Guest Column - April 2011
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Design Corner

Windows and Walls
A Double Standard in Energy Efficiency

By Bruce Lang

Many might think this is where the story ends. However, recent and impending revisions to the Department of Energy's Energy Star window performance standards will require windows possessing the coveted Energy Star designation to provide increased energy efficiency.

Glass available today that will meet the new and forthcoming Energy Star window performance standards include:

  • Triple-pane glass consisting of three panes of glass and two heat-reflective coatings. The good news is that by using a third pane of coated glass, triple pane improves insulating glass performance. The bad news is that triple-pane glass is 50 percent heavier than insulating glass, requiring stronger window framing and increasing cost accordingly.
  • Heat-reflective insulating glass containing a suspended transparent heat-reflective film inside the air space can dramatically increase insulation performance while reflecting unwanted solar heat. Single, double and even triple internal films that create as many as four separate cavities inside the insulating glass unit can achieve a center of glass insulation value of R-20—superior to an insulated wall.

Clearly, the advent of new high-performance glass technologies for windows, fixed glass and glass door applications has heralded the end of an energy-efficiency double standard for walls and windows. Suspended film insulating glass is saving energy at the Fitness Center of Durham College in Whitby, Ontario, Canada; the Montgomery County Regional Swim Center, Rockville, Md.; and the Westminster Recreation Center in Westminster, Colo.


Bruce Lang is vice president of marketing and business development at Southwall Technologies Inc. in Palo Alto, Calif. For more information, visit