Sealing Around the Crawl Space

For many years, the widely accepted opinion was to ventilate crawl spaces to control moisture, mold, and mildew. Thus, crawl space ventilation was written into many building codes, and builders duly installed vents to comply. Recently, the U.S. Department of Energy funded a study to determine the relative performance of sealed crawl spaces versus vented crawl spaces. The study found that a sealed and conditioned crawl space has many advantages over a vented crawl space, including lower energy consumption, lower moisture content in the home’s wood, lower humidity, and reduced fungus growth.

To seal a crawl space, the study recommends a number of procedures, including installing a standard waterproofing system; sealing all exterior wall penetrations and vents; installing a thick, plastic vapor retarder/barrier on the walls and floors; sealing all penetrations of ducts, electrical wires, and plumbing through the subfloor; insulating the spaces between floor joists; and installing a humidity management system.