Measurement method
Infiltration
Also: air leakage, infiltration factor
Uncontrolled leakage of outdoor air into a building through cracks, joints and gaps, driven by wind and temperature difference. It ventilates leaky old buildings by accident and lets outdoor pollutants — and radon from the ground — in.
Why it matters indoors
Infiltration is ventilation nobody chose. In old buildings it can exceed 1 air change per hour and keep CO₂ low at the cost of heat; in airtight new buildings it falls below 0.1 and mechanical ventilation becomes necessary. It also sets how much outdoor particulate matter and nitrogen dioxide reach the interior (the infiltration factor, typically 0.3–0.8 for PM₂.₅) and, through the floor, how much radon enters. Blower-door tests measure airtightness.
In the literature
- Determination of particle penetration coefficient, particle deposition rate… (2017). doi:10.1016/j.proeng.2017.10.126 CKB 0286
- Qiu et al. The Impact of Indoor Air Humidity on the Infiltration of Ambient Particles (2024). Buildings. doi:10.3390/buildings14041022 CKB 0319
- Fu et al. Investigation of outdoor air pollutant, PM2.5 affecting the indoor air quality in a high-rise building (2021). doi:10.1177/1420326X211038279 CKB 0290
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.