A roof lantern over a kitchen extension, planned around the steam

The lantern belongs over the part of the kitchen you use, and the kitchen plan decides that before the roof does. Draw the units, the island and the table first, then fit the glass to them.

The usual habit is to centre a lantern on the room because that is how it looks on an elevation. A kitchen rarely lives in the middle of its own floor. The run of units sits against one wall, the island sits a metre or so off it, and the dining table sits nearest the garden doors. If the lantern is centred on the room, it can end up over the walkway between island and table, where nobody stands, while the worktop stays in the shade of a flat ceiling.

We ask for the kitchen designer's plan at survey, or we sketch one on the day. Then we mark three positions on the ceiling:

• The centre line of the island, which is usually the strongest candidate for the glass.
• The edge of the wall units and any tall larder, where the light well must stop short.
• The fixing point for the extractor, which is a separate decision covered below.

Over an island, a lantern gives the worktop daylight from above, which is the direction that throws the fewest hard shadows across a chopping board. Over a dining table, it gives a softer, more even light, and it tends to be the part of the room people want to look up at. If the room is long enough, the two can be served by two lanterns in line, with a solid strip of ceiling between them. Sizing that is covered in our roof lantern size guide for extensions, and the choice between one long unit and two shorter ones is in the answer on which lantern shape suits a long, narrow extension.

Each kitchen layout asks the glass to do a different job. A skylight lantern over a kitchen is placed differently for an island layout than for a peninsula, a galley or an open dining end.

The table below sets out the four layouts we meet most often and what each one asks of the position.

The hob is the detail that changes things. If a hob sits in an island directly beneath the lantern, the extractor has to come down from somewhere, and the glass is a long way up. That can work, and it is covered in the extractor chapter, but it is a reason to consider moving the lantern a little towards the table, leaving a solid section of ceiling over the cooking.

A peninsula layout is the easiest of the four. The hob sits on the wall run or the peninsula nearest a solid ceiling, the extractor ducts straight up or sideways, and the lantern takes the table end. Nothing is fighting for the same piece of ceiling.

Steam and cooking vapour are warm, wet and looking for the coldest surface. Under a lantern, the coldest surface is the glass. Understanding that is the core of the planning.

A boiling pan puts a large amount of water vapour into the room in minutes. Warm air holds that moisture easily, and it rises. When it meets a surface cooler than its dew point, the water condenses. A modern double-glazed lantern has a warm inner pane, which is the point of the build, and in normal use it stays clear. The risk is at the edges and on the frame: the aluminium bars and the junction between frame and kerb are the cooler places, and a kitchen that produces steam every evening in winter will show it there first. Our answer on why a roof lantern gets condensation on the inside explains the physics, and the same reasoning applies here with a stronger source of moisture.

Three things keep the glass clear in a kitchen:

1. Capturing the steam at the hob before it rises, which is the job of the extractor.
2. A warm-edge spacer and a thermally broken frame, so the glass edge does not run cold.
3. Background ventilation, so the room's humidity is removed steadily and not just while the hood is running.

Approved Document F covers ventilation, and a kitchen has its own extract requirement, either at the hob or as a general extract in the room. Your extension's ventilation design has to satisfy it whatever glass you choose. We install to current Building Regulations, and the lantern specification is written with the ventilation in mind, not as an afterthought.

A lantern with opening vents can help in summer and on cooking days. It is not a substitute for extraction, because warm moist air leaves fastest when it is pulled out at the source. If vents are on your list, can a roof lantern have opening vents goes through what is possible, and our page on electric and opening rooflight installation covers the motors and rain sensors.

The extractor decides how much ceiling you need left solid. It is the one fitting in a kitchen extension that cannot be moved once the roof is built.

There are four common ways to handle the extraction, and each one puts different demands on the roof and the lantern.

A wall-mounted hood on the run of units is the simplest. The duct passes through the wall behind the hob to the outside, the lantern is nowhere near it, and the glass can go wherever the layout wants it.

A ceiling-mounted hood over an island needs a duct rising through the roof build-up. The duct has to pass between joists, inside the insulated roof and out through the membrane at a point clear of the lantern kerb. It needs its own upstand and outlet, and that outlet has to be kept well away from the glass. Decide this at the design stage, because it fixes where the joists may be cut and where the lantern cannot go.

A downdraft extractor built into the worktop draws the air downwards and out through the floor void or a wall. It leaves the ceiling clear, which is attractive under a lantern, although it needs a route for the duct below the floor or through the units.

A recirculating hood filters the air and returns it to the room. It needs no duct at all, so nothing touches the roof, but it does not take the moisture out of the house. In a kitchen under a lantern that is a weakness, because the water vapour still rises to the glass.

The duct outlet on the roof is a weather detail like any other penetration. It needs a proper upstand or a purpose-made outlet, and it needs to sit clear of the lantern's kerb so that the membrane work around each is not crowded. Our page on roof lantern kerbs and upstands shows how much flat deck the kerb itself wants around it, and the duct outlet needs its own share of that space.

A kitchen makes heat of its own, and a lantern adds heat from the sky in summer. The glass specification has to allow for both, or the room becomes the hottest in the house.

In summer, an oven and hob running on a sunny afternoon can leave a south-facing kitchen under glass very warm. The remedy is a mix of solar control glass, shading and ventilation, and each has limits. A solar control coating on the outer pane cuts the heat that enters, with a slight tint to the light. Blinds under the lantern cut glare and heat, but a blind inside the glass leaves the warmth in the lantern space, where it needs somewhere to escape. Vents at the top of the lantern let that hot air go.

Orientation counts heavily here. A lantern facing due south over a kitchen takes the sun for most of a summer day, while one on the north side of a house takes a cooler, steadier light. We go through that in roof lantern orientation and the summer sun, and the specific question of summer heat in a kitchen is answered in does a roof lantern make a kitchen too hot in summer.

Insulation matters the other way in winter. A kitchen under a lantern loses more heat through the glass than through an insulated roof, so the glass specification must satisfy the Part L limit for rooflights, and a thermally broken frame keeps the edge warm. The wider picture of how these limits affect the whole extension is in are roof lanterns energy efficient enough for Part L.

The lantern gives you daylight in the day and a black hole at night, unless the lighting is planned with it. Wiring goes in before the ceiling closes, so the layout has to be settled early.

A kitchen needs three layers of light: bright task light over the worktops, softer general light for the room, and something gentle for evenings. A lantern gives a fourth, which is the glow of the glass itself after dark. The work is deciding which of the four layers comes from where.

The flat ceiling around the lantern is the natural home for downlights. They need a clear band of plasterboard to sit in, and they need a void above them that is not filled with a duct or a beam. If you plan a run of pendants over the island, the fixing points have to be in the structure before the ceiling is boarded, and pendants hung beneath a lantern can block the view of the glass from the far end of the room.

Uplights set in the lantern's inner ledge, or in the light well, can wash the glass at night and give the room a soft, indirect light. They need an electrician who has seen the lantern drawing, because the cable route and the driver position both have to be settled at first fix. Our guide to lighting and blinds around a roof lantern covers the options, and the answer on putting lights inside a roof lantern deals with the ones that go in the frame itself.

Blinds belong in the same conversation. Electric blinds need power and a control cable at the time of the first fix, and a blind over a large lantern needs its own track or cassette. Decide on it while the ceiling is open.

A kitchen is already a loud room: extractor fans, dishwashers, hard surfaces and chairs on tiles. A lantern adds a new kind of noise, which is rain on the glass, and in a hard-surfaced open-plan room there is nothing to soak it up.

Rain drums on any thin, stiff surface, and glass is both. The noise in a heavy shower comes from the outer pane being struck and the inner pane passing the sound into the room. How much of it you hear is a matter of the glazing build, the seals and the frame, not the size of the lantern alone. A lantern with an acoustic inner pane of laminated glass, a generous cavity and well-seated gaskets is noticeably calmer than one with thin, matched panes. You can find the rainfall question in is a roof lantern louder in heavy rain than a flat rooflight, and the glazing choices in lantern glazing builds for a quieter kitchen.

In the Crawley area, some kitchens also hear the sky. Gatwick's flight paths run over the town and its villages, and a room with a lot of glass overhead hears more of it than one with a solid roof. Road and rail noise from the A23, the M23 and the Brighton main line reaches some neighbourhoods too. We listen for what the room actually hears at the survey, and the answer goes into the written quiet spec that comes with every quote. You can read how that document works on the quiet spec page.

A laminated inner pane also does a safety job. Overhead glass above a place where people stand should break safely, and good practice expects safety glazing in those positions. The reasoning is in should the inner pane of a roof lantern be laminated, and it is why we rarely suggest anything else over a kitchen.

A kitchen extension roof already carries a lot: insulation, a waterproof layer, sometimes a green or gravel finish, and the weight of the ceiling and services beneath. A lantern adds glass, and the opening needs structure around it.

A double-glazed aluminium lantern of kitchen size is heavy, and it sits on a timber or insulated kerb. The joists cut for the opening have to be carried by trimmers, and on a wider opening by a beam. If the extension is being designed now, the engineer can size the structure for the lantern from the start, and it costs little. If the lantern is being added to an existing flat roof, the structure has to be checked first. We cover when a steel or engineered beam is needed in does a roof lantern need a steel beam around the opening, and the cutting-in of an existing roof in can a roof lantern go into an existing flat roof.

The services under the roof need attention as well. Extractor ducts, downlight cables, blind wiring and any pipework all share the same joist zone as the lantern trimmers. A short coordination meeting between the kitchen fitter, the electrician and the roofer before the ceiling is boarded saves more trouble than any other single step in the job.

A lantern on a new extension is normally part of the extension's own approval, and on an existing one it is often permitted development. The details depend on height, position and the property.

A lantern projects above the flat roof, and that height is what planning rules look at. The limits for extensions under permitted development are set out on the Planning Portal, and an extension's overall height, and its distance from the boundary, come into it. Properties in a conservation area, or listed homes, are treated differently, and in those cases the position is checked for the address before any design is fixed. Our answer to does a roof lantern need planning permission explains the usual tests, and how high a roof lantern sits above the roof tells you what figure to use.

Building Regulations apply whatever the planning position. They cover the structure, the glazing performance, the safety glass and the ventilation, and a new kitchen extension will already be under Building Control. Where the work is notifiable, we handle the notification, and we install to current Building Regulations. The official guidance for householders is on the Planning Portal.

These are the questions that come up when the lantern is going over a room with a hob and a table in it.

Can a lantern go directly over the hob?

It can, but it is rarely the best position. The extractor needs a solid ceiling and a duct route, and heat and steam rise straight at the glass. Moving the lantern towards the table and leaving the ceiling over the hob solid makes the extraction simpler and the glass cleaner.

Will the glass steam up every time I cook?

With a well-specified lantern, a hood that captures the steam and some background ventilation, the glass should stay clear in normal use. The frame and edges are the first places to show moisture, which is why a thermally broken frame and warm-edge spacers matter in a kitchen.

Do I need an extractor if the lantern opens?

Yes. Opening vents help with summer heat and general air, but they do not take steam out at the hob. The extract required by Approved Document F still has to be met, by the hood or by another form of ventilation.

When should the lights and blinds be decided?

Before the ceiling is boarded. Cables for downlights, uplights and electric blinds are run at first fix, and the lantern drawing is what the electrician needs to place them. Adding them later means opening the ceiling.

If you would like a kitchen lantern planned around your own layout, with the ventilation, lights and glazing written down together, get a quote or message us on WhatsApp. You can also read how the price builds up in what affects the cost of a roof lantern.