Walkout Basement Underground plumbing

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Jeremy Weaver

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These are not great pictures sorry so Ill try and give as much information as possible here. I'm an electrician by trade doing some plumbing in walkout addition that was added sometime before I purchased this place. Concrete floor was never poured a few sections of concrete were in there which I removed. Anyway what we have here is 4 inch sewer line that goes through corner of this part of the house and out to septic tank. It comes out of basement which is next to this room then when this part was built they built over it. So few questions any info is appreciated. I included a really crappy sketch so here we go. I'm thinking add a 4x4x3 wye then 3 inch 45. Now the pipe would be plumb vertically and then use a double elbow or combo tee wye to branch to the toilet and over to the lav and part way to the lav wye off to the shower drain , and using the lav to wet vent this area, maybe I also need a shower vent in this situation? The other thing is does all this piping need to stay deeper then that ? If this is crap let me know again any info is appreciated. The strings hanging in the pictures are about locations of the stub ups I'm going to attach a plumb bob when setting pipe at right location. ok thanks

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wwhitney

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As to depth, I don't believe it's regulated, but it would be convenient to keep the DWV out of the slab and the gravel. I.e. if your build up going downward is finish floor -- concrete slab -- vapor barrier -- crushed rock as a capillary break -- filter fabric -- native soil, then it would be nice to keep the horizontal DWV in the native soil.

As to configuration, the standard thing to do is to combine the shower, lav and WC under slab all in a single horizontal "plane" (not really a plane as each pipe has to fall separately at 2% slope). The lav joins either the WC or shower first (under the IPC) as is convenient (shower in your case), then the combined drain joins the other fixture (WC in your case), and then the drain turns down. The shower trap arm is regulated to fall no more than 1 inside pipe diameter (typically 2") from the trap outlet elbow to the "crotch" of the wye fitting where it joins the lav. The WC, on the other head, has no such restriction. And of course the lav needs to be dry vented, either atmospherically through the roof, or with an AAV (for the IPC).

As to whether the combined lav/shower drain could turn downward and then combine with the WC drain on the vertical (as in your last sketch), I think that's subject to some debate. A permissive reading of the IPC section on horizontal wet vents would say "yes," as it is not explicitly prohibited, and the definition of "horizontal branch drain" allows for the presence of vertical segments. A possibly more common reading would be "no, it has to be a horizontal connection, since it's called horizontal wet venting."

Cheers, Wayne

P.S. In the event the building drain outside ever got blocked, is there an outside cleanout that would overflow first, i.e. at a lower elevation than your top of slab? If not, then a backwater valve may be wise and I think may be required.
 

Jeff H Young

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backwater valve connected only for the downstairs basement. the rest of plan not too detailed but generaly good
 

Jeremy Weaver

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As to depth, I don't believe it's regulated, but it would be convenient to keep the DWV out of the slab and the gravel. I.e. if your build up going downward is finish floor -- concrete slab -- vapor barrier -- crushed rock as a capillary break -- filter fabric -- native soil, then it would be nice to keep the horizontal DWV in the native soil.

As to configuration, the standard thing to do is to combine the shower, lav and WC under slab all in a single horizontal "plane" (not really a plane as each pipe has to fall separately at 2% slope). The lav joins either the WC or shower first (under the IPC) as is convenient (shower in your case), then the combined drain joins the other fixture (WC in your case), and then the drain turns down. The shower trap arm is regulated to fall no more than 1 inside pipe diameter (typically 2") from the trap outlet elbow to the "crotch" of the wye fitting where it joins the lav. The WC, on the other head, has no such restriction. And of course the lav needs to be dry vented, either atmospherically through the roof, or with an AAV (for the IPC).

As to whether the combined lav/shower drain could turn downward and then combine with the WC drain on the vertical (as in your last sketch), I think that's subject to some debate. A permissive reading of the IPC section on horizontal wet vents would say "yes," as it is not explicitly prohibited, and the definition of "horizontal branch drain" allows for the presence of vertical segments. A possibly more common reading would be "no, it has to be a horizontal connection, since it's called horizontal wet venting."

Cheers, Wayne

P.S. In the event the building drain outside ever got blocked, is there an outside cleanout that would overflow first, i.e. at a lower elevation than your top of slab? If not, then a backwater valve may be wise and I think may be required.
I was thinking to connect them together in the middle using a sanitary tee or combination wye as that would allow me to head right to the toilet amd then reduce size out of the other side of that fitting and head right to the lav ( in between wyeing off to the shower. So are they tying together horizontally then an immediate drop of a foot or so to a horizontal wye at the 4 inch? As to the outside being blocked this pipe travels about 8-10 feet then goes right into a septic tank. There is a vent or clean out that stubs up right before the septic tank. Also yes the plan was concrete -vapor barrier - rock- soil
Maybe I should add filter fabric in there also was deciding on adding slab insulation. Anyway yea wanted to keep all dwv in native soil just wanted to make sure this plan was feasible and not in violation. Any more info is appreciated thanks guys.
 

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I was thinking to connect them together in the middle using a sanitary tee or combination wye as that would allow me to head right to the toilet amd then reduce size out of the other side of that fitting and head right to the lav ( in between wyeing off to the shower.
Never use a sanitary tee horizontally to join drainage flows. Always use wyes or combos (combination of a wye+ a 45). Always orient so that a snake from the fixture will head downstream -- toward the city sewer or septic tank.
 

wwhitney

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I was thinking to connect them together in the middle using a sanitary tee or combination wye as that would allow me to head right to the toilet amd then reduce size out of the other side of that fitting and head right to the lav ( in between wyeing off to the shower. So are they tying together horizontally then an immediate drop of a foot or so to a horizontal wye at the 4 inch?
Sorry, I can't follow that description. Maybe you could make a roughly to scale floor plan with the pipes, fittings and pipe sizes?

One thing to note is that a sanitary tee can only be used in drainage with the barrel vertical. For a horizontal 3-way connection, you need a wye. Or a combo (wye + 45), but often it's possible to eliminate that 45 by moving the wye downstream and changing the pipe routing.

On that outside clean out, is it pressure tight, or if the septic tank filled up would the overflow spill out? And if the latter, is the overflow elevation below your basement slab elevation? If yes, then I would think you'd be OK without a backflow preventer.

Cheers, Wayne
 

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ok so sorry about the crappy description I've been trying to download some cad program to make up a drawing but didn't have much luck yet. I have some fittings I got free a few years ago and just laid some together to see what im talking about these fittings are not exactly how they would go together but an idea of what im trying to explain.(There also random sizes and short 90)So looking at third photo picture from standing on plywood, The WC is on the left then lav is across and that wyes off to the shower. Pipe would be 2 inch going over to lav and wyeing off to the shower (p trap at shower). The other side of the combo would go right to the WC on left. Is this feasible or is that an incorrect use of that fitting. I laid the fittings out two other ways to give some other examples of how maybe this should be done my thinking was if i can come up I can tamp a lot around that then branch of instead of coming out down low, but I want to do this correctly so yea. I can vent these things separately if need be or I can wet vent shower through lav and toilet separately or if they can be wet vented together. I think what I meant in the other post was a double 90 elbow instead of a sanitary tee in the middle above the 4 inch. Anyway guys hope the pictures are helpfully in trying to show this situation. Let me know If you need I can try an sketch something up I was trying but wasn't looking great. Thanks again and let me know what other info is needed.


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wwhitney

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With the vented lav, the horizontal wye you show in the first three pictures of the last post can wet vent the shower for you, as long as the 2" pipe from the p-trap outlet to the wye falls at most 2". The question with the way you show the WC tying in is whether the WC is wet vented by the lav. The arrangement shown is certainly fine if you separately vent the WC.

If you had your riser from the building drain closer to the door, and the lav/shower and the WC were approaching from opposite directions in the same plane and farther from the door than the riser, then they could join in that same horizontal plane (somewhat awkwardly, with a LT 90 on say the lav/shower to point towards the door, then a 45 and a wye (a combo) on the WC to join the lav/shower). And then that could turn downward to the join the building drain. That would be a standard horizontal wet vent.

I'm not sure about joining the WC with the lav/shower on the vertical as you show, I think it would be an OK wet vent, but I'd be interested to hear how others interpret the (IPC) wet vent rules.

BTW, the 3" combo shown for the WC is allowed to be a san-tee, and the bend on top where the lav/shower turns from horizontal to vertical doesn't need to be long turn, a quarter bend is fine. [When the change in drain flow direction is to horizontal (from either vertical or horizontal), then you need the LT90 or the combo. When the change of direction is to vertical (from horizontal), then you can use a quarter bend or san-tee.]

The options shown in pictures 4,5,6, and 7 in the last post don't help with any of the issues above.

Cheers, Wayne
 
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Jeff H Young

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that should work if trap arm on shower isn't over 8 ft at 1/8inch per foot fall.
 

Jeremy Weaver

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ok so let me go through this once more see if everything seems right. I wye off the sewer line with a 4x4x3 wye then add a 3"45. I then use the 3" combo bend to go over to the toiler and 90 up under its location. ( short or long 90 here?) Out of the top of the other side of the combo fitting I reduce to 2 inch and 90 over to towards the lav. (short 90 Ok here or long?) I then Wye off towards the Shower and if its close enough I wet vent it with the lav which I stub up in wall behind lav. If not I vent it separately. Also toilet needs to be vented separately in this situation. Does the toilet need to be vented in wall behind? Or can I run it over to adjacent wall and vent it that way? The wall it is behind is an exterior wall Sitting on block foundation. Ok So thank you for all the information. Let me know what you guys think.
 

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Also the vent/clean out ouside is a 6 inch pipe stubbed up with a cap on it (not glued) should this be something else? thanks again any info is appreciated
 

Jeff H Young

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yes short 90 I don't think you need a separate vent for w/C its wet vented by Lav.
 

Jeremy Weaver

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With the vented lav, the horizontal wye you show in the first three pictures of the last post can wet vent the shower for you, as long as the 2" pipe from the p-trap outlet to the wye falls at most 2". The question with the way you show the WC tying in is whether the WC is wet vented by the lav. The arrangement shown is certainly fine if you separately vent the WC.

If you had your riser from the building drain closer to the door, and the lav/shower and the WC were approaching from opposite directions in the same plane and farther from the door than the riser, then they could join in that same horizontal plane (somewhat awkwardly, with a LT 90 on say the lav/shower to point towards the door, then a 45 and a wye (a combo) on the WC to join the lav/shower). And then that could turn downward to the join the building drain. That would be a standard horizontal wet vent.

I'm not sure about joining the WC with the lav/shower on the vertical as you show, I think it would be an OK wet vent, but I'd be interested to hear how others interpret the (IPC) wet vent rules.

BTW, the 3" combo shown for the WC is allowed to be a san-tee, and the bend on top where the lav/shower turns from horizontal to vertical doesn't need to be long turn, a quarter bend is fine. [When the change in drain flow direction is to horizontal (from either vertical or horizontal), then you need the LT90 or the combo. When the change of direction is to vertical (from horizontal), then you can use a quarter bend or san-tee.]

The options shown in pictures 4,5,6, and 7 in the last post don't help with any of the issues above.

Cheers, Wayne
yes short 90 I don't think you need a separate vent for w/C its wet vented by Lav.
Never use a sanitary tee horizontally to join drainage flows. Always use wyes or combos (combination of a wye+ a 45). Always orient so that a snake from the fixture will head downstream -- toward the city sewer or septic tank.







Ok thanks guys anyone else have any other comments issues with this situation please let me know. Thanks guys for all the information.
 
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