Water under the crawlspace or in the basement is usually due to incorrect building. We will begin with methods of fixing a damp crawlspace or a damp and wet basement.
Number one: make sure the house has rain gutters and downspouts, and that the downspouts direct water away from the base of the house. One way to do this is to have the downspouts go into underground perforated tubes that lead water at least 20 feet away from the house. Another way is to have the rollup frog tongues, as some people call them, connected to the downspouts. When it rains and water fills the rain gutters and goes down. The downspouts, the fraud tongues rollout and direct water away from the house.
Number two: ensure that good ventilation is occurring in the crawlspace or the basement. This can be done by making a small outlet in the heating and air-conditioning system or by installing a small fan to create a continuous airflow and the crawlspace or basement.
Number three: look carefully outside, around the entire crawlspace or basement and make sure that the soil is slanting away from the base of the house at all places. This slant or slope insures that all rainwater is draining away from the crawlspace or basement. Some soil may need to be brought in, to even this up and make sure the water runs away from the basement or crawlspace in all areas.
Number four: inside a crawlspace, one should make sure that the crawlspace is level and clean and then covered with a few inches of dry sand. Next two layers of overlapping five mil plastic and that plastic should be covered with another two or 3 inches of dry sand. This will keep the moisture in the soil from evaporating up into the crawlspace and eventually going up into the insulation of the house.
A damp crawlspace or wet basement creates conditions suitable for mold and mildew. Mold and mildew are bad for your health, and bad for resale of your home.
Soon sellers and realtors will be required to have mold and mildew tests for homes before they can be sold or as part of a home inspection. In some areas a home inspection includes dampness, mold, and mildew inspection now.