Tub drain venting question

[Carloliveira]

Bathtub p-trap arm enters waste pipe through WYE with 1/8 bend and behind that WYE is the branch vent that connects to the main vent in the attic. Based on what I reviewed in the 2018 National Standard Plumbing Code, which is what my location follows, Figure 12.6.2 - (A) shows a vent has to enter above the center line of a waste pipe. After seeing some images online of a sanitary tee on its back offset 45 degrees, to work with height restrictions between the floor joists, installed in front of the WYE and 1/8 bend, my question becomes is that the only way or can someone suggest something more creative? I need the trap to remain between the height of the floor joists so I don't lose any basement head space. All pipe here is 1.5" and sloped 1/4 per foot. Thanks in advance.

 

[wwhitney]

Your basic challenge is that you can't have any horizontal dry vents under the floor (or lower than 6" above the fixture flood rim). So if the vent upstream of the wye is a dry vent, your existing configuration, and your proposed configuration in the marked up 4th photo, violate that limitation.

The typical way to dry vent a tub drain is to route it under a wall and take the vent off straight up. Within the maximum length and fall (one pipe diameter) limits from the trap.

Or you can look at wet venting the tub.

Cheers, Wayne

 

[Sponsor]

 

[Carloliveira]

Your basic challenge is that you can't have any horizontal dry vents under the floor (or lower than 6" above the fixture flood rim). So if the vent upstream of the wye is a dry vent, your existing configuration, and your proposed configuration in the marked up 4th photo, violate that limitation.

The typical way to dry vent a tub drain is to route it under a wall and take the vent off straight up. Within the maximum length and fall (one pipe diameter) limits from the trap.

Or you can look at wet venting the tub.

Cheers, Wayne

So if I soak in what you said about dry vent with no horizontal run below flood rim see attached photo....thanks again....p-trap arm swings towards verticle vent pipe into san-tee long sweep elbow on bottom.

 

[wwhitney]

Yes, that works if you have enough height to make it fit.

To minimize the height, you can use a street san-tee into a LT90. Moreover, if the drain exiting the LT90 will be parallel to the trap arm entering the san-tee, you can rotate the san-tee 45 degrees around the side entry to reduce the height further. Then you need a (possibly street) 45 at the top of the san-tee for your vent to turn to true vertical. [0-45 degrees off true vertical all count as vertical for the plumbing code.]

Cheers, Wayne

 

[Jeff H Young]

lower the drain as low to bottom of joists you can get and you might have room for that spigot santee in joistbay to go to the tub

 

[Carloliveira]

Yes, that works if you have enough height to make it fit.

To minimize the height, you can use a street san-tee into a LT90. Moreover, if the drain exiting the LT90 will be parallel to the trap arm entering the san-tee, you can rotate the san-tee 45 degrees around the side entry to reduce the height further. Then you need a (possibly street) 45 at the top of the san-tee for your vent to turn to true vertical. [0-45 degrees off true vertical all count as vertical for the plumbing code.]

Cheers, Wayne

Alright so final rough sketch....turn trap around to LT90 into San tee street rolled 45 degrees for clearance 45 elbow to connect vent and waste discharge from San tee street into LT90 and downstream with 1/4 slope...thanks again

 

[wwhitney]

OK, that geometry isn't what I described exactly, but:

The first LT90 after the trap, is that horizontal, or rolled 45 degrees? It can't be rolled, the vent takeoff has to be at an elevation no more than one pipe diameter below the trap outlet. But if it's horizontal, that's OK, although then I'm not clear on the san-tee on its back geometry.

Do you absolutely have to hit the existing vent location below the floor, rather than shift left or right within the wall? I assume the wall is perpendicular to the joists, based on the tub drain/overflow geometry.

Cheers, Wayne

 

[wwhitney]

P.S. How old is the current arrangement? There's definitely not a lavatory draining down the vertical pipe that is your vent? That would make it a wet vent and the current configuration fine.

Cheers, Wayne

 

[Carloliveira]

OK, that geometry isn't what I described exactly, but:

The first LT90 after the trap, is that horizontal, or rolled 45 degrees? It can't be rolled, the vent takeoff has to be at an elevation no more than one pipe diameter below the trap outlet. But if it's horizontal, that's OK, although then I'm not clear on the san-tee on its back geometry.

Do you absolutely have to hit the existing vent location below the floor, rather than shift left or right within the wall? I assume the wall is perpendicular to the joists, based on the tub drain/overflow geometry.

So it will be best to try first LT90 horizontal into Street San-Tee no roll vent pipe straight out of the top out of San-tee Street 90 due to floor joist proximity out of San-Tee, and downhill slope straight pipe after that.

 

[wwhitney]

Just how tall are your joists?

If you use a street san-tee into a LT90 with the outlet parallel to the san-tee side inlet, they are 5-1/4" apart. If you then rotate that assembly 45 degree about the san-tee side inlet (or LT90 outlet), the height difference becomes 5-1/4" * sqrt(2)/2 = 3-3/4".

So using a san-tee to vent the tub trap arm will cost you 5-1/4" in height minimum if you have the san-tee vertical as usual, or 3-3/4" of height if you are able to put the barrel of the san-tee at 45 degrees off plumb.

If you want 0" of height loss for the vent takeoff, you can point the tub trap arm directly at the vent location and use an upright combo (or perhaps san-tee on its back, if the NSPC allows that) for the vent takeoff. But then you have the problem that the drain is facing the wrong way in the joist bay, so you'd need two LT90 to turn around, along with possibly drilling a joist.

Cheers, Wayne

 

[Carloliveira]

P.S. How old is the current arrangement? There's definitely not a lavatory draining down the vertical pipe that is your vent? That would make it a wet vent and the current configuration fine.

Cheers, Wayne

Just did that arrangement 2 weeks ago replacing what was already there due to a leak at tub drain and trap. It's strictly a dry vent that branches from the main vent (a re-vent I guess pro's call it) in the attic. Moving it closer to the trap to one side presents a problem with current water supply lines in that wall, would have to open wall to move supply lines and not an option right now unfortunately. Bottom line is its not a wet vent. Thanks for your patience Wayne you are a gentleman.

 

[wwhitney]

To minimize the height, you can use a street san-tee into a LT90. Moreover, if the drain exiting the LT90 will be parallel to the trap arm entering the san-tee, you can rotate the san-tee 45 degrees around the side entry to reduce the height further. Then you need a (possibly street) 45 at the top of the san-tee for your vent to turn to true vertical. [0-45 degrees off true vertical all count as vertical for the plumbing code.]

Below is a very crude attempt to illustrate what I mean by the above, as an elevation overlaid on a picture. Lines are vertical pipes or horizontal pipes perpendicular to the joists; pipes parallel to the joists are represented by circles, their cross section.

Starting at the upper right corner of the green drawing, that's the outlet of the tub waste and overflow tee. Then a trap possibly higher than currently with the u-bend pointing away from the joist (how much you rotate the u-bend lets you adjust how far away from the joist you end up). Then the trap elbow has the outlet pointed towards the camera parallel to the joist.

Then you put a street san-tee tilted 45 degrees at the cross section of the joist bay that has your vent takeoff. The top gets a 45 to hit your vent location, the bottom of the san-tee gets a LT90 to point back down the joist bay, away from the camera, parallel to the joists.

Now whether this would all fit properly, I'm not sure. The LT90 drain outlet might hit the trap u-bend; if that's an issue, you have enough distance between them (parallel to the joists) to jog the drain with a 22.5 or a 45. The u-bend outlet might not get you far enough away from the joist to hit the location where the san-tee has to be; in that case you could rotate the outlet 22.5 or 45 degrees to hit an elbow to end up parallel to the joist and offset more.

Hope this helps.

Cheers, Wayne

 

[Carloliveira]

Below is a very crude attempt to illustrate what I mean by the above, as an elevation overlaid on a picture. Lines are vertical pipes or horizontal pipes perpendicular to the joists; pipes parallel to the joists are represented by circles, their cross section.

Starting at the upper right corner of the green drawing, that's the outlet of the tub waste and overflow tee. Then a trap possibly higher than currently with the u-bend pointing away from the joist (how much you rotate the u-bend lets you adjust how far away from the joist you end up). Then the trap elbow has the outlet pointed towards the camera parallel to the joist.

Then you put a street san-tee tilted 45 degrees at the cross section of the joist bay that has your vent takeoff. The top gets a 45 to hit your vent location, the bottom of the san-tee gets a LT90 to point back down the joist bay, away from the camera, parallel to the joists.

Now whether this would all fit properly, I'm not sure. The LT90 drain outlet might hit the trap u-bend; if that's an issue, you have enough distance between them (parallel to the joists) to jog the drain with a 22.5 or a 45. The u-bend outlet might not get you far enough away from the joist to hit the location where the san-tee has to be; in that case you could rotate the outlet 22.5 or 45 degrees to hit an elbow to end up parallel to the joist and offset more.

Hope this helps.

Cheers, Wayne

-1 foot trap arm 1/4" slope
-4 foot run 1" slope
-Street 90 out of bottom of sani-tee from trap arm

-Short radius 90 on 1.5" PVC change of direction permitted per my local towns accepted code for draining of one fixture only see attached below 2018 National Plumbing Standard Code

 

[Jeff H Young]

Darn I was affraid a long sweep wouldnt fit. not the greatest and not the first to use a medium sweep there probebly is ok I dont see an easy way out Id be ok leaving it alone , I mean your kinda stuck . 1/4 inch snake down overflow cover on plastic pipe you could clear a stoppage on it not really a problem though its not going to get past UPC code with a hard ass inspector though itll work

 

[Carloliveira]

Darn I was affraid a long sweep wouldnt fit. not the greatest and not the first to use a medium sweep there probebly is ok I dont see an easy way out Id be ok leaving it alone , I mean your kinda stuck . 1/4 inch snake down overflow cover on plastic pipe you could clear a stoppage on it not really a problem though its not going to get past UPC code with a hard ass inspector though itll work

I'm gonna be honest here but the old cast that was 3/4 built up on all walls let me pass a snake so I'm sure I could snake this hot mess if needed.....no issue and meets my locality code to be honest

 

[Jeff H Young]

I'm gonna be honest here but the old cast that was 3/4 built up on all walls let me pass a snake so I'm sure I could snake this hot mess if needed.....no issue and meets my locality code to be honest

Didn't know it met code for you . I like the long sweep better but you'll be ok

 

[Carloliveira]

didnt know it met code for you . I like the long sweep better but youll be okj

2018 national plumbing standard code one fixture 1/4 bends allowed I've attached a picture