Most flood-proofing systems have openings that need to be closed and kept watertight during a flood. A panel closure is any flat, firm sheet of material used to block one of these openings. It may be plywood, aluminum, steel, wood planking, Plexiglas, or any rigid material. It can be permanently attached or designed to be set in place quickly in an emergency.
A panel should be:
- Strong, but not brittle.
It should resist the impact of floating debris.
- Durable when wet.
It should not dissolve or come unglued in water. If you’re using plywood, choose an exterior grade. Don't use particleboard.
- Weather resistant.
The panel should be painted, galvanized, or otherwise sealed to prevent weakening by rot, rust, sunlight, or corrosion.
- Resistant to termites, wildlife, and pets, if permanently installed.
When flood-proofing systems fail, it is often because the closures were improperly designed or installed. In a system designed to hold back 3 feet of water, the panel closure itself must be strong enough to withstand a force of about 180 pounds per square foot at the base of the panel and a total of about 300 pounds per linear foot of panel. Never use closures and pumps to create a difference of more than a couple feet between inside and outside water levels, unless an engineer certifies the structure's ability to withstand the forces generated. Differences in pressure can cause walls to collapse.
The force from water against a panel is transferred to the frame. In addition to using panels with sufficient strength, be sure the frames, mountings, and structure are strong enough to support the panels.
Install panels so water pressure tends to push them closed, not open. Use gaskets between hard surfaces to improve the seal. Plastic sheeting can be used on the face exposed to water to assist with sealing.
In some localities, such as seashore communities prone to hurricanes, crawlspaces are left open to allow floodwaters to pass beneath the building.