My ceiling use web joist 24" O.C. with an opening of about 20.5 inches. I purchased roxul mineral insulation for the 24 O.C, but is 24" wide so won't fit in the opening between 2 studs.
Since I have to cut the insulation, what should the width be? 20.5", 21.5" or?
Also, the wall sorrounding the room use 2x4 staggered studs with 2x6 plates, leaving a clearance of 2" in the middle on the plate. Would be ok to use 3.5" wide insulation. By code I'm required to use R21.