What Is the Difference Between a Skylight and a Rooflight?

Homeowners say skylight. Architects, builders and manufacturers lean towards rooflight. Both describe glass in the roof, and a supplier will answer to either one without blinking. The split is more about habit than about two different products, and in the trade you will hear people swap between them in the same breath.

The terms start to matter when a form or a regulation picks one. Building regulations, planning rules and product catalogues use particular words for particular things, and the sorting below helps when you are reading a quote or a council page.

• Skylight everyday name for any window in the roof
• Rooflight trade term for glazing set into a roof of any pitch
• Roof window a rooflight on a pitched roof, with a sash that opens like a window
• Roof lantern a raised glazed structure on a flat roof, with panes on several sides

A roof window is the one with a frame, a sash and hinges, set into a sloping roof so it can be opened, cleaned from inside and used like a wall window. It sits flush with the tiles or slates and is the usual choice for a loft room, a landing or a bathroom under the pitch.

A flat rooflight is a different build. It sits on a raised kerb over a flat or near-flat roof, and many are fixed, though some open on a hinge or with an electric motor. Over a kitchen extension on a newer estate that is the usual shape. Our pages on roof windows and flat roof rooflights cover each in full.

The practical difference shows when you plan the air. A pitched roof window with a tilting sash and a vent bar lets a loft room breathe overnight. A fixed flat rooflight brings daylight but needs a separate way for air to move.

The energy rules draw a line. In an existing home, Part L sets two different thresholds: windows in the roof must reach 1.4 W/m²K or Band B, whereas a rooflight may be 2.2 W/m²K. Which term applies depends on how the unit is built and where it sits, and our rooflight building regulations guide goes through the choices.

Ventilation is the other split. Under Part F, an opening roof window can count towards purge ventilation for a room, which is the quick airing a room gets when you throw the windows open. A fixed unit cannot do that job, however good the glass is.

Planning takes the opposite view. Class C permitted development treats a rooflight as a rooflight whatever it is called, and applies the same limits to any of them on a house. Our planning guide explains those limits.

The choice follows the roof and the room, not the word. On a pitched slope of a Victorian terrace, a roof window is the natural fit, and a tilting or top-hung sash gives the room real fresh air. On a flat-roofed rear extension, a flat rooflight or a roof lantern brings daylight from above, and an electric opening version adds airing where you cannot reach a handle.

Bathrooms and landings are the places where opening matters most, because steam and stale air have nowhere else to go. A fixed unit is a good choice where you only want daylight, such as a stairwell with a window elsewhere on the landing. We show opening options on every quote so the comparison is on paper before you decide. For more on picking one, read how to choose a rooflight.

Ring any firm in Bristol or Bath and all three terms will be understood, so do not worry about picking the wrong one. What helps more than the word you pick is describing the roof: pitched or flat, which room, and whether you want to open it. That tells us what to bring to the survey. The survey is free, the quote is written and itemised, and there is no obligation.

If you are replacing a unit that is already there, the word you use makes no difference either. A like-for-like swap leaves the roof alone, as this swap answer explains, and the time it takes is in the page on how long to fit a skylight. For the whole range across Bristol and Bath, begin at the Avon Skylights homepage.