We recently had a pole barn built to convert into a mother-in-law cabin. When they wrapped the house, the builders used an R-7 insulation wrap similar to that used in roofing underlayment rather than a Tyvek-type wrap. The problem is, it is not a breathable vapor barrier, and we are wondering about insulating inside of this wrap. Some friends of ours actually cut out the insulation between the wall strapping, but the builder insists that there is no problem with this type of building wrap, even for insulation and drywall (beyond the “barn” application, which, presumably leaves the inside open). We are curious whether anyone has had trouble or experience with this type of building in a “finished” building, or any other feedback. Thanks. Oh, we are in the pacific northwest, which has a fair bit of moisture, if that matters.
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Is this similar to what they use for steel buildings where a thin ply of fibreglas is sandwhiched between two plys of a white plastic film?
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Unless the insulation has changed in the last couple of years the white plastic is only on one side of the insulation (interior). I worked on a lot of metal buildings and a few pole barnes, and have never seen the insulation sandwhiched between layers of plastic.
That said, IMHO the insulation value of the stuff is terrible. We did an IR scan of a metal building and every where the insulation crossed a girder or purlin it was no better than 1/2 inch or 1/4 rigid foam. Every seam that was stapled together also showed a lot of leakage. I suspect that is where the misterious buldges come from. I spent a few winters looking for roof leaks that I now think was condensation.
Dave
I never installed it but I was called as a roofer to fix "leaks" a number of times where it was present. Most of what I looked at was bagged both sides. It IS worthless. On that we surely agree. .
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
I think this is the same stuff you are talking about - the builders wrapped the other building in Tyvek, Lord knows why they used the insulated wrap on this building, but it is just the white plastic on the inside, stapled to the posts and strapping, like you said.
That said: the plastic is on the interior, then insulation, then T-111, then we will be siding on top of the T-111. For the interior, we skinned the strapping with 2X4 for insulation and backing, and were going to do blow-in insulation, then drywall. Should we worry about the lack of breathability considering all of these things?
Yes, you have a VP inside of the wall assembly, not a good idea. If it were mine, I would cut the plastic off completly. You will loose that R-7 insulation in the process, but the only place you are getting anywhere close to that is where the insulation bulges away from the T-111 between the strapping or purlins. The insulation is glued to the plastic and if you cut just the plastic, you may be able to peel it off and the isulation might stay. since you are goig to blow cellulose, you will end up with a far better insulated wall than you bought from the barn builder.
Do search at this site on Vapor Barriers, and you will gain some real insight on wall assemblies, temperature gradiants, dew points, and lot more stuff that can affect your building choices.
Dave
Thanks for the info, Dave! I will definitely check the site for vapor barriers, and really appreciate your feedback! Erik
I worked in a heated metal building with insulation encased in plastic. It started to develop mysterious bulges in the winter. We had a great time poking them and watching the "no problem" pee out by the gallons.
Boy, You sure turned this into a short thread fast!
Just for giggles -
Was it built over the same kind of soil as your house? That really was a bad siphon problem! LOL.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Mother-in-Law in a pole barn.
.
I like the concept...........................(-:
I was going 70 miles an hour and got stopped by a cop who said, "Do you know the speed limit is 55 miles per hour?" "Yes, officer, but I wasn't going to be out that long..."
That midwestern sense of humour is well polished, I see!.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius