The glass of an electric rooflight can go in during one visit. The wire that makes it move has a longer journey: from a power source, across a loft or through a roof build-up, to a frame that may sit above plaster, a stair void or a sealed flat roof. Where the power comes from and how the cable gets there are settled before the unit is ordered, because they change which model suits the house.
Wiring is also the part of the job that surprises people, since the cable route is invisible on a brochure photograph. For the wider choice of units, rooms and sensors, start with our electric opening rooflights page.
Mains, low voltage or sun
The motor inside an electric opening rooflight is made for one kind of supply, so the supply is fixed when the unit is ordered. Changing your mind afterwards usually means changing the motor, and sometimes the whole opening mechanism.
A mains unit has a motor that takes household voltage directly. A low-voltage unit has a motor that runs on a far smaller voltage, fed through a transformer that steps the mains down. A solar unit carries a small photovoltaic panel and a rechargeable battery, so there is no cable to the glass at all, only the wiring inside the unit itself.
None of the three is better in every house. Mains suits a roof where an electrician can already reach a spare circuit. Low voltage suits a thin cable that has to squeeze through a tight void. Solar suits a roof with no practicable route for any cable, provided the slope gets daylight for part of the day. We pick between them at the survey, with the ceiling void in front of us.
| Supply | Where the power comes from | What the house must provide |
|---|---|---|
| Mains | A fused connection from a household circuit | A spare circuit or spur, and a cable route from the consumer unit |
| Low voltage | A transformer plugged into or wired to the mains, then a thin cable to the motor | A dry, ventilated place for the transformer and a route for the thin cable |
| Solar | A panel on the unit charging its own battery | A slope that gets daylight, and access to replace the battery in time |
What a mains-voltage unit asks of your wiring
Connecting to household voltage is fixed electrical work in a dwelling, and that work has its own rules under Part P of the Building Regulations. It sits alongside the roof opening, as a separate piece of paperwork with a separate person responsible for it. Our answer on whether an electric rooflight needs an electrician goes through who does what, and we settle that before the quote is fixed.
In practice the electrician starts at the consumer unit, to see whether a circuit with spare capacity exists or whether the rooflight can share an existing lighting circuit. Next comes isolation: a switch or fused spur that cuts the supply to the motor when someone needs to work on it. The cable itself must suit the load and be clipped along its route.
A mains cable is thicker and stiffer than a low-voltage one, and it cannot be pushed through every gap. Where the ceiling below is finished and the loft above is floored, the electrician may need to lift boards. A rooflight in a new extension is far easier, because conduit can be laid before the ceiling is boarded and the cable drawn through afterwards.
Settle this before the order
Ask whoever will do the electrical work to look in the loft or ceiling void first. Their route decides whether a mains, low-voltage or solar model goes on the quote.
Low voltage and the transformer
A transformer is a small box, and it has to live somewhere. In a loft it can sit on a rafter or a board beside the unit. In a house with no usable loft, a cupboard on the landing or the airing cupboard may be the only choice. It should be dry, reachable for a future visit and clear of insulation heaped over it, since transformers give off a little heat.
The benefit of low voltage is the cable. The run from the transformer to the motor is thin and flexible, so it can follow a rafter, slip behind a lining board or drop down a stud wall, routes that would not take a mains cable. The trade-off is distance. A long thin cable loses some of the voltage along its length, so the further the motor sits from the transformer, the thicker the conductor has to be. We check the run against the cable sizes in the instructions for the unit at the survey.
Several units from one transformer
A landing with two roof windows, or a bathroom with a rooflight and an extractor, raises a question: can one transformer drive more than one motor? Some control systems are designed to, and the instructions state how many. We specify the transformer to suit the number of motors it will serve, and list it separately when we write the quote.
A thin low-voltage cable can follow a rafter where mains cable cannot
Solar units and the light they need
A solar rooflight collects its energy through a small panel set into or beside the frame, and stores it in a battery that works the motor. With no cable to run, it is the quietest answer for a finished house where a route through plaster would be intrusive. A chalet bedroom with a sloping ceiling lined in new plasterboard is a good example.
The panel only works if the slope gets daylight. A roof facing south or west receives direct sun for much of the day, while a slope in the shade of a taller neighbour, a tree or its own chimney stack may charge slowly. Overcast weather also lengthens the recharge. We look at the shading at the survey, at the time of day when the sun is lowest on that roof.
A solar unit has two parts that eventually wear: the battery and the panel's connection to it. The battery is replaced after a number of years, and the unit should be built so that this is possible from inside the room, without opening up the roof. Our page on solar powered skylights covers where this option works best.
When the power goes off
A mains or low-voltage unit may stop in whatever position it was in when the supply failed, and some designs include a manual override. Because that matters for a roof window that doubles as a bungalow escape window, we look at it in the guide on an electric rooflight in a power cut.
Is solar realistic for this roof?
- Find the slope Which way the rooflight faces and how much of the day the panel sees the sky.
- Check the shade Trees, a chimney stack or a taller building that blocks low sun.
- Look at the access Whether the battery can be reached from the room when it eventually needs changing.
- Compare the cable If a short mains or low-voltage route exists, set it against the solar option.
Finding a cable route through a finished house
In a new build the cable route is drawn before the plaster. In an existing house it has to be found, and the best route is rarely the shortest. The survey follows the cable from the glass back to the switch, through whatever the house offers.
With a loft above, the route is easy: along a rafter, down the wall plate and into the wall cavity or a surface trunking beside the door. With a loft that has a floor laid over the joists, boards may need lifting for a few metres. In a room-in-the-roof, where the slope itself forms the ceiling, the cable runs behind the lining in the space between the rafters, and a cut-out in the plasterboard may be needed at the switch end. A stair void is the awkward one. It often has no loft directly above, and the glass sits over open air, so the cable approaches from the edge and drops down the wall beside the stairs.
Surface trunking as a last resort
Where no hidden route exists, slim trunking on the wall is a tidy fallback. It can be painted to match, and it keeps the plaster intact. We show you the line it would take at the survey, and you decide whether it is acceptable before anything is ordered.
Flat roofs and extensions
On a flat roof, the cable has to cross the weatherproof layers. It usually enters through the side of the upstand or through a sleeve in the roof build-up, sealed so that water cannot track along it. A roof with a warm build-up, where insulation sits above the deck, needs the sleeve to be sealed at every layer it crosses. This is a job for the person fitting the roof covering, working with the electrician, and it is one reason we prefer to take the whole job on rather than split the cable from the roof.
| Where the rooflight is | Likely route | Watch for |
|---|---|---|
| Pitched roof with a loft | Along a rafter, down the wall plate to the switch | A floored loft where boards must be lifted |
| Loft room with sloped ceilings | Behind the lining between rafters | A cut-out in the plasterboard at the switch end |
| Stair void | Down the wall beside the stairs | No loft above, so trunking or a chase may be needed |
| Flat roof extension | Through a sealed sleeve in the upstand or roof build-up | Every waterproof layer the cable crosses |
Switches, remotes and sensors: what connects where
The control sends a signal to the motor, and there are two ways it can do that. A wired control, such as a wall plate or a keypad, has a cable running to the motor or its control box. A radio control, such as a handheld remote, sends the signal through the air to a receiver at the unit. Some systems combine the two, so a wall plate and a remote can both work the same glass.
The rain sensor is wired differently. It sits on the outside of the unit and connects to the motor's control box, so it can override whatever the switch last asked. If the rooflight is on a low-voltage system, the sensor draws a trickle of power from the same transformer. On a solar model, it is built into the unit's own electronics.
Choosing the position of the switch
The switch goes where a hand reaches for it: beside the bedroom door, at the foot of the stairs, near the bath but outside the splash zone. A bathroom brings its own limits, as the zones around a bath or shower restrict what can be fitted close to water, and the electrician follows them when siting any wall plate. A remote in a drawer avoids the question altogether in a damp room.
Moving a wall plate after the plaster is dry means cutting and making good again, so we agree the position on the wall with you at the survey.
Wiring words on a spec sheet
- Fused spur
- A fused connection taken from an existing circuit to feed one fixed appliance.
- Transformer
- The box that reduces the voltage for a low-voltage motor.
- Receiver
- The small radio unit at the rooflight that listens for the remote.
- Isolator
- A switch that cuts the supply to one unit so it can be worked on safely.
Testing, paperwork and what you keep
After the cable is run and the glass is in, the electrical work is tested before the ceiling lining is closed. The motor is driven through its full travel, the end stops are set so it does not strain at either end, and the rain sensor is wetted while you watch to prove that it closes the unit. Every control is shown to you, and any manual override is explained.
The roof opening and the electrical work each have their own paperwork. We handle the Building Control notification where the work is notifiable, and the person who connects the supply provides the electrical certificate that goes with their part. Keep both with the house papers. A later buyer's solicitor may ask for them.
Your quote lists the motor, the transformer or battery, the controls, the electrical work, the roof work and the making good indoors as separate lines. What moves the total is explained on our electric rooflight cost page. A cable route through a finished ceiling can add more than the motor itself, and a free survey with a fixed written quote is the way to see that before you commit. Our workmanship is covered by a 10-year guarantee in writing.
To begin, message 07880 284133 on WhatsApp showing the stair void, bathroom ceiling or loft slope you have in mind, or use the quote form.
