(1) Single-stack systems may be used under the following conditions-

a) all soil and waste branch pipes shall be separately connected to the vertical soil stack;

b) the minimum depth of water-seals shall be 75 millimetres for waste-water fittings, and 50 millimetres for soil-water fittings;

c) the waste-pipe used in conjunction with a 32-millimetre-diameter trap from a lavatory basing shall have a minimum diameter of 40 millimetres, a maximum fall of 1 in 25, and a maximum length length of 3 metres;

d) the minimum size if waste-pipe from bath or sink fittings shall be 40 millimetres in diameter;

e) no horizontal waste-pipe shall be connected to the vertical soil stack so that its centre line is on a level with, or within 200 millimetres below, the centre line on a soil branch;

f) a large radius bend of at least two one-eighth bends shall be installed at the foot of the vertical soil stack;

g) the minimum vertical distance between the lowest branch connexion and the invert of the sewer shall be 500 millimetres for buildings up to three storeys, and 750 millimetres for other buildings;

h) no offsets in vertical stacks below the topmost fitting shall be permitted unless venting is provided to relieve any back pressure.

(2) The rate of flow in the vertical soil stack of a single-stack system as calculated in terms of sections 33 and 34 shall not, at any point, exceed the rate given in column 2 of Table VIII for the corresponding size of vertical pipe in column 1.

(3) Alternatively to subsection (2), the rate in a 100 millimetre-diameter vertical pipe may exceed 70 d.u but shall be provided and connected to the vertical pipe at each floor level, either directly or to the anti-siphon horn adjacent to a 100 millimetre soil-water fitting.

TABLE VIII