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 - any construction material that is used to join air barrier materials, air barrier assemblies and air barrier components and which has a air leakage rate not greater than 0.02 L/(s•m2) at a pressure differential of 75 Pa (cfm/ft2 at a pressure differential of 1.57 lb/ft2).
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 building enclosure that form part of the plane of air tightness.
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.
An air barrier material is any building material that has a air leakage rate that is not greater than 0.02 L/(s•m2) @ a pressure differential of 75Pa (0.004 cfm/ft2 at a pressure differential of 1.57 lb/ft2). The air barrier material needs to be identified in the project documents and it provides the primary plane of air tightness. As you look at the typical materials used in a building you can find hundreds of materials that meet this requirement.
Having installed a material that meet the requirements to be a air barrier material in a building does not automatically provide you with a continuous plane of air tightness. To achieve an airtight building enclosure you need to join the various air barrier materials together using an air barrier accessory. The air barrier accessory connect one air barrier material to another air barrier material and also connects one air barrier assembly to another air barrier assembly. Air barrier accessory materials are also used to connect an air barrier component to a air barrier assembly.
An air barrier assembly is simply a collection of air barrier materials connected together using air barrier accessory materials (caulks, tapes, strips, fasteners, etc) to provide a continuous plane of air tightness for that assembly (i.e. wall assembly). The maximum allowed air leakage rate of an air barrier assembly is 0.2 L(s•m2) @ a pressure differential of 75 Pa (0.04 cfm/ft2 at a pressure differential of 1.57 lb/ft2).
An air barrier system is simply the whole building - all six sides of the building. The air barrier system is a collection of air barrier assemblies and air barrier components tied together using air barrier accessories 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 is typically not be greater than 2.0 L/(s•m2) @ a pressure differential of 75 Pa (0.4 cfm/ft2 at a pressure differential of 1.57 lb/ft2) (or as required by a code or specification).