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Drainage and venting fixture unit values
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.