Drain and Venting Plan Advice - 1/2 Bath & Laundry

[Bbradyc5]

Ok looking for some advice on how to route drains and vents on my new half bath backing up to new laundry area that already have under slab sanitary line connections roughed in. Included pic to try and show how they connect to main sanitary line. Particularly interested in how/what fixtures to group. 4” for toilet and other two drains are 2” shown in pics. I am guessing there are more than one way to skin this cat so I am very interested to hear suggestions on how you would tackle this.

 

[wwhitney]

Looks like your underslab layout is suboptimal. Tell me if you agree that the pictures show that the 2" line directly behind your WC (the one by the cold supply stub up, I'll call it A) connects to the WC first, and then the other 2" line (the one by the red supply stub up, I'll call it B) connects to the combined drain downstream of that.

That connectivity means that A has to be your lavatory drain to wet vent your WC. Then B can be your laundry standpipe or your laundry sink. Which is backwards of what is desired. So if you don't want to break concrete, for the layout drawn you'll have to have the drain lines A and B cross each other. Since I don't see any rough ins for vents, I assume you'll be using AAVs?

If you're OK with exposed plumbing on the laundry room side, then you can jog B out of the wall towards the laundry, and then have a san-tee for your laundry standpipe or laundry sink, and a riser to an AAV. Your lavatory trap can be vented by an AAV under the sink, and the fixture drain can go horizontally through the wall to turn down to A. If you don't want exposed plumbing on the laundry room side, the simplest thing would be to furr out the wall by 2.5" (or just build another 2x4 wall against the existing wall).

Also, with just a single 2" stub out, you can only have one trap on the laundry side. That's because the IPC (in force in MI) requires that when a laundry standpipe fixture drain meets another drain, the combined drain is enlarged to 3". So one option is to just put in a laundry tub and drain the washing machine to the tub. The other option is to have the laundry tub share the laundry standpipe's trap, that's a newish option under IPC 802.4.3.1. This link explains it:

http://media.iccsafe.org/news/icc-enews/2018v15n13/2018SC-IPC802.pdf

Cheers, Wayne

 

[Sponsor]

 

[wwhitney]

An alternative to having the 2" drains cross each other in the wall is this:

Put your laundry standpipe and trap in the wall where you want them, with the trap on the higher side of the typical range (say 18" above the floor). You can have a san-tee directly over the B stub up, and a riser to an AAV in a ventilated box in the wall.

The the lavatory drain (A) going upstream can just turn horizontal (medium 90) below the standpipe trap and trap arm. Once behind the vanity cabinet, rise up a bit if necessary (LT90 or 45) and then emerge from the wall with a medium 90. Then your AAV is on the trap arm in your vanity cabinet. I guess if the heights work out right, you could just start at the slab, hit a low 45 or 60, and then hit a medium 90 to come out of the wall into the vanity cabinet, that would be fewer elbows.

Cheers, Wayne

 

[Bbradyc5]

Looks like your underslab layout is suboptimal. Tell me if you agree that the pictures show that the 2" line directly behind your WC (the one by the cold supply stub up, I'll call it A) connects to the WC first, and then the other 2" line (the one by the red supply stub up, I'll call it B) connects to the combined drain downstream of that.

That connectivity means that A has to be your lavatory drain to wet vent your WC. Then B can be your laundry standpipe or your laundry sink. Which is backwards of what is desired. So if you don't want to break concrete, for the layout drawn you'll have to have the drain lines A and B cross each other. Since I don't see any rough ins for vents, I assume you'll be using AAVs?

If you're OK with exposed plumbing on the laundry room side, then you can jog B out of the wall towards the laundry, and then have a san-tee for your laundry standpipe or laundry sink, and a riser to an AAV. Your lavatory trap can be vented by an AAV under the sink, and the fixture drain can go horizontally through the wall to turn down to A. If you don't want exposed plumbing on the laundry room side, the simplest thing would be to furr out the wall by 2.5" (or just build another 2x4 wall against the existing wall).

Also, with just a single 2" stub out, you can only have one trap on the laundry side. That's because the IPC (in force in MI) requires that when a laundry standpipe fixture drain meets another drain, the combined drain is enlarged to 3". So one option is to just put in a laundry tub and drain the washing machine to the tub. The other option is to have the laundry tub share the laundry standpipe's trap, that's a newish option under IPC 802.4.3.1. This link explains it:

http://media.iccsafe.org/news/icc-enews/2018v15n13/2018SC-IPC802.pdf

Cheers, Wayne

Thanks for the feedback Wayne, not sure if it makes a difference on your assumptions but all three lines (WC, and both 2" lines are independent of each other and connect directly to the main sanitary line (sorry for ultra crude mark-up). Laundry side will definitely be finished and I want to avoid having to bump wall out. Are AAV's acceptable as my vents or is there any reason I cannot extend the two 2'' (A&B) lines up (one going thru roof) and connect them horizontally?

 

[wwhitney]

The issue is that water that goes down W will first hit the junction with A, then the junction with B. What happens downstream of that doesn't matter. Because it hits A first, A has to be your lav drain to provide a WC vent via horizontal wet venting. The IPC restricts horizontal wet venting to bathroom group fixtures; the laundry can't drain through the wet vent , so B can't be your lav drain.

As to venting, the two vents (for A and B) can combine at any elevation 6" above the flood rim of the associated fixtures. And if you'd prefer to vent out the roof rather than use an AAV, that's fine. AAVs are allowed under the IPC, so unless MI has an amendment about them, one or two AAVs would be fine.

Cheers, Wayne

 

[Bbradyc5]

The issue is that water that goes down W will first hit the junction with A, then the junction with B. What happens downstream of that doesn't matter. Because it hits A first, A has to be your lav drain to provide a WC vent via horizontal wet venting. The IPC restricts horizontal wet venting to bathroom group fixtures; the laundry can't drain through the wet vent , so B can't be your lav drain.

As to venting, the two vents (for A and B) can combine at any elevation 6" above the flood rim of the associated fixtures. And if you'd prefer to vent out the roof rather than use an AAV, that's fine. AAVs are allowed under the IPC, so unless MI has an amendment about them, one or two AAVs would be fine.

Cheers, Wayne

Got it thanks again. I think I am going to see if I can find a way to run lav drain over to “A” to wet vent the WC and then try to implement the new alternative IPC method you listed where the utility sink will connect to laundry drain w/o trap. I like the idea of using AAV’s instead of having to penetrate flat roof of garage. The Michigan code states

P3114.7 Vent Required
Within each plumbing system, not less than one stack vent or a vent stack shall extend outdoors to the open air.

...So my question would be is this considered part of the main house plumbing system even though it is a detached garage and therefore I can claim that this code is covered by main roof vent in house.

 

[wwhitney]

Yeah, I don't know the answer to that one, I can see arguments both ways. You don't have any plumbing vents through the roof in the detached garage?

I think my second suggestion is a better layout, and you can use an AAV in the lavatory cabinet, independent of whether you vent the laundry standpipe via a roof vent or via an AAV.

Cheers, Wayne

 

[Plumber01]

...So my question would be is this considered part of the main house plumbing system even though it is a detached garage and therefore I can claim that this code is covered by main roof vent in house.

In my area, it's ok to use the house venting to count as long as the main line from the garage ties into the main line from the house. Cross sectional area must still be met though which isn't usually a problem.

Best to check your local codes though.

 

[Bbradyc5]

In my area, it's ok to use the house venting to count as long as the main line from the garage ties into the main line from the house. Cross sectional area must still be met though which isn't usually a problem.

Best to check your local codes though.

Ok thanks, that gives me a bit of confidence to that angle if it comes up.

 

[Bbradyc5]

The issue is that water that goes down W will first hit the junction with A, then the junction with B. What happens downstream of that doesn't matter. Because it hits A first, A has to be your lav drain to provide a WC vent via horizontal wet venting. The IPC restricts horizontal wet venting to bathroom group fixtures; the laundry can't drain through the wet vent , so B can't be your lav drain.

As to venting, the two vents (for A and B) can combine at any elevation 6" above the flood rim of the associated fixtures. And if you'd prefer to vent out the roof rather than use an AAV, that's fine. AAVs are allowed under the IPC, so unless MI has an amendment about them, one or two AAVs would be fine.

Cheers, Wayne

OK would appreciate a review of what I ended up with. Everything is dry fit right now. I went with the strategy to wet vent the toilet and bath sink and then do the laundry sink and washer per the IPC alternative as shown in attached image. Both bath and laundry vent pipes will terminate to AAV’s in wall boxes. I’m sure i exceeded the wall stud notching limits but I will add reinforcement plates if the inspector has an issue (it’s a non load bearing wall). Appreciate the feedback and my first go at doing rough in plumbing so hopefully it’s not too hack

 

[wwhitney]

I don't see any plumbing violations. I guess you didn't like my suggestion to allow you to avoid crossing the drain lines in the wall.

That one stud with notches on opposite sides, I would definitely reinforce that. Looks like a 2x6 with 2-1/2" notches, so only around 1/2" of material in the middle. Maybe a couple Simpson HSS2-SDS1.5 on the two notches.

Cheers, Wayne

 

[Bbradyc5]

I don't see any plumbing violations. I guess you didn't like my suggestion to allow you to avoid crossing the drain lines in the wall.

That one stud with notches on opposite sides, I would definitely reinforce that. Looks like a 2x6 with 2-1/2" notches, so only around 1/2" of material in the middle. Maybe a couple Simpson HSS2-SDS1.5 on the two notches.

Cheers, Wayne

Thanks again, i couldn’t visualize your option and i figured this was the safe way I knew I could get everything connected. Will definitely reinforce stud and appreciate the suggestion. Definitely a big help on this first foray for me.