The short answer
Fitting a new rooflight in place of the old, frame and glass together, is notifiable under the Building Regulations as a controlled fitting. A new sealed glass unit set into a sound frame, with nothing else changed, needs no notification. The Building Control notification, where one is needed, is something we deal with for you.
The two jobs, side by side
The rule turns on what comes out of the roof. If the frame stays and a new sealed glass unit goes into it, the work is outside the notification rules. If the frame comes out as well, you are fitting a new controlled fitting, and the work has to be notified to Building Control.
| Item | New sealed unit only | Whole new rooflight |
|---|---|---|
| What comes out | The glass unit | Frame and glass together |
| Notifiable | No | Yes, as a controlled fitting |
| Part L limit for the new fitting | No new fitting is installed | 2.2 W/m²K if it is a rooflight; the ordinary window figure if it is a roof window |
| Paperwork you keep | Our quote and invoice, with the maker's warranty | The same, plus the Building Control completion certificate |
| Usually costs | Less | More |
Our page on replacing a misted sealed unit covers the glass-only job in detail, and the hub page on misted rooflight replacement sets both routes out together.
What the Part L limits mean for a replacement
Part L of the Building Regulations sets the thermal performance for fittings in existing homes. Table 4.2 in the 2021 update lists 2.2 W/m²K as the figure for a rooflight. A roof window is judged as a window, so it must reach 1.4 W/m²K, and the other option is Band B for its window energy rating.
Which limit applies depends on whether the new unit is a rooflight or a roof window. The maker's data states the class of each unit, and we confirm which one applies to your opening at the survey and specify the glass, frame and edge spacer to meet it. Our guide to rooflights and the Building Regulations explains the wider rules, and our answer on rooflight U-values explains how the figures are read.
Who handles the notification
Your local authority Building Control and a registered building control approver are the two places notifiable work can go, the second being the private route, known by that name since April 2024. Either way, the body is told before work starts, may inspect, and issues a completion certificate (a final certificate on the private route) when the work is finished.
On a whole rooflight replacement we handle that notification for you and the cost is shown on the quote. You do not need to chase the council or hunt for an approver yourself. The certificate is worth keeping with the deeds or the house file, since a solicitor acting for a buyer may want to see it when you sell.
- Notification handled by us where the work is notifiable
- Completion certificate passed to you
- Part L limit written into the specification
When a glass-only job becomes a whole replacement
A glass unit can only go into a frame that can hold it. During the survey we look for the signs that make a new frame the better choice.
- A frame that has bowed, rotted or cracked at the corners, so a new unit would not sit true.
- A unit size that is no longer made, or a frame with no room to take a modern, thicker unit.
- Staining or damp marks round the edge that point to a failed flashing or upstand rather than a failed seal.
- A wish to change the rooflight itself, such as a bigger opening, an opening vent or a different glass specification.
In those cases the quote prices the whole replacement, and the notification comes with it. Where the frame is sound, the glass-only route usually costs less and we say so.
What about a new opening
A newly cut opening in a roof is, in its own right, building work as far as the Building Regulations are concerned, whatever the planning position. Putting a rooflight where there was none involves cutting rafters or joists, weatherproofing the roof and meeting the Part L limit, so it is a bigger job than a like-for-like swap. Whether planning permission is needed is a separate question, and our rooflight planning guide covers it.
For a swap of the whole unit in the same opening we check the planning position for the address, because the position can differ for a listed building, under a planning condition, or where an Article 4 direction applies. The council decides.
To see which route fits your roof, book a free survey and the written quote will set the glass-only and whole-unit options side by side.
Related questions
Do I need a certificate after a glass-only replacement?
None is required for the glass unit, because that job is outside the notification rules. You get our invoice and the maker's warranty for the unit, and we keep the workmanship guarantee of 10 years attached to the job.
Does a like-for-like skylight swap still count as a new fitting?
When the frame and glass both come out, the new unit is a controlled fitting and the work is notifiable, even in the same opening and at the same size. Only a swap of the sealed glass unit alone sits outside the notification rules.
Which U-value must my new rooflight meet?
For any rooflight newly installed in an existing dwelling, Part L 2021 (Table 4.2) expects 2.2 W/m²K or better. A roof window must meet the ordinary standard for windows, 1.4 W/m²K, or else reach Band B for its window energy rating, as declared by the maker.
Can I use a private building control company?
A registered building control approver can act instead of the council, the private route known by that name since April 2024. We handle the notification whichever route is used, and tell you which one the quote assumes.