Earlier this month, a popular Washington, D.C.–based architecture commentator took to one hometown newspaper to mull local developers’ propensities for all-glass new construction. Was the material’s popularity, combined with limitations like the city’s famous height moratorium, producing look-alike buildings? The thought piece imagined differentiating future projects with traditional materials or higher-flying design. And while these proposals sparked dialogue well beyond the nation’s capital, the essay neglected perhaps the most immediate solution for diversifying the cityscape: Manufacturers offer glass products in a greater variety of colors, sizes, reflectivity levels, textures and performance options — even bent glass is possible — than ever before.
Designing a glass façade is no longer a question of choosing between a few off-the-shelf products. Glass appearance and performance may be highly suited to a project’s goals instead, and the end results are anything but look-alike. Carefully specifying a glass façade nowadays can optimize the environmental footprint of a building, functionality for its occupants and the design team’s creative expression. Tailoring individual building exteriors inevitably produces more variety in the urban fabric.
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Guardian SunGuard® SN 54 installed at Walgreens. Photo by Max C. Kim / Bad Mood Saloon
However liberating, the new generation of glass façades also places more responsibility on the shoulders of the architect. He or she must choose wisely among the vast possibilities, while considering the desired exterior appearance. For example, different aesthetics can be achieved through coatings on glass or tinted glass — or both. Other aspects of appearance, namely transparency and reflectivity, can also be achieved through coating and tinting. Light transmission options span approximately 30 percent to more than 60 percent. Meanwhile, reflectivity can range from very low, for greater transparency, to high reflectivity. Tinted glass can also impact the desired transparency and reflectivity.
Performance requirements must be considered along with aesthetic choices. A prospective building’s shape and orientation impact its exposure to direct and indirect daylight, which itself impacts energy use and occupant experience and comfort. Rooms on the building perimeter, in particular, require consideration of daylighting and level of glare. For example, the south façade occupants will have different needs from those on the north side of the building.
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Guardian SunGuard® AG 43 installed at Nic on Fifth. Photo by Brandon Stengel / farmkidstudios.com
The use of low-emissivity (Low-E) coatings can help buildings manage energy use and contribute to sustainability. Low-E coated glass is also known as spectrally selective glass, as long as its ratio of visible light transmittance to solar heat gain coefficient is 1.25 or better, as per the U.S. Department of Energy’s definition. More generally speaking, by blocking solar heat and maximizing daylight penetration, low-E coatings significantly improve the energy efficiency of glass and building alike: Reducing energy consumption and peak demand related to heating, cooling and electric lighting allows downsizing of HVAC equipment. In addition, low-E coatings can have a relatively neutral appearance, as evidenced by projects like the Envoy Hotel in Boston, for which Guardian’s low-E SunGuard® SuperNeutral® 68 coating on clear glass achieved a very impressive light-to-solar-gain ratio of 1.80. Considering these collective improvements, architects are specifying low-E glass in commercial and residential projects at a swift pace.
When energy codes and LEED®requirements dictate even greater solar control, another solution may be to specify coatings with higher reflectivity, such as Guardian SunGuard® AG 43 glass, found on the LEED Silver–certified residential tower The Nic on Fifth in Minneapolis. Reflectivity offers the dual benefits of reducing solar heat gain as well as glare. Different glass options may be reflective on the inside as well, making it difficult for occupants to see views, so mockups or samples should be reviewed to assure proper light transmission and visibility.
Guardian SunGuard® SuperNeutral® 68 installed at Envoy Hotel. Photo by Warren Jagger Photography
For the best ratio of visible light transmittance to solar heat gain, architects should consider triple silver coatings (three layers of silver sandwiched within other metal layers). One example of a triple silver product application is Guardian SunGuard® SNX 62/27 glass installed at Owego Elementary School in Owego, New York, which also features SunGuard® IS 20 glass; this fourth surface coating improves the thermal barrier even more.
Recognizing that architects and specifiers have to navigate myriad offerings, manufacturers like Guardian Glass have created suites of tools for analyzing façade products. A leader in glass manufacturing, Guardian has developed intuitive software for glass and glazing system analysis, which includes a performance calculator that compares glass options for light transmission, U-factor and solar heat gain; a building energy calculator that analyzes energy costs for a variety of exterior envelope scenarios; and a visualization tool for evaluating glass appearance in various lighting conditions.
Guardian SunGuard® SNX 62/27 installed at Owego Elementary School. Photo courtesy of Guy Cali Associates
Guardian’s Glass Analytics online platform helps refine product choices and better assures the success of an end product like the Honolulu Walgreens flagship store, for which Guardian SunGuard® SuperNeutral® 54 glass was chosen for clear views and low reflectivity. This aesthetic, combined with SuperNeutral® 54’s high performance, delivers the architect’s vision: Giving the appearance that walls do not exist, as in a traditional Hawaiian structure.
Of course, not all decision-making can take place virtually. Architects should carefully review samples to make final selections before specifying. Outdoor mockups under slightly overcast conditions show the most accurate rendering of transmitted and reflected color. Meanwhile, angle of observation, interior lighting and potential effects of glare must be considered during various times of the day, and under varying lighting conditions, to more accurately determine whether or not design intent has come to life. When evaluating samples indoors, architects should use a black background to observe reflection, which is the best indication of what the glass will look like from outside.
By carefully evaluating the building’s future use and occupants’ needs, the naturally occurring light on all façades at all times of day across seasons, using digital tools to review performance and aesthetics and getting outside with actual samples, architects and building teams are arming themselves with all the pertinent information to make the best choice for façade glass. The result is glass that will not only deliver on performance, but also help shape beautiful, interesting and memorable buildings and cityscapes of our future.
The SunGuard® glass product line from Guardian Glass North America offers excellent solar control and a wide variety of colors and performance levels. SunGuard® glass products provide innovative, leading solutions for appearance, economics and energy efficiency, and are available through an international network of independent Guardian Select® fabricators. For more information about Glass Analytics, and the many product choices that are available to you, visit guardian.com/commercial.
