Last summer Southern California saw record breaking temperatures for prolonged periods. This year will likely see similar stretches of extreme temperatures. Recently, many of our clients have asked us how they can prevent heat damage to their homes. While there are many insulation and cooling options that can protect your home from heat, there’s one part of the home that often gets overlooked and that is the windows.
Extreme weather can not only heat up your home or business but it can also shatter your windows. Broken windows in the summer can often be attributed to thermal stress. A few years ago, we helped a client whose newly installed windows—nine of them—had mysteriously cracked without any apparent impact. After investigation, we concluded thermal stress was indeed the culprit.
Our advice at Helfrich Associates is always: don’t put off until tomorrow what you can fix today, this week or this month. As structural engineers working with homeowners and insurance companies, we’ve seen lots of damage to homes ranging from accidental fires to wind to quakes to neglect. Accidents happen, but damage from deferred repairs or maintenance is preventable and often gets more costly the longer you wait.
In addition if you’re living in an un-remodeled Southern California classic 1950’s or 1960s’ ranch home, then you likely don’t have the latest generation of advanced material dual pane window technology with its insulating advantages for the hot summer months as well as in the cold winter season. New dual pane windows can reduce the load on your HVAC system—and the monthly bills too.
Thermal heat stress occurs when different parts of a window experience varying temperatures, such as when sunlight heats different sections of the glass, especially if partially shaded by eaves or awnings. This phenomenon is most common during spring and autumn due to significant temperature fluctuations between day and night. Other causes include changes in shading, such as the removal of a large shade tree or new construction nearby.
In this case involving cracked or broken windows, we began by reviewing the temperature and wind data for the home’s location using the Weather Underground website. For example, this data could tell us that the temperature ranged from a high of 81°F to a low of 37°F, with wind speeds varying from 0 to 24 mph and gusts up to 38 mph.
We also reviewed extensive photographic evidence of the damage. After reviewing the photos, we knew this wasn’t a case of an impact break, because there were no spider cracks emanating from a single point, which would be evidence of impact breakage. So, we knew it wasn’t a case of local kid mischief throwing rocks or swinging bats, etc., or an attempted break-in either.
In this particular case, the data after analysis told us and the homeowner that thermal stress breakage was the problem because the window glass was cracked perpendicular to the edge, which indicated thermal stress cracking. Photo evidence taken from the home, along with the site weather conditions identified above, indicated temperature differentials which caused thermal stress in the glass sufficient to crack the windows.
Cool night time temperatures, warm day time temperatures, a vacant house (which most likely cooled to approximately outside temperatures at night), the sun starting to warm the glass in the afternoon, and the inside temperature of the house being cool — these combined factors caused the glass to warm differentially, thus creating thermal stress and causing the glass to break.
There are limited options to prevent such breakage. This is due to the natural expansion and contraction of glass. Potential solutions include installing thicker panes of glass or working with an architect to place windows in areas with less intense sun exposure during construction. Some manufacturers also produce glass designed to be more resistant to breakage.
Have you experienced window breakage due to thermal stress? Share your story in the comments. If you need assistance with your windows, contact us for expert help in diagnosing and resolving whatever the issue might be or if you need assistance in determining how best to get more sunshine in your current home with the latest technology solutions.