What causes a cracked windscreen?

With summer finally on its way, it’s worth pointing out that hot weather leads to more cracked windscreen claims as glass expands in the heat. Here is everything you need to know.


A cracked windscreen can cause major safety hazards – it can obstruct a driver’s vision and even prevent the airbag from opening in the event of an accident. Those little windscreen nicks could become a big problem very quickly.

Summer often sees a surge in calls to windscreen repair companies for replacement glass services. This is often because glass expands in the heat and, when external heat is combined with air conditioning and pre-existing chips, it causes windscreens to crack.

The difference in temperatures between the heat outside and the cold interior of your car can put pressure on the windscreen and cause pre-existing chips or cracks to grow larger and spread.

Can direct sunlight cause windscreen cracks?

Direct sunlight is as damaging to glass as it is to humans and one of the top causes of windscreen cracks. The heat alone will not cause windscreen cracks, however cooling the glass rapidly when it is heated is a direct cause of extensive cracking.

The hot and cold temperatures cause the windscreen to expand and contract respectively, which weakens the structure of the glass, therefore making it more prone to damage.

The process usually begins when cars are parked in direct sunlight without any method of protection, for example a sunshade. Summer sunshine will heat the glass of the windscreen, causing the interior of the car to heat up also. Of course, when you get into the car, the first thing most drivers do is blast the cold air conditioning at its maximum setting to cool down, however this could be detrimental.

It is important to avoid a significant difference between the temperatures of the interior and exterior.

How to stop windscreen cracks

Unfortunately, there is nothing we can do prevent gravel, stones, or rocks from hitting our windscreens while we are driving, but there are some things we can do in the hotter months to reduce the risk.

  • Examine the glass frequently, as small chips which can easily be caused by loose gravel or stones on roads can be very difficult to notice, yet can lead to large cracks under the right conditions, i.e., the summer sun.
  • To prevent your windscreen from cracking, park in the shade and avoiding direct sunlight for extended periods of time, or purchase a simple sunshade.
  • If your windscreen is hot from the sun when you enter your car, do not try to cool your car by ramping up the cold air conditioning straight away.
  • A similar rule applies in winter, where you must never use boiling water to clear an icy windscreen, as a crack is your most likely result.
  • Check your windscreen wipers for dirt and debris which could aggravate any existing cracks you may not have noticed.
  • When you are on the road, maintain a safe distance from the vehicle in front. If something were to fall from their vehicle, you may have time to move out of the way.
  • It is important to have any small windscreen chips or cracks repaired as soon as possible to prevent them from spreading, and to avoid the greater inconvenience and cost of having to replace your windscreen entirely.
  • If you have repaired windscreen chips or cracks yourself, you may find that your vehicle now has poor glass quality. Proceed with caution and ensure any future chips or cracks are repaired by the professionals.

Can you drive with windscreen damage?

If you are hoping to put the repair off for a while, due to concerns over costs or because it appears to be very small, think again. Driving with a cracked windscreen could be considered a motoring offence.

The Highway Code states that all vehicles need an MOT, which ensures they are roadworthy under Rule 97. These regulations also say glass surfaces like wing mirrors or windows cannot obstruct vision so as not compromise safety while driving.

Legally, drivers need to have full visibility of the road, so if that view is blocked, it can result it a fixed penalty of three points on your licence as well as a fine. If you are involved in an accident while driving with a cracked windscreen, it could make it more likely that it would be deemed to be your fault.

If you have a chip of 40mm anywhere on the windscreen, your car will fail its MOT. If it is smaller, at 10mm and in front of the driver, that is also an instant fail. If you have any chips or cracks on your windscreen, ensure you get them fixed before heading to your MOT.

As your car should be in roadworthy condition to drive it, you will need to avoid driving it if there are cracks on the windscreen and until the windscreen cracks are repaired. The good news is that there are many windscreen repair services which can come directly to you, helping you to avoid the risk of driving with a cracked windscreen.

Can a cracked windscreen be repaired?

To find out whether you can repair the windscreen crack, it is important to know that the size and severity of the chip determines whether it can be easily repaired or require an entire windscreen replacement. Contact a windscreen repair specialist to find out whether the crack is repairable.

As a rule of thumb, if you have a small crack up to the size of a £1 coin, a simple windscreen repair should do the trick, depending on where it is on the windscreen. You can do this yourself with a windscreen repair resin kit, generally available online, or preferably, use a specialist technician such as AutoGlass.

Take a look at this handy video by AutoGlass which can help you decide if your windscreen is repairable, or will need replacing:


Using a professional windscreen repair services offers a far greater guarantee that the work has been carried out to higher safety standards. The last thing anyone wants is to be driving and another stone hits the existing crack repair and it smashes the windscreen.

A specialist technician repairs cracked windscreens using superior quality tools and resins than you are able to purchase online yourself. They will clean the entire crack prior to refilling it, ensuring that no particles or moisture remain in it which could cause issues with integrity later.

How much does it cost to repair a windscreen crack?

The longer you leave it, the more expensive it could become.

You will find that many repairs are inexpensive, sometimes even free, and completed in under 30 minutes.

The AA estimates that the average repair costs between £50 – £70, while a full windscreen repair will set you back from £100 to around £500 depending on the vehicle you are driving.

Sometimes windscreen repair services are available in supermarket car parks, and many are willing to travel to your home or place of work to carry out a repair.

How do you repair a windscreen crack?

As this depends on the size, there are a couple of different options available to you in how you go about repairing your windscreen crack or chip.

If you have a small crack in the windscreen, of up to 10mm long, it is quicker and cheaper to tackles this right away, even if it does not impact the drivers view. If left it can spread across the windscreen.

A chip can be repaired by injecting an acrylic or epoxy adhesive into it to seal it and prevent any dirt or moisture from entering it.

Larger cracks in the windscreen can sometimes still be repaired without replacing the window but will need specialist repair. However, it is worth noting that cracked side or rear windows are usually likely to need replacing as opposed to repairing so contact the professionals in the first instance.

Any window crack could have grave consequences in the event of an accident.

Are windscreen cracks insured?

Most comprehensive insurance policies do cover windscreen repair, so it is often best to call your insurer to find out what you are covered for if you are not sure.

Many insurers will direct you to their windscreen specialists who will work with you directly to resolve the problem. This could involve a simple repair on your doorstep, or you may need to have your windscreen replaced, however if you are covered for it, it is important to take their advice and do whatever is necessary to keep you safe on the roads this summer.

If you have a policy with us and are not sure what you need to do, give your local A-Plan branch a call and we will be happy to help you.