[AIVC, Air infiltration and ventilation glossary, 1992]:the uncontrolled outward leakage of indoor air through cracks, interstices, and other unintentional openings of a building, caused by the pressure effects of the wind and/or stack effect.[ASHRAE Standard 62.1]:uncontrolled outward air leakage from conditioned spaces through unintentional openings in ceilings, floors, and walls to unconditioned spaces or the outdoors caused by pressure differences across these openings due to wind, inside-outside temperature differences (stack effect), and imbalances between outdoor and exhaust airflow rates.[EN 16798-3:2017, 11]:Leakage of air out of building through leakage paths in elements of structure. (EXF; colour Grey)[EN 12792-2003, 138]:uncontrolled passage of air from a space through leakage paths in the shell of that space. (coded grey)