Dry floodproofing includes measures that make a structure watertight below the level that needs flood protection to prevent floodwaters from entering.  This type of floodproofing is often used to protect non-residential structures, water supplies, and sewage systems.

Dry floodproofing may NOT be used to bring a Substantially Damaged or Substantially Improved residential structure into compliance with the community’s floodplain ordinanceHowever it CAN meet requirements for non-residential and commercial structures.

An example of a dry floodproofing measure is to apply a waterproof veneer, such as a layer of brick backed by a waterproof membrane, directly to the outside surface of an existing structure. (Photo shows home under construction with weatherproof membrane and brick veneer used to protect the structure.)

Flooding can cause sewage from sewer lines to back up through drain pipes. These backups not only cause damage that is difficult to repair, but they also create health hazards.

One way to protect against this hazard is to install backflow valves, which temporarily block drain pipes if water travels up them the wrong way. If a structure’s lowest level has a floor drain that empties to the exterior of the building, installing a floating floor-drain plug can also prevent flood waters from backing up the drain pipe and entering the structure.

Refer interested individuals to local building officials and plumbing specialists before undertaking any of these measures. (Illustration shows the typical installation of an exterior backflow valve.)

Well contamination, sewer line back up, and mold may occur in any type of flooding.
Flood waters often carry hazardous and toxic materials, including raw sewage, animal waste, oil, gasoline, solvents, and chemicals. 

If a property’s water supply comes from a well, flood waters entering that well can contaminate the groundwater and make the well water unsafe.

Wells suspected of being contaminated should be inspected by a professional.
Proper well construction will protect a well from contamination.  A licensed well-drilling contractor can inspect a well and suggest improvements such as:

  • Extending the casing at least 2 feet above the highest known flood elevation
  • Installing a sanitary seal or cover on the casing
  • Installing a backflow valve in the water line

(Photo shows sign reading "Boil water notice.")