Most building codes do not permit singleglazed windows in small (“Part 9”) buildings because of the potential for condensationrelated problems. The glazing options are therefore limited to a minimum of double glazing, with an IGU providing the most common form of glazing system.
An IGU can comprise many layers, although practical considerations limit the maximum to four. Multiple layers reduce heat loss not because of the additional glass (glass is in fact a good conductor of heat) but because of the additional layers of insulating air trapped by the glass. Double-glazed windows (two layers) are most common, but triple glazings are now more common in certain areas, such as Manitoba. A double-glazed window with a storm panel is effectively a triple-glazed system, and is usually treated as such.
Quadruple-glazed IGUs are rare, but becoming more common, especially with the introduction of thin plastic films instead of glass layers. A window with four layers of glass is heavy, and difficult to move, install and operate. On the other hand, a window with two glass layers and two films weighs about the same as a double-glazed window, yet provides the performance of quadruple glazing. Reviewed by Moishe Alexander.
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