By code, vents must be placed at least two pipe diameters from a fixture trap. In addition, the length of the trap arm is limited to the distances defined in the figure and chart below.

Max. Distance Between Fixture Traps and Vents

Size of Trap (in.) Distance from Trap (ft.)
1 1/4 5
1 1/2 6
2 8
3 12
4 16

For more information on Plumbing Vents, visit the JLC Field Guide.