Should I Vent a Crawlspace in Zone 6?
user-6445625
| Posted in General Questions on
Dear GBA Experts,
I am building a house in a Zone 6 climate in NY State with a crawl space – rat slab, vapor barrier, 2″ foam, gravel, with closed cell inside foundation walls and batt insulation in floor joists. Do I need to vent? There is no ducting or mech equipment in the crawl.
Thanks!
Brad
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Replies
I'm assuming you mean "should I vent the crawlspace TO THE OUTDOORS" here. I would say NO, since you've insulated the walls and the floor of the crawl space. Code minimum for those walls is likely R15 here though, which you aren't meeting with only "2" of foam". Even with polyiso, which is the highest R per inch of the commonly available rigid foam materials, you'd need about 2.5" thick material here. With EPS, you'd need just over 3.5" of material.
My recommendation here would be to put more rigid foam on the walls, AT LEAST R15 worth (ideally a bit more), and don't bother insulating between the joists since insulation in the floor won't be needed. Do NOT vent the crawlspace to the outdoors, since your crawlspace is both insulated and within the building envelope.
Bill
Thanks, Bill, this is very helpful.