The Electrical Side of an Electric Rooflight Installation
An electric rooflight needs a permanent 230 volt supply terminated at a fused connection unit near the opening, from which the low-voltage control gear inside the rooflight is fed. The electrician runs and certifies everything from the consumer unit to that fused spur. We do the rooflight, the actuator and the control gear, and we terminate into the tested supply. That split matters, because we are rooflight installers, not electrical contractors. We do not run mains cable ourselves. This page explains the fused spur, the low-voltage side, how the cable is protected through the roof build-up, where Part P applies, and exactly who does what.
What the electrical supply has to provide
Three things have to arrive at the rooflight for a mains electric unit to work.
- A permanent 230 volt supply, taken from a suitable existing circuit, usually a lighting circuit or a dedicated spur, and terminated at a fused connection unit within reach of the opening.
- A low-voltage feed to the actuator. Most domestic actuators run at 24 volts, so a transformer or driver steps the mains down. On many units this driver sits within the control gear we install; on others it is a separate module the electrician terminates. Which arrangement applies depends on the unit, and we confirm it at specification.
- A control connection, either a control cable to a wall switch or a wireless receiver, so the unit can be told to open and close.
The fused spur and the low-voltage side
The fused connection unit is the boundary. On the mains side of it is the electrician’s work: the circuit, the cable, the protection and the certificate. On the rooflight side is ours: the control gear, the low-voltage wiring within the rooflight assembly, and the commissioning.
Keeping the transformer or driver and the control receiver inside the warm, dry envelope of the building matters, and it matters more near the coast. A control unit sited in a cold roof void condenses, and condensation on electronics is a slow way to kill them. We site the control gear inside the insulated envelope wherever the design allows, and on coastal work that is not optional.
Protecting the cable through the roof build-up
A cable passing through a roof is passing through the one part of the building whose whole job is to keep water out, so how it is routed and sealed is not a detail to skip.
- No cable entry on the weather side. The supply terminates inside, at the fused spur, and the low-voltage feed enters the rooflight through the manufacturer’s sealed cable entry, not through a hole drilled in the flashing.
- Sealed glands where the design allows. Any point where a cable passes through the frame is a route for damp air, so we use sealed entries and, on coastal work, marine-grade glands.
- Protected from abrasion and heat. Cable run through joists or a service void is protected where it passes through structure and kept clear of anything that runs warm.
- Kept out of the cold void where it can. A warm-roof service void is preferable to a cold, ventilated void where condensation forms.
Sequencing is everything. On a new extension the electrician runs the cable at first fix, before insulation and plasterboard. On a finished room, the cable route is surveyed before anything is ordered, because discovering after the roof is open that the nearest circuit is under a newly laid floor is how a job runs a thousand pounds over. We survey the route ourselves, first, and put a real figure in the quote rather than the words “supply by others”.
Part P, and where it actually applies
Electrical work in a dwelling is covered by Part P of the Building Regulations, and its scope is narrower than most people assume. Being clear about it prevents both overcharging and corner-cutting.
Notifiable work under Part P in England is essentially new circuits, work on the consumer unit, and any electrical work in a location containing a bath or shower. Adding a fused spur to an existing circuit outside such a special location is not notifiable in itself, though it must still be carried out to BS 7671, the wiring regulations, and certified with a minor works certificate.
| Task | Whose work |
|---|---|
| Circuit selection and cable sizing from the consumer unit | Electrician |
| RCD protection, isolation, testing | Electrician |
| Terminating the fused connection unit near the opening | Electrician |
| Electrical installation or minor works certificate | Electrician |
| The opening, structure, upstand or trimmers | Us |
| Flashing and weathering | Us |
| Mounting the rooflight and actuator | Us |
| Control gear and low-voltage wiring within the rooflight | Us |
| Commissioning, rain sensor setting, pairing controls | Us |
The trade boundary, stated plainly
We are skylight installers. Our 25 years sit in openings, structure, flashing and weathering, and in the rooflight itself. Running mains cable from a consumer unit is not our trade, and we do not pretend it is. We work with electricians registered under a competent-person scheme, so where the work is notifiable it is self-certified through their scheme rather than going through a building notice, and you get the certificate. If you already have an electrician you would rather use, that is genuinely fine. We give them the technical requirements in writing before the job, the supply, the fused spur position, the low-voltage arrangement, so nobody is guessing on the day.
What we will not do is run mains cable ourselves and hope. It is the wrong trade for us, and on life-safety work like an AOV it is doubly so, where the control panel and fire alarm interface are set out on the AOV smoke vent installation page.
Cable, protection and testing, in plain terms
You do not need to be an electrician to understand what the electrician is providing, and knowing it helps you read a quote.
- The circuit. The supply is usually taken from an existing lighting circuit or run as a dedicated spur from the consumer unit, sized for the small load an actuator draws. The actuator itself is a modest current, so the cable is not heavy, but it still has to be selected and protected properly.
- RCD protection. The circuit feeding the rooflight is protected by a residual current device, which trips on an earth fault to protect against shock. On a modern consumer unit this is already in place; on an older board it may need adding, which affects the electrician’s figure.
- Isolation. The fused connection unit near the opening gives a local point to isolate the rooflight for maintenance, so the unit can be worked on without killing other circuits.
- Testing and certification. The electrician tests the installation and issues a certificate, an electrical installation certificate for new circuit work or a minor works certificate for a spur added to an existing circuit. That document is yours to keep, and it matters if you sell the house.
How long the two electrical visits take, and where they sit around our roofing work, is on the how long it takes answer.
Coastal control gear, sited to survive
Near the coast, the electrical side needs more care than inland, and it is a genuine differentiator rather than an upsell. Salt-laden air corrodes standard fittings, so within about a mile of open sea at Felixstowe, Harwich, Frinton, Aldeburgh or Southwold we specify 316L stainless fixings and brackets, because the molybdenum content is what resists chloride attack that would seize a standard fixing in a couple of winters. Just as important is where the control gear lives. A receiver or transformer sited in a cold, ventilated roof void condenses, and condensation on electronics is a slow way to kill them, so we site the control gear inside the warm, dry envelope and use sealed cable entries and marine-grade glands where the design allows. Estuarine locations such as Woodbridge, Wivenhoe, Shotley and Pin Mill sit on tidal saline water with moderate salt loading rather than open-sea conditions, so upgraded fixings and sealed entries make sense there without the full marine specification.
When you can avoid the electrical work entirely
If the cable route is genuinely awkward and would damage a finished room, a solar unit removes the whole electrical side, because it carries its own panel and battery and needs no notifiable work at all. On a retrofit that is often the better answer, and we cover it on the solar powered rooflight installation page. The wider choice, and how the cabling drives the budget, sits on the electric skylight installation service page, with timings on the how long it takes answer.
Common questions
Do I need an electrician as well as you?
For a mains unit, yes, and the split is clean. The electrician runs the circuit from the consumer unit, terminates a fused connection unit near the rooflight, and issues the certificate. We do the opening, the structure, the flashing, the rooflight, the actuator, the control gear and the commissioning. We work with electricians registered under a competent-person scheme so notifiable work is self-certified rather than going through a building notice, and you are welcome to use your own. For a solar unit, no electrician is needed at all.
Is adding a rooflight spur notifiable under Part P?
Not usually. Notifiable work under Part P is essentially new circuits, consumer unit work, and electrical work in a room with a bath or shower. Adding a fused spur to an existing circuit outside those special locations is not notifiable in itself, though it must still be done to BS 7671 and certified with a minor works certificate. Where the work does become notifiable, our electricians self-certify it through their competent-person scheme.
Why will you not run the mains cable yourselves?
Because it is not our trade. We are rooflight installers, and our experience is in openings, structure, flashing and the rooflight itself. Mains work from a consumer unit belongs to an electrician who can certify it, and doing it properly protects you. We handle everything on the rooflight side of the fused spur and hand the electrician the technical requirements in writing beforehand so the two halves meet cleanly on the day.
Get a fixed price including the electrical connection
Tell us the room, the roof type and where the consumer unit sits. We survey the cable route ourselves before anything is ordered and give you one written price covering the rooflight, the controls and the electrical connection as a real figure, not a caveat, fixed after survey with a 10-year workmanship guarantee.
Request a fixed quote for electric rooflight installation, wiring included in the figure, across Ipswich, Suffolk and north Essex.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.