Is There Such a Thing As Too Much Glass?

High-performance curtain wall design
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Sponsored by The Ornamental Metal Institute of New York
By William B. Millard, PhD
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Lou Podbelski, AIA, senior vice president at Hayward, Cal.-based smart-glass firm Halio, describes a market on the verge of expansion, as perceived drawbacks yield to R&D advances. Visual light transmission through older smart glass began around 60 percent, dropping by stages to 20 percent, 6 percent, then a very dark 1-2 percent, he notes; the full range of adjustment could take 20 to 30 minutes, as algorithms waited to ensure that exterior changes from clouds to full sun were not temporary anomalies —making the transition “a day late and a dollar short,” not optimizing energy before reaching the desired tint. Today's advanced smart glass can make the full change from clarity to darkness as a smooth three-minute transition that occupants can stop anywhere during the process. “The one thing preventing electrochromic technology from getting adopted,” Podbelski comments, “even though it saves energy and provides wellness and productivity gains, is the price.” With the IRA credit lowering that obstacle through 2024, now is the moment to test this industry's transformative potential.

Others may be further from prime time. VIG is theoretically promising, Selkowitz says, since “heat doesn't transfer in a vacuum,” even one so tiny that nearly invisible microspheres or cylinders are used to hold the panes about a third of a millimeter apart. Maintaining the vacuum is a problem: “You have to make this super-tight seal, even better than a normal insulating glass unit, because if you get any crack or defect at the edge, the vacuum is gone,” and performance drops from R10-12 back to R2. Fabrication requires high-temperature heat sealing; “the bottom line is, it's complicated and expensive,” though VIG is finding applications in historic preservation, where older buildings' frames require “a glass element that's 8 or 12 mm thick, and you can't get that in an IGU.”

Aerogel is further back in the R&D process, Selkowitz adds, though recent reports describe advances in clarity and aesthetics (Carroll et al., 2022). Krypton gas (replacing argon) is useful in ¾-inch IGUs but carries pricing vulnerabilities, he says: “Most of the krypton comes, it turns out, from Ukraine and Russia, and it's also used in satellites for thrusters; [Elon] Musk uses it in all his little satellites up there to keep them on track. So the cost went up by a factor of five or 10…It's added two or three dollars a square foot to the price of the window.” Embedded photovoltaics offer the possibility of harvesting energy to power building systems, shades or louver systems, or an electrochromic window itself, but create tradeoffs with visibility and raise questions of scale. With photovoltaics among multi-system energy-sparing strategies, “if you really wanted to do a net-positive building today, you could,” Hoffman suggests, “as long as the energy use intensity inside the building was manageable...There are several Net Zero buildings, but I can't point to one that's actually proven to be net positive.”

Along with software tools widely used in the glass industry (see, LBNL helped create the National Fenestration Rating Council, which maintains a standardized, nonproprietary database of glass products' properties. A second DOE-supported group, the Attachments Energy Rating Council, provides similar ratings for shades, blinds, and associated products. Selkowitz also cites a new collaborative, the Partnership for Advanced Window Solutions, dedicated to accelerating the adoption of high-performance windows and attachments, beginning in the residential sector and later broadening to commercial. These resources are indispensable for designers and specifiers aiming to keep up with this fast-changing field.


As Shannon points out, “We've gotten very skilled at creating glass buildings that can appear to be monolithically glass and hide the stuff you don't want to see: the spandrel, some of the column construction, and so on. And we're also doing that because we have to meet energy code, and no matter how good the glass is, we need a certain percentage of opaque area.” The concept of a wholly transparent building is a limit that can never be reached.

Some future-watchers look to technology transfer from the information-technology and automotive fields for breakthroughs. “The automotive industry in glass is actually larger than the architectural glass industry,” Shannon says. “One time I was challenging somebody on why we aren't doing these things, and they said, 'Because we sell more glass to General Motors and Ford than we do to you.'” The super-thin glass used in triple- and quad-pane products has become far cheaper, Selkowitz observes, with the smartphone industry driving demand. True paradigm shifts are likely to cross industry-sector borders.

“We innovate; we don't experiment,” Shannon summarizes. “Buildings are not a great place for an experiment, because [with] experiments, some go well and some don't; there's a hypothesis, and a good scientist is as much informed by the failure of his hypothesis than he is by its confirmation. A building owner is not going to be happy if we disprove our hypothesis by building a building that doesn't work.”

“The root problem,” Patterson comments, “is that the industry does not yet well understand these issues of resilience and sustainability.” Citing Bjarke Ingels's dictum that “sustainability is a design problem,” he reminds the profession that its urgency mandates dramatic rethinking: “If we were a rational society, we would have a moratorium on building until we figure out how to do it without negative consequences to the environment. Of course, that is a total non-starter”—yet the time to start is immediately.


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Bill Millard, is a New York-based journalist who has contributed to Architectural Record, The Architect's Newspaper, Oculus, Architect, Annals of Emergency Medicine, OMA's Content, and other publications.


The Ornamental Metal Institute of New York The Ornamental Metal Institute of New York is a not-for-profit association created to advance the interests of the architectural, ornamental, and miscellaneous metal industries by helping architects, engineers, developers, and construction managers transform designs into reality.


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Originally published in Architectural Record
Originally published in December 2022