What a walk-on rating actually covers
A walk-on rooflight is tested for two kinds of load: weight spread across the whole pane, and weight pushed down through one small spot. Furniture is judged against both, and it is the second one that catches people out.
The figures quoted by several UK manufacturers for domestic walk-on glass are a uniformly distributed load of 1.5 kN per square metre and a concentrated load of 2.0 kN. In everyday terms, 1.5 kN/m² is roughly 150 kg resting evenly on each square metre, and 2.0 kN is roughly 200 kg pressing down on a small area. These are typical figures, not a promise about every product: ratings differ between makers and between sizes, so the number that counts is the one declared for the unit on your roof. Our guide to walk-on rooflight load ratings explains the two figures in more depth and why units quoting only an older, lower concentrated load are worth avoiding.
The rating is also only as good as what holds the glass up. The pane has to sit on continuous, level edge bearing in a properly formed opening, and a design load assumes that support is in place. If you are planning heavy use from the start, say so at the design stage, because it may affect the specification and whether a structural engineer is needed for the opening.
Why table legs and planters behave differently from people
The same weight can be harmless when spread out and a problem when it sits on four narrow feet. Point loads, not total weight, are what decide whether a piece of furniture is suitable for walk-on glass.
A person standing on a pane spreads their weight through the soles of two shoes and moves about. A table carries its weight, plus anything on it, plus people leaning on it, through four small feet that never move. A metal chair rocked back onto two legs concentrates a seated adult onto two tiny contact points. None of this is usually a problem for a domestic walk-on unit carrying a current rating, but it shows why the concentrated load figure matters more for furniture than the headline "walk-on" label.
Planters are where the arithmetic turns. Take a square planter half a metre each way and 40 cm deep, filled with soil. Wet soil is heavy, and that planter can weigh somewhere around 150 to 200 kg once it has been watered, all sitting on a quarter of a square metre. That works out at several times the uniform load that a typical domestic walk-on rating allows for the same area. Pots of that size belong on the surrounding terrace, not on the glass.
| Item | How it loads the glass | Usually suitable? |
|---|---|---|
| Garden chairs | Light, four small feet | Generally yes |
| Small bistro table | Light, fixed feet | Generally yes |
| Large planter, wet soil | Heavy, constant | Check first, often no |
| Stone or concrete bench | Heavy, point loads | Check first, often no |
| Hot tub or water feature | Very heavy, constant | No |
Treat the table as a guide only. The declared rating for your unit, and the advice of the maker or your engineer, overrides it.
Protecting the surface and the finish
Weight is one question; wear is another. Furniture that is dragged, rocked or left in one place for years can mark the slip-resistant finish on the top pane.
Walk-on glass normally has a sandblasted or ceramic frit finish on its upper face so it grips underfoot, and the slip resistance of walk-on glass depends on that finish staying intact. Bare metal feet and grit trapped under a chair leg act like sandpaper. Soft, wide felt or rubber feet spread the load a little and stop scuffing. Lift furniture rather than dragging it. Our answer on whether walk-on glass scratches covers the care side in more detail.
Anything that sits flat on the glass, such as a pot saucer or a rug, also holds water against the surface. That leaves marks and can undo the work done to keep water moving off the glass; the guide to drainage around flush walk-on rooflights explains why standing water matters.
The room underneath pays for it too
Every chair on the glass is a shadow in the room below. Before deciding where the furniture goes, think about where the light is meant to land.
A walk-on rooflight exists to light the space underneath it: a basement, a kitchen extension below a terrace, a lower-ground room under a courtyard. A dining set parked over the pane throws a hard, moving shadow onto the floor or worktop below, and in a Cambridge terrace where that pane may be the only real daylight into a deep rear room, the loss is noticeable. Keeping the glass clear of anything bulky gives the room below the full sky, which on the flat, open ground around the city is a lot of light.
When we plan a terrace, we look at how the space above will be used as well as how the light falls below, so the glass sits where people walk rather than where a table will end up. The guide to walk-on rooflights for roof terraces goes through that layout thinking, and how we plan the light explains the wider method. In summer, a clear pane also throws a bright pool of sun into the room below; our guide to glare below walk-on glass covers how finishes soften it.
Questions people also ask
Can I put a hot tub on a walk-on rooflight?
No. A filled hot tub weighs well over a tonne and is far beyond any domestic walk-on rating. It needs its own structural support on a solid part of the roof or ground, designed by an engineer, away from the glass.
What happens if the glass is overloaded and cracks?
Walk-on units use laminated glass, so a damaged pane is designed to stay in place rather than fall. It still has to be replaced, and the load that caused it should come off straight away. Our answer on whether walk-on glass is safe if it cracks explains how the layers behave.
Can I specify a higher load rating so I can use the space freely?
Often, yes, within what the maker offers. A higher rating usually means thicker glass and a heavier unit, which affects the opening and its supports, so it is best decided early. Tell us at the survey how you plan to use the space above and we will build that into the specification for your walk-on rooflight installation.
Are outdoor rugs a problem on walk-on glass?
They add little weight, but they block light to the room below and hold moisture and grit against the finish. Use them on the surrounding terrace instead of on the pane.
