Walk-On Rooflight Installation in Bristol Daylight through a floor you can walk across

The chapters that follow cover what a unit has to carry, what keeps feet from slipping, where on a house one belongs, how it is fitted into a floor, and the rules and costs around it. If you want the weight figures straight away, the guide to walk on rooflight load rating has the detail.

Use sets the rating. A single pane set in a landing that two adults cross each morning is a light duty. A roof terrace with a table, chairs and a barbecue is a heavier one. A courtyard that a delivery driver might cross with a trolley is heavier again. The makers publish ratings in kilonewtons per square metre (a kilonewton is roughly the weight of a hundred kilograms hanging from the glass), and the structure under the glass has to be able to carry the same load. So the rating on the data sheet is a promise about the whole assembly, not about the glass alone. The page on walk on rooflight load rating sets the uses out against the likely rating, in plain terms.

Glass build-up

Under the walking surface there are usually three or more layers. The top one takes the wear and carries the anti-slip finish. The middle layers carry the load and hold the glass together if one is damaged. The lowest layers, in a sealed double or triple unit, insulate. Each layer is a specific thickness, chosen by the maker for the span and the load. A wider opening needs thicker glass or more layers. That is why a unit that spans a small hatch cannot simply be stretched into a large floor panel. The guide to walk on rooflight glass thickness explains how the build-up changes with the span.

This is why we do not use ordinary rooflights as walkways, and why we ask before fitting a walk-on unit to a roof that is also an access route. The tested rating belongs to a unit as sold. Changing the glass, the support or the bedding takes it outside that test, and then nobody can say what it will carry.

Supports under the glass

The ledge that the glass rests on is as important as the glass. It has to be level, sound and continuous, carried by a kerb, a lintel or a trimmed frame that takes the load back down into a wall or a beam. In an old house the surrounding joists and lath are not always what they seem, so the survey includes a look at the timber and, where it is needed, a structural engineer's input on the opening. A glass unit does not forgive a soft edge.

The dots or bands also change how the glass looks. A fine dot pattern leaves the view largely clear but the daylight a little softer. A heavier pattern grips better and also diffuses more. The options are shown against the likely use in the guide to walk on rooflight slip resistance, with notes on what each leaves you to clean.

Keeping the grip you paid for

A finish only works if it is kept clean. Algae and dirt gather in the textured parts first, and a build-up of both takes the edge off the grip. A soft brush and warm water with a little washing-up liquid is the regular answer, and for a terrace that shades over in winter, a gentle clean each spring and autumn stops the film from forming. A close pressure washer can mark some printed finishes, so we leave you the maker's cleaning notes.

Edges and surroundings count as well. A lip where the glass meets the deck can catch a toe, so we aim for a flush or near-flush finish, and where the decking steps up we keep the step plain and obvious. Lighting below also helps: a lit basement under a terrace turns the glass into a gentle glow in the evening, and an unlit one leaves the surface as a dark square in the dusk.

Think about footwear and pets too. High heels, stiletto points and some hard dog claws all put weight into small areas, which is the point-load case again. None of this makes a walk-on rooflight delicate. It means the finish should suit the household, and it is far better to say so at the survey than to find out on the first wet Sunday.

The roof terrace over a kitchen

Terraces on top of flat-roofed rear extensions are common on Victorian and Edwardian terraces, and the room below is often a dim kitchen or dining room. A glazed panel set in the terrace floor brings daylight down, and from the kitchen it reads like a section of sky. The glass sits in the deck with a drained upstand around it, so rain runs off and away. The surrounding deck then has to be level with the glass, within the tolerance of the fittings, so a toe does not catch. Our guide to a walk on rooflight roof terrace covers drainage, deck heights and railings.

A small opening in a deck can often be trimmed with doubled joists (extra timbers fixed on both sides of the cut to carry the load around it). A larger one may need a steel beam or a masonry lintel, specified by a structural engineer. We do not guess at that. Where the opening needs an engineer's detail, we arrange it, include it on the quote as a line of its own, and have it checked before we start cutting.

How a fitting runs

1. The room below is cleared, floors are covered and any services in the way are checked and moved.
2. The deck or paving is lifted, the opening is marked, and temporary props go under the joists.
3. The opening is cut, trimmed and strengthened, and any beam or lintel is fixed.
4. An upstand or ledge is formed, insulated and waterproofed to the roof or the tanking around it.
5. The glass is lifted in, bedded and sealed, then checked for level and drainage.
6. The surrounding deck, paving or finish is brought up to the glass.

Glass for walk-on units is heavy, so a lifting plan comes into the job. On a rear terrace in Totterdown that might mean a hoist; in a Clifton basement, a hand-over through the house. The route in is agreed with you beforehand, with floors and doorways protected.

Before the team leaves each evening, an open terrace is covered and sealed, so the room below stays dry overnight. One team carries out the whole fitting, from the first cut to the final seal, so the person who forms the ledge is the person who beds the glass.

Sealing and drainage

The edge where glass meets structure is where most problems start in any rooflight. For a walk-on unit that edge is horizontal, which makes it more demanding: water does not run away on its own. So we form falls in the surrounding surface that lead water away from the unit, use a gasket and sealant matched to the maker's specification and, in a terrace, tie the waterproofing into the roof covering as a continuous layer. The finished unit stands slightly proud of the deck only if the design calls for it.

Drainage can be more than a detail. If a walk-on rooflight forms part of a terrace, rainwater from the whole terrace will pass near it. That needs a drain or outlet with its own capacity and a route that does not run across the glass.

Taking out a complete walk-on unit and fitting another is notifiable building work, dealt with by Building Control. Changing only the sealed pane while the old frame stays generally does not. When notification applies, we send it in for you, either to the council or to a registered approver, and you are handed the certificate once the work is signed off.

Planning in brief

Rooflights usually do not need planning permission in England, as long as they stand no more than 150mm proud and sit under the ridge line. A walk-on panel set flush in a floor is rarely a protrusion at all. A flat or maisonette has no such rights at all. A listed house must have listed building consent first, which matters across much of Bath, a World Heritage Site where a good part of the city lies in a conservation area, and in Clifton and Kingsdown in Bristol. Where an Article 4 direction applies to a conservation area, those rights are gone, so ask the council. The full rules are set out in our planning guide for rooflights.

Two other regulations come in sideways. Part K sets no legal need for laminated glass in a house roof, yet a walk-on unit is made with it because of the loads it faces. Nothing in the regulations sets a minimum amount of daylight for a house already built, so panel size is a design choice. What Building Control looks at is the structure, the insulation and the weatherproofing at the edge.

What moves the price

No honest price can be given without seeing the opening, because walk-on rooflights vary widely. The size and the rating come first, since a larger span needs thicker or more layers of glass. After that come the glass type, the frame and the finish, then the structure around it: forming a hole in a plain timber deck is a small job, while carving through a stone vault and fitting a lintel is a large one. Access for lifting the glass, scaffolding for a terrace and making good inside add the remainder.

You can see broad market figures on the costs page, while walk on rooflight cost takes each factor in turn. After a free survey you receive an itemised written quote, free of any commitment, and ten years of workmanship guarantee stand behind the fitting.

Where we work

Our visits cover the Bristol and Bath area and the surrounding towns. Pages for places such as Keynsham and Hanham describe the houses we see most in each, and the roof windows and flat roof rooflights pages cover the options for the rooms where a fixed floor panel will not do the whole job.