How Do Windows Crack?

Window cracks can be extremely frustrating to deal with. Not only does it mean that the integrity of the window has been compromised and the temperature-controlled air of your home can sneak out through the crack, no matter how miniscule it may be, but it also means that it’s now necessary to replace your window.

Replacing a window, or even just replacing a single glass pane of a window, can be an expensive process. When the crack has clearly not been caused by an unexpected impact like a falling tree branch or a stray children’s sports ball, you may be wondering: how do windows crack?

What are the causes of window cracks?

Other than the obvious cause (i.e. your window being struck by a hard object), it might seem perplexing to wonder why or how your window cracked, especially if the window is relatively new. However, once you are able to uncover the cause of the window crack, you’ll be able to adjust for the future so that it doesn’t happen again.

Other than cracks caused by impact, window cracks can be caused by the following things: temperature (or thermal stress), pressure, or manufacturing defects.

What is a thermal stress crack on glass?

Thermal stress cracks are caused by a temperature gradient on the glass of the window. They are more common in large windows with a surface area that is partially shaded by an overhang or other type of large object casting a shadow and causing a contrasting coolness to any heat cast by the sun on the rest of the window. 

Basic chemistry tells us that heat causes molecules to expand and cold causes them to contract. If your window is doing both at the same time, chances are that the glass will be placed under a lot of stress from the opposing influences. This thermal stress, if bad enough, can lead to a crack in your window. 

If you think about it, this makes perfect sense. For example, when you take a glass baking dish out of a hot oven and immediately pour ice cold water onto it, if the dish is thin or fragile enough, it will break. Similarly, if you placed a balloon outside in extremely cold temperatures, then brought it inside and touched it with your warm hands, the balloon will pop.

What is a pressure crack?

Pressure cracks are less likely to occur than thermal stress cracks and will usually only happen to insulated windows, but they are something to watch out for. Simply put, pressure cracks occur when the window glass is forced to undergo extreme pressure changes, such as what is often caused by weather. 

Cracks caused by pressure can also happen if the window is installed at drastic elevation levels, whether it is very high or very low. They are usually fairly easy to identify: pressure cracks appear as curves similar to an hourglass shape in the glass. 

How do manufacturing defects cause cracks in windows?

Manufacturing defects can also cause cracks in windows, especially if the window uses insulated glass that has not been sealed or tempered properly. In general, you want to make sure that you are buying high-quality windows from manufacturers that have good reputations. Also, if you are installing new windows in your home, make sure you are consulting a professional or have a solid DIY knowledge beforehand.

While manufacturing defects are less and less common nowadays, if you think the crack in your window might have been caused by one, reach out to the company that made the window and confirm the status of any warranty or lifetime guarantee. If the manufacturer determines that the crack is due to their defective production, chances are they will replace it at no cost to you.

How do avoid cracked windows?

A cracked window and the ensuing repair are both incredibly annoying to deal with. Not only does it cost a lot of money, but it can often be an inconvenient thing to deal with if you have a hectic or busy lifestyle. One of the ways that you can avoid having to go through this is by doing what you can to prevent window cracks in the first place.

The best way to avoid thermal stress cracks is to not have a window installed in a place that might deal with a significant temperature gradient, such as partially obscured by an overhanging object. Similarly, you can remove any objects or structures causing the temperature difference between shadow and heat.

Avoiding pressure cracks is a little more difficult, since it is essentially impossible to control the weather or elevation levels. However, you can be proactive and invest in sturdy windows that are strong enough to withstand intense weather. Some windows are also designed specifically for a unique elevation level, so consider looking into that if you live in a particularly high or low area.

As mentioned previously, avoiding manufacturing defects can really only be done by ensuring that the windows in a home that you purchase or already own are made by a company that has a good, trustworthy reputation. It is also good to verify what kind of warranties or manufacturers guarantees are in place at the time of purchase. \

Final Tips and Conclusion

All in all, window cracks can be caused by a number of things. The most common caused of window crack, besides sudden impact, is thermal stress caused by drastic temperature differences. Cracks can also be caused by pressure and manufacturer defects, though these are less common occurrences. Understanding the cause of the crack in your window can help you avoid future fractures and frustration.

Sometimes, repairing a cracked window doesn’t mean you have to pay to have the entire window replaced. Rather, if the crack is minor, you might be able to replace a single pane of the window, which will be less expensive and likely less of a hassle. If you find a crack in your window, it is always a good idea to ask for advice from a professional or window expert.