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Individual fixtures Minimum size trap and
trap arm b
Number of units
Bar sink 1-1/2 inch 1.0
Bathtub or combination bath/shower 1-1/2 inch 2.0
Clothes, washer, domestic, 2-inch standpipe 2 inch 3.0
Dishwasher, domestic, with independent drain 1-1/2 inch a 2.0
Kitchen sink, domestic, with or without food waste grinder and/or dishwasher 1-1/2 inch a 2.0
Laundry sink, one or two compartments 1-1/2 inch a 2.0
Lavatory (wash basin) 1-1/4 inch 1.0
Shower stall 2 inch 2.0
Water closet, 1.6 GPF gravity tank 3 inch 3.0

a Provide a 2-inch (51-mm) minimum branch drain beyond the trap arm.
b Trap sizes shall not be increased to the point where the fixture discharge may be inadequate to maintain their self-scouring properties.

Maximum unit loading and maximum length of drainage and vent piping

Size of pipe, inches 1-1/4 1-1/2 2 2-1/2 3 4
Maximum units
Drainage piping a
1 2b 16c 32c 48d 256
Horizontal 1 1 8c 14c 35d 216c
Maximum Length
Drainage piping vertical, feet 45 65 85 148 212 300
Horizontal (unlimited)            
Vent piping (see note)
Horizontal and vertical
maximum units
1 8c 24 48 84 256
Maximum length, feet 45 60 120 180 212 300

a Excluding trap arm
b Except sink, urinals and dishwashers
c Except six-unit traps or water closets
d Only four water closets or six-unit traps allowed on any vertical pipe or stack; and not exceed three water closets or six-unit traps on any horizon branch or drain.

NOTE: The diameter of an individual vent shall not be less than 1-1/4 inches nor less than one half the diameter of the drain to which it is connected. Fixture unit load values for drainage and vent piping shall be computed from the above table. Not to exceed one third (1/3) of the total permitted length of any vent may be installed in a horizontal position. When vents are increased one pipe size for their entire length, the maximum length limitations specified in this table to not apply.