The worry that follows any opening rooflight is a simple one: what if it rains while nobody is in? A rain sensor answers it. It senses moisture on the glass or beside it, tells the motor to close, and the rooflight shuts before the room gets wet. Without one, an electric rooflight is only as safe as the last person to remember to close it.
This guide covers how rain sensors work, the other controls that go with them, and how to choose a set-up that suits your household. It is written for anyone choosing an electric rooflight, or thinking about adding a sensor to one that is already there.
How a rain sensor works
Most sensors have a small heated plate. When a drop lands on it, the water changes the electrical signal across the plate, and the sensor sends a close command to the control unit. The heating keeps the plate dry in dew and light mist so it does not trigger without cause, and it dries the plate quickly after a shower so the rooflight can open again if you have asked it to.
Some roof windows come with the sensor built into the frame. On a flat rooflight or an older window, it is a separate unit fixed on the roof close to the glass, wired back to the control. Either way it works as a switch that overrides the others: if it is raining, the rooflight shuts, whatever else is asking it to open.
Where the sensor is fitted
Placement is the part that makes or breaks a sensor. It has to be in the open, tilted to shed water, and close enough to the rooflight that it sees the same weather. A sensor tucked under the edge of an eaves overhang can stay dry while rain falls on the glass a metre away. One placed in the lee of a chimney stack may miss rain driven from the west.
On a flat roof the sensor goes on the upstand or beside it. On a pitched roof it is often fixed on the frame or in a small bracket on the slope. We settle the position at the survey, because the right spot depends on the roof, the direction it faces and what stands around it. The sensor has to be fixed firmly and sealed against the roof covering, because a cable entry is a place where water can find a way in if it is done carelessly. Cables are run through the roof structure and hidden, and we photograph the hidden work for you.
Keeping the sensor clean is the one maintenance task. Leaves, bird droppings and a film of dust can stop a sensor from reading properly, and a wipe with a damp cloth once or twice a year is enough. It is worth doing at the same time as the glass, and the position should be one you can reach safely, which is another reason we think about access when we choose where it goes.
Wall switches
A wall switch is the most basic control and the easiest to live with. It sits beside a light switch, usually with an up, stop and down action, and anybody in the house can use it. For a rooflight above a staircase or a kitchen island, it means the glass opens with a touch rather than a pole.
The cable to a wall switch is best laid when the ceiling or wall is already open. Where the room is finished, a wireless switch avoids chasing a route through the plaster, and it can be fixed anywhere with a screw or sticky pad. Our guide to electric rooflight cost shows what each control adds to a quote.
Handsets and remotes
A handheld remote works on radio, so it does not need to point at the rooflight. It opens, closes and stops the glass from anywhere in the room, and one remote can control several rooflights or group them together. It is a good fit for older relatives, for anyone with limited reach, and for a kitchen where hands are often full.
Remotes get mislaid, and so a wall-mounted holder for the handset is a sensible small extra. The batteries last a long time but need changing eventually, and it helps to keep a spare. A wall switch alongside the remote is often the best of both: the switch is always there and the remote adds convenience.
Heat sensors and timers
A heat sensor opens the rooflight when the room reaches a temperature you set, and closes it when it falls back. That suits a loft room that climbs in summer or an extension with a lot of south-facing glass. It works well with a rain sensor, because the rain sensor holds priority and shuts the glass if the weather turns, whatever the temperature says.
A timer is simpler: it opens the rooflight at a set hour and closes it later, which is useful for night-time cooling of a loft bedroom. Both are options on the better control units, and they need to be chosen at the survey so the control unit is the right one and the wiring is laid for it.
A wind sensor is worth a second look on an exposed roof. Houses on the edge of a village or on higher ground take a stronger gust than a terrace in a sheltered street, and a lid held wide open in a gale puts a strain on the hinge and the motor. A wind sensor closes the glass before that happens, and it is cheap protection for a unit that will otherwise cost more to replace.
Whichever sensors you choose, they should feed one control unit, with the rain sensor given priority. Several separate controls fighting over one motor is a recipe for a rooflight that opens and closes at odd moments. A single unit with a clear order of priority is easier to live with and easier to explain to the rest of the household.
- Rain sensor: closes the glass when it rains, and overrides everything else.
- Heat sensor: opens the glass when the room is too warm.
- Timer: opens and closes at set hours.
- Wind sensor: closes the glass in a strong gust, on models that offer it.
Phone and home-system control
Some control units link to a phone app or a home system through a wireless gateway. That lets you open the rooflight from another room or check it has closed when you are away. It costs more than a switch or a remote, and it depends on the home network, so a weak signal in the loft can be a nuisance.
It is a useful option for a household that already runs its heating or lighting from a phone. For a household that does not, a switch with a sensor is simpler and gives the same protection. We give you a clear walk-through of whichever control you choose at handover, and the makers' details go in the folder with your guarantee.
Choosing a set-up for your house
The right set of controls depends on who lives in the house and how the rooflight is used. A family kitchen with young children and a busy routine suits a wall switch, a rain sensor and a remote kept on a high shelf. A loft bedroom for a teenager suits a heat sensor and a timer, so the room cools itself overnight without anyone having to remember. A bathroom suits a simple switch beside the door and a rain sensor, because the rooflight is opened and shut within minutes.
For a home where someone is away often, a phone link and a rain sensor give peace of mind in the plain sense: you can check the rooflight is shut from wherever you are. For a holiday let or a second home, the same applies with more force.
Keep the list short. Each extra sensor or control is something else that needs a wire, a battery or a setting, and every addition is a thing the household has to learn. A rain sensor plus one way of controlling the glass covers most homes well, and the rest can be added later if you find you want it.
Living with the settings
Controls are easy to get wrong in daily use, even when they are well chosen. A rain sensor that closes the rooflight in a light shower is working as intended, but it can feel like a nuisance if you wanted the air. A heat sensor set too low will open the glass on a mild morning. Most units let you adjust the threshold, and a short walk-through at handover covers where those settings live and how to change them.
A manual override is worth having.
A switch that lets you hold the rooflight open or closed, whatever the sensors say, stops the control from arguing with you. It also helps in winter, when frost or snow on the roof can make the system behave oddly, and when a sensor might read frost as moisture and keep the glass shut when you want a short burst of fresh air.Think about who else uses the house as well. A teenager who leaves a loft room for school, a lodger, a relative who stays for a month: each of them needs to know how the rooflight behaves. A label by the switch, or a one-line note in the handover folder, saves a good many questions.
When the power goes off
A sensor does nothing without power, so it is fair to ask what happens in a cut. Mains-powered units usually have a manual release, or a battery back-up on some models, that lets you close the rooflight by hand. Solar units keep a charge in the battery and work through a short outage as usual. Our page on what happens to an electric rooflight in a power cut goes through each type.
It is worth asking about the back-up at the survey rather than after the fit. A rooflight in a bathroom, where it might be opened for long periods, needs it more than one in a landing that is only opened briefly.
Fitting, wiring and the paperwork
The low-voltage wiring from the transformer to the rooflight and the sensor is run inside the roof and the ceiling, and the connection to the house supply is made by someone qualified to do it. The page on whether electric rooflights need an electrician explains the split in more detail.
Adding a sensor to a rooflight that is already installed is a small job. Cutting a new opening for one is not, and that brings Building Regulations into it. Where the work is notifiable, we handle the paperwork and file it in your handover folder with the makers' warranties and your 10-year workmanship guarantee.
The survey is free. We can look at the roof, suggest where the sensor should go and write the control choices into a quote with each line priced. The main page on electric opening rooflights covers the rest of the job, and you can ask for a survey with the form below.