The short answer
Sometimes. Self-cleaning glass carries a thin coating on the outer face that reacts to daylight and loosens organic dirt, then lets rain sheet across the pane and carry it away. It cuts the washing on a roof that gets steady rain and a fair pitch. It does not clean the inside, remove moss or bird mess on its own, or replace a wash in dry spells.
The coating helps, but it is not a cleaning service. How much it saves depends on the pitch, the trees around and the weather.
What the coating does
The glass looks like any other, but the outer face has a very thin coating applied in manufacture. Two things happen on it. In daylight, the coating reacts with ultraviolet light and starts to break down organic dirt, such as pollen, sap and traffic film, so it loosens its grip on the pane.
How does the rain finish the job?
The same coating draws water out into a thin sheet instead of letting it gather in beads. A sheet of water runs across the pane and carries the loosened dirt off with it, leaving fewer streaks than ordinary glass does when it dries. Pollen, fine dust and tree sap are the kinds of dirt it handles best. That is why the glass is called self-cleaning: it is working with sun and rain, not on its own.
Both steps need light and water. A roof under a dense tree gets less light and a roof in a dry spell gets less rain. The effect builds up over days, not minutes, and it continues for as long as the coating survives, which is why rough cleaning methods are a poor idea.
What it does not do
The name promises more than the glass delivers, and it is better to know the limits before you pay for it.
Will it stop moss, droppings and leaf mould?
Not reliably. The coating works on loose organic film, not on a thick layer of bird mess, a drift of leaves in the gutter line or moss that has taken hold at the bar. Growth that settles in the corners and along the edges of each unit stays put. Hard water marks are another limit: limescale left where rain evaporates is mineral, not organic, and the coating does not dissolve it. The inside face is ordinary glass, so condensation marks and dust indoors are still yours to wipe.
It also needs rain to rinse. A shallow-pitched roof sheds water slowly, so dirt can dry on it. A steep one rinses better. Our answer on cleaning a conservatory roof covers what to use and what to avoid, and the one on moss on a polycarbonate roof deals with growth on plastic.
When it is worth paying for
The coating is an option on new glass units, not something sprayed on an old roof, so the decision comes up when you replace glass or swap polycarbonate for it.
Is it worth it on my roof?
It earns its keep on a roof that is awkward to reach, with a reasonable pitch and plenty of weather. It matters less on a roof you can wash easily from a safe position, or one sitting under a tree that drops leaves and sap faster than any coating can handle. Ask what the extra costs on your roof and what the supplier says about the pitch. The extra is part of the price of the units, so it is quoted within one written total.
Treat it as a way to clean less often, not never. Think about where the water goes too: a coated roof that rinses well still needs clear gutters, or the runoff pools at the eaves and leaves a tide line. If you are weighing glass against plastic, our answer on replacing polycarbonate with a glass roof covers the other points to check.
Looking after the glass
A coated pane can last, provided it is not scratched or stripped. Use plenty of clean water, a soft brush or a sponge on a pole, and mild soapy water if it needs more than rinsing. Avoid abrasive pads, scrapers and strong chemicals that can mark or remove the coating.
Do I still need to clean it?
Yes, now and then. A rinse with a hose after a dry spell, and a check of the bars, caps and gutter line for growth, keeps the roof looking right. Marley advises against high-powered jet washes on tiles and slate for the damage they do, and the same restraint is wise on a glazed roof: gentle methods only. Wash from a safe position, such as a pole from the ground, and never stand on a conservatory roof, which is not made for walking on.
If you want to know whether coated units suit your frame and pitch, send a picture of the roof as seen from the lawn, plus the room size. The survey that follows ends in one written total for the glass you pick, and the supplier's care instructions for the coating go in your paperwork, so whoever washes the roof later knows what to avoid. Our conservatory roofs page shows the other coverings.
More on coated roof glass
Can I add self-cleaning glass to my existing roof?
Not as a spray or a film in any way that lasts. The coating is applied to the outer pane when the unit is made, so it comes with new glass units. If your roof is polycarbonate, you would need to move to glass first, which brings the frame weight check described above.
Does self-cleaning glass work in the shade?
It works more slowly. The coating relies on daylight to loosen dirt, and a roof under trees or in the shadow of a wall gets less. It still sheds water, but leaf litter and sap in the shade stay stuck, so expect to clean those roofs by hand more often.
The full picture: Conservatory roofs in Taunton ยท More short answers