The short answer
A roof window is a window set into a pitched roof, in line with the slope, and it usually opens. A rooflight is the wider term, and it most often means fixed glazing over a flat or low-pitched roof, on a raised upstand. Pitched loft room: roof window. Flat roof extension: rooflight. The roof decides, not the brand name.
Start with the roof you have
The shape of the roof settles most of this choice before any product is considered, so look up at the ceiling and the outside slope first.
A pitched roof slopes, and a roof window is made for that slope. The frame sits in the plane of the tiles or slates, with flashings that lap over and under the roof covering so that water runs down and around it. Loft conversions, dormer-free bedrooms and landing windows in 1950s and 1960s semis are the typical places for one.
A flat roof is nearly level, with only a slight fall to carry water to an outlet. Glass laid flush with it would let water sit, so a flat rooflight is fitted on an upstand, a raised kerb a little above the roof surface. The glazing is usually a fixed pane or a low dome of glass, sometimes with a hinged opening version. Kitchen extensions and rear additions are where these go.
The in-between cases are what cause confusion. A very shallow pitched roof, such as a lean-to, can take either type, depending on its angle. Manufacturers state a minimum pitch for their roof windows, commonly somewhere around 15 degrees, so below that a kerb-mounted rooflight is the safer route. The same applies in reverse: a rooflight is not made to hang on a steep slope in the way a roof window is.
Side by side
A quick comparison makes the working differences clear before the detail.
| Feature | Roof window | Rooflight |
|---|---|---|
| Usual roof | Pitched | Flat or low pitch |
| Sits on | The rafters | A raised upstand |
| Opens | Usually | Sometimes |
| Cleaned | From inside | From outside |
| Typical room | Loft bedroom | Kitchen extension |
Treat the table as a rule of thumb, not a law. There are fixed roof windows, and there are opening rooflights with electric motors, which we cover under electric and opening rooflight installation.
Opening, cleaning and reach
Day to day, the biggest difference is what you can do with the unit from inside the room.
Most roof windows pivot or hinge, so the sash can be turned towards you, and the outer pane can be reached and cleaned without a ladder on the roof. That is useful in a loft room, where the window is often a main source of air as well as light. In a bedroom it also makes a practical second route for ventilation in summer.
A fixed flat rooflight offers light and nothing else. It cannot be cleaned from inside, and it sits out of arm's reach, so a rinse from outside now and then is the usual routine. If the extension needs fresh air too, an opening version with a manual pole or a motor is the option, and it should be chosen with the room's ventilation in mind rather than added later. Air movement matters on glazed ceilings, where warm room air meets cold glass.
Escape is one more reason roof windows matter in loft rooms. A bedroom created in a loft has to meet fire safety rules, and a window of a suitable size and position can form part of the escape route. The rules sit in Part B of the Building Regulations, and our guide to Building Regulations for rooflights shows where each part applies.
Light, warmth and sound
Both types let in daylight, but they deliver it differently, and they behave differently when the weather turns.
A roof window in a slope tilts its glass towards the sky at the angle of the roof, so it catches a wide arc of light and sends it in at a slant. A flat rooflight looks straight up. It lights the middle of the room more evenly, and it tends to give more overhead light for the same area of glass. Neither is better in general. Where the light needs to land, and at what time of day, is what matters, and our guide to positioning a skylight in a room helps you work that out.
On warmth, both are governed by Part L, which sets the performance the glazing must reach when it is new or replaced. The glass build, the frame and the seal at the edge all count, so the thermal result comes from the whole unit, and our page on energy efficient rooflights goes into it.
On sound, the slope makes a real difference. Rain runs off an angled roof window quickly, while a flat rooflight holds a film of water across its pane, so the two produce different noises. Either can be made quiet with a laminated acoustic inner pane, good seals and a solid frame or kerb. That choice goes in the quiet spec we write for each room.
Which words people use, and why it matters
The vocabulary overlaps, and the overlap causes wrong orders.
In the trade, a rooflight covers glazing in a roof of any shape, and a skylight is the everyday word for the same thing. A roof window is one specific product within that family. If you ask three suppliers for a skylight you may be quoted a roof window, a fixed flat unit and a glass lantern. Our page on what the words rooflight and skylight mean untangles the terms, and our guide to choosing a rooflight takes the next step.
So when you describe what you want, say what kind of roof it is, what room is under it and whether it needs to open. Those three facts are enough for a sensible quote. If you would like us to look at your roof and say which type fits, send the details through the quote form. Both families are installed across our service area, and the roof window and flat roof rooflight pages cover each in full. The main page, skylight and rooflight installation in Crawley, links to the rest.
Choosing between them: common questions
Can I put a roof window in a flat roof?
Not in the usual way. A roof window depends on a slope to shed water over its flashings, so a flat roof needs a kerb-mounted rooflight. Some opening rooflights look similar from inside, but they sit on an upstand outside.
Is a VELUX a rooflight or a roof window?
The brand is best known for roof windows, but the name is used for many products. Check the product type rather than the label.
Does a roof window need planning permission?
Often a pitched roof window falls within permitted development, but the rules differ for some properties, including conservation areas, so the position is checked for the address. Our page on adding a rooflight under permitted development sets out the usual conditions.
Which one lets in more light?
That depends on the size of the opening and the roof angle more than on the type. A larger flat rooflight over a dark extension usually changes a room more than a small roof window on a slope. The guide to sizing a rooflight explains how to match size to room.