What is a rain sensor rooflight or skylight?
A rain sensor is a small detector mounted on the outside of the frame, wired into the control system, which closes the rooflight automatically when it detects water. It is what turns an opening rooflight from something you open when you are in the room into something you can leave open while you are out.
How it detects rain
By what water does to a surface.
A sensing element on the frame changes its electrical behaviour when water lands on it, and the controller reads that change as rain and drives the unit shut.
It is a simple and reliable arrangement.
How quickly it reacts
Seconds rather than minutes. The pane starts closing almost as soon as the first drops land, and the closing itself takes as long as the actuator takes to run its stroke.
A little rain gets in and that is the whole of it.
Why a little rain gets in anyway
Because it has to be raining before it knows.
The sensor detects rain rather than predicting it, so a few drops arrive before the unit closes, and on a heavy sudden shower that can be more than a few.
It is worth knowing rather than being surprised by.
What it does not do
Reopen afterwards, on most systems. The unit closes and stays closed until somebody opens it again, which is deliberate, because a system that reopened on its own would open into a lull in a storm.
Whether it handles wind
Not by itself.
A rain sensor senses water. Wind protection is a separate sensor on the systems that offer one, and it is worth asking about on an exposed site.
What it changes about how the unit is used
Everything, honestly. An opening rooflight without a sensor gets opened for ten minutes while somebody is cooking. One with a sensor gets left open all day.
That difference is why it is the first thing we would specify.
On a solar unit
Frequently included as standard. Solar powered opening windows generally come with a sensor built in, which is part of why they suit a retro fit so well.
How they work is on can you get a solar powered VELUX.
On a mains unit
An option, and a cheap one. The sensor is a small component and the cost is mostly in wiring it back to the controller, which is trivial if it is planned with the actuator.
Where it is mounted
On the frame, exposed, and clear of shelter.
It has to see the rain, so it is positioned where it will get wet as soon as the pane would, rather than tucked under an upstand.
Keeping it clean
The only maintenance it has.
Dust, salt and leaf residue on the sensing surface can slow it or, near the coast, occasionally trigger it, and a wipe once or twice a year settles that.
False triggers
Uncommon, and usually explicable.
Heavy dew, a hose, a window cleaner or salt spray on a windy day near the sea will all read as rain, which is the sensor doing its job rather than failing.
Overriding it
Possible on most systems and rarely wanted.
A manual override lets a unit be held open in rain, which has occasional uses and is generally left alone.
With more than one rooflight
One sensor can close a group.
Where several units are on the same control system, a single sensor generally closes all of them, which is simpler and cheaper than one each.
That is on can two rooflights open together.
With a temperature control
The two work together and rain wins.
A unit set to open on temperature and close on rain behaves sensibly in a British summer without anybody touching it.
That is on can a rooflight open automatically on temperature.
In a power cut
It cannot close the unit.
Without power there is no actuator, so a mains unit left open in an outage stays open, which is an argument for a backup on anything that will be left open unattended.
The options are on can an electric rooflight be opened in a power cut.
On an escape window
Worth understanding clearly.
An escape window has to be openable by hand regardless of what any sensor or control does, so automation never sits between a person and the opening.
The requirement is on can a roof window be an escape window.
Its life
Years, and it is a replaceable component.
Like any exposed electronic part it eventually wants replacing, and it is changed on its own rather than with the unit.
Whether it is worth it
On a flat roof unit, without question.
The whole value of an opening rooflight is being able to leave it open, and that is exactly what the sensor makes possible.
Where it sits on a lantern
On the frame near the opening face.
A lantern sensor is mounted where it is exposed to rain but not where it collects water running off a face above it, which would leave it wet long after the rain stopped.
Position is the whole of the installation.
On a pitched roof window
The same principle with an easier geometry.
A sensor on the frame of a pitched unit sits in the open and drains readily, which is one reason they are so reliable on roof windows.
Whether it can be added later
Usually yes on a compatible system.
A sensor is a component that pairs with an existing controller, so a unit installed without one can often gain one without disturbing the roof.
It is worth checking the system supports it before assuming.
What we include
We include a rain sensor on every powered opening unit we quote, because an opening rooflight without one is used a fraction as often and the difference in price is small.
The whole picture is on the electric rooflight installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.