Tips for Cutting Batt Insulation

Preparation

• Careful cutting can be frustrating, as batt insulation, faced or unfaced, can be thick, fuzzy or made of fibers that are tough to separate. To prepare for cutting, make sure you have an adequately sharp utility knife and proper safety equipment. As batt insulation contains at least some percentage of fiberglass, you will need safety goggles and a respiratory mask to protect yourself from loose particles. It is also a good idea to wear work gloves to guard against accidental nicks from the sharp razor edge of the knife, and a long sleeved shirt and pants to prevent scratching and irritation from the batt.

Measuring

• If you want to cut your batt to size before installation, make sure to measure your walls and surfaces beforehand. When cutting batt to size, it is better to cut your pieces a bit wider than too narrow; wide batt can be stuffed to fit or trimmed on the fly, while narrow batt will require patching with even thinner strips to avoid heat escape.

Cut to Size

• Lay the batt on a solid, flat surface, such as a concrete floor. Mark any needed measurements on the facing with a felt-tip pen, then lay a 2-by-4 board onto the batt to use as a cutting straight edge. If the batt has one faced and one unfaced side, cut with the unfaced side facing upward, as this allows you to compress the batt more effectively. Push down hard on the board to compress the batt, making it as thin as possible, then cut the batt in short strokes using the utility knife.

Cut-In-Place

• Install the batt as desired, then, when you come to an edge that requires trimming, fold the batt edge in half against the wall or surface, and hold it firmly. Use the utility knife to slice down the length of the batt, using the fold for leverage and cutting against the stud face. If you need to measure the cut before you slice, to ensure that you do not cut the batt so it is narrow, press the excess against the wall and use a straight edge and a felt-tip pen to mark where the cut should be. Then fold and cut, using the marked line as a guide.