Interior Foam Insulation vs exterior
I thought I had things all figured out. I’m in central Wisconsin, Zone 6, I was planning on 2×6 construction with (2) 1″ Layers of exterior polyiso held by 3/4″ furring strips via fastenmaster’s specs. Hardieboard only requires 3/4″ screw penetration, good to go…but all the 5/4 and 4/4 trim (frieze, band corners) made by Smartwood, Miratec, Azek, Certainteed requires 1 1/4 penetration. Using vinyl siding with basic corners are about the only option which would be fine, but I would still have to foam between the furring stips and it still doesn’t provide a solution for bump-out windows with decorative trim that more or less has to be made with 4/4 boards. Exterior foam also makes cultured stone nearly impossible, and I have yet to find a manufacturer that supports exterior foam (2″ anyway.) Short of using 2×4 furring strips (still not supported by Certainteed), there are no manufacturer approved solutions.
The only solution I can come up with is to ditch exterior rigid insulation and put interior rigid insulation between the studs and drywall. But I need a little guidance.
1) Do I still need an interior vapor barrier? I was planning on dense pack cellulose between studs, what is the best way to hold the insulation in?
2) Do I still need 2″ foam or can I get away with less? I was thinking if I used 1/2″ to 1″ I could save having to us furring strips.
3) Should I still try to keep the exterior structural sheathing airtight ( ie tape seams) ? Or do I need to make it easier to dry to exterior?
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