I am taking the paneling off a room that was an attached garage converted to a room. The walls are 2X4, but then they have 3/4 inch cork like material between the studs and the outer wall. It's not exactly cork. The material is mostly between the outer wall and the studs. So in many places I could place another 3/4" of insulation. Initially I was going to go with the R13 faced batts for 2X4 walls, but I could fit in a little more insulation, but the R19 faced batts are for 2X6 walls so the insulation would be compressed.
Any suggestions what I should put up? Just stay with the R13?
I'd go with R15 then
It will give you a better R value then the compressed R19
If you want buy some rigid foam board & fill the extra inch
Some people also "peel" fiberglass insulation thinner & use that to fill in