Insulation for 1978 house 3/12 roof, attic, and cathedral ceilings
I just purchased a 2,200 s.f. 1978 house that needs better insulation and air sealing. The interior was beautifully remodeled 6 years ago and it received high quality siding and windows. The conundrum is that it has a 3/12 roof framed with 2×8 rafters (16 o.c.), 4 valleys, half of the house has a 3/12 cathedral ceiling and the other half has an attic. I live in zone 6a with an average of 6’ snow. The house gets ice dams and I don’t want to be clearing the roof forever. I’m braced for a costly solution that includes a SS metal roof. The conundrum is that one builder recommends a insulation on top/hot roof solution and another recommends tearing off the roof decking to get at the attic and the cathedral bays and using closed cell foam to insulate and air seal everything. Each approach works better for one part of the house or the other. Which would be best overall? Thank you!
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Replies
Have you read this article?
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
I dislike spray foam and would do almost anything to avoid it.
In zone 6 one would like to get up to R60 for the roof and that is a lot of foam sheets stacked on the roof.
Walta
You should read these. Both those solutions need modification. You should have a vented roof deck, there are details in both of the linked articles for you to see how and why this is done.
https://buildingscience.com/documents/building-science-insights/bsi-141-shakespeare-does-roofs
https://buildingscience.com/documents/insights/bsi-046-dam-ice-dam
Personally I would go with an assembly that adds exterior insulation and a second roof deck above with venting via furring strips from a fascia vent.