Air leakage is the uncontrolled movement of air through gaps, cracks, and penetrations in a building’s envelope, contributing to energy loss, comfort problems like drafts, and potentially carrying moisture into wall or attic spaces where it could condense and cause hidden damage.
This uncontrolled air movement differs from intentional, controlled ventilation, which is deliberately designed and managed, whereas air leakage occurs through unintended gaps that weren’t specifically designed as air pathways at all.
Blower door testing provides a standardized, quantifiable measurement of a home’s total air leakage, giving builders and energy auditors an objective number to compare against code requirements or track improvement after air sealing work.
What Contributes to Air Leakage?
- Gaps around windows, doors, and other penetrations
- Unsealed rim joist areas
- Electrical, plumbing, and duct penetrations
- Attic hatches and recessed lighting fixtures
Why Is Air Leakage Important?
Excessive air leakage contributes significantly to energy loss and comfort problems, and it can also introduce moisture into wall or attic cavities where it might condense and cause hidden mold or rot, making air sealing a genuinely important factor in both energy performance and building durability. This dual impact has driven increasing building code attention to air leakage limits alongside traditional insulation requirements.
Because air leakage often occurs through small, individually modest gaps that add up to a significant cumulative effect, systematic air sealing addressing many small penetrations throughout a home typically produces better results than focusing exclusively on one or two obvious large gaps. This systematic approach to sealing tends to outperform focusing on just one or two obvious problem areas. This focused strategy makes the most of limited time and budget for sealing work.
Air Leakage vs. Air Sealing
Air leakage is the problem, uncontrolled air movement through the building envelope. Air sealing is the solution, the process of identifying and closing the gaps and penetrations responsible for that leakage.