Sealing the Attic

To save energy immediately, begin by sealing the gaps that lead from your living areas to the attic. Some of these gaps accommodate wiring and pipes, while others result from poor craftsmanship and the normal settling of the building. But all of them serve as passageways for heated air to escape.

That's because houses act like big chimneys. Warm air rises to top of the building, increasing air pressure near the ceiling. The difference between that pressure and the lower pressure outside on a cold day drives the warm air through any crack, crevice or gap it can find. The high pressure at the top also creates low pressure near the bottom of the house, which pulls cold air in through openings around the foundation or slab.

Energy experts call this the stack effect. The larger the spread between inside and outside temperatures, the greater the pressure differences and the stronger its pull. However, if you have mold or condensation problems in your home during winter, don't do any sealing until you've tackled the moisture situation.

What insulation can't do. An insulated attic isn't necessarily a sealed attic. Insulating materials are designed to slow down heat loss through solid materials rather than to stop airflow. Insulation works with weatherizing to create a thermal boundary between the inside and outside of your home. Unfortunately, most homeowners pay attention solely to the insulation part of the equation. "Half the money people pay for insulation is often lost due to leaks," says Michael Lamb, a home-energy specialist for the Energy Efficiency and Renewable Energy Clearinghouse, a McLean, Virginia-based information network sponsored by the U.S. Department of Energy (DOE). "If homeowners sealed the attic floor before insulating, they would save a lot more energy."

Filling the gaps. Spotting the holes and gaps you need to seal is easy in an uninsulated attic. Lay planks across joists and stay on them so you don't step through the ceiling. Then check for gaps around anything that comes through the floor. Examples include the tops of light fixtures, pipes, wiring, the chimney and heating and cooling ducts. Also check for gaps around the top plates of interior partitions.

If your attic is insulated, you'll need to roll back batts to get at the gaps. Wear pants and long sleeves, gloves, eye protection, and a dust mask. Gray or black smudges in the insulation signal air leaks. If your attic is insulated with loose-fill insulation, which can't be peeled back, you might want to call a professional weatherization contractor to locate the leaks. Then seal as many of them as possible.

• Instead of insulation, use latex caulk to fill gaps up to about 3/8 inch wide. For holes up to about 1 inch wide, use expanding urethane foam (it comes in a can). Be careful — the foam is hard to get off of clothes and hands. A new latex sealant from DAP ($3.50 per 12-oz. can) cleans up with soap and water. • For larger holes, create a plug from a piece of drywall. Cut it to fill the hole, push it into place and then seal the edges with urethane foam. Or, use fiberglass insulation stuffed into plastic bags. • Seal gaps around chimneys and stove flues with a sheet-metal collar and caulk. • Insulate and apply weather stripping around the edges of the hatch or door that leads to the attic. • On cathedral ceilings, apply caulk in spots where drywall meets exposed beams.

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