Hi all, My garage drywall is all torn up - tons of holes in it, tape lines, blah blah, blah. But the ceiling is relatively level and functional. The vertical walls are torn up with big cracks in the drywall/seperations at seams, holes, etc. I'm planning on ripping down all the VERTICAL wall drywall in the garage, sealing, vapor barrier, and re-insulating it and then re-drywalling. But since the ceiling is such a huge PITA, and the drywall is level, I had this idea: Could I nail/screw 1" thick foam panels to the entire ceilingto provide an air barrier and an R-4 to R-6 gain vs. what is in the ceiling right now. Then put 1/2" (Not 5/8") drywall screwed into the foam, taped, etc. I'd lose 1.5" of drywall ceiling height, gain r-4.5-6.5 (depending on foam, and including .5 r-value for drywall) But I wouldn't create an absolute disaster area, I'd gain alot of sound insulation from the garage, and it'll be far easier to accomplish. Is this doable? Any downsides? Joe P.s. I figure my attaching drywall straight to a 1" foam backer, I can get away with thinner drywall (like .5", maybe thinner?) by screwing it into the foam more frequently.