Why Vented Crawlspaces Are So Yesterday.

It was once thought, and actually mandated by the International Residential Code, that homes built on crawl space foundations should be vented to the exterior. The original purpose of these vents was to bring in fresh air from the outside and circulate it with the air in the crawl space, along with providing an escape for accumulated moisture. Initially, it seemed that venting solved the problems of crawlspace moisture and air circulation. Many homeowners, however, who still experience mold and decay, termite and other pest problems, along with increased condensation, misunderstand the problem and simply increase this ventilation.

Lots of older homes were built without central air conditioning, and were cooled by putting fans in the windows. These days most people consider air conditioning to be a necessity. And, in most cases, ductwork is installed in the crawl space where the ducts can most easily connect to the various living spaces within the home. These conditions have radically changed how homes "breathe."

We now know that venting is not a great solution for keeping crawl spaces clean and dry. Indeed, venting will only help increase moisture levels if the outside air is dryer than the air inside, or when enough hot outside air enters and warms the area. New studies have shown that as air enters the crawl space through the foundation vents and comes in contact with surfaces that have been cooled by the cold air in the ducts, the dew point is reached and condensation occurs. And when condensation forms on various surfaces within the environment, you have the ideal environment for mold, mildew, and the accompanying problems they create in your home.

Installing a high-performance vapor retardant material to cover the crawl space floor can help solve the problem. The Your Crawl Space vapor barrier effectively blocks water vapor and eliminates the need for vents altogether. As some building codes still mandate these sorts of vents, please check with your local building department before opting not to install them.

Common Crawl Space Terms