Smooth glass with a film of rain on it asks a lot of a pair of shoes. Makers of walk-on glass answer by putting a finish on the surface, something for the sole to bite on, and the finish they pick shapes both the grip and the view from the room below.
Frit and etching are the two names that come up. This guide takes them one at a time, then looks at the light, the slip-resistance claims and the cleaning, with the same eye on all of it: how the pane behaves on a wet afternoon with someone walking across it.
Why a wet pane is the test
Drizzle settles on glass as a fine, even film. A pane has no texture to break that film up, so the sole of a shoe meets water first and glass second. Bare feet after a dip in the garden, a pair of wet trainers coming back from the shed, a child in socks: the terrace sees all of them, and the glass has to cope with every one.
Dirt makes it harder. Grit tracked from the lawn and a few leaves lying flat on the glass change how the surface feels long before they change how it looks. A finish that works on a clean, damp pane still has to work when the pane has had a week of ordinary use.
A terrace pane lives outdoors, and the weather decides what is lying on it from one day to the next.
That is the reason to judge the finish in the conditions it was bought for. A dry sample held in the hand tells you what it looks like, and little about what it does under a wet shoe.
Judge the finish with wet shoes on, and keep the dry sample for judging the looks.
Frit: a pattern fired onto the surface
Makers describe a frit as a pattern of small dots or lines baked onto the glass. The pattern gives the surface a texture you can feel, and because it is a pattern, you can see it. That makes frit a design choice as well as a safety one: the spacing, the colour and the shape of the marks all show.
Ask the maker how much of the pane the pattern covers and what colour it is. Colour matters from both sides, because from the terrace it reads as part of the surface and from the room below it reads as a mark against the sky.
Ask, too, where on the pane the pattern sits. A finish on the top surface is the one under the sole, and the maker can tell you how the pane is built up beneath it. These are worth settling before a unit is chosen for your roof.
| Finish | How makers describe it | What to check |
|---|---|---|
| Frit | a pattern of dots or lines baked onto the glass | spacing, colour, how much of the pane it covers |
| Etching | the glass surface roughened to a frosted look | how it looks wet, how it cleans |
Etching: a roughened surface
Makers describe etching as working on the glass itself. The surface is roughened, and the result is a frosted look that scatters light instead of passing it straight through. There is no pattern to see, only an even, matt face.
That frosted face suits some rooms and frustrates others. Looking up through an etched pane, you tend to see brightness but no clear outline of the shoes above, which suits a bathroom or a utility room beneath a terrace. A room where you want to see clouds go by may call for something else.
Ask how the finish is applied and whether it covers the whole pane or only part of it. Ask to see it wet, too, because a frosted surface can look quite different once the rain is on it, and a sample sprayed with a bottle tells you more than a dry one.
What the finish does to the light
Any finish is a layer between the sky and the room, so it can change the light that arrives. A pattern covers part of the glass and a frosted face scatters what passes through it. How much that matters depends on the room under the terrace and on what you want from it.
A cellar room that has never had daylight gains from any glass at all, and a finish is a small price for the extra brightness. A kitchen extension where the glass is meant to feed a worktop with light is a closer call, and the room tells you which finish to lean towards. Describe the room at the survey and the finish can be chosen to suit it.
Look from below as well as from above. The person on the terrace sees the top of the finish, and the person in the room sees its underside against the sky. A sample held up to a window gives you that second view for nothing.
Questions for a fritted pane
- How much of the glass does the pattern cover?
- What colour is it from the room below?
- Can I see a sample against the sky?
Questions for an etched pane
- Does the frosted face cover the whole pane?
- How does it look and feel when it is wet?
- How does it clean after a muddy week?
Slip-resistance claims, and the questions behind them
Some makers publish a slip-resistance figure for a finish. A number means something only if you know where it came from, so ask for it and for the details behind it.
Find out which test produced the number, and whether the glass was tested wet or dry. A figure from a dry test says little about a terrace after rain. Check, too, what surface the number describes: the finish as made, or the finish after it has been walked on. When two makers quote figures, find out whether the two figures come from the same test before you compare them.
Keep the answers with the datasheet, next to the load rating, so the two live together in your file. Our guide to walk-on rooflight load ratings deals with the other half of the paperwork.
Reading a grip claim
- Which test? Ask the maker to name it.
- Wet or dry? A terrace is judged wet, so ask for the wet result.
- Which surface? The finish as made, or after use.
- Same test as the other maker? Figures from different tests cannot be lined up.
Who crosses the glass
The finish has to suit the people on it, so write down who they are. A toddler in socks meets the surface differently from an adult in walking boots, and a relative with a stick puts a small rubber tip on the glass at one point. Garden furniture dragged to a new spot meets it again, with legs that scrape.
Think about the route as well as the people. A pane at the back door sees every wet shoe that comes in from the garden, while a pane at the far end of the terrace may see only the occasional visitor. Put the panel where the route is easiest to keep clear, and the finish has less to deal with.
Tell us who uses the terrace when you book the survey. We take it into account when we look at where the unit sits, how the terrace falls and what the room below needs from the glass.
Keeping a gripped surface clean
A textured finish can give dirt somewhere to settle, so a gripped pane may need cleaning more often than a smooth one. Wash it with plenty of clean water and a soft brush, clear the grit from the frame and the surround, and ask the maker which cleaning products suit the finish on your glass.
A self-cleaning coating is one option. Pilkington lists roof-lights among the applications for Activ, and describes the coating as working with daylight to start breaking the dirt loose, so rain can rinse it off. Whether a coating can sit alongside a particular grip finish is a question to settle with the maker before anything is ordered.
Water that stays on the glass leaves marks, so the way the terrace drains matters too. Rainclear, writing about its flat glass rooflights, advises at least 5° of slope on the kerb so that water drains instead of pooling. A walk-on unit has its own demands, and the survey works out how the falls and the outlet will treat yours.
Grip beyond the glass
A grip finish covers the glass and nothing else. The feel underfoot changes at the edge of the pane, where timber decking, paving or roof covering meets it, so walk that line in wet shoes and notice where the change comes. A surround that has gone green or slimy takes the benefit away from the best finish on the pane.
Look at where the water goes, too. A terrace with a clear fall to an outlet leaves the glass with a thin film, where a terrace with a dip beside the frame leaves it with a puddle. Standing water beside the frame after rain is easy to spot from an upstairs window.
Leave a clear, level step onto the glass, and keep planters and furniture away from the pane edge, so the walking route is obvious. The planning and Building Regulations side of a walk-on panel is covered in our skylight planning permission guide for Wales, since a roof people walk on can turn into a roof terrace.
Choosing the finish at survey
The free survey is where the finish meets the real terrace. We look at the roof, the falls, the surround and the room below, and you tell us who walks across the glass and when. A fixed written quote follows, and a written guarantee covers our workmanship for 10 years. To start a conversation sooner, ring 01792 929062 or send us a WhatsApp message.
If you want the full picture of what the glass costs, read how much a walk-on rooflight costs. A shorter answer on traction sits in are walk-on rooflights slippery when wet, and can you walk on a skylight sets out the case for walk-on units in the first place. The full range sits on the walk-on rooflights page.