2 inch Roxul Comfortboard on interior of cathedral ceiling
We are building a small house here in North Idaho (CZ5) with a cathedral ceiling framed with 11 7/8″ I-joists. The roof is vented and 3:12 single pitch. The roof/ceiling assembly is as follows from outside-in:
*Standing seam metal roof
*Solitex UM underlayment with embedded 3-D mesh (vapor open, for drainage/drying of backside condensation)
*5/8″ CDX plywood sheathing
*1 1/2″ site-built ventilation baffles (between top flanges of I-joists)
*1″ XPS attached to bottom of top flange of I-joists (to create bottom of baffle)
* R-30 (7 1/4″) Roxul comfortbatt in rafter bays
* R-15 (3.5″) Roxul comforbatt slightly compressed to fit in remaining depth of rafter bay
* Intello Plus smart vapor retarder/interior air barrier membrane from ProClima attached to bottom flange of I-Joist.
*** Proposed 2″ rigid insulation to address thermal bridging
* 2x furring
*1.5″ service cavity
* Plywood ceiling
This assembly gets us to +/- R-50 in the ceiling while staying vapor permeable (though I know there’s a slight reduction if we compress the batts). My question is: We are looking to address the thermal bridging through the I-joists (and pick up another R-8 or so) and are considering using 2″ Roxul comfortboard on the interior here. We’d like to avoid using foam for IAQ and vapor concerns. Does anyone know whether the comfortboard would be appropriate here? The Roxul application guide shows using comfort board on the interior of basement walls, but not anywhere else on the interior.
Thanks in advance for your responses!