Elevated 

Residential 

Structures 

FEMA 54 I March 1984 

Federal Emergency Management Agency 
Elevated 

Residential 

Structures 
Acknowledgments 

Many people contributed valuable assistance to the preparation of this manual. We wish to acknowlege especially the 

guidance provided by Melita Rodeck and, later, John Gambel, the Federal Emergency Management Agency's technical 

representatives in this work. John Gambel's advice was 

particularly valuable in determining the final content and 

form of this manual. In addition, this project would not 

have been possible without the help of Richard W. Krimm, 

Assistant Associate Director of the Federal Emergency 

Management Agency's Office of Natural and Technological 

Hazards, who saw the importance of increasing architects' 

involvement in flood damage mitigation efforts. Finally, 

Ray Fox provided a wealth of useful advice in additio~ to 

his technical services throughout the course of the project. 

Prepared by 

The American Institute of Architects Foundation 

1735 New York Avenue, N.W. 

Washington, D.C. 20006 

Charles R. Ince, Jr., President 

Earle W. Kennett, Administrator, Research 

Donald E. Geis, Program Director and Project Manager 

Karen N. Smith, Administrative Manager 

Paul K. McClure, Editor 

Technical Consultants 

Raymond R. Fox 

Professor of Civil Engineering 

The George Washington University 

Washington, D. C. 

Mark Riebau 

Assistant Chief of Floodplain and Shoreland Management 

Wisconsin Bureau of Water Regulation and Zoning 

Madison, Wisconsin 

Cost Consultant 

Daniel Mann Johnson & Mendenhall, Architects-Engineers 

Washington, D.C. 

Paul Brott, Vice President 

Ernest Posch, Estimator 

The Design Studies section of the manual was developed on 

the basis of background data and design concepts submitted 

for the 1976 version of this manual by Zane Yost and 

Associates, Bridgeport, Connecticut; KEF Corporation, 

Metairie, Louisiana; Keck and Keck Architects, Chicago; 

Duval/Johlic Architects-Planners, San Francisco; Louisiana 

State University, Department of Architecture ; Rhode Island 

School of Design; University of California at Los Angeles, 

School of Architecture and Urban Planning; and University 

of Miami, School of Architecture. 

ii 

Graphics and Book Design 

Assarsson Design Company 

Washington, D.C. 

Allan G. Assarsson, President 

Mark P. Jarvinen, Layout and Graphic Design 

Jeffery Banner, Graphic Design 

Photographs 

Raymond R. Fox, Dames & Moore, pp. 64 and 124 and 

Figures 4.23 and 4.26; Federal Emergency Management 

Agency, p. 1 and Figure 4.1; U.S. Geological Survey, 

pp. vi, 122, and 123; U.S. Department of Housing and 

Urban Development, p. 118 and Figure 2.3; Philip 

Schmidt, U.S. Department of Housing and Urban Development, Figure 2.7; National Park Service, pp. iv and 

112; Spencer Rogers, p. 18; Rosenthal Art Slides, Figures 

3.1 and 3.2; AIA Library, Figures 3.3 and 3.4; U.S. 

Army Corps of Engineers, pp. 3 and 115; Davis and 

Associates, Figure 4.49; Pittsburgh City Planning Department, p. 4; PARNG Photo, p. 2; and James K. M. Cheng, 

p. 98. 

Most of the photographs and design data in the Recent Design 

Examples section were supplied by the designers of the 

buildings shown there. All other photographs were taken 

by Donald E. Geis of The American Institute of Architects 

Foundation. 

Disclaimer 

The statements contained in this manual are those of The 

American Institute of Architects Foundation and do not 

necessarily reflect the views of the U.S. Government in 

general or the Federal Emergency Management Agency 

in particular. The U.S. Government, FEMA, and The 

American Institute of Architects Foundation make no 

warranty, express or implied, and assume no responsibility 

for the accuracy or completeness of the information herein. 

This manual was prepared under Contract No. EMC-C-0579 

with the Federal Emergency Management Agency . 
Table of Contents 

ACKNOWLEDGMENTS 

PREFACE 

ENVIRONMENTAL AND REGULATORY FACTORS 

FLOODING AND THE BUILT ENVIRONMENT 

Riverine Flooding D Coastal Flooding 

FLOODPLAIN MANAGEMENT 

National Flood Insurance Program D Base Flood Elevations DA and V Zones 

SITE ANALYSIS AND DESIGN 

SITE SELECTION AND ANALYSIS 

SITE DESIGN 

Site Flooding Characteristics D Access and Egress D Vegetation D Flood Water 

Drainage and Storage D Dune Protection 

ARCHITECTURAL DESIGN EXAMPLES 

DESIGN STUDIES 

Bridgeport D Charleston and Newport D San Francisco D Chicago 

AESTHETIC CONSIDERATIONS 

RECENT DESIGN EXAMPLES 

Logan House D Summerwood on the Sound D Breakers Condominium D 

Campus-by-the-Sea Facility D Starboard Village D Gull Point Condominiums 

DESIGN AND CONSTRUCTION GUIDELINES 

FOUNDATIONS 

Fill D Elevated Foundations D Shear Walls D Posts D Piles D Piers D Bracing 

FRAMING CONSTRUCTION AND CONNECTIONS 

Framing Methods D Floor Beams D Cantilevers D Concrete Flooring Systems D 

Floor Joists D Sub.flooring D Wall Sheathing and Bracing D Roof Connections 

RELATED DESIGN CONSIDERATIONS 

Glass Protection D Utilities and Mechanical Equipment D Building Materials D 

Insulation D Breakaway Walls D Retrofitting Existing Structures 

COST ANALYSIS 

RESOURCE MATERIALS 

GLOSSARY 

SOURCES OF DESIGN INFORMATION 

FEMA REGIONAL OFFICES 

STATE COORDINATING OFFICES FOR THE NFIP 

PERFORMANCE CRITERIA 

REFERENCES 

ii 

v 

4 

8 

9 

13 

18 

22 

35 

45 

64 

65 

80 

92 

98 

112 

113 

116 

118 

120 

125 

136 

iii 

Preface 

Whenever possible, residential structures should 

not be located in flood-prone areas. Flooding in 

these areas is virtually assured at some point in 

the future, bringing with it the potential for 

property damage-no matter how well a structure 

is designed-as well as danger to building occupants. However, it is not always possible to 

avoid flood-prone areas. This manual is for 

designers, developers, builders, and others who 

wish to build elevated residential structures in 

flood-prone areas prudently. 

The readers of this manual are assumed to have 

knowledge of conventional residential construction 

practice; the manual is limited to the special design 

issues confronted in elevated construction. 

This is a revision of a manual of the same title published in 1976 by the Federal Insurance Administration. This revision reflects changes since 1976 

in floodplain management techniques and regulations, improvements in construction materials 

and practice, increases in construction costs, and 

additions to the relevant literature. This revision 

also contains increased information on elevating 

structures in coastal areas, although all the techniques described here apply to both coastal and 

riverine areas unless otherwise stated. 

A second document, published by the Federal 

Emergency Management Agency (FEMA), Design 

Guidelines for Flood Damage Reduction, supplements this manual's discussion of elevated residential structures with information on the full range of 

other floodplain management strategies. 

A third document, Design and Construction 

Manual for Residential Buildings in Coastal High 

Hazard Areas, is published jointly by FEMA and 

the U.S. Department of Housing and Urban Development. It provides structural engineering guidelines and other information on designing structures 

in coastal areas subject to severe wind and velocity 

wave forces. Structures in such areas should not be 

designed without consulting it. 

v 
ENVIRONMEN~fAL AND REGULATORY FACTORS 
Flooding and the 

Built Environment 

Rivers and seacoasts have always been focal points 

for development. Access to water has provided 

drinking supplies and sanitation, an important 

source of energy, and a valuable part of the transportation system. Recreational opportunities and 

aesthetic enjoyment further stimulate waterside 

development. 

This development pattern, however, leads to a conflict between the natural and built environments. 

The need for direct access to water places human 

settlements in low-lying areas that are subject to 

periodic flooding by rivers and the sea. In the 

United States, more than six million dwellings and 

a large number of nonresidential buildings are 

currently located in the nation's 160 million acres 

of floodplains. Flooding of these floodplains is 

responsible for more damage to the built environment than any other type of natural disaster. The 

total flood damage in 1978, for example, was an 

estimated $3.8 billion. The following year, 

Hurricane Frederic alone caused $1.8 billion in 

damages. 
2 

RIVERINE FLOODING 

Floods are part of the natural hydrologic process. 

Riverine flooding is associated with a river's 

watershed, which is the natural drainage basin that 

conveys water runoff from rain and melting snow. 

Water that is not absorbed by soil or vegetation 

seeks surface drainage lines, following local topography and creating rivers and other streams. 

Flooding results when flow of runoff 

is greater 

than the carrying capacity of watershed streams. 

Riverine flooding usually involves a slow buildup 

of water and a gradual inundation of surrounding 

land. However, flash flooding, a quick and intense 

overflow with high water velocities, can result from 

a combination of steep slopes, a short drainage 

basin, and a high proportion of surfaces impervious 

to water and unable to absorb runoff. 

In addition to the direct threat to buildings, 

development in riverine floodplains alters natural 

topography, modifying drainage patterns and 

usually increasing storm water runoff. Develop-

ment also displaces much of the natural vegetation 

that formerly absorbed water and decreases the 

permeability of the soil by covering it with buildings or with nonporous surfaces for roads, side-

-

walks, and parking. The effect of these changes is 

to increase the severity of flooding throughout the 

riverine environment. 

COASTAL FLOODING 

Coastal flooding is generall y due to srvc rc occanbased storm systems. Hurri canes, tropical torm ~, 

and ex tratropi cal storms such as "northeasters" arr 

the principal causes, with flooding occurring wh

en 

storm tides are higher than the normal high tidr, 

and arc accompanied by water moving at relatiwly 

high velocity and velocity wave action. The 

maximum intensity of a storm tide occurs at 

high tide, so storms that 

persist through srveral 

tides are th e mo

st severe. 
The velocity and range of coastal floods vary in 

part with the severity of the storm that induces 

them. The damaging effects of coastal flooding 

are caused by a combination of the higher water 

levels of the storm tide and the rain, winds, waves, 

erosion, and battering by debris. 

The extent and nature of coastal flooding is also 

related to physiographic features of the terrain and 

the characteristics of the adjoining body of water. 

Pacific coastal areas are vulnerable principally to 

earthquakes, tsunamis (seismically induced tidal 

waves) and other natural forces that can trigger 

excessive erosion, mud slides, and flash flooding. 

Great Lakes coastal areas are subject to erosion and 

severe winter storms. The Atlantic and Gulf Coasts 

are consistently exposed to the forces of hurricanes, lesser tropical storms, and northeasters. 

Coastal flooding is most frequent on the Atlantic 

and Gulf Coasts, which are made up of a succession 

of barrier islands, beaches, and dunes. These 

physiographic elements are maintained in dynamic 

balance as sand is moved by wind, waves, and 

ocean currents. This self-replenishing beach-dune 

system takes the brunt of the force of storm 

surges and helps buffer inland areas. 

In coastal areas the removal of beach sand and the 

leveling of dunes, along with the construction of 

seawalls, jetties and piers, are common practice. 

These can help destroy the shoreline's natural protection system, exacerbating the impact of storm 

surges and high winds. 

3 
4 

Floodplain Management 

There have long been attempts to moderate the 

impact of riverine flooding, with major federal 

efforts in the Unit

ed States since 1936. Until 

recently, these 

efforts have been concentrated on 

flood control measures devised to reduce or 

eliminate flooding it

self-chiefly dams, levees and 

similar stru

ctural works. Despite a number of 

positive results, these measures have not succeeded 

in reducing flood damage significantly. 

Since the mid

-l 960s, therefore, federal policies 

have reflec

ted a recognition that structural works 

need to 

be complemented by nonstructural measures. Rather than trying solely to prevent floods, current floodplain management programs address 

the need to reduce the losses incurred when 

inevitable flooding does happen. Elevating residential structures above the 

reach of 

flood waters, the subject of this manual, is only 

one of se

veral floodplain management techniques 

currently used to redu ce flood damage. For 

example, construction is prohibited in critical 

floodplain areas (t

ermed floodways) unless it has 

been determined that 

construction will not increase flood levels elsewhere. Where buildings are 

already locat

ed in these critical areas, they can 

eith

er be relocated out of the flood area, elevated, 

or floodproofed to 

reduce the damage they will 

suffer in a flood. Buildings that are badly damag

ed 

by flooding can be razed or floodproofed rather 

than being restored to their original, vulnerable 

condition. Va

cant land in flood-prone areas can be 

purchased by the local community and reserved for 

recreation, farming, or oth

er safe uses. 

These and other floodplain management techniqu es (discussed in DPsign Guidelin es for Flood 

Dumag<> R<>durtion , 

cited in the Preface) can be 

used in a 

coordinated way to respond to each 

communit

y's various needs, resources, and flood 

hazards. El

evated residential structures, if used at 

sites appropriate for them, can be useful com-

ponents of 

effective floodplain management. 
NATIONAL FLOOD INSURANCE PROGRAM 

The National Flood Insurance Program (NFIP) is 

the federal government's principal administrative 

mechanism for reducing flood damage. Established by Congress in 1968, the NFIP is administered by the Federal Emergency Management 

Agency (FE1\1A). The NFIP insures buildings and 

their contents in flood-prone areas, where conventional insurance had, prior to the NFIP, been 

generally unavailable. 

The NFIP provides this insurance only in communities that agree to implement comprehensive 

land-use planning and management to reduce the 

likelihood of floo<l damage in their jurisdictions. 

Community response to this incentive generally 

involves the adoption of zoning, building code, and development regulations that place various require- ments and restrictions on new construction and on substantial improvements to existing construction. 

Note that some lorn/ governments have adopted 

codes and ::::oning ordinances that are ronsiderably 

more reslricliv<' than the minimums required by 

FEMA. The resu ll is Iha t fam iliaril y with design 

requirements in on<' rommunity cannot be r<'lied 

on elsewher<'. 

The rate structure of the FIP's insurance premiums reinforces the intent of these regulations 

by charging higher insurance rates for buildings subj ect to greater hazard. These insurance rates are 

set primarily on the basis of designated hazard 

zones and the elevation of the building or 

structure 

in relation to the level of flooding likely to occur 

in each zone. This differential rate structure 

provides a significant financial incentive to locate 

buildings in less hazardous zones or to increase 

buildings' flood safety by elevating them higher 

than the NFIP's minimum elevations. 

5 
1····-·~-

1 

I 

GULF OF MEXICO 

ZONE C 

Figure 1.1. Flood Insurance Rate Map 

ON POST-TYPE FOUNDATION 

A Zones V Zones 

bottom of 

lowest 

structural 

member 

Figure 1.2. Elevation Requirements for PostType Foundations 

6 

It is thus vital to be aware of the NFIP rate structure, as well as local regulations, when siting and 

designing new development or substantial improvements to existing construction. This information 

can be obtained from local insurance agents, public 

officials, and regional FEMA offices. 

BASE FLOOD ELEVATIONS (BFE's), A ZONES, 

AND V ZONES 

The NFIP and related local and state regulations 

define likely flood levels on the basis of the "100-

year" flood, which is the flood that has a one 

percent chance of being equalled or exceeded 

during any given year. Over a 30-year period, there 

is at least a 26 percent chance that this "base" 

flood will occur. 

The base flood elevations (BFE's), or likely flooding levels, at different sites in a community during 

the 100-year flood are determined on the basis of 

historic records, climatic patterns, and hydrologic 

and hydraulic data. A community's BFE's are 

mapped on flood insurance rate maps (FIRM's), 

which are provided by FEMA for use by local 

floodplain managers and FEMA officials (see 

Figure 1.1). 

FIRM's generally show flood-prone areas as either 

A Zones or V Zones. Riverine flood-prone areas 

and coastal flood-prone areas subject to storm 

surges with velocity waves of less than three feet 

during the 100-year flood are generally classed as A 

Zones. FEMA's design standards (see Figures 1.2 

and 1.3) for A Zones call for the top of a building's 

lowest floor (including basements) to be elevated 

to or above the BFE. "Coastal high hazard areas" 

are shown on FIRM's as V Zones. The V Zone is 

the portion of the floodplain subject to storm 

surges with velocity waves of three feet or more 

during the 100-year flood. FEMA standards for 

V Zones require the lowest portion of the 

structural members supporting the lowest floor to 

be elevated on pilings or other columns to or above 

the BFE. In addition, the space below the lowest 

floor in a V Zone must not be used for human 
habitation and must be free of obstructions. 

NFIP requiremrnfs for A and\' Zones as of January 

1984 arc summarized in Figure 1.4. 

Note that FIRM's are based on a variety of assumptions about expected flood severity, development 

patterns, etc. The actual level of flooding from a 

100-year flood may be significantly greater. In 

addition, the "500-year" flood level, which would 

be significantly greater than the 100-year flood's, 

could conceivably occur once or even more often 

during a building's lifetime. These uncertainties 

are further reasons for locating buildings in less 

hazardous zones or elevating them higher than the 

NFIP's minimum elevations. 

ON SLAB FOUNDATION 

A Zones 

lowest floor 

Figure 1.3. Elevation Requirements for Slab Foundations 

BOTH A AND V ZONES (Numbered and Unnumbered) 

All structural components must be adequately connected and anchored to prevent flotation, collapse, or permanent 

lateral movement of the building during floods. 

Building materials and utility equipment must be resistant to flood damage . All machinery and equipment servicing 

the building must be elevated to or above the Base Flood Elevation (BFE), including furnaces, heat pumps, hot water 

heaters, air-conditioners, washers, dryers, refrigerators and similar appliances, elevator lift machinery, and electrical 

junction and circuit breaker boxes. 

Any space designed for human habitation must be elevated to or above the BFE, including bedroom; bathroom; kitchen; dining, living, family, and recreation room; and office, professional studio, and commercial occupancy. 

Uses permitted in spaces below the BFE are vehicular parking, limited storage, and building access (stairs, stairwells, 

and elevator shafts only, subject to design requirements described below for walls). 

A ZONES (A1-A30) 

Buildings must be elevated such that the lowest floor (including basement) is elevated to or above the BFE on fill, 

posts, piers, columns, or extended walls. 

Where fully enclosed space exists below the BFE, walls must be designed to minimize buildup of flood loads by 

allowing water to automatically enter, flow through (in higher velocity flooding), and drain from the enclosed area. 

For low velocity conditions, vents, louvers, or valves can be used to equalize flood levels inside and outside enclosed 

spaces. For high velocity conditions, breakaway walls (see below) or permanent openings shou ld be used. 

V ZONES (V1-V30) 

Buildings must be elevated on pilings or columns such that the bottom of the structural member supporting the lowest 

floor is elevated to or above the BF E. 

Build ings must be certified by a registered professional architect or engineer to be securely fastened to adequately 

anchored pilings or columns to withstand velocity flow and wave wash. 

Space below the lowest floor must be free of obstruction or enclosed with breakaway walls (i.e., walls designed and 

constructed to collapse under velocity flow conditions without jeopardizing the building's structural support. 

Fill may not be used for structural support. 

No construction is allowed seaward of the mean high tide line. 

Figure 1-4. Key Floodplain Requirements of the National Flood Insurance Program as of January 1984. 

7 
SITE ANALYSIS AND DESIGN 
Site Selection and Analysis 

SITE SELECTION 

Whenever possible, site selection should avoid 

flood-prone areas. If this is not possible it should 

be recognized that the risk and severity of flooding 

generally decreases with the distance from the 

river channel or from coastal waters. However, this 

is not always the case, so it is important to check 

the level of expected floods in relation to the 

proposed site. If the base flood elevation (BFE) 

has not been determined, it would be wise to consult local flood history data before making a final 

site selection. 

The regulations of the National Flood Insurance 

Program ( FIP) specifically prohibit building or 

landfill in a floodway, if such has been designated, 

if the results would obstruct the flow of flood 

waters and thereby increase flood heights. 

Similarly, building in a coastal high hazard area 

is also not permitted unless the structure is landward of the mean high tide level. 

Development should be diverted away from 

identified mudslide or erosion-prone areas. Only 

where site and soil investigation and proposed construction standards assure complete safety for 

future residents should such sites be considered. 

Overall, customary site selection criteria should be 

used to evaluate the suitability of a site. Drainage, height of the water table, soil and rock formations, topography, water supply, and sewage 

disposal capability should be considered along 

with economic and planning criteria such as 

cost, access, and compatible land use. 

SITE ANALYSIS 

The site elements of primary importance for 

analyzing an elevated residential project are 

flooding, soil, and wind characteristics. 

9 
Figure 2.1. Hydrostatic Forces 

Figure 2.2. Hydrodynamic Forces 

10 

Flooding Characteristics 

Floodwaters impose hydrostatic forces and hydrodynamic forces. Hydrostatic forces result from the 

static mass of water at any point of flood water 

contact with a structure. They are equal in all 

directions and always act perpendicular to the 

surface on which they are applied. Hydrostatic 

loads can act vertically on structural members 

such as floors and decks, and can act laterally on 

upright structural members such as walls, piers, and 

foundations (see Figure 2.1). 

Hydrodynamic forces result from the flow of 

flood water around a structure, including a drag 

effect along the sides of the structure and eddies 

or negative pressures on the structure's downstream side (Figure 2.2). These are more common 

in flash floods, coastal floods, and when flood 

water is wind-driven. 

A number of hydrologic factors must be evaluated 

in the design of an elevated structure: 

DPpth of expected flooding and, in coastal 

areas, height of wave crests, which will determine the required elevation of a building and 

the hydrostatic forces to be expected. 

Frequency of flooding, which is the amount 

of time between occurences of damaging 

floods. This will have an important influence on site selection. 

Duration of flooding, which affects the length 

of time a building may be inaccessible, as well 

as the saturation of soils and building materials. 

Velocity of flood waters and waves, which 

influences both horizontal hydrodynamic 

loads on building elements exposed to the 

water and debris impact loads from waterborne objects. 
Rate of rise, which indicates how rapidly 

water depth increases during flooding. This 

determines warning time before a flood, 

which will influence the need for access and 

egress routes elevated above floodwaters and 

whether valuable possessions can be kept 

underneath the structure and moved only 

when flooding is imminent. Flash flood areas 

often receive little or no warning of flooding. 

Another hydrologic factor is ice, which in northern 

climates can cause serious damage to structures if 

flooding should occur during the spring before the 

ice melts. In some cases winddriven ice or ice jams 

have completely demolished bridges, homes, and 

businesses, snapping large trees and pushing 

buildings completely off their foundations. 

Floating debris can be equally dangerous in this 

regard. There is little that can be done to avoid 

these phenomena short of avoiding sites where 

they are especially likely to occur. 

Hydrologic data concerning a site, including both 

technical studies and historical records, can often 

be provided by the local or state government and 

federal agencies such as the Federal Emergency 

Management Agency, the U.S. Army Corps of 

Engineers, and the U.S. Geological Survey. If 

needed information is not available from these 

sources, engineers familiar with hydrologic and 

hydraulic techniques can analyze the flooding 

potential. 

Soil Characteristics 

The characteristics of the soil in a flood area-soil 

bearing capacity, for example-can be important 

in determining an appropriate design. Highly 

erodable soil would not be desirable for use as fill 

in elevating a structure in a high velocity area 

unless the fill is properly protected. When erosion 

removes soils supporting building foundations, the 

foundations can fail (see Figure 2.3). 

Figure 2.3. Erosion Caused This 

Foundation to Collapse. 

11 
Figure 2.4. Wind Forces 

12 

Soil data can be obtained from soil survey reports 

published by the Soil Conservation Service of the 

U.S. Department of Agriculture. It may be 

desirable to consult a qualified soils engineer 

familiar with the soils at the site. 

Large-scale topographic maps of ground elevations 

can be used to determine natural drainage patterns, 

mudslide- and erosion-prone areas, and the feasibility of using fill. Local or state agencies or the U.S. 

Geological Survey can often supply this information. Detailed topographic maps (2-foot contour 

intervals or less) must usually be developed as part 

of the site-specific investigation and are necessary 

for developing grading and landscaping plans. 

Winds 

Buildings elevated off the ground can be more 

vulnerable than other buildings to wind (see Figure 

2.4). Data on expected winds appear in building 

codes and Standard A58. l of the American 

National Standards Institute. Design and Construction Manual for Residential Buildings in 

Coastal High Hazard Areas, cited in the Preface, 

discusses designing for wind in coastal areas. 
Site Design 

Site design for elevated structures should follow 

standard planning criteria applicable to any site 

work. Typical factors to consider include slopes, 

natural grades, drainage, vegetation, orientation, 

zoning, and location of surrounding buildings, as 

well as expected direction of flood flow. 

SITE FLOODING CHARACTERISTICS 

Buildings should be positioned in the area of the 

site that will experience the lowest flood levels and 

velocities. In coastal areas, this means as far back 

from the beach as possible and, if feasible, behind 

dunes. Buildings should be oriented to present 

their smallest cross-sections to the flow of 

floodwater. This reduces the surface area on which 

flood and storm forces can act. 

When multiple buildings are to be placed on the 

same site, the objective of site design is the same as 

for an individual building. One approach is to 

disperse buildings throughout the site, applying 

the criteria discussed above to each building. An 

alternative to such dispersal, when local zoning 

ordinances allow (e.g., a planned unit development 

ordinance), is to group buildings in clusters on the 

safest parts of the site, leaving the more vulnerable 

areas open. This approach not only reduces flood 

damage but can also allow greater flexibility in 

protecting the natural features on the site (see 

Figure 2.5). 

Adjacent buildings, bulkheads, or other structures 

should also be considered in site layout, both for 

their potential to screen and divert flood waters 

and water-borne debris and for their potential to 

become floating debris themselves. Bulkheads 

also tend to divert flood waters around their ends, 

adversely affecting adjacent sites. 

~~ I 

-· 

Figu re 2.5. Planned Unit Development 

Ordinances Allow Greater Flexibility in 

Site Design 

13 
A~fA M0~1 Aff~1E'!7 f>Y 

IMPA.Cf Of !7?0~ 5 ANI? 

1uesuL.f:Nl~ 

lKANGif SHm 10 ~!:DUlf: 

tl':S!S1ANG!' 10 fl.000- ~-­

WAIE?f. 

Figure 2.6. Site Design to Reduce Flood Hazards 

14 

ACCESS AND EGRESS 

Access to and egress from a building can be facilitated by locating parking and driveways- as well as 

the building-in the area of a site least likely to be 

flooded. Access and egress are important during 

flooding to ensure that building occupants can 

evacuate and that police and fire protection and 

other critical services can continue to be provided. 

12.f"-Of.lff\Ji 61f.UCfU~E- 10 

ut:'Ult:- IURBU!..ffileLANP5lAl'IN6o Hf'U'5 iO 

DE'fi.fCT !/Efl~ S 
In new developments, roads should be located 

to approach buildings from the direction away 

from the floodplain, so that access roads will 

be less likely to be blocked by flood waters and 

debris (Figure 2. 7). To reduce potential erosion, 

siltation, and runoff problems, roads should not 

disrupt drainage patterns, and road crossings 

should have adequate bridge openings and culverts 

to permit the unimpeded flow of water. If roads 

are to be raised, the slope of embankments should 

be minimized and open faces stabilized with 

ground cover or terracing. 

VEGETATION 

Vegetation aids in slowing the rate of storm water 

runoff by holding wat er, thus allowing it to filter 

into the ground or evaporate gradually. In 

addition, vegetation helps prevent erosion and 

sedimentation from flooding. Natural vegetation 

should be retained wherever practical, and new 

plantings should be introduced in locations that 

will be most affected by runoff. 

Crushed stone can be used to control erosion under 

low-lying elevated structures and other locations 

where vegetation is difficult to maintain. 

Larger bushes and trees can be sited to deflect 

floating debris away from elevated foundations. 

Landscaping can also be used to screen elevated 

foundations from view. Trees, plantings, fencing, 

etc., can all provide this dual function of utility 

and aesthetics. 

FLOOD WATER DRAINAGE AND STORAGE 

Good site drainage in riverine areas allows flood 

waters to recede from a site without eroding it or 

leaving standing water that causes damage to 

structural elements or health hazards from stagnant 

water. 

Water enters a riverine site either from precipitation or as surface runoff from upstream portions of 

the watershed. What happens to this water can be 

a major determinant of the degree of flooding and 

Figure 2.7. Improperly Sited Streets Can Block 

Emergency Egress and Access 

15 
16 

the amount of flood damage. Site development 

that increases the volume of storm water runoff 

can increase flooding levels. Ideally, runoff rates 

after development should not exceed the rates 

before development. 

Site design should work to protect the individual 

site as well as to minimize increased flood levels 

elsewhere. A number of key factors such as the 

amount of nonporous surface and the amount of 

on-site surface water storage can in part determine 

the ability of a site to absorb water. Land-use 

regulations in some communities require developers to defray part of the cost of developing 

regional water retention sites to offset the effects 

of development. 

On the site, open channels can be used both to 

divert water away from erodable areas, such as 

short steep slopes, and to collect and transport 

water runoff to larger drainage courses. Channels 

with grass cover are appropriate where the channel 

gradient and consequent water velocity are low; 

they then serve as percolation trenches by allowing 

gradual infiltration while water is being transported. Where vegetation cannot be established, 

concrete and asphalt paving or riprap can be used 

as channel linings. However, such linings can 

increase the velocity of runoff, and consideration 

should be given to velocity checks to control the 

rate of flow. 

On some sites it may be possible to use fill 

material-from either on-site or off-site-to 

improve drainage and control runoff. Special consideration should be given to soil conditions and 

slope stability, as well as flood water velocities and 

duration, to avoid erosion during flooding. When 

restructuring topography, exposed cut and fill 

slopes, as well as borrow and stockpile areas, 

should be protected. Runoff should be diverted 

from the face of slopes, and slopes should be 

stabilized with ground cover or retaining walls. 
DUNE PROTECTION 

Dunes provide a natural shoreline defense against 

storm surges and waves. Most coastal communities require that construction be behind the 

primary dune and that dunes not be cut or 

breached by site features such as walkways or 

beach access roads. Cross-over walkways should 

be provided (see Figure 2.8). 

Existing dunes should be maintained through 

vegetation and sand fencing, which limit wind 

losses and promote further dune growth. If no 

dunes exist and the beach is sufficiently wide, 

successive tiers of sand fencing can induce dune 

formation; some communities require this before 

a residence can be built. 

I 

I I 

~, 

, 

I 

I 

I 

I 

I I 

Figure 2.8. Dune Access 

17 
ARCHITECTURAL DESIGN EXAMPLES 

-
Many of the twentieth century's most important 

buildings have been elevated residential structures. 

The rise of modem architecture, inspired by the 

raised houses of Le Corbusier in the 1920s, was 

made possible by structural innovations. The Villa 

Savoie at Poissy (1929), for example, is lifted 

above the ground on pilotis, freeing the lower level 

for parking and affording a spatial continuity with 

the landscape (Figures 3.1 and 3. 2). In his 

Towards A New Architecture Le Corbusier was 

exultant about the possibilities of elevated design: 

The house on columns! The house used to 

be sunk in the ground : dark and often humid 

rooms. Reinforced concrete offe rs us the 

columns. The house is in the air, above the 

ground ; the garden passes under the house. 

Figure 3.2 

Figure 3.1 

19 
Figure 3.3 

20 

Since the Villa Savoie was centered on a dome-like 

rise in a large pasture, Corbusier did not need to 

concern himself with the problem of flooding. 

Other masters of modern architecture, however, 

have used the principles of elevated residential 

design to create aesthetically satisfying and functionally sound responses to hazardous flood conditions. 

Mies van der Rohe's Farnsworth House (1950), 

considered one of the great icons of modern architecture, owes at least some of its appearance to its 

flood-prone site (Figures 3.3 and 3.4). Built along 

the Fox River in rural Illinois, the house was 

designed to accommodate a body of water that 

overflows its banks each spring. Mies' solution to 

the problem was to raise the plane of the first floor 

above the flood level, creating his first clear-span 

building. The resulting structure seems to float 

above its site. 

Good design and good flood protection must continue to be treated together. Good design entails 

effective use of the site and careful consideration 

of the needs of the surrounding neighborhood and 

community. The best houses provide a clear 

transition from ground to dwelling, integrating the 

foundation with the rest of the structure. Creative 

landscaping with trees, shrubs, and fences can 

enhance the appearance of elevated structures by 

softening the effect of potentially harsh or barren 
exposures. Inventive landscaping also helps to 

control erosion and protect Lhe dwelling from the 

impact of debris and high velocity flooding. 

Effective use of terracing and level changes can 

help achieve continuity with the surrounding areas 

and, equally important, provide a sense of variety 

by indicating the different functions that occur 

simultaneously on a single site. 

Such site considerations arc but one part of a total 

elevated design scheme. The following examples 

are concerned with some of the many other 

important factors involved in floodproof design. 

Figure 3.4 

21 
Figure 3.5 

22 

Design Studies 

The f'ollm\ ing design studies wnc dn-clopcd L) a 

number of archiLccLural l'irrns and architectural 

sc hools using th<' information presented in this 

manual. 

LJRIOGEPORT, CONNECTICUT 

\\ iLh an d<'' ation ff<JU irenwn l of l 0 feet abu\ c 

grade, the architect ... ha><' csi~nt d tlw:-c lu:-..ur: 

to\\ nlww;cs around a raised ce ntral social dcc h. 

(Fi~urcs :~ . .>and :.3.6). Parh.i111! is local ed IH'11caL11 

the deck. \cccss lo tlw deck and lo the tow11 -

hous1':- i::- pro' idcd b) ::- lair,., and a timber ramp. 

T!w ra111p pro' ides acl'css for t'liildrcn . the handicappt·d and thC' cf dnl:. D11ri11 μ, lime::- of flooding. 

Lh(' ramp can abo L<' used for dri' inμ, au lornohiks 

and rcsc111· \chicles up tlic deck lc\C'l. Steel girders 

resting on corH·rcl<' piers support boLh Lhc social 

deck and the townho11 se::; (Figure' 3. 7). The <leek 

has a do11blt' floor construction , allowing a1l<lcd 

insula tio11 an <l pro Lee Lin g utili l) se rvices. 

i. 

~ l 

I 
t. 

Flood Level 

Figure 3.7 

Concrete 

Pier 

Access Ramp 

Figure 3.6 

Attick Storage 

t 

---~-=-=-

:• 

' , 

. 

23 
24 

CHARLESTOWN AND NEWPORT, RHODE 

ISLAND 

The architect here has chosen two case study 

areas, Newport and Charlestown, Rhode Island, 

with distinctly different cultural and natural 

conditions that affect flood design considerations. 

Newport is a compact commercial and recreation 

center that has many residences along the water's 

edge. The area studied in Newport is a protected 

harbor with access from Rhode Island Sound into 

Narragansett Bay. The portion of Charlestown 

that is the second study area is a beachfront area 

with vacation house development. Most development is in a coastal A Zone. Both study areas have 

high development pressures. 

In both areas historic, scenic and community 

values influence the design of elevated structures. 

In Newport the close proximity of a Historic 

District injects height, bulk, material, and size 

considerations into any planned development. 

(In the case of historic structures in floodplains 

listed on the National Register of Historic Places or 

a state inventory of hi

storic places, restoration may 

be accomplished without 

eleva ling thr first floor 

through a variance procedure.) Similaily in 

Charlestown, simply elevating stru

ctures, witho11t 

regard for the natural environment, could produce 

ungainly and visually distracting elements. It 

is 

necessary in flood area design to not only meet 

engineering requirements, but to also be cognizant of the visual effect such design will have on 

the prevailing character of the area. 

Charlestown 

An inventory of critical natural factors was made 

to determine how and where development should 

take place in the Charlestown floodplain. As a 

result, specific land area within the floodplain was 

deemed acceptable for residential development. 

The analysis then proceeded to the evaluation of 

methods of elevation appropriate to the development area. 
Base Flood Level 

Figure 3.8 

For numerous functional and aesthetic reasons, 

earthfill with heavy stone revetment was chosen 

as the method for elevating residential structures 

in Charlestown (Figure 3.8). The homes were 

clustered to keep down the cost of fill and because 

the land available for safe building in the floodplain was limited (Figure 3. 9). A small-scale, 

I 

I 

I 

I 

\ 

Figure 3.9 

\ 

/ 

·.:. / 

25 
26 

single-family scheme was chosen for visual continuity with earlier buildings (Figure 3.10). All 

houses, a small amount of private space, and all 

utilities are located on the common filled area. 

Low intensity land uses such as parking, road and 

driveways, playgrounds, etc., are located on the 

lower surrounding areas. Ramps and steps are used 

to accommodate the height differences from 

parking to the finished first floor. 
Newport 

Development in the wharf area in Newport, Rhode 

Island, is structured by a combination of natural 

and cultural conditions. Although separated from 

the older historic areas of Newport by a highway, 

its proximity to them requires special consideration of height, materials, and size. It is in a special 

flood hazard zone, yet its water's edge location 

makes it visually attractive. Changes in the use of 

the wharf area and its new relationship with neighboring areas have resulted in an expansion of commercial and residential development. The low 

height above sea level means that new structures 

would have to be raised approximately to the level 

of the highway to comply with local flood regulations. For the restoration of historic buildings, 

however, there is no need to elevate the first floor 

as long as a variance is obtained. 

Analysis indicated that the optimal solution would 

be a combination of elevation techniques, because 

different zones in the wharf area are suited to different elevation strategies (Figures 3.11 to 3.13). 

Base Flood 7 ' 

Figure 3.11 

Figure 3.12 

27 
.. 

'. . 

· ' 

\ 

" 

~- ,. 

1' 

/ ~ 

~ 

,f;. ~ 

t ·" ,/ 

·t ,_ 

~ 

• ' .,. '. 

/ a 'ii. -· 

Figure 3.13 

28 
In the area farthest from the water, earth fill offers 

flood protection and a gradual level change from 

that of the highway. A transitional middle section 

could combine berming with raised structures. 

Level changes can be integrated by linking 

extended decks with ramps and stairs. In the area 

closest to the water, raised structures would not 

alter the water-to-land relationship or block views. 

Commercial uses are most likely to locate in the 

filled area, where first floor spaces are usable. 

Residential, restaurant, and small office uses are 

more suitable to the raised structures, which afford 

increased privacy and better views. 

Spaces under and between the new buildings 

can be used for pedestrian malls and thus reinforce the tourist and commercial uses of the 

area. Decks, balconies and trellises can connect 

different building levels. Utilities for the raised 

structures could be run beneath these raised 

decks and trellises and then into the fill, being 

protected from flood damage. This manipulation 

of the spaces and level changes created by flood 

protection enhances the visual intricacy and human 

scale of the wharf. 

29 
Figure 3.14 

30 

I 

/ 

SAN FRANCISCO, CALIFORNIA 

Pacific coast flooding is generally associated with 

high seas and rains. Ocean storms accompanied by 

high winds have caused considerable erosion and 

damage to beach and coastal floodplain property. 

Inland rain storms, on the other hand, falling on 

the mountainous terrain cause major canyon and 

valley flooding. Both coastal and canyon flooding 

are dangerous high-velocity situations. Slow-rising 

and lower-velocity conditions occur on coastal 

marshes and low-lying riverbeds. 

The architect has developed several very interesting 

and distinctive residential concepts for single- and 

multi-family housing. The use of landscaping, 

fences, and exterior decks minimizes the elevated 

appearance of the structures while providing functional visual highlights. Structurally the two 

concepts are quite different. Although both 

concepts use wood posts, the single-family 

residence uses a two-way structural grid supporting 

prefabricated housing units, while the multi-family 

structure is conventional wood frame construction 

built upon a wood-post-supported platform. 

Parking for both residential concepts is under the 

structure. 

!' ~--, \ .. --.../ ,_ '\ 

' .., 
Single-Family Residential Concept 

A two-way wood post structural grid supports the 

living units at levels above the base flood and serves 

to organize and unify the various units with 

minimal impact on the ecology of the area (Figures 

3.14 to 3.16). A seven-foot clearance beneath the 

horizontal structural members allows for parking, 

storage, and sheltered recreation space separated 

from and below the living units. The reduced land 

coverage of this design is in keeping with the 

architect's concern for efficient land use. Shared 

facilities, clustering buildings, etc., further give 

these houses a unique identity and sense of 

community. Within the prescribed vernacular of 

poles, decks, railings, and fences, architectural 

variety with continuity is achieved. The fences are 

strapped together to prevent pieces from floating 

away if damaged during a flood. Water heater and 

furnace and air conditioning equipment are located 

18 inches above base flood level with all ductwork 

in second floor or attic space. 

Figure 3.15 

31 
Base Flood Level 

Water Heater 

50 gal. Emer. 

Supply (min.) ---"'--l....!--~ 

All Ulilities ana 

------+---Drains Above the 

Base F load Level 

-- ,__,,.... r-""-~~~~~~+M~+=-~~~~...J..L...., ----

Figure 3.1 6 

32 

Utilities Vault 

Gas 

Electric 

Telephone ,_ ,---, ____ "\ 

0 0 l \.::. ____ J 

Septic 

Tank 

Ii 
Multi-Family Residential Concept 

To reduce costs, the architects have designed a 

conventional wood frame structure built upon a 

wood post platform (Figures 3.17 and 3.18). 

Raising the first floor to at least eight feet above 

grade provides an opportunity to put parking 

under the building. This reduces the area of the 

sit e that has to be built upon and places cars closer 

to apartments. However, parking under the 

structure requires fire separation. Exposed 

entrance stairs and fencing minimize the elevated 

appearance of the structure while providing visual 

variety and privacy. 

Figure 3.18 

Figure 3.17 

33 
J 

1 

t l 

. 

~t . -. Stream Flow -t> , !"- '\,r" !' ... ~ ,... ~ 

I . . . • - ;~ c l .,) .f ~· J • ,/ '"-

;. ~ ....... ;,· ..,, -- ,,, ~ ..__. . ~ - ,, ,, J .... • -'I 

I • I , . 

, I 7 

'\..... -· 

~-...._ .L 

[ 

L 

~I I I 

I 

-· 

ti= ! I ' 

TI 

~· 

.\ j· 

' • ' 

I 

- -~ 

t J ' - · l 

Figure3.19 

Figure 3.20 

34 

CHICAGO, ILLINOIS 

Flooding in the Midwest is of two types: riverine 

and lake flooding. The characteristics of both are 

usually slow rise and low velocity. However, flash 

flooding and lake shore scouring can and do occur . 

The Great Lakes area, more specifically, the 

Wisconsin, New York, Ohio, and Michigan lake 

shores, have experienced growing problems of lake 

flooding and slow erosion caused by the increasing 

occurrence of high waters and high winds. 

Garden Apartment Concept 

Although elevated eight fe et and constructed of 

reinforced concrete block, this rowhou se does not 

appear to be designed for a potential flood condition (Figures 3.19 and 3.20). The covered parking 

and entrance level is handsomely integrated with 

the above living levels by reinforced concrete block 

walls that organize the entire structure. The walls 

are constructed parallel to the direction of possible 

water flow. Unfortunately, the architect enclosed 

the stairway-entranceway, with a potentially 

serious effect on flood insurance rates. 
Aesthetic Considerations 

There is a common misconception than an elevated 

residential structure will be inherently unattractive-a box on stilts (Figure 3.21). This is not true. 

Elevated structures offer challenging design opportunities to be aesthetically appealing as well as 

functionally sound. 

Residential development requires a significant 

financial investment, and if it is aesthetically 

appealing it contributes lo the economic value of 

the area, both for the owner and for the community as a whole. All communities have both 

positive and negative examples of this. Good 

quality tends to foster better quality, and poor 

conditions lead to even poorer conditions. 

Appealing design can thus be an important element 

of making the most of our limited development 

resources. 

Figure 3.21 

35 
Figure 3.22 

Figure 3.23 

36 

SITE DESIGN 

Integration of development and site should be 

done so that the two complement each other. A 

careful site analysis can give many clues to the best 

design of the building for its relation to topography, location and orientation, and location of 

fenestration (views, etc.), entrys, and parking. 

Landscaping-creative use of trees, shrubs, fences, 

walls, etc.-serves two purposes. It integrates the 

elevated portion of the development with its 

surroundings and, at the same time, helps control 

erosion and protect the dwelling from the impact 

of debris and fast-moving water (Figures 3.22 and 

3.23). 

The relationship and compatibility of development 

with the surrounding neighborhood and community should be considered in order to give a 

sense of continuity with the surrounding areas, 

rather than an unattractive "hodge-podge" of unrelated development. · 

Terracing and level changes can be used to give a 

sense of variety and to identify different uses, as 

well as to integrate building with site. 

~---!)UILOlk!Gi '?lfVA1fl7 6Y 

511'.UC:IUl<.AJ..- l-'lf:'ANS 
BUILDING DESIGN 

The integration of the foundation with the site and 

the building is perhaps the most important aesthetic challenge when designing elevated structures. 

Many elevated structures give the impression that 

the support foundations are treated separately 

from the building and the site, giving the impression of a building set on spindly legs (figure 3.24). 

It is essential to recognize that the foundation is an 

integral part of a building, rather than only "something to set the building on." A well-designed 

elevated residence should provide a smooth transition from ground to dwelling, with the foundation 

integrated with and complementary to the building 

itself. 

Other special considerations when designing 

elevated residences include the design of any 

needed stairs and the use of the areas under the 

structure. More general considerations include the 

shape and form of the building (configuration, 

shape of roof, etc.), textures and color of building 

materials, the use and treatment of balconies, 

terraces, railings, windows, shutters, screens, and 

entries, and the arrangement of interior spaces. 

Figure 3.24 

37 
Figure 3.25. This wood structure successfully uses 

the same material throughout the buildingfoundation, structure, treatment of railings, wall, 

and roof material, as well as connection and 

anchorage details. The design honestly expresses 

the structure, foundations and other building 

elements. While it is obvious this is an elevated 

structure, it still feels very much a part of the site. 

The foundation members are also integrated well 

with the building itself (see also Figures 3.54 to 

3.57). 

Figure 3.26. This is an example of integrating the 

site, the building, and the fou ndation so they relate 

well to each other. Th is foundation appears to be 

part of the building rather t han sti lts holding it up. 

It shows how a modest, simpl y designed bu ilding 

can also be very aestheticall y appealing through the 

use of natural materials and int eresting treatment of fenestration and lighti ng f ixtures. Simple 

but well-thought-out landscaping ti es the bu ilding 

effectively to the site. 

Figure 3. 27. This is a good example of how the configuration of a cluster layout can contribute to 

functional advantage as well as visual appeal. The sawtooth arrangement allows for two sides of each 

unit t o have access/ view to the ocean. This form also breaks up the long, contin uous (and often monotonous) wall approach, thus adding variety and interest. With th is configuration t he materials, treatment 

and form of the units can be simple but still attractive. 

38 
Figures 3.28 to 3.29. This is an excellent example of cluster-type elevated residential development. 

The development is well-integrated with the site; the various levels seem to roll over and blend with the 

dune. The vegetation and simple fencing add much to this marriage. The individual units also relate very 

well to each other, providing a good example of an overall development's being "more than the sum of 

its parts." The individual units provide the individual amenities-privacy, plan layout, etc.-while still 

being a part of a comprehensive whole with a strong sense of community. The form, scale and character 

of the development are also excellent. The sloped roofs, the balcony treatment, use of levels, and the 

articulation of the other elements add variety and a character that complements the site and overall 

development. The use of materials-color, texture, scale- also contributes to the design's appeal (see 

also Figures 3.63 to 3. 70). 

Figure 3.30. The exterior treatment of this development adds visual appeal to a development that 

could otherwise be quite monotonous. The 

exterior colored panels with white structure and 

coordinated interior panels provide interest, 

as does the simple treatment of balconies with a 

variety of planes, panels, railing and roof trellis 

members. 

39 
Figure 3.31. This is a good example of how a simple structural grid infrastructure can be used as a basis 

for a relatively modest, well-designed and visually appealing residence. The plan is simple, developed 

around the columns, but provides a very livable, interesting and functional space. The cantilevered 

balconies also add interest as well as defined exterior areas. The roof shape contributes to a spacious 

interior that makes the house feel larger than it really is, allows in natural light through the transom 

windows, and through its form adds much to the overall aesthetic appeal of the design (see also Figures 3.40 through 3.45). 

40 
Figure 3.32. The diagonal battens used to enclose 

the stairwells for protection provide an aesthetically appealing screen-textural affect. The colored 

awnings also add a necessary highlight to an 

otherwise colorless exterior. Notice also the pole 

light fixture. 

Figure 3.33. Passersby have to look very carefully 

to see that this development is actually elevated. 

Good use of landscaping and building form 

includes attached and detached units. 

Figure 3.34. This structure uses a mixture of materials, texture and color very successfully and provides 

a variety of form for visual appeal. The space under the building remains open and light through a 

combination of white unobstructed walls and piers, landscaping, and layout relative to other buildings. 

A human scale is accomplished by breaking the building up into different heights and sections, rather 

than an imposing three-story box, as is often done (see also Figures 3.58 through 3.62). 

41 
42 

Figures 3.35 and 3.36. This is a good example of 

using a variety of shapes and forms (wall surfaces, 

planes, balconies, etc.) as well as wall treatments 

(materials, texture, color) to create a sense of 

variety essential for an aesthetically pleasing 

development. 
Figure 3.37. In the interior, color, scale, texture, and floor arrangement must be given careful attention 

(see also Figures 3.40 through 3.45). 

43 
Figures 3.38 and 3.39. Well-designed elevated residential structures can take many forms and styles. The 

principles in this manual are applicable to any style. 

44 
Recent Design Examples 

The projects in this section are some of the best 

design examples discovered in a state-of-the-art 

survey conducted as part of the development of 

this manual. While these examples range from a 

single-family detached unit to a multi-family high 

rise, there appears to be a clear trend toward higher 

density, cluster-type development. This is 

probably due to higher land values and the experience gained from major floods over the last couple 

of decades. This is a promising trend that encourages professional design involvement in residential 

structures and leads to a more comprehensive 

approach to elevated residential and other development in flood-pron e areas. 

Virtually all the recent design ex amples that were 

submitted in response to our survey were coastal, 

as opposed to riverine, projects. This suggests that 

the state of the art is being set for the most part 

in coastal areas, especially in the higher-use resort 

areas. It should be noted, however, that what is 

being done in coastal areas can often be applied 

successfully in riverine, lake, and other floodprone areas as well. 

45 
Figure 3.40 

46 

THE LOGAN HOUSE 

Tampa, Florida 

Architects: Rowe Holmes Barnett 

Architects, Inc., Tampa, Florida 

The Logan House (Figures 3.40 to 3.45), located 

adjacent to a federally protected tidal estuary near 

Tampa, Florida, exemplifies a skillful blend of 

flood protection and energy conservation. The 

natural site of the house, only four feet above sea 

level, suggested the possibility of flooding. Flood 

regulations required Rowe Holmes Associates to 

elevate the structure an additional six feet. They 

chose, however, to raise the house almost eight feet 

to be able to use the first level as both a carport 

and protected outdoor living area. 

The 2,000-square-foot structure is designed in 

what is known in Southern vernacular as the 

"dog trot" style, incorporating a long breezeway/ventilating device covered with the same 

roof as the house but open on the sides. The 

wood frame house is supported on 10-inch-square 

pressure-treated pine poles augered deep into the 

soil to withstand hurricane forces common to this 

area of the country. The floor serves as a horizontal diaphragm to provide the pole structure additional rigidity. 

Several of the features that protect the Logan 

House from flood damage also promote energy 

conservation. For example, elevating the structure, 

the major flood protection strategy, helps draw 

cool (lower) air up and through the house. 

A central utility core-unfortunately located on 

the lower level where it is vulnerable to storm 

forces-is serviced by a stairway, allowing protected access to the carport and outdoor space . 
kitchen dining living 

' ' 

~- p~ 

, L •:i -------e- b• ro 'il ~- - . ---------------

Figure 3.41 living level 

0 ' 

~.- ·--~ ·· ·. ' .......... 

. 

. ~ ~ ~ - . 

.,,. 

[ 

Figure 3.42 

Figure 3.43 

'. ' I f! SS 

section 

south elevation 

.T 

47 
Figure 3.44 . 

Figure 3.45 

48 
SUMMERWOOD ON THE SOUND 

Old Saybrook, Connecticut 

Architects: Zane Yost & Associates, Inc., 

Bridgeport, Connecticut 

Summerwood on the Sound (Figures 3.46 to 3.50), 

a 76-unit cluster development, won a 1979 design 

award for architects Zane Yost & Associates, Inc. 

The development is built on a peninsula tidal 

estuary protected by a barrier beach. 

Equal in importance to protecting the buildings 

from flooding was the preservation of the salt 

marsh ecological environment. For this reason, 

the architects chose to locate the units only along 

the natural contours of the 30-acre site. For 

further protection of land as well as buildings, 

the structures are elevated above flood level, 

topping crawl spaces with internal drains to permit Figure 3.46 

flood water to pass in and out. The wood frame 

structures are covered with horizontal siding and 

use picket fences to soften the effect of the raised 

structures. Redwood stairs and decks adorn the 

water side of the units. 

Although the overall density on the site is low 

(2.5 units/ acre), the clustering of the units makes 

for a comfortable neighborhood scale. 

Figure 3.47 

49 
Figure 3.48 

Figure 3.49 

50 

SITE PLAN 

Front Elevation 

Rear Elevation 

r• LL!, 

;;;--to 100 
51 
Figure 3.51 

52 

THE BREAKERS CONDOMINIUM 

Redington Beach, Florida 

Architect: Rowe Holmes Barnett 

Architects, Inc., Tampa, Florida 

The Breakers Condominium in Redington Beach, 

Florida (Figures 3.51 to 3.53), is composed of 38 

two-bedroom units oriented to take advantage of a 

spectacular ocean view. Using a "double saw-tooth 

stepback" plan, the architects oriented the 

buildings around a communal atrium garden, 

creating a pleasant internal garden on an otherwise 

flat and treeless site. 

The 1,200-square-foot units, completed in 1973, 

are composed of exterior masonry walls and flatslab and column construction to reach a height of 

12 feet above sea level, which is the 100-year 

high flood elevation. A heavy Spanish stucco 

finish and louvered privacy screens made of redwood soften the effect of the typical condominium 

construction. 

All the units share the atrium garden on either 

their entry or walkway sides. The units also share 

a game room and beachside pool and deck. 
site and first floor plan ~ 

Figure 3.52 

longitudinal section 

Figure 3.53 

53 
Figure 3.54 

SECTION 

Figure 3.55 

54 

..... 

0 ' 

CAMPUS-BY-THE-SEA FACILITY 

Catalina Island, California 

Architect: Leonard E. Lincoln, AIA, 

Palo Alto, California 

Catalina Island (Figures 3.54 to 3.57), developed as 

a resort center in the 1920s, is located 21 miles off 

the coast of southern California. Many of the 

original structures built on the island were 

destroyed by flash floods in 1980 when storm 

waters cascading down a series of ravines swept 

them off their concrete pier foundations. 

The newly replaced key facilities of Campus-bythe-Sea, a conference center, are no longer threatened by such flooding. For example, the new 

three-level dining complex makes use of poles that 

serve as both foundation and roof support for the 

7,000-square-foot structure. The structure is 

supported by 55 poles, ranging from 25 to 40 feet 

in length. These poles are set on concrete pads, 

which were poured at the base of 10-foot-deep 

caisson holes. The poles were specially pressuretreated to resist decay and termite attack. A 

preservative (pentachlorophenol) was carried by a 

low-viscosity petroleum gas, allowing for deep 

penetration through the sapwood into the 

heartwood. 

Several of the new two-unit cabins on the site have 

also used this kind of structure, and more similar 

construction is expected to take place in the 

near future. 
Figure 3.56 

==-·'·· 

• • 

• 

L '" ....... 

,.· / 

• 

FLOOR PLAN ..... 

0 ' 

Figure 3.57 

-·------·-.... --... ~ 1 

KITCHEN 

• 

DINING ROOM 

• • • 

II 

• 

• 

• • 

I 

I 

I 

• • • 

• • • 

DECK 

• • • 

• • • 

55 
Figure 3.58 

Figure 3.59 

56 

STARBOARD VILLAGE 

Pensacola Beach, Florida 

Architects: Davis & Associates, 

Architects & Planners, PA, 

Orlando, Florida 

Starboard Village (Figures 3.58 to 3.62) is a 

33-unit condominium project consisting of six 

low-rise buildings on the Gulf of Mexico. All the 

living areas are raised above grade, allowing parking 

at ground level. Each building is designed with a 

module using a one-story unit with two-story units 

above. All structures are concrete frame and slab 

systems, supported on concrete-piling with shear 

walls designed to withstand hurricane forces. 

Wood-accented stucco as the primary finish maintains a residential quality. The architects exercised 

special care in locating the air-conditioner units, 

mounting them under concrete stairs and on the 

underside of the second floor concrete slabs. 

Wood louvers then enclose the units. 

\ 
TYP. FLOOR PLAN 

Figure 3.60 

SECTION 

Figure 3.61 

-.-.-

0 5 1 0 1 5 

••• . ,. 

0 5 1 0 1 5 

57 
Figure 3.62 

58 
GULL POINT CONDOMINIUMS 

Perdido Key, Florida 

Architects: H. Shelby Dean-Richard H. Fox, 

Architects, Anniston, Alabama 

The design of this 16-unit condominium (Figures 

3.63 to 3. 70) on the Gulf of Mexico successfully 

integrates storm protection, energy conservation, 

function, and economics. 

The architects used pile construction to elevate 

the units several feet above the minimum required 

by the National Flood Insurance Program. This 

was done because analysis of the flood insurance 

premium rate structure showed that the added 

margin of safety from the additional elevation 

would qualify the units for significant savings in 

annual insurance costs. 

Figure 3.63 

59 
GULF OF MEX! 0 

w 

I f-

<t: W ~z z 

I

. X_J 0 

ow f- ococ ~ . ~o >-

I ~~ ~~ I : > _J : J_ ............. -----····•·'·•·······-··,,, . .-.,., .. .,, n•· -~·--········· ····.· ·· •· 1 

I 6 I 

I 

I 

i I 

3:1 

kl 

~r-

: 1 

I 

I 

t:; I :::;) 

"' 

~ UJ I zz 

ou _, I 

_J"' 

<t:U 

.... <t: I en"' 3: 

C3 ~ . ~ 

"""'"'""'~i;;;-.;..,--~:. --~ ~ 

--· __ GLJLF BEAC_H HIGHW,A.Y SR 292 (100.' R/w) ·--·-

SCALE 

=====================

SITE PLAN =- ----- 10 50 -

Figure 3.64 

60 

The huildings' exteriors are of cedar. The buildings 

were configured to reduce the impact of hurricane 

winds while maximizing views and privacy. At the 

same time, fenestration was placed to maximize 

natural ventilation. This and the use of insulated 

glass have reduced the need to use the units' airconditioning. 

A variety of forms and shapes provide visual 

interest and a variety of living spaces for the units' 

occupants, who use the units mostly as vacation 

homes. The units are situated around a central 

pool and landscaped area, which provides the occupants a well-defined community space . 

.,.., 

n _. __ 

SOUTH jL~VATION 

Figure 3.65 

- ~-·--:-··•'"la
Figure 3.66 

SECTION 

Figure 3.67 

~ lD 

- rl > x _ N .... rl 

N - rl z x _ o 

Q ~· 

FLOOR PLAN ·a· 

-..-.- 1 !* -... -'*;o .:a 

10 15 = 

61 
62 
" 

.. 

·. 

Figure 3.70 

63 
DESIGN AND CONSTRUCTION GUIDELINES 
Foundations 

The common methods of elevating residential 

structures are earth fill, elevated foundations, 

shear walls, posts, piles, and piers. The selection 

of an elevation technique depends on a number 

of variables, including hydrologic factors, physical conditions at the site, and cost. The determination of the appropriate technique requires 

analysis of these factors in the context of federal, 

state, and local regulatory requirements. In some 

cases it can be advantageous to use a combination 

of elevation method~. For example, a building 

raised on fill at one end and piers or posts at the 

other coulcl J irovide ground floor access at the 

ern I of llte building away from the floodplain 

while minimizing obstruction of flood waters 

at the end nearer the stream channel. 

The following discussion of the design and construction of elevated residential structures is based 

on accepted building practice. Generally, a conservative approach has been taken in order to 

ensure compliance with the building codes most 

widely used in the United States. In addition, the 

performance criteria presented later in this manual 

can be used to review a building's expected response to flooding. Analysis of flood-induced 

loads and soil conditions, as well as normal loads, 

stresses, and deflection of structural members, is 

required to ensure satisfactory building performance. 

Note that foundations in V Zones should be 

designed in accordance with Design and Construction Manual for R<>sidential Buildings in 

Coastal High Hazard Areas, cited in the Preface. 

65 
Figure 4.1. Elevation by Earth Fill 

66 

FILL 

At many A-Zone sites with low-velocity flooding it 

is feasible to elevate structures on earth fill (Figure 

4.1 ). Earth fill is a widely used elevation technique 

that with proper construction practices and 

materials can be the most economical means of 

elevating a building two or three feet above grade 

or in some locations even higher. Fill should not 

be used in V Zones, where high-velocity flooding 

occurs, or at sites where fill would constrict the 

flow of flood waters and cause increased flooding 

heights or velocities. 

The advantages of fill (as opposed to piles or 

similar elevated foundations) include its generally 

traditional appearance, ease of access to the lowest 

floor (i.e., no stairs are required), the ability at 

many sites to connect the filled area to higher 

ground for emergency evacuation in a flood, the 

safety of building elements from deterioration 

caused by exposure to flood waters, and th~ 

thermal insulation the earth provides the bottom 

of a house. In cold climates, furthermore, spring 

flood water under a house elevated on piles can 

freeze, with the danger of uplifting the structure. 

A site's topography and soil conditions may pre. 

elude use of fill. Before fill is put in place existing 

vegetation and any unstable topsoil must be 

removed. The fill should then be placed in layers 

not exceeding 12 inches deep, with layer compacted with pneumatic or sheepsfoot rollers 

or vibrating compacting equipment. For most 

residential applications, compaction to 95 percent 

of the maximum density obtainable with the 

Standard Proctor Test Method issued by the 

American Society for Testing and Materials (ASTM 

Standard D-698) is usually sufficient. 

Provision must be made for adequate surface 

drainage and erosion protection. Riprapping may 

be required for critical exposed slopes of a fill 

pad. 
ELEVATED FOUNDATIONS 

In some situations site topography, poor soil 

conditions, aesthetics, or cost considerations may 

make it desirable to use an extended masonry or 

reinforced concrete foundation to elevate a house 

up to three or four feet above grade. Such a foundation can be bermed with earth fill to provide 

easy access and a conventional appearance. 

Elevated foundations must be designed to withstand both hydrodynamic forces caused by 

velocity waters and hydrostatic forces caused by 

standing water. This may require added reinforcement in the walls. Where the foundation is not 

bermed with fill, a further design consideration 

would be the provision of sufficient openings in 

the foundation to allow the unimpeded flow of 

flood waters through the foundation. This can 

help minimize both hydrodynamic and hydrostatic forces without affecting the strength of the 

foundation if designed properly. 

SHEAR WALLS 

Shear walls, although more commonly used for 

motels, apartments, and other more massive 

structures, can also be used to elevate smaller 

residential structures (Figure 4.2). 

A shear wall acts as a deep beam in resisting 

forces in the plane of the wall. Structurally, 

the most critical design consideration is the low 

resistance of a shear wall to lateral forces. Shear 

walls should thus be used only in areas subject to 

low- to moderate-velocity flooding and should be 

placed parallel to the expected flow of flood 

waters. It is important that load and impact 

forces be determined for the entire range of flow 

directions. In addition, a shear wall's vulnerability 

to lateral forces makes it critical that connections 

between the wall and the foundation elements 

below grade be well designed. 

Figure 4.2. Elevation by Shear Walls 

67 
Figure 4.3. Elevation by Posts 

' 1"'-olf------wooo POGI 1"REA1fD 

Will-I PRE'5E'RVA1 1VS-

---+-- --¥-f'INrORL!i-D lONl. 

lOU..AR Pt:RM115 

S\-VJ.WWH'. f;'M&D1-iff.JI OF f'Oi.ES 

Figure 4.5. Reinforced Concrete Collar 

68 

POSTS 

Post foundations (Figures 4.3 and 4.4) use long, 

slender wood, concrete, or steel posts set in predug holes. Posts can be round, square, or rectangular in section, though square and rectangular 

posts are easier to frame into than round ones. 

With steel pusts, wide flange shapes or pipe or 

square tube sections are usually used. 

Figure 4.4. Elevation by Posts 

Post foundation holes are dug by hand or machine. 

Posts longer than 16 feet generally require machine 

assistance for safe handling. Posts are generally 

less resistant to lateral forces from flood waters 

than piles or reinforced concrete masonry piers. 

Bearing capacity and stability of posts can be 

improved by pouring a concrete bearing pad at the 

bottom of the hole and/or pouring a concrete 

collar around the post after it has been partially 

backfilled (Figure 4.5). 

Post Embedment 

The depth to which posts should be embedded 

depends on soil conditions, including the depth of 

the frost line; vertical loads; lateral loads from 

flood waters, debris impact, and wind forces; the 

anticipated erosion and uplift; and the spacing and 

size of the posts. 

The following comments and sketches indicate 

embedment techniques for wood posts; steel and 

concrete posts' requirements are similar. 
Hole Depth and Post End Bearing. Wood posts are 

generally embedded 4 to 8 feet. Hole excavations 

beyond 8 feet become uneconomical, so piles are 

used. 

If design loads are small and the allowable soil 

bearing capacity is adequate, i.e., dense sand or 

medium-stiff clay, the post can be set on undisturbed earth at the bottom of the hole (Figure 

4.6). 

For larger loads and/or poorer soil conditions, a 

concrete pad should be poured into the bottom of 

the hole (Figure 4. 7). The pad should be approximately as thick as half its diameter, with a minimum thickness of 8 inches. 

If extremely poor soil conditions are encountered 

it may be necessary to use concrete backfilling or 

piers, as discussed below, or to drive a group of 

piles and cast a pile cap for each post to bear on, as 

shown in Figure 4.8, anchoring the posts securely 

to the caps. This can be more expensive than other 

foundation types. 

Figure 4.7. Post on Concrete Bearing 

Pad 

0 ·, 

-+---eAC.KflU... 

•. 

0 . 

..------fOUNDAilON Bt:-ARIN6r 

AR.f:A 

Figure 4.6. Earth Bearing 

Figure 4.8. Post/Pile Foundation 

69 
ANCHOR 6\ RAP 

~~ t----HOOKE-D ROO 

Plf~ \0 FOO'llN&t 

0 , · .. 

0 • . 

Figure 4.9. Post/Pier Foundation 

--+---POUR:l::O lONlRE'rf 

UC,l(.FIU... 

.----FOUNDAflON ~AR NGi 

AR~f>... . 

Figure 4.10. Concrete Backfill 

70 

Wood posts can also be supported entirely out of 

the ground on concrete piers (Figure 4.9). More 

thorough maintenance is possible with this approach, but additional bracing may be required 

for lateral stability. 

Hole Size. In post construction the hole should be 

a minimum of 8 inches larger in diameter than the 

greatest dimension of a post section. This allows 

for alignment and backfilling. 

Backfilling. Clean, well-compacted backfill is 

necessary to ensure a structure with good lateral 

stability and resistance against wind and water 

uplift. Common backfill materials are sand, gravel, 

crushed rock, pea gravel, soil cement, concrete, and 

earth. 

Granular fills that provide good drainage are 

generally considered the best. Drainage around the 

posts at grade level should be positive to keep 

water from collecting and deteriorating the posts. 

Backfill materials should be mechanically tamped 

to adequately compact them. Wetting such backfill materials as earth or gravel will aid compaction. 

Backfilling the hole with concrete rather than 

gravel or sand, as shown in Figure 4.10, adds stability to the structure and increases the bearing 

area. Shallower embedment may be possible with 

this method. 

Soil cement is an economical alternative to concrete and attains strength nearly equal to it. Soil 

cement is made by mixing the earth removed from 

the dug hole with cement in a ratio of 1 part 

cement to 5 parts earth (plus water as directed by 

the manufacturer). To achieve the best results 

all organic matter should be removed from the 

earth, and it should be sifted to remove all particles larger than 1 inch. 
Anchorage 

Lateral forces and flood forces are less likely to 

overturn or uplift posts if the posts are anchored 

to a foundation. Two ways to anchor posts are to 

embed them in concrete or to fasten them to metal 

straps, angles, plates, etc., that are themselves 

anchored in concrete footings, piers, or pile caps. 

Figure 4.11 shows one method of anchoring wood 

posts in concrete. Large (5/8- to 3/4-inch in 

diameter) spikes or lag bolts are driven into the 

post around its base. The post is placed into the 

hole and secured to bracing restraints to prevent 

movement through the footing while the concrete 

sets. 

The metal fastening method of anchorage can be 

used above or below ground. Figure 4.12 shows a 

square wood post lag bolted to a metal shoe that 

is anchored in a pier. In Figure 4.13, heavy gauge 

galvanized steel straps are used to anchor the wood 

post to a concrete pad. 

WIXJO POST 

ANCHOR GHOf 

--"--+---f?.flNfOU!?t? CONCRHi:-

0 

·. t! 

() .. 

. 

.. ~ c; 

I> 0 b , 

. ~· 

. c.. 

· .. .. 

Plf:R 

Figure 4.12. Metal Angle Anchorage 

Detail 

----wroo !'OS1 1 R£1'1TE9 

WllH P'Ri:OSC:-RVA1 1VE: 

Figure 4.11 . Spike Anchorage of Post 

...-.+----wooo f'OS'f 1REAff:t? 

C,.RAOE 

6,. o;-. - ec> 

o,( & /: '. ~-~jo 

Wl1H f'R.fSfRVA11Vf 

~AL-VAJJIZ.E'O S°fl<.AP 

Figure 4.13. Galvanized Strap Anchorage Detail 

71 
Figure 4.14. Pile Foundations 

72 

PILES 

Pile foundations (Figure 4.14) use long, slender 

wood, steel, or reinforced concrete piles that are 

driven or jetted into the ground. Vertical loads can 

be carried by driving piles to a load-bearing layer, 

such as rock (end-bearing piles), or by driving the 

piles deep enough into the earth to develop enough 

friction between the surface of the piles and the 

surrounding soil to carry the load (friction piles). 

Friction piles, which can also have an end-bearing 

component, are most often used for typical light 

residential loads. 

Piles are structurally stronger than posts and are 

therefore more suitable for the extreme wind and 

water forces and erosion in coastal V Zones. Piles 

in V Zones should be designed in accordance with 

Design and Construction Manual for Residential Buildings in Coastal High Hazard Areas, cited 

in the Preface. 

Pile Materials 

Piles can be concrete, steel, or wood. In coastal 

areas, where steel piles are not desirable because of 

corrosion problems, concrete piles can be particularly good when combined with precast concret~ 

floor beams; such structural systems can be 

efficient, economical, and flood resistant. 

Concrete piles can be particularly suitable for 

buildings of more than two stories. 

The vulnerabilities of different pile materials 

to environmental conditions are discussed in the 

materials section later in this manual. 

Wood piles are probably the most widely used 

foundation for elevated residential structures. 

In some locations, square timbers are preferred 

over round piles because of cost, availability, and 

ease of framing and connecting the structural floor 

beams to the piles. The most popular suitable sizes 

(in inches) are 10 x 10 and 8 x 8 square roughsawn 

members. 
Round timber piles are also frequently used. 

Generally, round piles are available in longer 

lengths than square timbers, and for lengths 

greater than about 25 feet round piles are frequently the only piles available. Round piles are 

often preferred because they can provide greater 

cross-sectional area, peripheral area, and stiffness 

than square sections, particularly the 8 x 8 timbers. 

A minimum tip diameter of about 8 inches, and a 

butt or top diameter (at the floor beam level) of 

about 11 inches or more are recommended for 

round piles. 

Pile Embedment Methods 

A major consideration in the effectiveness of pile 

foundations is the method of inserting piles into 

the ground. This can determine the amount of the 

piles' load resistance. It is best to use a pile driver, 

which uses leads to hold the pile in position while 

a single- or double-acting hammer (delivering about 

10,000 to 15,000 foot-pounds of energy) drives 

piles into the ground. A pile driver 

should be used 

for precast concrete piles and steel piles. 

The pile driver method, while cost-effective for a 

development with a number of houses being constructed at one time, can be expensive for a single 

residence. An economical alternative, the drop 

hammer, consists of a heavy weight (several 

hundred pounds) that is raised by a cable attached 

to a power-driven winch. The weight is then 

dropped 5 to 15 feet onto the end of the pile. 

Drop hammers must be used with care because 

they can damage wood piles. 

Disadvantages of pile driving include difficulties 

with alignment and with setting a driver up on uneven terrain. The advantage is that the driving 

operation forces soil outward from around the pile, 

compacting the soil and causing increased friction 

along the sides of the pile, which provides greater 

pile load resistance. A much less desirable but 

frequently used method of inserting piles into 

sandy coastal soil is "jetting." Jetting involves 

passing a high pressure stream of water through a 

pipe advanced alongside the pile. The water blows 

73 
Figure 4.15. Pier Foundations 

74 

a hole in the sand into which the pile is continuously pushed or dropped until the required depth 

is reached. Sand is then tamped into the cavity 

around the pile and the end of the pile pounded 

with the heaviest sledge hammer or other weight 

available. Unfortunately, jetting loosens not only 

the soil around the pile but also the soil below the 

tip. Therefore, only low end and side friction load 

capacity is attained, and the piles must be inserted 

deeper into the ground than if they were driven. 

If the soil is sufficiently clayey or silty, a hole can 

be excavated by an auger or other means. The hole 

will stay open long enough to drop in a pile. Some 

sands have enough clay or silt to also permit the 

digging of a hole. Then sand or pea gravel can be 

poured and tamped into the cavity around the pile. 

Again, this does not provide as good load resistance 

as driving the pile into the ground, and longer piles 

are necessary. With short wood piles, some final 

driving with a sledge hammer can be helpful. 

Soil Conditions and Embedment Depth 

Local building codes often specify the required 

cmbedment depths of piles, e.g., to al least 6 feet 

below grade. Such codes often do not take into 

account the conditions al specific sites; a soils 

r ngineer should be consulted in doubtful situati ons. In addition, DPsign and Construction 

Manual f or R esidential Buildings in Coastal Iligh 

Hazard A reas, cited in the Preface, provides useful information on this subj ect. 

The required depth of pile embedment depends 

primarily on the number of piles used, the size and 

weight of the structure, and the type of soil at the 

building site. The pile depth is also influenced by 

the lateral forces from flooding and wind and 

debris impact, the manner in which the piles are 

inserted into the soil, and the need to allow for 

erosion of the soil that supports the piles. 

In riverine environments the soil types and the 

anchorage provided by the frictional force of 

the soil against the sides of the pile vary widely. 

Sand is the dominant soil component in most 

coastal areas, but in some areas there may be 
an underlying layer of several feet of clay. Generally, clay soils provide greater load-bearing capacity 

with less penetration than sandy soils. 

Clay soils are also less susceptible to erosion. The 

depth of erosion of sandy soils caused by wave 

action is virtually impossible to predict. Piles 

supporting residential structures on sandy coastal 

shorelines should penetrate the ground deeply 

enough to provide resistance to wind and water 

loads even after extensive erosion has occurred. 

Posts are often backfilled partly with concrete to 

improve their resistance to lateral forces. The same 

technique can be used with piles. After piles are 

driven, the area around each pile is dug out and a 

thick concrete collar is poured, extending several 

feet below grade. Such collars provide protection 

from minor erosion, add some deadweight to the 

structure, and increase piles' pull-out resistance. 

PIERS 

Pier foundations (Figure 4.15) are suitable in areas 

away from a river or coastline where flood waters 

\ 

~ 

l\ 

HE.M7EK 

/JO\ST 

I ANlHOK 5TRA!' I 

:: I II ii 

II " 

IZ.'x ft' ~I FDRL:l'P 

:: " EiR.llK F\EK 

" " ~ " 

II " II 

" c<RAOE II I u II ... ... _JJ 

II II 

" ' ANC:HOfl...~.S II 

/ 

{ " . . ·11 - - II . ~ ·, : 6 , . .. 11 • • 4 11 . .. II ,, .. • ~I " ... . II . " .. Z't'xZ.'t' MINIMUM ' ·. :~~-~~~ ~ • .;.. ..:. .:.. 0' e>A'OE. \711"\EHSION . - . • • . • .. .. . 

move with low velocity and erosion will be Figu re 4.16. Reinforced Brick Pier 

minimal. 

Pier foundations use brick, concrete masonry 

blocks, or poured-in-place concrete to elevate 

structures. To resist horizontal wind and water 

forces, piers should rest on substantial spread 

footings or a grade beam, with reinforcing steel 

rods extending from these elements through 

the full height of the piers to resist tensile stresses. 

Pier Materials 

The vulnerability of pier materials to environmental conditions is discussed in the materials 

section later in this manual. 

Brick and Concrete Masonry Piers 

Brick piers and concrete masonry piers should 

be a minimum of 12" x 12" and reinforced with 

steel rods (Figures 4.16 and 4.17). Hollow concrete masonry units should be filled with concrete. 

r:-_,'."'" -."."7· : 11"' · ~-':"' ! it':-._":'-,"."': • .-l-. ----f'O~E.r7 c.Af' 

r1t==~:;1,----AN?~DR ~\....T5 J ~ 

~ 

" 

;: 

" ,, 

" :~ -r.---_ 

1: !! rv>-----rni'\fl'Kll/>b-~ )( 4- · '1 H/ 4 " . 1, ... 'jr. . . .. . 

• .. . ~ . • II ·• , ' . ~ •. • - • . -~ · · 11 •• -·~J-.. -+---Z't"x2-'t'xt>'MIN. 

: • · .. ,f .' i,.:·; " · ' • ~At€. \?IMl'.N510N .• 7- -:--~---

Figure 4.1 7. Reinfo rced Concrete Masonry Pier 

75 
Figure 4.18. Wal I Foundation 

76 

Reinforced brick piers can be used to elevate 

structures 1 Yz to 6 feet off the ground. Concrete 

masonry piers are effective for elevations of 1 Yz to 

8 feet. In general, the height of reinforced concrete masonry piers should be limited to a maximum of ten times their least dimension. Square 

piers are preferable. If the piers are rectangular 

the longer dimension should not exceed the 

shorter dimension by more than 50 percent. 

According to the National Concrete Masonry 

Association, the allowable working stresses for 

concrete masonry piers are the same as those for 

the design of concrete masonry walls. The pier 

masonry should be laid with type Mor S mortar. 

The association also recommends that the spacing 

between piers supporting floor joists not exceed 

8 feet in the direction perpendicular to the joists, 

nor 12 feet in the direction parallel to joists. 

These minimum requirements apply whether the 

pier is free standing or laterally braced. In cases 

where exceptionally large loading conditions may 

exist, the pier cross-section should be increased 

and/ or additional reinforcement added. A larger 

cross-section can be obtained by using piers several 

feet in length. The long dimension should be 

placed parallel to anticipated flood flow, as in 

Figure 4.18. In coastal areas, however, flood _ 

forces may come in at an angle, loading such a pier 

adversely, so alternatives should be considered. 
Poured-in-Place Concrete Piers 

Poured-in-place concrete piers are essentially reinforced concrete columns. They are cast in forms 

set in machine- or hand-dug holes. The holes can 

be widened or belled at the base to form a footing 

integral with the pier, or, as shown in Figure 4.19, 

a separate footing can be poured. If soil conditions 

are appropriate the footing can be eliminated and 

loads left to end bearing and friction between the 

soil and pier (Figure 4.20). Poured-in-place piers 

of the latter type can be particularly effective for 

larger homes or developments of single-family 

homes and townhouses. 

Poured-in-place concrete piers can be used to 

elevate a structure lYz to 12 feet or more. The 

dimensions, reinforcement, and spacing of concrete piers depend on the type of building framing 

used and on building and environmental loads; 

structural analysis is required. 

Pier Footings 

Pier footing sizes are a direct function of soil 

bearing capacity and loading, and can be computed 

on the basis of local codes. Depth of pier footings 

depends on local frost penetration levels and 

expected flooding, wind, and erosion levels. 

Footings in areas with soils of high volume change 

potential can be unstable, and should be designed 

with the guidance of a soils engineer. 

BRACING ELEVATED FOUNDATIONS 

• · 11· . r i 1' I 

LJ D 

·I· 1: 

·' ' ·1 I . I. 

·, ,,) : /_Q A no<- "' 

0 l ,___"-"l-'-l~V'>V-L..-1' . 0 j l---'"---..11"-----"'-" __ _, I •.O . 

, -I· . () ' 0 

, ". I ....---..,.-..-.. ,..u.-....... : o · ~ • 1 · o ·1 °. · o. · · 0 ~ . • 0 0 • • • • .' • 0 

':-r "a: e-: ~~ -.-;" . . . . . . . , 

Rf'.:1~1'::171"00[1~. 

Z4' X Z4'XB' t.'\11-J • 

Figure 4.19. Reinforced Concrete Pier 

- - --c:iALVANIZfP efAM 

....i;:=:;i....., A.NC.HOR W/ '1- -%'Ji .. :~ . ,:, : . G;AJ...V. f\0\...fS ~ 11 

o :4 • I[! . \NfO ,..,.,f.l<'.;"~ .-- ,~ o. 111 ..,.,, ~, ... 

o:~ . •:: o .. 'i . <:> 111 _. l l:::J c~ I 11 

. 1,;; I 

'"I 1 • . 1------,,,.,...----1 I I. 1--------------t · I -I o 0 1 ° 1,,_...---e/'(> soNOw&=: 

I •. I C.OIJC Pl~ l> I o I o 

_- 1 .- I " :z 

:i C> . . 

Elevated foundation elements must be braced 

when analysis indicates that their size, number, 

spacing, and embedment will not be sufficient to 

resist lateral forces. Even in areas where lowvelocity flooding is anfo:ipated, bracing can provide added assurance that the structure will withstand the impact of floating debris or greater-thanexpected flood or storm forces. Although bracing Figure 4.20. Drilled Pier Foundation 

placed underneath a structure may be struck by 

floating debris, the effects of this on a structure's 

survivability are generally outweighed by bracing's 

beneficial effects. 

77 
Figure 4.21. Knee Brace 

Figure 4.22. Diagonal Bracing 

78 

Knee Braces and Diagonal Bracing 

Knee braces (Figure 4.21) and diagonal bracing can 

be effective in providing lateral strength. Lumber 

more than 2 inches thick is usually recommended. 

Bolts are preferred over nails for connecting 

bracing, because of bolts' greater resistance to 

pullout forces. Knee bracing is usually bolted 

between the floor joist and post or pile. 

Diagonal bracing (Figures 4.22 and 4.23) is bolted 

at the base of one post or pile and fastened in a 

like manner to the adjacent post or pile just below 

the floor beams. Although diagonal bracing is 

more likely than knee bracing to be struck by 

floating debris, this is generally outweighed by the 

greater lateral stability with diagonal bracing, 

especially in higher elevated structures. Steel rods 

can sometimes be used to diagonally brace wood 

posts or piles. The rods are fitted through drilled 

holes flooded with wood preservative and fastened 

with nuts and cast beveled washers. Welded 

connections or drill holes can be used to provide 

rod bracing in steel post or pile foundations. Such 

rods are usually 5/8 to 3/4 inches in diameter. 

Steel diagonal ties, while effective, require considerably more monitoring and maintenance than 

wood because of steel's susceptibility to corrosion. 

Figure 4.23. Diagonal Bracing 
Shear Walls and Floor Diaphragms 

In areas with low- to moderate-velocity flooding, 

shear walls placed parallel to the flow of flood 

waters and firmly attached to piles or posts can 

help brace them (Figure 4.24). 

With wood shear walls, the plywood sizes, the 

strength of wall edges, and the walls' anchorage are 

all important to effective bracing. 

A shear wall can be used in conjunction with a 

floor diaphragm (Figure 4.25) to transfer horizontal forces or reduce embedment depth when, 

for example, solid rock is reached when digging 

foundation holes. A floor diaphragm can be used 

with either pole frame or platform construction. 

Floor diaphragms usually call for 1/2- or 3/4-

inch plywood. 

The severe lateral forces encountered in coastal 

V Zones can require the use of trusses, grade 

beams, or slabs to provide adequate support. 

These are discussed in Design and Construe lion 

Manual for Residential Buildings in Coastal High 

Hazard Areas, cited in the Preface. 

Figure 4.24. Shear Wall Bracing 

fl.a:J!1. D1Af'HICA6il-1 

HO!'.IZON1J..\.- f>fJ,L:ll.JG, 

SHEA~ WAUVf: ~1 1c.AI.- ~~CllJ6i 

Figure 4.25. Floor Diaphragm Bracing 

79 
Figure 4.26. Toe Nailing Provides 

Limited Pull-Out Resistance 

80 

Framing Construction and 

Connections 

The framing construction and framing connections 

in an elevated home can be critical to its ability to 

withstand flood forces with minimal damage. 

Construction in most non-flood areas must support 

loads imposed by the weight of the building 

materials (dead load), weight of people and objects 

(live load), and modest loads imposed by wind. 

Under normal conditions and with typical methods 

of framing construction and framing attachment, 

these loads act downward through gravity to hold 

the building's structure together. 

However, these loads represent only a portion of 

the loads imposed on any structural system in 

flood-prone areas, particularly in coastal V Zones. 

Additional forces can be applied to these structures 

by floating debris, velocity flooding, extreme 

winds, and wave action. These buildings' structural 

system must be capable of withstanding these loads 

and still support the structure and its contents. 

Coastal V Zones are virtually certain to be 

subjected to the extremes of these forces, and 

homes there should be designed in accordance with 

Design and Construction Manual for Residential Buildings in Coastal High Hazard Areas, cited 

in the Preface. 

Even in riverine and coastal A Zones, however, 

prudence suggests that homes be built with a 

margin of safety beyond that needed in non-flood 

areas. Consideration should also be given to the 

possibility that flood forces may be greater than 

those anticipated on the basis of past floods or 

hydrologic analyses. Coastal areas pose the additional danger that shifting dunes or other storminduced topographic changes can transform relatively safe A Zones into V Zones, which experience the full force of ocean storms. 

Measures to provide a home with an extra margin 

of safety to resist these forces are not expensive, 

e.g., having floor joists 12 inches on center instead 

of 16 inches on center, or using deformed shank 

or annular ring nails because of their greater holding 

ability. Nor are the needed craftsmanship and 

anchorage methods uncommon to the carpentry 

trade. Simple nailing, for example, especially end or 
toe nailing, provides little resistance to flood forces, 

partially because of the tendency to split the wood 

in the toe-nailed member (Figure 4.26 ). Bolts, lag 

bolts, or nails in metal anchors at right angles to the 

direction of force (Figure 4.27) are well-known 

methods of increasing structural strength. 

The following paragraphs discuss prudent framing 

construction and connections practice from the 

bottom up, starting with the foundation-to-floorbeam connections and floor beam construction 

and ending with wall-to-roof connections. 

FOUNDATION-TO-FLOOR-BEAM 

CONNECTIONS 

Post and Pile Foundations 

The connection of a post or pile foundation to 

the framing system of a structure is influenced by 

the method of framing used and the cross-sectional 

shape of the post or pile. 

Framing Methods. Two different methods for 

framing into post or pile foundations are in common 

use today: platform construction and pole frame 

construction. 

Platform construction entails simply cutting posts 

or piles off at the desired elevation and framing 

them with beams to support floor joists and deck. 

The platform thus formed serves as the first 

habitable floor and construction platform for any 

type of conventional framing structure desired 

(Figure 4.28). 

Figure 4.27. Metal Framing Anchors 

Figure 4.28. Platform Construction 

81 
Figure 4.29. Pole Frame Construction 

Figure 4.30. Exterior Pole Framing 

8'2 

In what is termed pole frame construction, the 

posts or piles are extended up to or through the 

roof, with beams framing around them as supports 

for floor joists and roof rafters (Figure 4.29). This 

method securely ties the entire structure together 

and is excellent for sites where lateral forces may be 

strong. 

A basic problem with piles is their alignment. 

Posts can be plumbed and aligned easily before 

they are backfilled, but piles must be jacked and 

pulled into position. This can be more of a problem 

with pole framing than platform construction. A 

solution is to locate piles either on the interior or 

exterior of a structure, not in the walls. Then, as 

shown in Figure 4.30, allowance can be made for 

alignment variations. 

Cross-Sectional Shape. Square posts or piles usually 

require only conventional framing techniques. With 

round posts or piles, however, the framing is somewhat more complicated, and it is generally best to 

frame the posts with a pair of beams, girders, or 

rafters-one on each side. 

The roundness of wood posts is not a problem 

when using bolted or spiked connections as shown 

in Figure 4.31. The framing is then the same as 

for any other timber member. 

Figure 4.31. Bolted Connection to Round Pole 
Another connection method is to eliminate the 

curve of the post or pile by clapping and then connecting with bolts, gusset plates, or other devices. 

As Figures 4.32 and 4.33 show, a clapped post will 

form seats that assist the beams in carrying vertical 

loads. Posts that are small in section, however, 

should not be clapped or they will be weakened. 

Generally, there should be a thickness of post or 

pile for the bolts to bear on equal to the total 

thickness of the floor beam. Two bolts should be 

used to connect beams to each post or pile. 

Spike grid connections (Figure 4.34), standard in 

bridge and warehouse construction, are less common in residential practice. A single curved grid 

inserted between the post or pile and the beam 

substantially increases the strength of the bolted 

connection. With the curved side of the grid against 

the pole and over predrilled holes, a high-strength 

threaded rod is used to squeeze the two wood 

surfaces together, forcing the tooth of the spike grid 

into the grain of both members. The high-strength 

rod is then replaced with a conventional bolt of the 

proper size. A flat spiked grid is used to connect 

two flat surfaces, and a double curved spiked grid to 

connect two rounded surfaces. 

Figure 4.34. Spiked Grid 

Figure 4.32. Dapped Gusset Plate Connection 

Figure 4.33. Dapped Pole Connection 

83 
----Z #- 4 t7A R? WRL>f'Pet7 

t\f(!?!.HJt7 TOf OF ~M • 

TIE: 1HRU f'IE:R 4lt7 

1~ rro r00fl1'.1£1 

.... - •. - ,""" . ,~"'- •. -.>--~--FOOTllJb; -W..OW 

r, ,! "'+ ~-.-: fro'.'.:JT U/JE:: 

Figure 4.35. Concrete Masonry Unit Pier 

...... ...... Y4° qBE:J., 6TR.Af' --'~"""'ll ~!-'OR • E:MeeP 

IC." MIW. lfJTD 

f'IE:R 6.l'--Jt7 "BefJt7 

E:IJP l/JTO J?ilJT• 

B?L.1 THl<'.Ll eeAM C.1Jt7~~f" 

AfJCHoRT I e- "5"f l<-AP TO 

Vf1\Y I CL>. L. 

Re /J~IJ<=i 

I~ !"IE;fZ. 

Figure 4.36. Masonry Pier- Strap Anchor 

84 

Pier Foundations 

Pier foundations are generally used for platform 

framing construction rather than pole framing 

construction. 

Piers can be connected to floor beams in several 

ways. A pier's reinforcing steel rods can be extended from the pier and bent over or into the 

floor beam (Figure 4.35). A metal strap wellanchored in the pier can be bolted through the 

beam (Figure 4.36). Or (Figure 4.37) steel anchor 

bolts can be embedded in the pier and bolted 

through the beams with nuts and large-diameter 

washers . 

-....._ 

' ...... ...... 

" " -....._ 

' I 11?1f>l-..1E:1E:R MllJ -'~..-

ALL TH1".J:W fi'CD 

WITH ~HER 

AfJP Lil.IT f>.T TOP 

OF E£l>.M • 

EMe>EV l<o'' f.o\11'.J. 

M-IP ft:fJV E:N!/ 

llJfO ~/JRY 

J?llJT = 

T/e 1?00 TO 

Vi::fZTlCL\.L.. 

f\E:I fJ R'.JR.CI~ 

llJ PIE;!<... 

Figure 4.37. Masonry Pier-Bolt Through Beam 
The bolts should be at least 1 inch in diametc::r and 

embedded at least 12 inches in concrete piers and 16 

inches in masonry piers. If two floor beams abut on 

a pier, each must be anchored separately (Figure 

4.38). 

--JOl6TS 

r---- AfJCHCR ec>L T'J 

AT ?Pl-ICE: 

---+--SOL-IV' lv1tl'SONIZY ~ OR COi.JC. 

~ 

~ 

Figure 4.38. Beam Splice on Pier 

85 
I 0f'AN I 5f'Af.l 

Figure 4.39. Floor Beam with 

Cantilever Overhang 

86 

FLOOR BEAMS 

The floor beams attached to foundation elements 

in tum carry the floor joists and subflooring. Since 

floor beams that are as long as the width or length 

of residential structures are often difficult to find 

and hard to handle, it is common to use splices. 

Splices may occur in several places and need not 

always be located directly over supports. 

Floor beams are often 4 x lO's or up to 6 x 12's, 

but they may be built up using standard framing 

lumber, such as two, three, or four 2 x lO's or 2 x 

12's, spiked or bolted together. Where beams 

are built up using a good grade of lumber for the 

laminated members, the strength of the builtup beam can equal that of a solid member. All 

members of the built-up beam should be continuous between supports, because splices materially 

reduce strength. Built-up members should include 

only one splice at any one location. The ends and 

tops of built-up members should not be directly 

exposed to the weather. 

The primary floor beams spanning between supports 

should span in the direction parallel to the flow of 

potential floodwater. This orientation allows the 

first transverse member perpendicular to flow to be 

the floor joist. Thus, in the case of an extreme flood 

the beams would not be subjected to the full force 

of floodwater along their more exposed surfaces. 

This also reduces the potential for floating debris to 

damage the structure, and places the lowest obstacle 

to flow above the floor beam. 

CANTILEVERS 

A cantilever is a projecting beam that extends 

beyond its support. The beam must be continuous (not spliced) over the last support prior to 

the cantilevered section, and depends on the vertical 

load applied for counteracting reactions (Figure 

4.39). The practical limit recommended for a 

cantilever is normally one-third the length of the 

beam span prior to the cantilever. 
The advantage of this method is that it can reduce 

the number of piles, poles, or piers required for a 

given area, as illustrated in Figure 4.40. Reducing 

the number of piles can result in potentially lower 

cost and fewer obstructions to the flow of floodwater and debris. Residences supported in this 

manner have the additional advantage of having the first row of piles set back, reducing the 

visual impact of elevating the structure. A cantilever design may use longer spans for the main 

floor beam and thus may require larger beams. 

+o' 

.--- ------.--------.-- - -----.--- - - - --· I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

' I 

~ • • • ~ I 

I 

I 

I 

I 

' I I ' 

- - - - - --•-- - -- ___ .. _ ----- -_._ _ - - ---_, l ~· l 10' l 10' l 10' l ... .. " If 1 

1YPICAL Pit.<' ~~IW!C..8-IP~f 

lo PIU?S ~fQU11<'£~ 

.w' 

:--.---- --- ---.---- - --- --.--- --- ------: I I 

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~· • • ·~ r ~ 

~ 5j I 

I 

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~---- -------- --------- -- -------- l 

>\ A ,, 11· I\ 

l 11· Ir l 11· ., .J .. 

Figure 4.40. Cantilever Used to Reduce Number 

of Foundation Elements 

87 
ZX<D SOLIP 

WOOi/ ~UX.Kl l..16'; 

"-IAILe!I ff1WE:8/J 

~ fYJE::MfSE:!<.'3 

AIJt7 ft>.0H JOI '?T. 

Figure 4.41. Wood Joist Anchors 

ME:CHANICA\.... 

FM1f:;f-JE:.!i:.'? 

(HUli:.RiCM.11:: GLIF":>) 

!'X:;1WE:E:;f-..l ~M 

AND Jo1-:i1~. ~ 

Figure 4.42. Metal Hurricane Clips 

88 

CONCRETE FLOORING SYSTEMS 

Recently developed flooring systems using precast, 

prestressed concrete for floor beams, joists, and/or 

subflooring can often be useful in elevated structures. Construction and connection techniques for 

these systems are beyond the scope of this manual. 

FLOOR-BEAM-TO-FLOOR-JOIST CONNECTIONS 

A positive connection is also required beneath 

the first floor level between the floor joists and 

floor beams (Figure 4.41). Metal connectors now 

available provide strong positive connection (Figure 

4.42). Metal straps can also be used provided proper 

nailing is done and a sufficient number of straps is 

installed. At the minimum, every other joist and 

wall stud should be anchored with a strap, and even 

more for more severe loads (Figure 4.43). A good 

wood connector has also been developed. The 

capacity of these connections depends directly 

on the number of nails and their individual capacity to resist loads transverse to their axis. Pullout 

resistance along the axis is not used; rather, the 

nails are placed at right angles (perpendicular) to 

the loads being transferred between the wood 

members. The number of nails counted in figuring 

the total connection capacity of a given joint is the 

lower number that exists on either side of the 

joint. For example, in the connection of a floor 

beam to a floor joist, if five nails are in the beam 

and four are in the joist, the capacity of the 

connection is limited by the four nails on the joist. 
FLOOR JOISTS 

Cross-bridging of all floor joists is recommended 

to stiffen the floor system. The elevation makes 

the floors (particularly the first floor) more accessible to uplift wind forces, as well as to the forces 

of moving water and floating debris. Effective 

cross-bridging requires: 

nominal 1 x 3 's 8 feet on center maximum 

solid bridging same depth as joist 8 feet 

on center maximum. 

SUBFLOORING 

Two methods are commonly used for subfloor 

construction: nominal 1 x 4 or 1 x 6 boards placed 

diagonally over the floor joists (either tongue-andgroove or square-edge with expansion space between 

boards) and plywood subflooring used to create a 

floor diaphragm. When a plywood subfloor is 

planned, guidelines for thickness and methods of 

attachment in relation to joist spacing can be 

obtained from the Plywood Construction Guide 

published annually by the American Plywood 

Association. A well-constructed, firmly attached 

subfloor can be an important asset in resisting lateral 

forces. 

Subflooring is typically nailed directly to the floor 

joists. Nailing with annular ring nails or deformed 

shank nails is recommended. These nails provide 

extra strength against pulling out when the floor 

system is exposed to loads other than gravity. 

A system of nailing and adhesive application of 

plywood with tongue-and-groove joints along the 

long edges of the sheet avoids the need for blocking along these edges. This produces a more level 

floor and offers a stronger diaphragm action to 

resist horizontal flood forces. 

5TR.ArF\NG. 

WRAPPE:t? 

AROLJt{ t7 F~ooRB~ 

PIER 

Figure 4.43. Metal Strapping 

89 
GbLVA~ I Z.cD 

ME:TAL '?TRAP 

-+- - 0TUD 

L 6Uf>F1DO~ 7 

Figure 4.44. Stud-to-Stud Connections 

___ -+-+-'.....,_,,_l-5fUD- ---_,._-

'50UD 5~~/..1HIN<1 

NA\LliOfO AUM&M8{;!t5 ---4l----t!il 

Figure 4.45. Plywood Anchorage 

90 

FLOOR-JOIST-TO-WALL CONNECTIONS 

Elevated structures experience increased wind 

forces because wind speeds increase with elevation. 

Exterior walls are used as tension members to 

transfer wind uplift forces at the roof down to 

resistance provided by the foundation. It is usually 

necessary to use galvanized metal strap connections 

from alternate exterior wall studs to the floor joists 

or floor beams and from first floor studs to second 

floor studs (Figure 4.44). The capacity of these 

connections depends on the number of nails used. 

Manufacturers' brochures can be used to ascertain 

connectors' capacity and thus the spacing required. 

WALL SHEATHING 

Plywood is the most common sheathing in use for 

exterior walls (Figures 4.45 and 4.46). The major 

advantages of plywood are that it braces the wall 

framing to resist racking stresses and it forms a 

continuous tie from floor beam to top plate when 

properly installed. 

Plywood used for sheathing structures elevated up 

to 10 feet above the ground should be exterior 

grade and not less than 1/2-inch thick. Nailing 

should be with sixpenny nails, spaced 6 inches 

along the edges of the panel and 12 inches on 

intermediate studs. 
Structures elevated more than 10 feet should be 

sheathed with 3/4-inch exterior grade plywood, 

nailed with eightpenny nails, spaced as before. 

Deformed shank or annular ring nails and plywood 

with exterior glue are recommended. 

WALL BRACING 

Bracing vertical walls against racking is a common 

building practice, especially for weak materials 

such as some of the newer insulated sheathing. 

Wind forces and lateral forces from moving water 

are also significant factors in determining whether 

and to what extent to brace vertical walls. 

Common wall bracing methods are a let-in diagonal 

wood brace, diagonal boards and plywood. A 

common method similar to the let-in diagonal brace 

is a light-gauge galvanized steel strap nailed 

diagonally to each stud at the outside corners and 

framed walls. 

WALL-TO-ROOF CONNECTIONS 

Probably the most critical structural connections 

for wind resistance are those between walls and 

the roof. For single-family residences, the roof 

structure is usually roof rafters of 2 x lO's or 2 x 

12's or roof trusses built up of 2 x 4 's or 2 x 6 's. 

Whether rafters or trusses are used, they should be 

spaced at about 16 inches or 24 inches on center (16 

inches is the more common spacing). Roof connections are critical because these connections are 

limited in number-at most they can occur at every 

roof rafter or truss. 

A number of available galvanized metal connectors 

place the nails in an orientation to best resist uplift 

and lateral forces. Manufacturers' brochures provide 

the necessary design information. 

llt"--1t--- fX'ffflOR f'L-.YWOOC? W~U... SHr:~'IHINGi 

lON11NUOUS FW~ 

'\OP Pl..A'ft;; '(O MAIN 

fl-DOR B~AM 

Figure 4.46. Wall Sheathing Tie from 

Roof to Ceiling 

91 
Figure 4.47. Shutters for Window 

Protection 

1<>+---++-- Sewage 

Water 

Electric 

Figure 4.48. Protective Utility Shaft 

92 

5H\JTTE.R IN CLO~E~ 

f05\TION 

Related 

Design Considerations 

GLASS PROTECTION 

Even moderate storms or routine high winds can 

cause large losses of glass in buildings, particularly 

along a coast. Broken glass may allow rain and 

floodwaters and high winds to enter the structure. 

Water damage can ruin furnishings and eventually 

damage structural members. Wind allowed into an 

elevated structure increases the uplift load on the 

structure as it applies pressure to the ceiling and 

wall surfaces. 

Exterior shutters can be used to protect glass. For 

small openings the traditional louvered shutter 

offers some protection. Additional protection is 

possible using 1/2-inch plywood attached to the 

back of the shutter, which will take the direct 

forces from the storm (Figure 4.4 7). This method 

allows coverage of fairly large areas of glass. 

UTILITIES AND MECHANICAL EQUIPMENT 

Structures in flood-prone areas are commonly 

served by combinations of electricity, water, 

sanitary sewer, gas (both natural and bottled), 

and telephone. Typical installations for these 

utilities expose them to potential damage from 

flooding and storm action. In the case of an 

elevated first floor, the connection from an underground utility line to the floor above further 

exposes the line to possible damage and/or contamination by flooding and storm action. Underground services are also susceptible to damage 

when erosion of the protective soil cover leaves 

them exposed during flooding. 

Damage to utility lines can lead to contamination 

of drinking water, discharge of effluent from sewer 

lines, gas explosions, and fires and/or shock from 

damaged electrical systems. 

The most vulnerable section of any underground 

utility line is the portion between the ground and 

the place it enters the elevated first floor. A minimum amount of protection can be obtained by 

locating these utility risers on the sides of interior 

elevated foundation elements opposite the direction 
of flood water. This can minimiu damage from 

velocity water or (1o ating debris. A more secure 

method is to place all utility lines coming from 

underground within a protecti ve, floodproofcd 

shaft under the elevatt> d first floor (Figure 4.48). 

If electrical and telephone lines are supplied from 

overhead service lines, they should be connected 

through the utility company's meter system above 

the expected reach of flood waters. However, this 

requirement is often in conflict with the power 

company's policy regarding the reading of meters 

and their location. If this is not possible, the connection should be made within a waterproof Figure 4.49. Elevated Condenser Units 

enclosure. All distribution panels or other major 

electrical equipment should also be located above 

expected flood waters. Branch circuit wiring should 

be fed from the first floor ceiling downward to minimize wiring on the first floor. 

All mechanical equipment (furnaces, hot water 

heaters, air-conditioners, water softeners) should 

also be elevated above expected flood waters (Figure 

4.49). An attic location, if available, would provide 

the equipment maximum safety. Heating and/or 

cooling syst ems using ductwork to carry tempered 

air should be provided with emergency openings 

at their lowest elevations and a minimum slope on 

horizontal duct runs in order to allow the system to 

drain in case it becomes submerged. Figure 4.50 

illustrates some of these concepts. 

Septic tanks should be floodproofed to ensure 

that flooding does not cause the tank to rise out of 

the ground if the tank is partially empty, as well 

as to ensure against discharge of efflu ent. 

OVERHEAD UTILITY Lit-JES 

BEAL..t::t7 WE:L.L 

HEAD 

- - -

BUILDING MATERIALS Figure 4.50. Locating Utilities 

One way to increase the safety of building materials 

is to elevate the building higher than the minimum 

floodplain management requirements. Even then, 

however, flood waters may still reach building 

materials, so they should be protected. 

A building elevated above grade has the underside of 

its floor area exposed to climatic and flood 

93 
94 

conditions, and will require special attention to 

protecting building materials. The climate and the 

desired appearance will determine whether the 

exposed underside of a floor should be sealed. 

Sealing exposed floors can protect subfloors and 

joists from the elements, improve insulation, and 

help conceal utilities. 

The material used to enclose floor spaces should 

be resistant to water damage or inexpensive to 

replace if it is not resistant to damage. Exterior 

grade plywood treated with preservatives is waterresistant and can be effective. Gypsum products 

should not be used unless an acceptable level of 

performance is assured. Regardless of the material 

used, some provision must be made to allow water 

that may find its way into the floor sandwich 

during storms and flooding to drain out, and for 

the joist spaces to dry out. 

Wood 

Wood exposed to the elements should be protected 

by treatment with any one of a number of chemical 

preservatives to make the wood resistant to fungi 

attack, insects, bacteria, and rot. Connections 

should be designed so that water will not collect on 

or in them. They can be protected with protective 

flashing, by treating saw cuts and drill holes with 

preservatives, and by painting connections. The 

American Wood Preservers Institute, Tyson's International Building, 1945 Gallows Road, Vienna, 

Virginia 22180, can provide specific guidelines. 

Steel 

In riverine areas steel framing and foundation 

members exposed to the elements should be protected by galvanization or by painting with rustretardant paints. The need for painting can be 

eliminated through the use of surface oxidizing 

steels (high strength low alloy). 

In saltwater environments, exposed structural steel 

shapes, beams, pipes, channels, angles, etc., undergo 

very rapid corrosion, and their use should be 

avoided. Small connecting devices such as bolts, 

angles, bars, and straps should be hot-dipped galva-
nized after fabrication and coated with a protective 

paint after installation. Standard galvanized sheet 

metal joist hangers and other connecting devices 

deteriorate rapidly despite their galvanized coating 

and also require additional protective coatings. 

Small anchoring devices, nails, spikes, bolts, and lag 

screws should, whenever possible, be hot-dipped 

galvanized. With sheet metal clips and hangers, the 

special nails used should also be galvanized. Regular 

inspection, maintenance, and replacement of 

corroded metal parts is necessary when steel is used 

in the coastal environment. Steel rods used to 

reinforce concrete or masonry piles or piers require 

special precautions to prevent saltwater from 

reaching the steel through hairline cracks in concrete 

or through masonry joints. This is discussed below. 

The American Iron and Steel Institute, 1000 

Sixteenth Street, Washington, D.C. 20036, can 

provide specific guidelines. 

Concrete and Masonry 

The durability of reinforced concrete and masonry 

block can be improved by the use of chemical 

additives mixed with the concrete and mortar and 

by special treatments and coatings. Additives are 

numerous and vary from those that will prevent 

spalling due to freezing to those that will improve 

strength. Surface treatments and coatings, such as 

silicone and epoxy paints, can be used to reduce 

water absorption and penetration and to prevent 

damage by airborne pollutants. Guidance in the 

use of concrete and masonry can be obtained 

from the Portland Cement Association, Old Orchard 

Road, Skokie, Illinois 60076, and the National 

Concrete Masonry Association, P.O. Box 781, 

Herndon, Virginia 22070. 

INSULATION 

Like exposed walls of conventional structures, the 

exposed floor of elevated residences must be 

insulated against heat losses and heat gains. 

Depending on the climate, two factors should be 

considered. First, elevating a building will expose 

plumbing; such plumbing must be insulated against 

95 
IN5Ul.A110N 

IHi"'~f--- !2X1. C,RAPI' P\..YWOOD ---~ 

11 ~ ...... lt'"--- WA.1~ ~\5IA.N1' C,Y~UM BO. 

SPfJ..Y l"OAM \NSUL.AflON 

Figure 4.51. Insulated Floor Section, 

Wood Post Foundation 

l!iii2'~l----WA.1ff R~ S1A.t-Jf C,YPSUK NJ. 

lllCl:l- - - IN6UL.A'flON 

liitl"'91't----!'-Xl GiRAW f'L-YWOOO 

Rlt;ID INSULA110N 

SfR..AY fOA.M 

IN'?UL-A 1'10N 

GON11NUOU5 ~W 

VE:-1-!i/ DF1.J...IN 

,,__---110--- -8<1. C,~!Jf' PL-YW~t1 

Figure 4.52. Insulated Floor Section, 

Foundation Wall 

96 

freezing. In extremely cold climates, heating 

cables may be necessary with the insulation. 

Second, insulated floor decks may be subject to 

floodwaters and should therefore have either 

impermeable, closed-pore insulation able to withstand water submersion or insulation that can be 

replaced economically (Figures 4.51 through 4.53). 

BREAKAWAY WALLS 

As indicated in Design and Construction 

Manual for Residential Buildings in Coastal High 

Hazard Areas, cited in the Preface, the area under 

an elevated structure in a V Zone must be free of 

obstructions or be constructed with breakaway 

walls (e.g., latticework) designed to collapse under 

stress without jeopardizing the structural support 

of the building (Figure 4.54). Loads from flood 

waters and waterborne debris are critical considerations in designing breakaway walls. 

RETROFITTING EXISTING STRUCTURES 

Existing residential structures in flood hazard areas 

can often be raised in-place to a higher elevation to 

reduce their susceptibility to flood damage. The 

principal consideration in raising existing structu-res 

is often the cost; generally, the technology exists 

to raise almost any structure, even multistory 

buildings, but the cost increases as the difficulty 

increases. 

Residential structures have been satisfactorily 

raised up to nine feet. Aesthetics, intended use, 

needed flood elevation, and structural stability 

influence the height selected. Generally, the 

additional cost to raise a structure an additional 

foot or so is small compared to the initial set-up 

cost. 

The new foundation for an ex1shng structure 

should be selected and designed as discussed 

earlier. 

Raising in-place is generally feasible for structures 

that are 1) accessible below the first floor for 

placement of jacks and beams, 2) light enough to 
be jacked with conventional house moving equipment, 3) small enough that they can be raised 

in one piece, and 4) strong enough to withstand 

the stress of the raising process. 

Wood frame residential and light commercial 

structures with first floors above the ground 

(normally with an 18-inch crawl space beneath the 

first floor) are particularly suited for raising. 

Wood frame structures with basements below 

the first floor are also accessible and lightweight; 

however, raising the superstructure does not 

protect the basement, and the basement should 

be filled with a granular material to provide structural stability for the walls. Brick, brick veneer, 

and masonry structures, while heavier and more 

difficult to handle, can also be raised. 

Utility equipment located in a basement can often 

be moved to a higher room, such as an upstairs 

closet, or an attic. It is important to ensure that 

the closet or attic floor can support the weight of 

the equipment. If necessary, an elevat ed addition 

can be built to house a furnace, hot water heater, 

and other equipment formerly housed in a 

basement. Protecting utility equipment in this way 

can be useful even if the house itself cannot or 

need not be raised. 

Raising a structure usually invoh·cs the following 

steps: 

- Disconnect all plumbing, wiring, and utiliti es 

that cannot be raised with the stru cture. 

- Place steel beams and hydrauli c jacks b<'n eath 

the structure and raise to desired elevation. 

- Extend existing foundation walls and piers 

or constru ct new foundation. 

- If a basement exists, remove water heater, 

furnace, et c., and fill basement with granular material to support basemen t walls. 

- Lower the structure onto the ex tended or nf'w 

foundation. 

- Adjust walks, steps, ramps, plumbing, and 

utilities and regrade site as desired. 

- Reconnect all plumbing, wiring, and utilities. 

- Insulate ex posed fl oor to reduce heat loss and 

protec t plumbing, wiring, utilities and insulation from possible water damage. 

)]~~~~~~~~~~~!e_ !-JSUL.A110~ 

l'U?NUM 

Figure 4.53. Double-Insulated Floor 

Plenum, Pier Foundation 

Figure 4.54. Breakaway Walls 

97 
COST ANALYSIS 
Once a community decides that the economic 

risk and environmental impact of dev

eloping 

floodplain land for residential use is acceptable, 

the dollar cost of that 

development must be 

evaluated. Two factors bear significantly on 

any such evaluation: first, the net cost of construction that meets the standards of the 

National Flood Insurance Program (NFIP) in 

light of the pot

ential and unpredictable hazard of 

flooding and the losses that may ensue; second, 

the cost differentials between construction on 

elevated foundations and conventional building methods. (Note that standards adapted by 

local jurisdictions are often more stringent than the 

NFIP's.) 

RPpeated studi es have shown that the savi

ngs 

that can be realized oYer th e lifetime of a struc-

ture by building on a raise d foundation are 

usuall y considerable when com pared with the 

one-time in

crease in construction costs for an 

elevated foundation. This is largely bec au s<' th t> 

the one-time foundation costs arc generally only 

fiye or six percen t of the total cost of a residrntial 

structure, while the flood insurancP savings that 

can be achieved over the life of a slru ctu re b~, 

elernting it can be considerable. 

The economic cost to the individual of building a 

home in the floodplain consists of both flood 

damages that will occur and the costs of whatever 

measures are taken to mitigate 

such damages. The 

cost of flood damages to the homeown

er may be 

partially shifted to federal, state, and lo

cal government through low-interest loans and tax deductions for losses incurred. In communities participating in the NFIP, the owner of a new home can 

purchase flood insurance. Essentially, flood insur

-

ance allows the homeown

er to spread the flood 

risk to others facing the same hazards and, more 

importantly, permits one to pay for expected 

flood losses, which are unpredictable as to size 

and time of occurrence, in pr

edictable annual payments. These are more manageable than unexpected flood losses, especially if more than one 

large flood happens to occur in a very 

short time. 

99 
r 

. i 

I I 

r, '

26'-0" 

,r 

' 

"'-"----.-..--"'' _ _J 

24'-0" 

50'-0" j 

FOUNDATION PLAN 

~ ~t--......:~;;;;;o~;o;~="""""~l'-~....;!11-+~~;1 1 

• ..___, _____ ____ ~===~~Ml#! -- . 

I 2!'·-o·· - L L _________ 5Q:,"1:_ _ 

-- ~ 

FOUNDATION PLAN 

I 

26'-0" 24'-0 " 

FOUNDATION PLAN 

" 11•~ "'"c hm tl"h1 

Emn.enct .. t 1S" M• " 

h4• 16 c..,, 81oct. 

8•8•16 8h o(t. Frou 

----- 4" Conc:Sl• b 

8•6- 6/8 W.tded Wir• R9infon:inti 

--1%"R\gldlntul111on 

'-....___ 4 mlt f'lut k: V•por Strrl• r 

4" Comp.cted Grawl 

Of Crulhtd Ston• 

FOUNDATION SECTI ON 

SLAB-ON-GRADE $4.61 per square foot 

% .. Dia. Ancl'lor Both 

Em09dcMd 1~ " Min - --- 8' 0,C. MH --.... 

Bx8x16 Block 

Fouodetlon 

Continuou1 

Fooling 

--!!!~--

FOUNDATION SECTION 16" 

CRAWL SPACE $5.13 per square foot 

2x10H...:l•r -

-======-l ?====-= ;==-l- 11." Plywood Dack 

1'." o,,, Ancl'lo• Boin 

Ernblddtod15" '-'!n --

8'0,C. M•• -....._ 

2x 10Joifl1 

18"0.C, 

:,,i~i.::;;::;;:;,--:~--J 1------t-r,rt---:::$.--3-2.10 Gird9< 

4)1,Mx11Y'll1'" C., 

PlettTKWeldtcl to 

Colurnn •nd Uggtd 

OfSpikedtt)G~ 

6"10 8"C.,,nrt.«1 

Gr....,.IOf Siona 

Over 0<11n T1 I• _,.,.._ u..._ '-.L.LContil'luou• 

BASEMENT $11.01 per square foot 

4 " Cone, Floor SI.ti 

6x6-616W91ded 

Wit'•Rtinforcing 

4 mU Pl .. tlc 

V"PO' S.,, ;.. 

20"•20"1l8" 

Footing 

Figure 5.1. Conventional Foundat ions (Estimates are spring 1983.) 

100 
COST COMPARISON APPROACH 

The costs of post, pile, and pier foundations are 

compared here to each other and to the costs of 

conventional slab, crawl space, and basement 

foundations. Cost data and estimating forms 

are provided for roughly estimating one's 

particular foundation costs. 

1. Slab-on-grade, crawl space, and basement 

foundations were selected as three of the most 

common types of residential foundations, and 

detailed drawings of them were prepared 

(Figure 5.1). Detailed drawings were also prepared for the three most typical elevation 

foundation types. These are post, pile, and 

pier foundations (Figure 5.2). (Regarding 

use of earth fill, see below.) 

FOUNDATION SECTION 

CONCRETE PIER $7.08 per square foot 

Double 2~12 

Gorde" 

WOOD POST $6.96 per square foot 

WOOD Pl LE $6.58 per square foot 

Figure 5.2. Elevated Foundations (Estimates are spring 1983.) 

FOUNDATION SECTION 

101 
Conventional Foundations 

Slab-on-Grade $4.61 per sq. ft. 

$5.13 per sq. ft. 

$11.01 per sq. ft. 

Crawl Space 

Basement 

Elevated Foundations 

Wood Post 

Wood Pile 

Concrete Pier 

Estimates-Spring 1983 

$6.96 per sq. ft. 

$6.58 per sq. ft. 

$7 .08 per sq. ft. 

Figure 5.3. Foundation Cost Estimates 

% Increase of 

Total House Cost 

Dollar Increase, 

Foundation 

Cost Only 

Elevated 

Foundations 

Wood Post 

Wood Pile, 

Concrete Pier 

Wood Post 

Wood Pile 

Concrete Pier 

2. The estimates are summarized in Figure 5.3. 

They are based on the foundation and deck 

of a 1,500-square-foot house, 28'x50', with 

a small offset. The total cost of this house 

is approximately $60,000, excluding land. 

All estimates were based on FHA construction practices. 

3. Using data from this cost sampling, the 

average cost of each conventional foundation 

type is compared to the average cost of each 

elevated foundation type. This comparison is 

done in two ways: first, each foundation as a 

percentage of the cost of the entire house 

(conventional foundations were established as 

base 100) and, second the dollar increase in 

the cost of the foundati on above. 

Conventional Foundations 

Slab on Grade Crawl Spaces Basement 

+5.9 +4.6 -10.1 

+4.9 +3.6 -11.1 

+6.2 +4.9 -9.8 

$3,525 $2,745 -$6,075 

$2,955 $2, 175 -$6,645 

$3,707 $2,925 -$5,895 

Figure 5.4 Cost Differentials, Conventional Vs. Elevated Foundations, for House Costing $60,000, 

Excluding Land. 

102 
4. Figure 5.5 graphically compares the cost of 

constructing the different types of foundations at various elevations. Note that 

increasing the elevation increases costs at a 

substantial rate only in the case of the fill 

option (which is based on the availability of 

usable fill material on the site). 

15 

14 

13 

,..... 12 

en 

"- 1 1 -52 

0 10 "'C 

.... 9 0 

en 8 'C 

c: 

«S 7 

en 

::s 6 0 

..c: 

... 5 

c: 

..._, 4 

~ 3 

8 2 

1 

0 

Slab+ Site fill 

(not permitted in zone V) 

J' __ • * Cone. piers / * ..- I I I 

~ ..,, * ,,. _ _. . Wood posts 1-----+---+----+---+----.---+--

i;' * # * •r , • • • • • ,- e •• Wood piles 

!----+--+--+-/- --'t ~- -. ~ • • -·· • 0 • --· -

- • ~ - .... 411• 

l----l--~,.---~----111.-• ,- • • - -

- Slab on grade 

0 1 2 3 4 5 6 7 8 9 101112131415 

ELEVATION (in feet) 

Figure 5.5. Relative Costs of Foundations Elevat ed to Different Heights 

103 
104 

Fill 

Fill can often be used in A Zones to elevate conventional foundations such as slab-on-grade. The 

cost of this approach varies widely, depending on 

the availbility, quality, and unit cost of fill as well 

as the height and compaction necessary. Local 

building officials or soils engineers should be 

consulted to evaluate local conditions. 

COST COMPARISON CAVEATS 

The comparative cost data given above do not take 

into account a number of factors that can affect 

either basic construction costs or long-term insurance costs. 

Insurance Costs 

Insurance rates under the NFIP vary greatly depending on the elevation of a building and other 

features related to flood safety. Differences in 

these rates can overshadow the construction cost 

differentials discussed in this chapter, and should 

be considered carefully in making design decisions. 

Design Assumptions 

Each house elevated on piles, posts, and piers was 

assumed to have 21 foundation elements. In addition, each element was assumed to be an average 

length that included the length below grade and 

the length between grade and the structure. These 

lengths are 16 feet for piles, 14 feet for posts, and 

15 feet for piers. In practice, both the number and 

length of foundation elements will vary depending 

on soil conditions, expected flood levels, etc. 

Earthquakes 

Constructing elevated foundations in earthquake 

areas may require additional structural expenditures that should be noted in cost estimates. Local 

building officials or a structural engineer should be 

consulted to evaluate local conditions. 
Stairs and Utilities 

Elevating a residence may result in increased cost 

for stairs and for utilities that must be elevated 

above grade. These costs were not considered in 

the estimates presented here since they vary with 

height of elevation, cost assignment, i.e., who pays 

for installation of utilities, and elevation method. 

Regional Cost Variations 

The cost data presented above are based on 

national averages, and do not take into account 

regional cost variations. 

Cost Inflation 

Building costs are difficult to predict because of 

the tendency for the cost of basic construction 

commodities-lumber, concrete, and steel- to fluctuate and to vary relative to each other. The costs 

here are estimated using data for the spring of 

1983. 

Non-Cost Considerations 

Cost is not the only determinant for selecting the 

material and method for elevating. Market acceptance (buyers and banks), architectural design integration, climatic conditions, site conditions, and 

anticipated flood hazards should also be considered. 

ESTIMATING FORMS 

The forms on the following pages can be used for 

making cost estimates for conventional and elevated foundations. 

105 
SLAB-ON-GRADE ESTIMATING FORM 

TO DETERMINE LOCAL COSTS 

Compute the following and enter: 

------ Square Footage of Floor Area 

Lineal Footage of Perimeter 

------ Square Footage of Foundation Wall 

Enter you costs (combine labor and material) and extend: 

Layout house on lot =$ 

Trench for footing x LF =$ 

Place footings x LF =$ 

Lay-up or form & pour 

foundation wall x SF =$ 

Fill & grade for slab x SF =$ 

Place vapor barrier, wire 

mesh & insulation x SF =$ 

Place & finish slab x SF =$ 

Grand Total $ _____ _ 

106 
CRAWL SPACE ESTIMATING FORM 

TO DETERMINE LOCAL COSTS 

Compute the following and enter: 

------ Square Footage of Floor Area 

Lineal Footage of Perimeter ------

------ Square Footage of Foundation Wall 

Number of Piers ------

Enter your costs (combine labor and material) and extend: 

Layout house on lot =$ 

Trench for footing x LF =$ 

Place footings x LF =$ 

Lay-up or form and pour 

foundation wall x SF =$ 

Place pier footings x Ea. =$ 

Lay-up or form and 

pour piers x Ea. =$ 

Backfill x CY=$ 

Floor Girder x LF =$ 

Floor Framing x SF =$ 

Insulation & sealer x SF =$ 

Subfloor x SF =$ 

Place floor slab x SF =$ 

Grand Total $ _____ _ 

107 
108 

BASEMENT ESTIMATING FORM 

TO DETERMINE LOCAL COSTS 

Compute the following and enter: 

Square Footage of Floor Area 

Lineal Footage of Perimeter 

Square Footage of Basement Wall Area 

Number of Basement Support Columns 

Enter your costs (combine labor and materials) and extend: 

Layout house on lot 

Excavation & spoil removal x 

Place footings x 

Place pier footings x 

Lay-up or form & pour 

foundation wall x 

Parge wall x 

Set drain tile x 

Backfill x 

Place vapor barrier 

and wire mesh x 

Place and finish 

floor slab x 

Place girder x 

Frame Floor x 

Place subf/oor x 

Grand Total 

=$ 

SF =$ 

LF =$ 

Ea. =$ 

SF =$ 

SF =$ 

LF =$ 

CY =$ 

SF =$ 

SF =$ 

LF =$ 

SF =$ 

SF =S 

$ _____ _ 
WOOD POST ESTIMATING FORM 

TO DETERMINE LOCAL COSTS 

Compute the following and enter: 

------ Square Footage of Floor Area 

Lineal Footage of Girders 

Number of Posts 

Enter your costs (combine labor and material) and extend: 

Layout house on lot =$ 

Auger or dig post holes 

and remove spoil x Oty =$ 

Place concrete punching 

pad x Oty =$ 

Place poles x Oty =$ 

Backfill poles and plumb x Oty =$ 

Set girder x LF =$ 

Frame floor x SF =$ 

Place insulation & sealer x SF =$ 

Place subfloor x SF =$ 

Grand Total $ _____ _ 

109 
WOOD PILE ESTIMATING FORM 

TO DETERMINE LOCAL COSTS 

Compute the following and enter: 

------- Square Footage of Floor Area 

Lineal Footage of Girders 

Number of Piles 

Total Lineal Footage of Piles 

Enter your costs (combine labor and material) and extend: 

Layout house on lot =$ 

Bring pile-driving equipment to site x =$ 

Furnish and drive piles x LF =$ 

Set girder x LF =$ 

Frame floor x SF =$ 

Place insulation and 

sealer x SF =$ 

Place sub floor x SF =$ 

Grand Total $ ------

110 
CONCRETE PIER ESTIMATING FORM 

TO DETERMINE LOCAL COSTS 

Compute the following and enter: 

Square Footage of Floor Area 

Lineal Footage of Girder 

Number of Piers 

Enter you costs (combine labor and material) and extend: 

Layout house on lot 

Auger or dig pier holes 

and remove spoil 

Place concrete footing 

Form & pour piers 

Backfill 

Set girder 

Frame floor 

Place insulation 

and sealer 

Place subfloor 

Grand Total 

=$ 

x Oty=$ 

x Oty =$ 

x Oty =$ 

x Oty =$ 

x LF =$ 

x SF =$ 

x SF =$ 

x SF =$ 

$ _____ _ 

111 
RESOURCE MATERIALS 
Glossary 

Base Flood Elevation (BFE) 

The elevation for which there is a one-percent 

chance in any given year that flood levels will equal 

or exceed it (see Special Flood Hazard Areas). The 

BFE is determined by statistical analysis of streamflow records for the watershed and rainfall and 

runoff characteristics in the general region of 

the watershed. 

Coastal High Hazard Area 

The portion of a coastal floodplain that is subject 

to high velocity waters caused by tropical storms, 

hurricanes, northeasters, or tsunamis. Labeled 

V Zones on Flood Insurance Rate Maps, these 

areas experience breaking waves of three feet or 

more. 

Debris Impact Loads 

Loads induced on a structure by solid objects 

carried by flood water. Debris can include trees, 

lumber, displaced sections of structures, tanks, 

runaway boats, and chunks of ice. Debris impact 

loads are difficult to predict accurately, yet reasonable allowances must be made for them in the 

design of potentially affected structures. 

Encroachment 

Any physical object placed in a floodplain that 

hinders the passage of water or otherwise affects 

flood flows. 

Existing Construction 

Those structures already existing or on which 

construction or substantial improvement was 

started prior to the effective date of a community's 

floodplain management regulations. 

Flood or Flooding 

A general and temporary condition of partial or 

complete inundation of normally dry land areas. 

Flooding results from the overflow of inland or 

tidal waters or the unusual and rapid accumulation of surface water runoff from any source. 

Flood Insurance Rate Map (FIRM) 

An official map of a community, issued or 

approved by the Federal Emergency Management 

Agency, that delineates both the special hazard 

areas and the risk premium zones applicable to the 

community. Zones are as follows: 

Zone A (unnumbered) - special flood hazard 

area inundated by the 100-year flood; determined by approximate methods with no base 

flood elevation shown. 

Zones Al-A30 - special flood hazard area 

inundated by the 100-year flood; determined 

by detailed methods with base flood elevations 

shown. 

Zone B - area between the limits of the 100-

year flood and the 500-year flood , or certain 

areas subject to 100-year flooding with average 

depths less than 1 foot, or areas protected by 

levees from the base flood. 

Zone C - area of minimal flooding; located outside the limits of the 500-year flood. 

Zone V (unnumbered) - area subject to wave 

action, without base flood elevation shown. 

Zones V 1-V30 - special flood hazard area of 

100-year coastal flooding with velocity (wave 

action); base flood elevations shown. 

113 
Floodplain 

Any normally dry land area that is susceptible to 

being inundated by water from any natural source. 

This area is usually low land adjacent to a river, 

stream, watercourse, ocean, or lake. 

Floodplain Management 

The operation of a program of corrective and 

preventive measures for reducing flood damage, 

including but not limited to flood control projects, floodplain land-use regulations, floodproofing of buildings, and emergency preparedness plans. 

Flood way 

The channel of a river or watercourse and the 

adjacent land areas that must be reserved to 

discharge the one-percent-probability flood without cumulatively increasing the water surface 

elevation more than a designated height, generally 

one foot. 

Hydrology 

The science of the behavior of water in the atmosphere, on the earth's surface, and underground. 

Hydrodynamic Loads 

As flood water flows around a structure it imposes 

loads on the structure. These loads consist of frontal 

impact by the mass of moving water against the 

structure, drag effect along the sides of the structure, 

and eddies or negative pressure on the structure's 

downstream side. 

Hydrostatic Loads 

Those loads or pressures resulting from the static 

mass of water at any point of flood water contact 

with a structure. They are equal in all directions 

and always act perpendicular to the surface on 

which they are applied. Hydrostatic loads can 

act vertically on structural members such as 

114 

floors, decks, and roofs, and can act laterally on 

upright structural members such as walls, piers, 

and foundations. 

Mean Sea Level 

The average height of the sea for all stages of the 

tide, usually determined from hourly height observations over a nineteen-year period on an open 

coast or in adjacent waters having free access to 

the sea. 

New Construction 

Structures on which construction or substantial 

improvement was started after the effective date 

of a community's floodplain management regulations. 

One-Hundred Year Flood 

(See Special Flood Hazard Areas). 

Permeability 

The property of soil or rock that allows passage of 

water through it. 

Regulatory Floodway 

Any floodway referenced in a floodplain 

ordinance for the purpose of applying floodway 

regulations. 

Special Flood Hazard Areas 

Areas in a community that have been identified as 

susceptible to a one-percent or greater chance of 

flooding in any given year. A one-percent 

probability flood is also known as the 100-year 

flood or the base flood. 

Stillwater Elevations 

The elevation that the surface of the water would 

assume if all wave action were absent. 
Storm Surge 

A rise above normal water level on the open coast 

due to the action of wind stress and atmospheric 

pressure on reduction on the water surface. 

Substantial Improvement 

Any repair, reconstruction, or improvement of a 

structure, the cost of which equals or exceeds 50 

percent of the market value of the structure either 

(a) before the improvement is started or (b) if the 

structure has been damaged, and is being restored, 

before the damage occurred. 

Watershed 

An area from which water drains to a single point; 

in a natural basin, the watershed is the area contributing flow to a given place or stream. 

Wave Height 

The vertical distance between a wave crest and the 

preceding trough. 

Wave Crest Elevation 

The elevation of the 100-year storm surge plus 

wave height. 

115 
Sources of Design Information 

Information Required Purpose or Implications of Data Possible Forms of Data Potential Sources of Data 

• National Flood Insurance Pro- • Requires local communities to • Program regulations • Federal Insurance Admm1stration 

gram (NFIP) implement floodplain regulations . • Insurance rate 1nformat1on and • Federal Emergency Management 

• Sets minimum standards for tables Agency 

floodplain regulations . • Flood Insurance Studies • State Floodplain Management 

• Prohibits federal funding tor • Flood Maps Coordinating Agency 

pro1ects 1n v1olat1on of floodplain Section 1362 Guidelines • Local Government Planning 

regulations Agency 

• Prohibits federal loan guarantees for proiects 1n v1olat1on of 

floodplain regulations. 

• Establishes flood insurance rate differentials for properties 1n 

flood-prone areas 

• Local Government Planning • Implements floodplain regulations . • Planning and Zonmg Ord1 nances • Local Government Planning 

Programs • Determines local floodplain • Zoning Maps Agency 

regulations based on NFIP • Building Codes • Local Government Enqineer 

guidelines (includes zoning and • Building Code Ott1c1als 

subd1v1s1on regulations . performance standards. Planned 

Unit Development ordinances. 

building codes , etc.) 

Note Local regulations can be 

set at a higher standard than 

NFIP m1n1mum standards. depending on local needs and 

circumstances 

• State Floodplain and Coastal • Provides statewide floodplain • State program regulations • State Floodplain Management 

Zone Programs development regulations and • State development guidelines Coord1nat1ng Agency 

guidelines • State Office of Coastal Zone 

• Regulates development 1n Management 

coastal zones • State Office of Natural or Water 

• Coordinates 1mplementat1on of Resources 

NFIP in !ocal 1ur1sd1cttons and 1n 

areas where multiple state 

agencies have an mterest 1n 

flooding 

• Clearinghouse tor Floodplain 

Management Information 

• Regional Planning Restrictions • Can provide additional regula- • Program regulations • Regional Authorities (e.g., Tenor Guidelines t1ons and guidelines for regional • Development guidelines nessee Valley Authority. Appa1ur1sd1ct1ons lach1an Regional Commission. etc .) 

• Coordinates act1v1t1es of differ- • Regional Planning Comrrnss1ons 

ent agencies within the region • River Basin Comm1ss1ons 

• Source of mformat1on and , tn 

some cases . technical assistance 

• Federal Agency Requirements • May include regulations relating • Program regulations • U S Army Corps of Engineers 

and Gu1del1nes (other than NFIP) to development 1n flood-prone • Environmental Protection Agency 

areas (e g , Corps of Engineers • Federal Emergency Managepermits for development on ment Agency 

navigable rivers) • State Floodplain Management 

• May involve federal funding , the Coord1nat1ng Agency 

use of which is restricted 1n • Local Planning Agency 

flood-prone areas 

• Proiects may require federal 

approval for development 1n 

flood-prone areas (e g Environmental Impact Statements) 

Information Required Purpose or Implications of Data Possible Forms of Data Potential Sources of Information 

• Flood Hazard Boundaries • Determines where floodplain • Flood Hazard Boundary Maps • Local Government Planning 

regulations . insurance. and fed- • Flood Insurance Rate Maps Agency 

eral f1nancmg restrictions apply • Flood Boundary and Floodway 

• Determines sp_ec1 f1 c flood haz- Maps • Local Government Municipal 

ard zones • Hydrolog1c Atlases Engineer 

• Determines variable flood 1nsur- • Local Zoning Maps 

ance rate zones • Flood Insurance Studies • State Floodplain Coord1nat1ng 

• Flood Depths • Indicates elevations at which • Flood Elevations Agency 

flood damage is likely to occur • Water Surface Profiles • State Office of Natural Re- • Determines approPnate butld- • Stream and Coast Cross-sections sources 1ng elevations for meeting • Flood Insurance Studies 

floodplain regulations and flood • Federal Insurance Adm1rnstra- insurance restrictions and rates tion • Indicates hydrostatic loads 1n 

flood-prone areas • Federal Emergency Manage-

• Flood Water Velocity • Determines hydrodynamic • Floodplain Technical Studies 

ment Agency 

loads 1n flood-prone areas • Hydrolog1c Studies • us Army Corps of Engineers • Determines debris-impact loads • Flood Insurance Studies 

in flood-prone areas 

• Indicates potential for erosion 

• us Geologic Survey 

and slope detenorat1on 

116 
• Warning Time • Indicates importance of 

emergency evacuation as part 

of the design program 

• Influences design of floodproof1ng 

techniques such as flood shields 

• Influences design of drainage 

systems 

• Influences design of wet floodproofing techniques 

• Duration of Flooding • Affects seepage into buildings 

and saturation of soils and 

building materials 

• Affects the length of time fac1h -

ties might be inaccessible or 

inoperable. 

• Affects building design relative 

to orientation configuration. and 

choice of floodproofing techniques. 

,____ 

• Frequency of Flooding • Influences site choice. 

• Affects choice of floodproof1ng 

techniques . especially those 

that require 1nstallat1on before 

every flood 

• Indicates need for special access 

• Climate and Weather • Indicates frequency and type of 

precipitation and, 1n turn. the 

type and magnitude of flooding 

that is hkely 

• Ground Water Level • Influences potential waler 

pressure on footings . foundalions. and floors. 

• Affects site design techniques 

for controlhng water runoff 

• Structural Flood Control Meas- • Existing measures can affect 

ures (e g .. dams. levees. chan- site 1f the hm1ts of the flood connel improvements) trol device are exceeded 

• Proposed measures can. when 

implemented alter basic flood data 

Information Required Purpose or Implications of Data 

• Phys1og1 aph1c Features • Affects location and magnitude 

of flooding on the site 

• ldent1f1es areas of the site that 

should be avoided or protected 

• Affects onentat1on. d1stnbut1on. 

and density of built elements on 

the site 

• Identifies physical constraints 

and advantages for site development 

• Topography • Influences s1t1ng of buildings 

• Indicates erosion potential 

• Indicates need for. and feas1b1I1ty of using, hll material on the site 

• Indicates appropriate site design techniques for controlling 

water runoff 

• Soil Characteristics • Soil porosity influences the rate 

of water runoff and flooding potent1al 

• Determines the feas1b11ity and 

design spec1f1cat1ons for use of 

ftll material to elevate buildings . 

the use of backfill around foundat1ons. and construction of 

earth berms 

• Indicates required depth for 

footings, p1hngs . or columns 

• Slope Stability • Affects ch0<ce of building sites . 

the use of fill material. and the 

design of foundations. footings. 

and pilings 

• Influences erosion 

• Indicates the need for terracing 

or ground cover to protect slopes 

• Vegetation • Aids m control of water runoff, 

and thus can be a factor 1n reduc1ng flooding levels 

• Water Storage • Aids 1n control of water runoff. 

and thus can be a factor 1n reduc1ng flooding levels 

• Recharges ground water supplies 

• Hydrographs 

• Floodplain Technical Studies 

• Historical Records 

• Flood Insurance Studies 

• Floodplain Technical Studies 

• Historical Records 

• Flood Insurance Studies 

• Floodplain Technical Studies 

• Historical Records 

• Weather Service Records 

• Histori cal Records 

.• Geologic Surveys 

• SO<I Analysis Reports 

• Feas1b1hty Studies 

• Design Spec1flcat1ons 

• Probability Reports 

Possible Forms of Data 

• Topographic Maps 

• Floodplain Technical Studies 

• Site Surveys 

• Topographic Maps 

• Floodplain Technical Studies 

• Site Surveys 

• SO<I Maps 

• SO<I Analysis Reports 

• Site Surveys 

• Analysis of combined effects of 

topography and soil charactenst1cs 

• Site Surveys 

• Site Surveys 

• Geologic. soil , and hydrolog1c 

surveys 

• Site Surveys 

• Regional Authorities 

- Tennessee Valley Authority 

-Appalachian Regional Commission 

River Basin Commissions 

• Hydrolog1c Engineering Consultants 

• Surveys by Professional Staff 

• U S Department of the Interior 

Water and Power Resources 

Service (operates west of the 

M1ss1ss1pp1 River ) 

Potential Sources of Information 

• Local Government Planning 

Agency 

• Local Government Municipal 

Engineer 

• State Floodplain Coordinating 

Agency 

• State Office for Natural Resources 

• SOii Conserva11on Service U S 

Department of Agriculture 

• U S Geologic Survey 

• Reg1onal Authonltes 

• Hydrolog1c and Civil Engineer1ng Consultants 

• Surveys by Professional Staff 

• U S Department of the lntenor 

Water and Power Resources 

Serv1ce(operates west of the 

Mtss1ss1pp1 River ) 

.. 

u 

I .. 

.c 

0 

~ 

117 
FEMA Regional Offices 

The Federal Emergency lanagement Agency (FEMA) was 

created in 1978 to provide a 

single point of accountability for 

all federal activities related to 

disaster mitigation and emergency preparedness and response. 

It was established as an independent agency in the executive 

branch to consolidate a variety 

of existing agencies and offices 

performing related functions. 

The Federal Insurance Administration (FIA), formerly a part of 

the Department of Housing and 

Urban Development, is only 

responsible for administering the 

National Flood Insurance 

Program. This responsibility includes assisting state and local 

governments in the implementation of flood-plain management 

programs and providing information on flooding to communities 

and individuals. Regional offices 

are the primary means by which 

FEMA 's programs are carried 

out at the state and local level. 

Region I 

Region II 

118 

Connecticut, Maine, 

Massachusetts, New Hampshire, Rhode Island & 

Vermont 

J.W. Maccormack Post 

Office Building, Room 442 

Boston, Massachusetts 02109 

(617) 223-9540 

New Jersey, New York, 

Puerto Rico & Virgin Islands 

26 Federal Plaza 

Rm. 1349 

New York, New York 10278 

(212) 264-8980 

Region III 

Region IV 

Delaware, District of 

Columbia, Maryland, 

Pennsylvania, Virginia & 

West Virginia 

Liberty Square Building 

105 South Seventh Street 

Philadelphia, Pennsylvania 

19106 

(215) 597-9416 

Alabama, Florida, Georgia, 

Kentucky, Mississippi, 

North Carolina, South 

Carolina & Tennessee 

1375 Peachtree Street, N.W. 

Suite 700 

Atlanta, Georgia 31792 

(404) 347-2400 
Region V Illinois, Indiana, Michigan, 

Minnesota, Ohio & 

Wisconsin 

300 South Wacker Drive 

24th Floor 

Chicago, Illinois 60606 

(312) 353-8661 

Region VI Arkansas, Louisiana, New 

Mexico, Oklahoma & Texas 

Federal Regional Center 

Rm. 206 

800 North Loop 288 

Denton, Texas 76201 

(817) 387-5811 

Region VII Iowa, Kansas, Missouri & 

Nebraska 

911 Walnut Street 

Room 300 

Kansas City, Missouri 64106 

(816) 374-5912 

VIII 

o Den er 

F~ral Emergency Management Agency 

Regional Offices and Boundaries 

VII 

VI 

" Denton 

Region VIII Colorado, Montana, North 

Dakota, South Dakota, Utah 

& Wyoming 

Federal Regional Center 

Building 710, Box 25267 

Denver, Colorado 80225 

(303) 235-4811 

Region IX Arizona, California, Hawaii 

& Nevada 

Building 105 

Presidio of San Francisco 

San Francisco, California 

94129 

(415) 556-8794 

Region X Alaska, Idaho, Oregon & 

Washington 

Federal Regional Center 

130 228th Street, S.W. 

Bothell, Washington 98011 

(206) 481-8800 

119 
State Coordinating 

Offices for the NFIP 

Each of the states, in cooperation with the Federal 

Emergency Management Agency, has designated a 

specific agency to coordinate implementation of 

the National Flood Insurance Program. This 

agency provides a link between federal, state, and 

local levels of government and between different 

state agencies with flood-related responsibilities. 

The designated agency will typically be a department responsible for natural resources, emergency 

services, or physical development, and is a focal 

point for information relating to flood insurance 

and floodplain management. It can be an 

important source of physical data, information on 

community eligibility for flood insurance, relevant 

state regulations, references to other agencies, and, 

in some instances, technical assistance. The 

authority of each state's coordinating agency 

varies, and can best be determined through direct 

contact. 

Alabama 

Alaska 

Arizona 

120 

Department of Economics 

and Community Affairs 

State Planning Division 

P.O. Box 2939 

3465 Norman Bridge Road 

Montgomery, Alabama 36105 

(205) 284-8735 

Department of Community 

& Regional Affairs 

Division of Municipal 

and Regional Affairs 

949 East 36 A venue 

Suite 400 

Anchorage, Alaska 99508 

(907) 561-8586 

Department of Water 

Resources 

Flood Control Branch 

99 E. Virginia 2nd Floor 

Phoenix, Arizona 85004 

(602) 255-1566 

Arkansas 

California 

Colorado 

Connecticut 

Delaware 

District of 

Columbia 

Soil & Water 

Conservation Commission 

#1 Capitol Mall 

Suite 2D 

Little Rock, Arkansas 72201 

(501) 371-1611 

Department of Water 

Resources 

P.O. Box 388 

Sacramento, California 95802 

(916) 445-6249 

Colorado Water 

Conservation Board 

State Centennial Building, 

Room 823 

1313 Sherman Street 

Denver, Colorado 80202 

(303) 866-3441 

Dept. of Environmental 

Protection 

165 Capitol A venue 

Hartford, Connecticut 06106 

(203) 566-7245 

Dept. of Natural & 

Environmental Control 

Division of Soil & Water 

Conservation 

Edward Tatnall Building 

P.O. Box 1401 

Dover, Delaware 19901 

(302) 736-4411 

Department of Consumer 

Regulatory Affairs 

614 H Street, N.W. 

Washington, D.C. 20001 

(202) 727-7577 
Florida Department of Community Iowa Iowa Natural Resources 

Affairs Council 

Div. of Resource Planning Wallace State Office 

and Management Building 

2571 Executive Ctr. Circle Des Moines, Iowa 50319 

East (515) 281-5029 

Tallahassee, Florida 32301 

(904) 488-9210 Kansas Kansas State Board of 

Agriculture 

Georgia Georgia Department of Division of Water Resources 

Natural Resources, 109 Southwest Ninth Street 

Environmental Protection Topeka, Kansas 66612 

Division (913) 296-3717 

19 Martin Luther King, Jr. 

Dr. , S.W., Room 400 Kentucky Department of Natural 

Atlanta, Georgia 30334 Resources 

(404) 656-3214 Division of Water 

18 Reilly Road 

Guam Office of Civil Defense Fort Boone Plaza 

Post Office Box 2877 Frankfort, Kentucky 40601 

Agana, Guam 96910 (502) 564-3410 

011-671-477-9841 

Louisiana Louisiana Department of 

Hawaii Hawaii Board of Land and Urban & Community 

Natural Resources Affairs 

P.O. Box 373 P.O. Box 44455, Capitol 

Honolulu, Hawaii 96809 Station 

(808) 548-7539 Baton Rouge, Louisiana 

70804 

Idaho Department of Water (504) 925-3730 

Resources 

State House Maine Bureau of Civil Emergency 

Boise, Idaho 83720 Preparedness 

(208) 334-4470 State House 

187 State Street 

Illinois Illinois Department of Augusta, Maine 04330 

Transportation (207) 289-3154 

Division of Water 

Resources Maryland Maryland Water Resources 

Local Flood Plain Programs Administration 

300 North State Street, Flood Management Section 

Room 1010 Tawes State Office Building 

Chicago, Illinois 60610 D-2 

(312) 793-3864 Annapolis, Maryland 21401 

(301) 269-3826 

Indiana Department of Natural 

Resources Massachusetts Massachusetts Water 

608 State Office Building Resources Commission 

Indianapolis, Indiana 46204 State Office Building 

(317) 232-4160 100 Cambridge Street 

Boston, Massachusetts 02202 

(617) 727-3267 

121 
Michigan 

Minnesota 

Mississippi 

Missouri 

Montana 

Nebraska 

Nevada 

122 

Michigan Department of 

Natural Resources 

Water Management Division 

P.O. Box 30028 

Lansing, Michigan 48909 

(517) 373-3930 

Minnesota Department of 

Natural Resources 

Division of Waters 

444 LaFayette Road 

St. Paul Minnesota 55101 

(612) 296-9226 

Mississippi Research & 

Development Center 

3825 Ridgewood Road 

Jackson, Mississippi 39211 

(601) 982-6376 

Department of Natural 

Resources 

1101 R. Southwest Blvd. 

P.O. Box 1368 

Jefferson City, Missouri 

65102 

(314) 751-4932 

Department of Natural 

Resources & Conservation 

32 South Ewing Street 

Helena, Montana 59601 

( 406) 449-6646 

Nebraska Natural Resources 

Commission 

P.O. Box 94876 

Lincoln, Nebraska 68509 

(402) 471-2081 

Division of Emergency 

Management 

Capitol Complex 

Carson City, Nevada 89710 

(702) 885-4240 

New Hampshire 

New Jersey 

New Mexico 

New York 

North Carolina 

New Hampshire Office of 

State Planning 

2112 Beacon Street 

Concord, NH 03301 

(603) 271-2231 

New Jersey Department of 

Environmental Protection 

Division of Water Resources 

P.O. Box CN 029 

Trenton, New Jersey 08625 

(609) 292-2296 

State Engineer 

Bataan Memorial Bldg. 

Santa Fe, New Mexico 

97501 

(505) 827-6140 

New York Department of 

Environmental 

Conservation 

Flood Protection Bureau 

50 Wolf Road-Room 422 

Albany, New York 12233 

(518) 457-3157 

North Carolina Department 

of Natural Resources & 

Community Development 

Division of Community 

Assistance 

512 North Salisbury Street 

P.O. Box 27687 

Raleigh, North Carolina 

27611 

(919) 733-2850 
North Dakota 

Ohio 

Oklahoma 

Oregon 

Pennsylvania 

State Water Commission 

900 E. Boulevard 

Bismarck, North Dakota 

58501 

(701) 224-2750 

Ohio Department of Natural 

Resources 

Flood Plain Planning Unit 

Fountain Square 

Columbus, Ohio 43224 

(614) 265-6755 

Oklahoma Water Resources 

Board 

12th Floor Northeast 

10th & Stonewall 

Oklahoma City, OK 73105 

(405) 271-2533 

Department of Land 

Conservation and 

Development 

1175 Court Street, N.E. 

Salem, Oregon 97310 

(503) 378-2332 

Department of Community 

Affairs 

551 Forum Building, 

Room 317 

Harrisburg, PA 17120 

(717) 787-7 400 

Puerto Rico 

Rhode Island 

South Carolina 

South Dakota 

Tennessee 

Texas 

Utah 

Puerto Rico Planning Board 

P.O. Box 4119, Minillas 

Station 

D-Diego Avenue 

Santurce, Puerto Rico 00940 

(809) 726-7110 

Rhode Island Office of State 

Planning 

Statewide Planning Program 

265 Melrose Street 

Providence, RI 02907 

(401) 277-2656 

South Carolina Water 

Resources Commission 

3830 Forest Drive 

P.O. Box 4440 

Columbia, SC 29240 

(803) 758-2514 

Department of Military and 

Veterans Affairs 

Division of Emergency and 

Disaster 

State Capitol 

Pierre, South Dakota 57501 

(605) 773-3231 

Department of Economic. 

and Community 

Development 

Division of Local Planning 

1800 James K. Polk 

Office Building 

505 Deaderick Street 

Nashville, Tennessee 37219 

(615) 741-2211 

Texas Dept. of Water 

Resources 

P.O. Box 13087, Capitol 

Station 

1700 North Congress 

Avenue 

Austin, Texas 78711 

(512) 475-2171 

Office of Comprehensive 

Emergency Management 

1543 Sunnyside A venue 

Salt Lake City, Utah 84108 

(801) 533-5271 

123 
Vermont Environmental Conservation West Virginia West Virginia Office of 

Agency Emergency Services 

Division of Water Resources Room EB-80 

State Office Building Capitol Building 

Montpelier, V errr,ont 05602 Charleston, WV 25305 

(802) 828-2761 (304) 348-3831 

Virgin Islands Disaster Preparedness Wisconsin Department of Natural 

Office Resources 

Box 1208 Flood Plain-Shoreline 

St. Thomas, VI 00801 Management Section 

(809) 774-6555 P.O. Box 7921 

Madison, Wisconsin 53707 

Virginia Virginia State Water (608) 266-1926 

Control Board 

P.O. Box 11143 Wyoming Wyoming Disaster and Civil 

Richmond, Virginia 23230 Defense Agency 

(804) 257-0075 P.O. Box 1709 

Cheyenne, Wyoming 82003 

Washington Department of Ecology (307) 777-7566 

Mail Stop PVll 

Olympia, Washington 

98504 

(206) 459-6288 

124 
Performance Criteria 

The following performance requirements and 

criteria identify a range of considerations that 

should be addressed during the design of residential 

structures for flood hazard areas. These 

performance criteria do not represent the entire 

range of items applicable to each requirement. 

Instead, a selective number of criteria have been· 

presented. 

The performance requirements and criteria are 

applicable to all structural materials and all construction methods used in flood hazard areas. 

Traditional or conventional construction solutions, 

as well as innovative techniques, are acceptable so 

long as the performance requirements and criteria 

are satisfied. 

DEFINITIONS 

Terms important to proper interpretation of the 

performance requirements and criteria are defined 

as follows: 

Applicable Codes 

The system of legal regulations adopted by a 

community setting forth standards for the construction, addition, modification, and repair of 

buildings and other structures for the purpose of 

protecting the health, safety and general welfare of 

the public. 

Community 

Any state or political subdivision thereof with 

authority to adopt and enforce floodplain management regulations for areas within its jurisdiction. 

Design Flood (Base Flood) 

The design flood is the base or 100-year flood used 

for purposes of compliance with the National 

Flood Insurance Program (NFIP). 

In coastal high hazard zones the 100-year flood 

includes wave height above the stillwater level. 

Design Loads 

The design load is the minimum loading condition 

that the building should be designed to resist. 

Some loading conditions most likely will be 

defined in the applicable codes while other load 

conditions (e.g., flood impact loads) will have to be 

determined. The following loads constitute the 

design load and should be considered as minimum 

loading conditions as defined in Criterion A.I 

(see below): 

Dead Load (D) 

The weight of all permanent construction. The 

dead load includes a) the weight of the structure 

itself, b) the weight of all materials of constmction 

incorporated into the building that are to be 

permanently supported by the structure, including 

built-in partitions, c) the weight of permanent 

equipment, and d) forces due to prestressing. 

Gravity Live Load ( L) 

Gravity live loads result from both the occupancy 

(floor) and the environment (roof) of the building, 

as stipulated in the applicable code. These include, 

where applicable, loads caused by soil and hydrostatic pressures. 

Wind Loads (W) 

Wind loads stipulated in the applicable code. 

Restraint Loads (R) 

Loads, forces, and effects due to contraction or 

expansion resulting from temperature changes, 

shrinkage, moisture changes, creep in component 

materials, movement due to differential settlement 

or combinations thereof. 

125 
Flood Loads (F) 

Loads caused by the design flood, which include: 

- Flood-induced dimensional changes such as 

swelling of wood or heave of expansive foundation soils 

- Water loads as defined in Section 602.0 of the 

Corps of Engineers' publication, FloodProofing RPgulations 

- Soil loads as defined in Section 604.0 of the 

Corps of Engineers' publication, FloodProofing R egulations 

Sections of 602.0 and 604.0 of Flood-Proofing 

Regulations (EP 116S-2-314, Office of the Chief 

of Engineers, U.S. Army, June 1972), are 

reproduced below: 

SECTION 602.0 WATER LOADS 

Sec. 602.1 Types 

Water loads, as defined herein , are loads or pressures on 

surfaces of the buildings and structures caused and induced 

by the presence of flood waters. These loads are of two 

basic types: hydrostati c and hydrodynamic. 

Sec. 602.2 Hydrostatic Loads 

Hydrostatic loads arc those caused by water either above or 

below the ground surface, free or confined, which is either 

stagnant or moves at very low velocities, or up to five (5) 

feet per second. These loads are eq ual to the product of 

the water pressure times the surface area on which the 

pressure acts. The pressure at any point is equal to the 

produ ct of the unit weight of waler (62.5 pounds per 

cubic foot) multiplied by the height of water above the 

point or by the height to which confined water would 

rise if free to do so. Hydrostatic pressures at any point 

are equal in all directions and always act perpendicular 

to the surface on which they are applied. For the purpose 

of these Regulations, hydrostatic loads are subdivided into 

the following types: 

Sec. 602.2.1 Ve rtical Loads 

These are loads acting vertically downward on horizontal 

or inclined surfaces of buildings or structures, such as 

roofs, decks or floors, and walls, caused by the weight 

of flood waters above them. 

126 

Sec. 602.2.2 Lateral Loads 

Lateral hydrostatic loads are those which act in a horizontal direc tion, against vertical or inclined surfaces, both 

above and below the ground surface and tend to cause 

lateral displacement and overturning of the building, 

structure, or parts thereof. 

Sec. 602.2.3 Uplift 

Uplift loads are those which act in a vertically upward 

direction on the undersid e of horizontal or sloping surfaces 

of buildings or structures, such as basement slabs, footings, 

floors, decks, roofs and overhangs. Hydrostatic loads acting 

on inclined, rounded or irregular surfaces may be resolved 

into vertical or uplift loads and lateral loads based on the 

geometry of the surfaces and the distribution of hydrostatic pressures. 

Sec. 602.3 Hydrodynamic Loads 

Hydrodynamic loads ... are those induced on buildings 

or structures by the flow of flood water moving at 

moderate or high velocity around the buildings or structures or parts thereof, above ground leve l. Such loads may 

occur below the ground level when openings or conduits 

exist which allow fre e flow of flood waters. Hydrodynamic 

loads are basically of the lateral type and relate to direct 

impact loads by the moving mass of water, and to drag 

forces as the water flow s around the obstruction . Where 

application of hydrodynamic loads is required, the loads 

shall be computed or estimated by recognized and authoritative methods. Methods for evaluating water velocities nnd 

related dynamic effects are beyond the scope of these 

Regulations, but shall be subj ect to review and approval by 

the Building Official. 

Sec. 602.3.l Conversion to Equivalen t Hydrostatic Loads 

For cases when water velocities do not exceed 10 fee t 

per second, dynamic effec ts of the moving water may be 

converted into equivalent hydrostatic loads by increasing 

the depth of water to the RFD [use the level of the base 

or design flood], by an amount dh, on the headwater side 

and above the ground leve l only, equal to : 

aV2 

dh = _________ , where 

2g 

V is the average velocity of the water in feet per second; 

g is the acceleration of gravity, 32 .2 feet per second ; 

a is the coefficient of drag or shape factor (The value of a, 

unless otherwise evaluated , shall not be less than 1.25) 
The equivalent surcharge depth , dh , shall be added Lo the 

depth measured between the design level and the RFD and 

the resultant pressures applied to , and uniformly 

distributed across, the vertical proj ect ed area of the building or structure which is perpendicular to the flow. Surfaces parallel to the flow or surfaces welled by the tailwater shall be considered subject to hydrostatic pressures 

for depths to the RFD only. 

Sec. 602.4 Intensity of Loads 

Sec 602.4.l Vertical Loads 

Full intensity of hydrostatic pressure caused by a depth of 

water between the design elevation(s) and the RFD applied 

over all surfaces involved, both above and below ground. 

Sec. 602.4.2 Lateral Loads 

Full intensity of hydrostatic pressure caused by a depth of 

water between the design elevation(s) and the RFD applied 

over all surfaces involved, both above and below ground 

level, except that for surfaces exposed to free water, the 

design depth shall be in creased by one foot. 

Sec. 602.4.3 Uplift 

Full intensity of hydrostatic pressures caused by a depth 

of waler between the design level and the RFD acting on 

all surfaces involve<l .... 

Sec. 602.4.4 Hydrodynamic Loads 

Hydrodynamic loads, regardless of method of evaluation, 

shall be applied at full intensity over all above groun<l 

surfaces between the ground level and the RFD. 

Sec. 602.5 Applicability 

Hydrostatic loads shall be used in the design of buildings 

and structures exposed to water loa<ls from stagnant 

flood waters, for conditions when water velocities do 

not exceed five (5) feet per second , and for buildings 

and structures or parts thereof not exposed or subject lo 

flowing water. For buildings and structures, or parts 

thereof, which are exposed and subject to flowing waler 

having velocities greater than fiv e (5) feet per second , 

hydrostatic and hydrod ynamic loads shall apply. 

127 
SECTION 604.0 SOIL LOADS 

Sec. 604.1 Applicability 

Full consideration shall be given in the design of buildings, 

structures and parts thereof, to the loads or pressures 

resulting from the presence of soils against or over the 

structure. Loads or pressures shall be computed in 

accordance with accepted engineering practice, giving full 

consideration to the effects that the presence of flood 

water, above or within the soil, has on loads and pressures. 

When expansive soils are present, the Building Official may 

require that special provisions be made in foundatio:i;i and 

wall design and construction to safeguard against damage 

due to this expansiveness. He may require a special 

investigation and report to provide these design and 

construction criteria. 

Flood Impact Loads (Fl) 

The loads caused by the design flood as defined 

in Section 603.0, "Impact Loads," and Section 

605.0, "Hurricane and Tidal Wave Loads," of the 

Corps of Engineers' publication, Flood-Proofing 

Regulations. In the case of Section 605.0, where 

no specific guidance is provided, design loads shall 

be recommended by a professional engineer. (Also 

refer to FIA-7, Design and Construction Manual 

for Residential Buildings in Coastal High Hazard 

Areas, cited in this manual's preface.) 

Section 603.0 of Flood-Proofing Regulations is 

reproduced below: 

SECTION 603.0 IMPACT LOADS 

Sec. 603.1 Types 

Impact loads are those which result from floating debris, 

ice and any floatable object or mass carried by flood 

waters striking against buildings and structures or parts 

thereof. These loads are of three basic types: normal, 

special and extreme. 

Sec. 603.1.1 Normal Impact Loads 

Normal impact loads are those which relate to isolated 

occurrences of logs, ice blocks or floatable objects of 

normally encountered sizes striking buildings or parts 

thereof. 

128 

Sec. 603.1.2 Special Impact Loads 

Special impact loads are those which relate to large conglomerates of floatable objects, such as broken up ice 

floats and accumulation of floating debris, either striking 

or resting against a building, structure, or parts thereof. 

Sec. 603.1.3 Extreme Impact Loads 

Extreme impact loads are those which relate to large 

floatable objects and masses such as runaway barges or 

collapsed buildings and structures, striking the building, 

structure or component under consideration. 

Sec. 603.2 Applicability 

Impact loads should be considered in the design of buildings, structures and parts thereof as stipulated below: 

Sec. 603.2.1 Normal Impact Loads 

A concentrated load acting horizontally at the RFD or at 

any point below it, equal to the impact force, produced by 

a 1,000-pound mass traveling at the velocity of the flood 

water and acting on a one (1) square foot surface of the 

structure. 

Sec. 603.2.2 Special Impact Loads 

Where special impact loads are likely to occur, such loads 

shall be considered in the design of buildings, structures, 

or parts thereof. Unless a rational and detailed analysis is 

made and submitted for approval by the Building Official, 

the intensity of load shall be taken as 100 pounds per foot 

acting horizontally over a one-foot wide horizontal strip at 

the RFD [use the level of the base or design flood], or at 

any level below it. Where natural or artificial barriers exist 

which would effectively prevent these special impact loads 

from occurring, the loads may be ignored in the design. 

Sec. 603.2.3 Extreme Impact Loads 

It is considered impractical to design buildings having 

adequate strength for resisting extreme impact loads. 

Accordingly, except for special cases when exposure to 

these loads is highly probable and the resulting damages 

are extremely severe, no allowances for these loads need 

be made in the design. 

Flood or Flooding 

A general and temporary condition of partial 

or complete inundation of normally dry land 

areas from: 
- the overflow of inland or tidal waters 

- . the unusual and rapid accumulation or runoff of surface waters from any source 

mudslides (i.e., mudflows) which are 

proximately caused or precipitated by 

accumulations of water on or under the 

ground. 

The collapse or subsidence of land along the 

shore of a lake or other body of water as a 

result of erosion or undermining caused by 

waves or currents of water exceeding anticipated cyclical levels or suddenly caused by an 

unusually high water level in a natural body of 

water, accompanied by a severe storm, or by 

an unanticipated force of nature, such as a 

flash flood or an abnormal tidal surge, or by 

some similarly unusual and unforeseeable 

event which results in flooding as defined 

above. 

PERFORMANCE REQUIREMENTS AND 

CRITERIA FOR RESIDENTIAL STRUCTURES 

IN FLOOD HAZARD AREAS 

PERFORMANCE REQUIREMENT A 

The building, its contiguous structure(s), and its 

service systems shall be designed to withstand the 

design flood without causing unacceptable risks to 

its occupants or to adjacent property owners. 

The building complies with Performance Requirement A if the following conditions are satisfied: 

Criterion A. l: Strength 

The building is designed to resist the following 

loads, acting simultaneously: 

1.1 D, L, R, and F 

1.2 D, L, R, F, and Fl 

1.3 D, L, R, W, F, and Fl 

1.4 D, R, and F 

1.5 D, R, W, F, and Fl 

Where the working stress method of design is used 

the following provisions apply: 

2.1 In load combinations 1.1 through 1.5 all loads 

are applied as listed or as required by the 

applicable codes for the same load combinations with loads F and FL 

2.2 Allowable (working) stresses cannot be 

exceeded for loading conditions 1.1 and 1.4. 

For all other loading conditions the allowable 

stresses can be increased by the amount permitted in applicable codes for design against 

load combinations including wind or earthquake load. 

Where ultimate-load design is used (such as 

instances where the American Concrete Institute, 

Building Code Requirements for Reinforced Concrete [ACl 378, ACI, Detroit, current edition], is 

applicable) load factors are applied as recommended in the applicable standard, and F will be combined with L, or factored as if it were a live load 

for loading conditions 1.1 and 1.4. For all other 

loading conditions loads F + Fl will be combined 

with W, or considered to be equivalent to a wind 

load. 

Test 

Structural analysis and/or physical simulation. 

Commentary 

The criterion provides a suitable margin of safety 

against structural collapse when the building is 

subjected to the base flood. The intent of the 

criterion is that the margin of safety for these 

buildings, when subjected to the base flood, be 

no less than the margin required for other buildings not subjected to flooding. It is assumed that 

loads F may act on the building over a long period 

of time, while loads Fl are short-term loads. Thus 

the margin of safety against load combinations 

containing Fl need not exceed that provided 

against wind or seismic loads. 

129 
The combined load of earthquakes and floods is 

not considered here because of the low probability of a flood and an earthquake occurring simultaneously. Where tsunami flooding is the base 

flood, earthquake loading should perhaps be considered concurrently. 

Criterion A.2: Stability and Flotation 

There shall be a factor of safety of 1.5 against 

overturning, sliding, and flotation under the 

following load: 

D + W + R + F +Fl 

Test 

Structural analysis and/or physical simulation. 

Commentary 

This criterion provides a suitable margin of safety 

against sliding and overturning. The most critical 

load combination is being considered. Tie-down 

devices can be used to achieve structural stability, 

provided it can be demonstrated that deterioration 

of these devices during the service life of the building or by flood conditions will not cause the 

factor of safety to fall below its stipulated value. 

Criterior A.3: Provision Against Debris and Scour 

Unless it can be demonstrated that the flood 

waters will be stagnant, or that there will be no 

floating debris during the design flood, the following provisions apply: 

1.1 Building on stilts shall comply with Section 

612.2.3 of the Corps of Engineers' publication, Flood-Proofing Regulations. This 

section is reproduced below. 

Sec. 612.2.3 Building on "Stilts" 

The building may be constructed above the RFD [use 

the level of the base or design flood] by supporting it 

on "stilts" or other columnar type members, such as 

columns, piers, and in certain cases, walls. Clear spacing 

of support members, measured perpendicular to the general 

130 

direction of flood flow shall not be less than eight (8) 

feet apart at the closest point. The "stilts" shall, as far as 

practicable, be compact and free from unnecessary appendages which would tend to trap or restrict free passage of 

debris during a flood. Solid walls, or walled in columns 

are permissible if oriented with the longest dimension of 

the member parallel to the flow. "Stilts" shall be of a type 

that causes the least obstruction to the flow and the least 

potential for trapping floating debris. Foundation supports 

for the "stilts" may be of any approved type capable of 

resisting all applied loads, such as spread footings, mats, 

piles and similar types. In all cases, the effect of submergence of the soil and additional flood water related 

loads shall be recognized. The potential of surface scour 

around the stilts shall be recognized and protective 

measures provided , as required. 

1.2 For flow velocities in excess of 5 feet per 

second the hydrodynamic loads in F shall 

be assumed to act over the entire width of 

the building, perpendicular to the direction 

of flow, and reasonable vertical clearance 

shall be provided for the passage of debris. 

The depth of all foundation elements shall 

allow for the potential effect of scour. 

Test 

Structural analysis and/or physical simulation. 

Evaluation of data and documentation for desigr.i, 

tests, and installation; evaluation of plans and 

specifications. 

Commentary 

Criterion A.3 is designed to prevent structural 

collapse caused by the accumulation of floating 

debris or the undermining of foundation elements 

as a result of scour. Part of the provision is designed to avoid debris accumulation. The other 

part provides adequate strength to resist the 

effects of the formation of a barrier over the 

entire width of the building. Buildings are exempt 

if it can be demonstrated that no debris will accumulate and no scour will occur. 
Criterion A.4: Disruption of Service Systems 

The service systems shall be designed to resist the 

loads stipulated in Criterion A.l with safety 

margins as stipulated in A. l against disruptions 

which may endanger human lives. 

Test 

Engineering analysis and/or physical simulation. 

Evaluation of data and documentation for design, 

tests, and installation; evaluation of plans and 

specifications. 

Commentary 

This criterion only applies to disruption which may 

cause fatal accidents, such as rupture of gas lines. 

Lesser load levels are stipulated in B. l for disruptions which constitute a health hazard. 

Criterion A.5: Execution of Rescue Operations 

The building is designed to permit the execution 

of rescue operations. 

During the duration and at heights of the design 

flood the building shall: 

1.1 Allow the safe evacuation of the occupants 

out of the building 

1.2 Allow the safe transfer of occupants from the 

building to rescue vehicles 

1.3 Provide means of access or adjacency for 

rescue vehicles. 

Test 

Evaluation of data and documentation for design, 

tests, and installation; evaluation of plans and 

specifications. 

Commentary 

Criterior A.5 is designed to prevent the entrapment of building occupants by rising water levels. 

Part of the provision is designed to provide means 

to evacuate the building (e.g., windows, roof trap 

door). The other parts provide for the accomodation and execution of rescue operations (e.g., by 

boat, helicopter). 

131 
PERFORMANCE REQUIREMENT B 

The building, its contiguous structure(s), and its 

service systems shall be designed to withstand the 

design flood without causing unacceptable health 

hazards to its occupants. 

The building complies with Performance Requirement B if the following conditions are satisfied: 

Criterion B. l: Disruption of Utility Connections 

Building utility connections shall be designed to 

resist the following loads: 

At loading conditions: 

1.1 D + L + R + W + F + Fl 

1. 2 D + W + R + F + Fl 

The building utility connections should not sustain: 

2.1 Permanently disrupted and/or broken attachment with their fixtures and/or supporting 

structural elements 

2.2 Lealrnge or escape of effluent that could 

contaminate drinking water 

2.3 Rupture of electrical service that could cause 

electrocution and/or fire. 

Test 

Evaluation of data and documentation for design, 

tests, and installations; evaluation of plans and 

specifications. Inspection and/or testing of built 

elements when deemed essential. Determination of 

conformances to generally accepted codes, 

standards and engineering and trade practices, 

where applicable. 

Commentary 

This criterion applies to all utility connections 

subject to the forces of the design flood. Utility 

connections which are designed to disconnect 

132 

during the design flood without the release of 

deleterious substances are exempt from provisions 

1.1and1.2. 

Criterion B.2: Provision Against Drinking Water 

Contamination 

There will be no contamination of drinking water 

with sewer effluent or flood water. 

Criterion 13.2 and Performance Requirement B 

are deemed satisfied if the following provisions 

are met. 

1.1 Approved backflow preventers or devices are 

installed on main water service lines, at water 

wells and/or at suitable building locations to 

protect the system from backflow or back 

siphonage of flood waters or other contaminants in the event of a line break or temporary 

disconnection. 

Devices are installed at accessible locations and 

maintained in good working order. 

1.2 Sanitary sewer and storm drainage system connections are provided with approved backflow 

preventers or devices installed at each 

discharge point. 

1.3 o storm or flood waters are drained into 

systems designed for sewage only, and vice 

versa. 

Test 

Evaluation of data and documentation for design, 

tests, and installation; evaluation of plans and 

specifications. 

Commentary 

Criterion B. 2 is designed to prevent contamination 

of drinking water with sewer effluent or flood 

waters. Also, the criterion is designed to prevent 

damage to fixtures and interior finishes (e.g., flooring, wall surfaces) from backflow or back 

siphonage of flood waters. 
Criterion B.3: Provision Against Contamination of 

Potable Water Wells 

Private potable water wells shall not be contaminated by toxic substances or impurities caused by the 

design flood. 

Criterion B.3 is deemed satisfied if the following 

provisions are satisfied. 

1.1 Private potable well water is not supplied from 

a water table located less than 25 feet below 

grade, nor from any deeper supply which may 

be polluted by contamination entering fissure 

or crevice formations. 

1.2 Each well is provided with a watertight casing 

to a distance of at least 25 feet below the 

ground surface that extends at least one 

foot above the well platform . 

.. ~""-#~ ..... ., •• - ·-- ••'•••• • 

Test 

Evaluation of data and documentation for design, 

tests, and installation; evaluation of plans and 

specifications. 

Geological analysis of site. 

Commentary 

Criterion B.3 is designed to prevent the contamination of water wells used as a source for potable 

water. Part of the provision provides against the 

contamination of the water supply source. The 

other part provides against the contamination of 

the water removal system. In any case, local 

health codes should be consulted. 

l 41 I \ '> l' • I • C I 

133 
PERFORMANCE REQUIREMENT C 

The building, its contiguous stru cture(s), and its 

service systems shall be designed to withstand the 

design flood without sustaining damage of unacceptable magnitude. 

The building complies with Performance Rel{uiremcnt C if the following conditions are satisfied: 

Criterion C. l: Provision Against Permanent 

Damage 

Under loading conditions 1.1 throu gh 1.3 the 

building as a whole, or any element th ereof, shall 

not suffer permanent damage which would require 

replacement or major repair, or which would 

extcnsi\'ely impair its intended function. 

1.1 D + L + R + W + F +Fl 

1. 2 D + W + R + F + Fl 

1. 3 D + L + R + F + Fl 

The criterion is deemed satisfied if stress and defl ection limits under loading conditions 1.1 

through 1.3 do not exceed those stipulated in 

applicable codes, or if it can be demonstrated that 

deflections caused by load combinations 1.1 

throu gh 1.3 can be accomodated by suitable detail 

and adequate flexibility of elements. 

Test 

Evaluation of data and documentation for design, 

tests, and installation; evaluation of plans and 

specifications. Inspection and/or testing of built 

elements when deemed essential. Determination of 

conformance to generally accepted standards and 

engineering and trade practices, where applicable. 

Commentary 

This criterion assures that the design flood will 

not cause excessive damage. Effects of swelling 

caused by increased moisture or inundation must 

be included in F. 

134 

Criterion C.2: Provision Against Unnecessary 

Damage 

All living areas, major utilities, furnaces, and airconditioning units shall not be submerged by the 

design flood. 

1.1 Living areas shall be considered habitable areas 

that provide for the essential needs of people: 

living, sleeping, dining, cooking and sanitation. 

Recreation areas, libraries, and other speciality 

areas are to be considered habitable areas and 

therefore should not be submerged by the 

design flood. 

1.2 The electrical system complies with Criterion 

C. 2 if lhc following conditions are satisfied: 

1.2.1 All portions of the electrical system 

installed below the design flood level 

are suitable for continuous su bmergence 

in water. Only submersible type splices 

are used and conduits located below the 

design flood level are self draining if 

subject to floodin g. 

1.2.2 Lighting panels, distribution panels, Hnd 

all other stationary electrical equipment 

are located above the design flood. 

1.3 The mechanical system complies with Criterion C.2 if the following conditions are satisfied: 

1.3. l Heating, air-conditioning, and ventilating are installed above the design flood. 

1.3.2 All duct work for warm air heating 

systems located below the design flood 

level is provided with emergency openings for drainage of du cts after a flood 

condition. 

1.4 The plumbing system complies with Criterion 

C. 2 if the following conditions are satisfied: 

1.4.1 Tanks, softeners and heaters are installed above the design flood. 
Test 

1.4.2 Plumbing below the design flood 

level will not suffer loss of stability 

or loss of tightness that will permit 

leakage or physical damage to fixtures and joints and connections that 

will permanently impair functioning. 

1.4.3 Utility connections designed to disconnect during the design flood are 

easily reconnected. (See Criterion 

B.l.) 

Evaluation of data and documentation for design, 

tests, and installation ; evaluation of plans and 

specifications. 

Commentary 

Criterion C.2 is designed to prevent unncessary 

damage of living areas, major utilities, furnaces, 

and air-conditioning units by the desig11 floo<l. 

Part of the provision is designed to elevate living 

areas and equipment above the design flood. Other 

parts are desig11ed to prevent the damage of utilities and mechanical/ electrical connections below 

the design flood. 

135 
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137