Properly weatherizing your attic can cut 10 to 30 percent off your
heating and cooling bills, according to the U.S. Department of Energy.
And while you might not want to spend the money (or the time) to do the
work, keep in mind that the federal government offers a 30 percent tax
credit up to a maximum of $1,500 on weatherization materials, and
utilities and states in place like Massachusetts, New York, and
Washington offer additional incentives that sometimes cover labor
costs.
There
are some simple things to remember when weatherizing your attic, such
as never using duct tape on, well, ducts. Also know that if some
conditions are present, such as if your insulation is wet or there's
mold or knob-and-tube wiring, you should hire a contractor to do the
work.
Otherwise follow this advice from the DOE's do-it-yourself guide
to attic insulation (PDF) and our own Complete Guide to Reducing Energy
Costs to seal up your attic and start saving money now. Download this PDF from the book for more details on insulating your attic and/or basement: Insulate Basement-Attic, and watch our video.
1. If you see dirty insulation . . .It means air is passing through the insulation from the heated space
below because most thermal-insulation products are not air barriers.
Search for the source of airflow, such as a large open chase or smaller
gaps around an electrical wire or junction box or plumbing pipes or
vents
2. If you see narrow gaps less than 1/2 inch wide . . .
Seal gaps with the appropriate caulking. If the crack is deep, use
flexible backer rod before caulking. (Gaps around heating-system flues,
chimneys, or recessed lights should be handled differently to avoid a
fire hazards; see the precautions below.)
3. If you see gaps more than 1/2 to 2 inches wide . . .
First, close up large openings using scrap wood or metal flashing that
you screw in place. Then caulk all seams and small gaps or seal using
expandable, spray-in water- or foam-based sealant. Remember, foam-based
sealants can expand to several times their original volume, crush
flexible vent pipes, and cause structural damage if too much is
applied. Water-based foams expand less; you can also use fiberglass
insulation stuffed in a plastic bag. When working, wear gloves, long
sleeves, and a dust mask specifically marked as being for fiberglass
insulation. And remember, foam-based sealant is also nearly impossible
to remove if you get it on your skin, and fiberglass insulation can
irritate skin.
4. If you see uninsulated areas around light fixtures or where chimneys and furnace flues penetrate through floors . . .
Most recessed light fixtures that protrude up into the attic should not
be covered with insulation, which could cause them to overheat.
Instead, use a similar barrier made of sheet metal, wire mesh, or
lumber to keep the insulation away from the light housing. These
fixtures also allow air to flow, but unfortunately most cannot be
sealed directly. You can build a larger box enclosure around each
fixture that can serve as the air barrier, or you can have the fixtures
replaced with a version that is an air barrier type rated for
insulation contact as well.
For chimneys or flue pipes, use a heat-resistant caulking or follow the
DOE's instructions to create a sheet-metal insulation dam that will
keep insulation 2 inches away from the heat source.
5. If you see joist edges showing above your current attic insulation . . .
Add another layer of roll insulation perpendicular to the joists. Use a
piece of scrap wood to push the first line into place under the eaves
but don't block airflow from the eave out into the attic space. While
the attic floor surface should be insulated, an air gap should exist
between the roof rafters so air can flow between the eave and the rest
of the attic. Don't use foil-faced insulation. The layer of insulation
below should have an existing vapor barrier.
In general, good building practice requires three barriers of
protection on the surface that separates the heated and cooled living
space of the rooms below and the unconditioned attic space above. These
barriers are the thermal insulation to slow the heat loss (or gain),
the air barrier to stop uncontrolled air exchange between the two
spaces, and the vapor barrier to prevent moisture migration. Typically,
the vapor barrier should be on the warm side of this dividing surface,
so in a warm climate it would be on the attic side of the thermal
insulation, and in a cold climate it would be on the living space side
of the thermal insulation. The air and vapor barrier can be provided by
one product or separate products or approaches.
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