Should I close my crawl space vents for winter?
We seem to get this question around this time every year. And, each year we say, “it depends.” On the one hand, air circulating under the house helps keep damaging moisture from accumulating. But leaving vents open in freezing temperatures can result in cold floors if there is not enough insulation present, or even worse, frozen water pipes.
“I’d avoid closing vents when you can,” said Rick Richart of Richart Builders and Remodelers in Vancouver. “Most crawl spaces have ground moisture even though they have a ground cover. Venting helps prevent the moisture being absorbed into building materials, such as the subfloor.”
When freezing temperatures are present, however, Richart and our energy counselors agree it’s time to close the vents. “Frozen pipes can happen when really cold air blows through the crawl space, especially if pipes are located near a vent opening,” Richart said.
• Moisture is the enemy: The biggest concern is moisture in a crawl space. Moisture can cause mold and mildew, which affects a home’s indoor air quality. Moist wood can cause an infestation of dry rot fungus or wood boring beetles — both of which will cause structural damage.
In areas with a high water table or if an underground spring is nearby, crawl spaces can even accumulate standing water. In that case, you may have to install a ditch around the perimeter to drain water away from the foundation. If the problem is severe, you’ll want to consider a pump to remove the water from the crawl space.
• Crawl space codes: To mitigate moisture problems, Washington’s building code says crawl spaces in new construction should have a ground cover of 6-mil poly black vinyl, overlapping a foot and running 12 inches up the foundation wall.
R-30 insulation should be installed between the floor joists, and firmly secured in place. Insulation will act like a sponge if it comes into contact with water, destroying any insulating capability.
• Good drainage helps: Richart said the ground around the foundation is common cause of water in crawl spaces. “You need to have a 5-foot positive slope away from the foundation. Landscaping can build up over time to where there is a negative slope that actually drains into the crawl space.”
Improperly located downspouts are another cause. “It’s quite common to see gutter downspouts go into splash blocks that pool and drain into a crawl space,” he said.
• Inspections pay off: Unless there is visible standing water there’s little way of knowing what’s going on in a crawl space without crawling in there. “It’s best to have an inspector look at it to determine any problems,” Richart said. “He’ll be able to offer solutions too if there are moisture issues.”
The Energy Adviser is written by members of the energy counselor team of Clark Public Utilities, who provide conservation and energy use information to utility customers. Send questions to energyadviser@clarkpud.com or to Energy Adviser, c/o Clark Public Utilities, P.O. Box 8900, Vancouver, WA. 98668. A panel of local energy efficiency and energy product specialists will review your questions. Previous topics are available at http://www.clarkpublicutilities.com.
