Missing vents?

[Jman]

Hello all,
I am building a polebarn home and I had a friend of mine (who does under slab plumbing for a living) do the drain rough-ins as I was too busy at the time to mess with it. This is what he installed (see picture). Inspector came by and approved it without actually looking at anything (go figure), and my concrete guys poured the slab before I had a chance to look at it myself. He told me all I needed to do was to run vent lines up from the sinks and washer drain and tie them together and run it out through the roof like normal. Now, I'm not a plumber by any means but it seems to me that there is a serious lack of venting for the toilet, tub/shower, and floor drain. Am I wrong here? I hope I'm just not understanding what he has going on here but I'm afraid I have a serious problem on my hands. FYI, the floor drain is just for condensate from a gas boiler if that makes any difference. Any input on if this will work or be a total disaster would be greatly appreciated. Thanks in advance

 

[Reach4]

I don't see a problem. I am not a plumber. Indiana uses IPC. You will need vents for the lavatory (bathroom sink), washing machine standpipe, and kitchen sink. At least one needs to be a roof vent. Others could be AAVs.

Bathroom group seems to be properly wet vented by the lavatory, and the floor drain seems to be included into the bathroom group.

https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf

Section 202 of Chapter 2 is the key to the maximum number and type of fixtures that can be accommodated by a horizontal wet vent. The definition of Bathroom Group is a group of fixtures consisting of a water closet, lavatory, bathtub or shower, including or excluding a bidet, an emergency floor drain or both. Such fixtures are to be located together on the same floor level.​

 

[Sponsor]

 

[wwhitney]

The only further comment I'd make is that the floor drain should have connected downstream of the bath/lav connection, rather than joining with the bath before it joined the lav. That's a violation of the wet venting rules, not sure how much it matters for a floor drain.

Cheers, Wayne

 

[Jman]

So it doesn't need a vent on the "upstream" side of the bathroom group? Will the tub and toilet not siphon out the p-trap on the floor drain? I don't have a complete understanding of wet vents but I catch on quickly, so bear with me here as I would like to understand how everything works

 

[wwhitney]

With a wet vent for a bathroom group, you have a dry vented fixture (typically the sink, as it has the highest trap and hence needs a vent connection at the highest elevation). Its drain then connects to one other fixture, and that connection provides the vent for the other fixture. As the pipe from the dry vented takeoff to the second fixture is both a drain and a vent for the other fixture, it's called a wet vent.

Then the wet vent can continue on to another bathroom fixture, then another bathroom fixture, up to 2 bathrooms worth under the IPC. In each case, a fixture's drain is either dry vented (the lav), or connects to a wet vent as its first connection. In either case the trap arm from the trap to the vent connection (wet or dry) has to meet the trap arm rules.

So the only mistake in the above layout is that the bath tub and the floor drain joined together without either being vented. If the floor drain weren't there, it would be fine. As it is, I'm not sure what problems may arise, perhaps that if you drain a full tub, the water will try to siphon the floor drain trap? The details are beyond my experience.

Cheers, Wayne

 

[Jman]

Hmm. I just figured there would be a vent at the start of the system that would supply air for the floor drain, tub, and toilet since the vented sink came afterwards in the chain. Sorry for this probably dumb question but how does something downstream supply air to something draining from upstream? Isn't it negative pressure that causes the vent to work? Or is it because the drain flowing from upstream doesn't actually fill the whole pipe with liquid, so the open air space left in the pipe allows the downstream vent to add more air as it rushes past?

 

[wwhitney]

For this answer, suppose the floor drain were not there, as it is connected at the wrong place. Then the two upstream most fixtures are the lav and the tub. You can't really say which fixture is more upstream; all you can say is that the lav/tub joint is the most upstream joint. Hence the requirement that one of those two fixtures (the lav) provides the vent for the whole wet vent system (and the problem with the floor drain joining upstream of the lav/tub joint).

Other than the fact that the vent is also a drain, and can therefore be connected horizontally to the tub trap arm rather than vertically, the wet vent for the tub through the lav drain provides the same air pressure relief for the tub trap that a dry vent would, when the lav isn't running. And the wet vent sizing rules take into account the water flow from the lav; a wet vent is allowed fewer DFUs of drainage through it than the same size drain would be allowed. So the wet vent is still able to do that while the lav is running.

Cheers, Wayne

 

[Jman]

Ok, I think Im understanding. So if the toilet would have been in between the lav and tub, it would not have worked because that would have been 3 fixtures tied to 1 wet vent. But since the toilet is after the lav it satisfies the 2 fixture to 1 vent requirement. Is that assumption correct? And thank you for the quick responses!

 

[wwhitney]

It's not a ratio thing, and the single dry-vented lav can wet vent the floor drain, the tub, and the WC. The issue is that each fixture needs to be vented before (dry vent) or as (wet vent) its drain joins another drain. That means the dry-vented fixture for the wet vent has to be one of the two upstream-most fixtures on the wet vent.

Cheers, Wayne

 

[Jman]

Ah ok. I get what you are saying. Thank you for clarifying that. The rest of the plumbing is all up to me now so let me ask you one more quick question then I won't take up any more of your time. My plan is to run the dry vents from the sinks and washer in 1 1/2" pipe up into the ceiling joist where they will tie in together and run at an 1/8 inch per foot rise over to where I will head out through the roof. Does that sound correct?

 

[wwhitney]

Yes. If your drain exiting the building is 3", then I think the (3) 1-1/2" vents could combine into a single 1-1/2" vent under the IPC, although I would say 2" or 3" is better. And shortly before the point where the vent exits the thermal envelope (your uppermost insulation), if you are in a cold climate you want to upsize the vent to 3" or 4" (not sure which) for the rest of the way through the roof. That is to reduce the possibility of the vent opening frosting closed.

Cheers, Wayne