Electric rooflights over a kitchen extension: clearing steam and summer heat

A kitchen is the hardest room in the house to ventilate, because it makes moisture and heat in short, strong bursts. An electric skylight over the kitchen earns its place by handling those bursts on demand.

Think about a normal evening. A pan of pasta boils for ten minutes and the air fills with water vapour. Vapour rises, meets the coolest surface in the room, and condenses there. In a flat-roof extension the coolest surface is often the ceiling or the glass itself. Over a winter the result can be a film of water on the inner pane, damp plasterboard near the upstand and, eventually, mould in the corners.

Summer brings the opposite problem. A flat-roofed extension with large glazed doors and a rooflight has a lot of glass facing the sun. Warm air collects under the ceiling, and because the room is open plan, it spreads into the rest of the ground floor. Opening a high-level vent is the most effective way to let that air go, since warm air leaves by the highest route if you give it one.

A manual opening rooflight can do the job, but it sits out of reach. Above a kitchen island, a pole or a crank handle means reaching across worktops, and in practice the vent stays shut. A motor removes that friction. If you want the full mechanics, our guide to how electric opening rooflights work explains the actuator, the control box and the limit switches. Here we stay with the kitchen.

Put the moving glass where the moisture and the warm air actually gather, which is usually over the island or the dining end and not over the hob itself.

The hob already has an extractor, and that hood needs a solid ceiling section to fix to and a duct route to outside. A rooflight directly above a hob also collects grease on the inside of the glass, which then needs cleaning from a ladder. Setting the unit a little away from the cooking zone, with the hood on its own section of ceiling, gives both of them room to work.

We mark the position on the ceiling plan against your kitchen layout before anything is ordered. The table shows the usual options and what each one trades away.

Which way the unit opens matters too. A hinged rooflight lifts one edge, so the open side should face away from the prevailing wind and from the hob, so that steam does not curl back into the room. A sliding unit parts across the ceiling and suits a wide opening. Our page on choosing between hinged and sliding rooflights compares the two.

An opening rooflight is a ventilator and a cooling vent. It is no replacement for the cooker hood, and the regulations treat the two as different things.

Approved Document F sets two kinds of ventilation for a kitchen. The first is extract ventilation at the source, which means a hood or fan that removes moisture and smells where they are made. The second is purge ventilation, a larger opening that clears the room quickly when the air is heavy. An opening rooflight is well placed to supply purge ventilation, and Approved Document F expects the openable area for that to be at least a twentieth of the floor area of the room. An extension that already has bifold or sliding doors may meet that with the doors open. The rooflight adds a high-level route that works when the doors stay shut.

On the extraction side, the guide figures in Approved Document F are an intermittent extract rate of 60 litres a second for a kitchen, or 30 litres a second from a cooker hood that extracts to the outside. Your hood or ducted fan supplies that, and the rooflight is planned around it. What the rooflight does is take the rest of the load: after a long roast, the extractor clears the vapour at the hob, and the motorised vent lets the warm, damp air that collects at the ceiling drain away.

There is a knock-on effect for the extractor. A hood pulls air out of the kitchen, and that air has to come from somewhere. With a recirculating hood, nothing leaves the building, so an open rooflight is more useful still. With a ducted hood, a slightly open vent nearby gives the fan a route for make-up air, which helps it work with less whistle at the grille. Keep the rooflight closed while the hood runs at full power if the vent is very close to the hood inlet, so the two do not simply swap air between themselves.

An opening rooflight cools a kitchen best when it is paired with a low opening, because air needs a way in as well as a way out.

Warm air rises, and in a room with a high vent it will leave through that vent whenever cooler air can replace it from below. This is the stack effect, and it is the reason a rooflight can do more than a window of the same size. Open the glass above the island, open one door or a low window on the shaded side of the room, and a slow current of air runs through the kitchen without a fan. We go through the physics and the sizing in our answer on whether an opening rooflight can help cool a house in summer.

For a kitchen, three points are worth settling in the design:

• Opening size. A larger opening moves more air, but it also lets in more rain if the weather turns, so the control choice matters as much as the size.
• The inlet. The low opening should be on the cooler side of the room, away from the hob and away from a south-facing wall of glass.
• Shading. Glass that faces the sun all afternoon adds heat faster than any vent can shed it, so the glazing specification and a blind are part of the plan.

The glass itself can be chosen to limit solar gain, with a coating that reflects part of the sun's heat while keeping the room light. Part L limits the total glazed area of an extension to 25 per cent of its floor area, plus any openings the extension covers, and that cap applies to rooflights as well as doors. A kitchen with wide glazed doors has already spent much of that allowance, so the rooflight is sized with it in mind. Our guide to energy efficient rooflights covers the U-value side of the same decision.

An electric rooflight needs a supply at the opening, and the cable route should be planned before the plasterboard goes up.

The unit runs on a low-voltage motor, fed from a small transformer or control box. That box sits somewhere reachable in the ceiling void or on a nearby wall, with a mains supply behind it. In a new extension the supply can be taken on a spur from a lighting or small power circuit, and the cable run is short. In an existing room, chasing the wall or lifting a few boards in the room above is usually needed. Either way, the electrical connection is made to current standards and, where the work is notifiable, the notification is handled along with the rest of the Building Control paperwork.

The kitchen adds a few rules. Sockets, switches and fused spurs near the sink have to sit at a safe distance from water. A control box that can be reached through an access hatch is better than one sealed behind a finished ceiling. And the cable should keep clear of the zone where a pendant light or a hood duct is going to pass.

Our page on wiring and powering an electric rooflight goes through cable sizes, isolation and access. If you are wondering who carries out which part, the answer on whether an electric rooflight needs an electrician sets it out.

The best control is the one that people use without thinking, and in a kitchen that means something you can operate with a clean knuckle while holding a spoon.

A wall switch beside the kitchen door is the plain choice. It is reliable and everyone in the house understands it. A handheld remote is handy for the dining end, although it tends to migrate to the back of a drawer. A wall keypad with presets lets you assign a single press to "open halfway" for a cooking session and another to "close", which suits a household that cooks every day.

Some systems also accept a timer or a temperature sensor, which is helpful on a summer day when nobody is home to open the glass. A sensor set to open the vent when the room passes a chosen temperature keeps the extension from baking while you are out. Pair it with a rain sensor so that the vent does not open under a cloud. The comparison in our guide to switches, remotes and keypads for electric rooflights shows what each option does in daily use.

Smart-home owners often ask whether the vent can be voice controlled. On some systems it can, and the answer on Alexa and Google Home with an electric skylight covers what to expect. A wall switch is still worth keeping as the backup, so the vent works when the wifi does not.

A rain sensor is the control that turns an opening rooflight into something you can leave alone.

A kitchen is a room where someone may leave the vent open and walk out to the garden, to the school run or to the shops. A small sensor on the outer frame detects the first drops and sends a close command. Some units close within seconds. The water that falls in the meantime is a few drops on the glass and the upstand, not on your worktop. Position the sensor where it sees the rain at the same time as the glass does, and check that the sensitivity setting suits how you use the room.

A rain sensor needs power to act, so the question of a power cut matters. Most systems have a manual release, and some can carry a battery backup. The answer on what happens to an electric rooflight in a power cut explains the options, and our page on rain sensors on electric rooflights covers setting and placement.

A rooflight in a kitchen has to be quiet in two states: the motor moving, and the glass sitting shut while it rains.

A well-chosen motor makes a soft mechanical sound for the few seconds that it runs, and then it is silent. The open position is another matter. With the vent open, the sound from outside enters the room almost as if the roof had a window in it, which is the reason to close the unit when a departure passes overhead or a train slows on the line. Opening and closing is a choice you make, and the glass does its job the rest of the time.

Shut, the quiet comes from the build. Rain on flat glass drums, and a kitchen with hard worktops, tiled floors and few soft furnishings gives that sound nothing to absorb it. The remedy is in the glazing. A laminated acoustic inner pane damps the glass, a sensible pane thickness and cavity change how the unit rings, and good seals keep the gap at the frame from whistling. The upstand is the last piece: a solid, well-insulated kerb stops the frame from acting like a drum skin. Our page on acoustic laminated glass in an electric rooflight explains how the glass and the opening mechanism go together.

Each of these choices is written into the quiet spec that comes with every quote. For a kitchen it names the noise we heard at the survey, the glazing build we propose and how the seals and upstand are finished. You can read it before you commit to anything.

The opening unit sits inside the same set of rules as the roof around it, and each one touches a different part of the job.

1. Part L governs the thermal performance of the glass and the 25 per cent glazing cap for an extension, and the frame and upstand have to be insulated to limit cold bridging.
2. Part F governs ventilation, including the extract at the hob and the purge ventilation route, so the extractor and the rooflight are considered together.
3. Part K sets safety glazing rules for doors and low panes, and above a room where people stand and work a laminated inner pane is the accepted good practice.
4. Part B applies to fire safety. In a kitchen that opens to the rest of the house, a motorised vent does not change the escape routes, but it should be checked against the plan.

We install to current Building Regulations, and where the work is notifiable we handle the Building Control notification. If the extension itself is being built by a separate contractor, tell us early so the rooflight opening is framed correctly by the builder. An opening framed to the wrong size can hold up delivery day, and a measurement taken at the survey avoids it.

Three details complete a kitchen rooflight: something to shade it, something to keep insects out and an upstand tall enough for the opening to clear.

A blind under the glass cuts glare on the worktop in the afternoon and holds heat back in a hot week. An electric blind can share a control with the vent, so one press opens the glass and lowers the shade. Our answer on fitting a blind to an electric rooflight covers the clearances the blind and the opening need.

An insect screen matters in a kitchen with food on the side and a vent left open on a summer evening. A fine mesh can be built into the frame, so the screen stays put when the glass opens.

The upstand under an opening unit may be taller than under a fixed one, to allow the sash to lift clear of the roof finish and of any snow or standing water. Kitchens with built-up roofs, where insulation and a green roof can add depth, are checked on the day of the survey.

These come up when a kitchen extension is being planned around an opening rooflight.

Can I fit an electric rooflight over the hob?

You can, but we would usually move it a little to one side. Grease collects on the inside of glass directly above a hob, and the extractor needs its own solid ceiling to fix to. The island or dining end gives a better result.

Will the vent let out the cooking smells?

It helps clear them after cooking, because warm air drains out at the top of the room. The extractor still does the main work at the hob, and the two together are better than either alone.

Is it worth having a motor in a kitchen?

A vent that is out of reach tends to stay shut. The motor is what makes the opening a habit. Our answer on whether an electric rooflight is worth it over a manual one compares them properly.

Can an existing fixed rooflight in my kitchen be swapped?

It depends on the kerb and the frame. See whether a fixed rooflight can be swapped for one that opens for the checks we make.

When you are ready to plan your own kitchen, send us the room size and the layout through the quote form or by WhatsApp. The wider range of opening units is covered on our electric and opening rooflight installation page.