What is air sealing?

When it comes to air movement in your home, there's a difference between healthy ventilation and wasteful infiltration.  Proper air sealing reduces the waste by eliminating cracks and air leaks that in most homes add up to the equivalent of one or two open windows.

Although you can spot some air leaks around doors and windows, much of the average home's air leakage is due to the stack effect.  As warm air rises, it leaks through holes in your ceiling and escapes through the attic.  To replace this air, cold air infiltrates your cellar through leaks and cracks in the foundation and walls.  This cycle leads to cold floors and uneven temperatures, and it's bad news for your health, since most of the air you breathe has passed through basement conditions.

The really frustrating part is that since air leakage has more to do with pressure than with temperature, the stack effect reverses in the summer, pulling warm air from the attic into your home as cool air escapes through foundation leaks.

Attic Air Sealing creates an air barrier that slows the stack effect and maximizes the performance of attic insulation.  Air movement dramatically reduces the effective value of insulation, so air sealing is crucial.  We use a variety of air sealing materials, including high-quality caulk and spray foam for smaller penetrations and leaks (like those along the attic joists at left) and rigid foam board for larger penetrations.  Then we blow in dense-packed cellulose insulation to create a thermal barrier and reinforce air sealing.

Basement or Crawl Space Air Sealing goes hand in hand with insulation because spray foam is the ideal material for both.  Basement encapsulation, which involves installing a drainage mat and vapor barrier to control moisture problems, also significantly reduces the stack effect.

Take me back to "Building Science."