Section H1 Foul Water Drainage


Foul water drainage

H1. (1) An adequate system of drainage shall be provided to carry foul water from appliances within the building to one of the following, listed in order of priority:

(a) a public sewer; or, where that is not reasonably practicable,

(b) a private sewer communicating with a public sewer; or, where that is not reasonably practicable,

(c) either a septic tank which has an appropriate form of secondary treatment or another wastewater treatment system; or, where that is not reasonably practicable,

(d) a cesspool.

(2) In this Part ‘foul water’ means waste water which comprises or includes:

(a) waste from a sanitary convenience, bidet or appliance used for washing receptacles for foul waste; or

(b) water which has been used for food preparation, cooking or washing.

Limits on application

Requirement H1 does not apply to the diversion of water which has been used for personal washing or for the washing of clothes, linen or other articles to collection systems for re-use.



In the Secretary of State’s view the requirement of H1 will be met if a foul water drainage system:

a. conveys the flow of foul water to a foul water outfall (a foul or combined sewer, a cesspool, septic tank or holding tank);

b. minimises the risk of blockage or leakage;

c. prevents foul air from the drainage system from entering the building under working conditions;

d. is ventilated;

e. is accessible for clearing blockages; and

f. does not increase the vulnerability of the building to flooding.

Introduction to provisions

1.1 The capacity of the system should be large enough to carry the expected flow at any point.

1.2 The capacity depends on the size and gradient of the pipes. Minimum sizes and gradient limits are given in the text.

1.3 The pipe sizes quoted in this document are nominal sizes used as a numerical designation in convenient round numbers approximately equal to a manufacturer’s size. Equivalent pipe sizes for individual pipe standards will be found in the standards listed in Tables 4, 7 and 14.

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