Upgrading with interior rigid foam in zone 6
I have the option to upgrade insulation from inside in a part of the house where we’ll be doing soundproofing.
House is currently brick veneer, air gap, asphalt felt, plywood, 2×6 with r19 fiberglass, polyethylene, drywall built in late 80’s
I was thinking going to :
R 22 rockwool I already own for non insulation benefits plus
Add one 1nch of polyiso on the south facing wall – no windows and
3/4 inch on the east and west facing wall with big windows that make up about 1/2 of the wall (my wife was against the idea of adding any insulation to those walls initially, we compromised).
Omit the polyethylene and pay really close attention to air sealing.
The 2 brands I can find in my area claim aged R6 for 1 inch and are foilfaced or R 5.5 unfaced.
Does it make sense to add the 3/4 inch of polyiso? do the downsides of reduced drying to the outside outweigh the small bump in R value? Will the new assembly allow for slightly higher indoor moisture in the wintertime? I get pretty annoying symptoms whenever RH drops below 30%.
On another note, I’m currently upgrading my rim joist insulation from fiberglass batts to 6 inches of eps (mostly done) + rockwool for fire protection. I thought I could add a few inches of rockwool to go beyond the rim joist and increase R value, like I was using 2×8 to frame a wall rather than 2×6. Does that work? Or is it better to just add a small amount the fire protection?
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