Controlling heat flow, airflow, moisture flow and solar and otherradiation will control the interactions among the physicalelements of the building, its occupants and the environment. Ofthese four, airflow “merits major consideration mainly because ofits influence on heat and moisture flow.” Airflow carries moisturethat impacts a material’s long-term performance (serviceability) andstructural integrity (durability). Airflow also affects building behaviorin a fire (spread of smoke and other toxic gases, supply of oxygen),indoor air quality (distribution of pollutants and location of microbialreservoirs) and thermal energy use. One key strategy in the controlof airflow is using air barriers.