Air leaks cost us dearly. According to the Energy Star™ program, most people could save about 20 percent on their heating and cooling costs by sealing up air leaks. A surprising number of older homes are riddled with holes in the “building envelope,” which is made up of the outside walls, roof and foundation. These leaks range from large, obvious holes — such as broken or missing windowpanes in the basement — to tiny, almost invisible cracks. Small cracks can have a big impact. An eighth-inch-wide, 6-foot-long crack between a door and a doorjamb, for example, is equivalent to a 9-square-inch opening!
On cold winter days, leaks in the building envelope let hot air escape and cold air enter. In the summer, cool air slips out and hot air seeps in. Air leaks also allow moisture to enter walls and ceilings, which may make them breeding ground for mould. Water in walls may lead to structural damage; framing, if constantly wet, begins to rot. Sealing air leaks not only lowers home energy costs, it leads to a healthier, more durable home. As home improvement projects go, this one is amazingly easy and inexpensive.
Find Those Air Leaks!
To seal air leaks, you first need to identify them, either on your own or with the help of a professional energy auditor. To identify leaks yourself, begin by looking for large openings in outside walls, then search for smaller, less visible openings. On windy days, you can find these leaks by feeling around doors and window frames, at the base of walls, and anywhere else with an opening from outside to inside walls. Be sure to check around electrical outlets and light switches (even those on interior walls.) Ceiling fixtures — especially recessed lighting — are another major source of heat loss in the winter.
Start in the Basement
Basements are a major source of air leaks, so they’re a good place to start. Begin by sealing the largest and most visible cracks in your basement or crawl space. Replace any broken or missing windowpanes, or install rigid foam insulation over the openings. Seal any gaps — such as those around dryer vent exhausts — with caulk or expandable liquid foam.
For large cracks (those wider than three-eighths of an inch and deeper than a half inch), professionals often use a tubular foam called backer rod. They will vacuum or brush dust and dirt out of openings, then stuff the backer rod into gaps with a screwdriver or small putty knife. Liquid foam insulation can also be used to seal larger gaps; the foam quickly expands, and after it’s dry, any excess is trimmed off. Exposed foam can also be sanded and painted. Like backer rod, liquid foam seals large openings, prevents airflow, and adds insulation, further reducing heat loss or gain. Liquid foam insulation is available at home improvement centers and hardware stores.
Caulk comes in small tubes or cartridges for use in caulking guns. When sealing with caulk or foam, be sure to clean the surfaces first. After the surface has dried, fill the gap with caulk or foam. Wipe up any excess immediately.
Be sure to seal heating, cooling, and ventilation ducts that run through the basement, as well as openings in the foundation wall where plumbing pipes exit. When sealing leaky ducts, many heating and air conditioning professionals use mastic sealant, which is by far the best product on the market for sealing leaky ductwork. It creates an excellent seal and outlasts the cheaper, less durable, metallic tape and duct tape (apparently, the only thing duct tape doesn’t stick to is ducts!).
Walls and Ceilings, Windows and Doors
Walls in living spaces often have numerous cracks, typically around doors and windows, and along baseboards. You can usually seal these openings with clear or paintable caulk. Air leakage is common at the base of walls, so pay special attention to these areas.
To seal electrical outlets and light switches, use foam gasket insulators made especially for this purpose, which can be found at hardware stores and home improvement centers. Be sure to turn off the power at the breaker box before you remove the screws holding the cover plate in place, then insert a foam gasket and replace the cover plate. Block the slots in electrical outlets that are not being used by inserting child-safety plugs.
Be sure to check the ceiling for air leaks. Recessed ceiling light fixtures are notorious for leakage. Leaky can lights should be replaced with new, airtight, recessed light fixtures, which is a job you may want to delegate to a professional electrician.
Exterior doors are another big source of air leakage, which typically occurs between the door and the jamb. These leaks can be sealed with weatherstripping. This product comes in several varieties and is usually placed against the doorstop on the top and sides of the finished opening. Before applying, remove the old weatherstripping and clean the surface well. You may want to wipe down the area with rubbing alcohol to remove dirt and other residue.
To determine how much weatherstripping you will need, add the perimeters of all windows and doors to be weatherstripped, then add 5% to 10% to accommodate any waste. Also consider that weatherstripping comes in varying depths and widths. Weatherstripping supplies and techniques range from simple to the technical. Calling a professional is in your best interest for this one.
Don’t forget to check the attic access door. Often located in back hallways or inside closets, this opening is usually uninsulated and unsealed, and is a major source of air leakage. Using a stepladder, remove the access panel. If uninsulated, glue a 2- to 4-inch layer of rigid polystyrene foam on the upper surface.
If your attic access is through a pull-down staircase, you can purchase a cover for it at a hardware store or home improvement center.
What Will You Save?
How much you save depends on how leaky your house was in the first place. According to Energy Star, sealing a home can result in savings in heating and cooling ranging from 5 to 10 percent in a house that’s already well-sealed, to as much as 30 to 40 percent or even more.
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