Interpretation No. 5055 – Venting System Requirements

Manual Reference Section: 5
Applicable Code: BC Plumbing Code (1998), Part 7, Section 7.5
Status: Approved (with subsequent revisions 5055-2 through 5055-5)

Background

Interpretation No. 5055 was among the more complex rulings issued by the Plumbing Officials’ Association of British Columbia. The original determination underwent four revisions, reflecting the technical difficulty of the venting scenarios presented and the need to reconcile field conditions with Code provisions. The enquiry addressed both wet venting and circuit venting arrangements as permitted under Section 7.5 of the 1998 BC Plumbing Code.

Subject Matter

The initial question concerned the conditions under which a wet vent could serve a group of fixtures on a single storey, and whether the pipe sizing requirements of Subsection 7.5.5 permitted a reduced-diameter wet vent where the fixture unit loading fell below certain thresholds. Supplementary questions raised in revisions 5055-2 through 5055-5 expanded the scope to include circuit venting of battery-installed fixtures, such as back-to-back lavatory groups in commercial washroom installations.

Ruling

The Association confirmed that wet venting was permitted for a group of bathroom fixtures on one floor level, provided that the wet vent section of piping was sized no smaller than the values stipulated in Table 7.5.5.A, based on the total fixture unit load carried by the wet-vented portion. A wet vent serving both a water closet and a lavatory, for example, required a minimum 76 mm (3-inch) diameter where the water closet connected downstream of the lavatory drain.

Regarding circuit venting, the ruling specified that a single circuit vent could serve a maximum of eight fixtures installed in a battery arrangement, in accordance with Subsection 7.5.8. The circuit vent pipe itself was required to connect at the most upstream fixture drain in the battery and extend upward to the vent header or open air without any reduction in diameter. All circuit-vented installations were required to include a relief vent at the downstream end of the battery where the total developed length of the horizontal branch exceeded the limits set out in the Code.

Pipe and fitting materials for all venting configurations were required to conform to the standards listed in Section 7.1, including CSA B181.1 for ABS drain, waste, and vent piping and CSA B181.2 for PVC equivalents.

Scope of Application

This interpretation, inclusive of its revisions, applied to residential, commercial, and institutional buildings. It did not supersede any requirements for stack venting or individual fixture venting addressed elsewhere in Section 7.5.