Fixture Traps

Trap Size
1. Use the following table to determine the minimum trap size for most plumbing fixtures.
2. Do not install separate traps on toilets, urinals, and other fi xtures that have traps in the fixture itself.
3. Do not install a trap that is larger than the drainage pipe into which the trap discharges. Example: do not connect a 2 inch trap to a 1 ½ inch pipe on the discharge side of the trap.

Trap Design
1. Install traps of standard design that: (a) have a smooth internal surface for water flow, and (b) are self-cleaning, and (c) do not have interior partitions or moving parts, and (d) are constructed using cast iron, cast or drawn brass, or approved plastic. Standard design for modern fixture traps is the P trap.

Trap Seal
1. Install traps with water seal of at least (≥) 2 inches and not more than (≤) 4 inches.
2. Install floor drain traps that have a deep seal (near 4 inches) design or a trap primer. Connect trap primer valves above the trap seal level.

Trap Installation
1. Set traps level with respect to their water seal.
2. Protect traps from freezing.
3. Provide access to traps with slip joints at the trap inlet or outlet.
4. Do not install more than one trap per fixture.
5. Limit the vertical distance between the fixture drain outlet and the trap weir to not more than (≤) 24 inches. Limit the vertical distance between the top of a washing machine standpipe and the trap weir to at least (≥) 18 inches and not more than (≤) 42 inches.
6. Limit the horizontal distance between the fixture drain outlet and the center of the trap inlet to not more than (≤) 30 inches. Note that this 30 inches horizontal distance may be eliminated or not enforced in some jurisdictions. Verify if this provision applies in your jurisdiction.

Prohibited Traps
1. Do not install the following types of traps: (a) bell traps, and (b) drum traps, and (c) S traps, and (d) traps with moving parts, and (e) building traps.

Traps Serving Multiple Fixture Drain Outlets
1. You may install one trap to serve not more than (≤) 3 kitchen sinks, or 3 lavatories, or 3 laundry tubs if the fixtures:
(a) are adjacent to each other and in the same room, and
(b) have drainage outlets not more than (≤) 30 inches apart, and
(c) have the trap installed at the center drainage outlet of three fixtures.
2. You may connect a laundry tray waste line to a clothes washing machine standpipe as described in Chapter 27.