Rigid foam insulation in a cathedral ceiling?
We are building a tiny house currently with cathedral ceilings and 2x6 rafters. I have access to large quantities of rigid foam and would like to make use of it. Can I fill the rafter spaces with layers of rigid foam and spray can foam the seams and cracks of each layer as an air barrier and keep the roof unvented? I would then like to add another layer of rigid under the rafters with taped seams to prevent thermal bridging and air leakage once again. Then I would strap under that so I could still install T&G on the ceiling. Above the rafters I could either go with 2x4 strapping then 30lb felt then metal roof, or half inch sheathing then felt then metal. With sheathing that would mean there would be no venting. I have read on here that I may not need venting if I have the seal of rigid foam with canned spray foam to seal. Any insight into this would be greatly appreciated. Oh and I am in climate zone 2b, pretty much in the rocky mountains of southern alberta. Cold and dry here. Thanks.
Posted Aug 5, 2014 12:41 AM ET
Edited Aug 5, 2014 6:03 AM ET
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