Do electric rooflights close automatically in rain?

The pad, and what actually triggers it

The sensor is a small plate mounted on the outside of the frame, usually at the head, with a pattern of conductive tracks across its face. Water bridging those tracks changes the resistance between them, the electronics read that change, and a close command goes to the mechanism. On some units the pad is gently heated so it dries out promptly once rain stops, rather than holding the window shut for the rest of a damp afternoon.

It is a contact detector, not a weather instrument. It knows that its own surface is wet. It knows nothing about cloud, wind, forecast or the state of any other part of your roof.

How quickly it moves, and why some rain gets in

The command is close to instant. The travel is not. A comfort vent typically takes somewhere in the region of half a minute to a minute to run from fully open to shut, because these mechanisms are geared for quiet, controlled movement rather than speed.

Add the few seconds the pad needs to wet through and you have a window that is still partly open through the first of the rain. On a light shower nothing reaches the floor. On the sort of downpour that starts at full intensity, some water comes through the opening before the sash seats. That is not a fault and no sensor on the market avoids it.

The failure mode nobody warns you about

Wind-driven rain arriving at a sharp angle can travel straight through the opening and land inside while the pad, which faces upward on the outside of the frame, stays comparatively dry. The room gets wet and the sensor never triggers.

This is most likely on a steeply pitched window facing into the prevailing weather, and it is a good argument for a shorter opening angle on exposed elevations. Snow is the other weak point. Dry snow can settle on the pad without wetting it enough to register, and the unit stays open while the roof turns white. Neither is common. Both are worth knowing before you rely on the feature.

Why it refuses to reopen afterwards

On most systems the sensor takes priority over your commands while the pad reads wet. You press open, the unit either does nothing or starts to open and immediately closes again. People assume the mechanism has developed a fault.

It has not. The system is doing exactly what it was bought to do, and it will release as soon as the pad dries. If you genuinely need the vent open in the wet, most systems allow the sensor to be overridden for a period through the remote or keypad, after which it re-arms itself automatically. It is worth learning that sequence when the unit is handed over, rather than looking for it in the rain.

Keeping the pad reading truthfully

The sensor is the one part of an electric rooflight that asks anything of you, and what it asks is small. A film of pollen, dust, moss debris or salt across the tracks changes how it reads. A heavily soiled pad can hold a residual reading and keep the unit shut, or dull the response enough that it triggers late.

Wipe it when you clean the glass, with water and a soft cloth. Nothing abrasive, no solvent, and no jet washer anywhere near it. Under a tree, or on a north slope where growth builds, do it more often. Broader upkeep is covered on what maintenance an electric rooflight needs.

What happens when there is no power

The sensor runs off the same control unit as the mechanism, so during a mains outage it is dead along with everything else. A vent left open stays open through the whole cut, sensor or not. On a solar unit the battery keeps both the mechanism and the sensor alive, which is a genuine and underrated advantage of that route.

When mains power returns and the pad is wet, most systems will drive the unit shut immediately without being asked. The wider picture is on what happens to an electric rooflight in a power cut.

Where a sensor changes the answer, and where it does not

Whether to specify one at all, on a unit where it is optional, is set out on whether you need a rain sensor.

What it is not, and what it does not replace

A rain sensor is not a security device. It closes a vent, it does not lock it, and an unlocked rooflight is not a barrier. Where a unit is reachable from a flat roof or a garden wall, the locking specification is what matters and it is a separate conversation.

Nor does a sensor make a poorly detailed rooflight watertight. Water that arrives through a shallow upstand, a flashing lap running the wrong way or a covering terminated at the wrong height comes in with the sash firmly shut. The perimeter detailing decides whether the unit stays dry. The sensor only decides whether it was open at the time.

We install new rooflights and full replacements across Oxford and up to twenty five miles by road, with fifteen years in the trade and a ten-year workmanship guarantee, fitting VELUX, Fakro, Keylite and Roto units. Electrical connection is carried out by a qualified electrician. Call 01865 704245 or email info@heritageskylightsoxford.co.uk.