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Air Sealing

common attic air leaks illustration

Air leaks through the ceiling, walls, foundation and other areas are typically the source of heating and cooling losses in Vermont homes and workplaces. Fortunately, there are ways to detect and stop these losses and gain the benefits of energy savings. Many programs that offer energy rebates & incentives require you to show how much you have improved the efficiency of your building. This is one reason why a blower door test is typically done before starting and after finishing home energy improvements, as it is often the best way to show a comparison.

Reducing the amount of air that flows in and out of a building can be a cost-effective way to cut heating and cooling costs, increase comfort and create a healthier indoor environment. The recommended strategy is to reduce air leakage as much as possible, add insulation and provide controlled ventilation, as needed. Adding insulation without sealing air leaks first can significantly reduce the insulation’s effectiveness in saving energy. Reducing air infiltration may also help prevent indoor humidity from getting into walls, which can cause issues with mold and indoor air quality.

Air sealing uses a variety of materials, including caulk, spray foam, metal flashing, weatherstripping, and rigid foam. Small gaps can often be filled with caulk, while holes measuring up to three inches in diameter can often be repaired with insulating spray foam. Holes larger than three inches are often closed off with foam board or sheetrock and then sealed with insulating spray foam. Caulk is generally used for cracks and openings between stationary building components, such as around door and window frames, while weatherstripping is typically used to seal components that move, such as doors and operable windows. Fire-rated caulk and metal flashing are used in high-temperature situations, such as around the chimney.  Commercial and multifamily buildings may also have special air sealing requirements.

A complete energy analysis typically includes a blower door test that identifies the location and extent of air leaks you should address. Generally, these are most significant in the basement and attic and can be filled with expanding foam, weatherstripping, and caulk. Air sealing projects are usually followed with adding insulation and other energy-saving measures. For example, air sealing doesn’t eliminate the need for proper insulation to reduce heat flow through the building envelope. Even new buildings may be good candidates for improvement: though they probably have more insulation than most older buildings, they may still be leaking air through piping and other channels.

Air sealing may have the added benefit of reducing or eliminating ice dams on the lower edges of your roof. In many cases, warm air is escaping from the occupied part of the building up to the underside of the roof in the attic. This begins melting the snow above it, sending trickles of water down the outside surface. Since the roof extends past the heated portion of the home, the water can cool quickly, and ice can build up until a dam is formed. New water coming down has nowhere else to go and can begin pooling up. This allows it to seep into the roof material and back through your ceiling and walls, causing staining and potentially damaging your building’s interior. By air sealing these passages where warm air escapes into the attic, your roof may stay cooler and the risk of ice dams may be eliminated or greatly reduced.

Some Benefits of Air Sealing

  • Can cut energy loss and improve indoor air quality

  • Can reduce cold drafts

  • Often a cost-effective energy upgrade

Some Considerations

  • A blower door test before you begin can help target your largest gaps

  • Air sealing measures should typically be done before adding insulation

  • Additional ventilation may be needed in a tighter building, and other health and safety issues should be considered with help from a qualified professional

  • Rebates may be available if a "before and after" blower door test shows your improvements cut air flow by a certain amount (this may vary, depending on circumstances)

Some Next Steps

You may want to visit the Health & Safety section to learn more before you make your thermal energy efficiency plan for your home or business.  Once you and your qualified energy professional have pinpointed the highest priority areas for air sealing, you can work to develop the best plan for moving forward.

Learn More

Visit the pages below to learn more about Weatherization: