What a walk-on rooflight costs

The opening dictates the glass, and the glass dictates a great deal else. A small square over a cellar stairwell is a short span. A long, narrow strip over a lightwell or a wide panel in a terrace is a long one. As the span grows, the glass must resist more bending, which means a heavier build-up of layers and a stronger frame to take its weight at the edges.

Shape matters as well. A square or rectangle is the simplest to make. A circle, a bevelled corner or an opening cut round a chimney breast adds cutting and templating time, and each added corner is a stress point the specification has to allow for.

Size also affects who can lift it. A panel that two people can carry into a house is one job. A panel that needs a crane, or a cradle slid through a window, is another.

We measure the opening itself and the structure that frames it. Walk-on glass cannot be trimmed on the day, so a mistake at this stage costs a remake. That is why the survey includes measurement of the structure around the hole.

A sheet of glass in a front window never has to carry a dinner party. Walk-on glass does, so it is specified by what it will carry. A hall floor that sees a family going to and fro is a different case from a roof terrace carrying a table, chairs and a barbecue, and a different case again from a lightwell cover that is only ever stepped on while the cellar is cleaned.

The more load the glass has to take, the more material goes into it. The build-up is a stack of toughened and bonded layers, and we choose it to match what you tell us the surface will do. The specification, not the sticker price, is what you compare between quotes. A quote that does not say what load the glass is designed for is a quote you cannot compare.

Heat adds another variable. Where the panel is in a roof and has warm room below, it behaves as a rooflight, and Part L sets a limit of 2.2 W/m²K for a rooflight on an existing dwelling. Glazing built to that figure usually uses a sealed double unit or better, with a coating on one of the layers, and the sealed unit costs more than a single plate. Glass in an internal floor between two heated rooms does not face the same test, and we confirm which case yours is at survey.

More on how glass is rated is in our guide to walk-on glass load ratings, and on layers and weight in how thick walk-on glass is.

A wet panel set in a terrace in January has to be safe to cross. Walk-on glass therefore gets a slip-resistant finish, and the options differ: a textured or etched surface across the whole top, a pattern of dots in a band or a lightly profiled face. Each gives a different grip and a different look from the room below, where a dense pattern lets less direct sun through while softening the view from underneath.

The frame is the next line. Aluminium frames are slim, take a powder-coat colour and sit flush or on a low upstand. A timber or steel support may be hidden below. The edge detail matters because water finds its way into any joint that is not sealed and drained, and because a visible frame is part of the look of the terrace.

Where the glass sits flush with a paved surface, the stone or the decking around it needs an edge that does not spall. Where the glass sits proud on a kerb, the step is part of the detail and the line of the roof beside it is tidier. Sill height, drainage and trim all appear as items.

Opening vents are not usual in a walk-on panel, and a ventilation need, if there is one, is a separate decision.

On a walk-on job the work below the glass can cost more than the glass itself. A roof or floor with an opening cut through it needs its joists trimmed, and the trimmers around the edge must carry the load that used to run across the hole. In a timber floor, that means new beams doubled up and fixed back to sound timber. In a concrete or masonry structure, it may mean a lintel, a ring beam or a steel section.

A structural engineer is often involved when a load-bearing element is cut. The calculation becomes part of the job, and so does the cost of getting it checked. Whether yours is needed is something we decide on the survey.

Waterproofing follows. On a terrace the covering beneath the paving has to be lifted, turned up round a new kerb and sealed so the join survives years of foot traffic. Over a cellar or lightwell, the glass is often the roof of a damp-prone space, and the drainage beside the frame has to carry water away.

What lies under the opening matters as well. A glass floor over a basement room needs the finished ceiling below to be made good. A rooflight over a habitable room needs its lining reformed. These finishing lines are part of the whole sum and are shown as their own lines on the quote.

Weight is the reason access appears on a walk-on quote more prominently than on most rooflights. Several layers of glass add up, and the panel has to be handled flat, upright or on edge without any twisting. A house with a wide side gate and a short route to the garden is one situation. A mid-terrace house with a narrow hall and a flight of stairs is another, and a rooftop terrace on the second floor is a third.

We look at the route on the survey: door widths, turns on the stair, the height of the terrace, and whether the road outside permits a lift or a delivery. Where the glass has to be raised over the building, a lifting arrangement is priced separately. Where it can be passed through a window or a door in a cradle, it is a labour line.

The same attention goes to the roof. Setting a heavy panel into a prepared opening is done by a team, and a weather window matters because the opening is exposed until the unit is in. For that reason a walk-on job is planned around the forecast, with temporary cover ready.

A new opening formed in a roof or floor counts as building work: the structure, the energy standard and where it applies, fire safety all come under the Building Regulations. We handle the Building Control notification where the work is notifiable, and the council or a registered building control approver signs it off. Their fee is a line on your quote.

Planning is a separate question. A walk-on panel set flush in a flat roof terrace may stand within the 150 mm limit for Class C permitted development, and one set on a tall kerb may not. A flat or maisonette has no householder permitted development rights at all, and a listed house usually needs listed building consent. Our skylight planning permission guide covers the full conditions, and the building rules for walk-on panels are in walk-on rooflights and the Building Regulations.

None of this alters the glass, but it can change what has to be drawn, calculated or submitted before work starts. We confirm what applies at survey.

The easiest way to compare is to line the documents up against the same list of questions. Where one quote answers a question and another leaves it blank, that gap will turn into an extra later, so ask for it now. Your own quote from us covers all of them and holds as written after the free survey, with the 10-year workmanship guarantee in writing. To start, send us the opening's details or message us on WhatsApp, 07880 284133.