Crawl Space Ventilation
Crawl space vents keep moisture from building up under homes and damaging building materials. Don't be tempted to seal them to save energy. Sealing them could cause costly moisture damage.
Foundation vents for the crawl space should be located on every wall, close enough together that there is at least one square foot of free vent area for every 25 linear feet of foundation. Free vent area is that area unobstructed by screens, louvers, or other materials. Heated crawl spaces and basements do not need vents. It is a good idea to cover earth floors with a moisture barrier like plastic to lower moisture levels. In an existing home, only about 80% of the exposed ground should be covered initially, to avoid problems caused by the home drying out too quickly.