International Residential Code 2009 (IRC 2009)

Heads up: There are no amended sections in this chapter.
Traps shall be of standard design, shall have smooth uniform internal waterways, shall be self-cleaning and shall not have interior partitions except where integral with the fixture. Traps shall be constructed of lead, cast iron, cast or drawn brass or approved plastic. Tubular brass traps shall be not less than No. 20 gage (0.8 mm) thickness. Solid connections, slip joints and couplings are permitted to be used on the trap inlet, trap outlet, or within the trap seal. Slip joints shall be accessible.
Traps shall have a liquid seal not less than 2 inches (51 mm) and not more than 4 inches (102 mm). Traps for floor drains shall be fitted with a trap primer or shall be of the deep seal design. Trap seal primer valves shall connect to the trap at a point above the level of the trap seal.
Traps shall be set level with respect to their water seals and shall be protected from freezing. Trap seals shall be protected from siphonage, aspiration or back pressure by an approved system of venting (see Section P3101).
Building traps shall not be installed, except in special cases where sewer gases are extremely corrosive or noxious, as directed by the building official.

The following types of traps are prohibited:

  1. Bell traps.
  2. Separate fixture traps with interior partitions, except those lavatory traps made of plastic, stainless steel or other corrosion-resistant material.
  3. "S" traps.
  4. Drum traps.
  5. Trap designs with moving parts.

Each plumbing fixture shall be separately trapped by a water seal trap. The vertical distance from the fixture outlet to the trap weir shall not exceed 24 inches (610 mm) and the horizontal distance shall not exceed 30 inches (762 mm) measured from the center line of the fixture outlet to the centerline of the inlet of the trap. The height of a clothes washer standpipe above a trap shall conform to Section P2706.2. Fixtures shall not be double trapped.


  1. Fixtures that have integral traps.
  2. A single trap shall be permitted to serve two or three like fixtures limited to kitchen sinks, laundry tubs and lavatories. Such fixtures shall be adjacent to each other and located in the same room with a continuous waste arrangement. The trap shall be installed at the center fixture where three fixtures are installed. Common trapped fixture outlets shall be not more than 30 inches (762 mm) apart.
  3. Connection of a laundry tray waste line into a standpipe for the automatic clothes-washer drain is permitted in accordance with Section P2706.2.1.
Fixture trap size shall be sufficient to drain the fixture rapidly and not less than the size indicated in Table P3201.7. A trap shall not be larger than the drainage pipe into which the trap discharges.

TABLE P3201.7
Bathtub (with or without shower head and/or whirlpool attachments) 11/2
Bidet 11/4
Clothes washer standpipe 2
Dishwasher (on separate trap) 11/2
Floor drain 2
Kitchen sink (one or two traps, with or without dishwasher and garbage grinder) 11/2
Laundry tub (one or more compartments) 11/2
Lavatory 11/4
Shower (based on the total flow rate through showerheads and bodysprays)   
Flow rate:  
5.7 gpm and less  11/2 
More than 5.7 gpm up to 12.3 gpm 
More than 12.3 gpm up to 25.8 gpm 3
More than 25.8 gpm up to 55.6 gpm 4
Water closet Note a

For SI: 1 inch = 25.4 mm.
  1. Consult fixture standards for trap dimensions of specific bowls.
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