Roofing Insulation

patmen

hello, want some opinions on how to properly insulate and re roof a gable roof slope 3in12 with T&G decking. The project entails an open beam and ceiling below where all the roof deck is exposed inside. Want to add insulation on the outside in the form of rigid extruded foam boards with an vapor barrier and tar paper or other materials that would
be the best method for a
cold climate where we can get up to four feet of snow accumulation on roof.
I have read many ways aout including or not including a plastic sheet or vapor barrier using two layers of foam or just one layer with tar paper etc. Wether to put tar paper on top of deck or on top of rigid foam. Will also leave an air space under the metal itself thx

PA woodbutcher

Best advice anyone can give you is to hire a qualified, insured contractor. You try and save money on this and do it yourself and it will cost you. I don't pretend to be a mason, why would you pretend to be a contractor?

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'The trouble with our liberal friends is not that they're ignorant; it's just that they know so much that isn't so.' - Ronald Reagan

apkole

As a QUALIFIED, PROFESSIONAL residential roofing contractor, we are currently looking at this same kind of situation. The roof is a 20 pitch A frame, 1" T&G, about 7' OC. This roof has been replace 3 times in the last 10 years. Seems no one has been able to get it right . . .

I will say this, though . . . vapor barrier is NOT adviseable from the research I've done so far.

Warren

Many years ago we built a home with a 5000 sq ft pool room. It had church type beams and cathedral ceiling. We put 2" t&g down first, then we covered that with ice and water shield, then we installed these special panels that were like 32x48 and about 4 inches thick. they were osb on each side with foam sandwiched insidw and had ventilation channels hollowed out. After that we put down another layer of ice and water shield on entire roof. As I recall we also used about 3 cases of caulking as the room had to be humidity controlled. I have seen other church type roof/ceilings that did almost nothing special and some worked ok and some (including my own church) had problems with mold,water and rot. I would never attempt one of these without consulting with a professional roof system designer(whatever that means????)

SLSTech

In a recent article (last 2 or 3 months) from FHB or maybe JLC they had an excellent article on this question
Here is another one using sprayed foam
http://www.taunton.com/finehomebuilding/PDF/Protected/021190074.pdf

You can also use SIP panels

You can also look this up on the buildingscience website

Sorry Patmen - it's hard to answer your question without even knowing where you are located & you might also want to do an intro here

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Jm H

Nail base is the answer to your question. They make a vented product that helps keep the deck cool.
Try your Firestone dealer or Atlas insulation products.