Where a lantern earns its place
The classic case is a single-storey rear extension: a kitchen-diner that runs back from the house, with folding doors at the garden end and the old back wall of the house at the other. Daylight comes in through the doors and fades as it travels. By the time it reaches the old house wall, there is not much left, and the middle room of the house, which used to have a window onto the garden, now looks into the extension instead. That is the room a roof lantern was made for.
Light from above behaves differently from light through a wall. A window lights the floor near it and throws a slanting patch across the room. A lantern sits over the middle of the space and lights it from the top down, so the far corners get their share and the room reads as bright from end to end. The raised glass roof also adds height: you look up into sky rather than at a flat ceiling, which makes a long room feel less like a corridor.
A lantern also suits rooms where people gather, because it gives the space a centre. Over a dining table or a kitchen island it marks the spot where the household ends up anyway. That is a design reason rather than a daylight one, but it is often the reason people choose a lantern over a flat rooflight in the first place.
How they are built and fitted, from the kerb up, is on our roof lanterns page.
Where it is not the best buy
A lantern is a bigger piece of kit than a flat skylight, with more glass, more frame and more to weather in. In some rooms that extra brings little extra.
- Small or shallow rooms. If the room is lit well enough from its doors or windows, or is too small to hold a lantern with a decent margin of ceiling round it, a flat rooflight gives the daylight without the bulk.
- Sun traps. A large glazed roof over a south-facing room with little shade can run hot on summer afternoons. Solar control glass and an opening vent help a great deal, but a smaller unit may simply suit the room better.
- Rooms overlooked from above. If upstairs windows look straight down onto the extension roof, a lantern becomes part of the view from those rooms, and a slim flat rooflight sits lower and quieter.
- Inner rooms with no flat roof over them. A hallway or inner bathroom under a pitched roof is a job for a different product altogether, often a sun tunnel.
None of these rules a lantern out by itself. They are the things that tip the balance, and our comparison of a roof lantern or a flat rooflight weighs the two side by side. Size matters as much as type: a lantern that suits the room in proportion is worth far more than one that fills the roof. Our guide to roof lantern sizes covers how to judge it.
The trade-offs to weigh honestly
Being worth it is about what a lantern costs you over the years, not only on the day.
Warmth. Glass loses more heat than a well-insulated roof, however good the glazing. Part L 2021 limits a new or replacement rooflight in an existing home to 2.2 W/m²K. That figure is the U-value: the lower it is, the less heat the glass lets go. Our quote states the figure for the lantern offered, and the glazing options that beat it are on our energy efficient rooflights page.
Upkeep. A lantern wants its glass cleaned now and then, and the covering where it meets the kerb checked over after a hard winter. Self-cleaning coatings on the outer pane reduce the chore rather than remove it. Electric vents and rain sensors want leaves kept off them.
The build. Cutting an opening in an existing flat roof means trimming the joists and weathering a kerb into the covering, and Building Regulations apply to that structural work. When the job is notifiable, we take care of telling Building Control. When the extension is still being planned, the opening goes on the drawings before the roof exists, which is the easiest time to add one. Planning is usually straightforward, though a lantern rises above the roof, so how the rules apply to your house is checked first; the detail is in our guide to skylight planning permission.
The price. A figure is set once the roof has been seen. What moves it is the size, the frame material, the glass, any opening vents, the structural work and the access. Our costs page sets out each of those so a quote makes sense line by line.
How to know for your room
The quickest test is to stand at the darkest end of the room on a dull afternoon. If you reach for the light switch there and nowhere else, and the roof above is flat, a lantern is very likely worth a serious look. If the whole room is reasonably bright and the issue is one gloomy corner, a smaller rooflight placed over that corner may be the better spend.
The roof itself has a say too. The joists decide where an opening can be cut without heavy engineering, the falls decide where the kerb can sit, and the covering decides how it is weathered. A lantern that suits the room but fights the structure can still be done, but it is a bigger job, and you should know that before you choose it. What we check on a finished roof is set out in can a roof lantern go on an existing flat roof.
That is what the free survey is for. We look at the room, then the roof, and tell you plainly whether a lantern is the right call or whether another skylight would serve you better. You then get a fixed written quote naming the product, the size and the work involved, and whatever we fit carries our 10-year workmanship guarantee. Book a survey, or send us a photo of the room on WhatsApp to start the conversation.