The short answer
Skylight is the American word and the everyday word for any window in a roof. In the UK trade, a roof window is a unit set in a pitched slope that you usually open and look through, while a rooflight is a fixed or opening unit on a flat or very low roof, often on an upstand. The two meet different energy limits in the Building Regulations.
Where the words come from
Skylight is a general term that has stuck with the public. On a UK website you will see it used for any glazing in a roof: a pitched window over a landing, a glass box on a flat extension or a tube that carries light into a hallway.
The trade, and the paperwork, prefer narrower words. Roof window means glazing laid into a pitched slope, rather like a wall window tilted back, with a frame, a sash and usually a hinge. Rooflight is the word for glazing set into a flat or near-flat roof, whether fixed or opening, often on a raised kerb. A lantern is a taller glazed feature with its own pitched glass roof, and a sun tunnel is a different sort of product again.
Knowing the words helps when you phone a supplier, read a quote or check the rules, since each term points to a different kind of product.
The practical differences on the roof
This product is designed around a slope. It comes with a flashing kit matched to the covering, so a slate roof gets a kit for slates and a plain tile roof gets one for tiles. It sits flush with the covering, opens by pivoting or hinging, and is generally within reach from the room below.
A rooflight on a flat roof sits on an upstand, a raised frame that lifts the glass above the surface so water drains round it. It is usually fixed, or opens with a vent or a motor. It is sealed into the waterproof layer rather than flashed to tiles. We explain why that edge matters on our page about the rooflight upstand.
The shapes differ too. A flat rooflight can be a large square, a long strip or a glass box. A pitched window is limited by the gap between rafters and the model sizes on the chart, as the page on roof window sizes shows.
How the building rules treat them
The Building Regulations draw a line. Part L treats them separately when you fit or replace one in an existing home: one limit for a roof window (1.4 W/m²K, with Band B as the rated alternative) and another for a rooflight (2.2 W/m²K). A rooflight and its kerb are judged as one assembly, with a tighter 0.35 W/m²K for a kerb made on site.
The planning rules are simpler. Both fall within Class C of the permitted development rights for houses, which allows a roof alteration only if it stands no more than 0.15 metres proud of the slope and stays under the original ridge height. A side slope has an extra condition on obscure glazing; we explain it on the page about obscure glass in side roof windows.
A listed house, or one under an Article 4 direction in a conservation area, may have lost the right, so ask the council's planning team first.
Which one suits which room
A loft room under a pitched roof wants roof windows. They give a view of the sky and can open for air, and they can serve as an escape route if sized correctly. A flat-roofed extension, such as a kitchen at the back of a terrace, usually wants a rooflight or a lantern, because there is no slope for a roof window to sit in.
A landing or a hallway with no outside wall may suit a sun tunnel more than either, and we compare these on the page about alternatives to skylights.
Conservation settings add another factor. A flush window that follows the roof line looks quieter from the street than a raised box. Some are made with a slim metal frame and a central bar to suit period buildings; our page on conservation rooflights covers that.
Cost, fitting and DIY
A standard roof window is one of the more routine jobs in roofing. MyBuilder's roof window guide, updated in August 2026, puts installation at £350 to £600 once labour and fitting are counted, with a standard centre-pivot window around £305 and scaffolding about £500. A flat rooflight is usually more because the roof has to be cut, an upstand built and the waterproofing detailed.
Those are national typical figures, not prices for your roof. Ours come in writing after the survey. Our page on roof window cost explains what moves the number.
If you are tempted to fit one yourself, read the page on DIY roof windows first. Cutting the hole is simple. Keeping rain out round the edges is where DIY jobs go wrong.
Picking the right word when you ask for a quote
When you ask us for a price, tell us what kind of roof the window will go into, the rough size you have in mind and what you want it to do. We do not mind whether you call it a skylight or a roof window. We work out which product you mean from the roof.
A short description and some photographs from the garden and the loft start the conversation. The survey comes next, and the price follows in writing. If the best answer turns out to be a repair, a replacement of an existing unit or a different product altogether, you hear that from us first.
For choosing the position, see where to put a roof window, and start from the skylights hub for everything else.