Minimum thickness of roof foam
I am building a 12'x18' room in climate zone 3c in Sonoma County Ca. The roof on the rest of the house is an unvented cathedral ceiling that has 3" of closed cell spray foam under the roof deck with dense pack cellulose filling the remainder of the 2x8 rafter bays. I have since learned that with the standing seam metal roof, moisture could get trapped in the roof sheeting if it gets wet. It has been 3 years and I have not noticed any problems. On the new roof I plan on putting 2" of polyiso on the roof deck. Two layers of 1" with staggered and taped seams. The 2x8 rafter bays will be filled with R30 Roxul. The metal roof will be attached with 3" screws through the foam and into the roof deck. I have read that all I need is R5 to meet code but then I read that I need a certain percentage of foam based on the total R value. Which is correct? Will this roof have a condensation/ moisture problem?
Posted Aug 2, 2014 4:51 PM ET
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