Cathedral ceiling rafter cavity and insulation
I am trying to figure out how best to use Rock Wool in my cathedral ceiling with the space that I have. I am using 2 x 12 rafters. I am not using spray foam. I was going to build my vent baffle from xps sheets for a 1″ air space sub roof sheathing…I was even willing to shrink that space down if needed. I live in zone 3 and would like at least R-35. So with my rafter space I start out with 11 1/2″ inches. No matter how I figure it with rock wool batting, I either end up with 2″ of dead air space that should be filled with something or 1/4″ too much for the space. My main question is, can you slightly compress (1/4″) the rock wool insulation to fit the cavity,or does it have too much density, and would you compromise the insulation value too much?
I know there are a million and one ways to fill that space, but I was looking for the best method with rock wool, with the least amount of steps.
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