PLUMBING
continued from page 20
forming a soil or waste stack. In this case, a cleanout will be required at the base of the stack. Above the first storey, the total number of fixture units connected to the wet vent must not exceed four per storey. A multi-storey wet vent is permitted to have one nominally horizontal offset, but no connection is permitted in that offset. The maximum length of this offset can be 1.2 metres for a two-inch or smaller wet vent, and 2.5 metres for a three-inch or larger wet vent. When a multi-storey wet vent passes through more than four storeys, the stack vent must be sized to be the same size as the wet vent.
Wet Venting Restrictions The number of water closets cannot exceed two. When two are connected, a symmetrical fitting must be used. The water closet(s) must be installed downstream of all other fixtures. Trap arms and fixture drains connecting to the wet vent must not exceed two inches in size, except if a three-inch emergency floor drain is installed. The size of the continuous vent only includes the fixtures being vented by the wet vented portion. The size of the wet vented portion may not reduce in size (except for the installation of a three-inch emergency floor drain). he length of the wet vented portion is not limited, but must have a minimum slope of 1:50.
Adding on It is permissible to add onto a wet vent. A separately vented branch or fixture drain may connect to a wet vent or a wet vented water closet trap arm. For calculation purposes, the separately vented branch or fixture drain’s hydraulic load is included in the size of the wet vented portion, but is not included in sizing the continuous vent. Keep in mind, the separately vented branch could be a separate wet vent itself.
22
M e c h a n i c a l
B u s i n e s s
0 8 . 1 0
WET VENTING RULES The size of a wet vent must conform to National Plumbing Code of Canada (NPC) Table 2.5.8.1., Ontario Building Code (OBC) Table 7.5.8.1., or British Columbia Building Code (BCBC) Table 7.5.8.1. These tables all contain the same instructions, and are summarized in Table 1 (See page 20). The table is divided into three columns. The first column gives the size of the wet vent. The second states the hydraulic load of a wet vent where the lowest connected fixture is served by a p-trap – meaning that it is not a water closet. The third column states the allowable hydraulic load, in fixture units, when the lowest connected fixture is a water closet, or two symmetrically connected water closets.
Rainier Bratsch-Blundel is a plumbing professor and the plumbing and steamfitting programs coordinator for apprenticeship and skilled trades at George Brown College. He is also an executive committee member with the Ontario Plumbing Inspectors Association. He can be contacted at rblundel@georgebrown.ca, or visit OPIA online at www.opia.info.