All About Thermal Stress Cracks in Windows

Thermal stress cracks are a common problem that affects many homeowners, especially those living in areas with extreme temperature changes.

Thermal stress cracks occur when the temperature difference between the interior and exterior of the window causes the glass to expand and contract rapidly. Read for more information about what thermal stress cracks are, what causes them, and how to prevent them.

What are Thermal Stress Cracks?

Thermal stress cracks are cracks that occur in glass windows due to rapid temperature changes. When the temperature inside and outside of the window changes rapidly, the glass expands or contracts at different rates, causing stress on the glass. If the stress is too much, the glass may crack, leading to a thermal stress crack. Thermal stress cracks typically run perpendicular to the glass and have a pattern that resembles an hourglass, as opposed to a starburst type pattern that appears from a direct impact hit.

What Causes Thermal Stress Cracks?

Several factors can cause thermal stress cracks, including:

Extreme Changes in Temperature

Rapid temperature changes are the primary cause of thermal stress cracks in windows. If the temperature outside is significantly different from the temperature inside, the glass may not be able to adjust to the changes, leading to cracks.

Poor Installation

Poorly installed windows may not have enough room to expand and contract, leading to thermal stress cracks.

Low Quality Glass

Lower quality glass is more prone to thermal stress cracks than high quality glass.

Sun Exposure

Direct exposure to sunlight can cause the temperature of the glass to rise, leading to thermal stress cracks.

How to Prevent Thermal Stress Cracks

There are several ways to prevent thermal stress cracks in your windows.

Use High Quality Glass

High quality glass is less likely to develop thermal stress cracks.

Proper Installation

Ensure that your windows are properly installed and have enough room to expand and contract.

Window Film

Applying window film can help regulate the temperature of your windows and prevent thermal stress cracks.


Proper ventilation can help regulate the temperature inside your home and reduce the temperature difference between the inside and outside of your windows.

Avoid Direct Sunlight

Avoiding direct sunlight on your windows can help reduce the risk of thermal stress cracks.

Thermal Stress Cracks Conclusion

Thermal stress cracks are a common problem that can affect any homeowner. They can be frustrating, and the cause of it might not be obvious at first. Unlike the window being at direct impact, stress cracks seem to appear out of nowhere.

By understanding what causes thermal stress cracks and how to prevent them, you can ensure that your windows remain intact and functional. If you have concerns about thermal stress cracks or want to replace your windows with high quality options, contact Reflect Window & Door for guidance and solutions.


Reflect Window & Door’s team of expert window contractors is available for almost any project, regardless of how small or large it may be, in Edmonton and surrounding areas including St. Albert, Sherwood Park, Northwest, Beaumont, Devon, Lamont, Calmar, Morinville, Redwater, Busby and Sandy Beach. Schedule a free consultation today!