June 2009
Q: Can you address the situation of venting versus not venting a crawl space? We have a new home on a crawl space. The builder said to keep the space vented, but I’ve read other articles that say the opposite. I just read an article about putting down heavy plastic on the ground, spraying the walls and adding a dehumidifier.
Charlee Kohler, Hertford
A: Recent research conducted by Advanced Energy in North Carolina has shown that a properly closed crawl space is a great improvement over a traditional wall-vented crawl space.
Two projects involving over three dozen homes in the Triangle and in Princeville have demonstrated that a closed crawl space dramatically reduces the humidity levels under the home.
Reducing crawl space humidity helps to eliminate odor problems, mold growth, buckling hardwood floors and damage from rot or wood-destroying insects. Installing a closed crawl space also reduces the amount of electricity needed to heat and cool a home. In Advanced Energy’s projects the annual reduction was more than 15 percent.
These results supported the creation of a whole new section in the North Carolina Residential Code in 2005 to provide minimum requirements for builders and consumers who want to install properly closed crawl spaces.
Closed crawl spaces are sometimes also called “unvented” or “sealed,” and the primary differences from a vented crawl space are that they have no intentional openings to the outside, a 100 percent vapor retarder covering the crawl space floor, and some type of drying method. A dehumidifier would certainly be an effective drying method. A less expensive method, such as installing a supply duct to provide conditioned air to the crawl space, has been used with great success in Advanced Energy’s research projects.
When installing a closed crawl space, a homeowner or contractor needs to ensure that they comply with requirements for fire-rated insulation products, termite inspection gaps, combustion safety and flood protection.
Advanced Energy has provided detailed recommendations, sample designs and links to the products and installers used in its research projects at www.crawlspaces.org. North Carolina homeowners can also contact Advanced Energy for answers to questions not covered on the Web site by calling (800) 869-8001 and submitting a consulting request to the building science team.
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Send your conservation ideas or questions to us:
P.O. Box 27306, Raleigh, NC 27611, or E-mail: editor@carolinacountry.com