Wiring an Electric Rooflight: What the Electrician Does

Wiring starts with a look at what is there. At the survey we check where the nearest suitable supply is, whether it has capacity for another small load, and how the cable could reach the window without crossing anything awkward.

The usual starting points are the lighting circuit on the landing below, a spur from a socket circuit, or a fused connection from the consumer unit. Which is right depends on the load, which for a roof window motor is small, and on the way the house has been wired over the decades. A Victorian terrace may have a mix of old and new circuits from successive owners. A 1930s semi may have been rewired once and extended since. A newer estate house will have a tidier layout, though the loft may be closed in by insulation and boarding.

What we write down

1. The position of the window on the slope and the height of the sash above the floor.
2. The nearest supply and the route the cable would take.
3. The control position, whether a wall switch, a keypad or a remote.
4. Any obstacles on the route: chimney breasts, water tanks, boarding, insulation.

The quote that comes after the visit shows the electrical work as a separate item, so you can see what the supply adds to the window price. The survey is free and carries no obligation.

With the supply identified, the route is planned. Cables like short, direct runs that stay out of the way. They should not be buried under insulation where heat can build up, nor run across the path of a joist where a drill might hit them later.

In a loft, the cable commonly runs along or beside the joists, up to the roof timbers and across to the window frame. In a finished room, it might run inside a stud partition, behind a boxed-in corner or through a gap above a ceiling void. Cutting into a decorated ceiling is the last resort, and the aim is always to find a route that avoids it.

Heat and damage both shape the route. A cable should not be squeezed under loft insulation where it cannot shed warmth, and it should not cross the line where a later shelf, picture hook or plasterboard screw might meet it. Where a cable has to pass through a joist, it goes through at a sensible height, away from the edges, in a drilled hole that is wide enough to let it move. Where it crosses a plastered wall, it runs in line with the switch or socket it serves, so anyone drilling later has a clue where it is.

The control point needs a decision of its own. A wall switch wants a back box and a cable. A keypad is similar. A handheld remote needs a receiver, which can sit in a ceiling void or on the window frame. A solar window needs none of this, which is why it appears so often in finished rooms.

The supply that finally arrives at the window may be mains or low voltage, depending on the window and its control unit. Some windows take mains directly, with a transformer in the control box. Others take a lower voltage from a power unit placed close by.

The thin cable on a low voltage system is easier to hide, and the power unit is the one place where the mains meets the system. The electrician decides the arrangement based on the model chosen. We do not choose a model by its wiring alone, but the survey does flag it, since it affects the route.

The cable that reaches the window is the electric skylight power supply in the plainest sense: one flexible lead plugged or wired into the frame, with enough slack to let the sash work. Our rooflight rain sensor page explains the small extra connection that serves the sensor, which shares the same supply.

The visit has a clear order. The electrician makes sure the supply is isolated before any work. The cable is run, clipped and protected, and the connection point near the window is prepared. The new circuit or spur is joined to the existing supply and the protective device is checked. Then the controls are fitted and tested.

Work on the roof and the electrical work are timed so neither blocks the other. The usual pattern is for the cable to be run to the opening before the window goes in, and for the final connection to be made after the window is in place. That keeps the roof open for the shortest time, and the slope is closed up weathertight each evening whatever stage the job is at.

Floors are protected throughout, and the cable route is made good afterwards. One team runs the job, so there is a single point of contact rather than a chain of trades each waiting for the next.

When the connection is made, the window is tested through its whole range: open, closed, intermediate positions and, if fitted, the response of the rain sensor. The controls are checked from where you will use them. The electrician tests the circuit and issues the paperwork for it.

At handover you should receive three things. First, a clear idea of how to operate the window and where the manual override is. Second, the electrical certificate for the circuit. Third, the details of the window and control unit, which are useful if you later add a second window or change the controls.

Keep the paperwork with the other house documents. Fitting a whole new rooflight or roof window is notifiable building work, and the Building Control notification is made by us where it applies. A 10-year workmanship guarantee covers our work, as set out on the guarantee page.

Planning a second electric rooflight is far easier when the first has been wired with the future in mind. A spare capacity on the supply, a junction box in a reachable place and a switch position with room beside it all make the next window less work.

That matters in houses that grow in stages. A loft room is converted first and a bathroom skylight added later. A kitchen extension is built, and a landing window follows. If the electrician knows about the plan, the cable can be laid with it in mind.

A manual window being changed over raises the question of reaching the frame without opening the finished room. Converting a manual rooflight to electric deals with it, and the answer sometimes points to a solar version instead.

• Spur a branch off an existing circuit
• Consumer unit the box where the circuits begin, with their protective devices
• Isolator a switch that cuts power to one item so work on it is safe
• Certificate the paper that records the electrical work and its test results

The wiring is rarely the largest part of the job, but it can swing the total. A short run in an open loft is a small line on the quote. A long route through a finished house is a bigger one, and it carries the cost of making good. Our page on electric rooflight cost explains what the factors are, and the broader costs page sets out UK market figures.

Questions worth putting to any installer are practical ones. Who does the electrical work, and who certifies it? Where will the control go, and have we agreed it? What happens to the cable run afterwards, and who makes good? And is there a manual override?

Our answers are on the quote and in the survey notes. Opening options are shown on every quote, with the electrical line item beside them. If the wiring looks heavy for your house, the quote also shows the solar alternative, so the comparison is clear. The electric and opening rooflight hub brings together the other guides on this subject.