1.5m2 shaft throughout building, no smaller than 1.0m2 at any internal point.
Head of Stair Vent Size
1.0m2 free area required to provide inlet air. Circa 0.7m2 Aerodynamic Free Area.
Shaft Vent Size
1.0m2 free area shaft vent on every level. Circa 0.7m2 Aerodynamic Free Area. Fire doors cannot be used as vents.
Maximum Corridor Length
Can't be greater than 7.5m or 30m (one and two routes of escape respectively). Changes when sprinklered.
Approved Document B, 2019 edition volumes 1 and 2, plus May 2020 amendments.
The shaft must have a minimum dimension of 0.85m in any direction.
The shaft must extend a minimum of 2.5m above the ceiling of the highest storey served by the shaft and must be 0.5m above any surrounding structures within 2m of it