building and rehab practices: overview » introduction » mitigating flood damages
For areas where moderate floods occur, with low flows and no more than a few feet of water, techniques to "floodproof" a home are generally the most useful and cost effective measures. [1] There are two general types of floodproofing - "dry" and "wet."

Dry floodproofing involves procedures to help create waterproof or water-resistant seals around the exterior of home to prevent water from entering. These measures can include the installation of new brick veneer over asphalt coating or by applying polyethylene film over existing walls. Homeowners can also use sandbags outside their homes to divert minor storm water and debris flows. [2]

Wet floodproofing serves to make uninhabited parts of the home (i.e., garages, unfinished basements) resistant to flood damage. These measures allow water to enter during flooding. Flood vents, which create permanent openings in a home's foundation walls, are one example of wet floodproofing. Wet floodproofing procedures have a particular advantage in that they are often less costly than other retrofits and do not significantly affect the appearance of a home.

In areas where more serious flooding tends to occur, elevation is generally the most effective measure. [3] Elevation involves raising major home appliances (washer, dryer, furnace, water heater, air conditioning fans and compressors) and the electrical system (electric panel board, service lines, wiring, outlets) above the base flood elevation (or BFE - see box for an explanation). In areas that are prone to extreme flooding, elevation may involve raising the whole existing home or building a new home above the BFE.

This type of overall elevation involves raising the lowest floor (including basement) to or above the BFE. Common techniques for this include elevation on file, elevation on piles, piers or columns, and elevation on extended foundation walls such as on a crawl space. [4] In order to provide a greater margin of safety, state and local flood management authorities often employ a practice called "freeboard." This is a required or recommended level of elevation for residential structures, expressed in a designated amount of feet above projected flood levels. This creates a margin of safety to compensate for the many unknown factors that could increase the height of floods above the BFE.
Base Flood Elevation

The base flood elevation (BFE) refers to the estimated level of water associated with the "100-year flood." The "100-year flood" is a severe flood reaching or surpassing a certain water level that has a 1-percent chance of occurrence in any given year. Designated "100-year flood" areas form the basis for the National Flood Insurance Program rates and regulatory floodplain management.

Click here to learn more about the "100-year flood" and the National Flood Insurance Program.

States and localities can both require and financially support major mitigation techniques, like elevation, in residential areas highly prone to major flooding. The city of Mandeville, Louisiana enforces strict residential building codes that require homeowners who have suffered severe flood damage to elevate their homes, but provides support to do so. Click here to leave this section and learn more about Mandeville's residential building codes and how improving residential building codes can help make homes more resistant to disasters.

Relocating Vulnerable Households

For areas that are especially vulnerable to the effects of severe storms, particularly floods, relocating a home to or rebuilding a family's home in a safer location may be the only viable option. This is often the case when an existing home lies in an area that has been subject to frequent, severe storm hazards, and in some cases, rendered uninhabitable. Relocation usually involves two options. The first is the buyout of property owner. A federal, state or local government agency can either demolish the homes and pay residents to move or physically relocate home if feasible. After relocation, the former home site must be deeded over to the respective public entity to be converted into open space. [5]

Several state and localities have used pre-disaster funding to institute such relocation programs. In 2003, the city of Birmingham, Alabama received a Predisaster Mitigation Grant grant through the state to purchase 65 flood vulnerable properties. Through the resulting effort, the city relocated 55 families. Following relocation, the city redeveloped the hazardous area where the homes were formerly located into permanent recreational parkland. [6]

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Measures for mitigating flood damages

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Measures for mitigating severe wind and rain damage

Providing education and training for making homes more resistant to disasters

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[1] Interview with Jim Schwab, senior research associate at the American Planning Association.
[2] Federal Alliance for Safe Homes website
[3] Interview with Jim Schwab.
Federal Alliance for Safe Homes website
[5] Interview with Jim Schwab.
In Action -- The Pre-Disaster Mitigation Grant Program. [PDF] 2006. Washington, DC: Federal Emergency Management Agency.