Wiring and power for an electric rooflight

A manual rooflight opens with a handle or a winding pole. An electric one opens with a motor, and that motor needs three things: a supply to run on, a cable to carry the supply, and a control to switch it. Everything in this guide comes back to those three.

The motor itself is usually one of two types. A chain actuator pushes a rigid steel chain out of a housing on the frame, unfolding it to lever the sash open, then reels it back in to close. A spindle or rack actuator does the same job with a threaded rod. Both are low-power devices. A single rooflight motor typically runs on 24 volts and draws somewhere between one and two amps while it is moving, so around 24 to 48 watts, and nothing at all once the unit is sitting open or shut. It is not a heavy electrical load. It is closer to a doorbell transformer than a cooker.

On top of the opening motor, an electric rooflight often carries extras that also want power or signal: a rain sensor that closes the unit automatically when the first drops land, an integral blind with its own small motor, or a wall keypad and a radio receiver. Each of those changes the wiring slightly, and it is worth knowing which ones you want before anyone lifts a floorboard, because they decide how many cores your cable needs.

There are three routes to getting power to the motor, and they are genuinely different pieces of work. Choosing between them early is the single decision that shapes everything downstream.

The first is a mains-fed unit with a transformer. A 230 volt supply is brought to a control box, usually a small power supply unit mounted in the loft or a cupboard near the rooflight, and that box steps the voltage down to the 24 volts the motor actually uses. From the box, low-voltage cable runs the last short distance to the frame. The mains connection is the notifiable part; the low-voltage side is not.

The second is a fully low-voltage installation where the transformer sits further back, sometimes serving several units, and only 24 volt cable reaches each rooflight. This is common on a run of skylights over one room, where one power supply drives the lot through a control panel.

The third route has no mains cable at the rooflight at all. A solar-powered rooflight carries a small photovoltaic panel on its frame, a rechargeable battery inside, and a radio receiver. The panel keeps the battery topped up, the battery runs the motor, and the whole thing is operated by remote or wall switch over radio. No cable is run to the unit for power. That option deserves its own chapter later, because in Southend it is often the sensible one.

The hard part of wiring a rooflight is rarely the connection. It is getting a cable from wherever the power is to a frame sitting in the roof, without tearing up a room to do it. The time to solve that is at the wiring stage, after the structure is up and before the walls and ceilings are lined.

On a flat-roof extension the run is usually short and kind. The control box sits in the void above the plasterboard ceiling or against a joist, and the cable drops down a stud wall to a switch position and back to a spur. Everything is hidden in the build-up and nothing is on show. This is the easy case, and it is why an electric unit added to a new flat-roof skylight installation is barely more work than a manual one.

A loft conversion is nearly as tidy, because there is almost always accessible space behind the plasterboard or under the eaves to route a cable. A rooflight going into an existing pitched slope over a finished room is the awkward one. Here the choice is between lifting a few boards in the loft above to drop a cable down a partition, cutting a chase into a wall and making good afterwards, or accepting surface trunking. It is precisely this situation, a motorised unit wanted in a ceiling that is already skimmed and painted, where a solar rooflight earns its keep, because it removes the cable run from the problem entirely.

South Essex has a great deal of housing where this matters. The 1930s semi with a rear kitchen extension is everywhere across south Essex, and those extensions are the classic home for an opening rooflight over a knocked-through space. If the extension is being built or reroofed, the cable goes in for nothing. If the room is finished and lived in, the route is the first thing to work out, not the last.

Where a rooflight is mains fed, the 230 volt supply is taken from a nearby circuit, most often a lighting or ring circuit, through a fused connection unit. That is the small switched plate with a cartridge fuse in it, and for a rooflight motor the fuse is a low rating, typically 3 amp, because the load is tiny and the fuse is there to protect the flex, not to carry a kettle. From the fused spur the mains reaches the control box, and everything past the box is low voltage.

Permanent electrical work inside a home falls under Part P of the Building Regulations. Adding a fused spur and wiring a control box is exactly the sort of work Part P covers, and it needs to be carried out and signed off by a qualified electrician so that the connection is safe and properly certificated. This is a genuine regulatory point, not a sales one: the electrical side of an electric rooflight is real electrical work and should be treated as such, with the proper testing and paperwork at the end.

Keep two Building Regulations threads separate in your head, because they run in parallel on this job. The rooflight itself is notifiable in its own right: Part L governs the thermal performance of the glass, and Part K covers safety glazing overhead. We make that Building Control notification to Southend-on-Sea City Council, or to the relevant local authority for your address, as part of every installation. The electrical connection is the second thread, sitting under Part P, and it is completed and certified by the electrician doing the wiring. Both need to be right, and both leave a paper trail.

How many wires the motor needs comes down to how many things the rooflight has to do. A bare opening unit reverses its motor to open and close, which a control box handles, so the cable to the frame carries the low-voltage motor conductors and little else. Add a rain sensor, an integral blind or a chain of units that must move together, and the wiring grows.

Rain sensors

A rain sensor is a small pad on the frame or the surrounding roof that detects moisture and sends the unit shut, usually within a few seconds of the first drops. It is the feature that makes an electric rooflight genuinely usable, because it means you can leave the house with the unit open and trust it to look after itself. The sensor needs its own signal line back to the control box, so specify it before the cable goes in rather than trying to add it afterwards.

Wall switches, remotes and radio

Control comes in three broad flavours. A hard-wired wall keypad is the most reliable and needs a signal cable run to it while the walls are open. A radio remote or a radio wall switch talks to a receiver in the control box over a wireless signal, which saves running a switch cable but relies on batteries in the handset. Many systems offer both, a wired keypad on the wall and a handheld remote for the sofa, and on a high ceiling the remote is not a luxury, it is the only way anyone will actually use the ventilation.

Groups and smart control

Where several rooflights open over one room, they are wired back to a shared control panel and operated as a group, so one press moves the lot. The same panels increasingly speak to home automation systems, letting the rooflights open on a temperature trigger or close on a weather feed. None of this changes the basic electrical load, but it does change how many cores and signal lines you commit to while the walls are open, which is why the control scheme is a design decision, not a finishing touch.

A solar rooflight sidesteps the wiring question altogether, and in this part of Essex it does more than that. The frame carries a small photovoltaic panel, an internal rechargeable battery and a radio receiver. The panel charges the battery in daylight, the battery drives the motor when you press the remote, and no power cable ever reaches the unit. Installation becomes a roofing job with a handset in the box, and the electrician’s visit is not needed at all.

The obvious limitation of any solar device is that it depends on the panel seeing enough light to keep its battery charged. That is exactly where Southend’s geography turns the limitation into an advantage. Southend-on-Sea faces south across the Thames Estuary with an open horizon, sunlight hours among the higher figures for England, and reflected light coming back up off the water onto every south-facing roof plane. A small PV panel on a south-facing Southend roof is sitting in about the best conditions this country offers. The retrofit that is hardest to wire, an opening unit wanted in a finished south-facing slope, is also the one where the solar option performs best.

There is a neat piece of physics underneath this. A south-facing rooflight is a solar collector, and on a clear summer afternoon it can be pushing several hundred watts of heat into the room below through the glass. The same sun that overheats the room is charging the panel that lets you open the rooflight to vent it. An opening unit at the top of a room clears stratified hot air far faster than any window at head height, because heat rises to exactly where the rooflight sits. That is why the glass and the opening belong together on a south aspect: solar-control glazing to cut the gain that gets in, and a powered opening to shift the heat that still builds up. It is the same reasoning that runs through our solar-control glazing work, applied to the ventilation rather than the pane.

Solar units are not right for everything. A deeply shaded north slope, a unit under a taller building, or a very large frame that wants a heavier motor can all argue for a wired supply instead. But on the bright south-facing roofs this stretch of coast is full of, the wire-free option is often the first one to look at, not the fallback.

The electrical side of an electric rooflight goes wrong in one way above all others: it is left until the room is finished, and then the cable has nowhere to go without damage. Everything below is about avoiding that.

1. Decide mains or solar before anything else. This one choice decides whether an electrician is involved at all, and it depends on your roof, not on a catalogue. Ask for the recommendation to be tied to your specific ceiling and cable route.
2. Settle the cable route before the ceiling closes, not at handover. If the ceiling is being built or opened up, the run costs almost nothing. If it is finished, ask exactly how the cable will get there and what making good it involves before you agree the price.
3. Name the extras up front. Rain sensor, integral blind, hard-wired keypad, group control: each one changes the cable, and adding one after the walls are lined means going back into the fabric. List them before the wiring is designed.
4. Confirm who does the electrical connection. The mains work sits under Part P and should be done and certified by a qualified electrician. Ask how the connection will be tested and what certificate you will be handed at the end.
5. Keep the two paperwork trails clear. The rooflight is notified to Building Control for Part L and Part K, which we handle. The electrical connection is certified separately under Part P. You should end up with both, and knowing that in advance stops either one being skipped.
6. Match the opening to the aspect. On a south or west-facing plane, treat the powered opening as part of the overheating answer, alongside the glass, rather than a convenience. On a north plane it is mostly about fresh air and reaching a high unit without a pole.

An opening rooflight is a small motor, a short cable and a switch, and once the route is planned it is one of the more straightforward things to add to a roof. The trouble only ever comes from deciding it late. We have been installing skylights and rooflights across south Essex for over fifteen years, every installation backed by a ten-year workmanship guarantee, and the wiring gets designed at the same time as the frame, not bolted on afterwards. The full picture of motors, controls and glass sits on our electric skylight installation page, and if you want the route worked out for your own ceiling you can ask us to look at the roof before anything is ordered.