Glossary

Air infiltration: The amount of air that passes between a window sash and frame, measured in cubic feet of air per minute, per square foot of area.

AAMA: American Architectural Manufacturers Association. AAMA is the source for performance standards and certification.

Daylight transmittance: A measure of the amount of visible outside light that comes inside through a window.

Low-emissivity (“Low E”) glass: Glass with a microscopically thin layer of metallic oxide applied onto or into a glass surface. The coating allows visible light to pass through but blocks ultraviolet and infrared solar energy and reflects long-wave (interior heat) energy to improve U-value.

Low-conductance spacers: Non-metallic materials designed to reduce heat transfer at the edge of an insulating window.

NWWDA: National Wood Window and Door Association.

Solar Heat Gain Coefficient (SHGC): A measure of the amount of directly transmitted and absorbed solar radiation that enters into the home through the glass. Lower numbers indicate higher performance.

Structural class AAMA: The window’s Performance Class (“R” is residential), followed by Performance Grade (stated as pressure in pounds per square foot).

Structural PSF: The structural load in pounds per square inch. The Uniform Load Structural Test is designed to test the strength of the test sample in accordance with ASTM E 330.

UV block: The percent of damaging ultraviolet rays blocked from being transmitted through the glass.

U-Value: The measurement of heat flow through a glazing system. Lower numbers indicate higher performance.

Water PSF: The amount of water resistance in pounds per square foot. This is an indicator of a product’s ability to resist water penetration in accordance with ASTM E 547 and ASTM E 331.