Tip 1: Cut fiberglass batts to exact widths
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A good insulation fit
Cut fiberglass insulation with a sharp utility knife and a straightedge.
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
concrete.
Tip 2: Avoid stuffing
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Stuffing a batt
Cramming a wide batt into a narrow space leaves air gaps due to the bad fit.
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
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Protective equipment
Goggles, gloves, a dust mask, a cap and long-sleeved coverings protect you from fiberglass irritation.
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
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Seal gaps
Expanding foam makes an airtight seal in leak-prone areas like around windows and doors.
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
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Notch around electrical boxes
Cut notches in batts to fit snuggly around electrical boxes. Airtight boxes have gaskets that seal against the drywall.
Do notch fiberglass
batts
around electrical
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
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Split batt
Fiberglass batts have a vertical weave that allow you to easily tear it open for insulating around electrical cables.
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
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Insulating behind a cable
Don't stuff batts behind cables. It leaves an open gap in front.
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
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Sealing holes in plates
Stop air leaks by sealing holes around wires and pipes with expanding foam.
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
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Paper-faced insulation
Paper-faced insulation is more difficult to cut and install.
Don't buy paper-faced
insulation
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
batts.
Tip 10: Buy friction-fit batts
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Sealing friction-fit batts
Seal batts with 4-mil poly, tape and acoustical sealant.
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
tape.
