Adding bathroom to detached building: Check my DWV design

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-dirt-

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Hi all:

I'm prepping for an addition to a detached building that we are converting to a guest studio/in-law suite. No plumbing currently to the structure, so will be framing up and pouring a ~ 5' x 16' slab adjacent to the structure with the drains and vent stubbed up in the slab pre-pour.

This will be for a small bathroom (shower, WC, and lav) plus a drain for the kitchenette/bar sink on the opposite side of the same wall. This will all drain to an ejector basin/pump to pump ~150' laterally, maybe 6' elevation, to the soil stack from the house to the septic tank.

I've sketched out what I think will work (attached). Please check to see if this is the most efficient way to handle this, as well as proper venting and use of fittings.

Thanks so much!

952fdbbc-ce90-42f8-b656-cf3efd427132.jpeg
 

wwhitney

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Up.codes says Alabama has adopted the IPC.

I'm not familiar with ejector pumps, so I can't comment on any of that. Is there a benefit to the 4" plumbing, or could it all be 3" and work just as well?

If you are dry venting the shower, the 2" wye has to be rolled up 45 degrees above flat. (So it's projected angle in plan view will be 35 degrees, not 45 degrees). If you use a 45 to turn horizontal in the slab, then when you turn up in the wall for the vent, the 90 should be a long turn 90. That's because you're below the flood level of the shower. [Those are UPC rules but I believe the IPC is similar.]

Where you have the two sink trap arms coming into a the common drain/vent, that fitting appears to be a double wye. It needs to be a double sanitary-tee or double fixture fitting. I've heard it can be difficult to rod through such a fitting and exit downwards as desired instead of across to the other sink. So it may be useful to add a cleanout just below the double sanitary tee or double fixture fitting.

Cheers, Wayne
 

-dirt-

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Up.codes says Alabama has adopted the IPC.

I'm not familiar with ejector pumps, so I can't comment on any of that. Is there a benefit to the 4" plumbing, or could it all be 3" and work just as well?

If you are dry venting the shower, the 2" wye has to be rolled up 45 degrees above flat. (So it's projected angle in plan view will be 35 degrees, not 45 degrees). If you use a 45 to turn horizontal in the slab, then when you turn up in the wall for the vent, the 90 should be a long turn 90. That's because you're below the flood level of the shower. [Those are UPC rules but I believe the IPC is similar.]

Where you have the two sink trap arms coming into a the common drain/vent, that fitting appears to be a double wye. It needs to be a double sanitary-tee or double fixture fitting. I've heard it can be difficult to rod through such a fitting and exit downwards as desired instead of across to the other sink. So it may be useful to add a cleanout just below the double sanitary tee or double fixture fitting.

Cheers, Wayne

Thanks Wayne! I'm fine with using 3" instead of 4" for the mini-mainline if that is accepted practice/code.

Thanks for the notes on the shower vent -- will be sure to take that into account.

I will replace the double wye in the wall for the two sinks with a double sani-tee and add a cleanout. Can the branch lines coming from the sides of the tee be 1.5" as long as the vertical run (down to drain, up to vent) remains 2"?
 

-dirt-

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I see a shower and a toilet upstream of the lav.

The shower is currently sketched out with a vent coming off just before the p-trap for the shower. Does this work?

Would eliminating that vent and instead putting one on the 3"/4? mainline at the top of the drawing where it runs under the wall be better?
 

wwhitney

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Thanks Wayne! I'm fine with using 3" instead of 4" for the mini-mainline if that is accepted practice/code.
3" is certainly all that the code requires. Whether there is a benefit to 4", I don't have the experience to know.

I will replace the double wye in the wall for the two sinks with a double sani-tee and add a cleanout. Can the branch lines coming from the sides of the tee be 1.5" as long as the vertical run (down to drain, up to vent) remains 2"?
Both of your vents only have to be 1-1/2" under the IPC. So your ideal fitting there is a 2" x 1-1/2" x 1-1/2" x 1-1/2" . Which is made as a double fixture fitting, but not as a double san-tee:

https://www.supplyhouse.com/Spears-P500-241-2-x-1-1-2-x-1-1-2-x-1-1-2-PVC-DWV-Double-Fixture-Fitting

Cheers, Wayne
 

wwhitney

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The only wet vented fixture is the toilet. The wet vent extends from the 2" wye that is the shower dry-vent take-off to the wye where the toilet comes in. The lav and kitchen sink are downstream of the wet vent, as required, and are dry vented.

So what's the problem?

Cheers, Wayne
 

-dirt-

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GH-plumbing.jpeg
I re-did the shower vent to change the wye to a sani-tee, so the vent line would exit the top of that drain line and the 90 over to the wall, then 90 up the wall.

Also, changed the double fixture setup for the sinks.

One big question: if I re-orient the bathroom to where the shower and sink positions are swapped (or the mainline runs the other way, whichever you want to look at it), would that necessitate a change in my purposed vents? since the WC will then run by the shower branch...

Thanks!
 

wwhitney

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I re-did the shower vent to change the wye to a sani-tee, so the vent line would exit the top of that drain line and the 90 over to the wall, then 90 up the wall.
So, the IPC maybe (probably?) allows what you've drawn. But using a wye rolled up 45 degrees, and a street 45 in it, would work better, as it would be a drainage pattern. Likewise when the vent enters the wall, a long turn 90 would be better.

The idea is suppose your ejector pump stops and the pit backs up and you don't notice until you see sewage in your shower. That sewage will also have backup up into the shower vent and around that 90 at the base of the wall. So when you clear the backup and everything drains, you want that horizontal vent under the floor and the fittings at each end of it to drain well.

One big question: if I re-orient the bathroom to where the shower and sink positions are swapped (or the mainline runs the other way, whichever you want to look at it), would that necessitate a change in my purposed vents? since the WC will then run by the shower branch...
Yes, the problem would be that the WC is now wet vented by the lavatory drain, rather than the shower drain, and you have the kitchen sink on the lavatory line. Wet venting is restricted to bathroom groups, so the kitchen sink would need to join the drain downstream of the WC if you want to wet vent the WC.

So either you'd need to dry vent the WC (same way you dry vent the shower), or you'd need to separate the lav and sink drains. For the latter, you could have two san-tees side by side; the vents could join at any height above 6" above the higher sink rim (presumably kitchen); the kitchen sink drain would stay separate and join the building drain with a wye downstream of the WC.

Cheers, Wayne
 

-dirt-

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So, the IPC maybe (probably?) allows what you've drawn. But using a wye rolled up 45 degrees, and a street 45 in it, would work better, as it would be a drainage pattern. Likewise when the vent enters the wall, a long turn 90 would be better.

The idea is suppose your ejector pump stops and the pit backs up and you don't notice until you see sewage in your shower. That sewage will also have backup up into the shower vent and around that 90 at the base of the wall. So when you clear the backup and everything drains, you want that horizontal vent under the floor and the fittings at each end of it to drain well.


Yes, the problem would be that the WC is now wet vented by the lavatory drain, rather than the shower drain, and you have the kitchen sink on the lavatory line. Wet venting is restricted to bathroom groups, so the kitchen sink would need to join the drain downstream of the WC if you want to wet vent the WC.

So either you'd need to dry vent the WC (same way you dry vent the shower), or you'd need to separate the lav and sink drains. For the latter, you could have two san-tees side by side; the vents could join at any height above 6" above the higher sink rim (presumably kitchen); the kitchen sink drain would stay separate and join the building drain with a wye downstream of the WC.

Cheers, Wayne

Ok, so best practice would be to revert back to the rolled wye and 45s for the shower -- got it. (Assuming this stays the order of fixtures)

For the re-orientation of the fixtures: would the shower still need to be vented, if the WC is vented?
 
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wwhitney

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IPC allows a dry-vented WC to wet vent a shower, to my understanding. If you separated the kitchen drain and came in downstream of the bathroom fixtures, the dry-vented lav could wet vent both the WC and the shower.

Cheers, Wayne
 
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