Air barriers are systems of materials designed and constructed to control airflow between a conditioned space and an unconditioned space. The air barrier system is the primary air enclosure boundary that separates indoor (conditioned) air and outdoor (unconditioned) air. In multi-unit/townhouse/apartment construction the air barrier system also separates the conditioned air from any given unit and adjacent units. Air barrier systems also typically define the location of the pressure boundary of the building location. In multi-unit/townhouse/apartment construction the air barrier system is also the fire barrier and smoke barrier in inter-unit separations. In such assemblies the air barrier system must also meet the specific fire resistance rating requirement for the given separation.
Air barrier systems are assembled from "materials" incorporated in "assemblies" that are interconnected to create "enclosures". Each of these three elements has measurable resistance to airflow. The minimum resistance or air permeances for the three components are:
- Material 0.02 l/(s-m2)@75 Pa
- Assembly 0.20 l/(s-m2)@75 Pa
- Enclosure 2.00 l/(s-m2)@75 Pa
Materials and assemblies that meet these performance requirements are said to be air barrier materials and air barrier assemblies. Air barrier materials incorporated in air barrier assemblies that in turn are interconnected to create enclosures are called air barrier systems.
