Second floor bathroom group with a horizontal Wye

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Ken Dahl

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I am doing a bathroom add-on to the second floor of a two-story home. Thus, my
options are a bit limited as far as where I put the drain lines and drain stack.

This all boils down to the use of a wye to combine the toilet drain and other bathroom drains on a horizontal. I just don't know how to do it.

I have a 3 inch stack that has been prepared especially for the new upstairs bathroom. So I need to drain a toilet, lav, and shower to the same place if possible, i.e. all three draining to the same horizontal line and into a 3 inch san tee. I planned to have the toilet flange about 2 feet from this soil stack.

The stack and the 3 inch sanitee I need to dump into. Notice the 10 inch spacing:
bath2-01.jpg


I was going to use this stack vent for the toilet. I guess if the toilet is vented elsewhere (see below) then this vent would not be necessary.
bath2a.png


I attached a drawing of the floorplan. The shaded red/pink area is where the soil stack is. Note the double wall there (a 2x4 and a 2x6). I also took some pictures of my dry run.

bath2-02.jpg


Closeup:
bath2-03.jpg


From the foreground:
  1. A 2x2 san tee with a 1 1/2" vent for the shower
  2. That's a 2 inch pipe horizontal, carrying shower waste
  3. A 2x2 combo with 1 1/2" swept in for the lav drain.
  4. More 2 inch pipe, carrying shower+lav waste
  5. A 3x3x3 wye, 2" main inlet, 3" inlet from toilet
  6. To the left is the toilet flange to a closet bend (hidden)
  7. The 3" drain continues to the waste stack, but it needs a horizontal 45 degree turn to get there
  8. The 3" waste stack has a 3x3x3 san tee, with a 2 inch bushing on the top for the vent.
I thought I had everything planned out correctly, but I am not exactly sure on the 3 inch toilet drain where it combines with the 2 inch horizontal drain from the shower and lav.

At some point I thought that the closet bend was going to be super close to my planned 2x3x3 inch Wye. But at the current configuration, I had to cut a 9 inch pipe. I guess I should ask if this is ever a permitted situation before I ask about the 9 inch spacing. With some work, I could reduce the distance from the closet bend to the wye to virtually nothing.

If this configuration won't fly, maybe I could replace the closet bend with a side-inlet 3x3x2 elbow? And send the lav/shower into the side of that fitting?

Or if I increased the size of drain/venting for the lav to a 2 inch, would that now make the toilet wet vent back upstream through the lav's stack? I believe this would be around 4 feet of wet venting for the toilet.

I guess if the wet venting is a problem, I could start the 3 inch drain where the lav is... since I was using a 3x3x3 wye with a 2x3 bushing anyway. Does a bushing cause this type of vent to be restricted?
 

Terry

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You can go six feet before venting the toilet.
The lav and the shower are venting the toilet, assuming you bring those vents up, tie together at 42" or higher and then vent through the roof. Or revent them to the existing 2" vent that you started with.
 

Ken Dahl

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Thank you Terry! That sounds good. It never dawned on me until afterward that the lav's drain was venting the toilet, too. It certainly is close enough. When I did the downstairs plumbing, I chose to increase the lav's drain to 2 inch to wet vent a new toilet down there. I used a 3x3x2 inch combo there as the situation was reversed: the sink flowed into the toilet's horizontal waste line. (whereas on the second floor here, I have less room plus the toilet needed to flow into the lav/shower horizontal drain line)

So.... do I need to increase my vanity sink's drain to 2 inch? It's just 1 1/2". My understanding was that by increasing the wet vent's drain, my toilet's vent becomes (more) assured.

As for the actual venting, it sure seems like the toilet doesn't "know" which direction its vent is, and so it would actually be vented at the lav, the shower's vent, and at the stack vent simultaneously, unless one of those pipes are somehow full of waste/soil. The shower's vent may be a bit of a stretch past 6 feet. When I started this layout, I was myself agnostic and thought of the stack vent as "the vent" for the toilet. I am happy to learn it the correct way!
 

krik

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So.... do I need to increase my vanity sink's drain to 2 inch? It's just 1 1/2". My understanding was that by increasing the wet vent's drain, my toilet's vent becomes (more) assured.

Increase the wet vent section of the sink drain to 2" (I believe this is a requirement, not optional). Unless you can get the shower trap arm less than 6' from the wet vent tie-in, it needs its own vent. Change shower and wet vent tie-ins from santees to wye + 45, because you need to use waste fittings below the flood rim even if used only for venting. And don't forget about cleanout(s) for that 2" horizontal run.
 

Ken Dahl

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Thanks Krik. I will skip the cleanout, per the advice from others to skip it on 2nd floor drains. And I can't think of a place to put it anyway.

The 1 1/2" sink drain already had a combo... I can bump this up to a 2 inch as I thought was necessary. (Same setup downstairs)

The use of a wye+45 may actually make little difference over a combo, but due to space constraints trying to stick a fitting through the bottom plate of the wall, a 45 to a combo laid at a 45 degree angle may give me more room there. I don't see the need to use a wye/45 over a combination wye/45... not here or in most other places.

At first, I didn't understand your shower vent recommendation until I really thought about it. I have heard it said countless times not to put a sanitary tee on its back. (My logic went like this: This is a vent... use a sanitee here, combos are needed for drains. Oops.) I think there may be an exception in some people's minds in the vent stack, essentially in the attic (as you alluded to), but the more I study I now find that dubious... I would bet there are inspectors who would disallow any sanitee on its "back" even there. Because the more I think about it, anyone who tried to use the vent system to snake/unclog a drain, and they encounter a sanitee on its back... the snake will effectively be blocked. I know that's true with vent elbows, too, but that seems to be a good practice even in the attic. I understand it is fine for venting, but I can see how (1) it cannot be relied upon up in a vent stack that may need to be snaked and (2) it was "unsanitary" where I was going to put it.

So I thought a sanitary tee was supposed to be used for venting here. I want to say thank you for this insight and I will correct it. I am holding off on the completion of this bathroom now that I have the 3 inch wye glued in place and the toilet flange set.

I will switch to two combos or (45/wyes) in my system. The first is going to be a 2x2x 1 1/2" combo for the shower vent. The second will be a 2x2x2 combo for the sink (wet) drain. Both of these will probably not be set vertically, so I was thinking of adding a 45 at the bottom plate and doing some fancy gluing to make it all work back towards the eventual fixture locations.

Thanks everyone!!

Now, as an aside. In my case why cannot I use the 2 inch vent stack, just a few feet away, as part of the toilet vent calculation? Isn't the toilet being vented by the vertical vent stack? Is this just against the plumber's rules? Because surely the toilet can't tell where its vent is located! In other words, if this had no 2" horizontal pipe for venting and no inflow from the shower/sink, the actual vent would begin at the stack. If anything, the vent back to the sink is farther, possibly wetter, and around a 135 degree corner.
 

krik

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Now, as an aside. In my case why cannot I use the 2 inch vent stack, just a few feet away, as part of the toilet vent calculation? Isn't the toilet being vented by the vertical vent stack? Is this just against the plumber's rules? Because surely the toilet can't tell where its vent is located! In other words, if this had no 2" horizontal pipe for venting and no inflow from the shower/sink, the actual vent would begin at the stack. If anything, the vent back to the sink is farther, possibly wetter, and around a 135 degree corner.

Because this isn't so much about protecting the toilet trap itself, but rather to protect upstream fixtures from being siphoned when the toilet is flushed. Before water and waste reach the vertical stack they will create siphoning action on the upstream sink/shower portion, so those need to be sized appropriately to prevent that. If the sink and shower didn't exist then, yes, it would work as you explain.
 
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