Floodproofing Improvements for Walls and Floors

Patricia Skinner  |  10/13/2012 7:12:28 AM

Wall Improvements for Flood Resistance

Wet Floodproofing Methods for Shallow Flooding

Limit Damage - Prevent Wicking
Damage from shallow floods is typically not confined to the area that was touched by floodwater, but includes areas that were wet by water wicking - creeping up the wallboard (commonly called sheetrock) and other porous building materials. You can reduce the damage from shallow flooding by creating gaps in the wallboard and other materials so wicking stops at the gap and you would need to replace only the wallboard or insulation below the gap. The wallboard gap can be disguised by decorative trim such as a chair rail. The gap can be filled with waterproof caulk or a gasket material. Similarly, use a non-wicking waterproof material to separate insulation in the upper wall from that in the lower wall creating the smallest possible gap in the insulation. For VERY shallow flooding you can avoid damage by trimming the bottom so it ends several inches above the floor. Use extra-wide baseboards to cover the gap. (See Diagram).

The anti-wicking technique confines flood damage to the lower part of the wall, even if you use customary building materials. If you have designed the system so paneling, wallboard, and insulation are easily removed and re-installed, you may be able to save them from flood damage.

Use the opportunity created by re-doing the walls to raise the electrical wiring, switches and outlets, ideally moving them to a location above the wicking gaps.

Create Flood-hardy Walls
A flood-hardy wall is one that can stay in place during the flood and require only cosmetic restoration - cleaning and painting, not replacement of materials. A flood-hardy wall (or flood-hardy lower wall section) consists of materials that are flood-damage resistant (see next section). It is designed so flood water enters and drains freely from the wall. Gaps at the top and bottom of the floodable section of the wall must be wide enough to allow flushing (to remove silt and contaminants) and air circulation (to dry the materials before harmful fungi and bacteria take hold).

Interior walls - and the inside face of exterior walls - can be made more flood-resistant with some simple interior finish alternatives:

  • Use paperless drywall (fiberglass mat gypsum) or create wainscoting with plywood or fiber-cement panels.
  • Place the material 4-5 inches above the finished floor, and cover the bottom gap with a wide, removable baseboard.
  • Leave a small gap between the lower and upper wall-finish material, and cover that gap with chair-rail molding.
  • Use only latex paint to finish the wall. Do not use wall paper on the lower wall. (Do not use vinyl wall paper on the upper wall nor any exterior walls in south Louisiana's hot, humid climate.)

Note: If you use these techniques on a wall that separates your home interior from the garage, make sure the garage-side of the wall maintains its fire-retardant properties (fire-rated materials, no gapping).

Exterior walls can present more challenges because they typically contain insulation and exterior sheathing. If your exterior wall has solid wood or steel studs, that part is flood-hardy. So the challenge is what to do about the insulation.

  • Flood damage-resistant insulation. The most flood damage-resistant thermal insulation is high density (closed-cell) foam. Two inches of closed-cell foam provides about the same insulating R-value as 3.5 inches of fibrous insulation. When it is spayed on, it also prevents air movement through the wall, which enhances its insulating properties.  THE PROBLEM with using sprayed-on, closed cell foam in a wall that is expected to absorb flood-water flood is that the foam will significantly RETARD drying of the sheathing. Sheathing is on the outside of the studs and behind the brick or siding). Even if that sheathing is water-resistant, it is likely to stay wet long enough for mold and wood fungus to become a serious problem. The preferred application would be to use two-inches of rigid foam board, cut to fit tightly between the studs and placed against the sheathing. After the flood, the foam boards should be removed, cleaned and put back in place.
  • Insulation that is not flood damage-resistant. Fiber-glass batts and other fibrous insulation can be used, but should be a type that can eaisily be removed before (or immediately after) the flood. It will have to be discarded if it gets wet. If you have advance warning of a pending flood, you may be able to remove (or fold up) the insulation so it can be put back after the lower wall cavity has been cleaned.

If exterior sheathing and or cladding (bricks or siding) is being replaced, there are materials and methods that can be used to improve the water and moisture resistance of the wall even further. Be sure to use references and methods designed for our hot, humid, rainy region, not other parts of the country. LSUAgCenter.com/Home has an excellent collection. 

Wet Floodproofing Techniques and Considerations
6-Tips for Reducing Future Flood Damage

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