In brief
Not when it is specified for outdoor use. Walk-on rooflight glass is supplied with an anti-slip treatment on the top surface, and the finish is chosen when the unit is ordered. Plain, untreated glass is slippery when wet, which is why an external walk-on unit is never left smooth. The right finish depends on where the glass is, how wet it gets and how often people cross it.
- An anti-slip surface treatment is applied to the top of the glass
- The finish is chosen at order, so it is part of the unit from the start
- Wet, shaded and sloping positions need more grip than a dry, sheltered one
- The treatment is on the outer face only, so the view through is kept
- Cleaning and care follow the maker's instructions
Why plain glass is not used outside
Smooth glass has very little grip, and a thin film of water is enough to take away what there is. With rain, dew, moss or a thin film of dirt on it, the surface becomes slippery underfoot. On a roof terrace, a path or the cover to a lightwell, that is a hazard, so the top face of external walk-on glass carries a treatment that gives the sole of a shoe something to hold.
The treatment is part of how the glass is made, not something applied on site afterwards. The top layer is finished at the factory, so the pattern is even across the pane and bonded to the glass. We specify the finish when the unit is ordered, and it is named in the written quote.
The kinds of anti-slip finish
Makers offer more than one way of giving glass grip, and each looks a little different.
- A fine pattern of ceramic dots fired onto the surface, which gives grip and is clearly visible from above
- An acid-etched or sandblasted surface, which has a frosted look and a soft texture
- A coated surface with a textured finish, used where the maker offers it
The dot pattern and the etched surface behave differently when wet and when dirty. The etched finish can hold dirt in its texture, and the dotted finish is easier to wipe but has more visible pattern. We talk through the options with you, at the survey or by phone, and show samples if the maker supplies them. The choice is a matter of grip, appearance and upkeep, and you can pick the balance that suits the place.
Choosing for the position
Where the glass sits changes what it needs. A unit on a sheltered terrace that is mostly dry is a different case from one in a shaded lightwell, where algae can grow on a damp surface. A sloping unit needs more grip than a flat one. A glass that will be crossed every day by several people needs a firmer finish than one that is only stepped on to be cleaned.
We ask where the glass is, how it drains and how it will be used, then recommend a finish. The guide to walk-on rooflights for roof terraces covers the typical terrace setting, and the page on walk-on rooflights over basements and lightwells covers the damp, shaded positions.
Grip, view and light
Any treatment on the glass affects how it looks. A dot pattern is visible from below as a faint speckle in bright light, and an etched surface softens the view and reduces the clear outline of the sky. In return, both bring grip. A treatment can sit on the top face only, so the underside of the glass, which faces the room, stays clear.
If the room beneath needs the clearest daylight possible, tell us. We can discuss a finish that covers only part of the surface, or that is chosen for light more than for grip, where the use of the glass allows it. The decision is yours, with our advice on where grip matters most.
Keeping the glass safe to walk on
Even a treated surface performs best when it is clean, and a quick look every few weeks in autumn, when leaves collect, is enough to catch a build-up early. Moss, leaf mould and algae build up on any exterior glass and reduce the grip, so a regular wash with a soft brush and water keeps it as intended. Harsh chemicals and hard scrapers can damage the treatment, and the maker's care instructions say what to use. We pass those instructions to you at handover.
In frost, treated glass behaves like any outdoor surface and can be slippery with ice, so care is sensible in winter. Anti-slip glass is designed to give grip in normal wet conditions, and it should be treated with the same caution as any outdoor step.
Where the finish appears in your quote
Your quote lists the unit, the glass build-up, the load class, the anti-slip finish and the manufacturer's quoted wait. The finish is written in as a specific item, so there is no ambiguity about what is being ordered, and you can ask a question about it before anything is made. The finish affects the price a little, along with the other build-up choices, and the page on what a walk-on rooflight costs explains what moves the figure. Our overview of walk-on rooflights sets out the range.
To choose a finish, book a free survey. We look at the position, talk through the options and put the specification in writing before the unit is ordered, so the surface you walk on is the one you agreed.
Related questions
- Can an anti-slip finish be added to glass already fitted?
- The treatment is made into the glass at the factory, so it is chosen at order. If a fitted unit has no suitable finish, we can look at it on a survey and tell you what options the maker offers.
- Does the finish wear off?
- A factory-applied treatment is made to last with normal use and cleaning. The maker's care instructions say what to avoid, and we hand them to you with the paperwork.
