I need to VENT (shower/tub)

tjdabomb70April 7, 2008

Background: Remodel work, bathroom. Double vanity relocated, broke up shower/tub to separate units. Sinks share one dedicated 2" vent to roof. All bath fixtures drain into a common 3", 1/4" per ft sloped horizontal (via long turn 3x3x2 wyes) then vertical 4" main. Large crawlspace where all drains and supplies are located.

My issues:

#1 I want to share one existing 2" vent through roof for both the shower and tub. The shower drain is ~2' from the vent I want to use and 4" from the main 3" horizontal drain. I put a 2" santee under the shower drain to be used as a horizontal vent that would travel 2' to the vent and hooked the p-trap after the santee to a 3x3x2 long turn wye into the horizontal drain. Is the santee/vent arrangement I have ok? If not, what should I do?

#2 I want to vent my tub drain by using the 2" vent shared by the shower. Unfortunately, the tub is about 10' away from the vent (as the crow flies), and the bathrom has finished walls (no putting in a dedicated vent here now). My thought here was to have a 2" p-trap at the tub drain

that is mated to a 2x2x2 long turn wye, head end with a CO, that goes ~6" to a 2x2x2 santee attached @45 degrees with a short arm to a 45 degree short ell that would get 10' of travel vent/pipe to the vertical vent 10' away. Is this ok? If not, what can I do?

I may be able to draw this out if my ramblings aren't mentally cohesive.


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Ron Natalie

No horizontal vent lines below the flood level of the fixture.
It sounds like you are also venting the shower side of the trap, which won't work either.

I can't even begin to visualize #2. If you did all this remodelling, why don't you open up the walls and run the plumbing and venting correctly rather than the disaster-waiting-to-happen you're working on now.

    Bookmark   April 7, 2008 at 3:05PM
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The bad news is that venting a tub or shower in the manner you suggest is prohibited by code. Code prohibits any horizontal venting until the vent reaches an elevation, which is 6" higher than the flood level rim of the highest fixture served by that vent.
The good news is that you may not need additional venting on the tub and shower.

Under the IRC (International Residential Code) all structures are required to have one "main vent" which must run undiminished in size from the house "main drain" through the roof. Once that is achieved any additional auxiliary vents may be reduced to ½ the diameter of the line they serve, but not less than 1-1/4". Your drain is 3" so you would only need a 1-1/2" vent.

Under the UPC (Uniform Plumbing Code) all vents are sized by the total number of DFUÂs (drainage fixture units) of the fixtures served by that vent. You have one tub (2dfuÂs), one shower (2dfuÂs) and 2 lavatories (1dfu each) and a water closet (3dfuÂs) for a combined total of 9dfuÂs.

The UPC allows a maximum of 24 dfuÂs on a 2" vent. Therefore under either code you would be able to vent the entire bathroom group with one 2" vent. The key then becomes where that vent is located in relation to all the drains.

There is a single pipe, which runs from the fixture trap to the vent or branch drain, which is properly called the "Fixture Arm" or "Waste Arm". By necessity that pipe must serve as both the vent and drain for the trap. Under the IRC the bottom of the fixture arm at the trap weir may not be higher than the top of the fixture arm at the trap, therefore we can mathematically compute the maximum length by dividing the pipe diameter by the pitch. Understanding that all pipes 3" or less are required a ¼" per foot pitch we can then determine the maximum length by dividing the pipe diameter by .25"

1-1/4" divided by .25" = 5Â
1-1/2" divided by .25" = 6Â
2" divided by .25" = 8Â
3" divided by .25" = 12Â
4" or larger divided by .25" = 16Â
There is an exception in the IRC that states a 3" or 4" that serves only a watercloset may run an indefinite length.

Installers must be very attentive to detail when running the fixture arm. If you inadvertently increase the pitch, it will ultimately shorten the allowable length.

The UPC begins with basically the same formula, but they then de-rate the length by approximately 40% thus we must use the lengths published in the Code Book.
1-1/4" = 2Â6"
1-1/2" = 3Â6"
2" = 5Â
3" = 6Â
4" or larger 10Â

I would need to see a drawing of your proposed layout showing all drains (including diameter and length) and the position of your existing 2" vent in order to determine whether you need any additional venting.

I have not mastered the technique for posting pictures on this forum. If you can post it here that is fine, otherwise you may email it to me direct.

    Bookmark   April 7, 2008 at 10:11PM
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Pup -

I emailed you the drawing about a month ago (this is my second, exact, post) and never heard back from you. Since I didn't hear back from you, I thought you found the edge of the Earth.

Did you never receive my email? Shall I try to send it again?

***Ron, I inherited the work, I got on the job after the walls were sewn up. Regardless, in terms of the tub, it is in a structural push-out which would have made a typical vent (up through the adjacent wall closest to the drain) impossible - the wall is mostly window and the rest stud/jack stud/header.

Thanks -

    Bookmark   April 8, 2008 at 12:29AM
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i didnt get the email...pls try again...


    Bookmark   April 8, 2008 at 12:56AM
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Pup -

I just re-sent the drawing - thanks.


    Bookmark   April 8, 2008 at 1:15AM
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