01Notification
Glass only, or the whole thing?
The rule turns on what you replace. A new sealed unit in an existing frame is treated differently from a new rooflight.
When a pane has misted, rooflight sealed unit building regulations are the worry, and this is the question that comes up as you weigh up the job. The answer is short, and it holds for any skylight or rooflight in an existing frame. Swapping only the sealed unit, meaning the glass and its spacer, leaving the frame and kerb where they are, is not notifiable to Building Control. Nothing is filed, and there is no certificate to wait for.
Replacing the whole rooflight, frame and glass together, is another matter. Part L of the Building Regulations, which deals with the conservation of fuel and power, classes that as a controlled fitting. The new rooflight has to meet the current thermal limit, and the work is notified to Building Control. We handle that notification where the work is notifiable, so you do not chase the council yourself.
| The job | Notifiable? | Why |
|---|---|---|
| New sealed unit in the existing frame | No | Only the glass changes, not the rooflight |
| New rooflight, frame and glass | Yes | A controlled fitting under Part L |
| New rooflight in a new opening | Yes | New controlled fitting, and may need a structural check |
02Why the line sits there
What Part L is protecting
Part L exists to stop heat being wasted. Fitting a new window or rooflight is where a home gains or loses a lot of it.
The Building Regulations treat a rooflight as a controlled fitting, in the same family as windows and doors. When you put a new one in, it must be at least as good as the standard of the day, which for a replacement rooflight is a U-value of 2.2 W/m²K or better. The U-value is how quickly heat gets through, in watts per square metre for every degree of gap between the inside and outside air, and a lower number means a warmer room.
A sealed unit sits inside an existing frame, and the frame stays as it was. That is why the rules treat glass-only work as a smaller step. It does not mean the unit can be anything. A new unit comes with a warm-edge spacer, a low-e coating and gas fill, so it should do more for the room than the old one managed when it was new. Our page on what U-value a rooflight should have explains the numbers behind it.
One practical point: the glass has to fit the frame it goes into. A unit that is a few millimetres out will sit badly, put stress on the edge seal and shorten its life. That is why we measure on site before anything is ordered, rather than working from an old order form or a guess.
- 2.2W/m²K, the limit a replacement rooflight has to meet under Part L
- 1.4W/m²K, a typical good double glazed rooflight
- 10year workmanship guarantee on our fitting
03Your side
What this means for your job
You never have to work out which route applies. We decide that at the survey and tell you in writing.
When we come to look at a failed pane, we check the frame, the seals and the kerb as well as the glass. If the frame is sound, the sealed unit route is open and no notification is needed. If the frame is warped, cold or past saving, replacing the whole rooflight is the better answer, and we handle the Building Control notification that goes with it. Our page on sealed unit or whole rooflight shows how that choice is made.
This is one of several questions we answer under misted and failed rooflight replacement. Planning is a separate question. Swapping glass in an existing opening changes nothing about how the roof looks from the street, so it raises no planning matter. A new opening is different, and our guide to whether rooflights need Building Regulations approval covers when the rules apply.
- We survey the rooflight and check what has failed.
- We tell you in writing whether glass alone will do.
- If it will, we fit the new unit with nothing to file.
- If not, we notify Building Control for the whole rooflight and fit it to current standards.
04Paperwork
What you are left with afterwards
A tidy job should leave you with clear paperwork, and a warm room you can see for yourself.
Keep whatever we give you in a folder with the house papers. A buyer or surveyor may ask one day what was done to the roof glazing and when, and a short written record answers that in a minute. For a whole rooflight, you receive the evidence that the work was notified and meets the standard, which matters when you come to sell. For a sealed unit alone, you have our written quote and the guarantee. Either way the work is covered by our 10-year workmanship guarantee, and one team does it from start to finish. Floors and furniture are protected while we work.
There is a sensible reason for treating the two jobs differently. Changing the glass alone leaves the opening, the frame and the roof build-up exactly as they were. Changing the whole rooflight alters the part of the roof that matters most for heat loss, so the regulations want it checked.
Glass alone needs no notification, but a new rooflight does, and we deal with it.
If you are not sure which side of the line your job falls on, ask for a free survey and written quote through our quote page.
Do I need to tell Building Control, or not?
Do I need a certificate for a new sealed unit?
No Building Control certificate is needed for glass-only work. You get our written quote and our workmanship guarantee instead.
Does the same rule apply to a VELUX window?
The same split applies: glass alone is not notifiable, and a whole new window is. Our page on replacing just the glass in a VELUX covers what is possible.
Will Building Control inspect my new rooflight?
For a whole rooflight, the work is notified and checked against the regulations. We organise that, so you do not need to contact the council.
Can a new sealed unit improve my heating bills?
If the old unit has failed, a new one with a warm-edge spacer, low-e coating and gas fill loses less heat. How much you notice depends on the size of the glass and the rest of the roof.
