About Air Barriers

Materials, Components, Assemblies & Systems

The term 'air barrier' needs to be better described. Many use the term when they actually mean a material, a component, an assembly or a system. These terms are defined as:

AIR BARRIER ACCESSORY – products designated to maintain air tightness between air barrier materials, air barrier assemblies and air barrier components, to fasten them to the structure of the building, or both (e.g., sealants, tapes, backer rods, transition membranes, fasteners, strapping, primers).

AIR BARRIER ASSEMBLY – the combination of air barrier materials and air barrier accessories that are designated and designed within the environmental separator to act as a continuous barrier to the movement of air through the environmental separator.

AIR BARRIER COMPONENT – pre-manufactured elements such as windows, doors and service elements that are installed in the environmental separator.

AIR BARRIER MATERIAL – a building material that is designed and constructed to provide the primary resistance to airflow through an air barrier assembly.

AIR BARRIER SYSTEM – the combination of air barrier assemblies and air barrier components, connected by air barrier accessories that are designed to provide a continuous barrier to the movement of air through an environmental separator.

AIR LEAKAGE RATE L/(s•m²•Pa) – the rate of airflow (L/s) driven through a unit surface area (m²) of an assembly by a unit static pressure difference (Pa) across the assembly.

AIR PERMEANCE – the rate of airflow (L/s) through a unit area (m²) of a material driven by unit static pressure difference (Pa) across the material.

DESIGN SERVICE LIFE – the service life specified by the designer according to the expectations (or requirements) for air barrier materials or assemblies.

ENVIRONMENTAL SEPARATOR – the parts of a building that separate the controlled interior environment from the uncontrolled exterior environment, or that separate spaces within a building that have dissimilar environments.

SERVICE LIFE – the period of time during which the air barrier assembly or any of its materials or accessories performs without unforeseen costs or disruption for maintenance or repair.

The air permeance of any air barrier material is 0.02L(s•m²) @ 75Pa. The air permeance of drywall is equal to this and is used as a control material. So any material that has a air permeance equal to or less that this value qualifies as a air barrier material. As you look at the materials used in a building you will find hundreds of materials that meet this requirement.

Having air barrier materials in a building does not provide you with a continuous plane of air tightness. To achieve this you must join the various air barrier materials together using air barrier components. These components connect one material to another material, a material to an assembly, and one assembly to another assembly. The air permeance of an air barrier component is 0.02L(s•m²) at 75 Pa.

An air barrier assembly is simply a collection of air barrier materials assembled together using air barrier components to provide a continuous plane of air tightness for that assembly (i.e. wall assembly). The maximum air leakage of an air barrier assembly should be 0.2 L(s•m²) @ 75 Pa.

An air barrier system is simply a collection of building assemblies lied together using air barrier components to provide a continuous plane of air tightness for the whole building enclosure. The air barrier system determines the air leakage of the whole building. The maximum air leakage of a whole building should be 2.0 L(s•m²) @ 75 Pa.

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