One way to protect a structure and its contents from flood damage is to seal the building so that floodwaters cannot enter. This method, referred to as “dry floodproofing,” encompasses a variety of measures:

• Applying a waterproof coating or membrane to the exterior walls of the building.
• Installing watertight shields over doors, windows, and other openings.
• Anchoring the building as necessary so that it can resist flotation.
• Installing backflow valves in sanitary and storm sewer lines.
• Raising HVAC and electrical system components above the flood level.
• Anchoring fuel tanks and other storage tanks to prevent flotation.
• Installing a sump pump and foundation drain system.
• Strengthening walls so that they can withstand the pressures of flood waters and the impacts of flood-borne debris.
• Building with materials that can withstand flood waters for at least 72 hours (examples: concrete, ceramic tile, pressure-treated lumber, steel, metal, brick, epoxy paint, foam, and closed cell insulation).
• Ensuring wells are properly constructed to avoid contamination from flood waters.

Keep these points in mind when you dry floodproof:

• Dry floodproofing is appropriate primarily for slab-on-grade buildings with concrete or solid masonry walls. Concrete and masonry are easier to seal, more resistant to flood damage, and stronger than other conventional construction materials.
• If you dry floodproof a “substantially damaged” or “substantially improved” building (as defined by the National Flood Insurance Program [NFIP] regulations) or a newly constructed building, and if the building’s lowest floor (including any basement) is below the BFE shown on the FIRM map for your community, your dry floodproofing must be certified as providing protection from the BFE. To obtain this certification, you must floodproof your building to a height at least 1 foot above the BFE. Check with your local floodplain manager or building official for more information.
• The height of your dry floodproofing should not exceed 3 feet. The pressures exerted by deeper water can cause walls to buckle or collapse. Before you use dry floodproofing to protect against greater flood depths, have a structural engineer evaluate the strength of your walls.
• If your dry floodproofing measures require human intervention before flood waters arrive, such as placing shields over doors and windows, you should have an operations and maintenance plan that describes all the actions that must be taken and lists the persons who are responsible. It must also include a schedule of periodic maintenance that states how often the dry floodproofing measures will be inspected and who will perform the inspections.
• The cost of individual dry floodproofing measures will vary with the size, condition, and use of your building, the dry floodproofing height, and the extent to which you use contractors and engineers.

In many cases, flooding on a property can be caused by poor drainage. If this is the case, it may be of great benefit to address the drainage issue with the professional advice of a licensed civil engineer.

An excellent source of information for protecting your property from flooding is FEMA’s Coastal Construction Manual. 

Elevating Existing Structures