Glazing Industry Fights Tightened Energy Standards

Several glazing industry associations successfully appealed changes to ASHRAE Standard 90.1 that would have reduced the amount of glass allowed in commercial building envelopes. The change would have reduced the maximum window-to-wall ratio from 40% to 30% and tightened the maximum U-factor and solar heat gain coefficient. A minimum for visual light transmittance was also added to the standard’s prescriptive path. The standard is being returned to committee so the glazing changes can be reconsidered.

The glass industry appealed what it called the “unnecessarily restrictive” glazing provisions in Standard 90.1 based on two things: first, industry groups claimed that the new provisions were not based on sound research on energy savings; second, the glazing industry felt it lacked sufficient representation on the committee that made the changes. The chair of the 90.1 committee, Mick Schwedler, said that he looks forward to opening the committee to broader representation. “Our goals are to make sure the standard reflects the energy-efficient glazing practices and technology, and to reach consensus,” he told EBN.

Thomas Culp, Ph.D., of Birch Point Consulting, who helped craft the appeal, says the addition of a visual light transmittance minimum “would harm more than 50% of commercial glazing products—yet without any energy savings in most cases.” He says he will join the committee and looks forward to the opportunity to revise the glazing provisions. “It has been a real challenge trying to educate the ASHRAE committee about modern glazing technology and the important role glazing can play in high-performance buildings.” He believes that the benefits of glazing—including daylighting—must be balanced with the energy drawbacks.

“This is bad news for those who care about energy efficiency,” said John Straube, Ph.D., P.Eng., of Building Science Corporation. “The reduction to 30% window-to-wall ratio was a good step forward.” Straube noted that while daylighting is an important goal, good design makes daylighting possible within the 30% limit. And windows will never insulate as well as walls—making the lower U-factor requirements in Standard 90.1 a good idea in Straube's book. “It should be embarrassing to look at the significant reductions in opaque wall U-factors and then compare them to how high the U-factor of the fenestration is,” he said.

Straube also disputes the claim that there are no technical studies to support lowering the window-to-wall ratio. “There are many studies that show that window-to-wall ratios greater than 30% result in more energy consumption in typical commercial buildings,” he told EBN. For more on the energy penalties of heavily glazed buildings, see “Rethinking the All-Glass Building,” EBN July 2010.

The Standard 90.1 committee is scheduled to meet in November to consider these and other issues.

– Allyson Wendt

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