Will an Electric Rooflight Close if the Power Goes Off?

People often assume a rooflight left open will shut itself the instant something goes wrong, the way a fire door might swing closed on its own weight. An electric rooflight does not work that way. The sash is driven by a low-voltage actuator taking its instructions from a control unit, and neither part does anything at all once the supply feeding them stops. A unit wired straight to the mains through a transformer has no reserve of its own, so the sash simply stays wherever it was in its travel when the power cut, open, part open or closed, until the supply comes back or someone reaches it another way.

That is worth knowing before a household assumes a power cut is a safe moment to leave a rooflight open over a bedroom or a stairwell. It is not unsafe in the way a stuck-open front door might be, but it is a rooflight that will let rain in exactly as long as the outage lasts, with nothing electronic standing between the room and the weather.

The point that catches people out is the rain sensor itself. It is fitted to almost every electric rooflight, watching for a bridge of water across two exposed contacts on the frame, and it is genuinely automatic in ordinary use. It is still part of the same wiring as the actuator, though, so it shares the actuator's fate in a power cut: no supply, no reading, no closing signal sent. A rooflight left open when the mains fails during a shower will not shut itself, whatever the sensor would otherwise have done a minute earlier. Our guide to rain sensors and automatic closing covers how that sensor behaves when the power is actually there, which is the case it is built for.

A rooflight powered through a solar panel and a battery, rather than a transformer wired to the house circuit, is not drawing current from the mains at all in normal use, so a general power cut in the street does not touch it directly. The actuator and control unit keep working off the charge already stored, which means the sash can still close on a rain signal or a switch press exactly as it would on any other day.

That is not the same as saying a battery system never runs out. A battery drained by several days of cloud, or one that has simply reached the end of a long dark spell without enough daylight to top it up, behaves the same as a mains unit with no supply: the sash stops answering until the charge returns. Our answer on whether solar-powered rooflights work in winter goes through how much charging a panel realistically gets on a short, grey Fenland day, and what that means for a unit relying on it through the darker months.

A mains-fed system with its own small battery backup sits between the two, and it is worth asking for at the survey stage on any rooflight over a room where an open sash in the rain would actually matter, a stairwell or a bed being the obvious cases. Our guide to powering an electric rooflight: mains, solar or battery sets the three options against each other in full, including what each one costs to run day to day rather than just what it does in an outage.

Every electric rooflight we fit carries a way to move the sash by hand, separate from the motor and the control unit entirely. On most flat rooflights that is a crank handle or a removable pole with a fitting that engages the actuator directly, turned by hand to wind the sash open or closed regardless of whether any circuit in the house has power at all. On a roof window set higher up, the same idea usually takes the form of a longer pole reaching a spindle at the frame, rather than a handle worked from a standing position below it.

• The override does not need the control unit or the sensors to be working, since it drives the actuator's own gearing rather than sending it an electrical signal;
• It moves the sash at roughly the same speed the motor would, rather than snapping it shut, so nothing is caught between the frame and the pane while it is used;
• It works the same way whether the rooflight is mains-fed, solar-fed or battery-backed, because it bypasses all three;
• It is worth every household knowing where the crank or pole is kept before the day they actually need it, not after.

Our guide to manual opening rooflights: winders, poles and gas struts goes through the same hardware in more depth, including the fully manual units it is drawn from, for a room where a household would rather not depend on power at all.

Whether a power cut actually matters for a given rooflight comes down to the room underneath it more than the rooflight itself. A vent over a landing that nobody sleeps near is a different case from one over a headboard or the top of a stairwell, and we talk through both at survey stage rather than defaulting every job to the same wiring. Who actually runs the cable or the transformer into place is covered on our answer to who connects the power for an electric rooflight, and the safety systems that keep working alongside the actuator, the pinch sensor included, are set out on safety on opening rooflights: pinch protection and restrictors, worth reading alongside this page since a pinch sensor shares the same dependence on power that a rain sensor does.

The electric and opening rooflight installation page sets out how this fits with the rest of the job, from the actuator and control unit explained on electric opening rooflights: how they work through to the sightline the finished frame leaves, which we plan and draw before any decision about power is finalised. If a power cut matters to you for a particular room, it is worth raising at the survey rather than after the glass is ordered, and you can book a home visit to talk it through against the room in question.

Will a rooflight left open in a power cut let rain in?

Yes, if it is fed from the mains alone and nobody reaches it with the manual override. The rain sensor shares the same power supply as the actuator, so it stops working the moment the mains does.

Can the manual override be used while the motor still has power?

It can, though there is rarely a reason to. The override exists for the case where the motor cannot be reached electrically at all, not as an everyday alternative to the switch.

Does a battery backup close the rooflight automatically, or only let it be closed by hand?

A battery backup keeps the whole system running as normal, so the rain sensor and the switch both still work exactly as they would on mains power, without anyone needing to reach the rooflight by hand.

Is a manual override fitted as standard, or is it an extra?

It is fitted as standard on the electric rooflights we install, since a household should never be left with no way at all to move the sash by hand.