Moving Toilet Location Under Slab

[Reach4]

If that line from above were draining a lavatory and wet-venting the toilet, then things would be done differently. Any thoughts on adding a lavatory?

 

[Girafdaniels]

I suggest rolling up the wye as far as possible while still maintaining 1" concrete cover on the pipe just before the elbow at the wall. [1" seems like it would work to me, depending on the floor covering, but I'm not a concrete expert.] Also, since you have a street 45 and a 22.5 in series on the wye branch inlet, you can play with those angles a little to be sure you get back to 2% slope as quickly as possible. You want all your elevation gain at the wye to be used for rolling the wye, minimizing the amount used by those two angles.

I assume you are going to back fill with clean soil or sand up to the elevation about 4" below the top of slab? You'll want to try to compact the fill, particularly under the pipes, which is one attraction to sand, it's easier to compact. To get the new slab to bond with the old slab, you want to be sure the old edges are rough, not smooth. You could epoxy in rebar stubs or (easier) add half-driven stainless tapcons along the edges for mechanical reinforcement and vertical locking but I'm not sure if that level of care is called for or not. Then you want to add a vapor barrier as was there previously (6 mil plastic is fine). For concrete, I'd suggest something like a 5000 psi bag mix, or maybe a mix with fiber (not sure). The important thing is not to use too much water, bread dough consistency is good.

Looks good, and good luck!

Cheers, Wayne

I was able to turn the wye up a little more, which you can see given the closer proximity of the 2” and 3” now that it’s all glued up. It all came together fairly well, given my limited experience and the benefit of your detailed advice.

Had planned to use the dirt/gravel mix I’d pulled out for fill before concrete, but like the idea of sand under the pipes, at the very least. Especially since I’m not readily able to compact anything under there now.

Was wondering about the vapor barrier treatment, so thanks for including that bit, too. I’ll try to tape it to the edges of the existing plastic, although I probably should’ve taken more care to cut it out cleanly.

Still need to add the 3” riser (I think it’s called?) to the elbow. Others here have suggested putting a “sleeve” around it before pouring concrete, but I haven’t been able to figure out exactly what that entails after looking through other posts/info. From what I’ve gathered, it’s a little foam wrap, that can be easily removed after concrete sets up...

Thank you!

 

[Sponsor]

 

[Girafdaniels]

If that line from above were draining a lavatory and wet-venting the toilet, then things would be done differently. Any thoughts on adding a lavatory?

Won’t ever add one that would use that line...

 

[Jeff H Young]

Kind of a pain in the butt Welcome to our world ! thats fine no problem .
Depending on the unseen piping having decent grade and normal turns , and what your thoughts are with a clean out . Id feel safe not having one

 

[wwhitney]

Others here have suggested putting a “sleeve” around it before pouring concrete, but I haven’t been able to figure out exactly what that entails after looking through other posts/info. From what I’ve gathered, it’s a little foam wrap, that can be easily removed after concrete sets up...

Good point, I forgot to mention that. A material like "sill sealer", the thin foam that goes between a mudsill and a concrete foundation, would be ideal, you could give it a spiral wrap with 50% overlap. You want to tape onto the pipe above the slab so it doesn't move around during the concrete placement, and then just cut off the portion above the slab. There's no reason to remove the part below the top of slab.

It's worth figuring out what your closet flange solution is going to be, and what the height will be. For example, if you want to use a 3" hub toilet flange, and the hub is going to go below the top of slab, you'll want to block out some of the concrete where the hub will go. A 3" DWV slip coupling (do those exist?) would be ideal, you could slide down so the necessary portion is below top of slab (1"-2"), tape it in place, and wrap it with the foam. In this case you'd remove the foam around the coupling below the slab.

Cheers, Wayne

 

[James Henry]

Unless you can snake that vent from the roof I suggest you put a clean-out in the wall. when the toilet backs up bad stuff will back up in the vent and may get stuck.

 

[James Henry]

Or put a clean-out on the vent in the attic.

 

[Jeff H Young]

Unless you can snake that vent from the roof I suggest you put a clean-out in the wall. when the toilet backs up bad stuff will back up in the vent and may get stuck.

there is an existing wye right next to the new one if that is served by C/O I wouldnt worry as its only 2 foot away but its always a good idea for a cleanout!

 

[Girafdaniels]

there is an existing wye right next to the new one if that is served by C/O I wouldnt worry as its only 2 foot away but its always a good idea for a cleanout!

I realized there's an exposed access to that vent line from the utility room next to the bathroom. So I'll skip adding the cleanout. Thanks for helping me think beyond what was right in front of my face!

 

[Girafdaniels]

Good point, I forgot to mention that. A material like "sill sealer", the thin foam that goes between a mudsill and a concrete foundation, would be ideal, you could give it a spiral wrap with 50% overlap. You want to tape onto the pipe above the slab so it doesn't move around during the concrete placement, and then just cut off the portion above the slab. There's no reason to remove the part below the top of slab.

It's worth figuring out what your closet flange solution is going to be, and what the height will be. For example, if you want to use a 3" hub toilet flange, and the hub is going to go below the top of slab, you'll want to block out some of the concrete where the hub will go. A 3" DWV slip coupling (do those exist?) would be ideal, you could slide down so the necessary portion is below top of slab (1"-2"), tape it in place, and wrap it with the foam. In this case you'd remove the foam around the coupling below the slab.

Cheers, Wayne

Very helpful.

Is the purpose of the foam sleeve, in this first case, to just keep the concrete off the pipe above slab? The pipe itself won't be moving much during the pour as it's pretty rigid with the current set up.

I'll sort out the closet flange before I pour the new slab. In some other threads, I've understood Terry to suggest that -- with modern toilets -- there's no real drawback to using a flange that fits inside a 3" pipe. Of course, that'd be an easier route and avoid blocking out concrete for an outside fitting. I actually had a 3" slip coupling in hand in case I needed it to tie in to the existing 3" drain line!

 

[wwhitney]

The primary purpose of the foam is this: concrete shrinks as it is curing. A hole in a shrinking material gets smaller when the material shrinks. So the concrete would start compressing the pipe. The foam avoids that.

For metallic pipes, the foam would need to be taped tight to keep concrete out, then it is also a barrier to avoid corrosion issues.

Cheers, Wayne

 

[Reach4]

I'll sort out the closet flange before I pour the new slab. In some other threads, I've understood Terry to suggest that -- with modern toilets -- there's no real drawback to using a flange that fits inside a 3" pipe.

I suspect he avoids gluing in an inside 3 inch flange on a new piping install. If you glue outside, then the inside could be used if the flange would need to be replaced in the future for some reason.
I wouldn't glue in an inside flange with a plastic ring, if you like to plan for contingencies.

 

[Girafdaniels]

The primary purpose of the foam is this: concrete shrinks as it is curing. A hole in a shrinking material gets smaller when the material shrinks. So the concrete would start compressing the pipe. The foam avoids that.

For metallic pipes, the foam would need to be taped tight to keep concrete out, then it is also a barrier to avoid corrosion issues.

Cheers, Wayne

Aha! Maybe I should wrap the 2” pipe that’ll be set within the slab, too...

 

[Girafdaniels]

I suspect he avoids gluing in an inside 3 inch flange on a new piping install. If you glue outside, then the inside could be used if the flange would need to be replaced in the future for some reason.
I wouldn't glue in an inside flange with a plastic ring, if you like to plan for contingencies.

Good point. I definitely like planning for contingencies, so this makes a lot of sense. Thank you for sharing.

 

[wwhitney]

Aha! Maybe I should wrap the 2” pipe that’ll be set within the slab, too...

Yes, it makes sense to wrap the upper half of the 2" elbow, I think. For the horizontal portions, just put your vapor barrier over the pipe, and pack underneath the pipe with soil/sand. With the concrete not encircling the pipe, the vapor barrier ought to be enough of a slip sheet.

The main downside of the concrete compressing the pipe isn't that it's going to crush the pipe (you can embed plastic conduit in slabs), it's that it will restrain the pipe. So if the pipe outside the slab wants to move for thermal or other reasons, that restraint can cause the pipe to crack as it emerges from the concrete.

Cheers, Wayne