The short answer
Usually yes. Swapping an old rooflight or skylight for a new unit is building work that has to meet today's energy and safety standards, and that normally means notifying Building Control. A true like-for-like swap is the simplest case. Changing the size or shape of the opening turns it into a larger job. We handle the notification where the work is notifiable.
Three kinds of swap, three different positions
People use the word replacement for very different jobs. Building Control looks at what physically changes, so it helps to sort your project into one of three groups before asking whether a notice is needed.
| The job | What changes | Usual position |
|---|---|---|
| Glass only | New sealed units, old frame stays | Still must meet Part L |
| Whole unit, same opening | New frame, glass and flashings | Notifiable |
| Bigger or moved opening | Roof structure altered | Notifiable, with structure |
The middle row is what the phrase like-for-like usually describes. The unit comes out, a new one of the same footprint goes in, and the roof around it is left alone. Even so, the new unit is a controlled fitting, and the regulations expect it to perform to current standards rather than to those of the year the house was built. That is the reason a simple swap still counts.
The top row is the grey area. Fitting new sealed units into a sound frame is cheaper, and it can be right where the frame is in good order. The glass still has to reach the required thermal performance, so we confirm with Building Control how that job should be recorded rather than assuming. Our guide to replacing an old skylight, like for like or a better unit weighs the two routes.
What the current standards ask of the new unit
A replacement has to be better than the one it replaces in a few specific ways. None of them are exotic, and most are simply what a modern unit does as standard.
Part L governs heat loss. Old rooflights, especially early double glazed units and single glazed domes, lose far more heat than anything sold now. A new unit has a low-emissivity coating and an insulating gas fill, and its frame has a thermal break, so the room under it is warmer in winter and cooler in summer. The build for this is set out on our energy efficient rooflights page.
Part K governs safety glazing. Glass overhead should not fall on anyone if it breaks, so the inner pane is laminated. Older units, particularly plastic domes and plain toughened panes, often fall short. If you are thinking about swapping a dome, see replacing a plastic dome skylight with glass.
Part F may come into play when a room depends on the old unit for ventilation. If a bathroom or landing relied on an opening rooflight for air, the new arrangement has to keep doing that job, which is one reason an electric or opening unit is sometimes the better choice. The detail is in electric and opening rooflight installation.
When the opening itself changes
The moment a replacement needs a different hole, the job moves from a swap to structural work. Everything in the notification process then applies in full.
A bigger unit needs the opening widened, which usually means cutting rafters or joists and trimming the new edges. A moved unit means closing one opening and forming another. Both alter the load path in the roof, so the structural detail is notified and inspected, in the same way as a brand new opening. We cover the reasoning in does a new rooflight need Building Control.
Ask about size early. It is tempting to go larger when the old unit is out, because the extra daylight is the whole point of a rooflight. Our answer on putting a bigger rooflight in the same opening explains what is possible within the existing frame and what is not. Sizing for the room is a survey decision.
Planning is separate again. A like-for-like swap normally changes nothing the council would care about, but a larger or differently placed unit may, and conservation areas have their own rules. Start with planning permission for rooflights and skylights.
How the swap runs with the notification in place
The order of events is simple, and the paperwork runs alongside the work rather than holding it up.
At the survey we look at the unit, the frame, the upstand and the ceiling reveal, and decide which of the three groups above your job falls into. The quote states the new unit and the glazing build, and the written quiet spec records why that build suits the room. Building Control is notified before the old unit comes out. The inspector looks at the work while it is open, and you receive the completion certificate when it is signed off.
A unit that has failed is the usual reason for a swap. If you can see fogging between the panes or a frame that no longer closes, our page on misted and failed rooflight replacement is the place to start, and the same page shows what to look for. To talk through your own unit, use the quote form or the wider skylight and rooflight installation in Crawley overview.
Questions before you swap a rooflight
Can I fit the new unit myself and notify afterwards?
Notification is meant to come before the work, so the inspector can see the stages that get covered up. Starting without it can leave you needing to open up finished work later. It is cleaner to notify first, and we do that as part of the job.
Does a new unit of the same size keep my old ceiling finish?
Often it does, since the reveal stays the same. Some disturbance is normal, and we make good inside.
Is a notifiable swap more expensive than an unnotified one?
The notification is one part of the price, and it is itemised in a proper quote. What affects the total is set out in what affects the cost of replacing a skylight.
What if my unit is old but still watertight?
You can leave it as it is. If you choose to swap it, the new one meets current standards, and is it worth replacing an old skylight helps you decide.