Windscreen damaged in the swept area

What causes it

• Stone impact thrown up by the vehicle in front, most often on motorways and freshly chipped surfaces
• Thermal shock — scraping ice off, or aiming hot air at a frozen screen, which turns a small chip into a long crack
• Body flex over potholes and speed bumps propagating an existing chip
• A poor resin repair, or a screen fitted with a stress point at the edge of the bond line

Advisory or failure?

The screen is assessed by zone. Zone A is a 290mm-wide strip centred on the steering wheel and inside the area swept by the wipers; damage larger than 10mm anywhere within it is a major defect and a failure. Across the rest of the swept area the limit is 40mm. Damage outside the swept area is not itself a failure unless it obscures the driver's view of the road, or the screen is damaged badly enough that its structural integrity is affected. The same measurements apply to anything else in the way — a sticker, a dashcam mount or a satnav bracket in Zone A fails on exactly the same 10mm limit as a stone chip. A repaired chip is measured as it now appears, so a clean resin repair leaving a small mark will usually pass where the original chip would not have.

Can you fix it yourself?

Possible with care

DIY resin kits exist and can work on a small, fresh, clean bullseye chip, but they are unforgiving: any moisture or dirt in the break stops the resin bonding, and a botched attempt leaves a permanent mark that a professional can then no longer repair properly. Since most fully comprehensive policies cover chip repair with no excess and no effect on the no-claims discount, there is rarely a good reason to do it yourself. What is genuinely worth doing is acting fast — put clear tape over a fresh chip to keep water out and book it in, because once a chip has spread into a crack it is no longer repairable. Full replacement is never a home job: modern screens are bonded structural components, and any car with a forward-facing camera needs it recalibrated afterwards.

What it costs

A resin chip repair is £50 to £90 and takes under an hour, and is free at the point of use under most comprehensive policies. A replacement screen for an older car with no electronics in it is £150 to £250 fitted. What drives the price to the top of the band and beyond is the glass specification: rain sensors, heating elements, acoustic laminate, head-up display and above all a forward-facing camera for lane keeping and autonomous braking, which must be recalibrated after fitting at £80 to £150 on top. Check the policy before paying anything — a windscreen excess is typically £75 to £115, which is often more than a repair and less than a replacement.

What happens if you ignore it

A chip in Zone A is a failure today and a crack across the whole screen after the first hard frost, at which point a £70 repair has become a replacement. A cracked screen also weakens a component the car depends on structurally — on most modern cars the bonded windscreen contributes to roof strength in a rollover and provides the surface the passenger airbag inflates against. Driving with your view of the road obscured by damage is an offence in its own right, quite separate from the MOT.

Other common defects

• Brake disc worn, pitted or scored
• Brake pads wearing thin
• Braking efficiency below requirement
• Tyre worn close to the legal limit
• See all defects →