The Crawlspace Argument: Open (Vented) vs Closed (Encapsulated)
by Joseph R. Provey | Sep 19, 2013 | Basements, Crawl Spaces, Foundations | 11 comments
A new way to solve an old problem
More than 27 million homes in the U.S. have crawlspaces. That number grows every year, as 15 to 20 percent of new homes continue to be built over crawlspaces.
That’s a lot of houses, most of which are probably suffering from a variety of problems.
They include excessive moisture and what comes with it: mold and mildew, wood rot, corrosion, poor indoor air quality, and insect and pest infestation. They also include excessive energy loss (especially where there are ducts in the crawlspace), cold floors, high fuel bills, and greater wear and tear on HVAC equipment.
Most of these problems are due to one-size-fits-all building codes, cost-cutting construction practices, inadequate waterproofing, insufficient air sealing, and using the wrong type of insulation. Fortunately, building scientists have revised their thinking about crawlspace design and have devised ways to eliminate or at least minimize the ills associated with crawlspaces. Codes are changing as well.
Caption: The South Atlantic, East South Central, and Pacific states have the largest concentrations of homes with crawlspaces, according to the Census Bureau’s Survey of Construction.
The closed-versus-vented question
Closed or “encapsulated” crawlspaces are now preferred to open, or vented, crawlspaces.
Closed crawlspaces are consistently better at controlling moisture that enters via the damp earth or from warm humid air that would otherwise infiltrate from the outdoors.
Tests done for the Environmental Protection Agency (EPA) by Advanced Energy have shown that closed crawlspaces maintain significantly lower levels of relative humidity (RH). In a multi-home test done in Baton Rouge, Louisiana, for example, the average relative humidity of closed crawlspaces barely exceeded 60 percent.
Meanwhile, vented crawlspaces in control homes had readings in excess of 80 percent. In a similar test in Flagstaff, Arizona – a colder, dryer climate – vented crawlspaces stayed below 70 percent RH, but sealed crawlspaces were less. They never exceeded 50 percent RH.
The winner: closed, encapsulated crawlspaces have lower relative humidity, which means less rot, better air quality and fewer pests.