Tip 1: Cut fiberglass batts to exact widths
It’s easy to insulate
your walls with fiberglass
insulation (at least when they’re
open!), but the job still requires
attention to detail to get the
maximum benefit. Every gap and
compressed batt leaves a path for
heat or cold to escape.
Do measure and cut the fiberglass
batt for an exact fit. Add about
1/4 in. to the measurement to ensure a snug
fit. Use a 4- to 6-in.-wide board or strip of
plywood as a straightedge to guide your utility
knife. Line up the edge of the board at the
proper width, compress the insulation and
cut it with a sharp utility knife. A scrap of
plywood under the batt will protect finished
floors and keep the blade from dulling on
Tip 2: Avoid stuffing
Don't stuff full-width batts
into spaces that are too
narrow. Crumpling batts to fit narrow spaces
creates uninsulated air pockets. And packed
insulation has a lower R-value.
Tip 3: Wear protective equipment
Do protect your skin, eyes and lungs when you're working with fiberglass. If
you're installing a lot of it, consider wearing a disposable coverall (inexpensive at paint stores and home centers).
Tip 4: Seal narrow gaps with foam
Do seal around window
and door jambs with
expanding spray foam. The main
purpose of the spray foam is to
seal the space around the window
to prevent air infiltration. Use
foam that’s labeled for window
and door insulating. This “minimal-expanding” type reduces the
chance of warping the jamb. If
there’s still space around the window
after the foam cures, lightly
stuff the remaining space with
strips of fiberglass insulation.
Tip 5: Notch batts around electrical boxes
Do notch fiberglass
boxes. Put the batt in
place, and use a scissors
to snip around
the box. Tuck the
snipped-out plug of
insulation behind the
box. Don’t wrap fiberglass
batts around electrical
boxes or stuff full
batts behind them. That creates
gaps and air convection
routes around the box.
Tip 6: Split batts around cables and pipes
Do split apart the batts to fit
around wires and pipes to
get the full value of the insulation.
Tip 7: Avoid stuffing batts behind pipes and cables
Don't tuck full-thickness
batts behind pipes and cables.
Compressing the fiberglass
decreases its insulating value and
creates voids between the insulation
and the drywall.
Tip 8: Plug holes in top and bottom plates
Do plug holes in the top and
bottom plates with
expanding spray foam. Even small
holes can let a lot of air escape.
Don't leave gaps around wires, pipes
or ducts unplugged. These gaps create
pathways for warm interior air
to leak into the attic, wasting energy
and causing attic condensation or
even ice dams in cold climates.
Tip 9: Avoid paper-faced insulation where possible
Don't buy paper-faced
for standard wall insulating
jobs. The paper facing
makes cutting the batts difficult.
And it's hard to create a
tight vapor retarder with paper-faced
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Tip 10: Buy friction-fit batts
Do buy unfaced friction-fit
batts and seal the walls
with a 4-mil poly vapor retarder. Seal
the gap between the bottom plate of
the wall and the floor with acoustical
sealant or caulk. Press the poly into the
sealant. Use special airtight electrical
boxes (see photo, Tip 5) or seal the poly to the
electrical box with acoustical sealant.
Tape the seams in the poly with sheathing