Small single stair buildings

For some low rise buildings, the provisions in paragraphs 3.26 and 3.27 may be modified and the use of a single stair, protected in accordance with Diagram 3.9, may be permitted where all of the following apply.
a. The top storey of the building is a maximum of 11m above ground level.
b. No more than three storeys are above the ground storey.
c. The stair does not connect to a covered car park, unless the car park is open sided (as defined in Section 11 of Approved Document B Volume 2).
d. The stair does not serve offices, stores or other ancillary accommodation. If it does, they should be separated from the stair by a protected lobby or protected corridor (minimum REI 30) with a minimum 0.4m2 of permanent ventilation, or be protected from the ingress of smoke by a mechanical smoke control system.
NOTE: For refuse chutes and storage see paragraphs 3.55 to 3.58.
e. Either of the following is provided for the fire and rescue service.
i. A high-level openable vent with a free area of at least 1m2 at each storey.
ii. A single openable vent with a free area of at least 1m2 at the head of the stair, operable remotely at the fire and rescue service access level.