IG units are hermetically sealed combinations of two or more lites of glass separated by a dry airspace. IG units improve the thermal performance of windows, thus significantly reducing heating and air-conditioning costs. IG units also reduce interior condensation in cold climates, and increase comfort near windows, thus maximizing the usable interior space.

Insulating glass (IG) units are used in a wide range of applications including:

  • Curtain Walls
  • Commercial/Residential Fixed and Operable windows
  • Storefronts
  • Sloped/Overhead Glazing/Skylights
  • Refrigerator doors.

Insulating glass use in residential and commercial construction has risen steadily over the years to where the majority of all new and renovation construction today includes IG units. IG units not only save on monthly heating and cooling costs, but they also reduce the initial size and cost of the heating and cooling equipment required on a project.

By combining Low-E coatings, tinted glasses, reflective coatings, laminated glass products and more, a wide variety of insulating glass configurations are available to satisfy a wide range of performance and aesthetic requirements. IG units can be fabricated to meet energy codes, sound control requirements, impact resistance, and blast resistance requirements. IG units can be designed to reduce heat loss and solar heat gain entering the building, with a minimal reduction of visible light transmittance.


IG units are hermetically sealed combinations of two or more lites of glass separated by a dehydrated airspace. Desiccated spacers are dual sealed with polyisobutylene primary sealant and an organic or silicone secondary sealant, depending on the project specifications and the application. (See the diagrams below.) Argon gas-filled IG units are available to further improve the insulating properties (reduce the U-Value) of a standard air-filled IG unit. The glass lites of an IG unit can be annealed, heat-strengthened, tempered or laminated, as needed, to meet building code requirements, safety glazing standards and design requirements. The lites of an IG unit can be of equal or unequal thickness.


The standard « commercial IG unit» is made up of two lites of 6mm glass and nominal 12mm airspace. Custom IG unit designs can be fabricated with glass thicknesses ranging from 4mm to 10mm and with airspace thicknesses ranging from 6mm to 20mm.

Maximum sizes for IG units are determined by a number of considerations. Size, thickness, weight, aspect ratio, application and load requirements are the factors utilized to make this determination.


Insulating glass units are used in essentially all exterior building applications, including vertical glazing, sloped glazing, overhead glazing and skylights, in vision areas. Depending on the glass type used, IG units can be designed for light and solar control; sound control; ultraviolet screening (to reduce fading); earthquake and blast resistance; security; and decorative applications. IG units are also used for interior applications such as sound control and to reduce energy usage for climate-controlled (hot or cold) rooms.

Residential Applications

Insulating glass has become the standard for both new and replacement residential windows. Most residential IG units are made with one outboard lite of clear glass and an inboard lite of clear glass, sometimes with a Low-E coating. Using reflective and Low-E glass will significantly improve thermal performance.

In cold climates, the Low-E coating is no placed on the #3 surface of the unit. This is done to maximize passive solar heat gain from the sun, while still improving (reducing) the winter nighttime heat loss (winter U-Value). In warm climates, the Low-E coating is positioned on the #2 surface of an IG unit to minimize solar heat gain. The U-Value remains unchanged for the second or third surface application.

Commercial Applications

Most commercial buildings spend the majority of their energy money on cooling loads, even in cold climates, due to the internal heat generated by lights, people, copiers, computers and other office equipment. Also, there has been an increase in the number and size of windows to maximize the use of natural daylight to reduce energy usage and lighting costs, as well as the positive effect on employee productivity. Therefore, the major emphasis in commercial buildings is to reduce heat gain (minimize the shading coefficient/the solar heat gain coefficient). Of lesser importance, but still quite significant in cold climates, is the need to minimize nighttime heat loss (winter U-Value).

There are now a large number of high performance reflective glasses that do an excellent job of reducing heat gain. And there are a number of Low-E glasses that not only improve (reduce) the winter U-Value, but also reduce heat gain.