Position of new shower drain tie-in to 3 inch main using sink wet vent

[joseph witowsky]

I am adding a shower to a 1/2 bathroom. At present, the 1/2 bath toilet and sink are vented using a wet vent and studor valve, originating from under the sink (See attached). Does it matter whether I tie in the shower drain upstream or downstream of the sink drain wet vent? I've marked the two tie-in location possibilities in green. Thanks.

 

[Reach4]

I think IPC is OK with either. Use wyes or combos in the horizontal plane.

 

[Sponsor]

 

[wwhitney]

The lav drain/wet vent should join either the WC fixture drain, or the shower fixture drain, before the WC and the shower join together. So if I'm interpreting your diagram correctly, the downstream option is preferred, as the upstream option joins the shower and WC drains together before either are vented (via the lav drain/wet vent).

Cheers, Wayne

 

[joseph witowsky]

The lav drain/wet vent should join either the WC fixture drain, or the shower fixture drain, before the WC and the shower join together. So if I'm interpreting your diagram correctly, the downstream option is preferred, as the upstream option joins the shower and WC drains together before either are vented (via the lav drain/wet vent).

Cheers, Wayne

Thanks, Wayne. I was thinking the same thing. I guess my question is, "are both viable", although one might be technically better than the other. Like Reach4 said, he thinks both are acceptable under IPC. Do you know otherwise? Thanks for your feedback, much appreciated.

 

[wwhitney]

I initially misinterpreted your question to be about whether the shower joins the lav drain upstream or downstream of the WC and was going to affirm Reach4's answer. So I think that was the question that Reach4 answered. But since you are bringing the shower drain to the WC drain, rather than the lav drain, it's required to be downstream of the lav drain connection.

Cheers, Wayne

P.S. In my earlier message I was less definite, as I was wondering about the possibility that the WC and the shower could be combined and common vented (IPC 911) via the lav drain/wet vent. But I reread IPC 911 and see that it requires an individual vent, meaning one vent for the two fixtures. Which rules out that idea, as the lav vent would be for three fixtures. IPC 911 is the only allowance I am aware of for combining two drains without their both being vented, so you can't bring the shower into the WC fixture drain before the wet vent takeoff.

 

[joseph witowsky]

I initially misinterpreted your question to be about whether the shower joins the lav drain upstream or downstream of the WC and was going to affirm Reach4's answer. So I think that was the question that Reach4 answered. But since you are bringing the shower drain to the WC drain, rather than the lav drain, it's required to be downstream of the lav drain connection.

Cheers, Wayne

P.S. In my earlier message I was less definite, as I was wondering about the possibility that the WC and the shower could be combined and common vented (IPC 911) via the lav drain/wet vent. But I reread IPC 911 and see that it requires an individual vent, meaning one vent for the two fixtures. Which rules out that idea, as the lav vent would be for three fixtures. IPC 911 is the only allowance I am aware of for combining two drains without their both being vented, so you can't bring the shower into the WC fixture drain before the wet vent takeoff.

Thanks for the clarification, Wayne. Regarding connecting of the shower waste line into the main 3" after the WC but before the wet-vent: If I have the shower drain line (2") connecting into the 3" main via rolling 45-degree angle, so the shower drain actually enters the 3" main from above vs straight horizontal, it seems to me that this would provide extra buffer against vacuum if a large slug of toilet water passes. In this way, I theorize there will always be a gap of air in the shower line and the toilet line, unless the toilet slug completely fills the 3" wasteline, which I believe, is pretty much impossible. Between the rolling 45 connection of the shower line and the lav wet vent just a few inches downstream, it seems to me (and please, correct me here if I'm off-base) the likelihood of issues with proper drainage should be close to nil, if not nil.

 

[wwhitney]

If I have the shower drain line (2") connecting into the 3" main via rolling 45-degree angle, so the shower drain actually enters the 3" main from above vs straight horizontal

That would violate the trap weir rule for the shower trap and potentially allow the shower trap to siphon.

For the 3" line, starting at the toilet flange and going downstream, the lav drain needs to come in first, then the shower drain. So move the lav connection upstream, or the shower connection downstream, to make sure that happens.

Cheers, Wayne