11. Ventilation, etc., when multistorey building
(1) Subject to the approval in writing of the local authority first being obtained, water closets and airlocks in buildings, other than hospitals and similar institutions, may be ventilated by one of the following methods ¾
(a) in buildings up to 4 storeys in height (measured from the floor of the lowest water closet to be so ventilated) the water closet apartment and airlocks may abut onto a ventilation shaft, open to the sky and carried to such height as may be necessary to prevent the deflection of wind currents down the shaft by neighbouring structures;
(b) no rooms, other than water closets, airlocks, bathrooms, urinals and slop hopper apartments may open onto such shaft;
(c) the area of such ventilating shafts and the maximum number of water closets, urinals, or slop hoppers to be served by any one such shaft, shall be in accordance with the following table ¾
Minimum area of ventilating shaft
Maximum permissible number of closet
pans or urinals on
any vent shaft
1 or 2
|1.5 square metres|
3 or 4
1st or 2nd storey 1.5|
3rd storey 1.85
Top storey 2.2
(d) no dimension of a ventilating shaft shall be less than 1.2 metres;
(e) in buildings in which the ventilating shaft is 3 or 4 storeys in height, a ventilating duct, having a clear area of not less than 0.2 square metre shall be carried from the bottom of the ventilating shaft to an external wall and shall be boxed throughout;
(f) every water closet or airlock which abuts a ventilating shaft shall have a window, capable of being opened to the shaft, with an effective glass area at least equal to one-fifth of the floor area of the apartment with a minimum of 0.35 square metre and in addition shall be provided with ventilating openings to the ventilating shaft, having a total clear area at any point of not less than 0.033 square metre per closet pan;
(g) where water closets are situated in a basement or cellar then, in addition to the other requirements of this subregulation, there shall be provided a ventilating duct carried through the roof, fitted with an approved cowl designed either to give a positive up draught or down draught in the duct at the option of the owner, and capable of changing the air in each water closet or airlock served by it at least 10 times per hour when subject to a wind velocity of 7 kilometres per hour, the inside and outside temperatures being equal; the area of the ventilating duct being not less than 0.015 square metre for each closet pan served by the duct.
(2) A water closet apartment containing not more than one water closet or slop sink may be constructed other than on an external wall if a horizontal duct, communicating directly with the external air at the ceiling level of the apartment, is constructed of the following dimensions ¾
Length not exceeding 1.37 metres measured from the inside face of the external wall to the inside face of the apartment wall, width and height not less than 900 millimetres and 610 millimetres respectively, measured internally.
(3) The water closet may be ventilated by a mechanical system of exhaust ventilation in compliance with the requirements of regulation 12.
(4) Every water closet permitted by the local authority to be ventilated in accordance with this regulation shall be separately lighted by electricity and provided with a separate switch within the compartment.
[Regulation 11 amended in Gazette 3 May 1974 p. 1439.]