Sealing Air Leaks for Increased Home Efficiency

Increase your home’s energy efficiency—and cut energy costs—by sealing air leaks in your home’s basement and walls.

| January/February 2012

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 air leaks. Many older homes are riddled with holes in the building envelope—the outside walls, windows, 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. For example, a 1/8-inch-wide and 6-foot-long crack between a door and a doorjamb is equivalent to a 9-square-inch opening!

On cold winter days, leaks in the building envelope let heated 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, increasing the risk of mold. Eventually, water in walls may lead to structural damage because framing, if constantly wet, begins to rot. Replacing rotted framing is expensive, as a neighbor of mine recently discovered. He found moisture damage in his home’s framing members, and fixing the mess cost him a whopping $125,000. Sealing air leaks not only saves energy, it leads to a healthier, more durable home. And as home improvement projects go, this one is amazingly easy and inexpensive.

Finding 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. Most professional energy audits cost a few hundred dollars, and they provide you with a thorough analysis of your home’s energy use. 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. You can also detect leaks with a stick of burning incense—air leaking into a home will deflect the smoke. Be sure to check around electrical outlets and light switches (even those on interior walls). Ceiling fixtures—especially recessed lighting and whole-house fans—are another major source of heat loss in the winter. Follow this step-by-step guide to conduct a full home energy assessment.

After you’ve found the air leaks in your home, you can hire a professional retrofitter to seal them, or you can do the work yourself. If you choose the latter, you’ll need some inexpensive supplies and tools, including clean rags, rubbing alcohol, a caulk gun, clear or paintable caulk, expanding foam insulation, weatherstripping, foam gaskets for sockets and light switches, a utility knife or scissors, a screwdriver and a stepladder.

Heat-Loss Hero: Basement Leaks and Types of Caulk

Basements are a major source of leaks, so they’re a good place to start. Begin by sealing the largest, most visible cracks in your basement or crawl space. Replace any broken or missing windowpanes, or install rigid foam board insulation over the openings. Seal any gaps—such as those around dryer vent exhausts—with caulk or expandable liquid foam. Next, seal cracks between the top of the foundation and the wall, which are often so large light shines through. Turn off basement lights and look at walls from inside to locate gaps, then seal them with caulk or foam. You can usually seal cracks from inside, though some may be easier to access from outside. Also insulate the cavity formed by the floor joists and the rim joist. Place batt or blanket insulation in the cavity, or use expanding foam insulation. For large cracks (wider than 3/8 inch and deeper than 1/2 inch), professionals use a tubular foam called backer rod, which you can find at a hardware store. Vacuum or brush dust and dirt out of openings, then stuff
backer rod into gaps with a screwdriver or small putty knife.

You can also use expanding foam insulation to seal large gaps. The foam quickly expands to fill the gap. After it’s dry, trim off any excess. Exposed foam can be sanded and painted. Like backer rod, liquid foam seals large openings, prevents airflow and adds insulation, further reducing heat loss or gain. Two types of liquid foam insulation are available at home improvement centers and hardware stores: polyurethane and latex. Polyurethane expands rapidly and extensively. It sticks to hands and clothing and is difficult to clean up. Latex foam expands less and is easier to clean. For openings wider than ½ inch, I use Dow’s Great Stuff Big Gap Filler, a polyurethane insulating foam sealant that fills, seals and insulates. For cracks less than ½ inch, I use Dow’s Great Stuff Gaps and Cracks polyurethane insulating foam sealant. These products work best if you use the whole can instead of storing some for later use. Smaller cracks can be sealed with clear or paintable caulk if you want it to blend in.

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