Can you walk on a skylight?

The glass in a walk-on unit is usually laminated, meaning layers bonded together instead of one sheet. It sits in a frame, the frame sits on a raised edge around the opening, which rests on the roof structure, so a person's weight travels down through every one of those parts. A unit that is meant to be stood on has all of that designed as one chain.

An ordinary rooflight is built for another job. Approved Document L (Wales) defines a rooflight as a glazed unit standing out of plane with the roof, mounted on a raised edge, and a roof window as one that lies in plane with the slope around it. Neither definition says anything about carrying people, and the same goes for roof lanterns, which the document does not name. The maker's data for the unit states what it is built for, and that data is the only fair guide to whether anyone should stand on it.

Start by finding out what you have. Unless the maker describes the unit as walk-on, assume it is not, and keep off it. That covers kneeling on it to clear leaves, leaning a ladder against it and stepping across it on the way to a gutter.

A dirty pane is better dealt with from the edge of the roof, or with a coating that does some of the work for you. One option is Pilkington Activ, a coating its maker lists for roof glazing, in which daylight breaks the dirt down and rain rinses it away. At the survey we look at how any unit will be reached, because glass that is awkward to get to stays dirty longest.

If a seller or a previous owner tells you the glass is fine to stand on, ask for the maker's statement of what the unit is built for, and for the rating in writing. A verbal assurance tells you nothing about the kerb or the joists under it.

A level or nearly level surface is what it needs. That means a flat roof that has been given a use: a rear terrace over a kitchen extension, a cover for a basement lightwell, or a walkway between two parts of a house with a hall or utility room underneath.

The room below changes the specification. A study with a desk beneath the glass wants glare considered, a basement utility room wants air that moves, and a bedroom under a terrace has its own needs again. We ask which room it is before we talk about glass. A pitched roof has no flat place to stand, and the product there is a roof window. Glass on a flat roof that nobody walks on is covered under flat roof rooflights.

One planning point comes with any roof people stand on. On roofs, gov.wales requires planning permission when a roof light brings a roof terrace with it. If your plan includes decking or seating over the glass, put that to the council before anything is ordered, and read the planning permission guide for Wales for the wider rules on roof alterations.

A rating means something only for the use it covers. When you compare units, ask whether the figure is for a person walking, a group standing or furniture, and then work out which of those will really happen on your roof. Reading one is covered in load ratings for walk-on rooflights.

The roof is the other half. On gov.wales, one reason given for needing Building Regulations approval of a new rooflight is that the roof has to carry its weight, or be strengthened until it can. Cutting a new opening usually disturbs the joists as well, and any that are cut have to be supported. For that reason we look at the joists and kerb before a unit is chosen.

You get a free survey first, then a fixed written quote. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver. To book, call 01792 929062 or use the survey form.