Vapor Barrier?


Old 02-20-02, 03:13 PM
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Vapor Barrier?

I live in Southern California and am gutting/remodeling an older house. As a transplant from the Northern Midwest, We always took extra care to use quality windows, intstall insulation with meticulous care, and use a poly-sheet type vapor barrier on the interior under the gyp. board. I haven't seen the vapor barrier used around here. Is it because it is really not necessary or is it because (like as in many other cases around here) contractors are too cheap and lazy to bother?

Also, I am installing fiberglass insulation in the attic over some old existing fiberglass insulation. The old insulation was originally R-19, but is now compressed down into about 3-4". The kraft paper vapor barrier is in bad shape. Would it make sense to simply roll out the new insulation (also kraft faced) over the top perpendicular the the existing with the kraft face down?
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Old 02-27-02, 01:14 PM
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You can go to, this is a DOE site on vapor barriers. After you read it, you'll see why this question is asked a lot. It does answer why you don't see vapor barriers used a lot in your area. Even if you look at some of the organizations that contributed to the DOE findings, they don't really agree.

One thing we all agree on is what they call an Air Barrier and on my site an Air Boundary and it's importance concerning moisture problems in insulation. Though my site emphasizes more on conserving energy, they do too but more emphasis more on moisture problems.

In your case I would recommend that you add more insulation without a vapor barrier because one is already present. Adding another one will cause a moisture problem.

When reading the DOE site, don't get caught up with "Perms". That's static pressure with vapor barriers and the ratings are usually put on them in this manner, SP-15
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