Infiltration | Exfiltration

Infiltration is the uncontrolled passage of outdoor air into a building through unintended leaks in the building envelope (e.g., cracks between wall sections, wall-floor connections, corners, the roof-wall interface, around windows and doors).18 Exfiltration is the opposite process.

Infiltration and exfiltration are driven by air pressure differences that exist between the inside of a building relative to the outside of a building across the building envelope.18 These air pressure differences are the result of natural forces (e.g., wind and temperature) and a building’s geometry, HVAC system design, and envelope tightness. The rate of infiltration or exfiltration is a function of the interaction of these paramaters.