Fiberglass batts come in standard widths to match 16-inch and 2-foot on-center stick framing. Irregular stud spacing and blocking don’t work well with standard batt dimensions so when possible, keep the framing simple and accurate. Avoid unnecessary blocking and odd spacing.
It’s faster to squeeze, jam, bend, or fold fiberglass insulation into an oddly shaped space rather than to carefully cut the batt to fit. But precisely trimming batts to fit snugly into place creates the contact that keeps conditioned air from leaking in or out, so make sure your crews take the time to trim it right.
Wiring runs across the center of stud bays. It’s quick to stuff a batt behind the wire, but that creates a poorly insulated void. Instead, have crews split batts at mid-depth; for a snug fit with no voids, tuck half behind the wire and the other half in front. Trim batts carefully around blocking, switch boxes, and receptacles, too.