Western Australian Consolidated Regulations

HEALTH ACT (LOCAL AUTHORITIES' SEWERAGE UNDERTAKINGS) MODEL BY-LAWS - SCHEDULE 1

METHOD OF COMPUTING THE SIZES OF SOIL PIPES, WASTE PIPES, COMBINED WASTE AND VENT PIPES, IN ACCORDANCE WITH THE REQUIREMENTS OF BY‑LAWS 95, 96 AND 97

1.         Fixtures

                In accordance with by‑law 95, classify the various fixtures and determine the maximum number of fixture units to be provided for in each portion of the system under consideration. Cleaners’ sinks and floor wastes which are not regularly in use during the period of maximum use of other fixtures need to be included in determining the number of fixture units to be provided for.

2.         Sizes of graded soil pipes, waste pipes and combined waste pipes

            (a)         By reference to by‑law 96, determine from the maximum number of fixture units served at the point under consideration the required sizes and grades of the soil pipes, waste pipes, and combined waste pipes in each portion of the system.

            (b)         Compare the sizes so obtained with the minimum permissible sizes for the particular case and adopt the larger.

3.         Sizes of vertical soil, waste, and combined waste stacks

            (a)         By reference to by‑law 96, determine from the maximum number of fixture units served at the point under consideration, the required sizes of vertical soil, waste, and combined waste stacks.

            (b)         Ascertain whether the number of fixture units connected to the stack within an 8 ft. length is within the permissible limits of paragraph (f) of by‑law 96 if not adopt such larger size stack as will comply with this requirement.

            (c)         Compare sizes so obtained with the minimum permissible sizes for the particular case and adopt the larger sizes, subject to paragraph (a) of by‑law 96.

4.         Size of main vents

            (a)         Determine the approximate vertical length of the main vent in storeys from its connection at its lower end with a soil or waste pipe or drain to the ceiling level of the top floor.

            (b)         From the table of permissible sizes in by‑law 97 determine for the maximum number of fixture units served by the vent, the required size for a vent of such a length.

            (c)         Compare the sizes so determined with minimum permissible sizes and adopt the larger.

5.         Sizes of branch vents

            (a)         Determine the approximate vertical length in storeys of the main vent from the point of connection of the branch vent under consideration to the ceiling level of the top floor.

            (b)         Determine the horizontal length of the branch vent from its connection with the main vent to the furthermost end of the portion under consideration.

            (c)         Allowing one storey for each 12 feet, or part of 12 feet, in horizontal length of branch vent, as determined by rule 5 (b) above, add this length in storeys to the length in storeys by rule 5 (a) above.

            (d)         Determine the number of fixture units served by the portion of branch vent under consideration.

            (e)         From the table of permissible sizes in by‑law 97 determine the minimum size of vent required for the above number of fixture units and for the total length of vent in storeys as determined by rule 5 (c) above.

            (f)         Compare the sizes so determined with the minimum permissible sizes and adopt the larger, subject to the provision that no vent need be larger than the soil pipe or waste pipe which it serves.