Electric Skylight Installation

Ventilation at the apex

Warm air is less dense than cool air, so it collects at the top of a room and stays there. That single fact is why an opening in the roof does something no window can. A window at head height exchanges air across a plane, slowly, because the driving force is small. An opening in the ceiling sits above the whole warm layer, and air leaves because it is buoyant rather than because a breeze happens to be blowing.

Pair that roof opening with anything at low level, a door, a window, a set of bifolds, and the room becomes a stack. Cool air is drawn in low, warm air discharges high, and the rate depends on the height between the two openings rather than on the wind. Over a stairwell that height is the whole building. It is the oldest ventilation strategy there is and it runs without a fan or a filter.

Two consequences follow. A modest opening at the top of a room usually outperforms a much larger one at the side. And the benefit is greatest at night, when outside air is cooler than the fabric of the house: a vent left open overnight purges heat from plaster, brick and screed. Cooking and drying clothes also put vapour into air that rises, so the apex is where humid air is best removed.

The case for electric

None of that happens unless the vent is actually opened, which is where most ventilation strategies quietly fail. That is the honest argument for motorising a rooflight.

The rooflights that ventilate best are, by definition, the ones highest in the room. A unit in a vaulted kitchen ceiling, over a stairwell, above a galleried landing or in the flat roof of a rear extension is well out of arm’s reach. Working it by hand means a telescopic pole, hooked into a control bar three or four metres up, wound, then the exercise repeated to close. Opening the vent because the room has become warm competes with the effort of fetching the pole, and the effort usually wins.

A motorised unit changes the calculation. The vent opens from a switch by the door in the time it takes to walk past it, so it opens in the morning and closes at bedtime as a matter of habit. Two further situations argue for electric regardless of reach: a bank of three or four rooflights, which nobody works individually by pole, and any opening forming part of a designed response rather than a comfort choice.

Specify it when the unit is chosen. A motor added later to a rooflight ordered as manual rarely performs like a factory-built assembly, and the cable route is far easier to form before the ceiling closes.

Chain, linear and spindle

An actuator is the mechanism that pushes the sash open and pulls it closed. The three types in common use differ enough that the choice is worth making deliberately rather than by default.

Chain actuators use an articulated push chain, rigid in one direction and folding in the other, so a long stroke coils away inside a compact housing. That housing is short enough to sit within the head of a rooflight frame, which is why chain drives dominate domestic opening rooflights: nothing protrudes into the room, nothing is visible outside, and the assembly reads as part of the frame. The limitation is force. A chain drive suits a sash of ordinary domestic size and is not the mechanism for a heavy vent or for smoke ventilation duty.

Linear rod actuators drive a telescopic rod out of a cylinder, usually in two or three stages, delivering more force and a longer stroke than a chain of the same size. That makes them the mechanism for large opening panels, whole-slope openers on lanterns and most smoke ventilation units. The trade is visibility: the cylinder needs somewhere to live, and the extended rod is a visible piece of engineering when the vent is open.

Spindle drives turn a threaded rod through a nut, converting rotation into travel. A thread of the right pitch will not back-drive, so the mechanism holds position without drawing power and without a brake. They are common on louvre ventilators and heavier units where sash weight would otherwise need constant restraint, and they are slower and more visible than the alternatives.

Mains or solar power

Both arrangements drive the same mechanism. What separates them is where the energy comes from, and that decides how much of the house has to be opened up.

Mains-wired units. A cable runs from the house installation to a low-voltage supply and on to the head of the rooflight. Power is continuous, so the actuator can be sized for the job rather than for an energy budget, travel is quicker, and there is no battery in the assembly. Mains units integrate most readily with a wider control system and are the only sensible choice where several rooflights work as a group. The cost is the cable route: straightforward in a new extension, less so in a finished room.

Solar-powered units. A small photovoltaic panel, usually integrated into the top of the outer frame, charges a battery that drives the actuator and the sensor. There is no cable at all, so the installation is contained entirely within the roof opening.

Where solar earns its place

The clearest case is a finished ceiling. Running a cable to a rooflight in an existing vaulted kitchen or a plastered loft room means lifting boards, chasing plaster, or dropping surface trunking down a wall nobody wants to look at. A solar unit avoids all of it, and in a period building the argument goes further: a lath and plaster ceiling is often original fabric, and cutting a route through it in a listed interior is an alteration in its own right. The second case is a rafter zone fully filled and closed on both faces.

What solar gives up

The panel needs daylight. A north-facing slope in the shade of a neighbouring building, or a roof beneath mature trees, charges more slowly, which on a unit worked several times a day shows up as a battery that never quite recovers. The panel also sits outside, which on a conservation-sensitive elevation is a visible addition. The battery is a consumable with a service life, so the head of the unit has to stay reachable. Force is more limited than a mains actuator of the same size, and solar is not the answer where an opening has a life safety function.

What rain sensors do

A rain sensor is a small pad on the outside of the frame that detects moisture landing on it and sends a close command to the actuator. That is the whole of it. It protects against the ordinary case: the vent is open, the house is empty, it starts to rain, and the unit closes on its own. What it does not do is worth stating just as plainly, because the gap between expectation and behaviour causes most of the complaints.

It does not forecast. The sensor reacts to water that has already arrived. The vent begins closing after the first drops land, and a slow actuator on a large sash takes an appreciable time to travel, so some water will come in. Over a timber floor or a stairwell, that is a reason to think about what sits underneath the opening.

It does not see rain that misses it. A sensor sheltered by the frame profile or an adjoining structure can stay dry while wind-driven rain enters the opening from another angle.

It does not detect snow or debris. Dry snow can settle without wetting the pad, and anything lodged in the opening is compressed by the closing sash rather than recognised as an obstruction.

It is not a security device. It closes a vent, it does not lock it, and it says nothing about whether the unit is a sensible thing to leave open in an empty house.

It can override you. On most systems the sensor takes priority while the pad is wet, so a unit refuses to open, or closes itself again, until it dries. People who have not been told this conclude the mechanism has failed. It has not. The pad also needs to stay clean, since dust and moss dull it over time, which is one more argument for keeping the head of the unit accessible.

Switches, remotes and apps

The control layer is chosen separately from the mechanism, and it is the part people live with.

Hard-wired wall switch. A rocker or rotary switch on a cable back to the control unit. The plainest arrangement and the most robust: no pairing, no battery, no radio. It is positioned during the electrical work, which means deciding early where somebody in the room will look for it. By a door is almost always right.

Handheld remote. A radio handset that pairs to the unit and can address several rooflights individually or as a group. Convenient and portable, which is also its weakness, because a portable control ends up down the side of a sofa.

Wall keypad. A battery-powered radio control on a magnetic or screwed plate. It behaves like a switch and needs no cable, so it goes on a wall already decorated and moves if the furniture changes. It is the usual answer for a solar unit, or a mains unit where no switch drop was wired.

App and home automation. With a gateway on the home network the rooflight becomes an addressable device: opened from a phone, scheduled, grouped with blinds, or driven by a temperature reading. It is the only way to have a vent that opens itself when the room reaches a set temperature.

Why one control should be physical

An app is a fine addition and a poor foundation. It depends on a phone that is charged, a network that is up, a gateway that has not lost its configuration after an update, and an account somebody still has the password to. More to the point, a house contains people who are not the account holder: a guest, a child, anybody in the room when the phone is upstairs. A physical control by the door is operable by all of them at the moment the rain starts. Our recommendation is at least one physical control in the room the rooflight serves, whatever is layered on top.

Wiring, supply and access

The electrical side is not complicated, but it is unforgiving about sequence. Nearly every difficult installation is difficult because a decision that belonged at the planning stage was left until the ceiling closed.

The cable route

A supply is taken from the house installation, through a low-voltage transformer or control unit, and on to the head of the rooflight, with a further run to any hard-wired switch. On a new extension or loft conversion it is pulled through while the rafter zone is open. On a finished ceiling the same route means opening up, which is where a solar unit stops being the expensive option. In a warm roof build-up, the cable penetration is a hole in a vapour control layer and is sealed as one.

Where the transformer sits

Most domestic systems run the actuator at low voltage from a transformer or control unit that has to live somewhere. That somewhere needs a supply, ventilation and access. What it must not be is buried under loft insulation, packed into a sealed ceiling void, or plastered in behind a finished surface. The positions that work are a loft space within reach of the hatch, a services cupboard, or a ceiling void with an access panel. The position is agreed at survey, because it decides whether anybody can get at the unit in ten years.

Isolation and future access

A local means of isolation is specified so the mechanism can be worked on without the rest of the room being dead, and it is labelled so whoever opens the consumer unit later knows what it serves. The equivalent point at the rooflight is the reveal detail. It is entirely possible to form a plaster reveal that looks handsome on handover while making the mechanism, the sensor and any battery permanently unreachable. We set it out so the frame head stays accessible.

Coordinating with an electrician

We install rooflights. The electrical connection is carried out by a qualified electrician and the two trades are coordinated rather than blurred. We set out the requirement: the position of the unit, the cable route, where the transformer and isolator sit, where each control goes, and what the system needs to be commissioned. The electrician provides and terminates the supply and certifies the electrical work. The order runs survey, then cabling while the structure is open, then our installation, then final connection, then commissioning. We would rather be brought in early with nothing to install than late with a ceiling in the way.

Commissioning and travel limits

A motorised rooflight is not finished when it is watertight, but when it has been set up, tested and handed over.

Travel limits. The actuator has to know where fully closed and fully open are. Closed is the position at which the sash compresses its gasket evenly around the whole perimeter. A limit set a couple of millimetres short leaves a unit that looks shut, whistles in a wind and lets water past in driving rain, and the cause is rarely suspected because the vent appears closed from the floor. Open is set against the geometry of the opening and the free area the room needs.

Travel path. The full sweep is checked against everything near it: a blind, a reveal return, a rafter edge, and on a top-hung unit anything on the roof above. A mechanism that meets an obstruction part way through its travel will keep pushing.

Controls and addressing. Each control is paired and tested, and where several units are installed they are grouped so a switch operates the ones somebody standing in the room expects it to.

Sensor test and handover. The rain sensor is proved with water rather than assumed. Then somebody in the house is shown where the isolator is, where the transformer sits, how to re-pair a control, and which panel to lift to reach the mechanism. It takes a few minutes and saves a phone call in three years.

Smoke vents and escape

Two categories of opening rooflight are governed by rules rather than comfort, and both are routinely confused with a motorised comfort vent. They are not specified the same way.

Automatic opening vents

An automatic opening vent, usually shortened to AOV, is a smoke ventilation unit. Its job is to clear smoke from a stairwell or lobby so people can get out and the fire service can get in. Everything about it differs from a comfort rooflight: the unit is tested and marked for smoke ventilation duty, the actuator is sized to open a heavy vent quickly against its own weight, and the system runs from a dedicated control panel with battery backup so it works when the mains has gone. It is triggered by the fire detection system or a manual call point, not a wall switch. It has no rain sensor, because closing on a wet day is the opposite of what it exists to do.

The specification does not come from the rooflight. It comes from the fire strategy for the building, which sets the vent position, the free area, the control arrangement and the interface with the alarm system. We install to that schedule and coordinate with the fire alarm contractor. The buildings this arises in around Oxford are usually converted period stock: a stairwell in a house divided into flats, the common parts of a small block, a college annexe. The constraint is that the vent must work and also sit on a roof not permitted to change.

Escape from a loft room

A rooflight in a loft conversion is often doing a second job as a means of escape, and the rules are specific: a minimum clear openable area, minimum unobstructed height and width, and a required height band for the bottom of the opening above the floor so somebody can reach and climb through. Those figures are set out in the Building Regulations guidance and are checked against the actual unit rather than assumed from a catalogue, because a rooflight can be large and still fail the clear opening test once sash and hinge geometry are counted. A centre-pivot leaves the sash across the middle of the opening, which normally disqualifies it; a top-hung unit or one with an escape hinge swings clear.

There is a specific point about motorisation here. An escape opening must be operable by hand, immediately, by somebody in the room, without power and without a control device. A rooflight whose only means of opening is a motor is therefore not, on its own, a satisfactory escape window. Where a unit serves both duties it is specified as a manually openable escape unit, or the escape provision is made elsewhere while the motorised rooflight does the ventilation.

Noise, speed and power

Noise. A motor at ceiling height in a quiet room is audible. A chain actuator produces a light mechanical tick as the links articulate, a spindle drive hums, and a linear actuator sits between them. None of it is loud, and all of it is noticeable in a bedroom at night in a way it is not in a kitchen. Slower mechanisms are quieter, which is a reason to prefer one over a bedroom.

Speed. Comfort vents open slowly and deliberately, in tens of seconds rather than instantly. The consequence worth knowing is that you cannot close one quickly. If a shower arrives while you are standing in the room, the vent takes as long to close as it took to open, which is precisely the gap a rain sensor covers. Smoke ventilation units are the exception and are required to be quick.

What happens in a power cut. A mains-driven actuator stops where it is. A vent that was open stays open and cannot be closed until the supply returns, unless the system has a battery backup, which is available on some control units and is worth considering over a stairwell. A spindle drive holds its position without power by design. A solar unit is unaffected and runs on its own battery until that depletes. A smoke ventilation system, by contrast, is designed around the assumption that the power has gone.

Some systems offer a manual override at the unit, which is only useful if somebody can reach it, and on the high-level installations that argue for motorisation, usually nobody can. So decide at specification what an open vent in a power cut would cost you.

Keeping the mechanism hidden

On a conservation-sensitive roof the rooflight is assessed on how it reads from outside, and a motorised unit introduces components a manual one does not. That is the difference between a specification which satisfies an officer and one which does not.

The starting position is that the roof plane must look as it did. A conservation-grade rooflight sits flush with the slate or tile rather than proud of it, is finished dark, and traditionally carries a single vertical glazing bar so it reads as a Victorian cast-iron light. Nothing about motorising it should disturb that reading, which in practice means the actuator is internal. A chain drive concealed within the head of the frame leaves nothing on the outer face and nothing on the roof, which is why it is the mechanism of choice on a designated elevation. What such a roof will not carry is an external arm, a bracket screwed through the covering, a surface-run cable crossing the slate, or an external control box.

Solar power sits awkwardly in this argument. A solar unit avoids opening up a historic ceiling, a real benefit on a listed interior where the plaster is original fabric and cutting a route through it is an alteration requiring consent in its own right. But the panel is outside, at the head of the sash, and on a prominent slope in a designated area it is a visible addition. Which consideration wins depends on how visible the slope is from public land and how significant the interior fabric is. It is a judgement, not a rule.

We are installers, not the local planning authority. What we can tell you is the kind of position your building is likely to be in and which arrangement of unit and mechanism tends to satisfy an officer looking at a roof slope. Where a determination is required it belongs to the council, and we say so plainly rather than guessing. Where you are working with an architect or a heritage consultant, we specify to their drawings.

What moves the price

A figure quoted for electric skylight installation in Oxford before anybody has seen the roof is close to meaningless, because the mechanism is the smaller half of the job and the building decides the larger half. What is useful is knowing which items move it.

The sequence we work in

The building first. What it is, what designations apply, and what the relevant roof slope is seen from. Much of this is settled before anybody visits.

The room second. How it is used, how high the opening will sit, what else can be opened at low level, and what the ventilation is being asked to do.

The mechanism third. Actuator type against sash size, mains against solar against the cost of the cable route, and whether the opening carries a safety duty.

The coordination fourth. Control positions, supply, transformer, isolation, access, and who is doing what in which week.

The price last. A number given before the first four steps is a guess, and usually a low one that gets revised once the ceiling is open.

Our workmanship carries a ten-year guarantee, with its coverage, exclusions and how to claim set out on its own page rather than in small print. We have been installing rooflights for fifteen years, we cover Oxford and up to twenty five miles by road, and we install VELUX, Fakro, Keylite and Roto units as new installations and replacements. If you are considering an electric skylight installation in Oxford, the useful first conversation is about where the opening sits and what has to reach it.