The purpose of a plumbing vent is to break the suction and allow water to drain quickly while preserving the trap seal that keep sewer gas from wafting into the house.
Login or Register to download the PDF version of this guide. ()
Locating Vents
Figure: Max. Distance Between Fixture Traps and Vents
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
Based on International Residential Code; local codes may vary. Min. slope of trap arm: 1/4 inch per foot for traps sized 1 1/4 to 2 inches; 1/8 per foot for traps sized 3 to 4 inches.
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 below.
Offset Vent Runs
A vent must rise at least 6 in. above the fixture flood rim before running horizontally. If necessary, a pair of 45- degree offsets may be used, as shown in the figure below.
Figure: Horizontal Offset
A vent must rise above a fixture’s flood rim before turning horizontally. If an offset is needed below the rim, use sixteenth or eighth bends. Do not use quarter bends.