Vented crawl space: Nothing but CC spray foam under floor?
Location: Massachusetts
I have a vented crawl space and I would like to keep it vented. There are no utilities in it and there will never be. As you’d expect, the floors are very cold in the winter and there is often a dank earthy odor in some rooms. I’ve done a lot of research on how to fix these issues, and weighing all the pros and cons of spray foam, decided to go with spray foam. So my question is, can I just have 4-6 inches of closed cell spray foam applied to underside of floor, covering joists and sills and never worry about the crawl space again? Any harm skipping the vapor barrier on the soil? It seems 4-6 inches of CC foam should isolate livng area from soil gases, vapors, odors and air flow, so if I’m not going to access the crawl space and i’m not going to have utilities in there, can I get away with just the spray foam? Will closed cell hold up long term being exposed under there? In my research i haven’t come across this type of setup–everyone is closing up there crawls and using vapor barrier on the ground and insulation on the perimeter wall…
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Replies
Steven,
1. Your local building inspector must approve the installation. In some jurisdictions, spray foam must be covered with a thermal barrier like drywall.
2. Poly on the dirt floor is always a good idea. It's easy to imagine that the spray-foam installer might miss some wood components or framing members in your crawl space, and it sounds like the crawl space will always be damp, putting lumber at risk for rot.
Thanks Martin, I'll check if I need to cover it, but I really hope i don't have to. There's not enough room down there to manipulate 4' X 8' sheets or even 4'x4'. And there's ~ 1800 square feet to cover.
The other proble with installing poly is the ground is very irregular. I just had it vacuum excavated to a depth of 3-4 ft where previously clearance from the bottom of joists was 0-24", with most of it being 0. They encountered massive rocks. Not a problem for spray foam installers, but it will be a nightmare trying to install the vapor barrier.
-Steve
Steve, your insulation company most likely would be able to install some poly for you and take care of permits. State your needs in writing when collecting bids and get all in the contract you sign.