Having enough insulation in your home is important for saving energy, but air leaks can defeat the benefits of insulation. www.EnergyStar.gov has a great, well-illustrated guide to locating and stopping energy-wasting air leaks in a home. Here are some ideas from EnergyStar:
More than any other time of year, you notice your home’s air leaks in the winter. Most people call these air leaks “drafts.” You may feel these drafts around windows and doors and think these leaks are your major source of wasted energy. In most homes, however, the most significant air leaks are hidden in the attic and basement. These are the leaks that significantly raise your energy bill and make your house uncomfortable.
COMMON HOUSEHOLD AIR LEAKS
Behind Kneewalls (side walls of finished attics)
Attic Hatch
Wiring Holes
Plumbing Vent
Open Soffit (the box that hides the recessed lights)
Recessed Light
Furnace Flue or Duct Chaseway (the hollow box or wall feature that hides ducts)
Basement Rim Joists (where the foundation meets the wood framing)
Windows and Doors
In cold weather, warm air rises in your house, just like it does in a chimney. This air, which you have paid to heat, is just wasted as it rises up into your attic and sucks cold air in all around your home—around windows, doors, and through holes into the basement.
A good way to start home sealing is to make a quick sketch of your home’s floor plan. This sketch will serve as a reference point once you get into the attic and will help you locate areas of leakage. In your sketch, make note of dropped soffits over kitchen cabinets or bath vanities, slanted ceilings over stairways, where walls (interior and exterior) meet the ceiling, and any other dropped-ceiling areas. These areas may have open stud cavities leading directly into the attic and can be huge sources of air leaks.
Plug the Big Holes First
Don’t worry about finding and sealing all the little holes in your attic; your biggest savings will come from plugging the large ones. Once in the attic, refer to your sketch to locate the areas where leakage is likely to be greatest: where walls (inner and outer) meet the attic floor, dropped soffits (dropped-ceiling areas), and behind or under attic kneewalls.
Look for dirty insulation—this indicates that air is moving through it. Dropped soffits may be filled or covered with insulation and hard to see. Push back the insulation and scoop it out of the soffits. You will place this insulation back over the soffit once the stud cavities have been plugged and the soffits covered.
MATERIALS CHECKLIST FOR SEALING ATTIC AIR LEAKS
Batt or roll of un-faced fiberglass insulation and large garbage bags (for stuffing open stud cavities behind kneewalls and in dropped soffits)
Roll of reflective foil insulation or other blocking material such as drywall or pieces of rigid foam insulation to cover soffits, open walls, and larger holes
Silicone or acrylic latex caulk & caulk gun for sealing small holes (¼ inch or less)
Several cans of expanding spray foam insulation for filling larger gaps (¼ inch to 3 inches) Special high-temperature (heat-resistant) caulk to seal around flues and chimneys
Roll of 14-inch wide aluminum flashing to keep insulation away from the flue pipe
Planks to lay across ceiling joists to make a walkway
The opening around a furnace or water heater flue or chimney can be a major source of warm air moving in the attic. Because the pipe gets hot, building codes usually require 1 inch of clearance from metal flues (2 inches from masonry chimneys) to any combustible material, including insulation.
These gaps should be sealed with lightweight aluminum flashing and special high-temperature (heat-resistant) caulk. Before you push the insulation back into place, build a metal dam to keep it away from the pipe. Use the same technique for masonry chimneys. The EnergyStar website has photos that explain this procedure.
Seal Small Gaps
Use expanding foam or caulk to seal the openings around plumbing vent pipes and electrical wires. Be sure to wear gloves and be careful not to get expanding foam on your clothes, as the foam is very sticky and nearly impossible to remove once it sets.
Stopping the Chimney Effect
Outside air drawn in through basement leaks is exacerbated by the chimney effect created by leaks in the attic. As hot air generated by the furnace rises up through the house and into the attic through leaks, cold outside air gets drawn in through basement leaks to replace the displaced air. This makes a home feel drafty and contributes to higher energy bills. After sealing attic air leaks, complete the job by sealing basement leaks, to stop the chimney effect.
Seal All Gaps and Cracks around Rim Joists
Though you may not be able to see cracks in the rim joist cavities, it is best to seal up the top and bottom of the inside of the cavity. The joist cavities are also a good place to install insulation if you have an unfinished basement.
EnergyStar.gov also recommends that you seal penetrations that go through the basement ceiling to the floor above. Generally, these are holes for wires, water supply pipes, water drain pipes, the plumbing vent stack (for venting sewer gases), and the furnace flue.