The short answer
A window set into the slope of a pitched roof is called a roof window. Glass that stands up on a kerb above a flat roof is a rooflight, and a rooflight built up into a glazed pyramid or box is a roof lantern. Skylight is the everyday word covering all of them. A dormer is something else: a small built-out structure with an upright window in its face.
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The names the building rules use
That is why a pitched loft slope gets a roof window while a flat extension roof gets a rooflight. A roof lantern counts as a rooflight, with extra height and glazed sides. Our pages on flat roof rooflights and roof lanterns cover the raised kind, and roof windows covers the flush kind.
| Name you hear | What it describes | Roof it belongs to |
|---|---|---|
| Roof window | Opening or fixed glazing level with the covering | Pitched slope |
| Rooflight | Glazing on a kerb or upstand above the surface | Flat or low roof |
| Roof lantern | A rooflight with a ridge and glazed sides | Flat roof, often over an extension |
| Skylight | Everyday word for any of the above | Either |
| Sun tunnel | A small dome joined to a ceiling diffuser by a reflective tube | Either, where a full window will not fit |
Dormers, loft windows and other labels that mislead
A dormer is a small structure that projects out of the slope, with its own side cheeks, a roof of its own and an upright window in the front. The window inside a dormer is an ordinary vertical window; the dormer is the box around it, with cladding, flashings and a small roof to be built and kept watertight. Building one changes the shape of the roof, which is a bigger undertaking than setting a window into the slope you already have.
Loft window is a catch-all. It can mean a roof window, a window in a dormer or a window in a gable wall, so we ask which one you mean at the start of a conversation. A bungalow with bedrooms in the roof may have all three in one house, each lighting a different room. Sun pipe and light tube are other names for a sun tunnel, and our section on sun tunnels explains where one makes sense.
Roof light written as two words turns up on plans and quotes and usually means a rooflight. If a drawing uses it for a window in a slope, the survey sorts out what is really intended.
Why the right name changes the specification
The name carries a performance limit with it. Under Part L for existing dwellings, a new or replacement roof window must reach 1.4 W/m²K, or Window Energy Rating band B at minimum, while a rooflight or roof lantern is held to 2.2 W/m²K. A quote written for the wrong product can be written to the wrong figure.
Planning follows the same split. A roof window in a house slope is usually permitted development under Class C, whereas a lantern on a flat roof normally stands more than 150 mm proud and needs planning permission unless the council confirms otherwise. The conditions, including the side-slope and height limits, are laid out in the permission guide for roof windows, and we check each one at survey.
On the quote itself, we write sizes in millimetres whatever the product is called, so you can lay two quotes side by side.
Flush with the tiles is a roof window; on a kerb is a rooflight
What to tell us when you are unsure of the word
Describe the roof and the room under it, and mention anything already in the slope, such as an old window or a vent. A pitched roof with a loft, landing or stairwell beneath points to a roof window. A flat roof over an extension, garage or porch points to a rooflight or lantern. A hall in the middle of the house with a loft above it may suit a sun tunnel.
A photograph helps. Send one to WhatsApp 07880 284133 or to info@orchardskylightsmaidstone.co.uk, and the free survey that follows settles the name. Ready for that visit? Ask for it here. The fixed written quote then lists the product under its proper name, with the size in millimetres beside it.
