Insulated glazing (IG) also known as double glazing (as most people call it) are double or triple glass window panes separated by an air or other gas filled space to reduce heat transfer across a part of the building envelope.
Insulated Glass Units (IGUs) are manufactured with glass in range of thickness from 3 mm to 10 mm or more in special applications. Laminated or tempered glass may also be used as part of the construction. Most units are manufactured with the same thickness of glass used on both panes but special applications such as acoustic attenuation or security may require wide ranges of thicknesses to be incorporated in the same unit.
To reduce shear effects on the sealed unit (a major cause of premature failure), manufacturers use a rule of thumb that permits a difference of 1 mm between the thickness of the panes of glass used in the unit and still maintain the warranty for the unit. For example, a unit may be ordered with a 4 mm pane on the exterior and a 3 mm pane on the interior. These variations are allowed for architectural and cost reasons. Other combinations can be specified and produced but the manufacturer may reserve the right to limit the term of the warranty or refuse to warranty the unit altogether.
For ease of description the surfaces of a double paned unit are named according to the following convention: Surface #1 (facing outside), Surface #2 (inside of outside pane), Surface #3 (outside of inside pane) and Surface #4 (inside surface of inside pane). Applying the corresponding nomenclature for triple paned units results in surfaces #1 through #6.
The performance of insulating glazing can be modified through the use of the following:
Read more about Insulated Glazing: Spacer, Construction, Thermal Performance, Heat Insulating Properties, Acoustic Insulating Properties, Longevity, Estimating Heat Loss From Double Glazed Windows