Don't Go Sideways- Proper Traps

Home Inspector with NCW Home Inspections, LLC

Improper Trap Installation


Such a simple plumbing item to do but so often done incorrectly... enter the fixture trap.


Plumbing fixture traps are devices that keeps a small amount of liquid every time the fixtures is used in it to create a trap seal.

The amount of retained liquid is called a trap seal. Without a trap to seal off plumbing fixtures, unwanted and nasty things such as methane gas and vermin can creep into the house.

In addition to a trap seal you want the trap to be self scouring or better stated self cleaning.

These need to be properly installed to function properly. Under normal conditions, traps are required to have a seal depth between 2 inches up to 4 inches. As the seal depth increases, so does the pressure required to push the fluid through the trap. If the pressure is too great, the water from a fixture may not be enough to cause the water to flow quickly through the trap and sediment can begin to accumulate at the bottom of the trap. And if the trap is not installed correctly then the mechinism for scouring will be impared.

From 2015 UPC

1002.2 Fixture Traps.

Each fixture trap shall have a protecting vent so located that the developed length of the trap arm from the trap weir to the inner edge of the vent shall be within the distance given in fable 1002.2, but in no case less than two times the diameter of the trap arm.

1003.1 general requirements.

Each trap, except for traps within an interceptor or similar device shall be self cleaning. Traps for bathtubs, showers, lavatories, sinks, laundry tubs, floor drains, urinals, drinking fountains, dental units, and similar fixtures shall be of standard design, weight and shall be of ABS, cast-brass, cast-iron, lead, PP, PVC, or other approved material. An exposed and readily accessible drawn-brass tubing trap, not less than 17 B & S Gauge (0.045 inch) (0.114 mm), shall be permitted to be used on fixtures discharging domestic sewage.

1005.0 Trap Seals.

1005.1 General.
Each fixture trap shall have a liquid seals of not less than 2 inches (51mm) and not more than 4 inches (102mm), except where a deeper seal is found necessary by the Authority Having Jurisdiction. Traps shall be set true with respect to their liquid seals and where necessary they shall be protected from freezing.

Oten these type of installation are fairly easy to correct but should always be done by a qualified person or profesional.




"Quality means doing it right when no one is looking."




If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.




NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  


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Comments (16)

Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Oh how, oh how can you condemn such creativity!  I especially like accordion trap materials!  They fit everything!  And there ain't no gases getting through all that water!

Oh, Henry Ford invented the garage door.  His first attempt at a car (a lawn mower with bicycle tires and a big seat) was fabricated in the shed behind the house he rented.  It was 1" wider than the door!  So he had to break out bricks and create a larger door to accommodate his car.  I couldn't resist the story when I saw the Ford quote at the end of the post! 

Well, he was inside the shed so no one was looking...

Feb 16, 2020 04:20 PM
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

You got to like the the "Flood" trap design. The accordian material ceate turbulance to help clear.... okay not :)


Feb 17, 2020 07:07 AM
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Ain't nun dat gas getn tru dat der woodr.  (perfect southern Virginian - it sound more real if you have no teeth)

And sure!  Turbulance!  You can hear the whoosh!

Feb 18, 2020 03:22 AM
Laura Cerrano
Feng Shui Manhattan Long Island - Locust Valley, NY
Certified Feng Shui Expert, Speaker & Researcher

Another very relevant topic for a specific set of folks! You don’t want the traps me wrong in any way.

Feb 22, 2020 07:11 AM


Aug 28, 2020 12:23 AM


Aug 28, 2020 12:23 AM


Sep 14, 2020 02:00 AM


Sep 14, 2020 02:00 AM