Electric and Opening Rooflights

What makes a rooflight electric

Three components turn a fixed unit into a motorised one: an actuator that pushes the pane, a control unit that feeds it power and takes the signal, and a switch or handset that tells it what to do. On a factory-built electric unit all three arrive together and the actuator is already fitted inside the frame, wired to a terminal block at the head.

The glass, the frame, the flashing and the kerb are identical to the fixed version. That matters because it means the weathering risk does not change when you specify a motor. What changes is that a moving joint now has to close onto a gasket with enough force, every time, for twenty years, and that a low voltage cable has to arrive at the head of the unit without crossing a route it should not.

The three ways an opening pane moves

Motorised domestic units move in one of three ways, and the choice is usually made by the roof rather than by preference.

• Top hung. Hinges along the top edge, the bottom swings out. Standard on flat roof units and on roof windows where the opening is used for ventilation and for reaching out.
• Centre pivot. The sash rotates about a horizontal axis roughly halfway up. Common on pitched slope windows, and it lets the outer face rotate inward for cleaning.
• Sliding. The whole pane travels sideways on a track over a fixed light. Used where a large flat roof opening is wanted and a lifted pane would be caught by wind.

Top hung is the default on flat roofs because water runs off the raised edge away from the opening. Centre pivot on a shallow slope leaves the lower half of the sash tipping inward, which is why it is not offered below the pitches the manufacturer states.

Chain drives, spindle drives and linear rams

The actuator itself is one of three mechanisms. A chain actuator holds a stiff articulated chain inside a slim casing that runs along the head of the frame. The chain is rigid in compression, so it can push the sash open and pull it shut, and the casing is shallow enough to hide inside a frame profile. Typical thrust is in the region of 250 to 300 newtons.

A spindle drive turns a threaded rod through a nut carried on the sash. It is slower, considerably stronger, and it self-locks under load, which is why it appears on larger and heavier panes. A linear ram is a telescopic rod driven by a motor at one end, usually mounted at the side of a kerb on a big flat roof unit where there is room for the swept arc.

Weight is the deciding number. A one metre by one and a half metre triple glazed sash is a serious piece of mass to lift against gravity on a flat roof, and specifying a chain rated for a smaller unit is how a motor ends up straining every cycle.

Stroke, and how far the pane actually travels

Stroke is the distance the actuator extends, and it decides the opening angle. A 200mm stroke on a one metre deep sash gives roughly eleven degrees. A 400mm stroke on the same sash gives about twenty three. Both are described in a brochure as opening.

The difference is what you feel in the room. Eleven degrees is background ventilation and a gap for warm air to leave. Twenty three degrees is a genuine purge that clears a kitchen of cooking air in minutes. On a flat roof, a longer stroke also lifts the trailing edge higher into the wind, so the frame and the hinge have to be rated for it.

Mains, low voltage and solar as power sources

There are three ways to feed an actuator, and each has a different implication for the building work.

Almost all domestic actuators run at 24V direct current. The mains side stops at a transformer or a control unit, usually sited in a cupboard or the roof void, and everything beyond it is extra-low voltage. Solar versions carry a small photovoltaic panel on the outside of the frame and a rechargeable cell inside it, which is what makes them the practical answer on a finished ceiling.

Cable routes, and the moment they cost nothing

Running a cable to the head of a rooflight before the ceiling goes on takes a few minutes. Running it afterwards means lifting boards in a room above, chasing a wall, or accepting surface trunking across a ceiling that was meant to be plain.

On a pitched slope the cable follows the rafter void down to a convenient point. On a flat roof it runs in the ceiling void between joists, and on a warm deck build-up with no void at all it has to be planned into the structure, because there is nothing to hide it in later. This is the single most common regret on rooflight jobs: the unit was fitted manual to keep things simple, and the wiring went in nowhere.

Where a cable is genuinely not going to happen, solar is the honest answer rather than a compromise.

Part P, and who does the electrical work

The 24V side of an electric rooflight is extra-low voltage and is not the notifiable part. The mains side is. Where a new circuit is run to feed a transformer, that work falls under Part P of the Building Regulations in England and has to be certified. Where the supply is taken as a fused spur from an existing circuit outside a special location, it is not a new circuit, but it still has to meet BS 7671 and it still wants testing and a certificate.

In practice the sequence is straightforward. The electrician runs and terminates the mains side and issues the paperwork. Sunspire fits the unit, makes off the low voltage connection at the head, and sets the controls. The Building Control notification for the rooflight itself is handled as part of the job.

Wall switches, handsets and app control

Every motorised unit needs at least one way to be told what to do, and most end up with two.

A hard-wired wall switch is the most reliable and the least loved, because it puts a plate on a wall that somebody spent time choosing. A radio handset removes the plate and introduces the problem of where the handset lives. Wireless wall plates split the difference: they look like a switch, they stick where you want them, and they run on a cell that lasts years.

App control adds scheduling and remote operation through a gateway on the home network. It is genuinely useful for closing a unit from work when the forecast turns. It is worth knowing that the gateway is the part that dates, not the motor, and that a unit which also has a wired switch will keep working long after any particular app has been retired.

Rain sensors, and how fast they react

A rain sensor is a small conductive plate on the outside of the sash. Water bridges the contacts, resistance drops, and the control unit drives the actuator shut. On most units the sensor is heated slightly so it dries quickly and does not hold the unit closed for an hour after a shower has passed.

The reaction is quick but it is not instant. From the first drops to a fully closed pane is typically ten to thirty seconds depending on the stroke, and heavy rain arriving as a wall of water will put some inside. This is why a sensor is a convenience rather than a guarantee, and why the sensible place for a purge opener is over a hard floor rather than directly above a dining table.

Wind, and what an open pane does in a gale

An open sash is a sail. At twenty three degrees on a flat roof, a square metre of glass presents a serious lever to wind coming across the roof, and the load goes into the hinges, the actuator and the fixings holding the frame to the kerb.

Manufacturers rate their units for this and the ratings are not decoration. On an exposed site, and much of the Essex coast fringe around Maldon, Burnham and Canvey qualifies, the sensible specification is a shorter stroke, a stronger drive, or a sliding unit that does not lift into the airflow at all. Rain sensors do not detect wind. A unit left open on a rising forecast stays open until somebody or a schedule closes it.

Manual override, and what happens in a power cut

A mains-fed actuator with no power does nothing. The pane stays where it is, which if it is shut is exactly what you want and if it is open is not. Solar units are unaffected, because the cell carries them through, and that is one of the quieter arguments for solar on a unit that also serves as a means of escape.

Most chain actuators can be released at the sash bracket with a hand tool, which lets the pane be pushed shut and hooked. Spindle drives generally cannot, because the thread is what holds the sash. Where a rooflight is the escape opening from a loft room, the clear opening dimensions and the way it is released by hand are part of the Building Control conversation, and they are settled before the unit is ordered rather than discovered at inspection.

Purge ventilation, and how quickly a room clears

Approved Document F asks for purge ventilation capable of clearing a room quickly, and the usual measure is an openable area of at least one twentieth of the floor area. For a four by five metre kitchen that is one square metre of openable area, which a single generous roof opener will not always provide on its own.

Height is what makes a rooflight efficient at this. Warm, moist, smoky air collects at the ceiling, so an opening at the highest point removes exactly the air you want gone, rather than mixing it around the room first. The measured effect in a tall extension is that a room clears in a few minutes with a roof vent open and a window cracked, against fifteen or twenty minutes with the window alone.

Where a room is long, two smaller motorised units placed apart do more than one large one in the middle. Air needs somewhere to come in as well as somewhere to go out, and two openings at different points along a ceiling set up a cross-draught rather than a single column of rising air fighting itself in one hole.

Two smaller actuators are also easier on the structure and easier on the wallet at replacement time, and they can be wired to one control unit and driven together or separately. On a long side return in a Victorian terrace, one at each end of the glazing run is usually a better result than a single wide opener, and it keeps each sash light enough for a chain drive.

Motor noise, and where it is heard

A modern chain actuator running is roughly the volume of a quiet extractor fan on its lowest setting, and it runs for twenty to forty seconds. It is not silent and nobody should promise that it is.

What varies is where you hear it. In a kitchen with hard surfaces the motor is barely noticed against everything else going on. Directly above a bed it is different, and a unit that closes itself on rain at three in the morning will wake a light sleeper the first few times. Where that matters, a slower spindle drive is quieter than a fast chain, and scheduling the close before bedtime removes the surprise.

Gaskets, compression and staying watertight when shut

A fixed rooflight is sealed by glazing tape and a bead. An opening one is sealed by a gasket that has to be squeezed to the right compression by the closing force of the motor, and that is a different problem entirely.

Get it right and the joint is as watertight as a fixed unit. Get it wrong and you have a hairline path that only shows in driven rain from one direction. The two things that put it wrong are an actuator that is not driving fully home, usually because a limit switch has drifted, and a gasket that has hardened with age and no longer springs back. Both are checked in minutes and both are the reason an opening unit wants an occasional look that a fixed one does not.

Hinged flat rooflights on a kerb

On a flat roof the opener sits on the same upstand as a fixed unit, and the kerb detail is unchanged: the covering is dressed up the sides, the unit lands on top, and the height from the finished surface to the top of the kerb is the number that keeps water out. Motorising the pane does not lower that requirement by a millimetre.

What it does add is a hinge line that must be square. A kerb that is out of level by a few millimetres across its length is invisible under a fixed unit and very visible under an opening one, because the sash will meet the gasket harder on one side than the other. Setting the kerb true is more important here than anywhere else, and it is a good reason to have the same trade build the kerb and set the unit. The wider detailing is covered on the flat roof rooflight page.

Motorised roof windows in a pitched slope

In a tiled or slated slope the actuator hides in the top of the sash and the flashing kit is the same one a manual unit would take. The pitch limits still apply, and a centre pivot electric unit has the same minimum pitch as its manual twin.

The useful detail is the control cable. It runs from the head of the window into the rafter void, which on a room-in-roof conversion means it wants to be in before the plasterboard, and on an unconverted loft is easy at any time. Trussed roofs on the estates at Great Notley and South Woodham Ferrers cap the width of any roof window, motorised or not, which usually means two narrower units rather than one wide one. The structural side of that is covered on the roof window page, and specific model ranges on the VELUX window page.

Electric blinds, and sharing the same power run

A rooflight blind runs in side channels within the frame because gravity will not hold it against sloping glass. Motorising it uses a small tubular motor in the head of the blind, and on most systems it takes its power from the same control unit as the opener.

That is the argument for deciding early. One cable, one control unit and one handset can drive an opener and a blackout blind on the same unit, and the second cable costs nothing at first fix. Retrofitting a wired blind afterwards usually means a solar or battery version instead, which works well but adds a cell to think about. On a south or west facing plane the blind is doing thermal work as well as blackout, which is where it overlaps with energy efficient specification.

Automation: timers, thermostats and humidity

Once a unit has a motor and a controller, it can be told to act on something other than a finger. Three inputs are worth having.

• Time. Open at seven, close at ten. The most useful and the least clever.
• Internal temperature. A setpoint that opens the unit when the room passes it, which is how night cooling is made to work without anybody remembering.
• Humidity. Genuinely valuable over a bathroom or a utility, where the unit opens when the moisture rises and shuts when it has gone.

Carbon dioxide sensing exists and is more common in commercial work than domestic. The general principle holds across all of them: automation should be paired with a rain sensor, because a unit that opens itself on temperature at two in the afternoon needs to be able to shut itself when the weather changes at three.

Reach, and the height at which electric starts to make sense

The blunt test is whether you can reach the handle. Below about two metres, a manual unit with a handle on the sash is fine and will be used daily. Between two and two and a half metres, a pole works and gets tiresome. Above that, a manual unit becomes an ornament within a month.

Vaulted ceilings are where this bites. A rear extension with a raised ceiling puts the glass at three metres or more, and the whole point of an opening rooflight in that room is the stack effect, which only works if the unit actually opens. A pole-operated unit at that height is a decision that quietly reverses itself, and it is the most common reason people come back a year later asking about motors.

Adding an opener to a unit that was fitted manual

Sometimes possible, sometimes not, and the answer is decided by the frame. Several manufacturers make retrofit kits that mount to their own manual sashes: the bracket screws to the frame, the actuator sits at the head, and a solar or wired supply feeds it. Where a kit exists for that exact model, it is straightforward work from inside the room.

Where the unit is a discontinued model, or a frameless flush design with no fixing point at the head, there is nothing to mount an actuator to. In that case the sensible route is a new opening unit into the existing kerb or opening, which is often a single day’s work and a good moment to upgrade the glass at the same time. That path is covered on the rooflight replacement page.

Grease, moisture and what servicing involves

An opener over a hob lives in a different atmosphere from one over a landing. Cooking aerosol carries fat, fat settles on every horizontal surface including the chain and the hinge, and over years it collects dust into a film that stiffens the action.

None of that is a reason to avoid an opener over a kitchen, because that is precisely where the ventilation is wanted. It is a reason to site it away from directly above the hob where the extract should be doing the work, and to wipe the visible mechanism when the glass is cleaned. In a bathroom the issue is moisture rather than grease, and the answer is a unit specified for humid conditions with stainless fixings.

There is little to do and it is worth doing. Once a year, run the unit through a full cycle and watch it. It should travel evenly, stop cleanly at both ends, and pull the sash tight against the gasket without labouring at the last few millimetres.

Every few years, clean the chain or spindle and put a light dry lubricant on it, check the gasket for hardening by pressing it with a thumb, and look at the hinge fixings. Batteries in wireless controls last two to five years. A solar cell in an opener is a serviceable part with a life measured in years rather than decades, and it is replaced rather than nursed. The mechanism itself, kept clean and not asked to lift more than it was rated for, will outlast several handsets.

What the survey adds when a unit is motorised

Everything a survey covers for a fixed unit still applies: the covering, the pitch, the structure, the ceiling line, the orientation and the access. A motor adds four more questions.

Where does the mains supply come from, and is a new circuit needed. Where does the low voltage cable run, and is that route open or closed. What is the sash going to weigh once the glazing specification is settled, and is the actuator rated for it with margin. And how exposed is the roof, because that governs the stroke and the drive. Those four answers are what turn a range into a fixed written price.

What moves the figure on a motorised unit

Sunspire quotes in two stages: a range by email once the basics are known, then a fixed written figure after a survey. On an electric unit, four things move the number between those points.

The actuator specification, because a spindle drive rated for a heavy triple glazed sash is a different component from a light chain. The power route, because a fused spur off a nearby circuit is a small item and a new circuit run across a house is not. Whether a blind shares the run, since doing both at once costs less than doing them a year apart. And the usual structural and access variables that apply to any rooflight. Broader cost thinking sits on the costs page.

Essex roofs, and where a motorised unit earns its place

The county’s stock decides this more than taste does. The rear extensions going up across Chelmsford, Braintree and Colchester almost always have a vaulted or raised ceiling, which puts the glass out of reach and makes an opener the only version that gets used.

Interwar semis across the commuter belt have loft conversions with roof windows at head height, where a manual centre pivot is perfectly sensible and a motor is a comfort rather than a necessity. Flat roofs across the Harlow and Basildon new town housing take hinged units on kerbs, and exposure on the estuary fringe pushes those towards a shorter stroke. Weatherboarded cottages in the Blackwater villages and the timber framed towns at Thaxted and Saffron Walden are a different matter again, where the conservation frame profile comes first and the opener has to fit within it. That is covered on the conservation rooflight page, and the coverage map on the areas page.

Installation day with an actuator in the job

For an electric roof window into a pitched slope, one day. For a hinged flat rooflight onto an existing kerb, one to two. Where a new opening is being formed, the timings match any other rooflight and the actuator adds an hour or two of setting up rather than a day.

The order is consistent: protect the room, strip back the covering, form and trim the opening, build or prepare the kerb, run and terminate the low voltage cable, set the unit, weather it, make the covering good, then finish the reveal. The controls are paired and the limits set at the end, with the unit run through several full cycles before anyone leaves. The roof is closed and watertight at the end of every working day.

The two questions to answer first

Start with reach and start with the cable. How high above the floor is the glass going to be, and is there a route to the head of the unit that is still open. Those two answers decide manual against electric, and wired against solar, before any product conversation is worth having.

After that it is the ordinary sequence: the covering, the pitch, the structure and the orientation. A photograph of the roof from outside, one of the ceiling from inside, and a rough room size are enough for a sensible range by email. Background reading on the rest of it sits in the guides, and how Sunspire works is set out on the about page.