​Requirement ​                              Unobstructed opening ​
            Dwellings ​       Buildings other than dwellings
​Country ​Exit free area/minWidth/minHeight
​England/Wales ​0.33m²/450mm/450mm
​Scotland ​​0.33m²/450mm/450mm
​Northern Ireland ​0.33m²/450mm/450mm
​Eire ​​0.33m²/450mm/450mm

 

MEANS OF ESCAPE

If specified for emergency escape purposes the roof window must have an unobstructed opening of not less than 0.33m² with neither the width nor the height less than 450mm.

The sketch below shows the position of the window within the roof plane.

escape.jpg

Also, please note that this is only for first floor escape less that 4.5m above the ground.