shower + lav draining into toilet drain with attic bathroom

[PerryNotMason]

hi all,
I'm installing a new small bathroom in my attic - the space is awkward and small, and my main question is about using space wisely.
I'm located in Portland, oregon for code purposes.

I intend on having a 3" toilet drain, as well as a lav sink and a shower in the new bathroom.
new bathroom is above an old 1923 kitchen i am remodeling, so i am placing any pipes in the walls/ceiling now while i have stud bays open/am working on the ceiling.
2 x 8 joists, 2 x4 walls in the house, so finding room for anything is complicated.
Here is my kitchen wall where most of the magic ✨ happens. It's real tricky.

There is a 2" cast iron kitchen sink drain directly below where i am working, but a 3"/4" is either on the other side of the house or in the slab or outside.
all three will have an fixtures in attic will have an AAV - they will be installed against a knee wall and so i can pop a vent that can draw air from that cavity no problem.

but finding a way to run drains has been really challenging, and the only feasible way i can make the toilet work is to drop through the ceiling of the room above, go around the top plate, then out through the soffit. I found a way to make that work, with only a small elbow jut out i can disguise.

plan on running the 3" drain along the outside of the house, and then connecting it to the drain that connects to the city in the spring when i dig up the yard, as that pipe is less than 4 feet away from the corner of the house I am working on. New sewer connection cam in 3 years ago.
Here is how the drain gets outside through the kitchen wall - photo taken after the one above.

Anyway - here is my question:
Can i join the 2" drain from the lav+shower with the 3" toilet after the toilet's AAV and before the pipe turns downward to drop through the ceiling? With a wye or santee, as long as I can get slope up to the lav and shower?

Or do i have to run a separate 2" pipe through the wall into the basement (i don't want to run it outside) and link up with the 2" old pipe from the kitchen?

I could do that to the left of the window, but i still have to get through the ceiling and I don't want to drill a hole through the double top plate for a 2" pipe as it is the exterior wall and rather load bearing.
I could also run the 2" pipe through a different kitchen wall near where the shower is, but the connection to a drain in the basement is much more complicated as there is ducting and electrical conduit and a chimney i'd have to work around in the basement where the pipe comes out of the wall.

Any advice on how to run the drain pipe would be helpful.
thanks a lot for your time.

 

[wwhitney]

all three will have an fixtures in attic will have an AAV - they will be installed against a knee wall and so i can pop a vent that can draw air from that cavity no problem.

Oregon uses the UPC, so I'm surprised that AAVs are allowed, but apparently so:

https://www.oregon.gov/bcd/codes-stand/Documents/sam-07-01airadmittancevalves.pdf

That said, you only need one AAV, for the lav. It needs to be 4" above the lav trap arm, and accessible for maintenance, and able to breath. If using a vanity cabinet, inside the vanity cabinet is a good place for it.

Then with the lav dry vented via the AAV, you can use the lav drain to wet vent the shower and the WC. The drain pattern you show does this already, as long as the shower trap arm, from the trap to where the shower drain joins the lav drain, is at most 5' long and falls at most 2".

but finding a way to run drains has been really challenging, and the only feasible way i can make the toilet work is to drop through the ceiling of the room above, go around the top plate,

It is allowed to run the 3" pipe through the top plate, even though that completely severs it. You'd want to ensure that the joist on either side of the 3" pipe has good bearing on a stud below it. And the continuity of the top plate needs to be reestablished with a metal strap on either the inside or outside edges of the top plate. See:

https://up.codes/viewer/oregon/irc-2018/chapter/6/wall-construction#R602.6.1

Can i join the 2" drain from the lav+shower with the 3" toilet after the toilet's AAV and before the pipe turns downward to drop through the ceiling?

Certainly; and if you want to have the lav AAV wet vent the WC, instead of using an extra AAV for the WC, that join needs to happen within 6' of pipe run (horizontal and vertical) of the closet flange.

Cheers, Wayne

 

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[PerryNotMason]

Oregon uses the UPC, so I'm surprised that AAVs are allowed, but apparently so:

https://www.oregon.gov/bcd/codes-stand/Documents/sam-07-01airadmittancevalves.pdf

That said, you only need one AAV, for the lav. It needs to be 4" above the lav trap arm, and accessible for maintenance, and able to breath. If using a vanity cabinet, inside the vanity cabinet is a good place for it.

good point about it needing to be accessible for maintenance. Yep, there will be a vanity for sure. I will install it there then.

Then with the lav dry vented via the AAV, you can use the lav drain to wet vent the shower and the WC. The drain pattern you show does this already, as long as the shower trap arm, from the trap to where the shower drain joins the lav drain, is at most 5' long and falls at most 2".

am i understanding correctly that if the run it is a bit longer than 5' (it is about 5.5 feet) that I would need a separate vent solution for the shower? (i can experiment with moving the lav trap over a bit first), if not, i'd like to know what my other approach should be.)

It is allowed to run the 3" pipe through the top plate, even though that completely severs it. You'd want to ensure that the joist on either side of the 3" pipe has good bearing on a stud below it. And the continuity of the top plate needs to be reestablished with a metal strap on either the inside or outside edges of the top plate. See:

https://up.codes/viewer/oregon/irc-2018/chapter/6/wall-construction#R602.6.1

Certainly; and if you want to have the lav AAV wet vent the WC, instead of using an extra AAV for the WC, that join needs to happen within 6' of pipe run (horizontal and vertical) of the closet flange.

Cheers, Wayne

i thought I had looked everywhere but somehow I missed this. I can absolutely do this, and then run the pipe outside. I have to fix the framing in this area anyway, so i will put some new studs between the top plate and the window to help strengthen the area. There is less than 6' pipe run, so this won't be a problem.

thank you very much!

 

[wwhitney]

am i understanding correctly that if the run it is a bit longer than 5' (it is about 5.5 feet) that I would need a separate vent solution for the shower?

Yes, the distance from a trap to its vent is limited to 60" for a 2" drain, see:

Chapter 10: Traps and Interceptors, Oregon Plumbing Specialty Code (OPSC) 2023 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

For a wet vent, the vent connection is where the fixture drain (carrying only the shower) joins the lav drain that is wet venting it. Your best option is to adjust the lav drain routing and/or the shower drain routing and trap location to stay under 5'.

i thought I had looked everywhere but somehow I missed this. I can absolutely do this, and then run the pipe outside.

Not clear why you want to run the pipe outside? If it's just to connect to the existing sewer outside the house, I would exit the building as low to the ground as feasible. I.e. generally out the basement / crawl space wall just about the foundation, if coring the foundation is too much trouble.

Cheers, Wayne

 

[PerryNotMason]

thanks wayne, thanks for that extra info.

I'd absolutely prefer not to run the pipe outside and along the house for several reasons.

but the reason i thought to do so is that this wall is pretty cramped with the window, vent pipe, supply lines etc. the only straight run down a stud bay i have available is to the very left (where there is no insulation visible in the top half) and to the very right (to the right of where you can see the existing vent)
I wasn't sure about completely severing existing studs to pass a 3" pipe through horizontally, I would love any advice on this.

the existing basement wall right underneath this photo

looks like this:


top half:
old 2" galvanized, with an additional arm here for a bar sink in the dining room.

bottom half:
entry point into foundation, with cleanout visible.

i'm not sure exactly which direction the in-slab drain leaves this area, but i think it's in the direction i indicated, judging by where the other 4" drain is (on the other side of the basement)my hesitation is that i'm not sure how i would get the cement out, and then how would i cut the existing in slab pipe to connect a fitting? I am guessing a flexible coupling?


if its possible, i'd prefer to do it this way but felt daunted by the prospect...

 

[wwhitney]

So, judging from the 2nd photo in the OP, the joist bay your current WC location is in lines up with the leftmost most stud bay over the window header in the kitchen.

That means in order to get into the stud bay to the left of the window, you need to get over to the left one bay somehow. Cutting through the king stud of the window opening is not an option for that. Options are:

1) Move the toilet; may not be possible, depends on what is to the left in the 3rd picture in the OP.
2) Cut a 3.5" hole in your 7.25" tall 2x8 joist. Generally a bad idea, although there is a product that claims to sufficiently reinforce the joist to allow that to happen, meaning I might consider it for one joist: https://joistrepair.com/
3) Put in a soffit in the upper left corner of your kitchen, so the WC drain can drop drop down below the 2x8s, go to the left one bay, and then enter the stud bay to the left of the window. For soffits, pay attention to the fireblocking--the stud bays should not communicate with the joist bays. This also means you don't have to cut the top plates.

Once your 3" drain is in that stud bay, looks like you can get through the bottom plate (not really structural between studs) and the subfloor, avoiding any rim joist (maybe hit a 45 at around the bottom plate) and pop into the basement. What you do from there is unclear:

1) If you're really lucky the 2" PVC kitchen drain enters a 3" fitting in the slab, in which case you could take the 3" drain there with minor concrete work.
2) You could run overhead to wherever you need to be to tie into a 3" or 4" drain, hopefully mostly in a joist bay.
3) You go outside through the rim joist.
4) You could trench the concrete, but that might be a last resort.

Cheers, Wayne