Fiberglass insulation typically is cheaper than spray foam or blown cellulose. But if you cut corners on hand labor, you’ll pay the price when it comes to performance. Studies show that voids and air gaps in a sloppy fiberglass batt insulation job reduce the thermal performance of the insulated wall, ceiling, or floor.

But fiberglass does perform at its rated R-value when you install it properly—filling cavities completely and making contact with the protective framing, sheathing, and wallboard on all sides.

Just as with any trade, builders have to train and supervise their insulation crews to make sure the job is done right. The key to quality is to ensure that the insulation fits snugly into the framing cavities, and that it’s protected from air movement. Installers must trim batts carefully to fit oddly shaped voids, cut and fit the material around blocking and electrical boxes, and split the batts to fit behind and in front of wiring. This care and effort will pay off in improved comfort, energy savings, and home energy ratings for your clients.

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.

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.

To insulate at their full rated R-value, batts need to make contact with wood on all sides. Teach your crews to push each batt snug against the sheathing, then fluff and pull the batt forward so it makes full contact with the sheetrock.