Hello,

I just finished insulating my heated, unvented crawlspace walls with unfaced fiberglass batts using the draping method. My house is older (1943) and the foundation in the crawlspace is cement block. The batts are nailed to the rim joist and cascade down the wall and over a portion of the floor. My question regards the vapor barrier. I already have a 6 mil plastic sheet covering the dirt floor, but am unsure whether I need one covering the fiberglass batts. Normally, I think you would add one on the warm side of any insulation, at least in my climate (Quebec). Even if there are is no stud wall to protect, I think it might prevent moisture from lowering the r-value of the insulation, and cut down on the musty odor. However, nowhere online (at least that I can find) mentions anything about a vapor barrier other than the one on the floor. Do I need one? How high should it go? There are also some practical issues: how to install a 6mil sheet over a huge mass of unfaced fiberglass batts with no framing to staple to, etc. I imagine if I do have to install one, it will be impossible to seal it correctly.

Some sites mention that the vapor barrier for the dirt floor should be continued up the masonry wall, but this would place it on the cold side in my case, which I thought shouldn't be done.

I see in some pictures that accompany a few how-to instructions that bagged or plastic encased batts were used, but I'm under the impression that these don't qualify as vapor barriers. Also, in any case kraft faced and bagged insulation are impossible to find in my area.

Sorry to be long-winded. Thanks!

Try searching the internet using "encapsulated crawl spaces". This sounds more like what you are trying to do, there are a lot of images to help get ideas. I have rolled the top edge of the plastic in a 1x4 and then screwed the 1x4 now wrapped in plastic to the plate. That is a big job.