A closed crawl space should include insulation on foundation walls, a ground vapor retarder, and mechanical ventilation. (Some local jurisdictions allow insulation in the floor instead of the wall insulation.) Unlike a conventional crawl space, a closed crawl space does not have wall vents and is air sealed to improve energy and moisture performance. A closed crawl space may also be referred to as unvented, conditioned, semi-conditioned, or sealed.

A closed crawl space should include insulation on foundation walls, a ground vapor retarder, and mechanical ventilation. (Some local jurisdictions allow insulation in the floor instead of the wall insulation.) Unlike a conventional crawl space, a closed crawl space does not have wall vents and is air sealed to improve energy and moisture performance. A closed crawl space may also be referred to as unvented, conditioned, semi-conditioned, or sealed.

A well-designed crawlspace is closed, dry, energy efficient, and practical to build. With proper insulating, air sealing, and moisture control measures, they offer homeowners a warm and comfortable floor and a cost-effective solution for challenging site and soil conditions.

But one of the most compelling benefits of a closed crawlspace is its ability to reduce a home’s heating and cooling loads. Using it as a conditioned location for ducts and mechanical equipment reduces energy loss and condensation potential. In addition, locating ducts in conditioned space reduces house air leakage to the outside—an added energy efficiency benefit.

With a more stable temperature, the conditioned environment of a closed crawlspace is a more suitable location for ducts and mechanical equipment than a conventional vented attic or vented crawlspace. Locating ducts and mechanical equipment in a dry, enclosed space also helps maintain good indoor air quality. With the whole-house fresh-air ventilation requirements becoming mandatory in the 2012 IRC, a closed crawlspace can be used to integrate fresh-air ventilation with other mechanical systems.

Also, plumbing installed in a closed crawlspace reduces standby heat loss from hot water pipes and minimizes the risk of pipes freezing, when compared with a vented crawlspace or attic.