The short answer
Self-cleaning glass is worth it on a conservatory roof that you cannot reach easily, provided you accept that it cuts the cleaning rather than removing it. A coating on the outer face breaks down organic dirt in daylight and lets rain wash it away. On a shallow roof, rain runs off slowly and leaves streaks, and the coating does nothing for bird droppings, pollen crusts or moss in the frame. It adds to the cost of the glazing units, so it suits a hard-to-reach glass roof more than a small, easy one.
How the coating works
Self-cleaning glass carries a very thin coating, applied at the factory to the outer pane. It does two jobs in sequence. First, daylight (ultraviolet in particular) triggers a reaction in the coating that loosens organic dirt such as pollen, leaf mould and the film that settles from traffic. Second, the coating attracts water so that it spreads across the pane in a sheet rather than beading. When rain arrives, the sheet carries the loosened dirt off with it, instead of leaving spots behind.
Notice the word "daylight". The coating needs a period of dry, bright weather to work on the dirt before the rain arrives. In a Hampshire winter, with weeks of grey cloud, it does less than it does in a bright spring. It also needs the glass to be clean when it goes in: a coating that is covered in builder's dust or silicone smears will not work until those are removed.
Why a roof is a harder test than a window
A vertical window drains quickly. Rain runs straight down and takes dirt with it. A conservatory roof is the opposite. Many sit at a pitch of only 15 to 25 degrees, so water runs off slowly and dries on the pane. Whatever the rain loosens can settle again at the lower edge, and you finish with a band of streaks along the bottom of each pane, near the gutter.
The coating also has no effect on things that are not organic dirt. Bird droppings dry hard and need scraping or soaking. Moss and algae grow in the frame channels and along the seals, not on the glass, so the frame still needs a wash. Overhanging trees drop sap and honeydew, and those sticky films resist the coating. Anyone with a large silver birch over the roof should not expect miracles.
What it adds to the cost
The coating raises the price of each glazed unit. We do not quote a flat uplift here, because it depends on the size of the units and the type of glass underneath. Your fixed quote follows the survey. As a rule of thumb, the saving shows up in time rather than money. If you pay a window cleaner for a conservatory roof every few months, the coating may take some visits off the calendar. If you clean the roof yourself in an afternoon with a hose and a soft brush, it will take a long time to pay back.
When it is worth choosing
It makes most sense on a large glass roof that is awkward to reach, for example one that sits over a patio door at first-floor height or backs onto a boundary wall. It also suits a roof that is going to be replaced with new glass anyway, because the coating can only be specified when the units are made. It makes less sense on a small roof you can reach from a ladder, or where trees overhang, or where you plan to switch to a solid roof soon.
If you are weighing glass against other choices, our guide to glass, polycarbonate or solid conservatory roofs sets out the differences in heat, noise and cost. For routine upkeep, whatever you choose, see how to clean a conservatory roof safely, because standing on the glass is never the answer.
Other glass options that tackle the same problem
Dirt is only one of the complaints people have about a glass roof. Heat in summer and cold in winter are usually bigger. Solar-control glass, which carries a different coating that reflects part of the sun's energy, tackles the first. A low-emissivity coating tackles the second by slowing heat loss through the pane. Some units combine these with the self-cleaning layer, and the combination is worth asking about if you are glazing a roof from scratch. The best-performing glass roof still cannot match a built-up solid roof for insulation, so be clear about which problem bothers you most before you pay for coatings.
Cleaning it properly when it needs it
Use plenty of clean water and a soft brush or sponge, and avoid abrasive pads and harsh chemicals that can mark the coating. Clean the frame and the gutter line at the same time, since dirt in the channels is what stains the glass beneath. Work from a ladder outside or a long-handled pole, never from the roof itself. Our overall page on conservatory roof replacement in Basingstoke covers the options if the glass is old and tired.
Every roof is different. A free survey with photos settles it for yours.
Get a free survey