How many electric rooflights can one switch control?

The arithmetic

Each actuator has a rated current. The control unit has a rated output. Add up the actuators running simultaneously and stay within it, with margin.

In practice a typical domestic control unit drives two to four comfortably. Beyond that, specify a larger unit or use more than one.

Simultaneous or staggered

The limit applies to actuators running at the same time. Some systems stagger the start so peak draw is lower than the sum, which allows more units on one controller.

Worth asking, because it can be the difference between one control unit and two.

Grouping

Most systems address units individually and as a group. In an open plan space with three rooflights that is genuinely useful: all three for a summer purge, one for background ventilation.

Set it up at handover rather than living with a default.

Two on one sash

Different matter. A wide sash needs two actuators, and they must be synchronised. Out of sync they twist the sash and damage the frame.

That is a specified synchronised pair, not two independent motors wired together.

Cabling

Each actuator needs a run back to the control unit, so the number of units affects first fix. Plan positions before the ceiling goes on, and run a spare while you are there.

Practical advice

Where three or more rooflights are planned, tell us at survey. The control strategy affects the first fix wiring, and getting it wrong means either a second control unit or cables in the wrong places.

Usually as many as you like, within a limit

Most manufacturers’ control systems allow multiple units to be grouped so that one switch or one remote button operates several together. The practical limit is set by the control unit rather than by the switch, and typical domestic systems handle a group of several windows comfortably.

Beyond that, a larger control unit or a second one wired in parallel handles it. On a domestic job you are very unlikely to reach the ceiling.

How grouping works

Each actuator is wired back to a control unit, and the control unit is what the switch talks to. Grouping is configured at the control unit, not at the window, so it can be changed later without touching the roof.

That matters: if you decide two years in that you want the two kitchen rooflights on one switch and the third on its own, that is a reconfiguration rather than a rewiring.

Where the cost sits

Each window still needs its own cable back to the control unit. Grouping saves you switches, not cabling.

The saving is real but modest, and the reason to group is convenience rather than economy: opening four rooflights at once rather than four times.

What to think about before grouping

Orientation. Rooflights on different slopes want opening at different times. Grouping a south facing unit with a north facing one means they always do the same thing, which is rarely what you want.

Rooms. Grouping across rooms means opening a bedroom window when you wanted to air the kitchen.

Rain sensors. On most systems a single sensor can close a whole group, which is sensible, and it means one sensor position has to represent the weather at all of them.

The usual arrangement that works is grouping by room and by slope, with a separate switch per group and a master control if you want one.

The switch itself

Worth putting beside the light switches at the room entrance rather than under the rooflight. That is where people reach for it without being shown, and it is the difference between a motorised window that gets used and one operated only when somebody finds the remote.

It needs a cable, which is why it is decided at first fix.

Solar units

Group in the same way through their own control systems, and because each carries its own power there is no wiring consideration at all. That makes retrofitting an additional unit into an existing group straightforward.

The two limits that actually apply

The control system limit. Each manufacturer control system has a maximum number of devices it will pair to one channel or one remote. That is a published figure and it is generous on most domestic systems.

The electrical limit. A wall switch or a controller has a current rating, and each motor draws current while it runs. Several motors starting simultaneously draw more than the same motors running steadily, and it is the inrush that decides whether the switch is adequate.

An electrician sizes this from the motor data. It is not something to establish by trying it and seeing whether anything gets warm.

Grouping, and why it is worth planning

Most systems let you assign units to groups, so one control operates a pair over the kitchen while another operates the one on the landing, and a third operates everything at once.

That grouping is set at commissioning and it is far easier to plan before the cable runs go in than to rearrange afterwards.

The one arrangement worth avoiding is putting every rooflight in the house on a single control with no subdivision. It sounds convenient and in practice it means you cannot vent the bathroom without opening the bedroom.

Planning the arrangement before the cables go in

The decision that matters is not how many a switch could handle but how you want them divided.

Most systems support groups: one control for the pair over the kitchen, another for the one on the landing, and a master that operates everything. Those groups are set at commissioning and they are far easier to plan before the cable runs than to rearrange afterwards.

The arrangement worth avoiding is every rooflight in the house on a single control. It sounds convenient and in practice you cannot vent the bathroom without opening the bedroom.

Where the practical limit shows up

Inrush current. Several motors starting at the same instant draw considerably more than the same motors running steadily, and it is the starting surge that decides whether a switch or controller is adequate.

An electrician sizes it from the motor data rather than by trying it and seeing whether anything gets warm.

Where a large group is genuinely wanted, the answer is usually a controller with relay outputs rather than a bigger wall switch.