What are the windows in roofs called?

Approved Document L (Wales) defines a roof window as a window installed in the same orientation as, and in plane with, the surrounding roof. It lies flat in the slope and can open on a hinge or a pivot. Picture a wall window tilted back to face the sky and you have the shape of it.

You are most likely looking at one when you stand in a loft room or on a landing under a pitched roof. A roof window brings in daylight and, with a sash that opens, air. It also frames a patch of sky, which is why people sometimes call it a skylight. Our roof windows page runs through the range, from manual to electric and solar versions.

The same document defines a rooflight as a glazed unit installed out of plane with the surface of the roof, on a kerb or upstand. It adds that a rooflight is also sometimes called a skylight. So the glossary treats the two words as one thing, and in general talk skylight is the loose word that covers everything from a kitchen extension's flat glass to a small unit over a stair.

A flat roof is a common home for a rooflight, with the upstand rising a little above the covering. Flat glass can be fixed or can open, and it can be a single pane or a larger unit built to span a wide opening. See flat roof rooflights for the options.

A lantern is a raised glazed structure, often with sloping sides and a ridge, standing on an upstand. From inside it gives height as well as light, so a kitchen or dining extension with a lantern over it feels taller than its walls.

The planning side differs from a flat unit, because a lantern usually stands well over 15 cm proud of the roof. That puts a lantern added to an existing flat roof outside permitted development as a rule, so it needs planning permission, and the council is who confirms how a given roof is treated. The roof lanterns page goes into the product.

Neither of these is a window in the usual sense. A sun tunnel is made of three parts: a small dome or lens on the roof, a tube that runs through the loft space, and a ceiling diffuser in a hall, landing or bathroom. From inside you see only the diffuser, which looks like a round ceiling light.

That makes it the answer to a room with no outside wall, such as a hallway between bedrooms. Some call these light tubes, and the two names mean the same fitting. Our page on sun tunnels explains the parts.

Velux is a maker's name, and VELUX sells roof windows and flat roof windows. The name has come to stand for the whole idea in many homes, much as a vacuum cleaner gets called a hoover. Our VELUX windows page is for that brand.

A dormer is another thing again. It is a structure built out from the slope, with a vertical window in its face, so it is part of the roof's shape and cannot be treated as a window fitted into it. If you want light and headroom in a loft, a dormer is a building project, and a roof window is a smaller one.

One more name turns up in searches: the walk-on rooflight, which is flat glass made to be stood on, set in a floor or a flat roof. The walk-on rooflights page covers it, and it is the one to ask about if you want light to pass down through a floor.

Some rules turn on the type. Approved Document L (Wales) gives roof windows and rooflights separate limits: a roof window should have a U-value no worse than 1.4 W/m²K, or a Window Energy Rating of Band B, and a rooflight 2.2 W/m²K.

Planning has rules of its own. Putting a rooflight or roof window into a roof slope of a house in a conservation area, a National Park, an Area of Outstanding Natural Beauty or a World Heritage Site is not permitted development in Wales, and needs a planning application. Our planning guide for Wales goes through the rest.

At the free survey we look at what you have and what you want, and then give a fixed written quote. Send a photograph on WhatsApp on 07880 284133 or use the form. We install and replace all of these, and a photograph tells us more than the name does.