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Apples are ripening on the branch, winter is near.

Dress your home for the winter: Air Seal and Insulate

Apples are ripening on the branch, the days are shortening, and the crisp smell of fall is in the air. While you may look forward to the crunch of autumn leaves under your feet, you're probably in no hurry for the crunch of winter heating bills.

If cold walls or ceilings, drafty doors and windows, ice dams and icicles come to mind when you think of your home in the winter, you're paying to heat air that leaks right out of your house. The EPA estimates a proper home sealing and insulating job can save you 20% on your heating bills. That's 10% of your total energy bill! If you'd rather spend your money on weekend ski trips than through-the-roof heating bills, take a weekend to air seal and insulate your home. A job well done will save you money and make your home a more comfortable winter retreat.

Seal first, then insulate! Stay cozy this winter.

You wouldn't go out on a cold, windy day in nothing but a holey sweater and expect to stay warm. A poorly sealed home can't fare any better.

Like a sweater, insulation only keeps us warm when air isn't passing through it. To get the full benefit of insulation, it must be properly installed, and there must be no air leaks.

Air sealing, or blocking places where air leaks from conditioned to unconditioned spaces or vice versa, is like putting a windbreaker on your house. Do this before adding insulation to get the full benefit.

From the top to the bottom

The attic is the single biggest source of air leaks in most homes. Particular trouble spots include anywhere walls meet the attic floor, behind and under knee walls (if you have a finished attic), anyplace where ceiling height changes, and canned/recessed lighting fixtures. Make a sketch of your floor plan highlighting any of these conditions. It will be a handy reference when you're up in the attic.

Assemble your tools and materials before going up to the attic to prevent a lot of trips up and down. You'll want lights, dust mask, gloves, knee pads, a utility knife, a bucket to haul tools and materials in, fiberglass or alternative batt insulation, plastic trash bags, spray foam, caulk and a caulk gun, blocking material like reflective foil insulation, rigid foam board, or drywall, and flashing, sheet metal snips, and high-temperature caulk for around the furnace flue.

Common air leaks into and out of the home.

Go first to the trouble spots mentioned above. Put rolls of batt insulation in the plastic bags and stuff them snugly into stud cavities, under knee walls, and around dropped ceilings. The goal is to stop uncontrolled air movement between conditioned and unconditioned spaces.

In some spots, this goal might be easier to accomplish by covering the hole with rigid foam or other blocking material and sealing the edges with spray foam. Around furnace flues or chimneys where temperatures get very high, be sure to use special high temperature caulk and to create a dam out of sheet metal to prevent the insulation from coming into contact with dangerously high temperatures. Download the Do it Yourself Guide to ENERGY STARŪ Home Sealing (pdf) for complete step-by-step instructions.

After you've hit the big spots, look around the attic for small leaks. They are usually hidden under the insulation where electrical junction boxes, wiring, or plumbing penetrate the attic space.

Some signs that air is leaking into the attic? Dirty insulation where dust is being filtered as air passes through or water stains where warm, humid air is passing through the insulation (these can be seen as frost in colder weather, where humid air rises to the attic and freezes).

Pull back the insulation, seal electrical juncture boxes with caulk. Seal wire and plumbing penetrations with spray foam. Once the caulk and foam have dried, push the insulation back into place.

Seal the attic access panel with weather stripping or try PATH's attic access insulation and air seal systems.

Don't forget the ducts

If your heating and cooling ducts run through the attic, seal them while you're up there. You'll need some additional materials: duct sealant (mastic) or foil backed tape (traditional gray duct tape fails quickly, mastic is the best option), duct insulation material rated at least R-6, and zip ties to hold the insulation in place.

Many contractors think wrapping the ducts in insulation adequately seals the ducts. This is not the case, so even if your ducts seem amply insulated, you should remove sections of insulation and check that the joints are fully sealed. Check this by turning on the system and feeling for air leaks. Where you feel leaks, apply mastic or foil backed tape, then insulate. This will help keep air at the desired temperature as it passes through the system, instead of using all that energy to heat and cool the attic!

Take it to the Bottom

After sealing the attic, go through the house and check doors and windows for air leaks. Use weather stripping and caulk where appropriate. If your windows are old, or have aluminum frames, you may consider replacing them.

In the basement, the most common spots for air leaks are at the top and bottom of the rim joists on each end of the house, wherever electrical, water, gas or ventilation requires penetration to the outside, and along the gap between the sill plate and the foundation, where masonry or cement meets wood. Caulk is best for sealing gaps under 1/4". For larger gaps (1/4"-3"), use expanding spray foam.

Traditional grey duct tape.

The orange line indicates where insulation should be installed.

Put on a Sweater

After you've sealed the air leaks it's time to make sure you have enough insulation. If you need to add more, this may be the perfect time to check out PATH's innovative insulation materials (pdf). Whether you opt for blown-in fiber insulation, alternative insulation that's blown or foamed through a membrane, or batt insulation, be sure to get up to the recommended R-value and evenly cover the entire area.

Content updated on 10/2/2007

Further Resources
Energy Efficiency in Remodeling: House Air Leakage
Technology Fact Sheet: Air Sealing- Seal air leaks and save energy
Energy Efficiency in Remodeling: Roofs & Ceilings
Tech Set 2: Durable Building Envelope
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