infiltration
unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage
en-GB/ˌɪnfɪlˈtɹeɪʃn/
en-US/ˌɪnfɪlˈtɹeɪʃən/
unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage