Air Sealing — The Insulation Step Most Homeowners Skip
You can have the highest R-value insulation money can buy, and still lose enormous amounts of conditioned air if your home isn’t properly air sealed. Air sealing is the process of closing the gaps, cracks, and penetrations that allow conditioned air to escape and hot outside air to infiltrate — and it’s arguably more important than insulation thickness alone.
How Much Air Leakage Is Normal?
Studies have found that the average American home leaks enough air to be equivalent to leaving a window open year-round. This infiltration forces your AC to continuously cool fresh (and hot) outdoor air entering the home, adding significantly to the cooling load.
Where Air Leaks Occur
Air infiltration points are often invisible and counterintuitive:
Electrical outlets and switch plates on exterior walls
Recessed ceiling lights that penetrate into the attic
Plumbing and wiring penetrations through top and bottom wall plates
Attic hatch or door
Fireplace dampers left open
Gaps around window and door frames
Dryer vents, exhaust fans, and other wall penetrations
The Stack Effect
In summer, the stack effect works in reverse — hot attic air can be drawn down into living spaces through ceiling penetrations as the AC creates slight negative pressure. Air sealing the attic floor is one of the most effective ways to interrupt this cycle.
Tools and Materials
Most air sealing is accomplished with basic materials:
Caulk for small gaps around window frames, baseboards, and trim
Expanding spray foam for larger gaps around pipes and wires
Weatherstripping for doors
Foam gaskets behind outlet and switch covers
A professional energy audit, which includes a blower door test, can identify exactly where your home’s air leaks are concentrated, making remediation far more targeted and effective.