The Attack on Glazing: Round Two

By Tom Culp
May 28, 2013

In 2009-2010, the industry successfully overturned an ASHRAE 90.1 proposal to reduce prescriptive glazing area by 25 percent. The proposal would have reduced the prescriptive limit on window-to-wall ratio from 40 percent to 30 percent, and buildings with higher WWR would have had to use the performance compliance path. The industry won the battle and overturned the proposal for several reasons, including the fact that daylighting had not been taken into account.

However, the attack on glazing area has returned. ASHRAE 189.1 is now proposing to reduce the prescriptive glazing area limit from 40 percent to 30 percent WWR for buildings less than 25,000 square feet. To put this into context, more than three quarters of all buildings, and one third of all floor space, are less than 25,000 square feet. This would affect many buildings such as schools, offices and assisted care facilities.

To comply with the reduced WWR, the industry would likely see fewer windows, shorter/smaller windows, a transition from strip windows to punched openings, and a transition from curtain wall to strip windows.

This new attack on glazing area is based on new energy analysis that includes daylighting; however, we still believe it is flawed or questionable. It uses incorrect criteria, and, most importantly, it ignores the human impact of windows and views. This is especially concerning since this is supposed to be a green standard that includes indoor environmental quality and occupant well-being.

Windows and daylight have a tremendous impact on human comfort and productivity. Numerous studies have shown that in offices, windows increase productivity and cognitive performance, and decrease absenteeism and turnover. In schools, student test scores have improved, with the presence of daylighting. And in hospitals, studies have shown a reduction in length of hospital stay, a lower reliance on post-surgical pain medication, and a reduction in the development of surgical post-op delirium.

The glass industry defeated the attack on glazing area in 2009-2010, and the industry can do it again, with the support of its members. The deadline for the public comment period in the WWR battle is June 17. Here is a guide to submitting public comments, including instructions for submittal and additional details about the issues of the proposal. 

The author is owner of Birch Point Consulting LLC, and code consultant for the Glass Association of North America and the Aluminum Extruders Council.