In brief
A walk-on rooflight is priced from a written quote after a survey, because the figure depends on the size of the opening, the load class the glass must carry, the glass build-up, the anti-slip finish and the structure underneath. Two walk-on units of the same footprint can cost quite different amounts once those are set. Each price is built for the job, and the quote shows what each item covers.
- Size of the opening, and how many panes it needs
- Load class, set by who and what will stand on the glass
- Glass build-up: the number of layers and the thermal performance chosen
- Anti-slip finish for outdoor use, chosen when the unit is ordered
- The structure beneath: kerb, frame, support and any engineer's design
Why the price is set after a survey
A walk-on rooflight is a structural piece of glass, not a standard window. It carries people, sometimes furniture, over a room or a void, and each of those decisions affects what is made. The glass is built up from several layers, the frame has to be matched to it, and the thing it sits on has to take the weight. For those reasons a figure given before anyone has seen the roof and the room below is a guess.
So we survey first. The survey is free, there is no obligation attached to it, and it ends with a written quote. It sets out the unit and glazing, then the maker's stated lead time, then what your builder must provide. Nothing in it is a surprise on the day, because each line corresponds to something we saw at the survey, whether that was the size of the opening, the room below or the way the roof is built. The page on rooflight costs covers how we price the whole range, and this page covers what is particular to walk-on glass.
Size and the number of panes
Walk-on glass gets thicker as it gets larger, because it must span the opening without flexing. A small square for a stair landing or a lightwell is a modest piece of glass. A wide opening over a basement or a terrace may need several panes with supporting bars or a frame between them, and each pane adds glass, framing and fitting time.
The handling matters as well. Large, thick panes are heavy, and several people may be needed to carry them, so access for lifting them to the roof or into a lightwell is part of the cost. We say in the quote what access has been allowed for, and why.
Load class and who will walk on it
The glass is specified for a load, and the load comes from how the area will be used. Occasional foot traffic to clean the glass is one case. A roof terrace with furniture and a party of people is another. A heavier use needs a thicker build-up, more layers and a stronger frame, and so it costs more. The reverse is also true: specifying more than the area needs adds cost without a benefit.
We ask how the glass will be used, who will stand on it and whether anything heavy will be placed on it, and we specify to that. The guide to walk-on rooflight glass and load ratings explains the classes in plain terms.
Glass build-up and finish
Walk-on glass is made of several layers bonded together, and the sealed unit for a heated room beneath adds insulating glazing. Choices about thermal performance, solar control and self-cleaning coatings all change the price. A rooflight in an existing home has to meet the Part L limit of 2.2 W/m²K, and the glazing named in the quote is chosen to meet it.
The top surface is finished with an anti-slip treatment for outdoor use, chosen when the unit is ordered. The treatment is part of the unit, so it is in the price from the start. The answer on whether walk-on glass is slippery describes the finishes.
The structure beneath the glass
The glass is only as good as its support. A walk-on unit sits on a kerb, a steel or concrete frame, or a purpose-built upstand, and that has to carry the load without moving. On a new build, the support can be formed as the structure goes up. In an existing house, forming the opening may need new beams or trimming, sometimes with an engineer's design.
Where a walk-on rooflight goes into a roof terrace or a basement ceiling, waterproofing and drainage around it count too. A terrace unit is set into a roof covering, and the roofer's work and ours need to meet cleanly. Our guides to walk-on rooflights on roof terraces and rooflights over basements and lightwells cover both settings.
Getting a figure you can rely on
If the project is at drawing stage, we can work from the drawings and check on site afterwards. Kerb or opening sizes are sent in writing to your builder or architect, matched to the exact unit, before the structure goes up, so the opening suits the glass. The order is then timed against the programme, counting back from the day the structure is due to be ready. That order of events keeps the glass from arriving long before there is anywhere to put it, or after the opening has been covered over.
If you are comparing a walk-on unit with an alternative, tell us and we can quote both. The hub page on walk-on rooflights shows the range, and the survey is free.
Related questions
- Is a walk-on rooflight dearer than a standard flat rooflight?
- Usually, yes, because the glass is thicker, built from more layers and held in a stronger frame. The structure beneath it also has to take a load. The quote shows each part so you can see where the difference sits.
- Can the quote be sent to my architect?
- Yes. The written quote names the unit, the glass and what the structure must provide, so an architect or engineer can check it against the drawings.
