The short answer
The main alternatives are a dormer, which adds headroom and a vertical window; a sun tunnel, which carries daylight down a tube into a landing or bathroom; a window in the gable wall; and a roof lantern on a flat roof. Each solves a different problem. A dormer usually needs planning permission on land in a conservation area or National Landscape, so check before you design anything.
Dormers: when you need space, not just light
A dormer is a small structure that projects from a sloping roof, with its own walls, a flat or pitched roof and a vertical window. It adds floor area and headroom under the slope, which a roof window cannot do. If the aim is a usable bedroom or bathroom in the loft, a dormer is often the right answer.
It is also a bigger job. The roof has to be opened up, the structure framed, the cheeks and roof clad and the new roof waterproofed, with flashings at every junction. Costs are well above a roof window, and a dormer is more noticeable from the street.
Planning rules differ. A dormer comes under Class B of the permitted development rights, which limits the extra roof space to 40 cubic metres for a terraced house and 50 for any other, and must stay under the existing ridge and must not stick out past a front slope facing a road. It is not permitted development at all on land in a conservation area or a National Landscape. See our page on roof window planning for the context.
Sun tunnels for dark halls and landings
A sun tunnel is a rigid or flexible reflective tube that runs from a small dome on the roof to a diffuser in the ceiling below. It moves daylight into a space with no outside wall, such as a landing, a hallway, a walk-in wardrobe or a bathroom.
It fits where a window would be too big, too costly or in the wrong place. The opening in the roof is small, the dome is low, and the tube can bend round obstacles. The trade-off is that it gives light but no view and no ventilation, and the amount of light depends on tube length and bends.
The ceiling end is a neat disc, which suits a hallway better than a bare skylight over the stairs. Our page on sun tunnels goes into the products in more detail.
Gable windows and wall windows
If the loft has a gable end, which is the triangle of wall at the end of a pitched roof, a window in that wall may be the simplest way to light it. A window in a wall needs no flashing kit, does not interrupt the roof covering and is easier to clean and open.
It is only available to some houses. A mid-terrace house has no free gable, and a semi-detached has one gable that may face a neighbour. Where the end wall is exposed, the window brings light from a different direction to a roof window, and sometimes the two together light a room evenly.
Planning is usually simpler for a window in an existing wall than for a roof alteration, but check, because conservation areas and listed buildings have their own rules. The outlook matters too: windows facing a neighbour raise privacy questions, and obscure glass may be needed, as discussed for side slopes on our page about obscure glass in roof windows.
Roof lanterns and flat rooflights
On a flat-roofed extension, the alternative to a pitched window is a rooflight or a roof lantern. A lantern is a glazed structure with its own pitched glass roof, standing on an upstand. It brings in light from several sides, makes a kitchen or dining room feel taller and gives a clear sky view.
It is a much larger, heavier piece than a roof window and needs a roof strong enough to carry it. Our page on roof lanterns goes through what is involved.
Overheating and glare are the usual complaints, so glazing with solar control and a way to ventilate are worth planning from the start. The raised frame it sits on matters as much for a lantern as for any other flat rooflight; see the page on the rooflight upstand.
Comparing the options side by side
| Option | Best for | Main drawback |
|---|---|---|
| Roof window | Light and ventilation on a pitched slope | Adds no headroom |
| Dormer | Extra space and a vertical window | Bigger job, planning limits |
| Sun tunnel | Landings, halls, bathrooms | No view, no ventilation |
| Gable window | Loft rooms with a free end wall | Only some houses have one |
| Roof lantern | Flat-roofed extensions | Heavy, can overheat |
Fitting time varies as widely as cost; our page on how long a roof window takes to fit gives a feel for the simplest job.
Choosing, and what we do first
Start with the problem. If the room is dark, a window or tunnel may do. If it is cramped, headroom is the issue and a dormer is the real answer. If the wall is shared and the roof is flat, a lantern or a rooflight is the likely route.
Where to put the opening matters as much as which type, and our page on where to put a roof window helps with that. Whatever you choose, ask your council's planning team whether it needs permission, and a building control body about the Building Regulations, as we cannot give legal advice.
We survey the roof, photograph it and write the quote. The structure, covering and access decide what is possible, and we tell you plainly if the cheaper, smaller option does the job properly. Start from the skylights hub for each topic.