Why Crawlspace Moisture Matters
Crawlspace moisture problems affect indoor air quality, structural integrity, and energy efficiency throughout the entire home. Moisture in crawlspaces promotes mold growth, wood rot, and insect infestation. The US Department of Energy estimates that unsealed crawlspaces account for 15 to 25 percent of a home’s total heat loss. Vented crawlspaces, once standard practice, have been shown to increase moisture problems rather than solve them because humid outdoor air enters the crawlspace and condenses on cool surfaces during summer months.
Encapsulation Process
Crawlspace encapsulation involves sealing the crawlspace from both the ground and the exterior environment. A heavy-duty vapor barrier of at least 6 mil polyethylene, though 12 to 20 mil is recommended, is laid over the entire crawlspace floor. The barrier extends up the foundation walls at least 12 inches and is mechanically attached and sealed at seams. waterproof coating to protect the foundation. vapor barrier installation in crawlspaces. All seams are lapped a minimum of 12 inches and taped with manufacturer-approved seam tape.
Foundation wall vents are sealed permanently to prevent outside air from entering. The crawlspace access door is weatherstripped and insulated. Any openings around pipes, ducts, and wires penetrating the crawlspace walls or floor are sealed with caulk or spray foam to prevent air leakage and pest entry.
Dehumidification and Conditioning
Once sealed, the crawlspace requires mechanical dehumidification to control moisture levels. A dehumidifier sized for the crawlspace volume maintains relative humidity below 60 percent. Some HVAC systems can be extended to provide conditioned air to the crawlspace, maintaining temperatures above the dew point to prevent condensation. granular base course for concrete slabs. A condensate pump removes collected water to the exterior.
Insulation options for encapsulated crawlspaces include rigid foam insulation on the foundation walls rather than between the floor joists above. This approach keeps the crawlspace air temperature closer to the conditioned space temperature, reducing heat loss through the floor above. The rigid foam must be covered with a thermal barrier for fire protection if the crawlspace is used for storage.