Homeowners considering alternatives for protecting their home from flood damage might consider wet floodproofing, dry floodproofing, and protective barriers. These methods have advantages and disadvantages to consider. They may fail if the wind and water forces and debris impacts are too great. “Floodproofing” does not mean that damage is not going to happen. It means the damage may be reduced and that the structure is made more flood or water resistant.
In addition, there are other alternatives including moving to a home outside the risk area, moving the structure itself to another location or elevating the structure. Before making a decision, contact local, area building officials, and flood plain managers about regulations. This module covers dry floodproofing.
Dry floodproofing means that techniques are applied to keep floodwaters from entering the structure. This involves sealing the structure to keep floodwaters out and to keep the structure dry below the flood protection elevation. However, keeping water out is difficult. FEMA guidelines suggest it may not be effective. Other professionals indicate that dry floodproofing is not acceptable for residential housing (Wendt & Aglan, Hurricane Season, 2006).
Research conducted at Tuskegee University shows that when the water level outside rose to 1 foot higher than the floor level, the dry flood proofed test structure started to leak. They managed to keep the water out for about ½ hour longer than if it had not been dry floodproofed.
Floodwater creates pressure on the exterior walls and floors that may cause the structure or walls to collapse and the floors to buckle. Water pressure and buoyancy underneath the structure may buckle the floor. When floodwaters are higher than about 2 to 3 feet, non-reinforced masonry and masonry veneer walls are much more likely to crack or collapse. Water may also enter through the floor.
Generally, dry floodproofing is used when the expected flood depths are low such as a few inches of water. The ability of the house structure to withstand the exterior flood pressure depends on the wall construction and the depth and movement of the water among other factors. Dry floodproofing is not recommended for houses with frame walls at the lower levels, or for houses with basements and crawlspaces.
Two alternatives for protecting a home from flood damage include wet floodproofing and dry floodproofing. Both of these methods have advantages and disadvantages to consider. If you have National Flood Insurance, regulations must be considered. It is important to contact local zoning and code offices, local or area Emergency Management Agency as well as housing professionals and construction engineers when considering these alternatives. Specific codes and requirements are in place by the National Flood Insurance Program and must be met. Some examples of additional information sources are listed here.
Federal Emergency Management Agency. Homeowner's Guide to Retrofitting: Six Ways to Protect Your House from Flooding, Chapters 3 and 7.