How to De-Ice a Frozen Windscreen Safely

A frozen windscreen is a ten minute job if you do it in the right order, and a cracked windscreen or a damaged wiper motor if you do not. The rule is simple: clear every window completely, inside and out, before you move. All windows should be demisted and fully cleared of any frost, snow or ice before setting off¹. The Highway Code requires you to be able to see out of every glass panel in your vehicle².

Use a scraper and de-icer, not boiling water. Run the engine with the heater on the windscreen if you need to, but stay with the car while it runs. And clear the roof, lights and number plate as well as the glass: clear ice off all windows, lights, number plate, and vehicle roof before you set off³.

Clear every window before you drive

The windscreen is only part of the job. Official guidance is consistent across the UK: clear ice, snow and condensation completely from your windscreen and all windows before setting off⁸. North Wales Fire and Rescue Service puts it plainly: "Don't simply clear a 'porthole' to look through."⁹ A small clear patch gives you a view straight ahead and almost nothing else, and the side windows and mirrors are what you need at junctions.

Set aside enough time to do it properly before work rather than rushing it⁵. The full list of what to clear is longer than most people think:

• Every window, inside and out, including the rear screen⁹
• The roof, because snow sliding forward onto the windscreen under braking blocks your view³
• Lights and the number plate, so you can be seen and identified⁴
• Mirrors, cleared completely of snow and ice¹⁰
• The inside of the glass, de-misted before you set off¹¹

The legal position is worth knowing. The Highway Code stipulates you must be able to see out of every glass panel in your vehicle⁸, and you must keep your front and rear windscreen clear of snow and ice before driving¹². Driving with snow or ice may potentially be a criminal offence if driving under reduced visibility¹³. That is the reason the guidance is so firm about the roof and the side windows, not just the bit you look through.

The arrangements are the same in all four nations, since the Highway Code applies across the UK. What differs is who is telling you: Traffic Scotland advises making sure you have full visibility through your windscreen and de-icing the car inside and out⁹, and Cornwall Council advises clearing your windows and mirrors before you set out and carrying a screen scraper and de-icer⁴. For the wider picture on winter roads, see Driving in Snow and Ice: Staying Safe on the Road.

Use a scraper and de-icer, never boiling water

The method is straightforward. Clear all windows using a scraper and de-icer, and do not drive off with a tiny hole cleared in the windscreen⁵. Keep de-icer spray handy to clear your windows quickly, because it is dangerous to drive without full visibility through your vehicle's windows¹⁴. An ice scraper and de-icer are basic winter items, listed in the Met Office winter car kit alongside jump leads, a reflective warning triangle, sunglasses, an in-car phone charger and a blanket¹⁵.

Boiling water is the mistake to avoid. A sudden change of temperature on cold glass risks cracking it, and any water left behind refreezes, often as a thicker sheet than you started with. No official source recommends it. Use de-icer and a scraper instead.

Two other things catch people out. First, do not add anti-freeze to your windscreen washer bottle: it is corrosive and will damage paintwork¹⁶. Use winter screen wash instead, which stops the water in the bottle freezing¹. Second, more often than not you will actually clear your windscreen faster using cold air than hot air⁶. That is worth knowing when you are in a hurry and the heater is still blowing cold.

For the washer bottle, top up with a good quality screenwash which protects down to at least -10C, and have some de-icer on hand in the house⁷. The two documents disagree, so check the label on the bottle and pick one that states its protection temperature clearly.

Run the engine with the heater on the windscreen, staying with the car

Running the engine for a few minutes before your trip helps clear the windscreen¹⁷. Set the heater to windscreen de-misting and open all the vents to keep your windscreen clear¹⁸. If your car is fitted with air conditioning, use it, as it will stop the windows from misting up².

The safety rule is the one people break. If you leave the car running to warm up while you go back inside, you are leaving an unattended vehicle with the keys in it, and you are not watching for anything going wrong. Stay with the car while the engine runs.

That advice comes from guidance on being stuck in a winter storm in a remote area, but the principle applies whenever an engine is running in still, cold conditions. If you are caught out and have to wait in the car, Ceredigion County Council advises running the engine and heater for about 10 minutes every hour to keep warm, opening a window slightly while it runs and clearing snow from the exhaust pipe²⁰. Move around to keep warm but avoid over-exertion, and make sure someone stays awake to watch for rescue teams¹⁹.

If you are likely to be out in bad weather, the Met Office winter car kit is worth keeping in the boot: ice scraper and de-icer, jump leads, a reflective warning triangle (ideally two), sunglasses, an in-car phone charger and a portable battery charger, and a blanket¹⁵. Transport Scotland also lists de-icer spray as part of a vehicle emergency kit, for the same reason: full visibility¹⁴.

Stopping the windscreen freezing overnight

A little preparation the night before saves the scraper work in the morning. The simplest measure is to stop the wipers sticking to the glass. In very cold weather, you can prevent your windscreen wipers getting stuck to the glass by putting something under them, like a thin piece of plastic, cardboard, newspaper or even some old socks⁷. Lift the blades gently, slide the material underneath, and remove it before you drive.

For misting on the inside, West Yorkshire Prepared suggests a household trick: clean the windscreen with shaving foam to prevent it misting up, though the barrier will need to be reapplied²¹. It is not a substitute for proper demisting on a cold morning, but it reduces how much condensation forms.

Other overnight measures from official guidance:

• Check the wipers before winter sets in. Top up anti-freeze and screen wash and check for wear and tear on wiper blades²².
• Keep the washer bottle full. Keep the windscreen and windows clean and the washer bottle filled with screenwash²³.
• Use a screen wash additive to keep your windscreen free of winter road grime caused by road salting and gritting²⁴.
• Check wipers, tyres and screen wash before setting off in icy weather²⁵.

There is no official recommendation in this guidance for covers, windscreen blankets or sprays applied the night before, so treat them as a matter of personal choice rather than a rule. What the councils and the Met Office do recommend is the simple, cheap routine: clear the glass properly, keep the washer bottle topped up with the right screenwash, and look after the wipers.

If the cold snap is part of a wider spell of severe weather, it is worth reading Getting Your Home Ready for Cold Weather and Ice as well, since the same conditions that freeze your windscreen can freeze pipes and leave you without water.

What can go wrong: cracked glass, smears and damaged wipers

Most frozen windscreen problems come from rushing. Here is what tends to go wrong, and how to avoid it.

Wiper blades are the part most often neglected. Regularly check your windscreen wipers and renew them if they are worn or damaged³. To test them, spray some washer fluid and check the wipers clean the windscreen, then run your fingers along the blades to check for splits¹⁵. A blade that smears is not doing its job, and in low winter sun a smeared windscreen can hide a cyclist or a pedestrian at a junction.

If the roads themselves are the problem rather than the glass, What to Do If You Hit Black Ice and How Much Longer Are Stopping Distances on Ice? cover what changes once you are moving. And if you want a full pre-winter routine for the car, the Car Checks Before Winter checklist sets it out step by step.