The answer
Walk-on rooflight Building Regulations approval is needed when the work is notifiable. A new opening in a roof, deck or slab alters the structure, and a replacement rooflight comes under the energy rules in Part L. We handle the Building Control notification, so you do not need to deal with the council yourself.
When a walk-on rooflight is notifiable
Two kinds of walk-on rooflight job are notifiable building work. The first is a new unit in a new opening. Cutting through a flat roof, a terrace deck or a ground slab alters the structure that holds the surface up, which brings in Approved Document A. The second is a replacement of an existing rooflight, which is covered by the energy rules in Part L, since the new unit has to meet the heat-loss limits for glazing in an existing home.
Both routes end the same way. We notify Building Control, the work is inspected at the stages that matter, and a completion certificate follows. The certificate is worth keeping with the deeds, because a buyer's solicitor may ask for it when you sell.
Building Control is either your local authority or a registered building control approver. Either can take the notification, and it is the same work for the same job. The planning side is a separate question, which our guide to planning permission and the Regulations explains.
What Building Control checks on loading
Loading is the first item, and for a walk-on rooflight it carries the most weight. The inspector wants to know that the structure round the new opening carries the glass, its frame and the people who will stand on it, and that the opening has not weakened the deck or slab around it.
A terrace or balcony is designed for people, so its structure has to carry more than a roof that nobody walks on. When a new opening interrupts joists or a slab, the load they carried is taken round it by trimmers or a beam, and the trimming is designed by a structural engineer where the span or the opening calls for it. Building Control looks at that design and then at the work as it goes in, including the bearing of the upstand on the structure below.
The glass has its own evidence. The maker states the load class of the unit and how it was tested, and the data sheet is part of the file. The class has to suit the use: people walking on a terrace need one class, and a surface crossed by vehicles needs another, with the way a class is read set out in load ratings and slip resistance.
Guarding at the edge of the terrace
Guarding is the second item, and it concerns the terrace more than the glass. A walk-on rooflight in the middle of a terrace is a floor surface, so the glass itself is not a guard. A terrace, balcony or flat roof that people use needs protection from falling at an edge with a drop of more than 600mm beside it, and Approved Document K sets the height and the strength of that guarding.
If the terrace already has a balustrade or a parapet, Building Control checks that the work on the rooflight has not removed or weakened it. If a new terrace is being formed, the guarding is part of the same notification. Walk-on units are laminated as well as toughened, so the glass holds together if a layer is damaged, and the maker's load class covers the glass itself.
A fixed walk-on rooflight also has to leave routes clear. It should not turn a step or a door threshold into a trip, and it should sit flush with or very slightly above the surface around it, to the maker's drawing.
Heat loss through the glass
The third item is energy. Part L of the Building Regulations limits the heat that new building elements can lose, and for a rooflight in an existing dwelling the ceiling is a U-value of 2.2 W/m²K. The lower the U-value, the less heat the glass lets out, so a double-glazed unit with a gas fill is the starting point, and triple glazing brings the figure down further.
A walk-on unit has thick laminated glass and a frame that carries load, so the glazing and a thermally broken frame are chosen to reach the limit, and the maker's data gives the U-value for the unit as supplied. We check that the unit named in the quote reaches the figure before it is ordered, so the notification and the product agree.
A solar-control coating limits heat gain in summer, and it is a separate choice from the legal limit.
Who looks after the notification
We do, as part of the installation. We prepare the notification, send it with the drawings and the unit's data, and arrange the inspections as the work reaches each stage. You do not have to approach the council or a private body yourself.
Other rules can apply to the room below, and they are separate from the rooflight. A basement being converted into a bedroom or a living room has its own requirements for damp-proofing, ventilation and escape, which the builder or designer of the conversion deals with. We work to the same drawings so the opening lines up with the rest of the scheme.
Conservation areas and listed buildings add a planning question before anything is ordered, and we check it at the outset. Flats are excluded from permitted development for roof alterations, so it is worth asking the council early; permission is usually required. To start, ask for a free survey through the quote form. Our terrace guide describes how an existing deck is prepared.