Hidden challenges to rearranging basement bath fixtures

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simwanders

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My wife and I recently purchased and moved into a 120 year old home in Arvada, CO. The home was moved to its current location in the 1940s so the oldest plumbing is from that time.

I'm working on finishing the bathroom (plumbed as a 1/2 bath, expanding to 3/4) in the basement for the mother-in-law to move in and trying to assess whether to keep the project as simple as possible or if there's a small additional lift to make for a much better bathroom.

This is the existing plumbing with directions the drains travel as best I can guess from the shape of the pipe entering slab:
Basement bath after demo.jpeg


My initial plan was to cut out the floor drain (started) and install a schluter shower in that space, and then leave the rest alone - toilet back in place, updated and slightly larger sink/vanity, and maybe use the 1.5" in the SE corner to add a wet bar to the next room over (likely with an AAV).

Upon discovering that busting out the concrete around the first drain wasn't so bad (thanks in large part to advice found here), I'm considering the pros and cons of trying to rearrange things a little - the existing layout makes for an awkward bathroom, but there's plenty of space to make it great. Here are the competing draft layouts:

As is, adding shower:
Screen Shot 2022-05-12 at 5.38.06 PM.png


Improved (I think) by moving drains:
Screen Shot 2022-05-12 at 5.41.25 PM.png


I suspect that there are many hidden challenges to a project like this and am hoping to get some sense of them before throwing myself in over my head. A few questions that stand out:
- Will it be possible/practical to basically flip/flop the drain directions branching off the horizontal 3" cast?
- Will I suddenly find myself replacing the entire cast iron drain line to make something like this work?
- Seems a stretch, but is it possible to just rotate and then reseal the presumed existing 3" wye for the toilet in order to move it to the other side of the main drain line?

Other tidbits:
- There is another floor drain in the basement 15 ft from the one I'm converting
- We are pressed to finish this bath before redoing the one above it by family needs. I will likely use a few AAVs to vent fixtures in the interim and then when we update the bath upstairs will tie these vents into the main stack.
- If we rearrange, will ensure 2" drain for shower, if not, will use existing 1.5" cast

Sorry for the long first post - trying to make sure all relevant info is included. Appreciate any insight or input and let me know what I've left out.
 

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John Gayewski

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There is nothing draining (from above) into that pipe your calling a vent stack?
 

simwanders

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There is nothing draining (from above) into that pipe your calling a vent they're
Good question - There is a main floor bath immediately above that drains into it (toilet, tub/shower, lav). Should have posted a better pic (and used correct terminology). Here's the full view:
NE Stack.jpeg
 

wwhitney

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As the the stack is carrying drainage from above, it is not useful for venting your basement fixtures. So right now as drawn neither the lav nor the WC is properly vented. You are most likely going to have to break up a fair amount of concrete to resolve that. Perhaps you can confirm whether the way the WC connects is as drawn via a short inspection camera into the closet bend.

What you need to end up with is:

- A clean out at the base of the drain stack from above, which is accessible from within the finished bathroom

- A vent for the lav, which can be an AAV underneath the lav, or a vent through the roof.

- The WC needs a vent, which is typically done via wet venting by the lav. But that requires the bathroom fixture drains (fixture drain = just 1 fixture) to combine together into a bathroom branch drain before that branch joins the building drain (the horizontal drain under the slab carrying everything). So any fixture (WC or shower) that is to the left of the stack in the picture, the fixture drain is likely to have to cross over the building drain. Hopefully the building drain is deep enough for that to be possible.

- The shower needs a vent, too, but the lav can wet vent it as well. The important point is that the lav joins the WC or shower first, and then the other fixture (shower or WC, respectively), and the combined drain joins the building drain.

Cheers, Wayne
 

simwanders

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That all makes good sense and thank you! Here's a rough sketch to make sure that I'm understanding correctly:

Basement redesign plumbing v1 - jpg.jpg


A few follow up questions:
- Is it possible to turn the existing WC branch 180° and reseal to use it as the start of the bathroom branch drain? I imagine getting it loose, turned, and resealed might be prohibitive but might save the challenge of installing a new branch drain. Will look into a short camera run to confirm how that all connects.
- Is the wet bar drain as drawn permissible? I think it will need an additional AAV given distance from the other side of the wall (approx 8ft) but not sure what that does to the wet vent as described for the WC and shower.
- Is there a better place for the clean out that doesn't involve tearing into the vertical stack?

Thank you again for the quick and thorough response!

Sim
 

wwhitney

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- Depends on what you have under the slab, but assume no. With no hub cast iron, easy to do, but I doubt you have that. With hub cast iron, no.

- No, the wet bar drain needs to tie in downstream of the lav/wc/shower. Horizontal wet venting is limited to bathroom fixtures, so the bathroom has to be separate from other fixtures. You could route the shower the other way around the 3" combo, and then the bar sink can parallel the bathroom branch drain until downstream of the WC. Note the shower trap arm extends from the trap outlet to the wye where it joins the WC/lav, and that trap arm is limited to one pipe diameter of fall.

- Not that I can see. But you'll be breaking into the horizontal drainage in the slab near the slab entry. So it won't be hard to take out the bottom of the stack, one end will already be free. It's critical to properly support the weight of the stack above before disturbing the stack.

Cheers, Wayne
 

simwanders

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- Depends on what you have under the slab, but assume no. With no hub cast iron, easy to do, but I doubt you have that. With hub cast iron, no.

- No, the wet bar drain needs to tie in downstream of the lav/wc/shower. Horizontal wet venting is limited to bathroom fixtures, so the bathroom has to be separate from other fixtures. You could route the shower the other way around the 3" combo, and then the bar sink can parallel the bathroom branch drain until downstream of the WC. Note the shower trap arm extends from the trap outlet to the wye where it joins the WC/lav, and that trap arm is limited to one pipe diameter of fall.

- Not that I can see. But you'll be breaking into the horizontal drainage in the slab near the slab entry. So it won't be hard to take out the bottom of the stack, one end will already be free. It's critical to properly support the weight of the stack above before disturbing the stack.

Cheers, Wayne
Got it. This is super helpful. Going to do some more figuring about what makes sense in the space and will be back. Really appreciate your help.
 

simwanders

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Alright, I'm back.

Here is an updated drawing based on the feedback I've received here:

Basement .jpeg


It seems that given the extent of work that this is going to take, I should make sure to plan as many future plumbing possibilities into this basement job as I can. A few things that I'd like to make possible through this process:

- Possibility to remove the main floor bath that is immediately above the basement down the road. It is a poorly laid out bathroom off of the kitchen and we'd eventually like to expand the kitchen back into that space. Any reason that I couldn't eventually remove the existing vertical stack and cap it given this layout?

- Possibility to make the next room over in the basement into a proper kitchen with sink and dishwasher for a rental/in-law unit. Would imagine venting it back to the new vertical 3" stack.

- Possibility to put a second main floor bath immediately above the basement kitchen (immediately behind the wall to the right of the proposed 3" stack and on the floor immediately above this basement). I imagine this one is a little harder to answer given lack of detail on the exact layout, distance from the stack, joist direction (they run left to right in this photo, perpendicular to the furring strips you can see in the pic), etc. But any thinking on the feasibility of putting a bathroom into that space would be appreciated along with any questions that might clarify my thinking.

- Lastly, can I cap the new 3" stack with an AAV for the time being and then extend it through the roof when I tackle the main floor projects a little way down the road?

All of this makes me wish I had a lot more money and could do it all in one fell swoop rather than staging it out like this, but c'est la vie I suppose.
 

John Gayewski

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The basement kitchen sink needs a vent. I would figure out something different for the shower your doing 360° worth of turns there. 180° on the trap arm alone (shower) which needs to be less than 8ft long.
 

simwanders

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The basement kitchen sink needs a vent. I would figure out something different for the shower your doing 360° worth of turns there. 180° on the trap arm alone (shower) which needs to be less than 8ft long.
That makes good sense - thanks for that! Here's one more iteration removing 90° of turn from the trap arm and thinking a bit more about limiting concrete work. Still interested in any insights on the questions above and whether there are other better ways to do any of this.
Basement v3.jpg
 
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