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906.4 Multiple branch vents.
Where multiple branch vents are connected to a common branch vent, the common branch vent shall be sized in accordance with this section based on the size of the common horizontal drainage branch that is or would be required to serve the total drainage fixture unit load being vented.
906.5 Ejector vents.
Ejector vent sizes shall be determined in accordance with Sections 906.5.1 and 906.5.2.
906.5.1 Sewage pumps and sewage ejectors other than pneumatic.
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 906.5.1. Where a building sump vent connects to a sanitary vent system, the sanitary branch vent shall be at least 3 inches (76 mm) in diameter.
Discharge Capacity of Pump (gpm) | Maximum Developed Length of Vent (feet) a | |||||
Discharge Capacity of Pump (gpm) | Maximum Developed Length of Vent (feet) a | |||||
Diameter of vent (inches) | ||||||
1 1/4 | 1 1/2 | 2 | 2 1/2 | 3 | 4 | |
10 | No limit b | No limit | No limit | No limit | No limit | No limit |
20 | 270 | No limit | No limit | No limit | No limit | No limit |
40 | 72 | 160 | No limit | No limit | No limit | No limit |
60 | 31 | 75 | 270 | No limit | No limit | No limit |
80 | 16 | 41 | 150 | 380 | No limit | No limit |
100 | 10c | 25 | 97 | 250 | No limit | No limit |
150 | Not permitted | 10c | 44 | 110 | 370 | No limit |
200 | Not permitted | Not permitted | 20 | 60 | 210 | No limit |
250 | Not permitted | Not permitted | 10 | 36 | 132 | No limit |
300 | Not permitted | Not permitted | 10c | 22 | 88 | 380 |
400 | Not permitted | Not permitted | Not permitted | 10c | 44 | 210 |
500 | Not permitted | Not permitted | Not permitted | Not permitted | 24 | 130 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m.
a. Developed length plus an appropriate allowance for entrance losses and friction due to 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.
b. Actual values greater than 500 feet.
c. Less than 10 feet.
906.5.2 Pneumatic sewage ejectors.
The air pressure relief pipe from a pneumatic sewage ejector shall be connected to an independent vent stack terminating as required for vent extensions through the roof. The relief pipe shall be sized to relieve air pressure inside the ejector to atmospheric pressure, but shall be not less than 1 1/2 inches (38 mm) in size.
907.1 Vent for horizontal offset of drainage stack.
Horizontal offsets of drainage stacks shall be vented where five or more branch intervals are located above the offset. The offset shall be vented by venting the upper section of the drainage stack and the lower section of the drainage stack.
907.2 Upper section.
The upper section of the drainage stack shall be vented as a separate stack with a vent stack connection installed in accordance with Section 904.4. The offset shall be considered the base of the stack.
907.3 Lower section.
The lower section of the drainage stack shall be vented by a yoke vent connecting between the offset and the next lower horizontal branch. The yoke vent connection shall be permitted to be a vertical extension of the drainage stack. The size of the yoke vent and connection shall be a minimum of the size required for the vent stack of the drainage stack.
908.1 Where required.
Soil and waste stacks in buildings having more than 10 branch intervals shall be provided with a relief vent at each tenth interval installed, beginning with the top floor.
908.2 Size and connection.
The size of the relief vent shall be equal to the size of the vent stack to which it connects. The lower end of each relief vent shall connect to the soil or waste stack through a wye below the horizontal branch serving the floor, and the upper end shall connect to the vent stack through a tee or inverted wye not less than 3 feet (914 mm) above the floor.
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