3 and details below)

1. The ability to construct the pile-to-beam connections designed by the engineer is directly dependent

on the accuracy of pile installation and alignment.

2. Misaligned piles will require the contractor to modify pile-to-beam connections in the field.

3. Badly misaligned piles will require removal and reinstallation, sister piles, or special connections, all

to be determined by the engineer.

Note: Pile-to-beam

connections must

be designed by an

engineer.
FS No. 13 – Wood-Pile-to-Beam Connections Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Note: Pile-to-beam

connections must be

designed by an engineer.

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 14

Reinforced Masonry Pier

Construction 

FS No. 14 – Reinforced Masonry Pier Construction Home Builder’s Guide to Coastal Construction	 08/05 Page 1 of 2

Purpose: To provide an alternative to piles in V zones and A zones in coastal areas where soil properties

preclude pile installation, yet the need for an “open foundation system” still exists. Examples of appropriate

conditions for the use of piers are where rock is at or near the surface or where the potential for erosion and

scour is low.

Key Issues

•	The footing must be designed for the soil conditions present. Pier foundations are generally not

recommended in V zones or in A zones in coastal areas.

•	The connection between the pier and its footing must be properly designed and constructed to resist

separation of the pier from the footing and rotation to due to lateral (flood, wind, debris) forces.

•	The top of the footing must be below the anticipated erosion and scour depth.

•	The piers must be reinforced with steel and fully grouted.

•	There must be a positive connection to the floor beam at the top of the pier.

•	Special attention must be given to the application of mortar in order to prevent saltwater intrusion into the

core, where the steel can be corroded.

Piers vs. Piles

Piers are subject to upward, downward, and horizontal loads. 

Pier reinforcement and footing size are critical to resisting 

these loads; therefore, pier and footing design must be 

verified by an engineer. 

In coastal areas, masonry pier foundations are not recommended in V zones with erodible soils, or in A zones 

subject to waves and erosion — use pile foundations in these areas.
FS No. 14 – Reinforced Masonry Pier Construction Home Builder’s Guide to Coastal Construction	 08/05 Page 2 of 2

Pier foundations are most

appropriate in areas where:

•	erosion and scour potential

are low,

•	flood depths and lateral

forces are low, and

•	soil can help resist

overturning of pier.

The combination of high winds

and moist (sometimes saltladen) air can have a damaging

effect on masonry construction

by forcing moisture into

even the smallest of cracks

or openings in the masonry

joints. The entry of moisture

into reinforced masonry

construction can lead to

corrosion of the reinforcement

steel and subsequent cracking

and spalling of the masonry.

Moisture resistance is highly

influenced by the quality of the materials and the quality of the masonry construction at the site.

Good Masonry Practice

•	Masonry units and packaged mortar and grout materials should be stored off the ground and covered.

•	Masonry work in progress must be well protected.

•	Mortar and grouts must be carefully batched and mixed. The 2003 International Building Code (IBC 2003)

specifies grout proportions by volume for masonry construction.

Recommendations for Masonry Piers in Coastal Regions

The small footings on the piers in this photograph did not prevent these piers

from overturning during Hurricane Iniki.
HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 15

Foundation

Walls

FS No. 15 – Foundation Walls Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Purpose: To discuss the use of foundation walls in coastal buildings.

Key Issues

•	Foundation walls include stemwalls, cripple walls, and other solid walls.

•	Foundation walls are prohibited by the National Flood Insurance Program (NFIP) in V zones.*

•	Use of foundation walls in A zones in coastal areas should be limited to locations where only shallow flooding

occurs, and where the potential for erosion and breaking waves is low.

•	Where foundation walls are used, flood-resistant design of foundation walls must consider embedment,

height, materials and workmanship, lateral support at the top of the wall, flood openings and ventilation

openings, and interior grade elevation.

Foundation Walls – When Are They Appropriate?

Use of foundation walls – such as those in crawlspace and other solid-wall foundations – is potentially

troublesome in coastal areas for two reasons: (1) they present an obstruction to breaking waves and fastmoving flood waters, and (2) they are typically

constructed on shallow footings, which are

vulnerable to erosion. For these reasons,

their use in coastal areas should be limited 

to sites subject to shallow flooding, where 

erosion potential is low and where breaking 

waves do not occur during the Base Flood.

The NFIP prohibits the use of foundation

walls in V zones*. This Home Builder’s Guide 

to Coastal Construction recommends against

their use in many A zones in coastal areas.

Deeply embedded pile or column foundations 

are recommended because they present less

of an obstruction to floodwaters and are less

vulnerable to erosion.

*	Note that the use of shearwalls below

the Design Flood Elevation (DFE) may

be permitted in limited circumstances

(e.g., lateral wind/seismic loads

cannot be resisted with a braced, open

foundation. In such cases, minimize

the length of shearwalls and the

degree of obstruction to floodwaters

and waves, orient shearwalls parallel

to the direction of flow/waves, do not

form enclosures). Consult the authority

having jurisdiction for guidance

concerning shearwalls below the DFE.
FS No. 15 – Foundation Walls Home Builder’s Guide to Coastal Construction	 08/05 Page  of 3

Design Considerations for Foundation Walls

The design of foundation walls is covered by building codes and standards (e.g., Standard for Hurricane 

Resistant Residential Construction, SSTD 10, by the Southern Building Code Congress International). For flood

design purposes, there are six additional design considerations: (1) embedment, (2) height, (3) materials and

workmanship, (4) lateral support at the top of the wall, (5) flood openings and ventilation openings, and (6)

interior grade elevation.

Embedment – The top of the footing should be no higher than the anticipated depth of erosion and scour

(this basic requirement is the same as that for piers; see figure at right and Fact Sheet No. 14). If the

required embedment cannot be achieved without extensive excavation, consider a pile foundation instead.

Height – The wall should be high

enough to elevate the bottom of the

floor system to or above the DFE (see

Fact Sheet No. 4).

Materials and Workmanship – 

Foundation walls can be constructed

from many materials, but masonry,

concrete, and wood are the most

common. Each material can be

specified and used in a manner to

resist damage due to moisture and

inundation (see Fact Sheet No. 8).

Workmanship for flood-resistant

foundations is crucial. Wood should

be preservative-treated for foundation

or marine use (aboveground or

ground-contact treatment will not be

sufficient). Cuts and holes should

be field-treated. Masonry should be

reinforced and fully grouted (see Fact Sheet No. 16 for masonry details). Concrete should be reinforced and

composed of a high-strength, low water-to-cement ratio mix.

Lateral Support at the Top of the Wall – Foundation walls must be designed and constructed to withstand

all flood, wind, and seismic forces, as well as any unbalanced soil/hydrostatic loads. The walls will typically

require lateral support from the floor system and diaphragm, and connections to the top of the walls must be

detailed properly. Cripple walls, where used, should be firmly attached and braced.

Flood Openings and Ventilation Openings – Any area below the DFE enclosed by foundation walls must

be equipped with openings capable of automatically equalizing the water levels inside and outside the

enclosure. Specific flood opening requirements are included in Fact Sheet No. 27. Flood openings are not

required for backfilled stemwall foundations supporting a slab. Air ventilation openings required by building 

codes do not generally satisfy the flood opening requirement; the air vents are typically installed near the

top of the wall, the flood vents must be installed near the bottom, and opening areas for air flow may be

insufficient for flood flow.

Interior Grade Elevation – Conventional practice for crawlspace construction calls for excavation of the

crawlspace and use of the excavated soil to promote drainage away from the structure (see left-hand figure

on page 3). This approach may be acceptable for non-floodplain areas, but in floodplains, this practice can

result in increased lateral loads (e.g., from saturated soil) against the foundation walls and ponding in the

crawlspace area. If the interior grade of the crawlspace is below the DFE, NFIP requirements can be met

by ensuring that the interior grade is at or above the lowest exterior grade adjacent to the building (see

right-hand figure on page 3). When floodwaters recede, the flood openings in the foundation walls allow

floodwaters to automatically exit the crawlspace. FEMA may accept a crawlspace elevation up to 2 feet

below the lowest adjacent exterior grade; however, the community must adopt specific requirements in order

for this type of crawlspace to be constructed in a floodplain.
FS No. 15 – Foundation Walls Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

DFE

If a stemwall and floor slab system is used, the interior space beneath the slab should be backfilled with

compacted gravel (or such materials as required by the building code). As long as the system can act

monolithically, it will resist most flood forces. However, if the backfill settles or washes out, the slab will

collapse and the wall will lose lateral support.

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 16

Masonry Details

FS No. 16 – Masonry Details Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Purpose: To highlight several important details for

masonry construction in coastal areas.

Key Issues

•	Continuous, properly connected load paths are

essential because of the higher vertical and lateral

loads on coastal structures.

•	Building materials must be durable enough to

withstand the coastal environment.

•	Masonry reinforcement requirements are more

stringent in coastal areas.

Load Paths

A properly connected load path from roof to

foundation is crucial in coastal areas (see Fact

Sheets Nos. 10 and 17). The following details show

important connections for a typical masonry home.

Roof framing to masonry wall.

Roof framing to interior masonry wall
FS No. 16 – Masonry Details Home Builder’s Guide to Coastal Construction	 08/05 Page  of 3

Durability – High winds and salt-laden air can damage masonry construction. The entry of moisture into large

cracks can lead to corrosion of the reinforcement and subsequent cracking and spalling. Moisture resistance

is highly dependent on the materials and quality of construction.

Gable endwall connection.
FS No. 16 – Masonry Details Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Quality depends on:

• Proper storage of material – Keep stored materials covered

and off the ground.

•	Proper batching – Mortar and grout must be properly batched

to yield the required strength.

•	Good workmanship – Head and bed joints must be well mortared and well tooled. Concave joints and V-joints

provide the best moisture protection (see detail above). All block walls should be laid with full mortar coverage

on horizontal and vertical face shells. Block should be laid using a “double butter” technique for spreading

mortar head joints. This practice provides for mortar-to-mortar contact as two blocks are laid together in the

wall and prevents hairline cracking in the head joint.

•	Protection of work in progress – Keep work in progress protected from rain. During inclement weather, the

tops of unfinished walls should be covered at the end of the workday. The cover should extend 2 feet down

both sides of the masonry and be securely held in place. Immediately after the completion of the walls, the

wall cap should be installed to prevent excessive amounts of water from directly entering the masonry.

Reinforcement: Masonry must be reinforced according to the building plans. Coastal homes will typically require more

reinforcing than inland homes. The following figure shows typical reinforcement requirements for a coastal home.

Gable Ends: Because of their

exposure, gable ends are more

prone to damage than are

hipped roofs unless the joint

in conventional construction at

the top of the endwall and the

bottom of the gable is laterally

supported for both inward and

outward forces. The figure at

right shows a construction

method that uses continuous

masonry from the floor to the

roof diaphragm with a raked

cast-in-place concrete bond

beam or a cut masonry bond

beam.

Continuous gable endwall 

reinforcement.

Masonry reinforcement.

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 26

Shutter

Alternatives

FS No. 26 – Shutter Alternatives Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

Purpose: To provide general information

about the installation and use of storm

shutters in coastal areas.

Why Are Storm Shutters Needed?

Shutters are an important part of a hurricaneresistant or storm-resistant home. They

provide protection for glass doors and

windows against windborne debris, which is

often present in coastal storms. Keeping the

building envelope intact (i.e., no window or

door breakage) during a major windstorm is

vital to the structural integrity of a home. If the

envelope is breached, sudden pressurization

of the interior can cause major structural

damage (e.g., roof loss) and will lead to

significant interior and contents damage from

wind-driven rain.

Where Are Storm Shutters Required 

and Recommended?

Model building codes, which incorporate wind

provisions from ASCE 7 (1998 edition and

later), require that buildings within the most

hazardous portion of the hurricane-prone 

region, called the windborne debris region

(see page 4 of this fact sheet), either (1) be

equipped with shutters or impact-resistant

glazing and designed as enclosed structures,

or (2) be designed as partially enclosed

structures (as if the windows and doors are

broken out). Designing a partially enclosed

structure typically requires upgrading

structural components and connections, but

will not provide protection to the interior of

the building. Designers and owners should

assume that a total loss of the building

interior and contents will occur in partially

enclosed structures.

Using opening protection (e.g., shutters

or laminated glass) is recommended in

Plywood panels are a cost-effective means of protection.

Temporary, manufactured metal panel shutter. The shutter is installed 

in a track permanently mounted above and below the window frame. 

The shutter is placed in the track and secured with wing nuts to 

studs mounted on the track. This type of shutter is effective and 

quickly installed, and the wing nut and stud system provides a secure 

anchoring method.

Note: Many coastal homes have large and unusually shaped windows, which will require expensive,

custom shutters. Alternatively, such windows can be fabricated with laminated (impact-resistant) glass.
FS No. 26 – Shutter Alternatives Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Colonial shutters Bahama shutter 

windborne debris regions, as opposed to designing a partially enclosed structure. The Home Builder’s Guide 

to Coastal Construction also recommends giving strong consideration to the use of opening protection in all

hurricane-prone areas where the basic wind speed is 100 mph (3-second peak gust) or greater, even though

the model building codes do not require it. Designers should check with the jurisdiction to determine whether

state or local requirements for opening protection exceed those of the model code.

What Types of Shutters Are Available?

A wide variety of shutter types are available, from the very expensive motor-driven, roll-up type, to the less

expensive temporary plywood panels (see photograph on page 1 of this fact sheet). Designers can refer to

Miami-Dade County, Florida, which has established a product approval mechanism for shutters and other

building materials to ensure they are rated for particular wind and windborne debris loads (see Additional

Resources on page 5 of this fact sheet).

Shutter Type Cost Advantages Disadvantages

Temporary plywood 

panels

Low Inexpensive Must be installed and taken

down every time they are needed;

must be adequately anchored to

prevent blow-off; difficult to install

on upper levels

Temporary manufactured 

panels

Low/Medium Easily installed on

lower levels

Must be installed and taken

down every time they are needed;

difficult to install on upper levels

Permanent, manualclosingMedium/High Always in place

Ready to be closed

Must be closed manually from

the outside; difficult to access on

upper levels

Permanent, motor-driven High Easily opened and

closed from the inside

Expensive

Shutter Styles

Shutter styles include colonial, Bahama, roll-up, and accordion.
FS No. 26 – Shutter Alternatives Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

Common methods for plywood shutter attachment to wood-frame and masonry walls. (For actual shutter design, refer to 

design drawings or see the Engineered Wood Association guidelines for constructing plywood shutters.)

Roll-up shutter Accordion shutter
FS No. 26 – Shutter Alternatives Home Builder’s Guide to Coastal Construction	 08/05 Page  of 5

Are There Special Requirements for Shutters in Coastal Areas?

ASCE 7 and the International Building Code (IBC) state that shutters (or laminated glazing) shall be tested in

accordance with the American Society for Testing and Materials (ASTM) standards ASTM E 1886 and ASTM E

1996 (or other approved test methods). E 1886 specifies the test procedure; E 1996 specifies missile loads.

The IBC allows the use of wood panels (Table 1609.1.4) and prescribes the type and number of fasteners to

be used to attach the panels. A shutter may look like it is capable of withstanding windborne missiles; unless

it is tested, however, its missile resistance is unknown.

When installing any type of shutter, carefully follow manufacturer’s instructions and guidelines. Be sure to

attach shutters to structurally adequate framing members (see shutter details on page 3 of this fact sheet).

Avoid attaching shutters to the window frame or brick veneer face. Always use hardware not prone to corrosion

when installing shutters.

What Are “Hurricane-Prone Regions” “Windborne Debris Regions”?

ASCE 7, the IBC, and the International Residential Code (IRC) define hurricane-prone regions as:

•	the U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed is greater than 90 mph (3-

second peak gust), and

•	Hawaii, Guam, Puerto Rico, the U.S. Virgin Islands, and American Samoa.

ASCE 7, the IBC, and the IRC define windborne debris regions as areas within hurricane-prone regions

located:

•	within 1 mile of the coast where the basic wind speed is equal to or greater than 110 mph (3-second peak

gust) and in Hawaii, or

•	in all areas where the basic wind speed is equal to or greater than 120 mph (3-second peak gust), including

Guam, Puerto Rico, the U.S. Virgin Islands, and American Samoa.
FS No. 26 – Shutter Alternatives Home Builder’s Guide to Coastal Construction	 08/05 Page of 5

Additional Resources

American Society of Civil Engineers. Minimum Design Loads for Buildings and Other Structures, ASCE 7.

(http://www.asce.org)

International Code Council. International Building Code. 2003. (http://www.iccsafe.org)

International Code Council. International Residential Code. 2003. (http://www.iccsafe.org)

The Engineered Wood Association. Hurricane Shutter Designs Set 5 of 5. Hurricane shutter designs for woodframe and masonry buildings. (http://www.apawood.org)

Miami-Dade County, Florida, product testing and approval process – information available at http://www.

miamidade.gov/buildingcode/pc_home.asp

FS No. 27 – Enclosures and Breakaway Walls Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Enclosures can be divided into two types, breakaway and

non-breakaway.

•	Breakaway enclosures are designed to fail under Base

Flood conditions without jeopardizing the elevated

building – any below-BFE enclosure in a V zone must be 

breakaway. Breakaway enclosures are permitted in A

zones but must be equipped with flood openings.

•	Non-breakaway enclosures, under the NFIP, can be used

in an A zone (they may or may not provide structural

support to the elevated building), but they must be

equipped with flood openings to allow the automatic

entry and exit of floodwaters. The Home Builder’s Guide 

to Coastal Construction recommends their use only in 

A zone areas subject to shallow, slow-moving floodwaters 

without breaking waves.

Breakaway Walls

Breakaway walls must be designed to break

free under the larger of the design wind load,

the design seismic load, or 10 psf, acting

perpendicular to the plane of the wall. If

the loading at which the breakaway wall is

intended to collapse exceeds 20 psf, the 

breakaway wall design must be certified. 

When certification is required, a registered

engineer or architect must certify that

the walls will collapse under a water load

associated with the Base Flood and that

the elevated portion of the building and its

foundation will not be subject to collapse,

displacement, or lateral movement under

simultaneous wind and water loads. (See the

sample certification at the bottom of page 2

of Fact Sheet No. 5.) Utilities should not be 

attached to or pass through breakaway walls.

Flood Openings

Where permitted and used in A zones,

foundation walls and enclosures must

be equipped with openings that allow the

automatic entry and exit of floodwaters.

Note the following:

•	Flood openings must be provided in 

at least two of the walls forming the

enclosure.

•	The bottom of each flood opening must be

no more than 1 foot above the adjacent 

grade outside the wall.

•	Louvers, screens, or covers may be installed

over flood openings as long as they do not interfere with the operation of the openings during a flood.

•	Flood openings may be sized according to either a prescriptive method (1 square inch of flood opening per square

foot of enclosed area) or an engineering method (which must be certified by a registered engineer or architect).

Details concerning flood openings can be found in FEMA Technical Bulletin 4-93, Openings in Foundation Walls.

Recommended breakaway wall construction. 

Open wood lattice installed beneath 

an elevated house in a V zone.
FS No. 27 – Enclosures and Breakaway Walls Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

Other Considerations

Enclosures are strictly regulated because, if not constructed properly, they can transfer flood forces to the 

main structure (possibly leading to structural collapse). There are other considerations, as well:

•	Owners may be tempted to convert enclosed areas below the BFE into habitable space, leading to lifesafety concerns and uninsured losses. Construction without enclosures should be encouraged. Contractors

should not stub out utilities in enclosures; utility stub-outs make it easier for owners to finish and occupy

the space.

•	Siding used on non-breakaway portions of a building should not be extended over breakaway walls. Instead,

a clean separation should be provided so that any siding installed on breakaway walls is structurally

independent of siding elsewhere on the

building. Without such a separation, the

failure of breakaway walls can result in

damage to siding elsewhere on the building.

•	Breakaway enclosures in V zones will result

in substantially higher flood insurance 

premiums (especially where the enclosed

area is 300 square feet or greater). Insect

screening or lattice is recommended

instead.

•	If enclosures are constructed in A zones 

with the potential for breaking waves, open 

foundations with breakaway enclosures are 

recommended in lieu of foundation walls or

crawlspaces. If breakaway walls are used,

they must be equipped with flood openings

that allow flood waters to enter the enclosure

during smaller storms. Breakaway enclosures in

A zones will not lead to higher flood insurance

premiums.

•	Garage doors installed in below-BFE enclosures of V-zone buildings — even reinforced and high-windresistant doors — must meet the performance requirement discussed in the Breakaway Walls section on

page 2 of this fact sheet. Specifically, the doors must be designed to break free under the larger of the

design wind load, the design seismic load, or 10 psf, acting perpendicular to the plane of the door. If the

loading at which the door is intended to collapse is greater than 20 psf, the door must be designed and 

certified to collapse under Base Flood conditions. See the Breakaway Walls section of this fact sheet for

information about certification requirements.

Siding on the non-breakaway portions of this elevated building was 

extended over breakaway enclosure walls and was damaged when 

breakaway walls failed under flood forces.
Enclosures and Breakaway

Walls

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 27

FS No. 27 – Enclosures and Breakaway Walls Home Builder’s Guide to Coastal Construction	 08/05 Page  of 3

Purpose: To discuss requirements and recommendations

for enclosures and breakaway walls below the Base Flood

Elevation (BFE).

Key Issues

•	Spaces below elevated buildings can be used only for

building access, parking, and storage.

•	Areas enclosed by solid walls below the BFE (“enclosures”)

are subject to strict regulation under the National Flood

Insurance Program (NFIP). Note that some local jurisdictions

enforce stricter regulations for enclosures.

•	Non-breakaway enclosures are prohibited in V-zone buildings.

Breakaway enclosures in V zones must meet specific

requirements and must be certified by a registered design

professional

•	Enclosures (breakaway and non-breakaway) in A-zone buildings

must be built with flood-resistant materials and equipped with

flood openings that allow water levels inside and outside to

equalize (see Fact Sheet No. 15).

•	For V zones, enclosures below the elevated building will

result in higher flood insurance premiums.

•	Breakaway enclosure walls should be considered

expendable, and the building owner will incur substantial

costs when the walls are replaced.

Space Below the BFE — What Can it Be Used For?

NFIP regulations state that the area below an elevated

building can be used only for building access, parking, 

and storage. These areas must not be finished or used for

recreational or habitable purposes. No mechanical, electrical,

or plumbing equipment is to be installed below the BFE.

What Is an Enclosure?

An “enclosure” is formed when any space below the BFE is

enclosed on all sides by walls or partitions. A V-zone building

elevated on an open foundation (see Fact Sheet No. 11),

without an enclosure or other obstructions below the BFE,

is said to be free-of-obstructions, and enjoys favorable flood

insurance premiums (a building is still classified free-ofobstructions if insect screening or open wood lattice is used to

surround space below the BFE). See FEMA Technical Bulletin

5-93, Free of Obstruction Requirements for more information.

 

Home builders and homeowners should 

consider the long-term effects of the 

construction of enclosures below 

elevated residential buildings and postconstruction conversion of enclosed 

space to habitable use in A zones and 

V zones. Designers and owners should

realize that (1) enclosures and items

within them are likely to be destroyed even

during minor flood events, (2) enclosures,

and most items within them, are not

covered by flood insurance and can result

in significant costs to the building owner,

and (3) even the presence of properly

constructed enclosures will increase

flood insurance premiums for the entire

building (the premium rate will increase

as the enclosed area increases).

Including enclosures in a building design

can have significant cost implications.

This Home Builder’s Guide to Coastal 

Construction recommends the use of

insect screening or open wood lattice

instead of solid enclosures beneath

elevated residential buildings.

WARNING

Breakaway walls that failed under the 

flood forces of Hurricane Ivan. 

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION FEMA 499/August 2005 Technical Fact Sheet No. 29

Protecting Utilities

FS No. 29 – Protecting Utilities Home Builder’s Guide to Coastal Construction	 08/05 Page  of 3

Purpose: To identify the special considerations that must be made when installing utility equipment in a

coastal home.

Key Issues: Hazards, requirements, and recommendations

Special considerations must be made when installing utility systems in coastal homes. Proper placement and 

connection of utilities and mechanical equipment can significantly reduce the costs of damage caused by 

coastal storms and will enable homeowners to reoccupy their homes soon after electricity, sewer, and water

are restored to a neighborhood.

Coastal Hazards That Damage Utility Equipment

•	Standing or moving floodwaters

•	Impact from floating debris in floodwaters

•	Erosion and scour from floodwaters

•	High winds

•	Windborne missiles

Common Utility Damage in Coastal Areas

Floodwaters cause corrosion and contamination,

short-circuiting of electronic and electrical

equipment, and other physical damage.

Electrical – Floodwaters can corrode and shortcircuit electrical system components, possibly

leading to electrical shock. In velocity flow

areas, electrical panels can be torn from their

attachments by the force of breaking waves or the

impact of floating debris.

Water/Sewage – Water wells can be exposed

by erosion and scour caused by floodwaters with

velocity flow. A sewage backup can occur even without the structure flooding.

Fuel – Floodwaters can float and rupture tanks, corrode and short-circuit electronic components, and sever

pipe connections. In extreme cases, damage to fuel systems can lead to fires.

Basic Protection Methods

The primary protection methods are elevation or component protection.

Elevation

Elevation refers to the location of a component and/or utility system above

the Design Flood Elevation (DFE).

Component Protection

Component protection refers to the implementation of design techniques that protect a component or group

of components from flood damage when they are located below the DFE.

Elevation of utilities and 

mechanical equipment is 

the preferred method of 

protection.

Electrical lines and box dislocated by hurricane forces.
FS No. 29 – Protecting Utilities Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

NFIP Utility Protection Requirements

The NFIP regulations [Section 60.3(a)(3)] state that:

All new construction and substantial improvements shall be constructed with electrical, heating, ventilation, 

plumbing, and air conditioning equipment and other service facilities that are designed and/or located so as 

to prevent water from entering or accumulating within the components during conditions of flooding.

Utility Protection Recommendations

Electrical

•	Limit switches, wiring, and receptacles below the DFE to those items required for life safety. Substitute

motion detectors above the DFE for below-DFE switches whenever possible. Use only ground-fault-protected

electrical outlets below the DFE.

•	Install service connections (e.g., electrical lines, panels, and meters; telephone junction boxes; cable

junction boxes) above the DFE, on the landward side of interior piles or other vertical support members.

•	Use drip loops to minimize water entry at penetrations.

•	Never attach electrical components to breakaway walls.

Water/Sewage

•	Attach plumbing risers on the landward side of interior piles or other vertical support members.

Recommended installation techniques for electrical and plumbing lines and other utility components. 
FS No. 29 – Protecting Utilities Home Builder’s Guide to Coastal Construction	 08/05 Page of 3

•	When possible, install plumbing runs inside joists for protection.

•	Never attach plumbing runs to breakaway walls.

HVAC

•	Install HVAC components (e.g.,

condensers, air handlers, ductwork,

electrical components) above the DFE.

•	Mount outdoor units on the leeward

side of the building.

•	Secure the unit so that it cannot move,

vibrate, or be blown off its support.

•	Protect the unit from damage by

windborne debris.

Fuel

•	Fuel tanks should be installed so

as to prevent their loss or damage.

This will require one of the following

techniques: (1) elevation above the

DFE and anchoring to prevent blowoff,

(2) burial and anchoring to prevent

exposure and flotation during erosion

and flooding, (3) anchoring at ground

level to prevent flotation during flooding and loss during scour and erosion. The first method (elevation) is

preferred.

•	Any anchoring, strapping, or other attachments must be designed and installed to resist the effects of

corrosion and decay.

Additional Resources

American Society of Civil Engineers. Flood Resistant Design and Construction (SEI/ASCE 24-98). (http://www.

asce.org)

FEMA. NFIP Technical Bulletin 5-93, Free-Of-Obstruction Requirements for Buildings Located in Coastal High 

Hazard Areas. (http://www.fema.gov/fima/techbul.shtm)

FEMA. Protecting Building Utilities From Flood Damage. FEMA 348. November 1999. (http://www.fema.gov/

hazards/floods/lib06b.shtm)

Elevated air conditioning compressors.

RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST G-

G.	FEMA Publications and

	 Additional References

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

and Commentary, ACI 318. 01-Jan-2005.

American Forest & Paper Association’s (AFPM) American Wood Council. 2005. National Design 

Specification for Wood Construction. 2005.

American Society for Testing and Materials (ASTM). 2000. Standard Test Method for High-Strain 

Dynamic Testing of Piles, ASTM D 4945. November 2000.

American Society of Civil Engineers (ASCE) 7-02. 2002. Minimum Design Loads for Buildings and 

Other Structures, ASCE 7-02. ISBN:0-7844-0624-3.

ASCE 24-05. 2006. Flood Resistant Design and Construction. ISBN: 0784408181. 01-Jan-2006.

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

FEMA. 1984. Elevated Residential Structures, FEMA 54. March 1984.

FEMA. 1995. Guide to Flood Maps: How to Use a Flood Map to Determine Flood Risk for a Property, 

FEMA 258. May 1995.
G- Building on strong and safe foundations

g fema publications and additional references

FEMA. 1996. Corrosion Protection for Metal Connectors in Coastal Areas for Structures Located in Special 

Flood Hazard Areas, FEMA Technical Bulletin 8-96. August 1, 1996.

FEMA. 2000. Coastal Construction Manual, FEMA 55. June 2000.

FEMA. 2000. Design and Construction Guidance for Community Shelters, FEMA 361. July 2000.

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

424. January 2004.

FEMA. 2004. Taking Shelter From the Storm: Building a Safe Room Inside Your House, FEMA 320. 

March 2004.

FEMA. 2005. Mitigation Assessment Team Report: Hurricane Charley in Florida, FEMA 488. April 

2005. 

FEMA. 2005. Mitigation Assessment Team Report: Hurricane Ivan in Alabama and Florida, FEMA 489. 

August 2005.

FEMA. 2005. Home Builders’ 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.

International Building Code (IBC). 2003. 2003 International Building Code. 01-Jan-2005. 

International Residential Code (IRC). 2003. International Residential Code for One- and Two- Family Dwellings. 01-Mar-2003.

Mississippi 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 THE GULF COAST H-1

H.	Glossary

3-second peak gust – The wind speed averaging time used in ASCE 7 and the IBC. 

A Zone – A Zones are the areas not listed as V Zones, but also identified on a Flood Insurance 

Rate Map (FIRM) as being subject to inundation during a 100-year flood. The associated flood 

elevation has a 1-percent chance of being equaled or exceeded in any given year. There are 

several categories of A Zones that may be identified on a FIRM with one of the following designations: AO, AH, A1-30, AE, and unnumbered A Zones. 

Allowable Stress Design (ASD) – A method of proportioning structural members such that elastically computed stresses produced in the members by nominal loads do not exceed specified 

allowable stresses (also called working stress design) (ASCE 7-02).

Base flood - A flooding having a 1 percent chance of being equaled or exceeded in any given 

year; also known as the 100-year flood.

Base Flood Elevation (BFE) – Elevation of the 1-percent flood. This elevation is the basis of the insurance and floodplain management requirements of the National Flood Insurance Program 

(NFIP).

Coastal A Zone – The portion of the Special Flood Hazard Area (SFHA) landward of a V Zone or 

landward of an open coast without mapped V Zones (e.g., the shorelines of the Great Lakes), 

in which the principal sources of flooding are astronomical tides, storm surges, seiches, or 

tsunamis, not riverine sources. Like the flood forces in V Zones, those in Coastal A Zones are 

highly correlated with coastal winds or coastal seismic activity. Coastal A Zones may therefore 
H-2 Building on strong and safe foundations

H Glossary

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 Special Flood Hazard Areas (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 (American Society of Civil Engineers [ASCE 7-02]).

Design professional – A state licensed architect or engineer.

Erosion – Process by which floodwaters lower the ground surface in an area by removing upper 

layers of soil.

Exposure Category B – A wind exposure identified in ASCE 7 and the International Building 

Code (IBC) as urban and suburban areas, wooded areas, or other terrain with numerous closely 

spaced obstructions having the size of single-family dwellings or larger. 

Exposure Category C – A wind exposure identified in ASCE 7 and the IBC as open terrain with 

scattered obstructions having heights generally less than 30 feet (9.1 meters). This category includes flat open country, grasslands, and all water surfaces in hurricane-prone regions. 

Flood Insurance Rate Map (FIRM) – An official map of a community, on which FEMA has delineated both the SFHA and the risk premium zones applicable to the community. The map shows the 

extent of the base floodplain and may also display the extent of the floodway and BFEs.

Freeboard – The height added to place a structure above the base flood to reduce the potential 

for flooding. The increased elevation of a building above the minimum design flood level to 

provide additional protection for flood levels higher than the 1-percent chance flood level and 

to compensate for inherent inaccuracies in flood hazard mapping.

Hydrodynamic forces – The amount of pressure exerted by moving floodwaters on an object, such 

as a structure. Among these loads are positive frontal pressure against the structure, drag forces 

along the sides, and suction forces on the downstream side.

Hydrostatic forces – The amount of lateral pressure exerted by standing or slowly moving floodwaters on a horizontal or vertical surface, such as a wall or a floor slab. The water pressure 

increases with the square of the water depth.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST H-3

Glossary H

Leeward – The side away, or sheltered, from the wind.

National Flood Insurance Program (NFIP) – The NFIP is a Federal program enabling property owners in participating communities to purchase insurance as a protection against flood losses 

in exchange for State and community floodplain management regulations that reduce future 

flood damages. Participation in the NFIP is based on an agreement between communities and 

the Federal Government. If a community adopts and enforces floodplain management regulations to reduce future flood risk to new construction in floodplains, the Federal Government 

will make flood insurance available within the community as a financial protection against flood 

losses. This insurance is designed to provide an insurance alternative to disaster assistance to 

reduce the escalating costs of repairing damage to buildings and their contents caused by floods. 

The program was created by Congress in 1968 with the passage of the National Flood Insurance 

Act of 1968.

National Geodetic Vertical Datum 1929 (NGVD 1929) – A vertical elevation baseline determined in 

1929 as a national standard. Used as the standard for FIRMs until 2000.

North American Vertical Datum 1988 (NAVD 1988) – A vertical elevation baseline determined in 1988 

as a more accurate national standard. The current vertical elevation standard for new FIRMs.

Scour – Erosion by moving water in discrete locations, often as a result of water impacting foundation elements.

Shore-normal – Perpendicular to the shoreline.

Slab-on-grade foundation – Type of foundation in which the lowest floor of the house is formed 

by a concrete slab that sits directly on the ground. 

Slug – A unit of mass in the English foot-pound-second system. One slug is the mass accelerated 

at 1 foot per second (fps) by a force of 1 pound (lb). Since the acceleration of gravity (g) in English units is 32.174 fps, the slug is equal to 32.174 pounds (14.593 kilograms).

Special Flood Hazard Area (SFHA) – Portion of the floodplain subject to inundation by the base 

flood.

Stem wall foundation – A type of foundation that uses masonry block and reinforced with steel 

and concrete. The wall is constructed on a concrete footing, back-filled with dirt, compacted, 

and the slab is then poured on top.

Strength Design – A method of proportioning structural members such that the computed forces produced in the members by the factored loads do not exceed the member design strength 

(also called load and resistance factor design) (ASCE 7-02).

V Zones – V Zones are areas identified on FIRMs as zones VE, V1-30, or V. These areas, also 

known as Coastal High Hazard Areas, are areas along the coast that have a 1 percent or greater 
H-4 Building on strong and safe foundations

H Glossary

annual chance of flooding from storm surge and waves greater than 3 feet in height, as well as 

being subject to significant wind forces.

Windward – The side facing the wind.
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST I-

I.	 Abbreviations and 	 	 	 	 	

	 Acronyms

A

ABFE Advisory Base Flood Elevation

ACI American Concrete Institute

AF&PA American Forest & Paper Association

ASCE American Society of Civil Engineers

ASD Allowable Stress Design

ASTM American Society for Testing and Materials

AWPA American Wood Preservers’ Association
I- Building on strong and safe foundations

I Abbreviations and acronyms

B

BFE Base Flood Elevation

C

C&C components and cladding

CMU concrete masonry unit

CRSI Concrete Reinforced Steel Institute

cy cubic yard

D

DFE Design Flood Elevation

DL dead load

E

ea each

F

FEMA Federal Emergency Management Agency

FIRM Flood Insurance Rate Map

FIS Flood Insurance Study

fps feet per second
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST I-

Abbreviations and acronyms I

FRP fiber reinforced polyester

ft feet

G

g gravity

I

IBC International Building Code

ICC International Code Council

IRC International Residential Code

K

kip 1,000 pounds

ksi kips per square inch

L

lb pound

lb/sq pounds per square foot

lf linear foot

LL live load

ls lump sum
I- Building on strong and safe foundations

I Abbreviations and acronyms

M

MAT Mitigation Assessment Team

mph miles per hour

MWFRS Main Wind Force Resisting System

N

NAVD North American Vertical Datum of 1988

NDS National Design Specification for Wood

NFIP National Flood Insurance Program 

NFPA National Fire Protection Association

NGVD National Geodetic Vertical Datum of 1929

NR Not Recommended

O

o.c. on center

P

pcf pounds per cubic foot

psf pounds per square foot

psi pounds per square inch
RECOMMENDED RESIDENTIAL CONSTRUCTION FOR THE GULF COAST I-

Abbreviations and acronyms I

R

ROM rough order of magnitude

S 

SBC Standard Building Code

SFHA	 Special Flood Hazard Area

SLOSH	 Sea, Lake, and Overland Surges from Hurricanes

sq	 square foot

SWL stillwater elevation

T

TBTO tributylin oxide

TMS The Masonry Society

U

UDA Urban Design Associates

u.n.o.	 unless noted otherwise

USGS United States Geological Survey

W

WWF welded wire fabrics