The answer
Yes, but only for the right house. Under Part B of the Building Regulations a window counts as an escape route for a floor no more than 4.5 m above the ground, so a roof window can serve a room in the roof of a bungalow or chalet bungalow. A loft room on a two-storey house sits higher than that, and there the escape has to be a protected stair. Either way, the window must open wide enough to climb through.
Why the height of the floor decides it
Escape rules rest on one practical idea: someone has to be able to get out of a window and be reached, or lowered to safety, by the fire service ladders. Those ladders only go so far, and a person can only be expected to climb out onto a roof or ledge from a limited height.
That is where the figure of 4.5 m comes from. Measure from the ground up to the finished floor of the room, and if it is no more than 4.5 m, a suitable window can count as the way out. Above that, a window will not do, however big it is.
In a bungalow or chalet bungalow the floor of a roof room is close to the ground, so a roof window is allowed to serve. On a typical two-storey semi or terrace in Nottingham, the loft floor is above the first floor ceiling, and the total is over the limit. There the regulations call for a protected stair: a stair enclosed in fire-resisting construction that leads down to the front or back door.
This catches people out because a loft room looks like a bedroom with a window. The window, part of any roof window installation, is useful for light and air, and it can be large and easy to open, but it is not the escape.
If you are planning a conversion and want the wider picture, our guide to roof windows for loft conversions covers how many windows to plan and where they sit.
How big the opening has to be
Where a roof window is the escape, the rule applies to the part you can actually climb through. The numbers are:
- a clear, unobstructed gap of at least 0.33 square metres
- at least 450 mm high and at least 450 mm wide, so a narrow tall slot does not count
- the lowest edge of that gap at most 1100 mm up from the floor
It is the openable area that is measured, not the size of the frame, and not the glass. A roof window with a big sash can still have a small clear gap if the sash swings into the opening or the hinges and arms take up space.
The 1100 mm limit trips up loft windows more than the others. A roof window sits in a slope, and the lower edge of the clear gap can easily end up higher than you expect, especially if the room has a knee wall beneath. Position matters as much as size. It is worth marking the intended spot on the slope and measuring up from the finished floor, not the joists.
The style of window changes the gap too. We compare the two main types, with the way each leaves its opening, in centre-pivot or top-hung roof windows.
Some manufacturers make a version of a window designed for escape, with a hinge arrangement that lets the sash open further or clear the gap. The maker's data sheet states the clear opening, and that is the number to check, rather than the catalogue size.
Rooms where it applies, and rooms where it does not
Think of escape as a question about the storey you are sleeping on or working on, not about the roof.
A bungalow with a loft bedroom is the standard example where a roof window is acceptable, as long as the floor is within the height limit and the window meets the opening sizes. A chalet bungalow, where rooms are built into the roof from the start, is the same.
A two-storey house with a loft bedroom above the first floor is the standard example where it is not. The room may have an excellent roof window, but the safe route out has to be a protected stair. The fire-resisting enclosure around that stair is part of the conversion, and it often changes the plan of the floor below.
What about a loft used as storage, or a small study with no bed? The rules depend on how the space is used and who may be in it, and the building control body decides what applies. Some roof spaces that are not habitable still need a safe route out. Ask before assuming the lighter rules apply.
A flat or maisonette adds its own complications, because the escape route is usually shared with other households and the approved fire strategy for the building comes into play. Planning controls differ too: permitted development for rooflights does not apply to flats and maisonettes.
None of this tells you what to do on your own house. What it does tell you is that the escape question comes first and the window comes second.
Who decides, and what we do
The decision about escape sits with building control, the council or a registered building control approver. They look at the drawings for the whole conversion, not just the windows.
Our part is to make sure the window we fit does what the drawing says. At the survey we measure the floor height, the intended window position and the roof construction around it. We then check the clear opening of the chosen model against the numbers above and tell you plainly whether it can serve as an escape.
If a window is meant for escape, we give the sizes and the model to your builder or architect so the approved drawings and the fitted window agree. Where the work is notifiable, the Building Control notification is ours to deal with, and the installation follows current Building Regulations.
The quote follows the survey, is fixed and in writing, and the fitting carries a 10-year workmanship guarantee in writing.
Escape-sized sashes are often the biggest glass in the roof, so the heat-loss side matters too. Our page on energy-efficient rooflights explains the glazing choices. Keep the floor in front of an escape window clear: a wardrobe below it defeats the point.