Triple-Glazed vs. Tempered Windows

Construction

• During manufacturing, tempered glass passes through a series of heating and rapid cooling processes. Surface and edge compression from these temperature changes gives tempered glass its strength and heat resistance. Triple-glazed windows, which may or may not contain tempered glass, consist of three sheets of glass separated by air or gas space. In some triple-glazed windows, a thin metallic layer coats the outer surface of the middle pane. Although triple-glazed windows can be too thick for some existing walls and frames, manufacturers can now produce slimmer triple-glazed windows that match wall and frame thicknesses.

Impact Resistance

• The number of pounds per square inch surface compression determines the strength of a particular type of glass. Tempered glass, with a minimum surface compression of 10,000 psi, has greater impact resistance than ordinary annealed glass, which has a surface compression below 3500. A broken tempered glass window crumbles into small rounded pieces, while a triple-glazed window made from ordinary glass can form large, hazardous shards.

Temperature

• The air gaps in triple-glazed windows create insulation and prevent drafts, heat loss and condensation buildup. Low-emissive windows, which have the inner metallic layer, send and reflect heat into a room and prevent heat loss better than ordinary triple-glazed windows. The higher surface compression gives tempered glass greater heat resistance than ordinary glass. Windows in public buildings or windows that undergo heat stress, such as door windows or skylights, often contain tempered glass.

Considerations

• Tempered glass requires careful handling and installation. A poorly handled tempered glass window may not break immediately upon impact, but it may shatter later after exposure to heat stress. Unlike most triple-glazed windows, which can crack or break in a limited area, an entire tempered window will shatter at once. Triple-glazed windows are often expensive and can be difficult to install and operate because of their thick, heavy frames.