Breaking the thermal bridge on the interior
I had a thought about a possible wall construction that I wanted to gauge with everyone. The primary reason I thought of it was for ease of building for a traditional builder – especially flashing complications and building out around windows if there was exterior rigid insulation. It involves using polyiso on the interior of a 2×6 stud wall. In my mind it allows me to use a thinner layer of rigid insulation with higher r value per inch, placing it on the warm side so it retains its r value in Michigan winters (climate zone 5). And it addresses the thermal bridging issue. The wall would be sheathed with zip system panels, with liquid flashing for the joints (establishing the air barrier on the outside), with a rainscreen of traditional furring strips or something like this Keene Driwall system:
It would be insulated between the studs with dense pack mineral wool or roxul batts. On the interior would be 1.5 inches of polyiso on the walls and ceiling followed by a 2×3 service cavity along the walls and ceiling. I could then use a combination of drywall or tongue and groove wood paneling for the interior walls.
If I went with rigid exterior insulation, I would’ve opted for rigid mineral wool, but with three gable ends in our design, and a vented attic, I would’ve had to continue the insulation up into these areas for continuity reasons in the exterior siding, not for needed insulation value. I can avoid this with doing it on the inside.
I know this sacrifices interior space, and that it is unconventional, with all the recommendations saying to add rigid insulation on the exterior. I just want to know if this is possible, and if it sounds any easier as far as buildability for a traditional builder. Admittedly, I’m still brainstorming here. Thanks again.