What are your recomendations regarding rock wool, dead air space, reflective polyisocyanurate and vapor and air barriers?
May be trying to educate myself and reading too much. First off I am in zone 6, Portland Maine. The outer roof consists of OSB, ice and water shield and asphalt shingles. No attic space, a complete living area. The wall outer layer is cedar shingle.
A portion of the roof (12'x26') is low slope roof (4/12) 2x10, have installed rock wool to an R38. The rest of the roof is 9/12 pitch 2x6, rock wool to R23. The 2x4 walls have rock wool to R15.
I really want to use foil faced (both sides) polyisocyanurate also on the interior. The final system must include the rock wool that is already installed.
I am trying to get a radiant barrier mostly to prevent heat transfer into the home during the summer, hence rigid polyiso-, and dead air space. OK, my plan, from the rock wool, 6 mil polyethylene sheeting, 1" dead air, 1 1/2 polyiso, 3/4 dead air, then 5/8 gypsum.
My concerns are the polyethylene sheeting causing trouble with exterior drying. But isn't the foil face of polyiso an air/moisture barrier? Is using both just too redundant? Am I really accomplishing anything with two dead air spaces to insure a radiant barrier?
A second idea is polyiso agaist the rock wool, then dead air space followed by the gypsum.
I think my biggest concern is exterior drying. Also on the low slope roof, it can't be vented so I am trying to keep it as cool as possible for winter snow, ice damming. Should I just simplify and install the gypsum right up against the rock wool?
Lots of complexities and questions. Suggestions ?
Posted Fri, 08/30/2013 - 10:32
Edited Fri, 08/30/2013 - 12:07
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