The short answer
Choose a flat skylight when the roof is small, the ceiling is low or the budget is tight. Choose a roof lantern when the extension is wide enough to carry one and you want height, light from several sides and a feature in the room. A lantern costs more and has more parts to specify quietly, but it gives the room something a flat pane cannot.
Three extensions, three answers
The choice is easier to see in rooms than in definitions, so take three typical cases and ask which glazing each one wants.
The first is a narrow rear kitchen, the kind a 1960s semi has after a single-storey addition. The roof is shallow and the room is long and thin. A flat rooflight over the cooking end brings daylight to the darkest spot, and there is not enough width for a lantern to look right. The flat unit wins.
The second is a wide open-plan kitchen and dining room across the back of a house. The room is broad, the ceiling could go higher, and the middle of the floor is far from any window. A lantern suits this well. It raises the ceiling in the centre, lets light in from four sides and gives the room a clear focus over the table.
The third is a home office or utility room at the side of the house, used a few hours a day. It needs light, not a feature. A flat skylight, properly specified, does the job without the extra height above the roofline or the extra cost.
In every case the roof was the first thing we looked at, and the room was the second. The glass type came after both.
What each one actually is
The two words are not opposites, which is why the comparison can be muddled.
A skylight, or rooflight, is the general name for glazing in a roof. In this comparison it means flat glass: a fixed or opening pane, or a run of panes, laid almost level on an upstand. A roof lantern is a particular kind of rooflight, a raised glazed structure with a ridge, sloping panes on all sides and aluminium or timber bars between them. It stands proud of the roof like a small glass roof on top of the real one.
Both sit on a kerb and both are sealed into the flat roof with a membrane dressed up to the frame. The lantern is taller and heavier, so the structure beneath it matters more, and its larger frame and bars need care to get right. Our page on roof lantern installation covers the build, and our page on flat roof rooflight installation does the same for the flat option.
Light, cost and sound compared
Three practical things usually decide the matter, and the table puts them next to each other.
| Point | Flat skylight | Roof lantern |
|---|---|---|
| Light direction | Straight down | From all sides |
| Ceiling feel | Flat | Raised |
| Cost | Lower | Higher |
| Rain sound | Simpler to quieten | More parts to specify |
On light, a flat rooflight is efficient. It puts daylight into the room below it and does not waste any on the walls. A lantern throws light across the ceiling and the upper walls as well, which softens the room and helps it feel taller. In a dark deep plan that extra bounce is a real gain.
On cost, a lantern is the bigger spend. It has more glass, a frame to build, more bars and a taller kerb. We do not list prices on pages like this one, but our costs page gives general market ranges, and our guide to what affects the cost of replacing a skylight shows which factors move the figure.
On sound, both can be made quiet. Flat glass presents one surface to the rain, so there is less to specify. A lantern has sloped panes, bars and a ridge, which means more places for a downpour to be heard if the build is thin. A laminated acoustic inner pane, well-seated gaskets and a solid upstand bring a lantern under control, and our answer on whether skylights are noisy in the rain goes through the detail. The build we propose for either is written into the quiet spec that comes with the quote.
Height, planning and the structure below
A lantern raises the roofline locally, and that has two consequences to check before you fall for the picture.
The first is planning. A lantern on a single-storey extension often falls within permitted development, but there are limits on height, and the position is checked for the address. The second is structure. A lantern adds weight and needs a kerb and a ring beam or roof structure capable of carrying it. For that reason the question of whether the opening needs an engineer comes up early, and our page on whether a rooflight needs a structural engineer explains when.
A flat skylight asks less of the roof. It needs a correctly framed opening and a kerb that is insulated and sealed, but it does not change the profile of the house. For that reason it is the usual pick for a replacement in an existing opening, where nothing above the roof can change. If you are swapping an old unit, see our page on replacing an old skylight for the like-for-like options.
Both types are installed to current Building Regulations, and we handle the Building Control notification where the work is notifiable. Part L governs the warmth of the glazing, and our page on Building Regulations for rooflights shows how each part applies.
How to decide without regret
A short set of tests keeps the decision honest.
- Measure the width of the room the glazing will serve. If it is narrow, a flat unit is nearly always the better fit.
- Ask whether you want the ceiling to rise. If height is part of the plan, the lantern earns its cost.
- Consider when you use the room. A dining room in the evening hears rain more than a utility room, so specify the glass to match.
- Think about the outside. A lantern is visible from the garden and sometimes from neighbouring windows.
Our page on how to choose a rooflight widens that into a full checklist. If you want us to look at your roof and say which suits it, send the details through the quote form. The wider picture is on the main page for skylight and rooflight installation in Crawley.
Skylight or lantern: what people ask next
Is a roof lantern always better than a flat rooflight?
No. It is a bigger feature, and it suits a wide room. In a narrow or low space it can look out of scale, and a flat unit gives the light you need for less.
Can I swap a flat skylight for a lantern later?
Sometimes. The opening, the kerb and the roof structure all have to suit the heavier unit, so it is a survey question, not a simple swap. Decide early if you think you might want one.
Will a lantern make my kitchen hotter in summer?
It can, because it admits light from more angles. Solar control glass, a sensible size and an opening or vented option keep the heat in check, and our page on energy efficient rooflights explains the choices.
Which is easier to keep clean?
A flat pane is simpler, because it is one surface at a shallow fall. A lantern has sloped panes and bars where dust and leaves collect, so it benefits from a rinse now and then.