What happens to an electric rooflight in a power cut?

If it was open

It stays open, and if it rains a rain sensor cannot close it because the sensor also needs power. That is the one scenario worth thinking about, and it is why the manual override matters.

The manual override

Most units have one. Usually either a detachable crank handle that engages the actuator directly, or a release that disengages the chain so the sash can be pushed closed by hand.

Find out which yours is at handover and keep the crank somewhere you will find it in the dark. Looking for it during a storm with the window open is the wrong time.

Where the rooflight is above reach, the crank needs a pole, and it is worth checking you actually own one.

Battery backup

Available on some systems, usually a small unit that holds enough charge to close the window and sometimes to cycle it a few times. On a flat roof rooflight in a kitchen it is worth considering; on a modest unit within reach it is unnecessary.

Solar units

Unaffected by a mains cut, because they are not on the mains. The battery in the frame is charged by the panel and keeps working.

That is a genuine advantage and it is rarely mentioned when people compare solar with mains.

After power returns

Most systems resume normal operation with no reset. Some remotes need re-pairing after a long outage, which is a two minute job described in the manual.

It stays exactly where it is

A chain actuator holds its position mechanically rather than electrically. Losing power does not release it, so nothing falls shut and nothing springs open. If the window was closed it stays closed; if it was open it stays open.

That is worth knowing before worrying about it, because the common fear is a rooflight dropping or flying open, and neither happens.

The scenario that matters

Open when the power goes, and then it rains. The rain sensor needs power too, so the automatic closing you rely on is not available.

That is the case the manual override exists for.

The override

Two forms, and which one you have depends on the model.

A detachable crank. A handle that engages with the actuator and winds the chain in by hand. Common on chain actuators.

A release mechanism. A catch that disengages the actuator from the sash so the window can be pushed closed by hand.

Find out which yours is at handover rather than in the dark, and keep whatever it needs somewhere memorable rather than in the packaging. On a rooflight above reach the crank needs a pole, and a pole you do not own is not much use.

When the power returns

Most systems resume normally. Some need the control unit to be reset or the window to be re-paired with its remote, which is a minute’s work and is covered in the manual.

Where a system has been manually overridden, it usually needs a full cycle under power to re-establish its position, which is worth doing rather than leaving it half calibrated.

Why solar is unaffected

Unaffected. They run from their own photovoltaic panel and battery, so a mains power cut does nothing to them at all.

On a rural property with an unreliable supply that is a quiet advantage, and it is one of the reasons solar is worth considering even where mains wiring would be straightforward.

Smart systems

Worth thinking about separately. A rooflight that opens by app depends on a hub and a network, and those go down for reasons other than power cuts: a failed router, an expired account, a manufacturer changing something in an update.

Over a twenty five year life none of those is unlikely, which is why a physical wall switch alongside app control is not a luxury.

What to ask before ordering

Whether the model has an override and which type. Whether the crank or pole is included or a separate item. And whether it can be reached from floor level or needs access at height. Three questions, one minute, and they cover the whole of this.

Without backup, it stays where it is

A mains powered actuator has no power, so the unit neither opens nor closes. If it was shut, it stays shut, which is the safe state. If it was open when the power went, it stays open, and the rain sensor cannot close it either because the sensor is part of the same system.

That is the scenario worth thinking about: an open rooflight, a storm that has taken the power out, and no way to close it.

What a backup battery provides

A backup battery holds enough charge to operate the unit a limited number of times without mains power, and it keeps the rain sensor live.

It is not a substitute for mains and it will not run indefinitely. It exists to close the rooflight when the power goes, which is the function that actually matters.

Batteries have a service life of a few years, and the failure is silent: the unit works normally on mains and does nothing in a cut, which is discovered at the worst moment. Test it deliberately once a year by isolating the supply and operating the unit.

Where backup is not optional

Where the rooflight forms part of a smoke ventilation strategy or a designed ventilation provision. There it is a required part of the system rather than a convenience, and it is specified and commissioned accordingly.

Manual override

Some units have a mechanical override allowing the sash to be released and closed by hand. Where a rooflight is over something water would ruin, it is worth asking whether the model offers one.

What you must not do is force a powered actuator by hand without an override. Driving a geared motor manually against its gearbox turns a temporary inconvenience into a replacement.