# P-Trap to vent minimum, Weir to Vent question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by mahuska, Aug 23, 2013.

1. ### mahuskaNew Member

Joined:
Aug 10, 2013
Location:
iowa
When sizing the weir to vent minimum on a P-trap is it measured from liquid edge in trap to start of vent inner diameter (=> than 2X trap arm diameter)?

Joined:
Nov 9, 2009
Location:
Victor, MT
It is measured from the liquid edge to the start of the vent, but it is impossible to not meet code requirements given the configuration of the fittings available. Set that quandary aside and move on to the next one.

4. ### mahuskaNew Member

Joined:
Aug 10, 2013
Location:
iowa
I have a tight shower location using a Kerdi line drain and if you use 2 pipe diameters as the minimum then the weir to vent distance is 5.75. If I just put the P-trap right on the 2" tee the distance is 3.75.

5. ### wjcandeeWise One

Joined:
Apr 27, 2012
Location:
New York, NY
I don't know what your pipe size is, but the minimum vent distance is never going to be 5.75. It's 2 pipe diameters -- inner diameter. 1-1/4" pipe will be 2.5" minimum. 1-1/2" pipe will be 3 inches. 2 inch pipe will be 4". 3 inch pipe will be 6 inches. See page 3 of this document: http://www.klickitatcounty.org/building/FilesHTML/pdf/plmbghandout0411.pdf One thing that is slightly confusing about that document, however, is that it says the minimum "trap arm" distance is whatever, but it illustrates the measurement for meeting code the correct way, then illustrates the "trap arm" as a different distance. The measurement you want is the illustration that shows the distance as being from the inside of the weir to the outer wall of the vent. not the "trap arm" markings under the connection points.

6. ### mahuskaNew Member

Joined:
Aug 10, 2013
Location:
iowa
Ok inner diameters make a lot of sense. 2 in pipe for a shower.

7. ### hjModerator & Master PlumberStaff Member

Joined:
Aug 31, 2004
Occupation:
Plumber
Location:
Cave Creek, Arizona
Unless you have an "anal retentive" inspector with a ruler, no one will ever check it , at least none have ever turned my installations down even with a trap tight to the tee.

8. ### hjModerator & Master PlumberStaff Member

Joined:
Aug 31, 2004
Occupation:
Plumber
Location:
Cave Creek, Arizona
Don't you just love idiots who post a long gibberish filled post in a foreign language, and then repeat it several times to be sure we don't miss it?

9. ### mahuskaNew Member

Joined:
Aug 10, 2013
Location:
iowa
I feel that I missed something

Joined:
Mar 9, 2016
Location:
Virginia