Famed for its robust design, both in terms of the frames and the glass used, double glazing is the favoured choice for many for its durability and security credentials. Gone, it seems, are the days of young boys working off the debt to replace a window pane shattered by a wayward football. 

However, as strong as they are, double glazed windows are not completely unbreakable and, although rare, there are a number of factors that may cause a double-glazed window to shatter. 

broken double glazed glass

Manufacturing error 

The most common cause of weakness in double glazing is manufacturing error, which is why you should only ever buy from a reputable supplier offering a warranty on their products. 


Scratches in the glass, caused during the manufacturing process, can create weak spots in the glass, leading them to be more likely to shatter under impact. Again, a reputable manufacturer with appropriate manufacturing procedures will ensure the glass is only cut at the edges. 

Temperature and humidity

There are environmental factors that can put a strain on your windows, particularly in the winter. When the temperature inside and outside the home contrasts too greatly, the window will be under increased pressure. The glass in your window will usually be strong enough to withstand this but extreme conditions or inherent weakness could cause the glass to crack spontaneously. 

South facing windows are at particular risk of this phenomenon as they receive most sunlight, particularly during the winter. Warming during the day and then cooling at night can cause the glass to crack. You can mitigate this by ensuring south facing windows have curtains to reflect the heat back onto the glass and keep the temperature of the window regulated. 

What to do with a broken window 

In most cases, a broken window should be covered by your warranty, particularly where a fault in the manufacturing or installation process have led to the breakage.

If your windows are out of warranty, it is important to replace the window as soon as possible. A cracked window will cause a draught in your home, making it harder to keep warm and negatively impacting your heating bills. There are also security concerns as a cracked window is easier to break fully, and this may even invalidate your insurance. 

At Progress Windows, we supply and install locally manufactured uPVC windows from reputable manufacturers, such as TruFrame in Leicester, and our window profiles from Liniar. Whether you’re looking for a new window installation, or replacement windows, or even just a repair, book an appointment with us to see how we can help.