About this chapter: Chapter 31 regulates connection locations, various venting system arrangements and the sizing of piping for vent systems. The proper operation of a gravity flow drainage system (Chapter 30) depends on maintaining an air path throughout the system to prevent waste and odor "blow back" into fixtures and siphoning of the trap seal in fixture traps (Chapter 32).
Code development reminder: Code change proposals to this chapter will be considered by the IRC—Mechanical/Plumbing Code Development Committee during the 2018 (Group A) Code Development Cycle. See explanation on page iv.
|SIZE OF TRAP (inches)||SLOPE (inch per foot)||DISTANCE FROM TRAP (feet)|
1 inch per foot = 83.3 mm/m.
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 to be the vent for the lower fixture drain, and shall be sized in accordance with Table P3107.3. The upper fixture shall not be a water closet.
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.
The waste stack shall be sized based on the total discharge to the stack and the discharge within a branch interval in accordance with Table P3109.4. The waste stack shall be the same size throughout the length of the waste stack.
Drainage piping below sewer level shall be vented in the same manner as that of a gravity system. Building sump vent sizes for sumps with sewage pumps or sewage ejectors, other than pneumatic, shall be determined in accordance with Table P3113.4.1.
|DISCHARGE CAPACITY OF PUMP|
|MAXIMUM DEVELOPED LENGTH OF VENT (feet)a|
|Diameter of vent (inches)|
|10||No limitb||No limit||No limit||No limit||No limit|
|20||270||No limit||No limit||No limit||No limit|
|40||72||160||No limit||No limit||No limit|
|60||31||75||270||No limit||No limit|
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute (gpm) = 3.785 L/m.
- Developed length plus an appropriate allowance for entrance losses and friction caused by fittings, changes in direction and diameter. Suggested allowances shall be obtained from NBS Monograph 31 or other approved sources. An allowance of 50 percent of the developed length shall be assumed if a more precise value is not available.
- Actual values greater than 500 feet.