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911.1 Individual vent as common vent.
An individual vent is permitted to vent two traps or trapped fixtures as a common vent. The traps or trapped fixtures being common vented shall be located on the same floor level.
911.2 Connection at the same level.
Where the fixture drains being common vented connect at the same level, the vent connection shall be at the interconnection of the fixture drains.
Exception: Where wet vents are permitted by this code, the wet vent connection may be located downstream of the interconnection.
911.3 Connection at different levels.
Where the fixture drains connect at different levels, the vent shall connect as a vertical extension of the vertical drain. The vertical drain pipe connecting the two fixture drains shall be considered the vent for the lower fixture drain, and shall be sized in accordance with Table 911.3. The upper fixture shall not be a water closet.
Pipe Size (inches) | Maximum Discharge from Upper Fixture Drain (dfu) |
1 1/2 | 1 |
2 | 4 |
2 1/2 to 3 | 6 |
For SI: 1 inch = 25.4 mm.
912.1 Horizontal wet vent permitted.
Any combination of fixtures within one bathroom group located in the same room is permitted to be vented by a horizontal wet vent. The wet vent shall be considered 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 to the horizontal branch drain. 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.
912.1.1 Vertical wet vent permitted.
Any combination of fixtures within one bathroom group is permitted to be vented by a vertical wet vent. The vertical wet vent shall be considered 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. Fixture drains shall connect above or at the same elevation as the water closet fixture drain. The dry-vent connection to the vertical wet vent shall be an individual or common vent serving one or two fixtures.
912.2 Dry-vent connection.
The required dry-vent connection for wet-vented systems shall comply with Sections 912.2.1 and 912.2.2.
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