If you get three general Contractors together and the topic of discussion turns crawlspaces and moisture management, you will most likely hear six opinions. The experts seem to have different and often conflicting opinions about what tack is the best to take. There has been much study on Crawlspace encapsulation during the last ten years. The US Environmental Protection Agency, the US Department of Energy, the Brilliance at Oak Ridge National Laboratories, and a non-profit research firm named Advanced Energy have done excellent and ground-breaking research in the region of crawlspace encapsulation. Their study findings were instrumental in the previous revision of the International Building Code. All of them agree in some, very important places.
When contemplating your home, think of it as one system. Your HVAC system, windows, insulation, attic, living area, and crawl space all work together. All these building components will need to be optimized and balanced to achieve maximum comfort, performance and energy efficiency. Your crawlspace is an important part of the system. Your Home is like a giant chimney. By natural convection, air is drawn in through crawlspace vents and air flows. Since warm air rises, the outside air is drawn through the living area along with mould spores, odors, and moisture absorber and drained through the attic. In the summertime, your crawlspace is obviously cooler than the ambient outdoor temperature. When the warm, humid outside air reaches the cooler crawlspace surface regions, the moisture condenses on framing, plumbing, wiring, insulating material and especially HVAC ductwork and sweats, exactly like an iced tea glass sweats in your kitchen table in the summertime. In the southeast it is not unheard of for crawlspace humidity to approach 100 percent and rain within the crawlspace.
The moisture from your crawlspace Creates an ideal atmosphere for wood destroying organisms, mold, and mildew. It can saturate and ruin the effectiveness of your insulation and encourage wood rot. And due to the chimney effect, the humid crawlspace air, filled with mould and mildew spores, eventually finds its way to your living area creating an unhealthy environment and causing your air conditioning to work overtime to dehumidify the air. Only a vapor barrier might help somewhat, but the majority of the moisture is coming from outside, not your dirt, crawlspace floor. So, the alternative to a vented crawlspace is an encapsulated sealed crawlspace. Crawlspace encapsulation involves sealing all outside vents, installing a high-performance vapor retarder on all exposed wall and floor surfaces at or below level, insulating the walls and rim joist, and conditioning the air.