If moisture levels still seem high after this time, go back and recover some of the exposed ground area. If the house has carpet, vinyl, or flooring materials other than wood, the crawlspace area can be fully covered with polyethylene. The sand weights down the polyethylene, preventing condensation of moisture on the undersurface. Sand absorbs condensation that occurs in the cold weather and prevents the deterioration of any of the plastic exposed to light. Installing polyethylene on crawlspace surfaces helps control excess moisture vapor.
Place vents to provide cross ventilation.
Foundation vents have a metal grid of about one-inch square with screen wire to exclude mice. There is usually an operating metal shutter on the vent. The pumps are electrically powered with automatic controls and are permanently installed in a reservoir or drain or at the lowest area where water accumulates. When a sump pump is installed in the crawlspace at the lowest point, a hole 20 x 20 x 20 inches is excavated to accommodate a piece of 12x12-inch flue liner. The sump pump is placed in the flue liner with guy wires from the pump to the floor joist.