DRY FLOODPROOFING: SEALANTS AND IMPERMEABLE MEMBRANES
INSIDE THE FLOODPLAIN

What Is It?

Cost: Sealants: $2.50 per linear ft. Membranes: $3.50 per sq ft. $5.70 per linear ft. (Estimates based on floodproofing for floods of approx. 3 ft.)
Applications: Easily integrated into retrofits and new construction. Overall costs will be lower for new construction.
Service Life: 10 years minimum. Most warranties are 10 years to lifetime.

Dry floodproofing techniques can be used to make a structure watertight below flood elevation. Impermeable membranes and sealants can be used to seal walls to reduce or prevent the penetration of floodwater through walls. Membranes and sealants are typically applied to exterior wall faces, making them cost-effective options for retrofitting existing buildings. Tests using sealed and sheet membranes used over concrete walls have yielded ¼ to 4 inches of leakage after over 24 hours of exposure to 3 feet of flooding. Particularly in structures with basements, walls and floors must be specifically designed to resist hydrostatic pressure. If design loads in dry floodproofed buildings are exceeded, buoyancy forces can actually cause more damage to a building than would have occurred if the building were simply allowed to flood.

The success of interior floodproofing in protecting a building from flood damage will depend on the depth, duration, and velocity of the flood. For buildings in the most vulnerable flood zones, dry floodproofing will be most effective when multiple measures are combined. Wall sealing should be combined with other measures like flood shields for maximum protection. Internal drainage systems (e.g. sump pumps) may also be employed, as sealed walls can still leak in longer, deeper flood events. Sealants and membranes should be inspected regularly for cracks and potential leaks.

Benefits

  • Cheaper than other retrofitting methods for floodproofing.
  • Applied to the building itself and does not require additional land (for floodwalls or levees).
  • Easily combined with other dry floodproofing measures (e.g. flood shields/barriers, sump pumps) for maximum protection.
  • Does not require human intervention during a flood event for protection.

Drawbacks

  • Membranes and sealants do not protect structures from high-velocity flood flows and wave action.
  • Dry floodproofing measures alone are insufficient to bring substantially damaged or substantially improved residential structures into compliance with floodplain management ordinances and laws.
  • Regular inspection and maintenance are required to ensure continued functionality.

Regulatory Impacts and Requirements

A summary of potential regulatory touchpoints follows below.
Sealants-and-Impermeable-Membranes

Financing Options, Incentives, And Rebates

Additional Resources

PROJECT EXAMPLES

SAMPLE OF SUPPLIERS

SOURCES

Photo credit: Labeled for reuse by Gulf Coast Community Design Studio