Best way to insulate and cover a 3:12 pitch roof in New England
I am putting a 32′ x 13′ addition onto my home which is an hour north of Boston. My architect has designed a 3 1/8 pitched non-vented “cold design” hip roof with 2 x 10 rafters, and R-38 closed cell spray foam insulation. Sheathing is 5/8 cdx covered completely with Grace ice and water shield and 3 tab archetectual style asphalt shingles.
The roof gets morning sun only and my contractor is concerned that there is a potential for ice dams and eventual roof leaks, since the sun may cause some melting of snow in the morning and possible refreezing in the afternoon when the temperature drops, causing damage to the shingles. Also he has seen in his 30 years experience that the self-sealing aspect on the nail holes through the Ice & Water Shield is not 100%.
The other concern I have is the possible toxicity and out gassing of spray foam due to the formaldehyde. I have looked into Icynene as it claims to be non-toxic after drying, but I am not sure if that is completely true.
My questions are as follows:
1. What would you recommend as the best system that would minimize the potential for leaks while being safe from a toxicity standpoint if I end up using spray foam. Also I have read that it is not ideal to use archetectual shingles on a 3 pitch roof as water does not shed as efficiently as regular shingles. If I do go with spray foam, would open cell or closed cell be better?
2. Would a standing seam metal roof be a better option altogether?
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