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  Glossary

The BSC Glossary provides definitions and brief explanations of important building science and construction terms, including common abbreviations and variations. We are working to make this resource as comprehensive and user-friendly as possible. Terms are cross-referenced and are also linked to further sources of information such as BSC documents and external websites. New terms are added, and older ones revised, on a regular basis. Please note that if the term you are looking for is not listed alphabetically, it may still be in the Glossary – for example, the term “mullion” is not listed on its own, but is used in the “Window” entry. Using the search box below will allow you to find such “hidden” terms.
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Absorption
Process whereby a porous material extracts one or more substances from an atmosphere, a mixture of gases, or a mixture of liquids (from ...
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ACCA
abbr. Air Conditioning Contractors of America. ACCA is a group of over 4,000 air conditioning contractors who work together to improve the ...
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ACH
abbr. air changes per hour. A common unit of measure of ventilation rate for a space, or air leakage rate for a building, defined as the ...
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ACT2
abbr. Advanced Customer Technology Test for Maximum Energy Efficiency.  The ACT2 project was initiated in 1990 by the Pacific Gas and ...
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Adhesion
Property that describes a material's ability to bond to a surface physio-chemically or chemically. Related terms: Adhesive, Adhesive Failure
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Adhesive
(1) A substance or compound used for bonding surfaces together, usually applied in the form of a liquid or paste. An adhesive and sealant ...
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Adhesive Failure
Loss of adhesion of a material to the surface to which it has been applied. Usually refers to a sealant line, floor finish, or ...
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Adsorption
(1) Process in which fluid molecules are concentrated on a surface by chemical or physical forces or both; (2) surface adherence of a ...
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Aesthetic Joint
A groove cut into a cladding system (often EIFS, precast, or stucco) that serves the function of decoration and/or to provide a starting or ...
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Aesthetic Reveal
See Aesthetic Joint.
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AFUE
abbr. Annual Fuel Utilization Efficiency. A measure of annual efficiency of conversion of primary gas or oil consumption to the production ...
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AHU
abbr. air handling unit. A mechanical space conditioning device comprising an enclosure, and a fan to move air. In many cases, an AHU might ...
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AIA
abbr. American Institute of Architects .  . A professional membership association for licensed architects, emerging professionals, and ...
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Air Control Layer (formerly Air Barrier)
The complete air control layer system is comprised of materials and assemblies, each with their own performance requirements. Related ...
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Air Control Layer Material (formerly Air Barrier Material)
A material that has sufficiently low air permeance and adequate strength that it can be part of an air control layer system. Recommended ...
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Air Control Layer System (formerly Air Barrier System)
Air control layers are three-dimensional systems of materials designed, constructed, and/or acting to control air flow across a building ...
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Air Current Tester
See Smoke Pencil.
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Air Infiltration
Uncontrolled inward leakage of air (that may contain entrained water vapor) through cracks and insterstices in any building element and ...
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Air Leakage
Uncontrolled and/or unintended airflow through a building enclosure or between units of occupancy. Leakage from indoors to outdoors is ...
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Air Pressure Boundary
The air pressure boundary is the boundary (comprised of a series of planes to form a three dimensional boundary) that generates the largest ...
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Air Retarder
A material or assembly that does not meet the performance requirements of an air control layer material or assembly, but that is ...
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Air-Impermeable Material
An air impermeable material is an air control layer. An air-impermeable material has an air permeance equal to or less than 0.02 l/s-m2 at ...
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Air-Permeable Material
An air-permeable material has an air permeance greater than 0.02 l/s-m2 at 75 Pa pressure differential when tested according to ASTM E 2178 ...
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ALA
abbr. American Lung Association. A non-profit organization that promotes lung health and improved air quality through education, advocacy ...
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ASHRAE
abbr. American Society of Heating, Refrigerating and Air Conditioning Engineers. A building technology society with more than 50,000 ...
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ASTM
abbr. ASTM International. A globally recognized leader in the development and delivery of international voluntary consensus standards. ...
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Back Wrapping
In EIFS, the carrying of the mesh reinforcement and base coat around the ends of the insulation boards, terminating between the insulation ...
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Backer Rod
A rod-shaped foam material (typically closed cell polyethylene) that is installed under compression in a joint. Sealant is applied over the ...
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Barrier System or Perfect Barrier
The general term to describe a rain control approach that relies on the perfection of a single plane of material(s) to resist rain water ...
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Base Coat
A compound used to embed and to cover the reinforcing fabric of an EIFS, depending on the system type. The base coat acts as the primary ...