Polyiso on both sides of sheathing?
So I have insulation challenges. I am pretty set on my walls, I have 2×6 construction. I am in the Austin area, and plan on using polyeurethane to seal all sheething joints, then following that up with 2in of polyiso on the exterior. I have considered using a STO liquid over the sheething, I think they even have one that you stick the insulation to, so am pricing that. Then a rainscreen, with cemplank over that.
So the questions.
If I have polyiso on the outside, do I dare put it in the inside cavity ? I have a real good deal on it, and figured I might use it most everywhere. Or I might just do open cell in the cavity. My concern with polyiso on both sides is that if moisture ever did get in there, it would not be able to get out.
On the roof, I was thinking 3 layers of the 2in polyiso would put me at r36, much closer to where I need to be, and then I might spray a light sprayfoam over that just to make sure it is airtight and no gaps might leak etc.
Thoughts ? Advice ?
I know it would be nice to put polyiso on top of the roof, but at 100square paying for the sheething twice just isn’t in the budget.
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