18-29-710.3 Underground drainage piping.

   Any portion of the drainage system installed underground or below a basement or cellar shall not be less than 4 inches (100 mm) in diameter.

Table 18-29-710A
Building Drains and Sewers

Diameter of Pipe (inches)	Maximum Number of Drainage Fixture Units Connected to any Portion of the Building Drain or the Building Sewer, Including Branches of the Building Draina
	Slope per Foot
	1/6 inch	1/8 inch	1/4 inch	1/2 inch
1 1/4	–	–	1	1
1 1/2	–	–	3	3
2	–	–	21	26
2 1/2	–	–	24	31
3	–	36	42	50
4	–	180	216	250
5	–	390	480	575
6	–	700	840	1,000
8	1,400	1,600	1,920	2,300
10	2,500	2,900	3,500	4,200
12	2,900	4,600	5,600	6,700
15	7,000	8,300	10,000	12,000

 

For SI: 1 inch = 25.4 mm, 1 inch per foot = 0.0833 mm/m.

a The minimum size of any building drain serving a water closet shall be 3 inches.

Table 18-29-710B
Horizontal Fixture Branches and Stacks a

Diameter of Pipe (inches)	Any Horizontal Fixture Branch	Maximum Number of Fixture Units that may be Connected to:
		One Stack of 3 Stories in Height or 3 Intervals	More than 3 Stories in Height
			Total for Stack	Total at One Story or Branch Interval
1 1/2	3	4	8	2
2	6	10	24	6
2 1/2	12	20	42	9
3	20	30	60	16
4	160	240	500	90
5	360	540	1,100	200
6	620	960	1,900	350
8	1,400	2,200	3,600	600
10	2,500	3,800	5,600	1,000
12	3,900	6,000	8,400	1,500
15	7,000	–	–	–

 

For SI: 1 inch = 25.4 mm.

a Does not include branches of house drain.