Messages and Online Forum Q&A

Re: Crawlspace foundation ventilation

From: info@builderswebsource.com
Category: Foundations and Basements
Remote Name: 63.198.181.43
Date: 16 Jun 2001
Time: 07:19 PM

Comments

Unless your crawlspace is heated or is an enclosed conditioned basement, the building code requires 1 foot clear ventilation per 150 feet of unconditioned crawlspace. This can be reduced to 1 foot per 1,500 feet if the crawlspace has a good vapor barrier over the native soil, or better, concrete rat proofing with a vapor barrier underneath.

You are correct that keeping moisture out to begin with is always a good idea (through french drains, proper grading, etc.). However, if you keep crawlspace moisture locked in, this can lead to premature rot, fungus and insect infestations (such as termites and carpenter ants).

It's always good to let things "breathe", particularly since moisture can come from many sources other than outside air, including through the floor from the house itself as well as the ground, cracks and crevices.

There are some products on the market, such as the SmartVent® shown here, which continually measure the interior and exterior humidity and temperature levels and turn on according to the imbalance between the two. This can be installed in the crawlspace to provide forced mechanical ventilation, providing optimal crawlspace ventilation and humidity levels.

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