Can I put Roxul over Sheetrock on the interior?
I was planning on creating a built in window seat/bed in a bonus room over the garage. We just purchased the house and I am guessing It’s likely one of the coldest parts of the house in the winter. It’s just above the garage doors. Likely has little insulation in the floor, vaulted ceiling so probably R13 at best. The house was built in 1991 +/-.
I am toying with the idea of furring out and insulating with some Roxul boards around the window and vaulted ceiling area. I was going to just put it right on top of the sheet rock and cover it up with bead board or something similar. My question is will mounting it right over the sheetrock cause any problems? The attached file will show the overall affect I am striving for. I’ll likely build it out of ikea components and plywood.
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Without knowing what's in the walls now, it's hard to say 100% for sure that there's no way it would cause a problem, but it's unlikely to cause a problem.
The potential problem I thought of was if there was a poly vapor barrier just behind the drywall, and a really bad insulation job behind that, such that the sheetrock is pretty much at outdoor temperature and the poly traps moisture.
I suggest that you make a little exploratory hole in the wall where it's going to be covered anyway to make sure you know what's in there, the post the results, plus your location or climate zone, so we can make sure it's OK, but it probably is.
I am in east TN (suburb of knoxville). There's a little access hole between the gable windows in this room. It looks like the batt has just been laid in so no poly that I can see. I was/am thinking the roxul would be better than board foam insulation for the same reason (i.e. moisture build up behind it.).
Assuming you are sure that there is no polyethylene in the assembly, your plan will work.
I'll add my usual advice: pay attention to airtightness at every stage of your work.