Exterior rigid foam details/concerns for roof
Finally am at the point of redoing my attached Ell roof on my 200+ year old colonial.
This is what I currently have.
Inside 3/4 inch pine (obviously very air leaky) cathedral ceiling, Behind that it appears to be a foil faced fiberglass. Prior owner did this some time in the 80’s. The sheathing is 1 x 10 running from peak to soffit ( again very leaky). There are 2 layers of asphalt shingles, then a 1 inch layer of Styrofoam insulation board with another layer of asphalt on top of that. Fun Fun!
At this point I am not opening up the ceiling inside. That will happen down the road.
From the exterior I had planned to strip everything down to the board sheathing. Was going to skin with 1/2 inch plywood, ice and water the whole thing to make an air barrier. Then put down 5 -6 inches of poly ISO on top of the ice and water. Then strap with 2 x4 from peak to soffit, throw sheathing on that, building paper, then install my enviro- shake shingles.
Dollar wise it would be much cheaper to skin the roof with Zip sheathing and tape seams. That would save me time and money. I just can’t get past the OSB thing. I am a plywood guy. Should I worry about that in a set up like this?
Can I get away without the venting above the rigid foam. I remember Dr. Joe stating it is a good idea. I am assuming if I stagger the rigid foam joints and tape each layer there should be no air pathways. Especially if I do the air barrier right under the insulation board.
This winter or next winter when I finally take down the interior ceiling to add insulation what would be the best option? I want the beams to remain exposed partly but now I would be concerned about the foam sandwich if I sprayed the underside of the sheathing?
Just looking for others opinions before I move forward. Feel free to poke holes in my plan if need be.
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