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Glossary of Terms A – B


American Architectural Manufacturers Association. A national trade association that establishes voluntary standards for the window, door, storefront, curtain wall, and skylight industries.


The ration of radiant energy absorbed to total incident radiant energy in a glazing system.


A thermoplastic with good weather resistance, shatter resistance, and optical clarity, used for glazing.


A microporous, transparent silicate foam as a glazing cavity fill material, offering possible U-values below 0.10 BTU/(h-sq ft-oF) or 0.56 W/sq m-oC).


(air infiltration). The amount of air leaking in and out of a building through cracks in walls, windows, and doors.

Air-leakage rating

A measure of the rate of air-leakage around a window, door, or skylight in the presence of a specific pressure difference. It is expressed in units of cubic feet per minute per square foot of frame area (cfm/sq ft). Formerly expressed as cubic feet per minute per foot of window perimeter length (cfm/ft) but not now in use. The lower a window’s air-leakage rating, the better its airtightness.

Annealed glass

Standard sheet of float glass which has not been heat-treated.


Heating above the critical or recrystallization temperature, then controlled cooling of metal, glass, or other materials to eliminate the effects of cold-working, relieve internal stresses, or improve strength, ductility, or other properties.


American National Standards Institute. Clearing house for all types of standards and specifications.


An inert, nontoxic gas used in insulating glass units to reduce heat transfer.


American Society of Heating. Refrigerating and Air Conditioning Engineers.


American Society for Testing and Materials. Organization that develops methods for testing of materials.


Window similar to a casement except the sash is hinged at the top and always swings out.


A mechanical device (normally spring-loaded) used in single-and double-hung windows as a means of counterbalancing the weight of the sash during opening and closing.

Bay window

An arrangement of three or more individual window units, attached so as to project form the building at various angles. In a three-unit bay, the center section is normally fixed, with the end panels operable as single-hung or casement windows.


A wood strip against which a swinging sash closes, as in a casement window. Also, a finishing trim at the sides and top of the frame to hold the sash, as in a fixed sash or a double-hung window. Also referred to as bead stop.


The ideal, perfect emitter and absorber of thermal radiation. It emits radiant energy at each wavelength at the maximum rate possible as a consequence of its temperature, and absorbs all incident radiance.


Building Officials and Code Administrators.

Bottom rail

The bottom horizontal member of a window sash.

Bow window.

A rounded bay window that projects from the wall in an arc shape, commonly consisting of five sashes.

Brick molding

A standard milled wood trim piece that covers the gap between the window frame and masonry.

Btu (B.T.U.)

An abbreviation for British Thermal Unit-the heat required to increase the temperature of one pound of water one degree Fahrenheit.


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