Div. B › Part 7 › 7.5 › 7.5.4 — Vent Pipes for Soil or Waste Stacks

7.5.4.4 — Offset Relief Vents

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(1) A soil or waste stack that has a nominally horizontal offset more than 1 500 mm long and above which the upper vertical portion of the stack passes through more than 2 storeys and receives a hydraulic load of more than 100 fixture units shall be vented by an offset relief vent connected to the vertical section immediately above the offset, and by another offset relief vent,

(a) connected to the lower vertical section at or above the highest soil or waste pipe connection, or

(b) extended as a vertical continuation of the lower section.

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 unit

means , when applied to a drainage system, the unit of measure based on the rate of discharge, time of operation and frequency of use of a fixture that expresses the hydraulic load that is imposed by that fixture on the drainage system.

nominally horizontal

means at an angle of less than 45° with the horizontal.

offset

means the piping that connects the ends of two pipes that are parallel.

offset relief vent

means a relief vent that provides additional air circulation upstream and downstream of an offset in a soil or waste stack.

relief vent

means a vent pipe that is used in conjunction with a circuit vent to provide additional air circulation between a drainage system and a venting system.

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.

storey

means , except for the purposes of Part 7 of Division B, the portion of a building, (a)that is situated between the top of any floor and the top of the floor next above it, or (b)that is situated between the top of the floor and the ceiling above the floor, if there is no floor above it.

waste pipe

means a sanitary drainage pipe that carries the discharge from a fixture directly to a waste stack, soil stack, sanitary building drain, branch or sewage system.

waste stack

means a vertical waste pipe that passes through one or more storeys and includes any offset that is part of the stack that conducts liquid waste from fixtures other than sanitary units.

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