01Short answer
When a roof window counts as a way out
A roof window can be the escape route from a room, but only when the opening is big enough, low enough and set up so a person can really climb out.
People ask this most when they are planning a loft room. Building Regulations expect someone sleeping on an upper floor to have a way out if the stairs are blocked by fire. In many houses that is a window big enough to climb through. In a room in the roof of a chalet bungalow or similar, where the floor is no more than 4.5m above ground, the window in the roof slope can be that window. A rooflight or skylight that fits the rules can do the job, and a fixed one cannot, because you cannot open it.
The guidance sits in Approved Document B (Fire safety, Volume 1, dwellings). It is guidance, which means the Building Control body looks at your actual design and decides whether it satisfies the law. That is why we always say: check with Building Control before you fix the window position. We handle the notification where the work is notifiable, and we raise the escape question at the survey, not after the frame is in.
02Sizes
The opening sizes the guidance asks for
Three numbers decide it: the clear area, the height and width of the opening, and how high the bottom edge sits.
The measure that catches people out is that it is the clear, openable area that counts. It is not the glass size, and it is not the size of the frame. Once the sash is open, the gap you can actually climb through must meet the figures below, and any bars, blinds hardware or handles that block the gap are taken into account.
Escape opening, Approved Document B guide
- Clear openable area
- At least 0.33 m²
- Height of the opening
- At least 450mm
- Width of the opening
- At least 450mm
- Bottom of opening above floor
- No more than 1100mm
Notice that 450mm by 450mm is only 0.2 m². So you cannot meet the area figure with a small gap that just scrapes the minimum height and width. You need both the 0.33 m² and the two edge lengths. A roof window with a wide, deep opening gets there more easily than a narrow one.
03Roof slope
What is different about a window in the roof
A wall window opens onto air. A roof window opens onto a slope, so the way you climb out and what is below you both matter.
The 1100mm limit is measured from the floor to the bottom of the clear opening. In a loft room the roof slopes down toward the eaves, and a window placed high up the slope can end up with its lower edge well above 1100mm. Placing it lower solves that, but then it can sit close to the eaves and the outside has to be safe to step onto. For roof windows the distance from the eaves also matters, and the guidance wants the person to be able to reach a place of safety. The exact limit depends on the design of the roof, so check with Building Control for your own house before the window position is fixed.
Two practical points follow. First, the usual centre-pivot roof window opens in a way that can leave a small clear gap at the bottom, while a top-hung window swings out and up and can leave a bigger one. Our page on top-hung versus centre-pivot roof windows explains the difference. Second, some makers sell a specific egress or escape window with a larger opening. If escape is the reason for the window, ask for that type.
Our roof windows page shows the full range we fit. Before you settle on a window, run through this list.
- The sash opens far enough to clear 0.33 m² once it is propped.
- Nothing fixed across the opening: no bar, no sill-mounted heater.
- The bottom edge is within 1100mm of the finished floor.
- You can reach a safe place outside, or the route is agreed with Building Control.
04Getting it approved
Steps before you order the window
Sorting the escape question before the order saves a window being the wrong size on the day.
- Tell us what the room will be: a bedroom, a study, a playroom.
- We measure the room, the slope and the floor level on the free survey.
- We work out where the window must sit to meet the height limit.
- We choose a model with a big enough openable area and confirm it with the maker's data.
- Building Control is notified, and any questions on escape go to them.
That is the same sequence for any loft room, and it sits alongside the rest of the loft design. If the loft is being converted, roof windows for loft conversions covers how the windows fit the wider scheme, and the wider rules are in do rooflights need Building Regulations.
Could I climb out of it if the stairs were blocked?
Can a fixed rooflight be an escape window?
No. An escape window has to open. A fixed rooflight gives you light only, so any escape route has to come from another window or from the stairs.
Does the window need to be a special type?
Not always. A standard roof window can be enough if the clear opening meets the sizes. Some makers offer escape models with larger openings, which can help when the slope is awkward.
Does every roof window need to meet these sizes?
No. The sizes apply where the window is the means of escape from a room. A rooflight over a landing or a bathroom for light alone is a different matter. Say which room it is when you ask for a quote.
Who decides if my window is acceptable?
Building Control. Approved Document B is guidance, and they judge your design against it. We handle the notification and raise any escape query with them where the work is notifiable.
