Cutting Fiberglass Insulation Requires a Sharp
Utility Knife, a Straight Edge, and a Smooth Cutting Surface
By Mark J. Donovan
Fiberglass insulation rolls and batting are used to insulate walls, floors, and
attic spaces. Fiberglass insulation is the most common type of house insulation.
Installing fiberglass insulation is something most homeowners can tackle,
however it is important to use the right tools. Cutting fiberglass insulation,
for example, requires a utility knife with plenty of extra sharp blades. You
also need a straight edge, such as a carpenters square or a 2 foot length of
2x4, to help compress the fiberglass insulation when cutting it.
Cutting Fiberglass Insulation for Standard Stud Bay Widths
To cut fiberglass insulation first measure the length of the wall stud bay.
Then roll out the insulation onto a smooth cutting surface area such as a
subfloor. Using a measuring tape, and the utility knife and straight edge, cut a
length of fiberglass insulation approximately one inch longer than your
measurement.
When cutting fiberglass insulation, place the straight edge across the length of
fiberglass insulation roll or batt where you’ve measured, and put your knee on
it to compress it firmly against the subfloor.
Then use your utility knife to cut through the insulation. Note that you may
need to make a few passes with the utility knife to cut through the insulation
cleanly.
If you are installing faced fiberglass insulation, cut it so that the face side
is down against the subfloor. This way you’ll be less likely to tear the facing
paper as you cut it.
Once you have cut the fiberglass insulation to length simply push it into place
in the stud bay.
Make sure to push it firmly up against the back wall of the
stud bay and then pull the outer edges of the insulation to the edges of the
wall studs. If you are installing faced insulation, the facing should face
the interior of the room. Staple the faced insulation tabs to the wall studs
on the inside edges.
Cutting Fiberglass Insulation for Narrow Bay Widths
To cut unfaced fiberglass insulation for narrow stud bays it is often better to
cut it in place, after it has already been installed in the narrow stud bays.
Photo By Mark Donovan
If cutting faced fiberglass insulation for narrow stud bays, it is best to cut
it as you would normal stud width bays. However, you’ll need to cut it to both
the proper height and width.
When cutting faced fiberglass insulation to the required width, simply press
down on the insulation with your straight edge, make a cut, and then move the
straight edge forward and cut again. Continue this process for the length of the
insulation piece.
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