airleakage

Air leakage refers to the uncontrolled movement of air through gaps, cracks, or openings in a building envelope, equipment, or ductwork, driven by pressure differences. It can cause energy loss, drafts, and reduced thermal comfort. In building science, air leakage is distinguished from intended ventilation and is usually minimized to improve energy efficiency and indoor air quality.

In buildings, common leakage paths include around doors and windows, electrical outlets, plumbing penetrations, attic edges, wall cavities, and around ducts. The main drivers are wind pressure on the exterior and the stack effect due to indoor-outdoor temperature differences, as well as mechanical ventilation systems creating pressure differences.

Measurement and detection of air leakage are typically performed with tests such as the blower door test, which quantifies air leakage rate at a standard pressure difference (for example, ACH50). Instruments and techniques such as smoke pencils, infrared thermography, and building simulations help locate leakage paths. Standards and procedures are published by organizations such as ASTM and RESNET.

Effects of air leakage include increased energy consumption and higher heating or cooling loads, as well as comfort issues like drafts. Uncontrolled leakage can promote moisture buildup, condensation, and mold risk, and may affect indoor air quality by drawing in outdoor pollutants or exhausting conditioned air through unintentional paths.

Mitigation focuses on improving the airtightness of the building envelope and ducts. Techniques include installing continuous air barriers, membranes, sealants, caulking, weatherstripping, properly sealing around doors and windows, minimizing penetrations, and ensuring well-sealed ductwork. Pairing airtight construction with a balanced ventilation strategy, such as mechanical ventilation with heat recovery, and performing envelope commissioning helps meet performance targets.