Help me Correct a (Plumbing) Wrong...

[Autodidact123]

Occasional lurker and first time poster.

To begin, I wish to honor Terry Love (sadly deceased) and this amazing forum - what an incredible resource Mr. Love managed to assemble, a true tribute to the man who has helped so many!

Now, on to my inquiry...

So, one thing led to another and I now find myself needing to correct a drainage/venting problem.

The Situation

This matter involves a long and narrow (IOW tiny!) 3/4 bath (8' x 4') located on the ground floor above a crawlspace in one-half of a side-by-side/townhouse-style two-story duplex. As shown below, the original toilet only provided ~14" of clearance in front of the bowl - IOW from the nose of the bowl to the wall there was so little clearance one had to basically shimmy past the toilet to go to or from the shower. How this ever passed inspection I'll never know - and an inspection was very likely conducted given that this bathroom was created as part of a post-fire renovation funded with insurance money (from what I've been able to gather, this occurred about five years before I acquired the property).

Here are a few shots of the bathroom:

The Issue

After purchasing a new toilet (keep reading) I discovered - I know, poor planning on my part - that the existing run of waste and soil pipe serving ths bathroom is flawed in its execution.

I should note that the exsiting branches serving the sink. the shower and the vent are all 2" Sch 40 PVC (thank goodness!) while the run from the toilet is 3" Sch 40 PVC.

Below, I've roughly hand-drawn the current drain layout (overhead view) and have also annotated some photos (compare to the drawing for context) to assist folks in hopefully seeing what I'm seeing. This looks to me like a boneheaded attempt at venting all three fixtures using a single vent (a combination dry vent and wet vent scenario) gone horribly awry.

From what I can gather, the shared vent is flawed because it goes horizontal when its still beneath the bathroom floor. As I understand it, vents can't turn horizontal until they reach 42" above the finished floor or 6" above the highest flood plane of the fixture(s) being served. I already addressed this exact problem in the ongoing kitchen renovation - the original vented kithen sink was located beneath a window and, among other problems, its vent turned horizontal well below the elevation of the rim of the sink. I fixed that (and the other problems) and the new installation now conforms to code (IPC in my state, I should note).

The Solution (at least the approach I'm thinking of taking - this is where I need advice)

I obviously want to address this latest issue.

As part of the larger renovation project that I'm accomplishing myself (jack of all trades with former pro-carpenty experience) - and to address the toilet clearance issue - I purchased an in-the-wall carrier (Gerberit for 2x4 wall) and the shallowest compatible wall hung toilet I could find (Duravit ME Compact) - this combination will provide over 22 inches of free area in front of the new toilet. Accordingly, I need to move the toilet riser from it's present location rearward into the center of the interior 2x4 wall (the wall located directly behind the existing toilet); in essence, shifting the riser's location 12-1/2" to the rear - the distance that the original riser was from the face of the wall framing (the orignal installer got one thing right).

To accomplish this, I think I can simply cut out the relevant soil and drain fitings and essentially shift the remaining components downstream to make up the difference between the orginal use of a sanitary tee laying on its back (which didn't meet code given that the distance from the rim of the closet flange to the center of the horizontal run of 3" pipe exeeded 12" - it was actually over 14 inches) and reliance instead on a combination tee (keep reading).

As an aside, I also want to change out the sink (for a shallower wall-hung version) and move its location a bit closer to the door (to provide proper space between it and the toilet) and will be relocating its riser plus running the copper supply pipes from where they currently emerge up through the floor into the wall so that, in the end, nothing will be mounted to the floor - everything will be wall-hung (and this includes a short of run of hydonic baseboard heat that I intend to run along the 4' length of wall next to the door; the supply and return will come up through that wall - another interior 2x4 wall - to feed it.

So, here's my rough drawing showing the current drain layout (overhead view):

The lower right hand corner depicts the bathroom door. The upper left hand corner is the shower. The upper right hand corner is the plumbng chase that conceals the shower'shot and cold water supplies and also the vent. To the rght is the wall to the bathroom where the sink riser is located (and where I intend to locate the riser for the in-the-wall toilet tank/carrier). The carrier wll be concealed behind a piece of cabinet grade birch plywod that will cover the entire installation making for simple removal should any part of the carrier or associated plumbing need to be accessed in the future (the birch panel will be screwed to the framing using stainless steel screws and finish washers, this will offer a stable mounting surface for the wall-mounted toilet and give me some piece of mind about any future need to access the entire installation.

And here are the annotated photos accompanying the drawing (I tried to match the terms used so that folks can bettre visualize what I'm seeing):

Here's the original 3" sanitary tee w/cleanout and attached toilet riser (in correct orientation):

Looking to the right, we can see the relative locations of the shower p-trap and riser and vent (both the horizontal run and where it turns and heads up to the roof):

Assuming I can get the drainage slopes right (which I should have no problem doing given that, if need be, I can drop the entre assembly down to lower starting and ending elevations - I have that flexibilty as shown in the photo depicting the access to the crawlspace) it seems the most obvious approach is to cut off the existing p-trap serving the shower and glue in its place another p-trap that will face the location of the existing vent (where it turns vertical for the run to the roof). Then I can connect the shower's trap arm to the vent via a sanitary tee (oriented vertically) and then connect the outlet of that a horizontal run of 2" pipe that heads toward the 2" connection on the 3x3x2 wye. A 45-degree albow at the end of that run of 2' pipe will turn the corner so that it can connect to the 3x3x2 wye located just downstream of the toilet.

Oh, in the image below (which depicts my proposed solution), the highlighted components depict my reuse of exisiting components - old work - while the non-highlighted components depict new work:

As for the connection to the in-the-wall toilet, I figure I can use a 3" combination tee laid on its side (fitted with a clean-out) connecting upstream of the aforecited 3x3x2 wye to a long sweep 90-degree elbow, the latter of which will connect to the new toilet riser which, itself, will emerge dead center through the bottom plate of the 2x4 wall immediately behind wherer the oroginal riser was located (sadly, the framing of this interior wall is nominally dimensioned unlike the native framing used pretty much everywhere else - the OD of 3" Sch 40 being 3.5" and all).

As an aside, I intend to replace the existing sink/cabinet with a shallower wall-mounted unit (to further improve access to and from the toilet and shower) and will need to relocate the existing sink riser (moving it along the wall closer to the door). Thus, this approach also plays well with with the need to relocate the sink riser given that I'm already shifting the drainline assembly in the direction of the door anyways. The existing sink riser is not anywhere close to centered on the sink so I want to fix this too.

The 2" and 3" hub couplings shown in my drawing depicting my proposed approach speaks to my intent of reusing as much of the existing plumbing assembly as I can. Note - I can't account for the origins of the brown staining which covers much of the existing PVC but, assuming it scrubs off, then I'll be reusing what I can.

A quick install of some LPV flooring over the existing linoleum (I don't have time to tear into the floor right now) will, along with tiling the shower surround, finish up this bathroom sub-project.

Given the nothing will be touching the floor post-renovation I can come back at a later date and properly address the slope in the floor (it needs the joist to be shaved to make it level) followed by tileing it - a job faciliated by the future ease of pullng the wall-mounted sink and wall-mounted toilet - I'll have ready access to the entire floor in just a few minutes.

OK, is my approach sound? What did I get wrong? Is there a better solution?

I don't beleive the sink needs its own (studor) vent but that could be easily accomplished. They're approved locally and I don't mind using one in this situation.

Please know that I am grateful for whatever guidance folks can provide.

 

[GReynolds929]

It'll be pretty amazing if you can fit a 3" pipe, elbow, wc carrier, and in wall tank in a 2x4 wall. I've only seen them in 2x6 or bigger.

 

[Sponsor]

 

[wwhitney]

Your drawing is acceptable DWV-wise for the shower and the WC, if you have the necessary height to accommodate the fall of a san-tee plus LT90 to go back horizontal. There are solutions for a vet take off on a horizontal trap arm where the drain path remains horizontal throughout.

As for the lav, it absolutely needs its own vent. Have you opened the wall behind there to see if it has a vent? If not, you need to add one, which can be a normal dry vent that reconnects to your vent in the corner, or an AAV, if your jurisdiction allows them.

Cheers, Wayne

 

[Autodidact123]

It'll be pretty amazing if you can fit a 3" pipe, elbow, wc carrier, and in wall tank in a 2x4 wall. I've only seen them in 2x6 or bigger.

Yeah, there are two versions available; one designed for 2x6 walls and the other designed for 2x4 walls. Pretty neat design overall - I'm looking forward to installing it.

 

[Autodidact123]

Your drawing is acceptable DWV-wise for the shower and the WC, if you have the necessary height to accommodate the fall of a san-tee plus LT90 to go back horizontal. There are solutions for a vet take off on a horizontal trap arm where the drain path remains horizontal throughout.

As for the lav, it absolutely needs its own vent. Have you opened the wall behind there to see if it has a vent? If not, you need to add one, which can be a normal dry vent that reconnects to your vent in the corner, or an AAV, if your jurisdiction allows them.

Cheers, Wayne

Nope, no lav specific vent - just what's shown in my drawing and photos. That said, what I failed to mention is that there is another vent (a dry vent serving both the kitchen sink that's located in that same residence - on the ground floor - and a washing machine in that unit's basement - the 2" pipe entering from the right in the photo showing the access to the crawlspace is the outlet of that associated drain (though it reduces to 1-1/2" as it approaches the kitchen sink); that 1-1/2" dry vent is located upstream maybe twenty feet from the lav in question) - plus, to the left of that same image and downstream about six feet away and on the other side of the party wall that separates the two units there's a main stack (old 4" cast iron) where all soil and wastewater drains from both units terminate (the two units share a single sewer lateral). I suspect that both of those act together to supply that lav with some "makeup" air. Or am I incorrect? Does it still needs its own vent? If so, I'm intrigued by the recessed AAV boxes and will likely opt for one of them, since that way the device is hidden (but easily accessible):

https://www.zoro.com/studor-1-12-or...torykitchen-mini-recess-box-20381/i/G7241967/

So, in summation, the two family property has a total of two full baths (2 toilets, 2 lav sinks, two tubs/showers all located on the second story and all vented by the shared 4" main stack), one ground floor 3/4 bath (venting as already discussed), two front loading washing machines (one directly wet vented by the main stack and the other by the aforementioned dry vent serving the kitchen sink which, BTW, ties in the attic into the vent serving the 3/4 bath), and one dishwasher (soon to be two) - the existing one vented along with a kitchen sink by an AAV and the other to be vented via the aforementioned dry vent off the kitchen sink.

Oh, and this property also has a house trap (4") that's vented with an enormous 4" vent. Given that vent's proximity to the stairs leading to one of the basements, someday I'll get around to cutting in a run of 2" vent to make it less obtrusive. Almost twenty years ago I stupidly replaced the housetrap after the original one rusted out - had this forum been in existence then I would have been able to learn that a) they're not required any longer by code in this area and b) that if I'd removed it I could have also jetisoned the vent. Oh well. Now the "new" housetrap will well outlive me (a.k.a "it's the next guy's problem").

My apologies for neglecting to mention these additional features.

Thanks so much for your expert guidance! I'm relieved to have received confirmation of the correct path forward.

 

[wwhitney]

. . . I suspect that both of those act together to supply that lav with some "makeup" air. Or am I incorrect? Does it still needs its own vent?

I did not unravel your lengthy textual description into a mental picture because I expect the following rule will give you the answer:

Any fixture trap needs to have its vent (wet or dry) connected to the fixture drain before that drain has fallen more than one pipe diameter from the trap outlet. So any drains or vents connected to the lav drain under the floor can not vent the lav.

Cheers, Wayne

 

[Autodidact123]

I did not unravel your lengthy textual description into a mental picture because I expect the following rule will give you the answer:

Any fixture trap needs to have its vent (wet or dry) connected to the fixture drain before that drain has fallen more than one pipe diameter from the trap outlet. So any drains or vents connected to the lav drain under the floor can not vent the lav.

Cheers, Wayne

Wayne - thanks so much for reinforcing that rule; it makes complete sense now.

Also, for a update, after opening the wall to modify the stud framing to accept the toilet carrier, I stumbled upon an 1-1/2" vent emanating from the sink (!). I'd relied earlier on peering through the rough cutout in the sheetrock where the drain from the sink enters the wall - in essence using a flashlight in an attempt to examine the in-wall connection. Well, I should have relied instead on my borescope since I clearly missed the existence of the vent. It turns out that, like most of the wall cavities in this unit, this wall cavity and everyting within it is painted with primer (somebody went nuts with a sprayer when the walls were still open), the net effect of which is that the vent blended in perfectly with the background, making it essentially invisible.

So, the good news, having since explored the wall cavity with my borescope, is that the sink vent exists and is correctly plumbed (it extends vertically from the top of a vertically oriented sanit-tee and doesn't go horizontal until many feet above the flood rim of the sink).

However, the bad news is that the Geberit in-wall toilet carrier I was sent is defective. It turns out that the German-made (at east that's what everyone keeps telling me) steel frame, when measured diagonally - and those measurements compared - is at least 6mm out of square. This results in a badly twisted frame which is all out of whack. I didn't realize the extent of the problem until I dryfit the carrier into my new wall framing but it's all screwed up. Hence, the carrier is going back to Geberit USA and a replacement is being shipped to me from the orignal retailer. Not at all a good first impression - this happens to be my first experience both with Geberit and the authorized online retailer I purchased from. A big part of the reason I paid the premium price for Geberit's carrier (rather than opting for one produced by one of their Chinese competitors) was to avoid exactly the mess I now find myself in. As a result, my confidence in Geberit is shattered.

As sad as it is, I guess the moral of the story is that literraly everything I don't make myself needs to be double and triple checked to ensure that it's not defective. I had a similar experience with a commerical kitchen sink I used in this same renovation. Two that were sent to me within a week of each other were both defective. I refused the first one which led to the second one being sent (which I also had to refuse) leading, thanks only to my persistance, the well known manufacturer (or at least I thought they were the manufacturer - turns out they were relying on a Chinese factory) to discover that they had an entire warehouse full of defective sinks. Resoluton of that saga took many months but should have taught me to not trust anything that I don't build with my own two hands. I guess, that's the reality of the situation we now find ourselves in - we need to question literally everything. What a mess. So, I've swiched back to building cabinets while I await arrval of the replacement carrier.

Thanks again.

 

[Paulypfunk]

If you are on the fence I might advise against using a Geribit in wall carrier. They are fussy and a pain to install and IMO they don’t flush all that well. If you need to work on anything inside the tank I hope you have a coordinated ten year old on retainer to get their hands inside the tank opening.
Also, the wall framing the carrier hangs on has to be ROCK SOLID! The problem with 2x4 framing is that it can flex. If your framing is flexing then your toilet is going to sag off the wall, or damage the drywall or pop tile seams. At the very least the caulk line behind the bowl tends to keep cracking open.
The design is kind of neat so I understand their appeal, but be sure your framing is reinforced. And also clear your schedule the day you plan to install the thing. And measure three times, cut once.