I have 2×4 framed home with fiberglass insulation located in the northeast (not enough). The home is 40+ years and probably lacks any kind of housewrap under the cedar siding. I would like to increase the R-value of the walls and add some “depth” to the inside of the windows (similar to 2×6 framing min.). I was wondering if attaching 2″ pink foam board over existing sheetrock and then refinishing inside with new sheetrock would be advised? I plan to extend the electrical boxes and frame out the windows/doors. I am slightly concerned about creating a moisture problem, especially if in the future I replace the siding and install house wrap to the exterior. Any thoughts or suggestions that would help are appreciated. Thanks.
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You might want to try foil-faced polyiso (the orange stuff)> Thermax is one brand, I think Celotex is another. 1" of this will not only increase R-value of the wall considerably, but also provide a vapor barrier if seams are taped, and be a heck of alot easier to sheet rock over than 2" of rigid extruded (pink or blue stuff).
This is a good cold climate system to use...from inside out: sheet rock, polyiso, FG, sheathing, felt,typar or tyvek, siding.
That sounds like a lot of work!!
If you weren't looking for the extra dept at the windows I would suggest insulating from the out side when you add the house wrap.
Good luck with your project!!!
Do a search for mooney wall. Similar to what you're thinking of. It uses foam board on the inside of studs. Then the studs behind the foam board are filled with cellulose. Wall board is mounted onto firring strips. A key advantage is insulating the thermal bridging of the studs.
Since cellulose blocks the moist air from moving into cooler areas and condensing vapor barriers probably weren't discussed much with the mooney wall. If you continue with your FG you'll want to be careful about sealing the foam board edges and penetrations to prevent condensation. You may consider switching to cellulose. Do the search, a couple long threads if i recall.
I believe Mike Smith uses it quite a bit in the northeast where you are.
eric