What Happens to an Electric Rooflight in a Power Cut?
A mains-powered electric rooflight fails safe in whatever position it is in when the power goes, and it cannot be driven until the supply returns. If it was closed, it stays closed and weathertight, which is the usual case. If it was open, it stays open. A solar rooflight is unaffected, because it carries its own battery, and its rain sensor keeps working throughout. An AOV smoke vent is the deliberate exception: it fails open on power loss, because in a fire it must clear the escape route.
Mains units: fail closed, held in position
The important word is held. A mains electric rooflight does not slam shut when the power cuts, and it does not fall open. It holds exactly where it was. Because most units spend most of their life closed, a power cut is usually a non-event: the unit stays shut and keeps the weather out. The scenario worth planning for is the unit being open when the power goes, because it will stay open until the supply comes back, and in a Suffolk squall that can mean water in.
Three answers, by how much it matters to you
- Accept it. On a kitchen rooflight, a power cut with the vent open is a nuisance and nothing more. Most people take this, because power cuts are rare and short.
- Battery backup. A backup unit sits between the supply and the control gear and holds enough charge to drive the unit closed at least once, sometimes several times. It is standard on smoke ventilation and a sensible option on any rooflight over a stairwell or a room you cannot easily reach.
- Manual override. Some chain actuators can be released and the sash closed by hand. Whether yours can depends on the model, and we confirm it at handover rather than leaving you to find out in the rain.
Never go up to a stuck-open rooflight in bad weather. If a mains unit is stuck open because the power has failed and the weather has turned, protect the room from inside and wait for power or help. Do not climb onto the roof and do not force the sash. Our rooflight stuck open in the rain page sets out the safe indoor steps.
Solar units: unaffected
A solar rooflight is genuinely immune to a mains power cut, because it does not use the mains at all. It carries its own panel and battery, so it opens and closes on demand through a power cut, and, crucially, the rain sensor keeps working, so the unit still closes itself if the weather turns while the power is down. That is a real advantage over a mains unit and it rarely gets mentioned. If power-cut resilience matters to you, it is a strong point in favour of solar, covered on the solar powered rooflight installation page.
AOV smoke vents: fail open, on purpose
An AOV does the opposite of a comfort unit. It fails open on loss of power or loss of the detection signal, because a smoke vent in a fire that has taken out the mains must still open to clear the escape route. Its control panel carries battery backup, commonly 72 hours of standby, so the system stays live through a mains failure. That fail-safe-open behaviour is a defining feature of life-safety ventilation and it is proved during commissioning. The full picture is on the AOV smoke vent installation page.
| Type | In a power cut | Rain protection during the cut |
|---|---|---|
| Mains comfort unit | Fails in position, cannot be driven | None while power is off |
| Mains unit with battery backup | Can close at least once on backup | Limited, backup dependent |
| Solar unit | Unaffected, works normally | Full, sensor keeps working |
| AOV smoke vent | Fails open, backup keeps it live | Not its job; life safety comes first |
If you are choosing between mains and solar and this is a deciding factor, the electric versus manual rooflight comparison and the main electric skylight installation page both cover it.
Common questions
Will my electric rooflight close automatically if the power fails while it is raining?
A mains unit will not, unless it has battery backup, because it cannot be driven without power. If it was open when the power failed, it stays open until the supply returns. A solar unit will, because it runs off its own battery and the rain sensor keeps working through a power cut. If a mains unit is stuck open in the rain, protect the room from inside and wait for power rather than going up to it.
Can I close an electric rooflight by hand in a power cut?
Sometimes. Some chain actuators have a manual release that lets you close the sash by hand, but whether yours does depends on the model. We confirm it at handover so you know before you need it. Never force a sash that has no release, because you will bend the actuator arm or snap a chain link and turn a power cut into a replacement.
What about an AOV in a power cut?
An AOV fails open, deliberately, because a smoke vent must still clear the escape route in a fire that has cut the power. Its control panel carries battery backup, commonly 72 hours, so the system stays live through a mains failure. This is the opposite of a comfort rooflight and it is the correct behaviour for life safety, proved when the unit is commissioned.
Get a fixed price with the right fail-safe
Tell us where the rooflight sits and how much a power cut with it open would matter. We advise whether battery backup, a manual override or a solar unit is the right answer for your situation, and give you one written price fixed after survey with a 10-year workmanship guarantee.
Request a fixed quote for electric rooflight installation across Ipswich, Suffolk and north Essex.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.