Brian:
Thanks for your comments. I sure do live in snow country (the cottage is near Peticodiac, New Brunswick, Canada), so roof ventilation is an issue. Here's what I plan to do - cover the ceiling with 3/4" T&G, followed by plastic vapour barrier on top of the T&G, followed by 2" rigid foam, followed by an air space (2" or 4"?), followed by another layer of 3/4" T&G, followed by cedar shingles.
On the floor, to get around the rodent problem, and the fact that my joists are only about eight inches off the ground, I plan to cover the entire floor with 3/4" T&G, followed by 2" rigid foam, followed by vapor barrier, followed by Kiln dried 1 1/2" T&G (the finished floor). Is this overkill? What do you suggest as nailers for the flooring and roof? I'm thinking of 2"x2", laid on top of the joists/rafters, but I'm worried about heat transfer.
Originally posted by Brian W:
Bryson:
If you live in snow country, a ventilated roof is essential for preventing ice-dams. When there is snow on the roof it forms an insulation sandwich with the installed roof insulation. The R-factor of the snow is about R-1/inch. Thus, you can quickly calculate that it would take about an R-90 roof to insure that the roof deck is always cold enough to prevent melting. Even if you are not in snow country, a ventilated roof will extend the life of your roofing material and prevent condensation between the roofing and the underlying deck.
The insulation in the floor must be applied with attention to vapor barriers (vapor from both the building interior and from the earth below. The goal is to prevent condensation from occurring on the structural timbers. In addition, you need to install some sort of physical barrier so that the insulation does not become a convenient nest for varmints. For the later, you could use metal screening similar to plaster lath.
