Design for Flood Damage Reduction

Patricia Skinner, Reichel, Claudette Hanks  |  1/6/2007 12:21:42 AM

Elevated Slab and Air Conditioner

The following are steps you can take to design your home to minimize flood damage.

Build above anticipated flood levels

Building above anticipated flood levels is the best flood protection method. The tool used most often for determining anticipated flood levels is the Flood Insurance Rate Map (FIRM). FIRMs are used to determine premium rates for flood insurance provided by the National Flood Insurance Program (NFIP). The maps are also used by communities to regulate new development, including housing and placement of fill in a floodplain (which diminishes its flood storage capacity). NFIP standards set minimum levels of protection. Exceeding those standards is wise. In some communities, exceeding the standards is required by local ordinances.

A flood map for an area shows the elevation (number of feet) above sea level that represents the “100 year” (or 1 percent chance per year) flood level, known as the base flood elevation (BFE). NFIP and the residential building code standards require building at or above the BFE of the building site. Building your home above BFE will reduce your flood insurance premium. Building two feet above BFE provides a good extra margin of protection and qualifies the house for a BFE + 2 insurance rating, which is significantly lower premium than the rate for BFE.  See articles below on Foundations in Flood Hazard Areas for more information on foundation types appropriate for different flood zones and Flood Maps and Permits.

Additional design features

Anchor exterior structures: Decks, porches, carports and other exterior structures that attach to your home will be exposed to the same flood forces as the house. Although these can be designed to break away from your house without damaging it, this is not recommended. You could suffer the loss of the attached structures, which could be thrown against other people’s property. All exterior structures attached to your home should be firmly connected to the house and securely anchored on the sides away from the house.

Slope Garage, driveway, entries, patios away from house: To prevent wind-blown water from entering the house, any paved surfaces adjacent to the house and capable of collecting and channeling water should be at least 4 inches below the living floor. They should also slope away from the house at a minimum slope of 1 inch per 20 feet. Unpaved areas should be at least 8 inches below the bottom of the first floor and slope at least 6 inches per 10 feet.

Elevate HVAC, electrical and mechanical systems: Elevate electrical wiring, plumbing outlets, heating, ventilation, air conditioning equipment and other mechanicals to the same level of protection as the main structure. Parts of elevated systems that must extend below BFE should be designed to prevent entry of floodwater.

Related Articles:

Flood Protection - Additional Features
Foundations in Flood Hazard Areas
Flood Maps and Permits

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