Rock wool insulation and smart vapor barrier
With my new house construction I was planning on using open cell foam and have asked some questions a few weeks ago, but as I have read more, I am more interested in rock wool insulation batts. First, because of the DIY aspect, and second because there is at least some potential that it is a bit easier on the earth. So, I have questions about the best installation method for my cathedral ceiling and 2 x 6 walls in zone 3.
First, cathedral ceiling is 12/12. Will have soffit to ridge vents. 2 x 12 rafters on 24″ center. Looking at R30 rock wool batts (would like R38 but with vent baffle space not sure I can make additional rock wool batts fit). Questions with ceiling are: Do I need a smart vapor barrier? How will this smart barrier work if I use latex paint on gypsum on the ceiling? Is the roughly 4″ gap from the outside face of the batts to the exterior roof sheathing a big concern..and if so what is the recommendation to deal with this gap? I don’t want to use spray foam in this process. And since the larger vent space is potentially there, would I need an actual vent baffle like smartbaffle in place?
Second, 2x 6 walls, 16″ on center, 9′ height. Looking at R 23 5.5″ rock wool batts. Do I need a smart vapor barrier like MemBrain and if so, again, how does it work if you use latex paint on gypsum board?
Thanks in advance!
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