Conditioned Space

The part of the building that is designed to be thermally conditioned for the comfort of occupants or for other occupancies or for other reasons.*

Building Enclosure

The building enclosure is the component (typically comprised of an assembly of numerous materials and layers) of a building that acts as an environmental separator between the indoor and outdoor environments. The thermal, air pressure, and rainwater boundary lie within the confines of the enclosure. A building enclosure controls heat flow, air flow, water vapor flow, rain penetration, groundwater effects, the transfer of light and solar radiation, noise and vibrations, contaminants, environmental hazards and odors, insects, rodents and vermin, and fire. A building enclosure provides strength and rigidity and must be durable, aesthetically pleasing and economical.

Air Retarder

Materials and assemblies that do not meet the performance requirements of air barrier materials and air barrier assemblies and air barrier systems, but are nevertheless designed and constructed to control air flow are said to be air retarders.

Air Barrier System

An air barrier system is an assembly of materials that together are designed, installed, or act to control the flow of air across the building enclosure. The pressure boundary of the enclosure should, by definition, be coincident with the plane of the air barrier system. The complete air barrier system is comprised of materials and assemblies, each with their own performance requirements.

Air Barrier

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.