(1) The provisions of this section shall not apply to shafts in dwelling-houses or to shafts enclosing stairways, air-ducts, incinerator-chutes, flues and ramps connecting storeys in buildings.

(2) All lift-shafts and hoist-shafts in a building shall be enclosed by walls having a fire-resistance rating of not less than on and a half hours. In such shafts, there shall be at least one opening in every 9 metres of the height of the shaft, fitted with an approved self-closing fire-door having a fire-resistance-rating of not less than one hour.

(3) Any enclosed shaft extending through the roof, and which is enclosed at the top, shall be provided with a lantern-light having unglazed or glaze openings equivalent in are to not less than 20 per centum of the cross-sectional area of such shaft, and, where such openings bare glazed, they shall be glazed with plain glass of not more than 3 millimetres in thickness:

Provided that instead of such lantern-light, a window glazed with similar glass and of equal area placed in the side of such shaft may be provided if—

a) The sill of such window is not less than 600 millimetres above the roof-covering at any point of the sill; and

b) Such window is not within 3 metres of a lateral boundary.

(4) Any shaft enclosure which does not extend through the roof shall have the top of such enclosure enclosed by a construction having a fire-resistance rating of not less than that of the walls of the shaft, and shall be provided with a ventilating-duct leading to the outside air.

(5) The ventilating-duct referred to in subsection (4) shall have a cross-sectional area equal to not less than 10 per centum of the cross-sectional area of the shaft, and the discharge-end of such duct may be glazed with plain glass not exceeding 3 millimetres in thickness.

(6) Any shaft which does not extend to the bottom of a building shall be enclosed at its lowest point by a floor construction having a fire-resistance rating of not less than that of the walls of the shaft

(7) Any room containing machinery for operating lifts shall be separated from the lift-shaft concerned by construction having a fire-resistance rating of not less than two hours.

(8) Every doorway in a room containing machinery for operating lifts shall be fitted with an approved self-closing fire-door having a fire-resistance rating of not less than one hour.