What moves a roof lantern cost, from span to kerb

Nobody can name the roof lantern cost for your extension from a brochure. The figure is the sum of a frame, a glazing build, an upstand, some carpentry, some access and a fair amount of care, and each of those can move on its own.

As a guide, the UK market typically prices a supplied and fitted lantern somewhere between £3,500 and £12,000. That is the same range shown on our rooflight and skylight costs page, and it is deliberately wide. A compact, standard-profile lantern over a small kitchen extension with easy access sits near the bottom. A long, made-to-measure lantern with an acoustic glazing build, a dark external finish and a crane lift sits near the top, and sometimes beyond it. Both are honest prices for different jobs.

None of this is a quote, an offer or a promise of any figure from Clear Skylights. A real number is written after a survey, and it comes with a written quiet spec that names the glass, the seals and the upstand in plain words. The rest of this page helps you understand what that number is made of, so you can see why two lantern skylight price factors that sound similar can produce quotes a long way apart.

The sections below follow the order in which the money usually moves: footprint first, then the frame, the glass, the base it sits on, the lift, the paperwork and the finishing. After that comes a way of comparing two quotes that look alike, and a run of questions people ask before they commit. The parent page on roof lantern installation in Crawley shows how the pieces fit into a whole job.

A wider, longer lantern needs more of everything, and the increase is steeper than the area suggests. The floor of your quote is set by the kerb size long before any choice of colour or glass.

Glass cost rises with area, which is easy to picture. The less obvious part is that big panes need to be thicker, and thicker panes weigh far more. A pane that one person can carry is a different object from one that needs two people and suction lifters, and the frame holding it has to be deeper and stiffer to take the load. The ridge of a long lantern also has to span between its end supports, so the section of aluminium grows as the lantern gets longer.

Weight then pushes on the structure below. A small lantern can often sit on a kerb carried by the existing roof joists. A large one may need its own steel or laminated timber support, which is priced separately from the lantern itself. Our page on whether a roof lantern needs a steel beam around the opening goes through when that happens.

A practical point for budgeting: decide the footprint before you compare products. A lantern one size step smaller can save more than a downgrade in glass ever would, and one size step larger can add carpentry you did not plan for. The roof lantern size guide for extensions sets out how the room, the falls and the ceiling decide what is sensible.

Shape matters a little too. A plain rectangular lantern with a simple ridge is the most economical form to make. Hipped ends, multiple ridges, curved profiles and lanterns with an unusual pitch all add cutting, mitring and glazing time. The guide to lantern shapes for a long, narrow extension explains which shapes earn their extra cost.

A lantern built to your exact opening costs more than a stock size, but it can save money elsewhere on the job. The trade-off is between the price of the lantern and the price of adjusting the roof to suit it.

Manufacturers offer a catalogue of standard sizes, and those are cheaper because the profiles, the cutting lists and the glass sizes are repeated. If your extension was designed around a standard kerb size, a stock lantern is usually the sensible choice. If the roof is already built to an awkward dimension, bending the roof to a standard lantern can cost more in carpentry and making good than a made-to-measure unit would have cost extra.

There is also a lead time difference. Stock frames can arrive within weeks. Made-to-measure frames with a special finish take longer, and a longer wait can mean a scaffold or a temporary weather covering staying up for more days. Our page on whether a roof lantern can be made to measure covers the practical side.

Most lanterns today have aluminium frames, and within aluminium the price moves with the profile, the finish and the number of bars. Timber and steel-look frames are a different price band again.

A thermally broken aluminium frame costs more than a simple one, because a plastic break separates the inner and outer metal and keeps cold from carrying through. It is the standard for a lantern over a heated room, and it also helps against condensation on the frame. A slimmer profile costs more than a chunky one, because slim sections need better alloys and tighter tolerances to carry the same glass. The aluminium roof lanterns page on frames, finishes and colours goes through the options.

The finish is a line on its own. A standard white or grey is usually the base price. A dual colour, with one shade outside and another inside, adds to it. A textured or metallic powder coat, or a specified colour match to your windows and bifold doors, adds more. Colour choice is a matter of taste first, and the guide to frame colour explains what tends to look right against brick, render and slate.

Bars are the third piece. Each glazing bar is a length of machined aluminium with its own gaskets and caps. More bars mean smaller panes, which are lighter and cheaper to handle, but they cost more in frame and they let in a little less light. Fewer bars mean larger panes, which look cleaner and cost more in glass and handling. Tie bars, where the span calls for them, add a small amount of material and a design decision. See roof lantern glazing bars and how many you need and why some lanterns have tie bars.

Glass is the largest single material cost in most lanterns, and the build you choose changes both the price and what you hear in the room. A standard sealed double-glazed unit is the starting point, and every step up has a reason.

The steps tend to go in this order. First, a toughened outer pane with a laminated inner pane, which is the usual safety arrangement overhead because a laminated pane holds together if it breaks. Second, a thicker outer pane or a different thickness on each side, which changes how the unit rings when rain lands on it. Third, a wider cavity or a third pane. Fourth, coatings: a low-emissivity coating for heat retention, a solar-control coating for a south-facing room, and self-cleaning glass for the outer face.

The noise side is where we spend most of our survey time. Rain on a lantern can sound like a drum in a kitchen extension, because a flat or shallow pane is a good membrane for raindrops. A laminated acoustic inner pane and unmatched thicknesses break up that ringing. Over a loft bedroom or a living room near the Gatwick routes, the M23 or the Brighton main line, the same choices help with aircraft, road and rail. We describe each build by specification, meaning pane thickness, interlayer, cavity and seals, and it goes on the quiet spec so you can see what you are paying for.

On cost, think of the glazing build as a set of switches. Some are cheap and sensible for almost every lantern, such as a laminated inner pane. Some are worth it only in the right room, such as solar control. Some, such as a third pane, add weight that feeds back into frame and structure. The pages on the best glass for a roof lantern, why the inner pane is laminated and glazing builds for a quieter kitchen describe each switch, and self-cleaning glass has a page of its own.

A lantern is only as good as the base it sits on, and the base is a real cost. It is also the line most often missing from a low quote.

The upstand, also called the kerb, is the short wall that lifts the lantern clear of the roof surface. It can be timber built on site, a ready-made insulated kerb, or a GRP moulding. Each carries the load, takes the waterproof membrane up its face and holds insulation that stops a cold bridge around the room's most glazed edge. A timber kerb is cheaper in materials and dearer in labour. A ready-made kerb costs more to buy and goes on faster. Either way, the height has to allow the membrane to turn up properly, and the detail has to work with the roof's fall. Our page on roof lantern kerbs and upstands explains the build.

The height of the finished lantern also influences the price in a quiet way. A taller upstand is more material, and a lantern that sits high may change how it looks from the garden and whether planning is a question. The page on how high a roof lantern sits above the roof explains the usual heights.

Then there is the roof itself. Fitting a lantern into a new extension roof is one task. Cutting a lantern opening into an existing flat roof is another, because the membrane, the deck and the joists are already in place and all have to be dealt with. If the existing covering is tired, the new upstand needs sound material to join to, and that can widen the scope. See whether a roof lantern can go into an existing flat roof. A lantern on a pitched roof has its own requirements, set out in the pitched roof answer.

The table sorts the drivers by how much they tend to move a lantern quote, and by whether you can choose them. It gives direction, not figures.

The pattern to notice is that the big drivers are mostly either choices you make early or facts about your roof that a survey reveals. The small drivers are the ones people spend the most time on, such as a second colour.

A fully assembled lantern is big, heavy and awkward. How it reaches the roof can decide whether a job needs two people, a hoist or a crane, and the quote should say which.

A lantern of modest size can be carried through the house or round the side and lifted by hand with a scaffold tower or a proper working platform. Larger units are often delivered as a built frame with the glass fitted on the roof, which keeps each lift manageable. A big, assembled lantern that has to go over a house with no side access may need a crane on the road, and that means road space, a booked slot and sometimes a parking suspension from the council. Those costs are real, and they are listed on a good quote instead of being discovered on the day.

The location matters. A back garden reached by a side passage is simple. A terrace with no rear access, a steep front drive or a narrow cul-de-sac with parked cars changes the plan. The post-war streets of Crawley and the towns around it vary a great deal in access, so we look at the route at the survey and describe it. The page on how a roof lantern is installed, step by step shows where the lift sits in the sequence.

Weather adds a small, honest allowance. A lantern frame needs calm conditions to lift safely, and a wet roof is slower to work. A lantern job therefore carries a margin for a day or two lost to wind, and a sensible quote will tell you how a delay is handled.

A lantern with opening vents costs more than a fixed one. The vents add hardware, a more complex frame and, if they are motorised, a power supply and controls.

Manual vents are operated by a pole or a handle, and they are the cheaper route. Electric vents need an actuator, a cable run from a nearby circuit and a control point, and the wiring must be done safely and to regulation. Rain sensors and remote controls add to the price again. On a lantern that could overheat a south-facing kitchen, a vent at the ridge is one of the best ways to let warm air out, so it can earn its cost. Where the room is shaded, a fixed lantern is simpler and cheaper. See whether a roof lantern can have opening vents and the hub page on electric and opening rooflight installation.

The orientation of the lantern and the heat it collects is a separate topic, and it feeds into which glazing you choose. Our pages on orientation and the summer sun and whether a lantern makes a kitchen too hot explain how that choice is made.

A lantern is building work, and the cost of doing it properly includes the regulations. Some of that is design, some is notification and some is simply the specification of the unit.

Part L of the Building Regulations sets the thermal performance for new glazed elements, and a lantern must meet it. That is one reason a lantern carries thermally broken frames and low-emissivity coatings as standard. Good practice on glazing safety overhead is why laminated inner panes are the norm. Part B can affect a lantern close to a boundary. Where a lantern is notifiable work, we handle the Building Control notification. You can read the official guidance on building regulations approval at gov.uk, and our page on whether roof lanterns are energy efficient enough for Part L goes into the thermal side.

Planning is separate. Many lanterns fit within permitted development, but the position is checked for your address and is never assumed, especially in a conservation area or on a listed building. The answer page on whether a roof lantern needs planning permission sets out the usual questions. If the extension is also going through an architect or a planning application, the lantern size is one of the things that needs fixing early, because it affects the drawings.

Structural design can also appear as a cost. If a beam is needed, it may need calculations from an engineer, and that is a cost for the project even when it is not a cost for the lantern. Agree who is responsible for it at the start.

The lantern is not finished when the glass is in. The ceiling lining, the plastering, the decoration and any blinds or lights are a real part of the job, and they are often left off a first price.

Inside the room, the opening needs a neat lining, usually plasterboard with a skim, and a clean junction to the ceiling. If you want it painted by the same crew, that is a line. If you will have your own decorator, say so. Blinds are a separate cost and a separate decision, since a lantern needs a blind that suits the shape, the span and the heat. See lighting and blinds around a roof lantern, blackout blinds and lights inside a lantern. The wiring for lights and blinds is cheapest when it is run before the ceiling is closed, so decide early.

The room underneath matters too. A kitchen extension has worktops, appliances and flooring that have to be protected while the work goes on, and the plan for that goes on the quote. Our page on planning a roof lantern over a kitchen extension covers the practical points, and the page for orangeries and garden rooms does the same for glazed rooms.

When two lantern quotes differ, the difference is almost always in what each one includes. A short, clean quote is not necessarily a cheap one, and a long quote is not necessarily dear. Compare the same items across both.

1. Kerb size, structural opening and visible glass, written as three separate numbers.
2. The glazing build, pane by pane, with the inner pane type named.
3. Frame finish, including whether the inside and outside colours are the same.
4. The upstand: who builds it, what it is made of, what insulation it carries.
5. Structural work: trimmers, beam, calculations, and who pays for each.
6. The lift: scaffold, hoist or crane, and whether permits are in the price.
7. Making good inside, and what state the room is left in.
8. Building Control notification, and the length and form of the guarantee.

Laid side by side, these eight lines usually explain the gap. A quote that says only "supply and fit lantern" has not yet told you what you are buying. Our guarantee is a 10-year workmanship guarantee, which is not insurance-backed, and the written quote states that plainly so you can weigh it against any other.

Most lantern price changes come from things nobody looked at before the number was given. A survey and a written scope remove nearly all of them.

The usual sources are plain. A deck that is weaker than it looked. A membrane that cannot take a new upstand and needs renewing around it. A kerb size that does not match the structure. A crane slot that has to be rebooked. A change of mind about colour after the frame has been ordered, which is the most expensive kind of change because the frame is made to order. Each of these can be spotted or prevented by a careful survey and by locking the specification before the order goes in.

Agree in writing what happens if something unexpected turns up once the roof is opened. A sound approach is that any extra is described, priced and agreed before the work is done. The quiet spec sits beside the quote and fixes the glass, the seals and the upstand, so there is one document that says what you are getting.

The quickest way to a real price is to tell us about the room, the roof and what you want from the glass. We then survey across Crawley and the 30 miles around and write the quote.

It helps to send a rough size, the type of roof and the room below. Photographs from inside and out save time, and so does a note of anything that bothers you, such as rain noise in the current extension. Use the quote form on this page, the get a quote page, or WhatsApp on +44 7880 284133. If you would rather compare lanterns with another form of roof glazing first, the page on choosing between a roof lantern and a flat glass rooflight helps, and lantern or fully glazed roof covers the larger choice.

Why does a lantern cost so much more than a flat rooflight?

A lantern is a built roof structure with its own frame, bars, ridge and upstand, where a flat rooflight is a single unit. More parts, more glass and more handling all add up, and the support beneath is usually heavier.

Will a quieter glazing build add a lot?

It adds glass, since a laminated inner pane and an unmatched outer pane use more material. Beside the frame, the upstand, the access and the labour, which stay the same, the increase is modest, and the survey shows whether the room needs it.

Is the cheapest lantern a false economy?

It can be, when the saving comes from a thinner frame, a basic glazing build or a missing upstand detail. Compare the eight lines above before you compare the totals.

Can I reduce the price without losing quality?

Often, yes. A standard size, a single-colour frame, a simple rectangular shape and fixed rather than opening vents all lower the price without touching the glass or the upstand. Keep the glazing build and the kerb detail, which are the parts you live with every day.