An escape window is not any window that opens. It is an opening large enough for a person to get out of and for a firefighter to get in, positioned low enough to be usable, in a room the guidance says needs one. Replacing windows is the moment this usually comes up, because you may not remove an escape opening a room already relied on.
Fire escape window regulations UK: which rooms need one
In the guidance for dwellings, upper floor habitable rooms that are not served by a protected stairway generally need either an escape window or direct access to one. Inner rooms, reached only through another room, and loft conversions are the two situations where it comes up most. A loft conversion changes the escape strategy for the whole house, which is why it is a building regulations job regardless of whether planning permission is needed.
Fire escape window size regulations UK: what the opening has to achieve
The guidance sets a minimum clear openable area and minimum clear height and width, measured through the opening rather than across the frame, and a maximum sill height above floor level so that it can actually be climbed through. The important word is clear: a window whose overall size passes but whose opening restrictor or hinge geometry reduces the usable aperture does not. Ask the supplier to confirm the clear opening of the specific product, not the frame size.
The trap when replacing windows
If a room has an escape window and the replacement does not provide one, the work has made the house worse and does not comply. It happens easily, because modern frames are thicker and a like for like frame size can give a smaller clear opening, and because changing from a side hung casement to a different opening style changes the aperture. Any competent installer surveys for this; it is worth asking the question directly on quotes for first floor bedrooms.
Restrictors, locks and children
Restrictors that limit how far a window opens protect children from falling and can conflict with escape. The resolution is a restrictor that releases without a key from inside, so the window is restricted in normal use and fully openable in an emergency. Key operated locks on an escape window are the wrong answer, because nobody finds a key in smoke. Approved Documents B and K are the two that meet here.
Questions people ask about fire escape windows
Does every bedroom need an escape window?
Not every one. It depends on the floor, whether the route out is a protected stairway, and whether the room is an inner room. Upper floor bedrooms without a protected stair are the usual case for one.
Can I fit a smaller window than the one I am replacing?
Not where the existing one is the room's escape window. The replacement must provide no less escape provision, and thicker modern frames can reduce the clear opening even at the same overall size.
Do roof windows count as escape windows?
They can, and escape rooflights are a specific product with the required clear opening and a sill height that works in a sloping roof. A standard roof window is not automatically one.
Are window restrictors allowed on an escape window?
Yes, provided they can be released from inside without a key so the window is fully openable in an emergency.