Unvented roof and condensation
I am planning to build a low slope (12%), unvented roof in climate zone 6. I read many articles on this site about that, and that’s what I think is a good way to go :
– Around 12″ of static air
– Trusses about 20″
– Fiberglass insulation R30 / 8″
– Roof deck / plywood 3/4″
– Air barrier membrane
– 4″ of polyurethane insulation
– 1″ of PSE insulation
– 2nd roof deck
– Roofing underlayment
– Heat-welded base sheet membrane SBS (SOPREMA)
So a total R-value of R-60, with half on the top of the structural roof deck and half under (min of 51% is recommended for the foam in climate zone 6).
When I simulate this situation with the coldest weather of my region (-12°C / 10°F), there’s a lot of condensation that appears in the complex.
What’s wrong with my conception ?
Since the upper layer of insulation is pretty thick (6″), I don’t want to add more, so what can I do (except ccspf under the deck) ?
Thank you in advance for your help, and sorry if I did some linguistic mistakes, since english is not my mother tongue.
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