Engineered venting systems shall conform to the provisions of Section 919.
A vent stack shall be required for every drainage stack that has five branch intervals or more.
Exception: Drainage stacks installed in accordance with Section 913.
Every dry vent shall rise vertically to a point not less than 6 inches (152 mm) above the flood level rim of the highest trap or trapped fixture being vented.
Exception: Vents for interceptors located outdoors.
The minimum required diameter of stack vents and vent stacks shall be determined from the developed length and the total of drainage fixture units connected thereto in accordance with Table 906.1, but in no case shall the diameter be less than one-half the diameter of the drain served or less than 11/4 inches (32 mm).
TABLE 906.1
SIZE AND DEVELOPED LENGTH OF STACK VENTS AND VENT STACKS
DIAMETER OF SOIL (inches) | TOTAL FIXTURE UNITS BEING VENTED (dfu) | MAXIMUM DEVELOPED LENGTH OF VENT (feet)a DIAMETER OF VENT (inches) | ||||||||||
11/4 | 11/2 | 2 | 21/2 | 3 | 4 | 5 | 6 | 8 | 10 | 12 | ||
11/4 11/2 11/2 | 2 8 10 | 30 50 30 | 150 100 | — | — | — | — | — | — | — | — | — |
2 2 21/2 | 12 20 42 | 30 26 | 75 50 30 | 200 150 100 | 300 | — | — | — | — | — | — | — |
3 3 3 | 10 21 53 | — | 42 32 27 | 150 110 94 | 360 270 230 | 1,040 810 680 | — | — | — | — | — | — |
3 4 4 | 102 43 140 | — | 25 | 86 35 27 | 210 85 65 | 620 250 200 | 980 750 | — | — | — | — | — |
4 4 5 | 320 540 190 | — | — | 23 21 | 55 50 28 | 170 150 82 | 640 580 320 | 990 | — | — | — | — |
5 5 5 | 490 940 1,400 | — | — | — | 21 18 16 | 63 53 49 | 250 210 190 | 760 670 590 | — | — | — | — |
6 6 6 | 500 1,100 2,000 | — | — | — | — | 33 26 22 | 130 100 84 | 400 310 260 | 1,000 780 660 | — | — | — |
6 8 8 | 2,900 1,800 3,400 | — | — | — | — | 20 | 77 31 24 | 240 95 73 | 600 240 190 | 940 729 | — | — |
8 8 10 | 5,600 7,600 4,000 | — | — | — | — | — | 20 18 | 62 56 31 | 160 140 78 | 610 560 310 | 960 | — |
10 10 10 | 7,200 11,000 15,000 | — | — | — | — | — | — | 24 20 18 | 60 51 46 | 240 200 180 | 740 630 571 | — |
12 12 12 | 7,300 13,000 20,000 | — | — | — | — | — | — | — | 31 24 20 | 120 94 79 | 380 300 250 | 940 720 610 |
12 15 15 | 26,000 15,000 25,000 | — | — | — | — | — | — | — | 18 | 72 40 31 | 230 130 96 | 500 310 240 |
15 15 | 38,000 50,000 | — | — | — | — | — | — | — | — | 26 24 | 81 74 | 200 180 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
- The developed length shall be measured from the vent connection to the open air.
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.
TABLE 906.5.1
SIZE AND LENGTH OF SUMP VENTS
DISCHARGE CAPACITY OF PUMP (gpm) | MAXIMUM DEVELOPED LENGTH OF VENT (feet)a | |||||
Diameter of vent (inches) | ||||||
11/4 | 11/2 | 2 | 21/2 | 3 | 4 | |
10 | No limitb | 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.
- 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.
- Actual values greater than 500 feet.
- Less than 10 feet.
Each fixture trap shall have a protecting vent located so that the slope and the developed length in the fixture drain from the trap weir to the vent fitting are within the requirements set forth in Table 909.1.
Exception: The developed length of the fixture drain from the trap weir to the vent fitting for self-siphoning fixtures, such as water closets, shall not be limited.
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.
TABLE 911.3
COMMON VENT SIZES
PIPE SIZE (inches) | MAXIMUM DISCHARGE FROM UPPER FIXTURE DRAIN (dfu) |
11/2 | 1 |
2 | 4 |
21/2 to 3 | 6 |
For SI: 1 inch = 25.4 mm.
The dry vent serving the wet vent shall be sized based on the largest required diameter of pipe within the wetvent system served by the dry vent. The wet vent shall be of a size not less than that specified in Table 912.3, based on the fixture unit discharge to the wet 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 913.4. The waste stack shall be the same size throughout its length.
TABLE 913.4
WASTE STACK VENT SIZE
STACK SIZE (inches) | MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS (dfu) | |
Total discharge into one | Total discharge for stack | |
11/2 | 1 | 2 |
2 | 2 | 4 |
21/2 | No limit | 8 |
3 | No limit | 24 |
4 | No limit | 50 |
5 | No limit | 75 |
6 | No limit | 100 |
For SI: 1 inch = 25.4 mm.
The size of a combination waste and vent pipe shall be not less than that indicated in Table 915.2.2. The horizontal length of a combination waste and vent system shall be unlimited.
Drainage stacks shall be sized in accordance with Table 917.2. Stacks shall be uniformly sized based on the total connected drainage fixture unit load. The stack vent shall be the same size as the drainage stack. A 3-inch (76 mm) stack shall serve not more than two water closets.
TABLE 917.2
SINGLE STACK SIZE
STACK SIZE (inches) | MAXIMUM CONNECTED DRAINAGE FIXTURE UNITS | ||
Stacks less than 75 feet in height | Stacks 75 feet to less than 160 feet in height | Stacks 160 feet and greater in height | |
3 | 24 | NP | NP |
4 | 225 | 24 | NP |
5 | 480 | 225 | 24 |
6 | 1,015 | 480 | 225 |
8 | 2,320 | 1,015 | 480 |
10 | 4,500 | 2,320 | 1,015 |
12 | 8,100 | 4,500 | 2,320 |
15 | 13,600 | 8,100 | 4,500 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
Horizontal branches connecting to a single stack vent system shall be sized in accordance with Table 710.1(2). Not more than one water closet shall discharge into a 3-inch (76 mm) horizontal branch at a point within a developed length of 18 inches (457 mm) measured horizontally from the stack.
Where a water closet is within 18 inches (457 mm) measured horizontally from the stack and not more than one fixture with a drain size of not more than 11/2 inches (38 mm) connects to a 3-inch (76 mm) horizontal branch, the branch drain connection to the stack shall be made with a sanitary tee.
Water closet connections shall be not greater than 4 feet (1219 mm) in developed length measured horizontally from the stack.
Exception: Where the connection is made with a sanitary tee, the maximum developed length shall be 8 feet (2438 mm).
The maximum developed length of individual fixture vents to vent branches and vent headers shall be determined in accordance with Table 919.2 for the minimum pipe diameters at the indicated vent airflow rates.
The individual vent airflow rate shall be determined in accordance with the following:
For SI:
where:
Individual vent airflow rates are obtained by equally distributing Qh,b into one-half the total number of fixtures on the branch or header for more than two fixtures; for an odd number of total fixtures, decrease by one; for one fixture, apply the full value of Qh,b.
Individual vent developed length shall be increased by 20 percent of the distance from the vent stack to the fixture vent connection on the vent branch or header.
TABLE 919.2
MINIMUM DIAMETER AND MAXIMUM LENGTH OF INDIVIDUAL BRANCH FIXTURE VENTS AND INDIVIDUAL FIXTURE HEADER VENTS FOR SMOOTH PIPES
DIAMETER OF (inches) | INDIVIDUAL VENT AIRFLOW RATE (cubic feet per minute) | |||||||||||||||||||
Maximum developed length of vent (feet) | ||||||||||||||||||||
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | |
1/2 | 95 | 25 | 13 | 8 | 5 | 4 | 3 | 2 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
3/4 | 100 | 88 | 47 | 30 | 20 | 15 | 10 | 9 | 7 | 6 | 5 | 4 | 3 | 3 | 3 | 2 | 2 | 2 | 2 | 1 |
1 | — | — | 100 | 94 | 65 | 48 | 37 | 29 | 24 | 20 | 17 | 14 | 12 | 11 | 9 | 8 | 7 | 7 | 6 | 6 |
11/4 | — | — | — | — | — | — | — | 100 | 87 | 73 | 62 | 53 | 46 | 40 | 36 | 32 | 29 | 26 | 23 | 21 |
11/2 | — | — | — | — | — | — | — | — | — | — | — | 100 | 96 | 84 | 75 | 65 | 60 | 54 | 49 | 45 |
2 | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 100 |
For SI: 1 inch = 25.4 mm, 1 cubic foot per minute = 0.4719 L/s, 1 foot = 304.8 mm.