While a window is most certainly a sum of all its parts, same as any component of a home, you might say the window glass is the most important part. It is after all the piece of hardware that allows us to see outside and allows natural light to find its way in.
Window glass comes in several forms. For most architectural applications, window glass is either annealed or tempered.
Annealed glass is not heat-treated for added strength and, when broken, will shatter into shards. While still found in many windows, annealed glass is restricted by most building codes, preventing its use in certain situations with a higher likelihood of breakage (i.e., in door panels, fire escapes, bathrooms, and windows at low heights).
Tempered glass, or safety glass, is heat-strengthened during the manufacturing process so that it will break into tiny squares if shattered. Glass doors, bathroom windows, and large windows usually are required to be made using tempered glass. Tempered glass panes also have a higher thermal resistance than standard, annealed glass.
Other types of window glass include glass block, frosted or obscured glass (for privacy), tinted and reflective glass. Window glass is often glazed or coated as well. Glazing occurs when two pieces of glass are hermetically sealed together, with a small air space between, to heighten thermal qualities. In other applications, a reflective coating may be applied, which acts similarly to glazing in thermal terms in that they seem transparent from the inside but reflects solar radiation on the outside, thus minimizing solar heat gain. Double- or triple-glazed windows with low emissivity (low-e) coating pretty much set the bar for window efficiency at this time.
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