What the glass is made to carry
Walk-on glass is not a roof window with a thicker pane. It is a laminated build of several toughened or heat-strengthened layers bonded together, set in a frame that carries the load into the structure around it. The point of the lamination is that if the top layer is damaged, the layers beneath keep carrying people.
Every walk-on unit is sold against a load rating from the maker, expressed as a load spread over an area, plus a point-load figure for a small contact area such as a heel. The rating is set for a given span of glass. A bigger pane needs a heavier build-up to reach the same rating, so the size on your quote and the rating cannot be read separately.
Our guide to walk-on rooflight load ratings explains how the figures are read and which one to ask for.
Daily use against occasional use
Where the rooflight sits changes the question. Glass in a hallway floor that is crossed every morning sees steady traffic. Glass in a garden path or terrace sees it in all weathers. Glass in a loft hatch might be walked on twice a year.
| Position | Typical traffic | What to check |
|---|---|---|
| Internal floor | Steady, in socks or shoes | Slip finish, edge trim |
| Terrace or path | Steady, wet and dry | Slip rating, drainage |
| Roof access zone | Occasional | Load rating, kerb |
A rated unit is designed for repeated loading, not only a single load. What changes between positions is the surface finish and the drainage around the frame, which is why the survey records how the glass will actually be used.
A family that crosses the glass many times a day, with children, a dog and a vacuum cleaner, is a good reason to choose the higher end of the rating range. The choice is made at the design stage, when changing the build-up means changing only the order.
Heavy loads that are not feet
People are only one kind of load. Daily use brings in other things, and the rating has to cover them.
- Furniture. A table or sofa leg puts its weight on a small area of glass. Tell us before the order if furniture will stand on the unit.
- Planters and pots. A full planter is a long-term point load, and it traps water against the surface.
- Wheelbarrows and trolleys. Moving loads on small wheels are harder on the glass than the same weight carried by a person.
- Ladders. The feet of a ladder concentrate weight in two small areas, so a ladder is best rested on the surrounding structure.
The point-load figure on the maker's data sheet is the one that answers these. If the use is unusual, it is put to the maker with the survey readings, before anything is ordered.
The frame and the support under it
Glass only performs to its rating if what holds it does too. The frame sits on a bearing, and the bearing sits on a structure that has to take the load without moving. On a floor, that structure is usually joists or a trimmed opening. On a flat roof it is the deck and kerb.
A frame that rocks or settles puts uneven pressure on the edges of the glass, and edges are where laminated panes are most sensitive. Level bearings, a stable kerb and clean packing under the frame are all part of the fitting, and the survey notes the condition of each before an order is placed.
Where the existing structure cannot take the load, the opening is strengthened first. That is structural work, so it is described on the quote as its own stage, and the Building Regulations route for it is covered in the Building Regulations guide.
What wears with daily use
Glass itself does not wear out in the way a carpet does, but its surface and its surroundings change over the years.
Grit carried on shoes scratches the top surface over time, and the anti-slip finish can dull where traffic is heaviest. Cleaning with a soft brush and water keeps the grit from grinding in. The edge seals and trims around the frame take the movement of the glass under load, so they are the first thing to look at if a gap opens.
Bright direct sun heats a floor-level unit, so a south-facing position can feel warm underfoot. Solar control glass is a choice that can be made at the order stage, and the solar control glass answer explains the trade.
Scratches on the top layer are cosmetic. Cracks that run through a layer are not, and the unit should be stopped from use and looked at.
What we measure before a unit goes in
Daily use is settled at the survey, not at the order desk. We measure the opening and the structure that will carry the frame: the span, the support on each side, and the height of any kerb. We also ask how many people will cross it and what else will stand on it.
That gives the maker the span and the use, and the maker returns the build-up and the rating that fit. The measured sheet we hand you records both, so the rating you were quoted is the rating written down. Details of the whole service are on the walk-on rooflight installation page.
faq
everyday use
Can children and pets run across it?
A rated unit carries normal household activity, including running. The slip finish matters more than the load rating here, so ask for the surface to be specified for bare feet or paws.
Do I need to clean it differently from other glass?
Use water and a soft cloth or brush, and avoid abrasive pads. Grit left on the surface does more harm than the cleaning.
Should I stop using it if I see a scratch?
A surface scratch is cosmetic. A crack through the glass is a reason to stop walking on it and have the unit looked at.
Does a rooflight that is walked on every day need servicing?
Follow the maker's care guide for the interval. A regular look at the edge seals and the surface is the habit to keep: clean the glass, check the trim is tight, and report any movement or gap.