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.)
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.
6. If you see a dropped ceiling above closets, cabinets, and showers in your main living areas . . .
Check that the spaces are enclosed, sealed, and insulated in the attic.
7. If you see uninsulated attic ducts . . .
Uninsulated ductwork running through unconditioned spaces can lose as much as 40 percent of a heating or cooling system's energy. Insulate with special insulation with at least an R-6 rating. Use metal-foil-faced tape or mastic-based duct sealant.
8. If you see an uninsulated attic hatch . . .
You can buy a molded insulation cover to place above the hatch or you can make one yourself from rigid-foam insulation panels and construction adhesive.
9. If you see attic insulation that ends before the eaves, leaving a gap that air can pass through . . .
Add roll or bagged foam insulation almost but not quite all the way up to the eaves. You can slide a rafter vent (shown) that will allow a small amount of air to enter the attic that will then be exhausted through your home's ridge vent or gable vents. (While it might seem strange to allow air into your attic via a rafter vent, a cold attic can reduce the chances of ice dams forming.)
10. If you see gaps in your basement . . .
Caulk or seal where the wood framing sits atop the foundation's rim or band joist to seal likely entry points for cold outdoor air. Caulk gaps between the foundation walls and basement floor. Also seal air pathways between the basement and the living space above if the basement is not heated and cooled. Insulate any wall, floor, or ceiling surface that separates heated/cooled living space from an area that you do not heat or cool.
Essential information: Get more details on saving money and energy on our Energy Saving & Green Living guide.