Air Sealing in the Basement and Attic

Air Sealing in the Attic

Air leaks into or out of a house through holes in the building envelope. Duct systems leak
mostly at points where two pieces connect. These two problems are responsible for 30 to
40% of the heating and cooling costs in a typical house. In a very leaky house, they can
make up 50% or more of those costs.

The attic is one of the biggest sources of leakage. Below, we'll take a look at a typical attic,
which has multiple sources of air and duct leakage.

Open Chase

A chase is a cavity (usually hidden behind the drywall) that carries wires, pipes, and ducts
through a house. They often run from a basement or crawl space all the way to the attic,
providing an easy way for air to move between conditioned and unconditioned spaces.
Pressure differences drive this air movement and can keep rooms adjacent to the chase
too cold in winter or too warm in summer.

An open chase                                                                  Same chase after being sealed

Electrical & Plumbing Penetrations

When wires go from a wall into the attic, the hole they pass through is always bigger than
the wires themselves. Current building codes require that these holes be sealed, but if you
have a house more than 10 or 15 years old, they may not be sealed. Even if your house is
newer, these holes may not be sealed. This applies to any kind of penetration from a wall
to the attic. Each of these holes may be small, but if there are a lot of them, they can add up
to a significant source of infiltration.

Unsealed hole for wires                                               Same hole after being sealed

Unsealed Top Plates

The horizontal framing lumber that runs across the top of each wall is called a top plate. Air
can leak between the wall and the attic at the seam where the ceiling drywall meets the top
plates. Again, there may be only a little bit of leakage in one place, but when you add it all
up, it's a lot.

The two photos above showing the electrical penetration also illustrate the sealing of top
plates. The gap between wood and drywall (left) is sealed with foam (right).
Air Sealing
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