Causes of moisture problems in a crawl space include water intrusion, moisture in the ground, heating and air conditioning systems, and limited ventilation. Water intrusion occurs when water from outside the crawl space runs into the area, creating a moisture problem. Improper landscaping around the home’s foundation, an improperly installed sprinkler system or a patio that slopes the wrong way increases the amount of water that intrudes the space.
Moisture also enters the crawlspace from the ground. With new construction, builders often install a layer of vinyl on the floor of the crawlspace to prevent this type of moisture problem. In older homes, builders often failed to install the vapor barrier. Without this protective plastic layer, a significant amount of water is able to enter the space.
When the air conditioning in a home is in operation, the ducts become very cold. The cold metal provides a place for moisture from the air to condense and drip to the floor. Insulating the ducts eliminates this border between the hot moist air and the cold air duct.
Foundation vents can help to reduce the moisture in the crawl space. With good cross ventilation, the moist air this space normally traps flows outside the foundation, keeping the crawlspace drier.