A rain sensor can only be added to an electric rooflight whose control system is designed to accept one. It is not a bolt-on for a manual unit. On a compatible motorised rooflight, fitting it means mounting the sensor pad on the outer frame where rain will reach it, wiring or pairing it to the control unit, and setting the sensitivity so it closes the sash when it gets wet. On a manual unit there is no actuator to drive the sash shut, so there is nothing for a sensor to trigger.
How a rain sensor works
The sensor is a small pad with two interleaved conductive tracks. Rain bridges the tracks, the resistance between them drops, the controller sees the change and drives the actuator to close the rooflight. Most systems then hold the unit shut for a set period, commonly ten to fifteen minutes after the pad dries, so a passing shower does not make the vent flap open and closed. Because closing depends on driving the motor, the whole thing only functions on a unit with an actuator and a controller built to read the sensor.
Where the sensor goes
- On the outer frame, where rain reaches it. The pad has to get wet to work, so it sits on the weather side of the frame, not tucked under a flashing.
- On the sheltered side, away from constant spray. On an exposed coastal roof we site the pad where driven spray does not hammer it continuously, usually the leeward side of the frame rather than wherever the instructions default to, so it reads rain rather than sitting permanently wet.
- Clear of run-off channels. Away from a point where water sheets across it constantly, which would hold the unit shut for no reason.
Pairing it to the control system
On most current systems the sensor is part of the control set and either wires directly to the control unit or pairs to it wirelessly, the same way a handset does. We connect it, then set the sensitivity: too sensitive and sea fret or heavy dew closes the unit needlessly, too dull and light rain gets missed. We set it at commissioning and check it, rather than leaving it on a factory default that may not suit your exposure.
You cannot retrofit a sensor to just any unit. If your rooflight is manual, a rain sensor is not an add-on, because there is no motor for it to close. If it is electric but on an obsolete system, the sensor has to be one the old controller can read, and on a retired range that is often unavailable. In both cases the honest route is a modern unit with the sensor built in. We cover the obsolete-controls problem on the obsolete controls page.
What the sensor will and will not do
It works well, and being clear about its limits matters more than selling the feature.
- Closing takes time. Detection is fast, but the actuator itself takes 30 to 60 seconds to run the sash home, so in heavy rain a small amount gets in during that window. On a hard kitchen floor this is nothing. Over a stairwell with carpet it is worth knowing.
- Light drizzle can be missed. Fine mist may not bridge the tracks reliably. Heated sensor pads help and are worth having near the coast, where sea fret is a real thing at Felixstowe and Aldeburgh on spring mornings.
- It needs cleaning. Salt, pollen and algae make a pad read unreliably. Fresh water and a cloth once or twice a year is all it takes. On coastal properties we say twice, and we say it at handover.
- Sensor closing overrides everything. If you have deliberately left the vent open, rain will still shut it. That is correct behaviour and occasionally an irritating one.
On genuinely exposed coastal sites a wind sensor is a sensible companion, closing the unit above a set wind speed so the actuator is not loaded in a direction it was not built for.
If your unit cannot take a sensor
The most common reason someone wants to add a rain sensor is that they have a manual or older unit that keeps letting rain in when it is left open. In that case the answer is usually a new electric unit with the sensor as standard rather than trying to graft one on. The wider picture, actuator, controls and sensor together, is on the electric skylight installation page. If you are still weighing motorised against manual, the electric versus manual rooflight comparison covers it, and for what happens when the mechanism itself has failed, see the failed opening mechanism page. If the remote has stopped responding, run through the first checks first.
Common questions
Can I add a rain sensor to my manual rooflight?
No. A rain sensor closes the unit by driving its actuator, so it only works on a motorised rooflight with a controller built to read it. A manual unit has no motor for the sensor to trigger. If rain protection is what you want, the answer is a new electric unit with the sensor built in, not a sensor grafted onto a manual one.
Do rain sensors actually work?
Yes, with two caveats. Detection is quick but the actuator takes 30 to 60 seconds to close the sash, so heavy rain gets a little water in during that window. And fine drizzle or sea fret may not bridge the sensor tracks, which is why we fit heated pads on coastal jobs. They also need cleaning, because salt, pollen and algae make a pad read unreliably. Fresh water twice a year keeps it working.
Where should the rain sensor be fitted?
On the outer frame where rain reaches it, but on the sheltered side of the unit rather than where driven spray hammers it constantly. On an exposed coastal roof we site it on the leeward side so it reads actual rain instead of sitting permanently wet. We set the sensitivity at commissioning to suit your exposure, rather than leaving it on a factory default.
Get a fixed price for a rooflight with a rain sensor
If your current unit will not take a sensor, tell us the make and model from the data plate on the sash edge and what it is doing. We will advise whether a sensor can be added or whether a new electric unit with one built in is the honest answer, and give you one written price fixed after survey with a 10-year workmanship guarantee.
Request a fixed quote for an electric rooflight with a rain sensor 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.