Wall insulation for a new room addition
I’m thinking about this (not so) future project. One option is 2×6 studding with R-19 (6″) fiberglass batts in between studs. To gain more R value and reduce thermal bridging I was thinking of adding probably 2″ of type II EPS (4.2 R per inch they say)to the inside of the studs, for about R-27 for the wall. I’m assuming this needs to dry to interior since plywood and/or OSB are pretty impermeable to moisture and would limit drying to the outside. Is that correct, and if so is 2″ of EPS adequately permeable for interior drying? I would have sheetrock over EPS.
Or, I could do same R-19 batts in between studs, and then 3″ of EPS on exterior (R 11.25 needed in this arrangement, for a total of about R-31). With taped sheetrock on the inside this would certainly be able to dry to the interior.
Is one of these better than the other? I will likely be using vinyl siding, and one issue is the poor compatibility of vinyl siding with exterior foam. The other is the challenge of the added thickness of the wall (this is also true with interior foam, but seems less of a challenge than the exterior thickness).
Advice and input would be much appreciated.