The short answer
Self-cleaning glass is worth it on a rooflight you cannot easily reach, and much less so on one you can wipe from a ladder or a landing. The coating helps rain wash away ordinary dirt, which suits a lantern or a flat rooflight at the back of an extension. It does not make the glass maintenance-free, and it only works on the outer face, so the inside still gets cleaned by hand.
What the coating actually does
The coating is a very thin layer applied to the outer face of the outer pane at the factory. It works in two steps. In daylight, the coating reacts with organic dirt, such as pollen, leaf mould and the film that settles from the air, and loosens it. Then, because the surface attracts water rather than beading it, rain runs across the glass in a sheet and carries the loosened dirt off with it.
So the coating needs two things to do its job: daylight and rain. Devon has plenty of both, which is one point in its favour here. But the coating is not a sealant or a shield. It is a surface treatment that slows the build-up of grime and makes each clean easier.
Where it earns its cost
The benefit is largest where cleaning is awkward. A roof lantern over a kitchen extension sits above a flat roof with a parapet or a pitched run of tiles beside it, and most people have no safe way to reach the middle of the glass. The same goes for a rooflight over a stairwell, or a roof window on a steep slope above a two-storey house. If the alternative is paying someone to come with a pole or a platform, the coating is a sensible spend.
It also suits glass that sits clear of overhanging things. A rooflight with an open sky above it, and enough pitch for rain to run, gets the full effect.
- Lanterns and flat rooflights over extensions, where reach is the problem.
- Roof windows high on a steep roof, or over a stairwell.
- Rooflights in the open, away from branches and chimneys.
Where it helps least
On a roof window within arm's reach of a loft bedroom, you can open the sash, turn it, and clean both sides in a couple of minutes. The coating saves you very little there.
Shelter weakens it too. Glass under a deep overhang, close beneath a tree, or on a very shallow pitch will not get the rinse the coating relies on. Bird droppings, tree sap, limescale from hard water and the dust left by building work are not the organic film it is designed for, and they will sit on coated glass much as they do on plain glass. A lantern that gets a visit from gulls near the Exe estuary will still want a rinse now and then.
There is a small visual point as well. Some coated glass reflects with a slight tint in certain light. Most people never notice it, but if you are matching a rooflight beside existing glazing it is worth looking at a sample.
Cleaning coated glass properly
Coated glass is cleaned the same way as any other glass, with one exception: leave out abrasive pads, scrapers and strong solvents, which can mark the surface. Clean water, a soft cloth or a soft brush, and a little mild detergent is enough. If you use a squeegee, keep the blade clean so it does not drag grit across the pane.
Do not expect the coating to last forever either. It slowly wears with weather and cleaning, so view it as something that makes the glass easier to look after for many years, not as a promise about a fixed lifespan.
Choosing it at order stage
The coating is applied when the glass is made, so it is a decision to take when you order, not something added after the rooflight is in. If you are fitting a new rooflight or replacing a whole one, say so while the specification is being written. If only the sealed glass unit is being renewed and the frame stays, ask whether the supplier can coat that size.
It sits alongside the other glazing choices that decide how a rooflight performs: the number of panes, the low-emissivity coating, the spacer between the panes and the laminated inner pane. Self-cleaning is a convenience layer on top, and it should not push out anything that affects heat loss or safety. Our guide to rooflight U-values covers the performance side, and the warm edge spacer answer covers another small detail that is easy to skip.
Cost depends on the supplier and the size of the glass, and it is an extra on the glazing, so ask for it to be listed as its own line in the quote. That way you can see what you are paying for and decide with the figure in front of you.
The inside is still yours to clean
The coating does nothing for the inner face of the glass or for the lining around it, and from the room those are the surfaces you look at every day. Dust settles on the sill of a splayed lining and on the inner pane. A wipe of the glass and a dry cloth along the lining edge twice a year keeps it looking as it did on the day it was finished.
Our finish schedule records how the lining is finished and whether it is painted, so you know which products are safe to wipe it with. It comes with every quote, and you can see how it works on the finish schedule page.
A simple way to decide
Ask yourself who will clean this glass, and how. If the answer is "someone with a pole, or nobody", the coating is a good addition. If the answer is "me, from a landing, in two minutes", spend the money elsewhere, perhaps on a better spacer or a deeper, better-finished lining.
If you are weighing it for a particular room, send us the details through the quote form and we will go through the roof, the access and the surroundings before recommending it or leaving it out. For the wider picture on glazing choices, see our energy efficient rooflights page.