Floodproofing includes any combination of structural and non-structural additions, changes, or adjustments to structures that reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures and their contents.
The intent of dry floodproofing is to make a building watertight to one foot above BFE or the DFE by applying a waterproof coating or impermeable sheeting to the exterior. All openings, such as windows and doors, must be closed off during a flood with temporary or permanent shields.
Dry floodproofing is not recommended for historic buildings as the coatings used are difficult to remove without damaging the underlying materials and would change the appearance of the building where they are applied. Applying a waterproof coating or impermeable sheeting to the existing foundation and exterior walls does not mean they will be able to withstand the physical forces of a flood. The building must still be anchored to its foundation in order to resist the forces of water and movement. This retrofit only works for buildings that are built on grade (i.e., built level with the ground) and have an impervious exterior wall material like brick or concrete. This retrofit also works best only for short flooding events since coatings may deteriorate during extended flooding.
Wet floodproofing involves planning for the home to flood and making preparations to reduce the damage when it happens. Wet floodproofing is achieved by raising utilities, structural components,, and contents above BFE. This treatment is only recommended for certain situations, such as a historic building that cannot be elevated or otherwise protected. This treatment requires some work in advance of a storm and more intervention than many of the other options available. Wet floodproofing is typically less expensive than other floodproofing options, but can lead to more interior damage as it allows water to enter and recede. Because the building is purposely allowed to get wet, it may take longer before it can be re-inhabited after a flood.
Permanent levees constructed around the building are another option but can be very large and costly. Levees require an engineer and permits to determine if they are appropriate for a site. Similar to levees, floodwalls are expensive to build and, though they require less space, may present some of the same issues. Both levees and flood walls may create the perception that they are forcing more flood waters towards a neighbors’ property. For both levees and floodwalls, it is important to consult building and zoning codes and check for utility lines before beginning construction. Local authorities must be consulted before constructing levees or floodwalls. A homeowner may be required to work with a Federal agency to design and develop a levee. Poorly designed and maintained levees or floodwalls can be more a threat than protection if they fail.
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