(1) The walls, floor and ceiling of every lobby, foyer and vestibule forming a component of an exit-way in any occupancy-unit which falls into grade A or grade B construction, as set out in section 4, shall be constructed of non-combustible materials.

(2) The headroom at every point in such lobby, foyer or vestibule shall be not less than 2,3 metres and the unobstructed width shall be not less than one-third greater than the sum of the widths of the exit-way components immediately discharging into it.

(3) The sum of widths of the exit-way components providing egress from any such lobby, foyer or vestibule shall be not less than the width of such lobby, foyer or vestibule.

(4) The floor of such lobby, foyer or vestibule may be in the form of a ramp, complying with the requirements of section 27.

(5) Such lobbies, foyers and vestibule shall not be used for trading or other activities, except such as are provided and conducted primarily for the convenience of the occupants of the occupancy-unit served thereby.

(6) Any structure or furniture used for any such activity shall be so located as not to reduce the required width of the lobby, foyer or vestibule, or form an obstruction within such required width.

(7) The total floor area occupied or covered by such structures or furniture shall not exceed 10 square metres or 20 per centum of total floor area of the lobby, foyer or vestibule, whichever is the lesser.