The short answer
A roof lantern price is built from six parts: the lantern itself, its glass, the kerb, the roof covering around it, any work to the joists, and the plaster finish inside. In the written quote every part is priced for more than one suitable lantern, which shows where the money goes.
The lantern and its frame
The lantern is usually the largest single part of the price. Three things move it most: size, frame and shape.
A bigger lantern costs more, and the step up is not always even, because larger panels need stronger bars. Aluminium frames cost more than uPVC ones but give slimmer bars and more colour choice. A slimline aluminium frame usually costs more than a traditional one of the same size. A made-to-measure lantern costs more than a stock size, and a pyramid shape can cost more than a rectangular hipped lantern.
Our guide to aluminium and uPVC roof lanterns compares the two frame materials, and our guide to roof lantern sizes explains how size is chosen.
The glass
Double glazing is the starting point. Triple glazing adds cost and weight. A solar control coating adds cost too, and on a south or west facing extension it often does more for comfort than a third pane. A self-cleaning coating on the outer pane is another option that changes the figure.
| Item | Lower | Higher |
|---|---|---|
| Frame | uPVC | Aluminium, slimline |
| Size | Stock size | Made to measure |
| Glass | Double glazed | Triple glazed or coated |
| Opening | Fixed | Hand or electric vent |
| Colour | Standard | Special or dual colour |
Colour can change the figure as well. Grey and black are standard colours on many aluminium ranges, while a special colour, or a different colour inside and out, is usually an extra and can lengthen the maker's lead time. If a lantern is needed by a particular date, a stock colour and size may be the better buy even where another option costs a little less.
Opening vents are priced separately. A fixed lantern costs least, a vent opened by hand costs more, and an electric vent with a rain sensor costs more again, with the wiring as its own line.
The kerb and the roof around it
Each lantern rests on a kerb, which is a raised timber frame around the opening. Building it, insulating it and dressing the roof covering up its sides is part of the price, and it belongs on any quote as its own line so two quotes can be compared fairly.
On a new roof the kerb and the covering are built in one go and the cost is modest. On a finished roof the covering has to be cut back and joined to the new upstand, and a covering that is almost spent can make it more sensible to re-cover the whole roof during the same visit as the lantern. Our answer on fitting a lantern to an existing flat roof explains that choice.
Joists, Building Control and the finish inside
A new opening that is wider than the gap between two joists means cutting joists and fitting trimmers either side. That structural work, and any calculation it needs, is priced on its own line.
A newly formed opening is building work in the Building Regulations sense, and swapping a complete lantern, frame and glass together, also has to be notified. Building Control is told about notifiable work by us, and the fee is included in the quote.
Inside, the kerb is lined, insulated and plastered so the light box looks like part of the ceiling. Lighting in the kerb, if you want it, adds an electrician's cost. Redecorating once the work is finished is left with you, and the quote says that plainly. If you would like the ceiling around the kerb made good and painted as part of the job, ask at the survey and it will be priced as its own line.
Why a lantern price needs a survey
Two lanterns with identical dimensions can differ a great deal in price once frame, glass, vents, kerb and roof work are counted, and the roof decides much of it. A number quoted before anyone climbs up to look would be a guess. For that reason the survey costs nothing, and the quote itemises every single part of each option.
- Each lantern priced line by line
- Kerb and roof work shown separately
- Lead time from the maker for each option
If you are still choosing between a lantern and something flatter, our answer on a roof lantern or a flat rooflight compares the two. To see numbers for your own extension, book a free survey and the lanterns that suit the roof are priced next to each other.
Related questions
Is a uPVC lantern much cheaper than aluminium?
It costs less for the same size, though the bars are wider and the colour choice is smaller. Where both suit the opening, each gets a price.
Is the Building Control fee part of a roof lantern price?
Where the work is notifiable, yes. We handle the notification and include it in the quote.
Is replacing an old lantern cheaper than fitting a new one?
It can be, because the opening and the kerb are already there. A kerb in good condition and the correct size can take the new lantern directly, without rebuilding it. If the kerb needs raising or the roof covering around it has failed, that work is added, and the quote shows it as a separate line.
Can I save money by having my builder build the kerb?
Often, yes, if the extension is being built anyway. We give your builder the kerb size in writing so the lantern fits it.