Planning answer
A walk-on rooflight in a roof terrace or balcony: will it work?
A terrace over a flat roof is a natural place for walk-on glass, because the same surface gives you somewhere to stand and light for the room underneath. What decides it is the glass rating, the drainage and the planning route.
The answer
Yes. A walk-on rooflight can be set into a flat roof used as a terrace or balcony, provided the glass is designed for the people, furniture and point loads it will carry, and the roof structure is checked. Planning depends on house or flat: a flat needs permission, while a house may fall under Class C if the rooflight stays within the 150mm projection limit.
Why put walk-on glass in a terrace at all?
It lets daylight drop into the room beneath a terrace without giving up the floor space above. The glass sits level with the decking, so you walk across it like any other part of the terrace.
A terrace on a flat roof often sits right over a room that has little or no daylight of its own: a kitchen, a stair, a bathroom or a landing. A walk-on rooflight turns part of the terrace floor into a window for that room.
Level with the decking
The glass is set into the roof so its top face is close to level with the finished terrace. That way you can walk across it, set a chair near it and sweep it with the rest of the surface. It does not stand up as a hump or a box, so it does not take away usable space.
What reaches the room under it
Light falls through the glass into the room underneath, and some of it reaches the next room too. A frosted or dotted finish softens the view up from below and stops the room feeling watched from above. The same trade-off appears in a different setting in the guide to glass over basements and light wells.
Does a terrace rooflight need planning permission?
On a flat or maisonette, yes: there is no householder permitted development. On a house, Class C can cover a rooflight within 150mm of the roof plane, but the terrace use itself is a separate question to put to the council.
The planning answer starts with the type of home, as it does for every rooflight.
On a house
A rooflight on a house is permitted development under Class C if it projects no more than 150mm beyond the plane of the roof slope and sits no higher than the highest part of the roof. A walk-on pane set close to the decking can sit well inside that figure. An Article 4 direction or a condition on an earlier planning permission can remove Class C, and a listed house needs listed building consent for almost any rooflight, with that consent deciding the job. A conservation area on its own does not remove Class C for a house.
On a flat
Flats and maisonettes have no householder permitted development. Planning permission from the council is required for a new rooflight on either Tyneside flat, upstairs or downstairs. The flat's title or lease names the roof's owner and whether the other owner must be consulted; study it and consult them first.
The terrace itself
Using a flat roof as a terrace, with railings or screens, raises its own planning questions about overlooking and height, apart from the rooflight. Ask your council whether the terrace is already approved. Rules for every kind of home are gathered in the planning permission guide for rooflights.
Which house is yours?
Upstairs flat
- Who decides
- Roof and roof space ownership, plus any need for the other owner's agreement, sits in the lease or title.
- Which rules apply
- A flat has no householder permitted development, so a new rooflight needs planning permission from the council.
Downstairs flat
- Who decides
- A downstairs flat may have a terrace over an extension, but the lease or title still says who owns that roof.
- Which rules apply
- Planning permission is needed here too, since flats and maisonettes have no householder permitted development.
House
- Who decides
- The owner decides, bound by the deeds and any covenant, and by party wall duties where a neighbour is affected.
- Which rules apply
- Class C can apply to the rooflight within its limits, unless an Article 4 direction or earlier condition removes it.
What does Building Control look at on a terrace roof?
The new opening is notified as building work, and the roof must carry the glass, the people and the furniture. Edge protection around a terrace is considered under the Building Regulations too.
A new opening in a roof counts as building work. It is notified to Building Control, either the local authority or a registered building control approver, and we deal with that notification where the work is notifiable.
Structure under the terrace
A terrace roof already carries more than a plain flat roof, and the rooflight adds an opening in the middle of it. The joists around the opening are trimmed and doubled, and the glass frame sits on a kerb or an upstand that is built to carry the design load. The detail comes from the survey.
Guarding and edges
If the terrace has a drop at its edge, railings or a parapet form a separate piece of design under the Regulations. That is a matter for the terrace, whether or not a rooflight is in it, and it is worth settling at the same time so one drawing covers both.
Thermal performance
For an existing dwelling in England, the limiting U-value for a rooflight is 2.2 W/m²K. A double-glazed sealed unit is used where the glass forms the weather barrier of a heated room.
How do water and furniture affect the glass?
The terrace must still shed rain, so the rooflight sits on a sealed upstand that follows the roof fall, and the glass must be rated for the furniture and planters you intend to put near it.
A terrace is a wet, busy surface, and the rooflight has to fit into both the water route and the way you use it.
Keeping the roof watertight
The roof covering is turned up around the edge of the opening and sealed to the frame. The terrace falls toward its outlet, and the rooflight is set so water runs off its top face and not along its edge. Decking tiles or boards are cut around the frame, so no water is held against it.
Furniture, planters and heels
A table leg or a chair with a narrow foot puts a small area under heavy pressure. Tell the supplier what will stand on or near the glass so the design covers it. The way those loads are set is explained under load and slip ratings.
Next step
Browse the range on the walk-on rooflights page; a request for the survey that precedes any price starts at the quote form.
Terrace and balcony queries
Can walk-on glass be set into a balcony floor?
It can be done where the balcony structure can carry the glass and its supports. The survey looks at the floor construction, the drainage and the edge protection before deciding. On a flat, the lease or title and planning permission come first.
Will a rooflight in the terrace overheat the space under it?
A big pane in the sun can heat the room, which is why solar control glass or a tinted layer comes into the specification. The aspect of the terrace and the size of the glass both play a part, and the survey takes them into account.
Can a rooflight be set into decking over a flat roof I already have?
Yes, where the roof can be opened and made good. A new opening is framed and sealed, and the decking is cut to suit. The structure under the existing covering is looked at first, since that decides what is possible.
Is a terrace rooflight different from one in a hallway floor?
Weather is the main difference. Outdoor glass sees rain, frost and algae, so it needs a firm grip finish, sealed edges and drainage. The wet-weather grip answer covers the grip side.