1. A. Individual Vent. An individual vent, installed vertically, may be used as a common vent for two fixture traps when both fixture drains connect with a vertical drain at the same level. Also, see §311.C of this code in regards to double sanitary tee pattern limitations on fixtures or appliances with a pumping action discharge.

   Figure 915.ACommon Vent

   (Fixtures Connecting at Same Level)

2. B. Fixtures on Same Floor Connecting at Different Levels in the Stack. A common vent may be used for two fixtures set on the same floor level but connecting at different levels in the stack, provided the vertical drain is one pipe size larger than the upper fixture drain but in no case smaller than the lower fixture drain, whichever is the larger, and that both drains conform to Table 913.A of this code. A minor fixture, such as a lavatory, shall enter the common vent above a major fixture, such as a water closet [i.e., a minor (having less fixture units) over/upstream of a major (having more fixture units) rule]. See Figure 915.A, Figure 915.B, and Section 915.D of this code.

   Figure 915.B (1 of 2)Common Vent

   (Fixtures Connecting at Different Levels)

   Figure 915.B (2 of 2)Common Vent

   (Fixtures Connecting at Different Levels)

3. C. Distance. The maximum distance allowed between back-to-back or side-by-side fixture traps and their vent, when vented by a "common vent", shall be in accord with the requirements of §913.A of this code. In addition, the following shall apply.

   1. 1. Two fixtures set back-to-back, or side-by-side connected to a common horizontal branch within the distance allowed between a trap and its vent may be served with one continuous soil or waste vent-pipe, provided that each fixture wastes separately into an approved double fitting having inlet openings at the same level. The vent shall be installed in a vertical position at the interconnection of the fixture drains or downstream of the interconnection in accordance with the distance of trap from vent requirements in Table 913.A of this code. See left-hand depiction of Figure 915.C in this code.

   2. 2. When not more than two fixtures are set back-to-back or side-by-side, within the distance allowed between a trap and its vent, they may be connected to a common horizontal branch served by a common vertical vent located between the two fixtures, provided the branch is one pipe size larger than either of the fixture drains, except as permitted by §923.A of this code. This vent shall not serve as a waste for any other fixture. A minor fixture, such as a floor drain, shall enter the common horizontal branch served by a common vertical vent upstream of a major fixture, such as a water closet [i.e., a minor (having less fixture units) over/upstream of a major (having more fixture units) rule]. See right-hand depiction of Figure 915.C in this code.

      Figure 915.CCommon Vent

      (Distance between Trap and Vent)

4. D. For the purpose of this Section, 3-inch (76 mm) or 4-inch (102 mm) floor or shower drains, up to and including 4-discharge fixture unit (dfu) water closets or pedestal urinals shall be considered as having 3-inch (76 mm) drains. For more than two fixtures on a common horizontal branch, see §925.A (Battery Venting) of this code.

   1. 1. Certain water closets and other plumbing fixtures (such as clinical sinks, flushing rim service sinks, etc.), in either public use or assembly use, have ratings exceeding 4 dfu. In such case, the horizontal branch serving such water closets or other plumbing fixtures shall be a minimum of 5-inch (127 mm) in diameter when a common vertical vent is used, as provided in §915.C.2 of this code.

Authority Note

AUTHORITY NOTE: Promulgated in accordance with R.S. 40:4(A)(7) and R.S. 40:5(2)(3)(7)(9)(16)(17)(20).

Historical Note

HISTORICAL NOTE: Promulgated by the Department of Health and Hospitals, Office of Public Health, LR 38:2861 (November 2012).