How does an electric skylight work?

Press open and a low-voltage signal reaches a control board tucked into the head or side of the sash. The board wakes the motor, which turns a gear that feeds a chain out through a guide. The chain is stiff in one direction and flexible in the other, so it behaves like a rigid arm as it extends and pushes the opening edge of the glass away from the frame. A typical roof window travels far enough to give you a gap of a few centimetres for background ventilation, opening wider for a full purge of stale air.

Larger units and roof lanterns often use a spindle actuator instead. Here the motor turns a screw thread, and a nut running along that thread drives an arm that levers the sash on its hinge. Spindle drives suit heavier glass because the load is spread along the thread rather than hung off a single chain point. Either way the motor is geared down hard, so the glass moves slowly and holds its position with the power off. Nothing drifts shut on its own, and nothing slams.

Built into the same board are the limits. The unit knows its fully open and fully closed positions and eases towards each one rather than driving into the frame. Most also read the current the motor is drawing, so if the sash meets a hand, a bird or a build-up of leaves on the way down, the resistance spikes, the board reads it and reverses. That obstacle detection is why an electric unit is usually the safer choice for a rooflight sitting well above head height, where you would never reach a manual handle in a hurry.

There are three supply routes, and which one you have changes how the skylight is installed and wired.

• Mains powered. The unit runs off a fused spur on the house circuit, stepped down to a safe low voltage inside or just outside the frame. This gives the strongest and most consistent drive, which matters for big glass, multiple units on one control, or anything you want opening dozens of times a day. It needs a cable run to the roof, so it is simplest to arrange while the ceiling below is open or during a loft conversion.
• Solar powered. A small photovoltaic panel on the outer flashing charges a battery hidden in the sash, and that battery drives the motor. There is no cable to the roof at all, which makes a solar unit the practical answer when running mains power up to the opening would mean lifting floors or chasing walls. The panel keeps the battery topped up through daylight, including the diffuse light of an overcast day, and the motor draws so little that a full charge lasts through a long dull spell.
• Low-voltage from a transformer. Some systems put a transformer at the switch or in the loft and carry safe low voltage up to the unit. It sits between the other two, trading a shorter mains run for a length of bell-type cabling to the roof.

Whichever route the power takes, the motor itself is a low-voltage item. You are not sending mains up to the glass, which keeps the wiring at the wet end of the job simple and safe.

A moisture sensor sits on the outside of the frame, usually on the top flashing where the first drops land. It is a small pad that reads a change in electrical resistance as water bridges its contacts. The instant it detects rain it signals the control unit, which overrides whatever you asked for and drives the sash closed. You do not have to be in, awake or even in the country.

Two things are worth knowing about it. The sensor reacts to the first drops, not to a downpour, so the glass is moving before real rain arrives. And because it closes on a signal rather than a schedule, it does not care what the forecast said. A dry morning that turns at lunchtime is exactly the situation the sensor exists for. On solar and mains units alike, the automatic close runs off the same stored or supplied power that opens the unit, so it still works during a power cut on a solar model and for as long as the backup lasts on a wired one.

The sensor closes the glass to a seal, not just to a gap. Once shut, the gaskets around the sash compress and the unit is as weathertight as a fixed rooflight. That is the part a manual opener cannot match: a manual unit left cracked open for ventilation stays open until someone climbs up and winds it shut.

The simplest control is a wall keypad, wired or wireless, with open, close and stop. Most units also ship with a handheld remote that talks to the frame over radio, so you can open a rooflight three metres up without leaving the sofa. Because the signal is radio rather than infrared, you do not need line of sight to the glass.

From there it scales. One remote or keypad can drive several units together, which is how a run of rooflights over a kitchen opens as one. Add a control gateway and the skylight joins a home system, so it responds to a phone app, to a voice assistant, or to rules you set: open at a set temperature, close at a set time, vent for ten minutes after a shower. The motor and sensor described above do not change. You are simply giving the control board more ways to receive the instruction.

Fit an internal blind to the same unit and it can run off the same battery or supply and the same controller, so the glass and the shade move together. On a hot room that pairing does more than either part alone, which brings us to where an electric unit earns its place.

Reach is the first reason. A rooflight over a stairwell, in a double-height space, or high on the slope of a loft conversion is one you will never operate by hand, so a manual opener there is a window that stays shut. A motor makes it a window you actually use.

Heat is the second, and this is where orientation matters in Southend. A room under a south-facing roof collects sun across the whole middle of the day, and along the estuary there is an open southern horizon and light bouncing off the water, so those rooms run hotter than the same room would inland. Hot air rises and stacks up against the ceiling, which is precisely where a rooflight sits. An electric opening unit at the highest point of the room lets that hot layer escape, and if it is set to open automatically when the room warms and close when the rain sensor triggers, it ventilates all day without anyone touching it. That night-purge effect, opening in the cool evening to flush the day’s heat out, is hard to get from a window you have to remember to wind.

Ventilation is not the same as solving solar gain, though, and it is worth being straight about that. Letting hot air out helps, but the better fix on a south-facing roof is to stop as much of the sun’s heat getting in through the glass in the first place, which is a question of the glass specification and its G-value rather than the motor. The two work together. We set out the glass side of it in our work on energy-efficient skylight installation, and pair a low G-value pane with an opening electric unit where a room needs both.

So decide first whether the opening is within easy reach or not, because that alone often settles manual against electric. Then work out how power would get there: if a cable run is awkward, a solar unit removes that problem entirely and is worth pricing before you rule electric out on wiring grounds. Note which way the roof faces, because a south-facing room wants the glass specification looked at alongside the opening, not instead of it.

Tell us the rough opening size, the orientation and whether power is easy to reach, and we will come back with a specification for the whole unit, glass included, and a price. Ring 01702 898232 or request a quote, and look at our electric skylight installation service for how the fit itself is done. If the room is one that overheats, our costs page shows where the glass and the motor together tend to land.