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TOPIC: Underlayment

Sealing T&G

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I have T&G ceiling that is leaking air. The roof is coming off down to the exterior aspect of the T&G. The question is the best yet most cost effective way to seal this. Spray foam is cost prohibitive plus would leave an uneven surface for the rigid foam insulation going over it. Choices per the roofers who have looked at the job are seal it with some form of plastic (one said his was 8mm thick another recommended 3 mm). 3mm or 8mm? does it make a difference since it'll be under so much foam anyway? Is using I/W overkill or a good idea this deep in?
Guest User

4/17/2010
I think that either one, properly installed, can stop air flow. Will that trap moisture, though, and cause condensation issues? Todd Miller
Todd Miller
Isaiah Industries, Inc.

4/17/2010
and that is a concern. According to the contracter no barriers really totally stop the passge of some moisture. I would expect that a solid sheet of plastic would block 99% of it though. Is there another alternative way to sealing the T&G (aside from spray foam) that has a reasonable cost? Air can certainly leak between the grooves now, I can feel it. What would you recommend doing?
Guest User

4/17/2010
"Sealing" the roof with plastic sheeting is not really sealing the roof. You are putting an air barrier up but as Todd mentioned, you are creating a very good opportunity for condensation and all of the issues that go with that (rot, mildew, ice, etc). You roof needs to be sealing with Ice/Water or spray foam or some other viscous material that will fill the grooves and stop the moisture/air movement. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

4/18/2010
Got it, I think. SO the thought is that even with the layers of foam above the plastic could allow some moisture under it. The Ice and Water, although also a layer has an adhesive so nothing would be able to pry it's way under in the way of mositure. Makes sense to me. One guy recommended painting on some sort of sealer because the Ice and Water was going to add considerably to the cost (I think they estimated me at about 35 Squares of roof). Any thoughts on that?
Guest User

4/19/2010