By Scott Hoover
Glass performs multiple, usually simultaneous functions in commercial buildings, unlike most other building materials. For example, glass can be used for:
- Aesthetics: Tints, reflective glass, and even clear glass can complement other building materials or make a statement on their own.
- Vision: Glass and lighting can work in tandem to produce the best view both into and out of a building.
- Energy Efficiency: New technologies and glass coatings allow glass to reflect heat energy to help keep buildings cool or warm, depending on the season and glass used.
- Safety: A range of shatter- and bullet-proof glass, along with fire-rated and other safety and security glass, is available. This glass is laminated, heat-treated, or wired.
During the 1980s, low-emissivity (low-e) coatings were developed to provide enhanced thermal control for building exteriors. These low-e products are used with clear glass for thermal control or combined with tinted (heat-absorbing) or reflective (heat-absorbing and reflecting) glass in an insulating glass unit (IGU) to achieve improved thermal and solar control.
The 1990s brought a new breed of low-e glass termed “solar control low-e” that not only possessed thermal control characteristics, but also solar control performance. These products enabled the trend of “transparency,” utilizing clear glass with solar control low-e coatings to maximize natural daylight and “opening” building views - both from the interior and the exterior.
In recent years, however, architects and building owners have discovered several issues and concerns regarding maximum visible light products. While those coatings maximized natural daylighting, they also yielded much glare. For instance, office building occupants often must close their window blinds to see computer screens effectively within their workspaces.
The high level of transparency also provides little or no occupant privacy. When viewing the building from the outside, the extreme levels of transparency of these products allow a clear view of desks, stacks of paper, furniture, the backs of file cabinets, etc., detracting from the design. Many of these buildings subsequently had shades drawn, at different levels, resulting in an exterior “checkerboard” effect that was not a design choice, much less a preference.
While these products are often specified and seen today (in more appropriate areas), there is a current trend moving on to a new, next generation of “hybrid” coatings.
Significant coating enhancements of the last couple years have been toward solar control low-e products that provide subtle reflectivity. They have been developed to address concerns regarding maximum visible light or transparency coatings. These hybrid coatings still provide high levels of visible light transmittance, but have a light, crisp “shine.” This shine, or subtle reflectivity, provides a more uniform exterior appearance, improving occupant privacy and comfort while reducing interior glare. Many of these products possess excellent solar and thermal characteristics in a single coating, eliminating the need for an IGU because increased energy efficiencies can be minimal. The coatings are applied to clear glass and tints, giving architects more design flexibility to use color and/or coordinate with other building materials; while bronze and gray continue to be prevalent, architects are increasingly incorporating blues, greens, and similar hues so that their buildings better relate to their natural surroundings.
Interior glass applications typically include furniture and floors (typically what’s called “heavy” glass, which is upwards of 1 inch or more thick, often laminated for additional strength), stairways, entryways, and even as room walls and dividers.
While aesthetics are important, depending on the application, other considerations include sound abatement (such as for meeting rooms), and fire and life safety (such as in schools and public buildings).
New Glass Options
In addition to the hybrid products, several new, and even improved, product categories have been introduced in recent years for both exterior and interior applications.
Advancements in glass manufacturing technology have provided more options for anti-reflective glass. Typically, anti-reflective glass has a light reflectance of less than 2 percent, whereas traditional clear glass has an 8-percent reflectivity. There are different ways to produce anti-reflective glass: pyrolytic, dip-coated, and thin film coating. Each process has its own benefits, including size options, level of anti-reflectivity, degree of color, and even security.
Until recently, manufacturing limitations have kept size choices for anti-reflective glass to small, usually interior, applications. To work around size limitations for large applications, architects were forced to use multiple frames, which reduced the anti-reflective impact. Now, depending on the glass manufacturer, sizes can range up to 96 by 120 inches or more, opening the possibility for more exterior applications and larger interior applications.
One benefit of anti-reflective glass that is not always considered is cleanliness. Even when dirty, anti-reflective glass can appear cleaner - versus clear glass - because of the lower level of light reflectance.
A relatively new glass available in North America is self-cleaning glass. Other than having a slight “sheen,” self-cleaning glass looks like traditional clear glass. The main difference is that it has a special chemical surface to enable two self-cleaning properties: One is the photocatalytic effect, in which the surface reacts to the sun’s ultraviolet light to continuously attack, loosen, break down, and get rid of dirt and other organic matter. The other effect, hydrophilic, causes water on the glass to sheet and rinse away dirt, rather than streaking and leaving water spots.
Though conclusive evidence is only starting to build, there are indications that the coating used to make dual-action, self-cleaning glass can positively impact indoor air quality.
Glass manufacturers are regularly developing new patterns and thicknesses for pattern and other decorative glass. In addition to aesthetics, pattern glass offers varying degrees of translucency. Each pattern design combines elegance and decorative effects, and allows architects and designers various options for emphasizing the natural light-enhancing properties of glass.
Scott Hoover is a 17-year veteran of the glass industry. He is involved with product development, sales, and marketing strategy for Toledo, OH-based Pilkington Building Products North America. The company is part of Pilkington PLC. in the United Kingdom, one of the world’s largest glass manufacturers.