Do flat rooflights and skylights need building control?
Forming a new opening in a roof is notifiable work and needs Building Control, whether through the local authority or an approved inspector. Replacing a unit in an opening that already exists is not normally notifiable, although the new unit still has to meet the limiting thermal standard. The completion certificate that follows a notified job is what matters years later.
What makes it notifiable
Cutting into the structure, rather than the glazing itself.
A new opening means joists trimmed and a load path altered, an insulation line interrupted, and a new junction in the weathering. All of those are matters the regulations cover.
Swapping a unit into an opening that is already there alters none of them.
What is checked
Four things on a flat roof rooflight.
The structural adequacy of the trimming around the opening. The thermal performance of the unit. The ventilation provision for the room. And reasonable provision against condensation at the junction.
The structural check
Straightforward on a modest opening and designed on a large one.
Joists cut for the opening are carried by trimmers spanning to the joists either side, sized for the span and the load.
On engineered joists it is a designed detail rather than a site decision.
The thermal check
Against a limiting U-value, which every current product clears.
The figure and how it is declared is on the limiting U-value for a replacement rooflight.
On a new extension the glazed area is also considered against a notional allowance for the extension as a whole.
The ventilation check
The one most often overlooked on a replacement.
Where a room’s background ventilation currently comes through the old rooflight, the new one has to provide it, and not every unit carries a vent.
It is checked at survey rather than discovered at fitting.
The condensation check
Reasonable provision at the junction, which in practice means the insulation and the vapour control layer.
Insulation carried to the frame and the vapour control layer sealed to it is what satisfies it, and it is also what makes the room comfortable.
Why it matters is on why is there condensation on my flat rooflight.
Local authority or approved inspector
Two routes to the same outcome. The council’s building control service or a private approved inspector, either of which issues the completion certificate. Which is used generally follows whoever else is involved in the project.
Competent person schemes
A third route where an installer is registered for the work.
Self certification under a scheme removes the separate application and produces a certificate through the scheme instead.
The obligation to meet the standard is identical; the paperwork route differs.
Why the certificate matters
Not on the day, and reliably years later.
A solicitor acting for a buyer asks for it, and reconstructing one after the fact is considerably harder than obtaining it at the time.
It is the single most practical reason to notify properly.
What happens if it was never notified
A regularisation application, which exists and has a fee.
An inspector examines work already done, which on a flat roof rooflight can mean opening up so the detail behind a finish can be seen.
It is straightforward, and more expensive and more disruptive than doing it at the time.
Enlarging an existing opening
New work rather than a replacement, and notifiable.
Making an opening bigger alters the structure and the junction, so it is assessed as new work even though a rooflight was already there.
Part of a larger project
Where the notification is generally already in hand.
Where an extension is being built, the whole project is notifiable and the rooflight is part of it rather than a separate submission.
Which of the two applies is agreed at the start so nobody assumes the other has done it.
Planning is separate
A different question with a different answer.
Building Control is about whether the roof is safe, dry and warm. Planning is about appearance and amenity, and a job can need one, both or neither.
The planning position is on do flat roof rooflights need planning permission.
Listed buildings
A third regime again, and none replaces the others.
Listed building consent is about the character of the building. It does not remove the Building Control requirement, and satisfying one says nothing about the other.
Who arranges it
We do, on a job we are carrying out, as part of the work rather than as an extra.
The certificate goes to the householder to keep, because it is theirs rather than ours.
What a flat roof adds to the check
Two items a pitched roof rooflight does not raise in the same way.
The fall of the deck around the new opening, because a kerb sited across a fall changes how the roof drains, and the continuity of the vapour control layer through a warm roof build up.
Both are specific to a deck rather than a slope, and both are looked at as part of the same inspection.
When the inspector visits
Generally twice on a rooflight forming a new opening.
Once with the opening formed and the structure visible, before it is closed up, and once at completion. The first is the one that matters, because it is the only chance to see the trimming.
Which means the work is sequenced around it rather than closed up and inspected afterwards.
What we notify
We notify where the work is notifiable, hand over the certificate, and check the ventilation position on every replacement because it is the requirement most often missed.
The whole picture is on the flat roof rooflight installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.