Techniques for Wet Floodproofing

Floods November 04, 2015 Print Friendly and PDF


Wet Floodproofing is a design method that allows water to move in the enclosed parts of a home's lower area, such as the crawlspace or an unoccupied area, and then out when water recedes. Materials and components used in these areas are selected for their ability to become wet, sustain minimal damage, dry, and be restored.

The advantage of wet floodproofing is that, as floodwaters come into the prepared enclosed areas they will reach the same level as the outside water. This equalizes the water pressure on both the inner and outer walls and may prevent structural damage caused by unequal pressure on the structure's walls.

All the materials below the flood protection elevation* must be resistant to flood or water damage. The materials and components of wall and floor systems should encourage drying in at least one direction.

(Source: Federal Emergency Management Agency, Homeowners' Guide to Retrofitting pp 98 and 110.)

Water exiting from a crawlspace during draining
Photo courtesy of H.A. Aglan, Tuskegee University
Raised water filter system above potential flood level | Photo courtesy of Shirley Niemeyer, University of Nebraska-Lincoln

Wet floodproofing is used for

  • Walkout basements.
  • Below-grade basements.
  • Crawlspaces or garages.


Before making a decision about the methods you want to use, know all the options.

  • Wet floodproofing may be less costly than some other flood protection methods, such as moving the home.
  • When flooding occurs, residents cannot live in the house as long as the floodwaters are inside or underneath the home.
  • Wet floodproofing does not prevent damage from heavy or fast-moving water and currents, wave action, and debris.
  • All materials, including finishing and construction materials, below the flood protection elevation should be flood- and moisture-resistant. If not, they must be removed or replaced with resistant materials.
  • Construction or remodeling methods should also allow for the structure, including wall and floor cavities or systems, to drain and dry. Wind-blown water and floodwater will enter through very small cracks into the cavities or systems. Water and vapors must be able to escape and dry in at least one direction, preferably two.
  • Equipment (furnace, water heater, washer, dryer, water softening equipment, etc.) should be relocated to a higher floor or elevated above the flood protection elevation. Utilities and electrical panels should be relocated to a floor above the flood protection elevation or to the attic.
Raise equipment above potential flood levels | Photo Credit: Shirley Niemeyer, University of Nebraska-Lincoln
  • Depending on local and area regulations and the National Flood Insurance Program, homeowners may not be able to use wet floodproofing for a basement in which all walls are below grade. They may be required to fill in the basement.
  • If floodwater contaminated with chemicals, sewage, and other materials enters the lower living level, the area will require intensive cleaning.
  • The area that is wet floodproofed has limited uses, such as parking and access.
  • Pumping out the wet floodproofed basement too quickly can result in structural damage. If the outside earth is still saturated, the outside of the wall may be under greater pressure than the inside of the wall, which can result in damage to the basement wall.
Raise utility entrances, electrical fuse or circuit boxes, and electrical wiring above potential flood levels
Photo courtesy of Shirley Niemeyer, University of Nebraska-Lincoln
  • Flood protection elevation is the elevation of the highest flood that a method is intended to protect against. The base flood elevation (BFE) for a flood zone means that the lowest living level has a 1 percent chance of being equal to the BFE level or exceeded by floodwaters in any year. (Sometimes referred to as 100-year flood.)

Summary

Two alternatives for protecting a home from flood damage are wet floodproofing and dry floodproofing. Both of these methods have advantages and disadvantages. If the homeowner has National Flood Insurance, regulations must be considered. It is important to contact local zoning and code offices, local or area emergency management agencies, housing professionals, and construction engineers when considering these alternatives. The National Flood Insurance Program has specific codes and requirements in place that must be met. Homeowners should obtain more information before making a decision about using these methods.

Resources

Federal Emergency Management Agency. Homeowner's Guide to Retrofitting: Six Ways to Protect Your House from Flooding, chapters 3 and 7.

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