The short answer
Yes, if you replace the whole rooflight or roof window unit. That is building work under the Building Regulations: it is notifiable, and Part L applies. Exchanging only the glass in a sound frame is not a controlled fitting. We handle the Building Control notification wherever the work needs one.
The two cases
When people ask about replacing a rooflight and the building regulations, they are really asking about one of two different jobs. They are treated differently, so it pays to be clear which you have.
- Whole unit replacement. The frame and glass come out and a complete new rooflight or roof window goes in, even in the same opening and the same size. This is notifiable building work.
- Glass only. A failed sealed glass unit is exchanged for a new one in a frame that stays in the roof. This is not a controlled fitting, so no notification is needed.
Most of the confusion comes from the phrase like-for-like. A new unit of the same size in the same hole feels like maintenance, but the Regulations look at what is fitted, not at how little the hole has changed.
Why a whole unit is controlled
The Building Regulations treat a replacement rooflight or roof window as a controlled fitting, because it affects how well the roof keeps heat in and the weather out. A new unit must be shown to meet the energy standard in Approved Document L. Fitting it also involves the roof covering, the flashings and the structure round the opening, all of which the Regulations care about.
For an existing home, the energy limit depends on the type of unit:
| Type of unit | Limit |
|---|---|
| Roof window, in a pitched roof | Window Energy Rating band B, or 1.4 W/m²K |
| Flat-roof rooflight or lantern | 2.2 W/m²K |
Any unit in a pitched roof counts as a roof window, a conservation rooflight included. Once the maker has confirmed the figure for the size quoted, the data sheet goes in the job records. Our guide to how u values relate to Part L explains how to read those figures.
What notifiable means in practice
Notifying Building Control means telling either the local authority's building control team or a registered building control approver, the term used since April 2024 for a private body, that the work is going to happen. They may inspect the work, and when it is done you receive a completion certificate. You keep that certificate with the house papers, because a buyer's solicitor may ask for it when you sell.
We make the notification ourselves and keep the paperwork moving, so you do not need to contact the council. Our Building Regulations answer covers new openings as well as replacements, which have a few extra checks.
Where a rooflight is replaced in a loft room, Building Control may also look at whether the room's means of escape is affected. An escape window serves only storeys within about 4.5 m of the ground, and a loft conversion on a two-storey house relies on a protected stair instead, so a roof window there is chosen for light and air.
What about the glass-only route?
New glass in a sound frame does not need a notification, and the Part L table does not apply to it. The job still has to be done properly: the new unit must seat correctly, be sealed against water and not weaken the frame. It also does not give you the energy gain of a new unit with a better frame, which is why we check whether the frame justifies keeping. Our guide on replacing the glass or the whole rooflight sets out how that decision is made.
If a glass-only job turns up damaged plaster or a worn frame once the old unit is out, we tell you straight away and talk through the options before going further. Nothing is added to the fixed written quote without your agreement.
Planning is a separate question
Replacing a rooflight in the same position is rarely a planning matter, but a new opening is assessed separately. In England, most rooflights in a house roof are permitted development under Class C, with limits on how far they stand proud; see the planning guide. Side-facing ones carry an extra privacy condition, so mention at the survey if the rooflight faces a neighbour. The same applies if you are unsure whether the roof has ever had its rights restricted, because that is quicker to check before the work than after it. The council can withdraw those rights in some places, and a listed building needs listed building consent regardless. Flats and maisonettes have no householder permitted development rights. Our planning guide covers the exceptions.
How we run it
The free survey confirms which route fits your roof, and a fixed written quote follows before any work. If the job is a whole-unit replacement, we notify Building Control, fit the new unit to current Building Regulations, with the roof flashed and sealed afresh, and splay the opening on the room side where the roof permits, then plaster it and make good. A 10-year workmanship guarantee covers the work. Should another quote for a whole-unit job make no mention of notification at all, ask about it before you accept, because the certificate is yours to keep and a missing one can cause questions at sale.
