Insulated Glass

Insulated glass (also called an insulating glass unit or IGU) is a factory-assembled window panel consisting of two or more panes of glass separated by a sealed perimeter spacer. The gap between the panes - typically 1/4 to 1/2 inch - is filled with dry air or an inert gas such as argon. The sealed unit traps that low-conductivity layer and prevents it from mixing with ambient air. The result is a window that transfers significantly less heat than a single pane of glass.

Single-pane glass has an R-value of roughly R-1. A standard double-pane air-filled insulating glass unit achieves approximately R-2 to R-3. Argon-filled units perform better because argon is denser than air and convects less. Units with a low-emissivity (Low-E) coating on one of the inner glass surfaces add another layer of performance by reflecting infrared radiation back into the building.

In garage doors, insulated glass appears in two places. First, it is used in window lites installed in the top section of a residential sectional door. Replacing single-pane lites with insulated glass units reduces the thermal weak spot that windows create in an otherwise well-insulated door. Second, full-view aluminum-framed door sections use insulated glass as the entire section face, with the anodized aluminum frame holding the IGU in place.

The sealed perimeter of an insulating glass unit is the component most likely to fail. When the seal breaks, moist air enters the gap and condensation forms between the panes. The cloudiness that results cannot be cleaned because it is trapped inside the unit. The whole IGU must be replaced. On a garage door section, this typically means replacing the window cassette or the full-view section rather than just the glass.

Insulated glass adds weight to a door section compared to a single-pane lite of the same size, which affects spring sizing. A technician should confirm that the counterbalance system is rated for the door's total weight when glass sections are replaced.