Self Cleaning Glass and Whether It Still Needs Cleaning

Self-cleaning glass cleans itself less rather than never. It has a permanent coating that breaks down organic dirt and uses rain to wash it away, but it still gets dirty during dry spells or if it sits under an overhang. You will still need to wash it occasionally, and using the wrong tools or chemicals can damage the coating for good.

What self-cleaning glass is

Self-cleaning glass features a thin, clear and permanent titanium oxide coating on the external pane. The glass manufacturer applies the coating at the factory during manufacture to bond it permanently to the surface. There is no spray-on equivalent you can buy to add to standard windows later.

You can buy the glass as a single pane or built into a sealed unit. This means the glass can be bought without replacing a whole window frame. It is often installed in places like conservatory roofs or skylights.

The coating relies on both daylight and rain to function. Because of this, it is not used for internal glass such as shower screens, indoor partitions or interior doors. Under normal circumstances, the coating lasts as long as the glass itself.

How the coating works with daylight and rain

The dual-action self-cleaning coating works in two distinct stages. First, the coating is photocatalytic. It reacts with daylight to break down organic dirt sitting on the surface. There is enough ultraviolet light to activate the coating even on north-facing glass.

You might notice slight silvery spots on the pane during this first stage. This simply means the coating is breaking down the dirt and the spots are temporary.

Second, the coating is hydrophilic. When it rains, the water does not form separate droplets on the glass. The rain spreads evenly over the pane in a thin film instead. This sheet of water washes away the loosened dirt and dries quickly without leaving streaks.

Why it still gets dirty and how to clean it safely

The coating breaks down organic dirt, but it cannot destroy everything. Road and building dust is mostly inorganic and is not destroyed by the coating. You have to wait for rain to wash this dust away or hose the glass down yourself. Heavy bird droppings take a while to break down and often need washing off manually before the coating can clear them completely. Coastal sand and salt also sit on the surface until rain or a hose clears them away.

The glass will also stay dirty if the rain cannot reach it. Deeply recessed windows or glass under an overhang get no rain and will need hosing. During long dry spells, dirt will build up on all the glass. You might also see streaks after light rain following a dry spell, as a light shower does not provide enough water to wash the loosened dirt away.

During long dry spells, or for glass under overhangs, you can clean the pane by simply hosing it down with clean, soft water. You should hose the glass from the top down and let it dry naturally. Do this in the shade or at the coolest part of the day. No rubbing or squeegee action should be needed to remove everyday dust, salt or bird droppings. The water will sheet over the glass and wash the loosened dirt away.

If glass you can reach safely from the ground needs more than a hose, you can wash it by hand. Leave roof glass and upper windows to a professional, and never go onto a conservatory roof. Hand cleaning should use a mild detergent solution, such as warm water with soap like washing-up liquid. Apply it with a gentle lint-free cloth, and then clean with a soft-water rinse. You must always apply water before trying to clean dirt off the pane. Dry rubbing will drag grit across the surface and risk permanent scratches.

What damages the coating and removing stubborn marks

The coated surface can be permanently damaged by inappropriate techniques. The manufacturer makes it clear that scratches from harsh metallic contact cannot be put right by polishing or any other method. You must keep certain tools and chemicals completely away from the glass.

• Do not let razor blades, steel wool or other metal objects touch the coating.
• Avoid using any cleaning products with abrasive particles or powders.
• Keep silicone away from the pane entirely.
• Do not use solutions containing hydrofluoric acid or fluorine compounds.
• Do not let harsh alkali solutions from adjacent brickwork cleaners touch the coating.

Building work and decorating can easily mark the glass. Fresh paint or sealant should be removed immediately with a solvent wipe before it sets. You can use acetone, isopropyl alcohol, methylated spirits or white spirit. Wipe the mark carefully without spreading the solvent over clean areas, then wash and rinse the glass. If you have sticky marks left by window labels, you can read more about how to remove sticker residue.

Dried paint, sealant or adhesive needs a different approach. You should wet the mark with a solvent-soaked pad until it dissolves, without rubbing. Residual cured sealant is harder to remove and abrasive materials must not be used. After solvent cleaning, the coating in the cleaned area is reactivated after five to seven days.

Silicone getting onto the glass should be left to dry and peeled off. You must never cut or scrape it.

Fresh mortar or cement splashes must be removed immediately with plenty of water and a soft sponge. You should dab the splash rather than rub it. Mortar or cement splashes, and the run-off containing them, can attack the coating. This cannot be put right once it has happened. If cement splashes are likely during building work, you need to apply film protection to the glass first. If you have cement on standard glass, check out how to remove paint and cement.

Hard water and white streaks

The manufacturer advises that rinse water should not be hard, and recommends using soft or distilled water. Water hardness is caused by dissolved calcium and magnesium and varies with local geology. According to the Drinking Water Inspectorate, hard water causes scale and leaves tide marks on basins, sinks and baths.

If your tap water is harder than 180 ppm, hosing the glass can leave milky-white streaks. You can minimise this by not hosing at the hottest time of day.

To reduce the marks, you can use a domestic water softener. You can also add a couple of drops of washing-up detergent per litre of rinsing water. If you already have white marks on standard glass, you can look up how to remove water marks.

Is self-cleaning glass worth choosing for new glazing?

Upgrading to self-cleaning glass normally costs a modest amount more than standard glass. It reduces how often you need to clean your windows and leaves fewer streaks after rain. It is often chosen for conservatory roofs, roof windows and large fixed panes that are difficult to reach.

It is not entirely maintenance free. You will still need to wash it during dry spells, and it requires careful handling to avoid permanent damage. Because it needs rain to wash the dirt away, it offers little benefit for glass positioned under deep overhangs or sheltered porches.

Hiring a window cleaner for self-cleaning glass

Many homeowners hire a professional to clean difficult areas like a conservatory roof or skylights. Many window cleaners now work from the ground with a water-fed pole rather than ladders.

Industry guidance hosted by the Health and Safety Executive explains that a water-fed pole is a telescopic pole fitted with a brush that delivers purified water. The purified water is an integral part of the cleaning process. The glass is scrubbed, rinsed and left wet. Because the minerals have been filtered out, the water is meant to dry without marks.

A first pole clean can leave some spotting until old residue has been rinsed out. Crucially, this purified water method suits the manufacturer's advice to rinse the self-cleaning coating with soft water.

Window cleaning is normally priced per visit according to the size of the property, the number and type of windows, access and frequency. It is not priced by the hour. Most domestic window cleaning is done on a round, where the same cleaner returns on a set cycle, commonly every four, six or eight weeks. A first clean or a one-off clean usually costs more than a regular visit. Extras like conservatory roofs, roof windows and glazed doors are priced on top. London and the South East cost more.

You must tell your window cleaner that the glass is self-cleaning before they start. You need to agree a gentle cleaning method that protects the coating.

• Ask them to use their water-fed pole with a soft brush head.
• Confirm they will not use scrapers or razor blades to remove stubborn marks.
• Check they will not use abrasive pads on the glass.
• Ask them not to use a squeegee unless they guarantee no metal parts will touch the pane.
• Agree that they will wash the glass gently rather than scrubbing heavily.

A quote is a fixed price, whereas an estimate is not. You should get a firm quote for the work. You should also watch out for cold callers who claim to be your usual cleaner and ask for payment, or cleans carried out without agreement followed by a bill. You should never pay months in advance.

Your rights and protections if things go wrong

Under the Consumer Rights Act 2015, a service must be carried out with reasonable care and skill. If it is not, the customer can ask for it to be put right or for money back. A service agreed on the doorstep, by phone or online normally carries a 14-day cooling-off period.

Public liability insurance is not a legal requirement, but it is the cover that pays if a cleaner damages property or injures someone. You should always ask for a current certificate to ensure you are covered if they scratch the coating permanently. Employers' liability insurance is compulsory for a business with employees.

If your cleaner needs to work at height, the Work at Height Regulations 2005 require the work to be properly planned, done by competent people and avoided where reasonably practicable. This is why many cleaners now work from the ground with poles. Ladders are not banned, and the Health and Safety Executive says ladders can be a sensible option for low risk, short duration work, including domestic window cleaning on lower floors. The law asks for competence, not a formal qualification.

Industry guidance produced with the Health and Safety Executive says water-fed poles must not be used near overhead power lines. You should point out any overhead cable to the cleaner before they start.

If you live in Scotland, most councils require window cleaners to hold a window cleaner's licence under the Civic Government (Scotland) Act 1982, and licence holders carry identification. Requirements vary by council.

You might also look for membership of the Federation of Window Cleaners. Established in 1947, it is a non-profit trade body with a code of practice, a safety accreditation scheme and training. Membership is voluntary, so treat it as one good sign among several.

Common questions

How does self-cleaning glass work?

It uses a permanent dual-action coating on the outside of the pane. Daylight breaks down organic dirt on the surface, and rain spreads over the glass in a thin sheet to wash the loosened dirt away.

Can you use self-cleaning glass indoors?

No, it is not used for internal glass such as shower screens. The coating needs both daylight and rain to function, so it only works on the external face of a building.

Can you buy a self-cleaning glass coating spray?

There is no spray-on equivalent. The thin titanium oxide coating is applied at the factory during manufacture and lasts as long as the glass itself.

Why is my self-cleaning glass roof dirty?

It might be covered in inorganic dirt like road dust or coastal salt, which the coating cannot break down. It might also be dirty because there has been a long dry spell, or light rain that was not heavy enough to wash the dirt away.

Your next steps

If you are planning to hire a professional to clean your windows or conservatory roof, you should make sure they know how to handle coated glass safely.

• Tell any window cleaner you contact that you have self-cleaning glass.
• Ask if they use a water-fed pole with purified water, which acts as a soft water rinse.
• Agree that no metal tools, scrapers or abrasive pads will be used on those panes.
• Ask for a current public liability insurance certificate before they start work.
• Point out any overhead power lines if they are working with long poles.

Taking a few minutes to agree the right method will keep your glass protected and working exactly as it should. When you are ready to get quotes, you can find a window cleaner near you to discuss your regular wash.