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David Stroud
Crawl space ventilation

I have a question about proper ventilation of a crawlspace.
I have experimented and found that opening my foundation vents in the spring and fall rather than in the summer is more effective. With the high humidity levels in the summer in Louisville, KY when I open my vents in the summer my HVAC supply plenium sweats excessively and my crawl feels more damp. I have now closed my vents in the summer and my crawl feels much less humid. I have a French drain system around the exterior of my crawl space. On the ground of my crawlspace I have 4 inches of gravel, 6 mil poly on top of that and 2 more inches of gravel on top of my poly - on the ground in my crawl. I have good slope and extended downspouts for exterior water control.
I now am also wondering if I shouldn't just leave my foundation vents closed all year round? (My house is 2 years old).
What do you think?

Timothy Miller
Re: Crawl space ventilation

Check the humidity level in all the seasons with them open compared to outside if lower i'd have them open.

Re: Crawl space ventilation

No ventilation isn't good either. Microorganisms require available moisture, not necessarily liquid water. When there is no air flow then the water molecules settle into microenvironments where the microorganisms can use them to grow or amplify themselves. Your understanding of the limitations on open vent crawlspaces in the hot humid months of the year is correct though. I would recommend that you encapsulate the crawlspace then condition the air space. This will save you money in energy consumption and help promote clean indoor air quality. For more information check out these resources: www.solutionsiec.com/crawl_space_science.html, www.americanbasementsolutions.com/, and www.crawlspaces.org/. They discuss the science behind crawl spaces, current systems available, and more.

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