The short answer
Yes, when the whole unit comes out. Replacing a whole rooflight or roof window, frame and glass together, is notifiable building work, because the new unit is a controlled fitting under the Building Regulations. Replacing only the sealed glazing unit, with the existing frame left in place, is not notifiable. So whether replacing a skylight is notifiable comes down to one thing: whether the frame is being changed.
Is replacing a skylight notifiable if the frame comes out?
A rooflight or roof window is a controlled fitting, in the same way a replacement window in a wall is. When the old frame is taken out and a new frame and glazing go in, the work has to meet the current energy standard and be notified to Building Control. That makes a full rooflight replacement notifiable work, even when the new unit is the same size and goes in exactly the same opening.
Typical whole-unit jobs include swapping an old roof window for a current model in its flashing kit, lifting off a tired flat rooflight and fitting a new one on the existing upstand, and taking out an old lantern frame to put a new lantern in its place. Our guide to replacing a rooflight walks through each of these on the roof.
If the opening changes size, the job goes further than a replacement. Cutting or trimming rafters to take a larger unit is a structural alteration, and the wider rules in our rooflight Building Regulations guide apply.
- Old frame out, new frame and glass in: notifiable
- Same opening, new unit of the same size: still notifiable
- Larger opening with rafters cut or trimmed: structural work as well
- Sealed glazing unit only, frame kept: not notifiable
When only the glass is changed
A sealed unit that has misted between the panes, or has a cracked outer pane, can often be replaced on its own while the frame stays put. That is not a controlled fitting change, so no notification is needed. The new glass should still be specified properly, with the right thickness, coatings and a laminated inner pane where that is recommended, but there is no Building Control step.
The choice between new glass and a new unit depends on the frame. A sound frame with a failed sealed unit suits a glass swap; a frame that has warped, rotted or lost its seals suits a whole new unit. Our misted and failed rooflight replacement service covers the glass-only route, and the answer on when to replace a skylight sets out the signs that point to a whole new unit. The frame decision is what makes a frame-out rooflight replacement notifiable work and a glass-only swap free of that step.
The two Building Control routes
Notifiable work goes to Building Control by one of two routes. The first is the local authority: for most homes in the area that means Swindon Borough Council or Wiltshire Council, depending on the address. The second is a registered building control approver, a private body registered with the Building Safety Regulator; that has been the term in use from April 2024.
Either route reaches the same place. The work is notified before it starts, the body checks that the new unit meets the regulations, and a certificate is issued once the job is complete. For a straightforward like-for-like replacement, the notification is light: it records the address, the unit and its thermal performance. We handle the notification where the work is notifiable, and the job plan names which route we are using for your house.
The Part L values the new unit must meet
The thermal standard for a replacement in an existing home is Approved Document L, the 2021 edition, Table 4.2. It sets limiting values for new and replacement fittings. A roof window, the type that sits in a pitched roof in its flashing, takes the same limit as a window. A rooflight, the type that sits on a flat roof or upstand, has its own limit.
Current units from the main manufacturers are made to meet these values, but the figure still has to be confirmed for the exact product and size, because the whole-unit U-value changes with the frame and the glass specification. The job plan names the unit and the figure we are working to.
| Fitting | Limiting value |
|---|---|
| Roof window (pitched roof) | 1.4 W/m²K, or Window Energy Rating Band B |
| Rooflight (flat roof or upstand) | 2.2 W/m²K |
What you keep at the end, and why it matters when you sell
When the work is signed off you receive the Building Control certificate for the replacement: a completion certificate from the local authority, or a final certificate from a registered building control approver. Keep it with the house deeds. You also receive the product details for the unit, including its size code and thermal figures.
The certificate matters most when the house is sold. A buyer's solicitor will ask whether any rooflights or windows have been replaced, and for evidence that the work was notified. A certificate on file answers the question in one line. Without one, the sale can stall while the seller looks for paperwork or arranges an indemnity policy, which is a cost and a delay nobody planned for.
- Building Control certificate for the replacement
- 10-year workmanship guarantee in writing
- Unit details: model, size code and U-value
- The manufacturer's product warranty, where the maker gives one
How the job plan records it
Every quote from Ridgeway Skylights comes with a written job plan, and the Building Control row answers this question for your job before you commit. It states whether the work is notifiable, which route we are using, when the notification goes in, and when the certificate should follow the fitting day. For a glass-only job the row simply says the work is not notifiable and why.
The unit row sits next to it, naming the replacement and the Part L figure it meets. That way the regulations side is settled on paper alongside the size, the lead time and the fitting date, and the certificate arriving afterwards is the expected last step rather than a loose end.