How much does a roof lantern cost?
There is no single figure, and anybody who gives you one over the phone is guessing. What can be given quickly is a range, based on the size you want, the roof you have and the glass the orientation calls for. What turns that range into a number you can rely on is a survey, because the roof decides most of the difference.
What follows is the anatomy of a lantern price: what the money is actually buying, which parts move the total most, and how to read two quotes that look nothing alike. Prices themselves belong in a written quote against your address rather than on a web page, which is why roof lantern installation here is priced in two stages.
Two figures, and why the first one is a range
The first figure comes by email once the basics are known: room size, roughly what you want, a photograph of the roof and one of the ceiling. It is a range, deliberately, because at that point nobody has taken a level across the roof or established which way the joists run.
The second figure comes after the survey and it is fixed and written. Between the two, the range narrows because the unknowns have been resolved rather than priced as risk. A single confident number offered before anyone has been up to look is not a better service, it is the same uncertainty with the buffer hidden inside it.
The four parts of a lantern price
Every quote breaks into the same four components, and they move independently.
| Component | What it covers | How much it varies |
|---|---|---|
| The unit | Frame, sealed units, any opening vent | Moderate, driven by size and glass |
| Structure | Trimming, any beam, propping, calculations | Very high, from nothing to substantial |
| Roofing | Kerb, insulation, covering, flashing, drainage | High, depends on the existing roof |
| Making good | Reveal, plaster, decoration, waste, access | Moderate, often left out of cheap quotes |
The common mistake is comparing quotes on the first row alone. Two lanterns of the same size from the same manufacturer will cost nearly the same. Everything else is where the quotes genuinely differ.
Size, and the point where it stops being linear
Cost does not rise smoothly with area. It rises gently up to a point and then steps, and the step happens for three reasons at once.
The first is glass. Sealed units are made economically up to a standard maximum pane size, and beyond that they become a special order with a longer lead time. The second is handling, because a pane above a certain weight cannot be lifted by hand and needs mechanical assistance or more people. The third is structure, since the opening widens past what timber trimming will carry. Those three thresholds sit close together, which is why the cost of a lantern is fairly predictable below them and jumps noticeably above.
Glass specification, and what each upgrade adds
The base specification on any lantern is toughened outer, laminated inner, low emissivity coated, argon filled. That is not an upgrade, it is the sensible starting point, and any quote that comes in unusually low is worth checking against that line.
The genuine upgrades are solar control coatings, which add a modest amount and are close to essential on a south or west facing plane; acoustic asymmetric panes, which add a little; self-cleaning outer surfaces, which add a little; and switchable glass, which is in a different category entirely. Triple glazing adds cost and weight and improves the whole unit figure less than fixing the frame would. The reasoning is on roof lantern glazing and solar control.
Structure and the roof, the two biggest variables
This is where two otherwise identical jobs separate. An opening trimmed in timber between existing joists adds a day of carpentry and no design work. An opening needing a beam brings a structural calculation, fabrication with its own lead time, propping, padstones, a day or so of extra labour and a heavier Building Control conversation.
The gap between those two situations is larger than the gap between a modest lantern and a generous one. It is also knowable early, from the direction of the joists and the width of the opening, which is exactly why the structural question gets asked at first contact rather than at survey.
The roof itself is the other half of the same story. A new extension where the kerb is built as part of the roof is the cheapest case, because the lantern is simply landing on something purpose made. An existing flat roof in good condition with a decent fall is next, since the covering is cut back, the kerb built and the membrane dressed up it.
An existing roof with no fall, standing water or a covering at the end of its working life is the expensive case, because the drainage wants sorting before glass goes in. That work has real value on its own account and it is not padding, but it is a separate line and it should be shown as one.
Making good, the part left off cheap quotes
The reveal between the ceiling and the lantern is plastered, and whether it is square or splayed changes both the cost and the result. Splaying costs a little more plastering and nothing at all in glass, and it is the cheapest improvement available on the whole job.
Then there is waste, which on a roof means a skip or a grab. Access, which on anything above single storey means a tower or a scaffold. And decoration, which somebody has to do. A quote that omits all four looks cheaper and is not, and the difference surfaces as a conversation on the day rather than on paper.
Aluminium against timber
Aluminium is the volume product and the sections are extruded, so a standard aluminium lantern in a standard size is the economical route and the one most Essex extensions take. Timber costs more to make, more to finish and more to keep up, and it earns that on a period property where it is the right thing visually.
Aluminium clad timber sits above both, since it is two frames in one. None of these is the correct answer in the abstract. The full comparison is on aluminium and timber roof lanterns compared, and the finish decision is best made against the building rather than the spreadsheet.
Comparing two quotes that look different
Line them up against six questions. Which manufacturer and model, and what external size. What is the whole unit U-value, not the centre pane figure. What structural work is included and who produced the calculation. Who is forming the opening and who is making good the plaster. Is the Building Control notification included. And what is allowed for waste and access.
A quote answering all six can be compared with another quote answering all six. A single line reading “supply and fit roof lantern” against a number cannot be compared with anything. General cost drivers across the range of work are set out on costs.
Where the money is well spent
Spend on the things that cannot be changed later: the thermal break in the frame, the glass specification, the insulation of the kerb, the fall of the roof around it, and the reveal. All of those are cheap during installation and expensive or impossible afterwards.
Be relaxed about the things that can be added: blinds, an actuator if the wiring is run at first fix, a controller. Four invisible details around the perimeter decide whether a lantern is still dry in a decade, and those four are the reason the workmanship carries a ten year guarantee rather than the price relying on the brand of glass.
Tell us about your roof
We start with the building, the covering and the slope. Then we tell you what will suit it, and what it will cost, as a fixed written number.
- Surveyed before it is priced
- 10-year workmanship guarantee
- Building Control notification handled
- New installations and replacements