Thermal stress is one of many factors that can cause glass to break, even when it is not impacted by a projectile.
Such failures usually are not a testament to the quality of the glass, but rather the result of temperature imbalance within the glass, which can occur when the center of a window or insulating glass unit (IGU) heats and expands while the edges remain cool.
The resulting thermally induced tensile stress on the glass edges can exceed the strength of the glass itself, causing it to break at approximately a 90-degree angle.
Working closely with the IGU fabricator and glass supplier, and conducting a thermal stress analysis at the beginning of the design phase can help architects specify the proper glass for their projects. Here are five thermal stress related rules-of-thumb to consider when specifying glass:
1. Clear or color? Glass can be clear, ultra-clear or tinted in colors such as gray, blue, green and bronze. Tinted glasses absorb solar radiation more than clear glass, which can cause them to collect heat and make them more susceptible to break from thermal stress.
2. Inner or outer surface? Reflective and low-emissivity (low-e) coatings, which improve the solar performance of glass primarily by reflecting solar radiation, can be placed on any one of four surfaces in a dual-pane IGU. While they are usually placed on the inner glass surfaces of the IGU, the coating orientation and the associated risk of thermal stress has to be taken into account.
3. Sunny or shady? Outdoor shading, including overhangs, adjacent buildings, and trees, is one of the most dynamic elements to consider when analyzing thermal stress. Minimizing locations where non-uniform shading of IGUs can occur will help avoid extreme temperature gradients. Interior shading devices, such as blinds or drapes, can increase glass temperature by reflecting solar radiation back through the glass or by reducing the convection and conduction of heat away from the glass. To minimize thermally induced edge stress, the air space around the window glass should be ventilated. There should be a gap of several inches between the glass and shades, blinds or drapes.
4. Where to place a vent? If heating vents, registers and grilles point directly at glass units, warm air will cause the glass to heat up and, under certain conditions, break. Make sure vents are carefully placed to reduce thermal stress risk and avoid placing them between the glass and interior shading devices.
5. How to frame it? Glass framing systems that have low heat capacity also can minimize the chance of a thermal stress break. Structural gaskets and narrow metal framing are favorable because they have less effect on the glass temperature around the edges. Conversely, massive framing – whether metal, masonry or even wood – can have more of an effect, resulting in thermal imbalance and risk of glass breakage.
To learn more about avoiding thermal breakage of insulated glass units and other glass-related topics, visit the PPG Glass Education Center at www.educationcenter.ppg.com.
Related Stories
Sponsored | | Oct 19, 2014
The Exploration Tower in Port Canaveral dazzles visitors
With a mission to provide the experience of a lifetime, the Exploration Tower at Port Canaveral, Fla., is designed to inspire, as visitors learn about the history and nature of the port and beyond. SPONSORED CONTENT
Sponsored | | Oct 19, 2014
What to do if your team is in a rut
Another brainstorming session, another slew of tired ideas. How can you push your team to be more creative and bring in new perspectives? SPONSORED CONTENT
| Oct 19, 2014
White House Visitor Center reopens in Washington, D.C.
Designed by SmithGroupJJR and Gallagher & Associates, renovated center shows public its unique role as office, stage, museum, park, and home.
| Oct 16, 2014
Must see: Illustrator interprets iconic windows concocted by renowned architects
Graphic designer Federico Babina has made a name for himself when it comes to art inspired by architecture, or more accurately, art inspired by architecture that's inspired by other forms of art.
| Oct 16, 2014
Henning Larsen Architects to design train station for planned Danish town
Danish firm Henning Larsen Architects won Frederikssung municipality’s architecture competition for a regional train station in the planned city of Vinge—Denmark’s largest urban development.
| Oct 16, 2014
Report: How to keep public libraries relevant in a digital age
Public libraries will avoid being relegated to the scrap heap of history in a digital age as long as they continue to serve as platforms for learning, creativity, and innovation that strengthen their communities, according to a new Aspen Institute report.
Sponsored | | Oct 16, 2014
Drilling deeper: The booming Bakken Shale region
The Bakken Shale region, which spans from central North Dakota to the northeastern corner of Montana, is rapidly growing as a result of the oil and gas boom. SPONSORED CONTENT
| Oct 16, 2014
Germany to commemorate Berlin Wall anniversary with 10-mile LED 'balloon' installation
The project, named Lichtgrenze (or Border of Light), makes for a colossal art installation dividing Berlin back to East and West. Eight thousand LED light-filled balloons, each 11 feet high, will line the path.
| Oct 16, 2014
Perkins+Will white paper examines alternatives to flame retardant building materials
The white paper includes a list of 193 flame retardants, including 29 discovered in building and household products, 50 found in the indoor environment, and 33 in human blood, milk, and tissues.
Sponsored | | Oct 16, 2014
Mill Brook Elementary School colors outside the lines with creative fire-rated framing solution
Among the building elements contributing to the success of the elementary school’s public learning areas is a fire-rated stairwell that supports the school’s vision for collaboration. HMFH Architects designed the stairwell to be bright and open, reflecting the playful energy of students. SPONSORED CONTENT