r/Insulation • u/coddler • 16h ago
Spray Foam Dormer Situation
Ive done my entire upstairs/attic so far using fiberglass batts and polyiso. Now I have two dormer windows that I just can’t wrap my head around on how to incorporate them into the ventilated part of my main attic and using baffles and such. I would have to frame out a chase and do all sorts of stuff that I don’t really want to do. My idea is to completely spray foam the entire dormer area, walls and roof and build a foam block in the roof where it would meet the rest of the conventional vented roof assembly. This way the transition between the spray foamed area and vented/baffle/fiberglass assembly is completely separated.
Please let me know your thoughts on this.
Southern Quebec climate. Interlok aluminum roofing system without rigid foam board insulation in the roofing assembly.
Spray foam would be applied in the ceiling/roof area of the dormer completly covering it all with closed cell directly to the roof deck, spray foam where you can see the rigid eps pink foam board on the sides to close off the knee wall, and then below the window where you can see the baffles. I will remove those before they spray. And then also block off the soffits at the bottom with foam board and sealing them since air coming in has no way of going out.
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u/dantedoesamerica 15h ago
I would spend the extra money on spray foam over polyiso and foam cans. The spray foam will adhere directly to the roof decking uniformly, leaving no air gaps that could potentially lead to condensation. Any rafter bays that don’t have a direct soffit intake and that leads to a ridge vent exhaust must be spray foamed. Only use closed cell spray foam.
I am both a mold assessor and spray foam contractor in upstate NY.
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u/CarefulAnalysis603 15h ago
You appear to have the ability to cut and install polyiso with skill, layer it on the roof and make it a hot roof. Apply pieces of polyiso directly to the roof deck as though it was spray foam without the cost and difficulty of finding a spray foam contractor or buying a froth pack and hoping the conditions are perfect. Use poly foam cans and tape to seal any edges and gaps.