The short answer
The roof you have chooses for you. A lantern stands on a flat roof and is a rooflight; a VELUX roof window sits in the plane of a pitched roof and is a roof window. A loft bedroom, a landing under the rafters or a pitched kitchen slope suits a roof window. A flat-roofed extension, hall or garage conversion suits a lantern. Only when a house has both do you need to weigh one against the other.
- Free survey, fixed written quote
- 10-year workmanship guarantee
Which class each product falls in
Approved Document L separates them. A rooflight is glazing set out of plane with the roof and raised on a kerb or upstand, and a lantern counts as one. A roof window sits in the same plane as the surrounding roof, which is how a VELUX in a tiled slope is built. The difference matters because Part L treats them differently: a new or replacement roof window must meet 1.4 W/m²K, or Window Energy Rating band B at least, while a lantern or other rooflight is held to 2.2 W/m²K.
The planning rules split in the same place. Class C permitted development usually covers a roof window on a house, subject to the Class C conditions on projection, height and side slopes set out in the permission guide below. A lantern normally stands proud of that line and needs an application unless the council confirms otherwise. Our roof window permission guide gives the full Class C wording.
| Point | Roof lantern | VELUX roof window |
|---|---|---|
| Roof it fits | Flat roof, on a kerb | Pitched roof, in line with the slope |
| Building Regulations class | Rooflight, 2.2 W/m²K | Roof window, 1.4 W/m²K or WER band B |
| Planning | Normally an application | Usually permitted development, Class C |
| Light direction | Glass on every side catches the sky | One sloping pane faces one way |
How the light behaves
A pitched window faces the way the slope faces. On a south-west slope it collects afternoon sun; on a north slope it gives even, cool light all day. A lantern has panes on every side and the sky overhead, so it collects daylight from whichever direction is brightest at that hour. In a sunlit room that can mean glare and heat, which is why solar-control glass is worth discussing for a south-facing lantern.
Height changes the feel as well. A VELUX in a loft makes the room under the rafters feel open without altering its shape. A lantern adds volume, and on a low flat ceiling it gives the room a ridge to look up at. A dark windowless landing under a pitched roof gains nothing from a lantern, because there is no flat roof to hold one.
Rain noise and blinds are worth a thought too. Glass in either product carries the sound of a downpour into the room below, and we can discuss laminated or acoustic glass if the room is a bedroom. A roof window takes a fitted blind made for its frame. A lantern is usually dressed with a blind inside the glazing or left bare, and for a bedroom or a study with a screen, that decision belongs in the survey.
Myth
A lantern is just a roof window with extra glass.
Fact
They belong to different classes under Approved Document L, so the energy limit, the way they are built into the roof and the planning route all differ.
Opening, cleaning and everyday use
Roof windows are usually reached by hand or by a pole, and a roof window can open on a pivot to give both ventilation and a view. A lantern with an opening vent has a smaller gap by comparison, and if a room needs air, an opening flat rooflight may do that job better. Our electric opening rooflights can take a rain sensor where a roof is out of reach.
Cleaning favours the pitched window, since rain runs off a slope and a short ladder or reaching pole will do. A lantern on an extension roof collects leaves in its glazing bars, and cleaning it is a job for a long-handled brush from a safe position.
Both products can be fitted with glass that resists dirt, and a self-cleaning coating reduces the effort on either. Neither removes the need to look at the flashing or the kerb junction now and then from a safe position, which tells you early if debris is building up.
A house with both kinds of roof
Take a bungalow converted into a chalet with a small flat-roofed rear extension. The bedrooms in the slope take roof windows, and the extended living room behind them takes a lantern. Each product goes where its roof allows, and a single survey covers both.
If cost is what separates your options, our VELUX window cost guide lists what moves a roof window figure, and the lantern cost guide does the same for lanterns. For both product ranges, see roof lanterns and VELUX windows, or book a free survey and a fixed written quote.
