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
Office Buildings | Jun 26, 2023
Electric vehicle chargers are top priority for corporate office renters
Businesses that rent office space view electric vehicle (EV) charging stations as a top priority. More than 40% of companies in the Americas and EMEA (Europe, the Middle East and Africa) are looking to include EV charging stations in future leases, according to JLL’s 2023 Responsible Real Estate study.
Laboratories | Jun 23, 2023
A New Jersey development represents the state’s largest-ever investment in life sciences and medical education
In New Brunswick, N.J., a life sciences development that’s now underway aims to bring together academics and researchers to work, learn, and experiment under one roof. HELIX Health + Life Science Exchange is an innovation district under development on a four-acre downtown site. At $731 million, HELIX, which will be built in three phases, represents New Jersey’s largest-ever investment in life sciences and medical education, according to a press statement.
Sports and Recreational Facilities | Jun 22, 2023
NFL's Jacksonville Jaguars release conceptual designs for ‘stadium of the future’
Designed by HOK, the Stadium of the Future intends to meet the evolving needs of all stadium stakeholders—which include the Jaguars, the annual Florida-Georgia college football game, the TaxSlayer.com Gator Bowl, international sporting events, music festivals and tours, and the thousands of fans and guests who attend each event.
Architects | Jun 22, 2023
Keith Hempel named President of LPA Design Studios
LPA Design Studios today announced the promotion of Chief Design Officer Keith Hempel, FAIA, to president of the 58-year-old integrated design firm. Hempel, who joined LPA in 1995, has been an integral part of the firm’s growth, helping to develop an integrated design process that has produced industry-leading results.
Industrial Facilities | Jun 20, 2023
A new study presses for measuring embodied carbon in industrial buildings
The embodied carbon (EC) intensity in core and shell industrial buildings in the U.S. averages 23.0 kilograms per sf, according to a recent analysis of 26 whole building life-cycle assessments. That means a 300,000-sf warehouse would emit 6,890 megatons of carbon over its lifespan, or the equivalent of the carbon emitted by 1,530 gas-powered cars driven for one year. Those sobering estimates come from a new benchmark study, “Embodied Carbon U.S. Industrial Real Estate.”
Virtual Reality | Jun 16, 2023
Can a VR-enabled AEC Firm transform building projects?
With the aid of virtual reality and 3D visualization technologies, designers, consultants, and their clients can envision a place as though the project were in a later stage.
Mechanical Systems | Jun 16, 2023
Cogeneration: An efficient, reliable, sustainable alternative to traditional power generation
Cogeneration is more efficient than traditional power generation, reduces carbon emissions, has high returns on the initial investment, improves reliability, and offers a platform for additional renewable resources and energy storage for a facility. But what is cogeneration? And is it suitable for all facilities?
Office Buildings | Jun 15, 2023
An office building near DFW Airport is now home to two Alphabet companies
A five-minute drive from the Dallas-Fort Worth International Airport, the recently built 2999 Olympus is now home to two Alphabet companies: Verily, a life sciences business, and Wing, a drone delivery company. Verily and Wing occupy the top floor (32,000 sf and 4,000 sf, respectively) of the 10-story building, located in the lakeside, work-life-play development of Cypress Waters.
Transit Facilities | Jun 15, 2023
Arlington, Va., transit station will support zero emissions bus fleet
Arlington (Va.) Transit’s new operations and maintenance facility will support a transition of their current bus fleet to Zero Emissions Buses (ZEBs). The facility will reflect a modern industrial design with operational layouts to embrace a functional aesthetic. Intuitive entry points and wayfinding will include biophilic accents.
Urban Planning | Jun 15, 2023
Arizona limits housing projects in Phoenix area over groundwater supply concerns
Arizona will no longer grant certifications for new residential developments in Phoenix, it’s largest city, due to concerns over groundwater supply. The announcement indicates that the Phoenix area, currently the nation’s fastest-growing region in terms of population growth, will not be able to sustain its rapid growth because of limited freshwater resources.