Elevation Can Keep a Structure High and Dry
Elevation means raising a structure so that the lowest floor is at or above the base flood elevation – the minimum level at which a flood has a 1 percent chance of occurring in any year. A new foundation is put under the elevated structure and stairs or landings then are built to provide access to the main floor.
When a structure is properly elevated, the living area will be above all but the most severe floods.
To decide whether elevating a structure is a good idea, consider these factors:
What is the risk of another flood impacting the structure? Properties in a Special Flood Hazard Area (SFHA), commonly referred to as a “100-year floodplain,” usually have a greater chance than others of being impacted. The term “100-year flood” really means that there is a 1 percent chance of a flood occurring in any year. A “500-year flood” has a .02 percent chance of striking in any year.
What kind of flooding could impact the structure? Take into account the potential water depth, the velocity of floodwaters (how fast they move affects the damage potential) and the frequency of flooding in the area.
What level of protection is needed? Should the elevation protect against a 1-percent flood, a .02-percent flood or some other level?
How long might floodwaters remain before receding? The longer the exposure, the greater the damage.
How would floating debris impact the structure?
Once these questions are answered, check with local building authorities to find out what is required or allowable by local or state codes and ordinances. This answer will determine, in large part, what can and can’t be done.
Next, check with a few qualified contractors who have previously done this type of work to determine what’s involved in elevating an existing structure, or building a new, elevated structure and the associated costs.
In some areas, local ordinances may require that a structure be elevated if it has sustained substantial damage (50 percent of the building’s pre-flood market value) from any cause, or if substantial improvements costing 50 percent of a building’s market value, are going to be made. Local officials will determine whether a structure fits either of these categories.
Elevating a structure can have the following benefits:
- The structure is compliant with a community’s local floodplain ordinance, which enables residents to purchase flood insurance.
- The flood risk to a building and its contents is reduced, thereby eliminating the need to move vulnerable items above the water during flooding, or losing contents altogether.
- Flood insurance premiums are reduced.
An additional benefit is that the existing lot often is adequate in size, enabling an elevation to occur without having to purchase additional land — a factor that may be required to accomplish other types of mitigation.
The Federal Emergency Management Agency (FEMA) offers a free publication, Above the Flood: Elevating Your Flood-Prone House (Pub# 347), that explains how to elevate a house. Download a copy online, or order a hard copy by calling 800-480-2520.
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