Vapor Barrier?!?

Old 10-17-16, 08:44 AM
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Join Date: Jul 2015
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Vapor Barrier?!?

I have heard PLENTY of opinions on vapor barriers. This seems to be one of the more controversial topics in home renovations. The answer on when to use one seems to depend on climate.

When installed directly behind drywall and in front of insulation:
Pros: In cold weather a vapor barrier keeps water vapor from going into insulation, causing mold
Cons: In hot weather, a vapor barrier it prevents water vapor from entering the house, getting stuck in the insulation, causing mold.

I am in Massachusetts, we get hot summers and cold winters. I just insulated my living room with R13 faced fiberglass. Some of the studs were spaced far so I don't have the paper face covering everything. Should I install a vapor barrier? I already put up ceiling drywall without a vapor barrier.
Old 10-17-16, 01:06 PM
Join Date: Oct 2008
Location: New England
Posts: 9,460
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Hi Sam,
Part of the confusion arises from changing thinking. It turns out that VB's were introduced for the wrong reason (paint peeling) and it took years for them to realize it wasn't solving the problem.
Search "GBA all about vapor diffusion". When I post the link they switch to requiring you to sign up for their 30 day free trial. Bummer. But when I click on the link from the search I get the web page. I saved a copy so I can at least provide a related quote if you can't access it.

Back on topic. The bottom line is, way up north and way down south may need a VB. MA is inbetween. The real problem comes from air leakage which can transport far more moisture than what passes by diffusion. As long as you don't have a vapor barrier on the outside, inside becomes optional.

Search "GBA vapor barriers" and see what else you can find for reading.


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