Insulated glass uses two or more panes separated by a sealed gap to reduce heat transfer through windows and glazed doors. Choosing a suitable unit means considering its gas fill, frame, coatings and solar heat gain alongside the local climate.
Window selection belongs within the architectural design process, before facade details and construction specifications are finalised.
What is insulated glass?
Insulated glass is a unit of two or more tightly sealed panels of glass sandwiched together with an air space between them.
This space is filled with air, argon gas, or krypton.
This system keeps indoor and outdoor air temperatures separated more efficiently than individual glass panels.
The term “insulated glass” is a bit of a misnomer, as the glass itself is not insulated, but the unit as a whole is.
This unit consists of an outer glass pane, a spacer bar around the perimeter of the glass,
a seal, a desiccant to absorb moisture, and an inner pane.
The spacer bar creates a consistent, even gap between the glass panels,
leaving room for the inert gas.
Some insulated glass units or “IG” units have three or four panes,
with the spaces between them filled with gas.
All of these components, including the glass, work together as one unit,
The practical way to repair an insulated glass unit is to remove the entire
insulated glass from the window frame unit and replace it, or to replace the entire sash (including the frame).
Types of insulating glass
While the concept of insulated glass does not change between varieties,
there are a few types of insulated glass units that you should be aware of.
They include double and triple panes (or glass),
as well as those with argon or krypton gas between the panes.
Double pane insulated glass units feature two panes of glass with insulating gas or air between them.
These are the most common forms of insulated glass units and are relatively inexpensive.
Three-pane insulated glass units feature an inner pane, an outer pane and a pane in between.
This creates two spaces to isolate gas or air, providing greater efficiency than double-glazed windows alone.
Krypton gas is the most efficient type of gas found in insulated glass units.
But it is expensive, and krypton gas is available in double and triple window units.
Argon gas is the most common inert gas found in insulated glass units due to its affordability and efficiency.
This gas is more efficient than units containing air alone, but less efficient than krypton.
These insulated glass units are not just for windows,
as they are equally popular and effective for exterior entry doors,
Sliding doors, French doors, and other exterior glass door openings.
Safety glazing, such as tempered or laminated glass, should be specified where required by the application and local building code.
How does insulated glass work?
The sealed gap between panes reduces heat transfer compared with single glazing. Air, argon or krypton in the cavity limits conduction, while low-emissivity coatings can reduce radiant heat transfer. The complete window also includes spacers and a frame, so glazing alone does not eliminate thermal bridging or air leakage. Compare the U-factor of the whole window when assessing heat transfer.
Understanding the Solar Heat Gain Coefficient (SHGC)
SHGC expresses the fraction of incident solar energy admitted through a window, both directly and after absorption and inward release. A lower value reduces solar heat gain and can be useful where cooling demand is high. In colder climates, some solar gain may be desirable. Select SHGC alongside U-factor, orientation, shading and daylight requirements; the lowest value is not automatically the best choice in every location.
