Insulation under a crawl space
Squantun
| Posted in General Questions on
I have insulation between the joists with the vapor barrier facing the warm floor. Is it a good idea to staple plastic sheets over the joists for an additional vapor barrier?
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Replies
William,
First of all, I don't recommend installing insulation between the floor joists above a crawl space. It's almost always better to seal the crawl space vents and to insulate the crawl space walls. To learn why, see Building an Unvented Crawl Space.
You don't mention what type of insulation you have installed between your floor joists, but I'm guessing that you have installed kraft-faced batts. Even if you want to insulate your crawl space ceiling, I think that it's a bad idea to install fiberglass batts in this location, for a variety of reasons: (a) It's hard to keep them in place, and they often fall down. (b) They are air permeable. (c) They don't perform well in a damp environment, and can get moldy in a crawl space.
If you want to insulate the ceiling of your crawl space, the best way to do it is with a continuous layer of foil-faced polyiso (rigid foam) attached to the underside of the joists. All seams should be sealed with a high quality tape.
Finally, to get to your original question: no, you definitely don't want to install a plastic vapor barrier on your crawl space ceiling.