18-29-915.1 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.

(Amend Coun. J. 10-14-21, p. 37722, Art. IX, § 6)

18-29-915.2 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 18-29-903.4. The offset shall be considered the base of the stack.

18-29-915.3 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.

18-29-916 Vent Pipe Sizing.

18-29-916.1 Size of stack vents and vent stacks.

   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).

Table 18-29-916.1
Size and Developed Length of Stack Vents and Vent Stacks

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)

18-29-916.2 Vents other than stack vents or vent stacks.

   The diameter of individual vents, branch vents, circuit vents and relief vents shall be not less than one-half the required diameter of the drain served. The required size of the drain shall be determined in accordance with Table 18-29-710B. Vent pipes shall be not less than 1 1/4 inches (32 mm) in diameter. Relief vents for soil and waste stacks in buildings having more than 10 branch intervals shall be sized in accordance with Section 18-29-914.2.

(Amend Coun. J. 10-14-21, p. 37722, Art. IX, § 7)

18-29-916.3 Developed length.

   The developed length of individual, branch, circuit and relief vents shall be measured from the farthest point of vent connection to the drainage system to the point of connection to the vent stack, stack vent or termination outside of the building.

(Amend Coun. J. 10-14-21, p. 37722, Art. IX, § 7)

18-29-916.4 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.

(Amend Coun. J. 10-14-21, p. 37722, Art. IX, § 7)

18-29-916.4.1 Reserved.

Editor's note – Coun. J. 10-14-21, p. 37722, Art. IX, § 7, repealed § 18-29-916.4.1, which pertained to multiple branch vents exceeding 40 feet.