Thom Zaremba
Thom Zaremba is a shareholder at Roetzel & Andress.

If your answer to the title question was glass, you’re right!

Glass is like nothing else on Earth. It’s as solid as brick or cement. But, with glass, walls come to life with the outdoors: sunrises, sunsets, blue skies, storm clouds, rain or wide-open spaces—all while keeping you high and dry, sipping a cup of coffee in your office or living room. Nothing but the magic of glass can do that!

Look at any new commercial building. You’ll see lots and lots of glass. Why? Because people love glass in their buildings! But do some people love to hate glass? Well, if they don’t, it’s hard to explain why others who represent the glass industry and I have been fighting the window-to-wall ratio (WWR) wars in energy codes for years.

WWR means the “ratio” of “windows” to opaque “walls” permitted by the energy codes. Currently, the WWR is 40% under most energy codes’ “prescriptive” provisions. It can, however, be increased if the building designer uses the provisions of the energy code’s “performance” path.

In its simplest terms, the performance path models the energy a building design would use and then compares that to the energy a building designed to the prescriptive path would use. If the building design would use the same or less energy than the prescriptive path, it is good to go. If not, you must change the design to use less energy.

For years, various energy conservation and other industry groups have attempted to reduce the typical 40% WWR prescriptive path limitation to 35% or even 30%, which would also automatically reduce the amount of glass permitted under the performance path.

Why do they keep doing this? Some energy conservation advocates claim it will somehow “save” more energy—a claim which, in turn, usually makes representatives from the opaque wall industries smile as their share of the WWR would increase if the amount of glass were to decrease.

However, is reducing the amount of glass in buildings the best—or even an appropriate—way to save more energy? My answer is—and always will be—an emphatic “No!”


Transparency is not the only thing that makes glass magic. Its magic is also found in the fact that it is constantly evolving. For example, a solar heat gain coefficient (SHGC) of 0.40 years ago was considered low. Now, energy codes routinely prescribe a 0.23 SHGC for southern climates. Likewise, windows with a 0.40 U-factor were deemed good for northern climates. Now, a 0.25 U-factor can easily be prescribed, thanks to advanced coatings and other improvements to glass.

Consistent, regular improvements to the energy performance of architectural glass are the best way to improve the overall energy performance of buildings. Reducing the amount of glass that may be used is not. After all, putting an “exit door” in every row of seats in an airplane might be safer, but it is not practical.

Likewise, reducing the amount of natural daylight and taking away our views of the outdoors by reducing the amount of glass in our buildings is not practical or healthy. Reducing the amount of glass would reduce the magic in our lives, architecture, sense of well-being and mental and physical health. I, for one, will continue to fight any effort to reduce the amount of glass in the WWR of building envelopes.

Thom Zaremba is a shareholder at Roetzel & Andress. He has more than 25 years of experience as a code consultant for the glazing industry on fire protection and structural and human impact issues. USGNN is pleased to welcome Mr. Zaremba as a blogger.

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