Each fixture trap shall have a protecting vent located so that the slope and the developed length in the fixture drain from the trap weir to the vent fitting are within the requirements set forth in Table 909.1.
Exception: The developed length of the fixture drain from the trap weir to the vent fitting for self-siphoning fixtures, such as water closets, shall not be limited.
TABLE 909.1
MAXIMUM DISTANCE OF FIXTURE TRAP FROM VENT
| SIZE OF TRAP (inches) | SLOPE (inch per foot) | DISTANCE FROM TRAP (feet) |
| 11/4 | 1/4 | 5 |
| 11/2 | 1/4 | 6 |
| 2 | 1/4 | 8 |
| 3 | 1/8 | 12 |
| 4 | 1/8 | 16 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 inch per foot = 83.3 mm/m.
The total fall in a fixture drain due to pipe slope shall not exceed the diameter of the fixture drain, nor shall the vent connection to a fixture drain, except for water closets, be below the weir of the trap.
A vent shall not be installed within two pipe diameters of the trap weir.