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906.1 Size of Stack Vents and Vent Stacks

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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).
DIAMETER OF SOIL OR WASTE STACK (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.
  1. The developed length shall be measured from the vent connection to the open air.

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