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Drainage and venting fixture unit values

Find information about how plumbing loading works within the Plumbing Code. For example, if you are adding a bathroom to your house, you can see whether an existing drain pipe is large enough.

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Drainage Fixture Unit (DFU) Values for Typical Household Fixtures (excerpt from Uniform Plumbing Code Table 702.1)

Individual fixtures Minimum size trap and trap armb 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 incha  2.0
 Kitchen sink, domestic, with or without food waste grinder and/or dishwasher  1-1/2 incha  2.0
 Laundry sink, 1 or 2 compartments  1-1/2 incha  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 must 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 pipinga vertical 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 6-unit traps or water closets

d Only 4 water closets or 6-unit traps allowed on any vertical pipe or stack; and not exceed 3 water closets or 6-unit traps on any horizon branch or drain.

Note: The diameter of an individual vent must not be less than 1-1/4 inches nor less than 1/2 the diameter of the drain to which it is connected. Fixture unit load values for drainage and vent piping must be computed from the above table.

No more than 1/3 of the total permitted length of any vent may be installed in a horizontal position. When vents are increased 1 pipe size for their entire length, the maximum length limitations specified in this table to not apply.

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