As architects consider specifying and designing with glass for building facades, the possibilities are vast. Manufacturers offer numerous glass products in a greater variety of colors, textures and performance options than ever before for interesting and beautiful design. And, architects can specify high-performance glass, delivered through greater light transmission, improved u-factor or desired levels of solar heat gain, or a combination of all of these. Creating a clear plan to the right glass can be streamlined by following these critical steps:
1. Identify design intent
What is the desired exterior appearance? Consider the following:
- Color: Color and appearance can be achieved through coatings or tints, or both. Color can also impact the desired transparency or reflectivity.
- Transparency and reflectivity: Light transmission options are available from 30 percent or below to above 60 percent. Reflectivity levels can vary from low reflectivity (more transparent) to medium or highly reflective. Designers have many options with today’s low-E coatings.
- Building shape and orientation: Determine how direct and indirect daylight will impact energy use and occupant experience. Rooms on the building perimeter require daylighting and glare control.
- Window-to-wall ratio: The amount of glass will affect HVAC, interior lighting systems and occupant productivity and well-being.
2. Consider the coatings
- Low-E glass reduces heat gain or loss by reflecting infrared energy (heat), while letting in larger amounts of visible light. The coating lowers the U-value and if desired, the solar heat gain and in doing so, improves the energy efficiency of the glass. Because of this and its relative neutrality in appearance, low-E glass continues to grow in popularity in commercial and residential projects.
- By blocking solar heat and making maximum use of daylight, spectrally selective glass-defined by the U.S. Department of Energy as glass with a light to solar gain of 1.25 or better-can significantly improve building heating, cooling and electric lighting, to the point of downsizing HVAC equipment, which reduces initial capital investment and ongoing energy costs.
3. Examine performance
While new coatings do an excellent job of letting in light and lowering solar heat gain, energy codes and LEED requirements, may dictate even greater solar control. Fortunately, there are many options including medium light transmitting coatings (40-50 percent) or silkscreened glass, either with or without coatings.
The higher the transparency, the easier it is to see in, and the more light penetration. Although daylighting is proven to improve mood, higher light transmission could result in glare or high solar heat gain, depending upon the product specified. A solution may be a glazing with higher reflectivity or use of a tinted float glass with a coating that still permits daylighting, but not as much direct light penetration. Also, consider the reflectivity from the inside looking out. Different glass options may be more reflective on the inside, making it harder to see out. Mockups will assess this effect and help architects understand that light transmission in the 30-50 percent range still permit a great deal of light into a structure.
4. Take advantage of glazing technologies
- When considering the light-to-solar-gain ratio, or, how efficiently the glazing is letting in light but blocking solar heat gain, triple silver (three layers of silver sandwiched within other metal layers) offers best-in-class performance.
- Performance can also be improved even more with the addition of a fourth surface coating, providing an enhanced thermal barrier. It boosts the performance of dual-glazed or triple-glazed low-E windows. These coatings are very durable and can typically be exposed to the interior of the building.
- If safety is an important consideration, laminated glass, a combination of two or more glass sheets with one or more interlayers of plastic (PVB or ionoplast), minimizes the risk of injury. In case of breakage, the glass will tend to remain in its frame, reducing injury from sharp edges and flying or falling glass particles. Laminated glass also blocks UV light, and can provide excellent solar control and reduce sound transmission.
5. Look at all the angles
Architects must look carefully at the samples to gain the best perspective on what the glass will look like when installed.
- Glass in outdoor or natural lighting, preferably in slightly overcast conditions, shows the most accurate rendering of transmitted and reflected color. Consider angle of observation, interior lighting and potential effects of glare.
- View glass outside during various time of the day, and under varying lighting conditions, e.g., cloudy versus sunny. This will provide a truer indication of how varying light conditions impact design intent.
- When evaluating samples indoors, use a black background to observe the glass reflection, which is the best indication of what it will look like from the outside.
Glass manufacturers will be glad to assist you to be sure you are viewing the glass in the most accurate fashion, and are happy to discuss these and any conditions of building with glass.
Artwork: ©Copyright, Chihuly Studio, 2012, all rights reserved. Photo: Ben Benschneider
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Chris Dolan is director of commercial glass marketing for Guardian Industries, Auburn Hills, Mich. For more information about high-performance glass and glazing, visit www.sunguardglass.com.