We’ve been hearing about the importance of crawlspace encapsulation systems and customers are asking about it. It is against code to cover vents in our region. Is it necessary to vent crawlspaces in the Pacific Northwest and if so, why?
Unless specifically excluded by your local jurisdiction, unvented crawlspaces are allowed under the 2003 version of the International Residential Code (IRC) as long as all the requirements outlined in the code are met. Unvented crawlspaces are sometimes referred to as mini-basements; code officials can often better understand the concept when it is explained in this way. More can be found on code implications of unvented crawlspaces at:
Crawlspace Ventilation FAQs
The primary reason that unvented crawlspaces have gained popularity over the past few years is the ability to control crawlspace moisture. In vented crawlspaces in the Southeast during the summer, for example, warm humid ventilation air that enters the crawlspace could cool off and condense and cause problems with mold, rot, and termites. This is contrary to the purpose of moisture removal that the vents are intended to serve. In dryer and cooler climates, the moisture problems in vented crawlspaces are much less dramatic. Unvented crawlspaces are typically semi-conditioned spaces that are not purposefully vented. Therefore, especially in hot humid climates, moisture can be managed effectively. In warm climates, unvented crawlspaces typically save energy in the summer when compared to vented crawlspaces (studies have shown energy savings of about 10% to 20% in the Southeast). In the winter, unvented crawls have little, if any, effect on energy consumption.
Closed Crawlspaces do Double Duty
The Northwest may not be the optimal location for unvented crawlspaces. The true indication is if condensation is an issue in the summertime. I wouldn't necessarily recommend unvented crawlspaces for energy conservation alone.