Div. B › Part 7 › 7.4 › 7.4.9 — Size of Drainage Pipes

7.4.9.2 — Serving Water Closets

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(1) The size of every drainage pipe that serves a water closet shall be at least 3 in.

(2) The size of every horizontal drainage pipe downstream of the third water closet fixture drain connection shall be at least 4 in.

(3) The size of every soil stack that serves more than six water closets shall be at least 4 in.

(4) The size of the discharge pipe serving a macerating toilet system shall be at least ¾ in.

(5) No vertical leg of the drainage pipe from a water closet or other fixture that has an integral siphonic flushing action shall exceed 1 000 mm.

OBC Definitions

Defined terms on this page

fixture

means a receptacle, plumbing appliance, apparatus or other device that discharges sewage or clear water waste, and includes a floor drain.

fixture drain

means the pipe that connects a trap serving a fixture to another part of a drainage system.

size

means the nominal diameter by which a pipe, fitting, trap or other similar item is commercially designated.

soil

means , except for the purposes of Part 8 of Division B, a portion of the earth’s crust that is fragmentary or such that individual particles of a dried sample may be readily separated by agitation in water, and includes boulders, cobbles, gravel, sand, silt, clay and organic matter.

soil stack

means a vertical soil pipe that passes through one or more storeys and includes any offset that is part of the stack.

vertical leg

means the vertical portion of a fixture drain and includes the portion of a drain from the outlet of a water closet bowl to the point where the connecting piping changes to horizontal.

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