Window opening for escape - uK building regs

[Alexmash]

Does anyone know where to measure a window opening from when calculating what's a viable escape route from the first floor?

We have 500cm from front window edge to open window (top hung) but only 400cm from edge of external cil. I can't find any concrete language as to where the opening should be measured from to pass building regs. 

Many thanks, 

[Temp]

Google says..

 

Minimum Dimensions: Both the clear opening width and height must be at least 450mm.

 

Total Area: The clear openable area must be at least 0.33m^2. If you make the opening width the minimum 450mm, the height must be at least 735mm to 750mm to hit the area required.

 

Height: The bottom of the openable area should be no more than 1,100mm (1.1m) above the internal floor level for safe access.

[Temp]

I suspect the BCO may want a ball 450mm in diameter to fit through it. Not literally (that's not in the regs) but by measurement.

 

We have a window a fraction too narrow but the BCO allowed it provided we fitted a thicker more fire rated door to that room.

[torre]

3 hours ago, Temp said:

a fraction too narrow but the BCO allowed it provided we fitted a thicker more fire rated door

Bit surprised with the focus on fire safety you'd get any concession on this one. Maybe they thought you'd slim down sweating while waiting to escape? 

 

4 hours ago, Alexmash said:

only 400cm from edge of external ci

50mm is more than a fraction, I think you might struggle to get that past a BCO. There's no point being able to climb halfway out of a window but jammed on the cill. Maybe if it's picked up on (or you're on the larger side anyway) you can look at whether it's easy to make the stairs a protected corridor instead? 

[Temp]

On 02/06/2026 at 23:01, torre said:

Bit surprised with the focus on fire safety you'd get any concession on this one. Maybe they thought you'd slim down sweating while waiting to escape? 

 

 

🙂

 

 

[Spinny]

Could you have a hammer to smash your way out through the window ?

Seems to be allowed for trains.

 

How long is it going to take to knot the bed sheets together ?

[kandgmitchell]

As Temp says above: the window needs an opening which is at least 450mm in either direction as well as being at least 0.33m2 in area - so that negates 450mm x 450mm. The dimensions relate to the opening which is why some upvc window hinges do not comply as they do not allow the window to swing fully open. The bottom edge of the opening should not be more than 1100mm off the floor.

 

The idea is to allow someone to climb out of the window, hang from the bottom edge and drop to the ground outside - hence only being allowed for first floor windows.

[Russell griffiths]

On 04/06/2026 at 21:46, Spinny said:

Could you have a hammer to smash your way out through the window ?

Seems to be allowed for trains.

 

How long is it going to take to knot the bed sheets together ?

Not a chance 

it has to be an openable window. 
i would not fancy your chances smashing triple glazed windows with the outer pain in laminated glass. 
 

 

[Russell griffiths]

We have been given a bit of leeway with one of ours as it is higher than 1100mm from the floor, bco has stated due to the amount of furniture in the room egress through the windows could be gained easily by using a piece of furniture to stand on. 

[Spinny]

Are we all supposed to have emergency ladders stashed in every bedroom ?

In theory a fit person in their twenties might be able to climb out at first floor level, hang down from the window ledge with their hands, and drop 6 feet onto concrete without killing themselves. However I don't fancy my chances of making such a move at an advancing age.

It'll be shouting ''help'' out of the window until the elderly neighbour arrives with a step ladder and a barbeque knife.

[Nickfromwales]

12 hours ago, Spinny said:

Are we all supposed to have emergency ladders stashed in every bedroom ?

In theory a fit person in their twenties might be able to climb out at first floor level, hang down from the window ledge with their hands, and drop 6 feet onto concrete without killing themselves. However I don't fancy my chances of making such a move at an advancing age.

It'll be shouting ''help'' out of the window until the elderly neighbour arrives with a step ladder and a barbeque knife.

If a fire is about to flame-grill you, you’d be out the window like a 21 year old.

 

I have advised exactly this for one of my current clients, eg that they stash drop down ladders in each of the FF bedroom fitted wardrobes, the type that hook onto the window frame and unroll to give a ‘rope ladder’. 
 

For £55, there’s no reason not to have at least one of these on the FF. 

 

 

I’ll take that over a pair of broken legs all day long. 

[Mr Punter]

15 hours ago, Russell griffiths said:

i would not fancy your chances smashing triple glazed windows with the outer pain in laminated glass. 

 

A while ago my next door neighbour locked themselves out of the house.  After a while it was decided to break a window at the back to gain entry.  I was voted for the job.  It took over 5 minutes with a hammer to get through the triple glazing.