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 1 1/4 inches (32 mm).
Diameter of Soil or Waste Stack (inches) | Total Fixture Units Being Vented (dfu) | Maximum Developed Length of Vent (feet) a Diameter of Vent (inches) | ||||||||||
1 1/4 b | 1 1/2 b |
2 | 2 1/2 | 3 | 4 | 5 | 6 | 8 | 10 | 12 | ||
Diameter of Soil or Waste Stack (inches) | Total Fixture Units Being Vented (dfu) | Maximum Developed Length of Vent (feet) a Diameter of Vent (inches) | ||||||||||
1 1/4 b | 1 1/2 b |
2 | 2 1/2 | 3 | 4 | 5 | 6 | 8 | 10 | 12 | ||
1 1/4 1 1/2 1 1/2 | 2 8 10 | 30 50 30 | – 150 100 | – | – | – | – | – | – | – | – | – |
2 2 2 1/2 | 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.
a. The developed length shall be measured from the vent connection to the open air.
b. Not permitted for water closets.
(Amend Coun. J. 3-27-02, p. 82090, § 3; Amend Coun. J. 10-14-21, p. 37722, Art. IX, § 7)