For many, glass façades are the epitome of contemporary urban architecture and design. Sleek, clean, modern—sometimes super-modern—a glass exterior gives the impression of an Emerald City of the future, rising above the bricks and mortar of yesterday’s Gotham. Yet with the climate crisis accelerating and its effects becoming ever more severe, can a material that admittedly is less energy efficient remain a part of our future? The answer is a cautious yes.

Form & Function

Glass provides two of the top things people want in a living space: light and air. It lets the light pass in and out, but does the same for heat and air conditioning—leading to higher HVAC use (and cost) and a larger carbon footprint than most masonry buildings of comparable size. That inefficiency has supposedly been the death knell for glass towers, be they residential or commercial—yet we see new glass buildings rising on the skyline regularly. What gives? In short, new technologies.

According to Antonio Argibay, managing principal of Meridian Design Associates, an architectural firm with offices in New York and Miami, “The pros in favor of glass façades are that they’re clean, sleek, and perceived to be modern. They also provide greater daylight and sight lines from the interior spaces, which have become increasingly smaller—thus the glass gives a sense of greater living space. The cons of glass are that even with high-tech assemblies, it’s less efficient—not only as a material, but because an opaque wall can be much better insulated. 

“With that said,” he continues, “different films have been used for quite some time to make the glass perform in a more energy-efficient manner and protect furnishings from harmful UV and [provide] shading control. These films are beneficial for existing installations where double- or triple-glazed units of sealed low-e [for emissivity] glass were not used. The technology of glass manufacture is much more advanced than it was even 30 years ago. These sealed multi-paned units have gasses in the cavities, and each surface is treated differently, with coatings applied either to reflect, absorb, or transmit solar rays for a desired aesthetic and energy performance. For example, modern glass units prevent the interior pane from being overheated, thus creating an additional source of heat to radiate into the space.”

“The overall trend within building codes is to minimize energy use in building operations, for obvious reasons,” says Terrence McDonnell, associate partner with the Chicago office of international architectural and structural engineering firm Klein & Hoffman. “Residential users and office workers alike want to be exposed to sunlight and view the outdoors—so aesthetically, as well as for mental health reasons, there will always be demand for glass exteriors. The real challenge for us today is how to balance the two competing interests. Historically, as the amount of glazing area increases on the exterior of a building, the more energy is required to control the interior environment. In winter we need to keep the interior heated, and in summer we need to keep the interior cooled. Throughout the year we need to control humidity and dew points so condensation does not occur on interior surfaces.” And that takes a lot of juice. 

John Lind, a senior associate with Pelli Clarke & Partners in their New Haven, Connecticut office, adds that on the plus side, “spaces with lots of daylight require less artificial illumination and reduce the amount of money spent lighting those spaces. From an energy point of view, the windows used in these structures are typically insulated, which creates a thermal break from interior to exterior. There is minimal transfer of hot and cold from inside to outside and back. Other materials may appear more efficient but are opaque, so you lose the benefit of daylight as a lighting and heating source. As energy codes get more strict, the recommended or required coatings on glass panels help improve the performance of the glass—and they’re getting better and better. There are a lot of different coating types, and each has its own performance criteria relative to reflecting or allowing daylight in, etc.”

New Tech

Glass technology has evolved in leaps and bounds—especially since the 1970s, with components and fabrication techniques that have significantly reduced energy consumption in buildings.  

Among the technologies that have helped improve the energy efficiency of glass façades, McDonnell lists “low-emissivity coatings—coatings that attempt to reflect the infrared portions of light, so they are not transmitted into the building while simultaneously allowing visible light wavelengths to enter the building.   Sometimes glazing systems are fabricated with two or more low-e coatings. There are also ceramic frit patterns—special silkscreen coatings of fine glass particles which are coated onto the glass. This also reflects the infrared portions of light, so they are not transmitted into the building, while simultaneously allowing visible light wavelengths to enter. [And there’s] dynamic glass—similar to transition lens sunglasses, this glass automatically adjusts to the intensity of the solar radiation, becoming a darker tint in high radiation, and clear when low or no solar radiation is present. This automatic transition can be controlled through a variety of methods and is known as thermochromic, electrochromic, or photochromic glass. Lastly, a combination of more than one of the above items may be used.”

Lind adds that “glass has certain thermal properties that bring daylight and heat through the glass. There are coatings that can be put on the glass that have high performance characteristics, including keeping some heat energy from coming through and reflecting it back to keep interiors cooler. Coatings can be manipulated to specific needs and desires. With today’s energy codes, we are also looking at other components and balance needs against what the systems can do together. One is spandrel glass. From outside it looks like glass, but from inside there’s a coating or a cavity called a shadow box to prevent anyone from seeing through into the space.”

Maintenance

In considering the viability of glass as a continuing option for façades, long-term maintenance is of course an additional consideration. On balance, glass is neither more nor less difficult to maintain than bricks and mortar. Where bricks and mortar may require replacement and repair, glass may as well. The key, say the experts, is to keep glass façades clean in order to maintain optimal functioning.

“One of the biggest priorities is to keep the façade clean,” says Lind. “Cleanliness improves both performance and appearance. We need clean windows to look out, and dirt can be seen especially from inside. The problem is that access to the façade is not always easy. The taller a building is, the more critical it is to include a building maintenance unit, or BMU. A BMU sits on top of the roof and can lift a cradle or carriage up the side of the building for cleaning and maintenance purposes. Normally these units are part of initial construction; they’re very difficult to add later. They can have a track system and a long arm to telescope out. A rig hangs from the arm and goes up and down with a tie-in for safety.”

Along with cleaning, “as far as maintenance is concerned,” says Argibay, “the most critical thing in glass buildings is the failure of gaskets, sealants, and other high-tech joint materials. Glass and aluminum are what make glass façades possible, and the failure is not in those materials themselves, but in what holds them together. There is nothing much you can do to maintain the elasticity and performance of sealants and gaskets as they start failing in about 10 years. They have to be replaced in part or whole.”

 “Maintenance of glass and glazing systems starts at the perimeter of the glass elements themselves,” says McDonnell. “Appropriate sealing or gasketing of the glass panels is key to weatherproofing glass enclosures. In addition, sophisticated designers can produce details that will make the ultimate replacement of sealants and gaskets after decades of exposure to the environment and wind load fatigue easier. Regardless of the difficulty of sealant replacement, preparing a written procedure that is project specific is akin to an Eagle Scout ‘being prepared.’”

With the days of Beaux Arts–style masonry and terracotta flourishes a thing of the past, glass is clearly here to stay as the look and feel of the modern era. As technology—and climate change—advance, residents will hopefully be able to enjoy energy efficiency and easier maintenance along with their light and air.

A J Sidransky is a staff writer and reporter for CooperatorNews. He is also a published novelist. He may be reached at alan@yrinc.com.