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Section P3108 Wet Venting

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P3108.1 Horizontal Wet Vent Permitted
Any combination of fixtures within two bathroom groups located on the same floor level shall be permitted to be vented by a horizontal wet vent. The wet vent shall be considered to be the vent for the fixtures and shall extend from the connection of the dry vent along the direction of the flow in the drain pipe to the most downstream fixture drain connection. Each fixture drain shall connect horizontally to the horizontal branch being wet vented or shall have a dry vent. Each wet-vented fixture drain shall connect independently to the horizontal wet vent. Only the fixtures within the bathroom groups shall connect to the wet-vented horizontal branch drain. Any additional fixtures shall discharge downstream of the horizontal wet vent.
P3108.2 Dry Vent Connection
The required dry-vent connection for wet-vented systems shall comply with Sections P3108.2.1 and P3108.2.2.
P3108.2.1 Horizontal Wet Vent
The dry-vent connection for a horizontal wet-vent system shall be an individual vent or a common vent for any bathroom group fixture, except an emergency floor drain. Where the dry vent connects to a water closet fixture drain, the drain shall connect horizontally to the horizontal wet-vent system. Not more than one wet-vented fixture drain shall discharge upstream of the dry-vented fixture drain connection.
P3108.2.2 Vertical Wet Vent
The dry-vent connection for a vertical wet-vent system shall be an individual vent or common vent for the most upstream fixture drain.
P3108.3 Size
Horizontal and vertical wet vents shall be not less than the size as specified in Table P3108.3, based on the fixture unit discharge to the wet vent. The dry vent serving the wet vent shall be sized based on the largest required diameter of pipe within the wet-vent system served by the dry vent.
TABLE P3108.3
WET VENT SIZE
WET VENT PIPE SIZE (inches) FIXTURE UNIT LOAD (d.f.u.)
11/2 1
2 4
21/2 6
3 12
4 32
For SI: 1 inch = 25.4 mm.
P3108.4 Vertical Wet Vent Permitted
A combination of fixtures located on the same floor level shall be permitted to be vented by a vertical wet vent. The vertical wet vent shall be considered to be the vent for the fixtures and shall extend from the connection of the dry vent down to the lowest fixture drain connection. Each wet-vented fixture shall connect independently to the vertical wet vent. All water closet drains shall connect at the same elevation. Other fixture drains shall connect above or at the same elevation as the water closet fixture drains. The dry-vent connection to the vertical wet vent shall be an individual or common vent serving one or two fixtures.
P3108.5 Trap Weir to Wet-Vent Distances
The maximum developed length of wet-vented fixture drains shall comply with Table P3105.1.

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