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
Hotel Facilities | Jul 28, 2022
As travel returns, U.S. hotel construction pipeline growth follows
According to the recently released United States Construction Pipeline Trend Report from Lodging Econometrics (LE), the total U.S. construction pipeline stands at 5,220 projects/621,268 rooms at the close of 2022’s second quarter, up 9% Year-Over-Year (YOY) by projects and 4% YOY by rooms.
Codes and Standards | Jul 27, 2022
Biden administration proposes drastic flood insurance reform
The Biden administration’s proposed major overhaul to the National Flood Insurance Program, or NFIP, would drastically alter how Americans protect homes and businesses against flooding.
Concrete | Jul 26, 2022
Consortium to set standards and create markets for low-carbon concrete
A consortium of construction firms, property developers, and building engineers have pledged to drive down the carbon emissions of concrete.
Green | Jul 26, 2022
Climate tech startup BlocPower looks to electrify, decarbonize the nation's buildings
The New York-based climate technology company electrifies and decarbonizes buildings—more than 1,200 of them so far.
Education Facilities | Jul 26, 2022
Malibu High School gets a new building that balances environment with education
In Malibu, Calif., a city known for beaches, surf, and sun, HMC Architects wanted to give Malibu High School a new building that harmonizes environment and education.
| Jul 26, 2022
Better design with a “brain break”
During the design process, there aren’t necessarily opportunities to implement “brain breaks,” brief moments to take a purposeful pause from the task at hand and refocus before returning to work.
Building Team | Jul 25, 2022
First Ismaili Center in the U.S. combines Islamic design with Texas influences
Construction has begun on the first Ismaili Center in the U.S. in Houston.
Codes and Standards | Jul 22, 2022
Office developers aim for zero carbon without offsets
As companies reassess their office needs in the wake of the pandemic, a new arms race to deliver net zero carbon space without the need for offsets is taking place in London, according to a recent Bloomberg report.
Codes and Standards | Jul 22, 2022
Hurricane-resistant construction may be greatly undervalued
New research led by an MIT graduate student at the school’s Concrete Sustainability Hub suggests that the value of buildings constructed to resist wind damage in hurricanes may be significantly underestimated.
School Construction | Jul 22, 2022
School integrating conventional medicine with holistic principles blends building and landscape
Design of the new Alice L. Walton School of Medicine in Bentonville, Ark., aims to blend the building and landscape, creating connections with the surrounding woodlands and the Ozark Mountains.