The short answer
It depends on the unit, because each walk-on rooflight is sold with a load rating from its manufacturer for a particular size and glass build-up. We choose the glass against that stated rating and the way the space will be used, and we write the rating into your quote. A rating only holds when the unit is fitted on the support the maker specifies.
Why there is no single figure
People often ask for one number for walk on rooflight weight, as if all walk-on glass were the same. It is not. The capacity of a unit depends on how many layers of glass it has, how thick they are, how large the pane is and how it is supported at its edges. A small pane in a thick stack takes more than a large pane in the same stack, and both differ from a unit built for light foot traffic only.
That is why the honest answer begins with the maker's data sheet and not with a round number. We never quote a figure from memory or from a different product. If a number matters to you, we give you the one in the manufacturer's literature for the exact unit we propose.
What a load rating covers
A rating describes what the glass assembly is designed to carry when it is installed as specified. Two different kinds of load are involved, and a good data sheet distinguishes them.
- Spread load: the combined weight of people and furniture across the surface.
- Concentrated load: the pressure from a small area such as a heel, a table leg or a planter foot.
Both matter. A pane can be comfortable under a crowd and still be asked to do something it was not designed for by a heavy item with narrow feet. Telling us what will stand on the glass lets us match the rating to the real use, and not just to the idea of someone walking across.
Support is part of the rating
The rating belongs to the glass and the way it is held. The frame or upstand must be level and well fixed, the glass must sit on the bearing the manufacturer specifies, and the structure beneath must be stiff enough not to flex. A timber opening needs its trimmers sized properly. A concrete slab or steel trim provides a firmer base.
A rating is a promise about a complete installation. Strong glass on a weak support is still a weak floor.
This is where fitting quality counts. Our installers bed the unit as the maker requires, check it for level, and make sure no corner is pinched. The fitting follows today's Building Regulations, and we notify Building Control wherever the job requires it. Swapping a whole rooflight is building work governed by Part L, whereas fresh glass alone within a sound frame sits outside that control.
Everyday use against the rating
Most domestic walk-on glass is bought so that people can cross a floor, stand on a landing or sit on a terrace. That is the use the common domestic ratings are written for. Occasional extras, such as a few friends on a terrace or a piece of garden furniture, are worth mentioning at the survey so the specification allows for them.
What should be avoided are uses outside the stated class. Heavy equipment, dropped masonry, vehicle loads and similar are different problems, and a glass unit is not the right answer to all of them. If your use is unusual, tell us early and we will say plainly whether a walk-on rooflight suits it.
How the glass copes with a bump
Laminated glass is built to stay together when it takes a knock. If a layer is marked or cracked, the bonded interlayer holds the pieces in place, so the stack continues to support the surface while it is dealt with. Many systems use the top layer as a sacrificial one that can be renewed on its own. If the top face is damaged, contact us before anyone tries to remove it, because the right method depends on the system.
Questions worth asking any supplier
Whoever quotes for walk-on glass, a short list of questions separates a considered specification from a guess. Ask for the manufacturer's published rating for your exact size. Ask what use class that rating is written for. Ask what the support detail must be for the rating to apply, and who is responsible for it being right. Then ask to see it all in writing.
If the answers come back vague, or a figure is offered without a data sheet behind it, treat that as a warning. A rooflight you will stand on deserves a specification you can read, keep with the house papers and hand to the next owner.
At the survey we also look at the room below. A heavier build-up changes the depth of the unit slightly, which can affect how the reveal is splayed and finished, and it is better to plan that now than to discover it on the day.
What goes in your quote
Your fixed written quote states the unit, its size, the glass build-up and the manufacturer's stated load rating for it, along with the use it is intended for. It also confirms the thermal figure, which for a flat-roof rooflight in an existing home must meet 2.2 W/m²K under Part L 2021. The fitting itself is guaranteed for 10 years.
For the glass in detail, read our guide to walk-on rooflight glass and loads. The service itself is on the walk-on rooflights page, and you can book a free survey to talk through your own opening.
