So I have seen on the galleries, "attic renovation" that tyvec was used on the exterior of the kneewall, attic side. I have a similar set up where the bathroom was built in the attic. The previous owner never put insulation in the wall so in the winter it was quite cold. To remedy, i put insulation in the knee wall from the attic side since the bathroom was finished. While it did help quite a bit i feel it should still be a bit warmer. Question being should i put the tyvek on the out side and seal it? Im sure this is designed to breath. Or do i take out the insulation, line the stud cavities with a continuous piece of plastic sealing it to the studs as i go and then reinsulate, then install tyvek to hold it up. Any insight would be appreciated.
Thumb and Hammer Forum » Home Improvements
attic knee wall
(5 posts)-
Tyvek is designed to be used for exterior applications and is normally taped and sealed to prevent air and moisture from penetrating from the outside of the building. I used it on the attic side of my knee walls specifically to help hold the wall insulation in place. As I pointed out, other materials that have been used for this purpose include chicken wire and even 1x2 strapping, neither of which is air tight.
Assuming that the building code in your area is similar the one in Ontario, you should have vapour barrier on the warm side of the knee wall and it should be air tight. I can tell you from experience that lining the stud cavities with a continuous piece of poly would be a royal pain, especially in a tightly enclosed space like a side attic. And any holes or gaps in the barrier would defeat its purpose.
What size are the studs making up your knee wall? How much insulation have you installed in the wall? If you only have R12 or R13, you could upgrade to R20. I don't know that the vapour barrier will have much effect on the temperature in your attic.
Another option, depending on your budget and if they could actually use the equipment in such an enclosed space, would be spray foam insulation. My understanding is that no vapour barrier is needed and it has a really high R value to boot. It might be worth looking into.
Posted 1 year ago # -
kevmitsu
MemberThanks for your reply, the stud size is standard 2x4 so i was only able to get R-13. The spray foam is an excellent product which also acts as a vapor barrier, I installed it on my crawlspace walls and am very pleased, though it is rather expensive and cannot justify for my bathroom. Can I get a R20 that with fit in the 2x4 stud cavity without having any stick out? I think im going to at least tyvek the attic side. I understand that the vapor barrier should be on the warm side and sealed, however the previous owner did neither. I just thought that lining with plastic would help with air infiltration. But if I can insulate more and use the tyvek on the attic side i think it will help. Thanks for your input
Posted 1 year ago # -
If you are doing R20, do NOT compress it so it doesn't stick out. Compressing the insulation will lessen its effectiveness and you will end up with much less R-value.
Don't worry about putting any barrier on the attic side. The most important barrier will be on the warm side of the wall. The ONLY reason I used Tyvek was to help hold the insulation in place. Just using Tyvek on the cold side will do virtually nothing to increase the R value of the wall.What purpose of the vapour barrier is to prevent moisture from infiltrating the wall and causing damage to the insulation and the structure. Since you have side attic access, you could periodically check on the condition of the insulation. In the winter, look for signs of frost on the underside of the roof and the rafters. If a problem exists, then you will have to address the vapor barrier issue. And make sure that the bathroom is properly ventilated. Broan has a new bathroom fan that senses humidity and operates automatically.
There is also vapour barrier primer (Benjamin Moore has such a product available in latex). Two coats of most oil based primers will also qualify as a vapour barrier.
Your main complaint is the cold, however. Upgrading to the R-20 insulation may be your easiest and most cost effective option at this point. If fact, if you use Roxul or a similar mineral wool insulation, the R-value can actually be 21.5.
Posted 1 year ago #
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