Do electric rooflights close automatically in rain?

How it behaves

The sensor is a small pad on the roof near the unit. Water bridging its contacts triggers the close, usually within a second or two of the first drops.

The window then takes fifteen to thirty seconds to shut, so a little rain does get in. In practice that is a few drops rather than a wet floor.

It does not predict

No forecast, no barometer. It is a wet contact. It reacts to rain that has already started, which is enough to prevent the outcome that matters.

It also cannot tell rain from a hose or heavy dew, so it will occasionally close for those. Harmless, sometimes puzzling.

Does it reopen

Usually not automatically, and that is the right design. A window reopening unattended when a sensor dries is worse than one staying shut. You reopen it yourself.

Some systems latch until reset. Worth knowing which yours does.

When it is worth having

Where you might open it and leave the room or the house. A kitchen or bathroom rooflight, or anything on a schedule.

Where you only ever open it while you are in the room, it is optional, though it is cheap at installation and considerably more expensive to add later because the sensor cable runs back to the control point.

Maintenance

Wipe it annually. A dirty sensor either misses rain or reads permanent moisture and refuses to let the window open at all, which looks exactly like a fault.

Only if a rain sensor is fitted

It is not automatic simply because a window is motorised. A rain sensor is a small detector on the frame that signals the actuator to close when it starts raining, and it is an option on some systems and standard on others.

We include one as standard on any motorised unit we fit, because it is what makes the motor worth having.

What happens when it triggers

It detects moisture on the sensor surface and triggers a close cycle. That takes fifteen to thirty seconds on a mains unit and thirty to sixty on solar, so a small amount of water gets in during the closing.

That is a few drops rather than a problem, and it is worth knowing rather than expecting it to close before the first drop lands.

Most systems will not reopen automatically afterwards. The window stays shut until you open it again, which is generally the behaviour you want.

What it enables

Leaving a rooflight open without thinking about it. That is the whole value: a window you have to remember to close before rain is a window you leave shut.

The useful version is night purge in summer: open it late, let the day’s heat leave the building overnight, and stop worrying about a shower at four in the morning.

The limitations

It needs power. In a mains cut the sensor is out too. A chain actuator holds its position mechanically so nothing moves, and the scenario to plan for is open when the power goes and then it rains. Find out how your manual override works at handover.

Solar units are unaffected by a mains cut.

It needs cleaning. A sensor caked in grime either misses rain or reads permanent moisture and refuses to let the window open at all, which looks exactly like a fault. Wipe it when you clean the gasket.

It does not detect wind. A dry gale will not close the window, and a large open sash in a gust is a load on the actuator.

Where it matters most

Any rooflight above reach. Any lantern vent, which is always high. Any coastal or exposed site, where weather arrives quickly.

On a flat roof unit it matters more than on a pitched one, because a horizontal opening admits considerably more water in a shower.

What to check at handover

That the rain sensor is actually fitted and working, which sounds obvious and is worth confirming rather than assuming from the quotation.

How the manual override works, demonstrated rather than described, and whether it can be reached from floor level or needs a pole. Then keep whatever it needs somewhere memorable rather than in the packaging.

And where the sensor sits, so you know what to wipe when you clean the gasket. A sensor caked in grime either misses rain or reads permanent moisture and refuses to let the window open at all, which looks exactly like a fault and produces a lot of unnecessary callouts.

Ten minutes at handover saves an unpleasant evening at some point in the next twenty five years.

Only with a rain sensor fitted

It is not automatic behaviour of the motor. A small sensor mounted on the outside of the unit detects moisture and signals the actuator to close. Without one, a powered rooflight left open in rain stays open.

Most manufacturers fit or offer one as standard on powered units, but it is worth confirming rather than assuming, particularly on a retrofitted opening kit.

How well it works

Well, with two caveats.

It responds to rain arriving, so a small amount of water enters before the unit shuts. On a light shower over a kitchen worktop that is a wipe. It is not a reason to leave the rooflight open in an approaching storm.

And it needs cleaning. A sensor coated in dust or pollen either stops responding, which is the dangerous failure, or starts closing the unit in dry weather, which is the irritating one. A wipe once a year handles both.

The power question

The sensor is part of the powered system. In a mains power cut it cannot close the unit unless there is battery backup, and storms are exactly when power goes.

That is the argument for backup on any rooflight over something water would damage. Batteries have a service life of a few years and fail silently, so test yours by isolating the supply once a year.

What it does not do

Detect wind. A rooflight open in a gale is a separate risk, and the answer is a wind rated unit or the habit of closing it.

Most systems allow the sensor to be overridden temporarily, which is useful on a warm evening when passing showers keep shutting the window.