How much snow and ice do I have to clear off my car before driving?
The Highway Code sets out exactly what must be cleared before you set off, including the bit most people skip. What the requirement covers, and how to do it in five minutes rather than twenty.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 4 min
- Safety
- caution
Short answer
Rule 229 of the Highway Code requires you to clear all snow and ice from all windows, make sure lights are clean and the number plates legible, demist the windows thoroughly, and remove any snow that might fall off into the path of other road users — which is the roof. A peephole scraped in the windscreen is not compliance, and snow left on the roof can slide onto your own screen the first time you brake hard.
Almost everyone knows the windscreen has to be clear. Far fewer know that the roof is explicitly covered, and that is the one that causes trouble — a slab of compacted snow that slides forward under braking blinds you completely at the exact moment you were braking, or leaves the car and hits the windscreen of the driver behind at combined speed. There is no offence specifically called "driving with snow on the roof", but a vehicle in a dangerous condition, or a driver whose view is obscured, are both things the law has plenty to say about.
Safety
Step by step
- Start the engine and put the demisters on first.Front and rear screen heaters, blowers on the windscreen, air conditioning on if you have it because it dries the air. Then go and do the physical clearing while it works from the inside. This is what turns a twenty-minute job into a five-minute one.
- Clear every window, not just a patch.Rule 229 says all snow and ice from all windows. That includes the rear screen and both front side windows, which are the ones people leave and then cannot see out of at junctions.
- Do the roof.Rule 229 requires you to remove snow that might fall into the path of other road users. A soft brush or a snow broom does it in seconds. This is the step most drivers skip and the one with the clearest legal basis.
- Clear the lights and the number plates.Also specifically named in rule 229. A rear light packed with snow is invisible in exactly the conditions where you need to be seen, and an obscured number plate is a separate offence in its own right.
- Clear the mirrors and the bonnet.Mirrors are in the rule. The bonnet is not, but snow on it blows up onto the screen as you gather speed and is trivial to sweep off while you are there.
- Lift the wipers before you scrape, and check they are free.Wiper blades freeze to glass and switching them on tears the rubber or strips the motor. Free them by hand first, and if they are frozen solid, wait for the demister to release them.
- Use a proper scraper and de-icer, not household improvisation.A plastic scraper and an aerosol de-icer, or a screenwash mix at winter concentration through the washers, is the fast and safe combination. A credit card scratches glass, and hot water risks cracking it.
- Check the snow is not blocking the air intake.The vents at the base of the windscreen feed the heater and demister. Packed with snow, the demister cannot work and the inside of the car fogs up as you drive.
Common mistakes
- Scraping a letterbox-sized hole and setting off — It fails the Highway Code requirement, leaves you unable to see anything at junctions, and is the classic example given when drivers are prosecuted for having an obscured view.
- Pouring hot or boiling water over the glass — The sudden temperature change can crack a windscreen outright, and it is far more likely to do so if there is an existing chip. The water then refreezes as a smooth sheet, which is worse than the frost was.
If it doesn't work
Windscreen refreezes as you clear it
Cause: Very cold glass and moisture from the air or from washer fluid — Fix: Get the demister working from inside first and use a de-icer rather than water. Screenwash at summer concentration will freeze on the glass and make it worse.
Wipers smear on the first use
Cause: Grit and ice on the blade edge — Fix: Wipe the rubber with a cloth before using them. A blade that has been dragged across ice is often damaged and needs replacing.
Doors frozen shut
Cause: Water in the seals — Fix: Push firmly on the door around the seal to break the bond rather than pulling the handle hard, which can tear it off. Prevent it with a silicone spray or a wipe of glycerine on the rubber seals in autumn.
Snow keeps blowing back onto the screen from the roof at speed
Cause: Roof not cleared — Fix: Pull over safely and clear it. It also means there is snow leaving your car, which is the part that affects other people.
Frozen washer jets
Cause: Screenwash too dilute — Fix: Use winter-strength screenwash concentrate. Plain water freezes and can crack the washer bottle or the pump, which is an avoidable repair.
Questions people ask
Is it actually illegal to drive with snow on the roof?
There is no offence with that name. Rule 229 of the Highway Code requires you to remove snow that might fall into the path of other road users, and separate legislation covers using a vehicle in a dangerous condition and driving with an obscured view. In practice, snow leaving your roof and hitting someone else is exactly the situation those provisions exist for.
How long can I leave the car running to defrost it?
That question has its own answer and it is more constrained than most people think — leaving a parked vehicle unattended with the engine running on a public road is prohibited by rule 123 of the Highway Code. The catalogue's guide on idling to defrost covers what that means in practice.
Does a windscreen cover help?
Yes, considerably, if you park outside. It prevents the frost forming rather than removing it afterwards, which is much less work, and it also keeps the wipers off the glass.