Glossary

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Tempered glass
Treated glass that is strengthened by reheating it to just below the melting point and then suddenly cooling it. When shattered, it breaks into small pieces. Approximately five times stronger than standard annealed glass; is required as safety glazing in patio doors, entrance doors, side lights, and other hazardous locations. It cannot be recut after tempering.
Thermal break
An element of low conductance placed between elements of higher conductance to reduce the flow of heat. Often used in aluminum windows.
Thermal expansion
Change in dimension of a material as a result of temperature change.
Thermal mass
Mass in a building (furnishings or structure) that is used to absorb solar gain during the day and release the heat as the space cools in the evening.
Thermochromics
Glazing with optical properties that can change in response to temperature changes.
Thermogram
An image of an object taken with an infrared camera that shows surface temperature variations.
Threshold
The member that lies at the bottom of a sliding glass door or swinging door; the sill of a doorway.
Tilt window
A single- or double-hung window whose operable sash can be tilted into the room for interior washability.
Tinted glass
Glass colored by incorporation of a mineral admixture. Any tinting reduces both visual and radiant transmittance.
Transmittance
The percentage of radiation that can pass through glazing. Transmittance can be defined for different types of light or energy, e.g., visible light transmittance, UV transmittance, or total solar energy transmittance.
Transom
A horizontal transverse beam or bar in a frame; a crosspiece separating a door or the like from a window or fanlight above it. Also, a window above a door or other window, built on and commonly hinged to a transom.
Transom window
The window sash located above a door. Also called transom light.
Triple glazing
Three panes of glass or plastic with two air spaces between.