Recommended Residential Construction for Coastal Areas - Building on Strong and Safe Foundations (FEMA P-550, Second Edition)

Book excerpt: 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®, International Residential Code®, 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.