PC 906 — Vent Pipe Sizing

Section PC 906: Vent Pipe Sizing

906.1 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 906.1 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 1 1/2 2 2 1/2 3 4 5 6 8 10 12 1 1/4 2 30 — — — — — — — — — 1 1/2 8 50 150 1 1/2 10 30 100 2 12 75 200 — — — — — — — 2 20 30 50 150 2 1/2 42 26 30 100 300 3 10 — 42 150 360 1,040 — — — — — — 3 21 32 110 270 810 3 53 27 94 230 680 3 102 — 25 86 210 620 — — — — — 4 43 35 85 250 980 4 140 27 65 200 750 4 320 — — 23 55 170 640 — — — — 4 540 21 50 150 580 5 190 28 82 320 990 5 490 — — — 21 63 250 760 — — — — 5 940 18 53 210 670 5 1,400 16 49 190 590 6 500 — — — — 33 130 400 1,000 — — — 6 1,100 26 100 310 780 6 2,000 22 84 260 660 6 2,900 — — — — 20 77 240 600 — — 8 1,800 31 95 240 940 8 3,400 24 73 190 729 8 5,600 — — — — — 20 62 160 610 — 8 7,600 18 56 140 560 10 4,000 31 78 310 960 10 7,200 — — — — — — 24 60 240 740 — 10 11,000 20 51 200 630 10 15,000 18 46 180 571 12 7,300 — — — — — — — 31 120 380 940 12 13,000 24 94 300 720 12 20,000 20 79 250 610 12 26,000 — — — — — — — 18 72 230 500 15 15,000 40 130 310 15 25,000 31 96 240 15 38,000 — — — — — — — — 26 81 200 15 50,000 24 74 180 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. 906.2 Vents other than stack vents or vent stacks. The diameter of individual vents, branch vents, circuit vents and relief vents shall be at least one-half the required diameter of the drain served. The required size of the drain shall be determined in accordance with Table 710.1(2). Vent pipes shall not be less than 1 1/4 inches (32 mm) in diameter. Vents shall be sized in accordance with Table 906.1 utilizing the drainage fixture units and the corresponding developed length. Relief vents for soil and waste stacks in buildings having more than 10 branch intervals shall be sized in accordance with Section 908.2. 906.3 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. 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. 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) 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.