U. S. Department of Homeland Security

Past storms such as Hurricanes Andrew, Hugo, Charley, Katrina, and Rita, and recent events such as Hurricane Ike continue to show the vulnerability of our "built environment". While good design and construction cannot totally eliminate risk, every storm has shown that sound design and construction can significantly reduce the risk to life and damage to property. With that in mind, the Federal Emergency Management Agency (FEMA) has developed this manual to help the community of homebuilders, contractors, and local engineering professionals in rebuilding homes destroyed by hurricanes, and designing and building safer and less vulnerable new homes. The intent of the manual is to provide homebuilders, contractors, and engineering professionals with a series of recommended foundation designs that will help create safer and stronger buildings in coastal areas. The designs are intended to help support rebuilding efforts after coastal areas have been damaged by floods, high winds, or other natural hazards. The foundations may differ somewhat from traditional construction techniques; however, they represent what are considered to be some of the better approaches to constructing strong and safe foundations in hazardous coastal areas. The objectives used to guide the development of this manual are: To provide residential foundation designs that will require minimal engineering oversight; To provide foundation designs that are flexible enough to accommodate many of the homes identified in A Pattern Book for Gulf Coast Neighborhoods prepared for the Mississippi Governor's Rebuilding Commission on Recovery, Rebuilding, and Renewal; To utilize "model" layouts so that many homes can be constructed without significant additional engineering efforts. The focus of this document is on the foundations of residential buildings. The assumption is that those who are designing and building new homes will be responsible for ensuring that the building itself is designed according to the latest building code (International Building Code(R), International Residential Code(R), and FEMA guidance) and any local requirements. The user of this manual is directed to other publications that also address disaster-resistant construction. Although the foundation designs are geared to the coastal environment subject to storm surge, waves, floating debris, and high winds, several are suitable for supporting homes on sites protected by levees and floodwalls or in riverine areas subjected to high-velocity flows. Design professionals can be contacted to ensure the foundation designs provided in this manual are suitable for specific sites. This edition of FEMA 550 introduces the Case H foundation, which is an open/deep foundation developed for use in coastal high hazard areas (V zones). It is also appropriate to use the Case H foundation in Coastal A and non-coastal A zones. Case H foundations incorporate elevated reinforced concrete beams that provide three important benefits. One, the elevated beams work in conjunction with the reinforced concrete columns and grade beams to produce a structural frame that is more efficient at resisting lateral loads than the grade beams and cantilevered columns used in other FEMA 550 open foundations. The increased efficiency allows foundations to be constructed with smaller columns that are less exposed to flood forces. The second benefit is that the elevated reinforced concrete beams provide a continuous foundation that can support many homes constructed to prescriptive designs from codes and standards such as the IRC, the American Forest and Paper Association's Wood Frame Construction Manual for One- and Two-Family Dwellings (WFCM), and the International Code Council's Standard for Residential Construction in High Wind Regions (ICC-600). The third benefit that Case H foundations provide is the ability to support relatively narrow homes. It is anticipated that Case H foundations can be used for several styles of modular homes.

The Federal Emergency Management Agency (FEMA), which is part of the Department of Homeland Security, works to reduce the ever-increasing cost that disasters inflict on the nation. Preventing losses before they occur by designing and constructing buildings and their components to withstand anticipated forces from various hazards is one of the key components of mitigation and is one of the most effective ways of reducing the cost of future disasters. The National Earthquake Hazards Reduction Program (NEHRP) is the federal program established to address the nation's earthquake threat. NEHRP seeks to resolve two basic issues: how will earthquakes affect us and how do we best apply our resources to reduce their impact on our nation. The program was established by Congress under the Earthquake Hazards Reduction Act of 1977 (Public Law 95-124) and was the result of years of examination of the earthquake hazard and possible mitigation measures. Under the NEHRP, FEMA is responsible for supporting program implementation activities, including the development, publication, and dissemination of technical design and construction guidance documents. Generally, there has not been much technical guidance addressing residential buildings unless they are located in areas of high seismicity or exceed a certain size or height. This is because most residential buildings were thought to perform fairly well in earthquakes due to their low mass and simple construction. While buildings may not normally experience catastrophic collapse, they can still suffer significant amounts of damage, rendering them uninhabitable. This is especially true when construction techniques are less than adequate. What is particularly important from FEMA's point of view is that, given the sheer number of this type of building, even minor damage represents a significant loss potential and temporary housing demand that will need to be addressed after an earthquake by all levels of government. This guide provides information on current best practices for earthquake-resistant house design and construction for use by builders, designers, code enforcement personnel, and potential homeowners. It incorporates lessons learned from the 1989 Loma Prieta and 1994 Northridge earthquakes as well as knowledge gained from the FEMA-funded CUREE-Caltech Woodframe Project. It also introduces and explains the effects of earthquake loads on one- and two-family detached houses and identifies the requirements of the 2003 International Residential Code (IRC) intended to resist these loads. The stated purpose of the IRC is to provide: "... minimum requirements to safeguard the public safety, health, and general welfare, through affordability, structural strength, means of egress facilities, stability, sanitation, light and ventilation, energy conservation and safety to life and property from fire and other hazards attributed to the built environment." Because the building code requirements are minimums, a house and its contents still may be damaged in an earthquake even if it was designed and built to comply with the code. Research has shown, however, that earthquake damage to a house can be reduced for a relatively small increase in construction cost. This guide identifies above-code techniques for improving earthquake performance and presents an estimate of their cost. Note that the information presented in this guide is not intended to replace the IRC or any applicable state or local building code, and the reader is urged to consult with the local building department before applying any of the guidance presented in this document. The information presented in this guide applies only to one- and two-family detached houses constructed using the nonengineered prescriptive construction provisions of the IRC. Applicable IRC limits on building configuration and construction are described.