Fitting to maintain air gap in wet/dry horizontal vent run

[Mexicockney]

All - I would love some DWV advice. I just had an inspector come by to check on my master bath remodel. He wanted me to "roll" a fitting to ensure that the horizontal vent pipe has elevation to ensure that there will be sufficient airflow to ensure proper drainage. I get that but I'm not certain that any of the fittings in my set up will accomplish the desired outcome. I am considering adding a couple 45's to elevate the horizontal vent pipe on the end of the run of waste fittings. Please have a look at the red boxes in my sketches and advise if you can. Any help will be much appreciated.

 

[wwhitney]

Your diagram does not show a compliant horizontal wet vent.

To horizontally wet vent, abandon and remove the old lavatory vent (or if it goes through the roof and you don't want to remove it all, leave it connected, but ignore as far as venting goes). Then provide a proper dry vent at the new lavatory location. Then join the tub to the lavatory drain individually, followed by the shower joining the combined tub/lav drain. The tub trap arm will be the tub fixture drain from the tub trap to wye fitting where the tub trap arm joins the lav drain; the shower trap arm will likewise be the shower fixture drain from the shower trap to where it joins the lav/tub branch drain.

Each of those trap arms is limited to one trap diameter of total fall, while falling at least 1/4" per foot. The NSPC, in use in NJ, may also impose an additional length limit on the trap arms; you'll have to check.

Lastly, it's unclear to me from your drawing how the WC is being vented. If it is relying on wet venting from the other bathroom fixtures, check the NSPC, but most likely you will need to upsize the branch drain to 3" starting at the wye where the shower joins the tub/lav. That's because the wet vent downstream of that juncture is carrying 5 DFU (1 for the lav, 2 for the tub, 2 for the shower), and a 2" horizontal wet vent is typically limited to 4 DFU.

Cheers, Wayne

 

[Sponsor]

 

[Mexicockney]

I updated my sketch based on your comments although I'm not at all sure that I interpreted you correctly. Not sure I can keep the existing vent pipe connected with this change.


To horizontally wet vent, abandon and remove the old lavatory vent (or if it goes through the roof and you don't want to remove it all, leave it connected, but ignore as far as venting goes). Then provide a proper dry vent at the new lavatory location. Easy to accomplish, OK

Then join the tub to the lavatory drain individually (Not sure I understand this statement or the next one), followed by the shower joining the combined tub/lav drain. The tub trap arm will be the tub fixture drain from the tub trap to wye fitting where the tub trap arm joins the lav drain; the shower trap arm will likewise be the shower fixture drain from the shower trap to where it joins the lav/tub branch drain.

Each of those trap arms is limited to one trap diameter of total fall, while falling at least 1/4" per foot. The NSPC, in use in NJ, may also impose an additional length limit on the trap arms; you'll have to check. (These are 2" traps so I'm pretty sure I'm good with this),

Lastly, it's unclear to me from your drawing how the WC is being vented. If it is relying on wet venting from the other bathroom fixtures, check the NSPC, but most likely you will need to upsize the branch drain to 3" starting at the wye where the shower joins the tub/lav. That's because the wet vent downstream of that juncture is carrying 5 DFU (1 for the lav, 2 for the tub, 2 for the shower), and a 2" horizontal wet vent is typically limited to 4 DFU. (WC is not a factor in this)

 

[wwhitney]

Yes, as long as the lav (not shown, off the bottom of the page) is properly dry vented, the above configuration wet vents the tub and the shower.

As to the WC, you need to know how it is vented. It is possible (likely?) that in the old configuration, it was being wet vented. If so, you'll need to maintain that wet vent or provide a new dry vent for the WC. And to maintain a wet vent for the WC, you'd need to change the wye where the shower joins the lav/tub (which have already combined) to a 3x2x2 wye, and provide a 3" drain line downstream of that. [Unless the NSPC is unusual and allows 5 DFU on a 2" horizontal wet vent.]

As to the vent in the upper left of your drawing, your current bathroom configuration doesn't need it, the dry vent for the lav (not shown) suffices. Now if that vent rises straight up through the roof, you obviously can't just abandon it is place, as it would let rain into the wall. But if are repurposing it to connect to the lav dry vent location, and you don't create any dead ends that would hold water if flooded, that would be fine.

Cheers, Wayne

 

[Mexicockney]

Yes, as long as the lav (not shown, off the bottom of the page) is properly dry vented, the above configuration wet vents the tub and the shower.

As to the WC, you need to know how it is vented. It is possible (likely?) that in the old configuration, it was being wet vented. If so, you'll need to maintain that wet vent or provide a new dry vent for the WC. And to maintain a wet vent for the WC, you'd need to change the wye where the shower joins the lav/tub (which have already combined) to a 3x2x2 wye, and provide a 3" drain line downstream of that. [Unless the NSPC is unusual and allows 5 DFU on a 2" horizontal wet vent.]

As to the vent in the upper left of your drawing, your current bathroom configuration doesn't need it, the dry vent for the lav (not shown) suffices. Now if that vent rises straight up through the roof, you obviously can't just abandon it is place, as it would let rain into the wall. But if are repurposing it to connect to the lav dry vent location, and you don't create any dead ends that would hold water if flooded, that would be fine.

Cheers, Wayne

Hi Wayne,

The WC is on a separate waste line/vent.

 

[Mexicockney]

Hi Wayne,

I have modified the layout in a way which I believe allows me to retain the old vent (useful or not) as well as include the new one at the vanity. I sort of anticipate that this inspector will want me to retain that vent. Please let me know your thoughts.

Many thanks.

Rigo

 

[wwhitney]

If the vent on the upper left were a 2nd lavatory, it would certainly be a fine layout (as long as neither lavatory is itself a double lavatory).

I'm not really clear on the status of adding an extra dry vent that is horizontal below the fixture flood rim (which would be prohibited if anything would be relying on that dry vent). I can't speculate as to what the inspector will say. You could call it a future lavatory hookup, if that would help.

I think it would be slightly better if the old vent joins the lav drain or branch drain rather than one of the trap arms.

Cheers, Wayne

 

[Mexicockney]

Hi Wayne,

I've been giving your last suggestion some thought. I'm not sure if I interpreted you correctly but here is a diagram that I hope capture's your suggestion. Please let me know what you think. Thanks again for your help with this.

Rigo

 

[wwhitney]

I'm not sure if I interpreted you correctly but here is a diagram that I hope capture's your suggestion.

Not quite. The point would be to connect this bonus vent directly to a drain carrying the lavs. You have it connected to the tub trap arm.

Cheers, Wayne

 

[Mexicockney]

Hi again Wayne.

So would it be accurate to say that the "bonus" vent could be eliminated from either of the last two versions of my diagram and this would be good to go? Would it also be the case that leaving the bonus vent may be technically outside of code but would not be functionally problematic (assuming everything sloped correctly relative to weir line etc). I guess my concern is that somehow leaving it in place might cause a trap to siphon or something along those lines.

Thanks, again,
Rigo

 

[Jeff H Young]

if the underground was concidered a vent Which I see no reason to define it as a vent since it serves no true purpose it could be then called a dry vent and prohibited . so to me as far as code and interpetation of code it would need to fall under a drain to be legal, since no fixture is getting installed a future perhaps and there are probebly requirements regarding future rough ins so the big thing is use proper Drainage fittings and slope on the underground.

 

[wwhitney]

if the underground was concidered a vent Which I see no reason to define it as a vent since it serves no true purpose it could be then called a dry vent and prohibited

Right.

so to me as far as code and interpetation of code it would need to fall under a drain to be legal, since no fixture is getting installed a future perhaps

Right, but that means that it can't connect to another trap arm, it should connect separately to the wet vent. Hence my suggestion.

Cheers, Wayne

 

[Mexicockney]

This is all very interesting and also a bit confusing!

Okay, I forgot to mention that I am considering putting a cleanout on the vertical portion of the "bonus vent". Does that impact this situation in any way?

Thanks again

 

[Jeff H Young]

Perhaps Im being redundant I agree connecting with trap arm Id call a no no as well. I would think this might get a raised eyeybrow some big shot inspector might come up with something. Id sure like to hear the specific violation.

cleanout I dont think would be an adverse idea. lav should have a cleanout and run 2 inch on underground my opinion

 

[Mexicockney]

Hey Jeff,

Inspectors aside, in your personal opinion does the "bonus vent" cause any functional issues? I am inclined to think my inspector wants it to remain but my real concern is that it actually works before I cover it up.

Thanks, again,
Rigo

 

[wwhitney]

Inspectors aside, in your personal opinion does the "bonus vent" cause any functional issues?

I have no opinion on the above, but if you make either the change shown below in purple, or the change shown in orange, then I'm confident there should be no functional issue. Either of those makes the "bonus vent" plumbed just like an extra lavatory would be.

[Although you couldn't actually use it for another fixture, as you have already maxed out the 2" wet vent for the shower, it's carrying the tub and 2 lavs, or 4 DFU. If you want the option to use it for a future fixture, you'd need to connect the bonus vent to the branch drain downstream of the shower.]

Cheers, Wayne

 

[Mexicockney]

Okay guys I'm optimistic that I may have this as advised.

One note. The slight jog that I am indicating on the horizontal run to the "bonus vent" is to avoid having to break more concrete. I'm hopeful that is not an issue. I haven't attempted to fit this yet and its possible I may be able to accomplish this without the extra fittings.

A couple more questions. Would there be any need to or benefit in rolling any of these wye fittings? Are the fittings I have indicated appropriate for this application in your opinion?

Many thanks!

Rigo

 

[wwhitney]

Would there be any need to or benefit in rolling any of these wye fittings?

Not for horizontal wet venting, 2% slope on all inlets is fine.

If you do roll the shower wye, you are limited in how much you roll it, as the total trap arm fall is limited to one trap diameter. That fall includes whatever fall occurs on the branch inlet leg of the wye.

For the tub trap arm, that's not an issue, as the trap arm is coming into the straight inlet of the wye.

Cheers, Wayne

 

[Jeff H Young]

I only see 2 reasons to run that vent under slab one reason being you wont be using the vent through roof and dont want to go on the roof to eliminate it completely. capping it below is kind of undesireable because it will trap water forever presumeably. the other reason is for future use. Sure more venting isnt a bad thing but following plumbing code has a degree of overkill in it and I see no practical benefit youll never know the differance. and that extra roof penetration could be your next roof leak .
I think Wayne has really explained things well and adressed all sides to this but you have good questions like the rolling up of wyes on trap arms ( not good ) No Idea why inspector would mention saving the vent maybe just to avoid the roof work?

 

[Mexicockney]

Hi there.

Actually I was considering combining the two vents together in the attic. I will have a shower, a tub and a double vanity on the 1-1/2" branch which will combine with a 2" vent stack going through the roof. I should be good on my DFU budget.

To be honest I'm not sure that my inspector is the most technically knowledgeable guy but to be fair neither am I. If he wants to see this vent and it won't cause me any functional problems I'm happy to give it to him. The last think I want to do is get into a technical p*ssing match with him. That sort of thing never ends well in my experience.


Rigo