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Topic:	Crawlspace Ventilation
Builder:	Ed Stahl
Company:	R.E.S. Contracting, Inc. PO Box 4198 Prescott, Arizona 86302
Phone:	(800) 565-9165
eMail:	rescon@commspeed.net
Web Site:	http://www.prescottbuilder.com

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Please Do NOT Ventilate Your Crawlspace

A few weeks ago I became concerned after reading the home improvement section of the local newspaper.  The author warned against unventilated crawlspaces in all situations.  In reality, ventilated crawlspace contributes to the very problem it's supposedly designed to resolve, while a properly designed unventilated crawlspace has been considered an advanced energy-savings technique for several years now.

What's The Problem?
Traditional crawl space ventilation typically uses passive foundation-wall vents that are supposed to let moisture escape to the outside.  Actual research shows however, that this type of venting may not only make moisture problems worse, but allows cold (or hot) outside air into the building envelope.  An alternative to this is to use crawlspace vents with exhaust fans (see diagram below) drawing conditioned air from the house into the crawlspace.  This actually reduces moisture problems while increasing the energy-efficiency of the home.

How It Works
Energy-savings using unventilated crawlspace is accomplished by moving the insulation to the exterior surfaces of these cavities-- affectively incorporating the crawlspace within the thermal envelope.  Of course, moisture must be properly controlled.  Potentially damp soil in the crawl space should be covered with cross-link poly film with sealed edges.  If standing water is present, there are bigger problems to address. 


What About Code?
The new International Residential Code (IRC) specifically allows exhaust vent systems in lieu of the traditional passive vents in foundation-walls.  To comply, a mechanically vented crawlspace design must have a continuously sealed, vapor-retarding ground cover, have no fixed ventilation openings to the outdoors, and be supplied with a continuously operating exhaust fan.

For more information on Code, go to:
http://resourcecenter.pnl.gov/cocoon/morf/ResourceCenter/article/131



For more information on unvented (conditioned) crawlspace, click here to read the
DOE Technology Fact Sheet on Crawlspace Insulation (pdf, 235 KB), or check out:
www.buildingscience.com/resources/foundations/conditioned_crawl.pdf

Ed Stahl is the founder R.E.S. Contracting, Inc, a custom home-building company located in Prescott, Arizona which specializes in high quality, energy efficient homes.