Why would a rooflight need a wind sensor?

An electric rooflight left open on a warm evening is, for a few hours, a flat panel of glass and frame held out at an angle above the roofline. In still air that is no problem at all. In a strong, sudden gust, the same open sash catches the wind the way a car door does when it is caught half open: the force lands on the hinge, the arm and the fixings all at once, and it lands hardest at the point of full extension, where the pull against the frame is greatest.

A rooflight is engineered to take that load within a stated range, and the actuator itself has a set stall force it can push against before something else gives. Past that range, the strain does not usually break the glass; it works on the hinge pin, the arm bracket or the seal at the edge of the sash, the parts that keep the unit weathertight and quiet for years. Closing the vent before the gust arrives, rather than after the strain has already happened, is the entire purpose of the sensor.

A small anemometer, usually a spinning cup wheel or a vane no larger than a domestic weather gauge, sits fixed to the outer frame or on a short mast beside it, clear of anything that would shelter it from the true wind. It feeds a running wind speed to the control unit, the same unit that reads the rain sensor and drives the actuator, and the installer sets a threshold speed above which the unit treats the reading as a close signal rather than background weather.

Once that threshold is crossed, the control unit drives the vent fully shut, in the same way it would for rain, regardless of how far open the sash was at the time. Our guide to how electric opening rooflights work sets the wind sensor in context alongside the motor, the switch and the other inputs the control unit listens to; on its own, the wind sensor is simply one more reading feeding the same decision the rain sensor already makes.

The threshold itself is not fixed by the sensor. It is a setting chosen for the installation, weighed against the size of the sash, the strength of the hinge and how exposed the roof actually is, so two rooflights on two different roofs can carry the same sensor and close at two different wind speeds.

Some rooflights carry a wind sensor because the household chose it; others carry one because the installation calls for it.

• Any rooflight that opens to a wide stroke, where the sash presents a large flat area to a gust at full extension;
• Sliding flat rooflights, where the whole pane moves clear of the kerb rather than tilting on a hinge, and a gust can catch the exposed edge of the moving glass itself;
• Rooflights fitted high on an exposed slope or a flat roof with open ground on every side and nothing nearby to break the wind first;
• Smoke vent rooflights over a stairwell, where the sensor's job stops being about the hinge altogether.

Our guide to hinged or sliding flat rooflights covers how the two opening methods differ, including which one carries the larger moving surface for a gust to act on. A smoke vent rooflight is the clearest case of all: our page on smoke vent rooflights on stairwells explains why that unit has to be stopped from opening into wind strong enough to push smoke back down the stairs rather than clearing it upward, which makes the wind sensor part of the fire strategy rather than an add-on chosen at the survey.

It is easy to assume one sensor covers all weather, but a rain sensor only answers moisture on its pad, and a wind sensor only answers air speed at the mast. Neither reading tells the control unit anything about the other. Our guide to rain sensors and automatic closing covers the pad, the wet-contact signal and how quickly the vent shuts once it triggers; a wind sensor closes the same vent, on the same actuator, but from a completely separate trigger.

Fitted together on the same rooflight, the two sensors simply give the control unit two separate reasons to close the same vent, and either one on its own is enough to trigger it. Closing on wind does not lock the vent: once the gust passes and the reading drops back under the threshold, the rooflight is free to open again on the next command from the switch, remote or timer, the same as after a rain-triggered close.

The ground north and east of Peterborough runs flat for miles, with little rising land or mature tree cover to slow a gust before it reaches a roof. Weather crossing that open ground tends to arrive with less warning than it would in a more sheltered street, and a wind speed that has been building steadily can turn into a sudden gust with almost no lead time for anyone to notice and reach a switch.

That matters most on the newer, flat-roofed extensions across townships such as Bretton, Orton and Werrington, where a rooflight is often set into an open expanse of roof with no chimney stack, parapet or neighbouring roofline to take the first force of the wind. A rooflight on a Fletton-brick terrace nearer the city centre sits at more of an angle to the prevailing wind and often has other roofs close by to break it, so the same sensor and the same threshold apply, but the margin it is protecting tends to be smaller in the first place. Around Stamford and the stone villages of the Nene valley, where slim conservation rooflights are more common than wide opening units, a wind sensor matters less simply because the openings themselves are narrower and lower to the roof.

A wind sensor is only as reliable as the control unit reading it, and that control unit needs power to take a reading, decide against the threshold and drive the actuator shut. Our guide to powering an electric rooflight: mains, solar or battery compares the three supply options in full; what matters here is that a supply failure silences the wind sensor exactly as it silences the rain sensor, leaving an open vent exactly as it was until power returns or someone reaches it by hand.

Some control units carry a small backup battery that keeps a limited period of sensor reading and motor drive alive through a short mains cut, closing the vent on a wind or rain trigger even without the mains supply present. Our answer on whether an electric rooflight will close if the power goes off sets out which systems carry that backup and what the manual override looks like on the ones that do not, which is worth understanding before choosing a control unit for a room that is often left unattended with the vent open.

Every decision on an opening rooflight is weighed against the sightline it sits inside, and a wind sensor is no exception. The anemometer mast is small and sits to the outer edge of the frame or kerb, below the eye position a sightline sketch is drawn from, so it plays no part in what is seen looking up from the bed, the sofa or the worktop. Fitting one is a question of protecting the mechanism and, on a stairwell, the smoke strategy, never a trade-off against the view the brand is built around; our sightline sketch is drawn the same way whether the specification includes a wind sensor or not.

A wind sensor also sits alongside the rest of the safety features built into an electric rooflight rather than replacing any of them. Our guide to safety on opening rooflights: pinch protection and restrictors covers what stops a hand or an object being caught as the sash moves, whatever has told it to close, and it applies just as much to a wind-triggered close as to one from a switch. Checking the sensor is working is a small part of the same annual look covered in whether electric rooflights need maintenance, and where several rooflights are grouped onto one smart home link, each unit's own sensor is worth testing individually rather than assuming one working sensor means they all are.

None of this changes what a wind sensor is there to do. It reads the wind, not the room, and it closes the vent before a gust can work on the hinge, the arm or, on a stairwell, the smoke strategy the whole system depends on. We set the threshold to the roof's real exposure at survey stage, alongside the sightline and the rest of the specification, as part of every electric and opening rooflight installation. Book a home visit and we will look at your roof and talk you through what it actually needs.

Does every electric rooflight need a wind sensor?

No. A small hinged unit on a sheltered roof with a modest opening stroke may not need one at all. It becomes standard rather than optional as the opening stroke, the sash size or the roof's exposure increases, and it is required on smoke vent units over a stairwell.

Can a wind sensor be added to a rooflight that does not already have one?

It depends on the control unit and wiring already in place. Some systems have a spare input ready for exactly this, and a mast can be added at the frame; others would need the control unit itself changed to add the extra sensor properly.

Does a wind sensor stop the rooflight opening at all in windy weather?

No. It only closes a vent that is already open once the reading crosses the set threshold. A closed rooflight can still be opened on a windy day; the sensor's job is to shut it again if the wind then rises past that point.

Is a wind sensor the same thing as a weather station?

No. A weather station reports conditions for someone to read; a wind sensor on a rooflight does one job only, feeding a live wind speed straight to the control unit so it can act on it in seconds, with nothing to check or interpret by hand.