I am considering building a chalet style home in the Northeast(upstate NY) MY question is this. With 2 x 8 roof rafters obtaining the required R-30 roof insulating specification seems difficult to do with the limited space. What products are available to achieve this ? Any info would be appreciated.
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With "chalet style" I envision large open spaces with high cathedral ceilings.
With catherdral ceilings, you want it tight as a drum. No moisture getting into the roof structure from the living space.
Consider rigid polyisocyanate insulation (4' by 8' sheets) attached to the face of the roof rafters. Horizontal furring strips over the PI, screwed through the PI and into the rafters. Then drywall screwed to the furring strips. Gap the sheets of PI, then after installing, foam the gaps with canned foam and tape over the foamed seams with Al tape. There's R-13 to R-14, and it still preserves the rafter space for additional insulation (cells or batts) plus vent space if you choose to vent.
If you choose an exposed T&G style ceiling instead of drywall, then run the furring strips vertically, shadowing the roof rafters. Then attach the T&G to the furring strips.
Foil-faced polyiso will give you a radiant barrier, a vapor barrier, an air barrier...overall it'll give you excellent thermal and acoustical performance.
However, no can lights, no poorly detailed penetrations, etc, through the polyiso, or you'll trash the performance and get into the typical problems most cathedral ceilings suffer from. There are ways to hide mechanicals without compromising the PI.
Hey Mongo, I'm doing foil faced PI (Thermax) on the walls of my place. Which is better to tape the gaps...AL tape or that red tyvek "contractors" type tape?
Also I'm using this as a vapor barrier...so what do you suggest to seal at the top and bottom corners? I've snugged the Thermax up tight to the ceiling SR, and the poly ceiling VB is tucked under, but there's still a gap at the bottom.
How big is the gap?
If too large, rip a strip of PI, place it, then Al tape the seams.
If small, you can seal the gap with canned foam, then bridge over that with 2" wide Al tape. 2" tape can make the transition from foil face of the PI, over the canned foam, to the subfloor.
Both Al tape and Tyvel tape stick well, but I use Al as I buy it bulk and always have it on hand.
Edited 2/10/2004 1:30:46 PM ET by Mongo
Thanks for the response. How thick are the 4' x 8' sheets of polyisocyanate insulation ?
They vary, but my yard stocks 1/2", 1", and 2". About R-6+ per inch.
I also see the half-inch and 2" at HD.