C 304.3 Size of Horizontal Branch or Vertical Stack

The maximum number of drainage fixture units allowed on a horizontal branch or vertical soil or waste stack of a given size shall be in accordance with Table C 304.3. Stacks shall be sized based on the total accumulated connected load at each story or branch interval.

TABLE C 304.3
HORIZONTAL FIXTURE BRANCHES AND STACKS

DIAMETER OF PIPE (inches)	MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS
	HORIZONTAL FIXTURE BRANCH1	ONE STACK OF THREE OR FEWER BRANCH INTERVALS	STACKS WITH MORE THAN THREE BRANCH INTERVALS
			TOTAL FOR STACK	TOTAL AT ONE BRANCH INTERVAL
11/2	3	4	8	2
2	6	10	24	6
21/2	12	20	42	9
3	202	482	722	202
4	160	240	500	90
5	360	540	1100	200
6	620	960	1900	350
8	1400	2200	3600	600
10	2500	3800	5600	1000
12	3900	6000	8400	1500
15	7000	6000	8400	1500

For SI units: 1 inch = 25 mm

Notes:

¹ Does not include branches of the building drain.

² A maximum of two water closets or bathroom groups within each branch interval or more than six water closets or bathroom groups on the stack.

Horizontal stack offsets shall be sized in accordance with Table C 304.2 as required for building drains.

Vertical stack offsets shall be sized in accordance with Table C 304.3 as required for stacks.