Controlling heat flow, airflow, moisture flow and solar and other radiation will control the interactions among the physical elements of the building, its occupants and the environment.  Of these four, airflow “merits major consideration mainly because of its influence on heat and moisture flow” (Hutcheon, 1953).  Airflow carries moisture that impacts a materials long-term performance (serviceability) and structural integrity (durability).  Airflow also affects building behavior in a fire (spread of smoke and other toxic gases, supply of oxygen), indoor air quality (distribution of pollutants and location of microbial reservoirs) and thermal energy use.  One of the key strategies in the control of airflow is the use of air barriers.