There is no hard line between a skylight and a rooflight. Both mean glazing set into a roof, and the two words are used for the same products all the time. In practice, "skylight" is the everyday word, and for most people it means a window in a sloping roof that lights a loft room, landing or bathroom. "Rooflight" is the trade and architectural word, and it covers everything from that same sloping-roof window to a glass panel in a flat roof and a lantern over a kitchen extension.
So the useful question is rarely which word is correct. It is which kind of roof glazing suits your roof and your room. This page sorts the names, explains how a roof window differs from a flat rooflight and a lantern, and shows where the choice changes the work done inside the house.
Skylight vs rooflight: where the two words come from
"Skylight" arrived first and is the older, plainer word. It describes what the thing does: it lets in the sky. Builders, estate agents and most homeowners still use it for any opening in a roof that has glass in it. In North America it is the standard term for all of it, and a good deal of British search traffic follows the American habit.
"Rooflight" is the British construction term. You will find it in architects' drawings, in Building Regulations guidance and in manufacturers' catalogues. It tends to be used where the glazing is a designed element of the building rather than a window that happens to sit in a slope. A rooflight might be a long strip of glass over a hallway, a flat panel over a stairwell or a glazed lantern that rises above a flat roof.
Roof window is a third name, and it is the most specific of the three. It means a window built to sit in the plane of a pitched roof, with a frame, a sash and usually the ability to open. VELUX is the best-known maker, and many people say "a VELUX" in the way they say "a hoover". When someone says skylight and means one of these, the precise word is roof window.
The main types of roof glazing
The names matter less than the products behind them. These are the six you are likely to meet, and each one has its own page on this site if you want the detail.
- Roof window
- A framed window fitted into a pitched roof, in line with the slates or tiles. It opens, usually by pivoting or tilting, and it is the standard choice for loft conversions. Roof window installation and VELUX window installation cover these in full.
- Flat rooflight
- A glazed unit on an upstand, called a kerb, set into a flat or very shallow roof. It can be a fixed pane, an opening unit or a modular glass panel. See flat roof rooflights.
- Roof lantern
- A glazed structure with a pitched or pyramid glass roof of its own, standing proud of the main roof. It is common over kitchen extensions and orangeries. The roof lantern page goes into specification.
- Sun tunnel
- A small domed collector on the roof joined to a reflective tube that carries daylight down to a room below. It suits bathrooms, hallways and landings where there is no room for a window. See sun tunnel installation.
- Conservation rooflight
- A slim, low-profile unit with a flat steel or bar frame, made to sit flush with old slate or tile, as an original cast-iron rooflight once did. It is designed for older buildings and sensitive roofs, as covered on the conservation rooflights page.
- Walk-on rooflight
- A heavily built glass panel set into a floor, terrace or flat roof so people can stand on it. It is specified to structural loading rules, so it is a different product from a standard rooflight with thicker glass.
Roof window or flat rooflight: the choice that matters most
If you strip the vocabulary away, most decisions come down to one fork. Is the roof pitched, or is it flat? A roof window belongs in a pitched roof. A flat rooflight belongs in a flat one. Putting the wrong one in is not a matter of taste, because rain runs off the two surfaces differently and the flashings and upstands are designed for those conditions.
| Point | Roof window | Flat rooflight | Roof lantern |
|---|---|---|---|
| Roof it suits | Pitched, with tiles or slates | Flat or very low pitch | Flat roof, usually on an extension |
| How it sits | In the roof plane, flush with the covering | On a kerb above the roof surface | On a kerb, rising well above the roof |
| Opens? | Usually, by pivot or top-hung sash | Fixed or opening, depending on the unit | Mostly fixed, with opening vents as an option |
| Daylight from the glass | Angled, good from low sun | Overhead, strong at midday | Overhead and from the sides of the lantern |
| Inside finish | Lining between frame and ceiling, often short | Kerb lining, then a ceiling opening | Deep lining or a plastered upstand around the lantern |
Two practical points follow from the table. A pitched roof can be fitted with a rooflight in the sense of a flat unit on a kerb, but it rarely looks right, so on slopes a roof window or conservation rooflight is the normal answer. And a flat roof can be given an opening rooflight that works like a window, which is why "skylight" for a flat roof is a perfectly sensible phrase, if a loose one.
Glass, frames and how they open
Whatever it is called, a rooflight is a window facing the sky, and it has a harder life than a vertical window. It meets rain, sun and condensation at an angle that exposes every weakness, so the specification of the glass and frame carries a lot of weight.
Modern units are double glazed at minimum, with a low-emissivity coating and a warm-edge spacer around the sealed unit to cut heat loss and condensation at the edge of the glass. Triple glazing is available on many roof windows and on some flat units. For overhead glazing, a laminated inner pane is widely recommended as good practice, because if the glass is ever damaged, the layer holds the fragments together rather than letting them fall into the room. Laminated glass is not required for every rooflight by the Building Regulations, but it is sensible overhead.
Frames are timber, usually pine with a white finish, or a polyurethane-coated core, or aluminium on larger and flat units. VELUX uses codes that tell the type apart: GGL is centre-pivot in white-painted pine, GGU is centre-pivot in white polyurethane, GPL is top-hung in white-painted pine and GPU is top-hung in white polyurethane. A centre-pivot window turns around a pivot at the middle of the sash, and a top-hung window is hinged at the top and swings out from the bottom, which gives more head room when open on a steep slope.
Other options include solar-powered or electric opening, rain sensors that close the window for you, blinds fitted between the panes or in the frame, and acoustic or solar-control glass for rooms that need it. They all attach to the same underlying choice of roof window, flat rooflight or lantern.
How a rooflight changes the room underneath
This is the part that the roof-only conversation skips. The glass is the same size whatever you call it, but the room's experience depends on the opening between the glass and the ceiling.
A roof window in a loft room has a short lining, usually less than a forearm deep. The finish is about crisp edges, a good paint line and a lining that meets the sloping ceiling without gaps. In a hallway with a flat ceiling below a pitched roof, the roof window sits a metre or more above the ceiling, and the opening becomes a shaft. That shaft needs insulating on the loft side, forming and splaying so it spreads daylight, and plastering or boarding on the room side. On a flat roof, the kerb adds a further upstand whose inner face is seen from below.
Lanterns have the biggest effect of all, because they are large and sit in the middle of a ceiling. Whether the opening is plastered to a crisp edge, with the lantern appearing to float above it, or lined with a visible timber trim, changes how the whole room reads. Our guide to how a rooflight is finished inside goes through the lining, splay, plaster and paint line step by step. Two houses with the same roof window can look quite different from inside, and the difference is nearly always in the finish.
Skylight or rooflight in your search and your quote
If you are collecting quotes, the vocabulary can trip you up. A firm that quotes for a "skylight" and one that quotes for a "rooflight" may mean the same thing or two quite different products. Before you compare prices, check that each quote names:
- the type of unit: roof window, flat rooflight, lantern, sun tunnel or conservation rooflight;
- the maker and model, and the glass specification;
- the frame size, so you can see whether the opening is the same as before or is being enlarged;
- whether it opens, and how;
- how the inside will be finished, and by whom.
The last item is the one most often missing. Some quotes stop at the roof and leave the lining, plaster and decoration as a separate job for you to organise. Brightview includes the inside in the same job, and every quote comes with a written finish schedule that records the lining shape, the finish material, the trim and whether it is left ready to paint. That means two quotes can be compared on what you will actually see.
Replacing a skylight is different from adding one
A like-for-like replacement and a new opening are different jobs, even when the product on the roof is identical.
A replacement goes into an opening that already exists, so the rafters are already trimmed and the lining is already formed. The work is mostly removing the old frame and fitting the new one with fresh flashings and insulation. That makes it quicker and less disruptive. It is still a regulated job: a whole new rooflight, frame and glass together, must be notified to Building Control, because the new window has to meet the energy standards. Fitting just a fresh sealed glass unit to a good frame is not notifiable.
A new opening is a structural alteration. Rafters are cut and trimmed, a new frame is built to carry the roof around the gap, and a ceiling opening is formed. The Building Regulations treat that as building work, and planning rules may apply as well. Replacement jobs sometimes turn into new openings when the owner wants a larger window, so settle the size early. The replacing an old skylight guide covers that side of the work in more detail.
Do the rules differ between a skylight and a rooflight?
No. The Building Regulations and planning rules deal with the building work, not with the word used for it. A roof window, a flat rooflight and a lantern are all roof glazing, and they are all judged on the same questions: how far they project, how well they insulate, how they affect the structure and whether the building is protected in some way.
On a house, rooflights are usually permitted development, so long as they stand no more than 150mm proud of the roof plane and stay below the roof's highest point. That allowance can be removed in conservation areas by an Article 4 direction, and listed buildings need listed building consent whatever the product is called. Flats and maisonettes do not have the same householder rights. The full rules, including how Building Control works and what changes on Dartmoor and Exmoor, are in our guide to rooflights, planning permission and Building Regulations in Devon, and the short version is also in our answer on whether skylights need Building Regulations approval.
One difference in practice: lanterns and large flat rooflights often sit on new extensions, where the roof build is part of the extension's own Building Regulations approval rather than a separate application.
Choosing between the types for your house
A quick way to settle the question is to start from the roof and the room, not the product.
- Loft room or sloping ceiling
- A roof window, usually in a size that fits between rafters. Top-hung units give more head room on a steep slope, and centre-pivot units give a better view out when you are standing.
- Flat ceiling under a pitched roof
- A roof window with a splayed lightwell, or a sun tunnel where the shaft is long and the room is small.
- Flat roof extension
- A flat rooflight if you want a clean, low look, or a roof lantern if you want a feature and more headroom of glass. Opening units help with ventilation.
- Older or protected building
- A conservation rooflight, which sits flush and uses a slim frame, with planning and Building Control checked first.
- Dark corridor, bathroom or landing with no loft above it
- A sun tunnel, which needs far less cutting of the structure than a window.
If you are still not sure, a survey settles it faster than a catalogue does. We look at the roof from above and the ceiling from below, measure both and say which product suits each. Ask for a quote and a finish schedule, and send photos of the room and roof if you have them. More on the full range is on the skylight and rooflight installation homepage.