Double-pane windows are made from a wide variety of glass types. While not all of them have tempered glass, this is certainly an option, and sometimes a requirement, depending on the window and home's location. The use of tempered glass offers the benefit of safety in addition to what double-pane windows already offer.
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Double-pane windows contain two sheets of glass with a small space between them. These windows can reduce energy bills by insulating the home. They also help decrease outside noise and keep noise from leaking from inside the home. These windows are made from various glass types -- some with a UV protective film or tint, and others with tempered and/or impact-resistant glass.
Tempered glass is heat-treated to potentially minimize injury in case of a window shattering. The manufacturer heats the glass sheet to a certain temperature, then cools it rapidly. When this occurs, the surface and edges of the glass cool more quickly than the center. This causes the surface and edges to compress, strengthening the sheet. This also causes the glass to "dice" or break into rounded granules instead of jagged shards, if broken.
Tempered Glass Windows vs. Impact-Resistant Windows
While some double-pane windows are designated as impact-resistant, these are different than those made with tempered glass. Impact-resistant panes have a polyvinyl film between them of between .015- and .090-inches in thickness. This material typically holds the glass pieces together when broken and prevents water or debris from entering the home. These are especially important in areas prone to natural disasters. Tempered glass windows may also be impact-resistant, if they have the film installed.
When It's Necessary
Different state and local building codes may require tempered glass in certain areas of the home. For instance, Florida requires tempered glass in areas of close human contact, like bathtub or shower enclosures. This also applies to windows, which are commonly placed on shower walls or above tubs. Just as impact-resistant windows are an important asset in areas with tornadoes or hurricanes, so are tempered glass windows. A building's immediate surroundings may also dictate the need for tempered windows -- as in a case where a golf course may be bordering a home, for instance.