When building or restoring a home where flooding could rise above the foundation, a drainable, dryable wall assembly is designed to survive with little or no damage and save you the cost and ordeal of gutting and replacement of most materials. After a flood, it can be washed out and dried quickly enough to avoid decay and reduce mold growth.
Illustration and model on-site at LaHouse Resource Center courtesy of Georgia-Pacific.
1) Elevate the structure above potential flood level, if possible.
2) Elevate equipment and wiring.
3) Build with cleanable materials that can get wet without damage.
4) Assemble materials so they can dry after they get wet. Avoid vinyl wallpaper.
A drainable, dryable wall uses durable materials assembled in a special configuration that allows the wall cavity to drain and dry out after a flood event. From the exterior to the interior of the wall, it contains:
1) Siding made from fiber-cement, vinyl or aluminum, brick veneer or other material that can withstand flooding.
2) Furring strips (thin strips of wood or plastic to create a drainage gap between siding and sheathing). Brick veneers have a drainage space, so furring strips are not needed, but weep holes at the bottom course should be protected from mortar droppings.
3) Rigid foam sheathing (nonabsorbent closed cell insulation, thus flood damage resistant).
Note: Home restoration alternative is rigid foam boards cut to fit inside stud cavity space or closed cell spray foam insulation installed to fill 60% of the cavity depth (i.e. 2 inches of foam in 2x4 framing).
4) Weather barrier or housewrap (to reduce water penetration during normal, non-flood conditions).
5) Plywood sheathing (provides wind resistance, impact resistance, nail holding ability, and better ability to withstand wetting compared to OSB or fiberboard sheathing panels).
6) Solid wood framing (for best results, use pressure treated wood to resist termites, decay and mold).
7) Paperless, moisture-resistant gypsum drywall (made with a fiberglass mat instead of paper and a moisture-resistant core to minimize absorption and eliminate food source for mold and termites).
Leaving drywall gaps behind removable crown or chair-rail and baseboard moldings provides space where the wall cavity can be flushed out and ventilated to dry. Gaps also prevent wicking from lower to upper panels.
Go to www.fema.gov website to see a list of other flood-hardy materials under Flood Damage Resistant Materials.