Fire Escape Window Regulations UK: Minimum Egress Window Sizes

A fire escape window is one of the least glamorous and most important parts of a loft conversion or new bedroom. It is also one of the easiest things for a quote to skip, because the window looks fine until you check the openable area and the cill height. Here are the numbers from Approved Document B and how to check your quote meets them.

The dimensions

The catch is that "0.33 square metres" is the clear opening, not the size of the glass. A window with a restricted opening, or one hinged so that the sash blocks part of the gap, can have plenty of glass but fail the escape rule.

One point in your favour, straight from paragraph 2.10: the route through the window may be at an angle rather than straight through. So a centre-pivot rooflight is not automatically disqualified because the sash sits in the middle of the opening. What matters is the unobstructed area a person can actually get through, measured honestly.

Where escape windows are required

• Ground storey habitable rooms need either an opening directly onto a hall leading to a final exit, or an escape window or door.
• Upper storey habitable rooms no more than 4.5m above ground level, where the storey is served by only one stair, need either an escape window or external door, or direct access to a protected stairway. The test is the 4.5m height, not the storey number, so a first floor sitting above a garage or a tall ground storey can fall the wrong side of it. Paragraph 2.3 also allows two rooms to be served by a single window, provided the door between them reaches it without passing through the stair enclosure and both rooms still have their own access to the internal stair.
• Loft conversions that create a storey more than 4.5m above ground level, which is the usual case when a two-storey house becomes three storeys, need a protected stairway down to a final exit. Approved Document B paragraph 2.21 requires the full escape route to be addressed with fire resisting doors and partitions. An escape window in the loft room is not a substitute at that height. Escape windows are the route only where the new storey is no more than 4.5m above ground.
• Bathrooms are not habitable rooms, so the requirement does not apply. Kitchens are counted as habitable rooms by Approved Document B but are specifically excluded from the escape window rule by paragraphs 2.1 and 2.2.

This is why our loft conversion headroom and staircase guide and this rule go together: the loft conversion has to solve both the stair and the escape.

The mistakes a quote hides

For checking the windows themselves once installed, see our guide to checking windows and doors.

What your quote should confirm

• That habitable rooms have a compliant escape window or a protected escape route
• The clear openable area (at least 0.33m²) and minimum opening (450mm each way)
• The cill height (no more than 1,100mm above floor)
• For loft conversions, how the fire escape and stair strategy works as a whole
• Mains-wired, interlinked smoke alarms (a related Part B requirement)

Check your quote

Fire escape is a building regulations requirement that is cheap to design in and expensive to fix later. If you are holding a loft conversion or extension quote, upload it and we check whether the escape windows and the wider fire safety points are addressed, or whether they are a missing building regs item that Building Control will catch. It takes under a minute.