Do electric rooflights close by themselves when it rains?

How a rain sensor works

A rain sensor is a small plate with a moisture detector, often heated, fixed on or beside the rooflight where rain will reach it. The first drops bridge the contacts on the plate, and the control unit reads that as rain and runs the motor to close the vent. On a heated plate the element dries it after the shower, so dew and mist are less likely to set it off.

Some sensors work with the motor controller directly, and others feed a wall panel or remote that holds the settings. The detail varies from maker to maker, so we read the data sheet for each unit on a quote and set the facts in the same rows.

What happens when it rains

The vent closes at the motor's normal speed, which takes a short while on a large sash. A light shower that begins while you are out is dealt with, and a heavy squall that arrives with the vent wide open can put some water on the sill before the sash is shut. The sash then seals against its gasket as it does on any other day.

Many units with a sensor stay shut until you open them again, and some can be set to reopen once the plate has dried. If you want the vent to stay closed all afternoon after a shower, check that setting on the specification.

Sensor or no sensor, side by side

With a manual unit the habit that keeps rain out is closing the vent before you leave the house, and many households manage that without trouble. The sensor earns its cost where nobody is at home to do that, or when the rooflight sits out of reach. Our guide to manual and electric rooflights puts the two on the same rows.

Keeping the sensor reliable

A sensor that is dirty or badly placed may fail to notice rain. Leaves, bird droppings and dust all coat the plate over a season, so a wipe with a damp cloth when you clean the glass keeps it responsive. Fix it where it sees rain falling and not under the lip of the frame or a gutter's shadow.

Give the plate a clear view of the sky, and keep it away from a downpipe or an overhanging branch that could make it wet when the rest of the roof is dry. We pick the position at the survey, with the roof pitch, the aspect and the nearest trees in mind.

• Sensor included or priced as a separate line
• Reopen behaviour stated on the specification
• Position agreed at the survey

Adding a sensor to a manual or older unit

A manual rooflight has no motor to tell, so a sensor alone cannot close it. Fitting one means adding a motor as well, and whether a motor kit exists depends on the maker and the frame. For a manual unit that is old or has no kit, replacing the rooflight can work out more sensibly than altering it.

Under the Building Regulations, exchanging the complete rooflight, glass and frame is notifiable, and where it applies our firm files the Building Control notification. Cabling is priced on its own line; our guide to electric rooflight wiring explains what the run involves, and our answer on what an electric rooflight does in a power cut covers the other thing people ask once the sensor is settled.

Book a free survey and we will check which of your rooflights could take a sensor and price the alternatives together.