Retrofit answer
Can you add a skylight to an existing roof?
A new opening in a roof already standing is a normal job. Whether yours can take one depends on the structure under the covering and on the permissions that go with your kind of home.
The answer
Yes. A new skylight can be cut into an existing pitched or flat roof, provided the structure can be trimmed to carry the load around the opening and the rules for your home are met. On a house that is often permitted development; on a flat, planning permission is needed. Cutting the opening is building work notified to Building Control.
What does the roof need to take a new opening?
Rafters or joists that can be cut and supported on new trimmers, and a covering that can be lifted and relaid. Most of this is checked from the loft and from outside at the survey.
A skylight is not stuck on the surface. It needs a hole through the roof's structure, and the structure has to carry its load round that hole.
On a pitched roof
The rafters are cut where the unit goes and the cut ends are supported on a trimmer fixed between the rafters either side. Rafters either side are doubled up to share the extra weight. Roof windows are made in sizes that fit between standard rafter spacings, so often only one or two rafters are cut.
On a flat roof
The joists are trimmed in the same way, and an upstand is built round the opening so the rooflight stands clear of the surface. The size of the opening is therefore limited by how much of the structure can be interrupted.
What the survey looks for
From the loft we see the timbers, their spacing and condition, and any wiring, pipework or insulation that sits in the way. From outside we see the covering and its type. Together they tell us whether the position you have in mind works, or whether a small shift left or right would give a simpler opening.
Which permissions apply to my home?
A house usually falls under permitted development. A flat needs planning permission. A listed house needs listed building consent. Every new roof opening is notified to Building Control.
The planning route follows the type of home. On a house, Class C permits a rooflight that projects no more than 150mm beyond the plane of the roof slope and sits no higher than the highest part of the roof. A flat or maisonette has no householder permitted development, so a new rooflight on one needs planning permission, and a Tyneside flat is a flat. An Article 4 direction or a condition on an earlier permission can remove Class C from a house.
Listed and shared
A listed house keeps Class C on the planning side, but almost any rooflight on it needs listed building consent, which decides the job. Owners of flats should read the lease or title for the roof and loft, and tell the other owner what is planned before placing an order.
Building Control
Cutting a new opening in a roof is building work. It is notified to Building Control, the local authority or a registered building control approver, and we deal with the notification where the work is notifiable. The full planning picture is set out in our rooflight planning permission guide.
Questions to settle before ordering
- Is the home a house, a flat or a maisonette?
- Is it listed, or covered by an Article 4 direction?
- Does an earlier planning permission carry conditions?
- Who owns the roof, according to the title or lease?
- Where in the roof is the light needed?
Does it matter which part of the building the roof covers?
Yes. A loft room, a landing and a flat-roofed extension each call for a different product, and a roof window used as an escape route has its own limits.
The same roof can hold several kinds of room, and they do not all need the same opening.
A loft room
A roof window brings light, headroom and air to a loft room. If the loft is to be a bedroom, the means of escape comes into the design. Under Approved Document B, a roof window counts as an escape window only for a room within 4.5 metres of the ground, while a loft conversion on a two-storey house needs a protected stair instead. Our roof window fire escape answer goes through it.
A landing or hall
A stair landing in a terrace or semi may sit directly under the slope, in which case a small roof window is enough. Where it does not, a sun tunnel is the alternative.
A flat-roofed extension
A flat-topped kitchen or garden room is the natural home of a flat rooflight or lantern, sized to the room. The opening is then planned with the upstand height in mind.
What happens to the room underneath?
Inside, the opening is lined and the insulation is carried round it, leaving no cold bridge. Thermal limits for the unit are set by Part L.
The roof is only half the job. A new opening also changes the room, so the finish inside is part of the work.
Lining the opening
Between the roof structure and the ceiling or rafter line, the opening needs a lined light well. It is normally splayed or squared and plastered or boarded so the light spreads into the room. Insulation is carried round it so the new opening does not become a cold bridge.
Thermal performance
Under Part L for existing dwellings in England, the limiting U-value is 2.2 W/m²K for a rooflight, and 1.4 W/m²K (or WER Band B) for a roof window. The unit we propose will meet the figure for its type.
Decorating
Plaster needs to dry before painting, so the room is usually decorated after the work rather than during it. Ready to ask? The quote form is where it starts, and the survey and fixed price follow.
Retrofitting questions, answered
Can a skylight go in a roof that is already insulated?
Yes. The insulation is cut back around the opening and carried up the sides of the light well, so continuity is kept. We look at what is there when we survey the loft.
Will it matter if my rafters are close together?
It can help. Where the gap between rafters matches the unit, fewer need cutting. A unit wider than the gap simply means a wider trimmed opening; the carpentry allows for it.
Can I add several skylights at once?
Yes, and it is often tidier to plan them together, since access and scaffolding are shared. Every opening is trimmed on its own, while one planning route covers the lot.
Does the roof covering limit what I can fit?
It decides the flashing kit, not whether a skylight can go in. Each covering has its own flashing kit, and flat roofs get an upstand with a membrane detail.