Picture a kitchen extension with a flat roof and a big, dim room underneath. A lantern is the fix people reach for: a tall, multi-sided glass roof with its own ridge, standing on a low plinth above the opening. It drops light into the centre of the room and, from outside, gives an otherwise featureless extension a shape.
The same piece is a standard part of an orangery, where a perimeter of masonry and a flat roof surround a central lantern. Because it is big and heavy, a lantern is more than a window. It is a small building sitting on your roof, with its own structure, its own drainage and its own thermal performance. This guide covers how it is made, how it is held up, what the rules say and what to ask a supplier. If you want something smaller, our guide to sun tunnels is a compact alternative.
What makes a lantern different from a rooflight
A flat rooflight is a low glazed unit that lies close to the roof surface. A lantern is taller, with sloping glazed sides that meet at a ridge, and often a bar-and-glass construction that you can see from below. It lets in more light at more angles, because the sides catch the sun at different times of day, and it gives height to the ceiling inside the room.
The consequence is size and weight. A large lantern is a fabricated frame, usually in aluminium, timber or a combination of the two, glazed with sealed units that are heavy in their own right. It arrives in sections, or as a single piece lifted by crane, and it needs a purpose-made base. Compare that with a small kerbed rooflight that two people can carry up a ladder.
Parts of a lantern
The kerb or plinth is the upstand fixed to the roof structure. The frame stands on it, with a ridge at the top and hips at the corners. Glazing bars run between, and the whole thing is capped with aluminium or lead to shed water. Cills and flashings seal the base. Each of those junctions can leak, so they are where a good fabricator spends the most effort.
Part L of the Building Regulations allows a rooflight 2.2 W/m²K for a new or replacement element in an existing home. A lantern is generally judged as a rooflight on this basis, and the figure to ask for is the whole assembly, not only the glass. Our guide to types of rooflights sets lanterns alongside the other kinds.
Sitting a lantern on a flat roof
A lantern needs a stiff, level base. On a new extension, the structural engineer designs the opening with beams and trimmers sized for the lantern's weight, and the roof joists are laid around it. On an existing flat roof, the same work has to be done in reverse: the old deck comes out in part, the neighbouring joists are propped and carried on new beams, and a fresh frame is formed. Nothing here is a job to improvise, and the lantern supplier's weight figures go to the engineer before anything is cut.
The kerb then goes on. It is built up from timber or a proprietary upstand, insulated, and wrapped in the flat roof's waterproofing. The membrane is taken up the face and finished beneath the lantern's own cill, so that water running down the glass cannot pass behind it.
Falls and ponding
The roof round a lantern must drain freely. British Standard guidance for flat roofs calls for a finished minimum fall of 1:80, and a design of 1:40 so that the finished roof still meets that figure after construction tolerances and deflection. A kerb is a dam in the path of the water, so a small sloped section behind it, sometimes called a cricket, steers water around the sides. Ask to see where the water goes, not only where the lantern stands.
Flat roofs are covered in our flat roofing pages, and the roof covering choice affects how neatly the lantern base is finished.
Orangeries, conservatory roofs and the lantern
An orangery is built like a house extension: masonry piers or walls with large windows, a flat or low-pitched roof, and a lantern in the middle. A conservatory, by contrast, is mostly glass, often with a pitched glazed roof. The two get confused, and the confusion matters because a lantern added to a conservatory is a different job.
If you want to replace a conservatory roof with a solid one, with or without a lantern, the work is a material alteration, so a building control application is needed. Homebuilding and Renovating, last updated 17 July 2023, notes that the frames are then asked to carry a heavier load. MyBuilder's conservatory roof guide, updated 21 August 2026, gives structural reinforcement as £500 to £2,000, in addition to the roof itself. A lantern is heavier than a polycarbonate sheet, so the existing frame needs checking before you assume it can take one.
Fitting a lantern to an existing orangery
If the orangery was built with a lantern opening and a base in place, a replacement or a repair is a simple matter. If the roof is a solid flat roof with a polycarbonate or glass panel, the roof will need altering. Fabricators measure from the opening on a site visit and make the lantern to fit, which is why there is a lead time.
Roofing works on an orangery are a mix of masonry, joinery and waterproofing. We handle the roof covering and the weathering of the base, and we coordinate with the lantern supplier on the details where the two meet.
Frames and glass: aluminium, timber and what sits in them
Most lanterns today are aluminium, with a slim profile, a factory finish and thermally broken bars that reduce cold bridging. Timber lanterns are warmer to look at from inside and suit period houses and orangeries, but they need regular decoration and a good paint or stain system. Some products have timber inside and aluminium outside, which gives the look of wood and the weather protection of metal.
The glazing is normally a sealed double glazed unit. A self-cleaning outer coating helps keep the glass clear, but it works by letting rain rinse the pane, so it does less on a shallow pitch. A solar-control coating limits heat gain on a south-facing roof, at the price of a slightly cooler, greener tone. Laminated glass is the usual choice for the inner pane because of the risk of falling fragments.
Heat in summer, cold in winter
A lantern concentrates glass in one spot, which makes it a place where heat comes in and goes out quickly. In summer, blinds fitted underneath, or automatic ones, prevent a room from becoming a greenhouse. In winter, what counts is the thermal performance of the whole assembly, whatever the glass is called. Our guide to skylight overheating covers the problem in more detail.
Vents and opening lights
Some lanterns include trickle vents or an opening light to let heat out. A motor can drive it from a switch or a rain sensor. It is a good feature in a kitchen, where warm air rises, but it adds a moving part to a roof, so it is worth discussing before ordering.
Planning permission and Building Regulations
Because a lantern alters the profile of the house, planning needs thought. Under Class C of the General Permitted Development Order, a roof alteration may extend no further than 0.15 metres from the existing slope and may not exceed the existing ridge height. A lantern is much taller than that on a flat roof, so it often falls outside Class C, and the extension itself may have its own height limits. Whether permission is needed depends on the specific house and what is already there, and the planning officers at your council are the people to ask. Swindon Borough Council's planning pages recommend pre-application advice.
A listed building needs listed building consent for any work that changes its character. In a conservation area or a National Landscape, the usual rules on appearance apply with extra weight, and an Article 4 direction can remove permitted rights. See our guide to planning rules for roof windows for the wider picture.
Building Regulations
Fitting a lantern involves structural change, thermal performance and, in a kitchen, ventilation, so building control is involved. Swindon Borough Council runs its own building control team, and a registered building control approver is the private option. Should the work be notifiable, we go over consent with you and lodge the notification, while an engineer supplies the structural calculations.
Cost and what moves it
Lanterns are priced by size, frame material, glass specification and how complex the roof underneath is. A small, standard lantern is a different purchase from a large, bespoke timber one. Fitting costs vary as well, because a crane lift, scaffolding and a structural opening all add to the job.
MyBuilder's conservatory roof guide, updated 21 August 2026, puts a conservatory roof replacement at £2,000 to £10,000 or more, with glass at £3,000 to £8,000 and solid roofs at £5,000 to £10,000. Those are typical national figures for a whole roof replacement, so they say little about a lantern on its own. What a lantern costs is settled by the survey, and our written quote comes after it. Most cost factors for glazing jobs are in our roof window cost guide, and the skylights hub links the rest.
Check what a quote includes
Whichever quote you take, find out whether VAT and scaffolding are included, who is responsible for the structural opening, and whether the price covers the roof covering around the base. A lantern price that stops at the glass leaves the weathering to someone else.
Lead times
Because lanterns are made to measure, there is a wait between the survey and the lift. The roof around the opening can be prepared in the meantime, with temporary weatherproofing over the hole if the old roof has been cut open ahead of delivery.
Looking after a lantern
A lantern is easier to keep than it looks, and most trouble comes from neglect of the same few places. Leaves and moss collect in the gutters of the glazing bars and against the cill, and hold water against the seals. Wash the glass from a safe position using clean water and a soft brush, and avoid abrasive pads that scratch a coating.
Look at the visible sealant at the glass edge once a year, the flashing at the base and the paint on timber frames. The flat roof around the kerb needs checking too, because standing water there points to a fall problem. Our roof window maintenance page has a seasonal checklist, and the page on roof window flashings explains how those junctions are meant to be built.
When a lantern leaks
Most leaks come from the junction between the lantern and the kerb, or from a failed seal in the glazing bar. Condensation between the panes means the sealed unit has failed. If the roof covering around the base has split, water can enter below the lantern and look like a lantern fault.
When you send us photographs and a few measurements through the enquiry form or WhatsApp, we will say what the survey should check. What follows the survey is a written quote with photos of your roof. Our 10-year workmanship guarantee is also written down, and the site is tidied away when we finish.