New DWV design for bathroom renovation

[Ron Benchetrit]

Hi all,
Love this forum, I read it all the time and I'm finally on a DIY project of my own. I'm renovating our bathroom and considering a new design for the DWV into our septic. I'm installing a wall mount TOTO wt172m (so this changes the outlet.) The current setup also has some minor venting issues due to internal rust clogging the old cast iron so I may as well redo it all. It's in a crawl space with roughly 3' of height to work with.

Does my new design look like it will work? Are the double WYEs stacked vertically ok? Is the one 2" vent sufficient or should I add a second vent off of the 3" toilet drain? Any and all suggestions much appreciated.
Ron

 

[Reach4]

Nice illustration. I note there is also a 4" x 4" x 3" x 3" double wye available. I don't know if it makes things any better.

https://www.supplyhouse.com/Spears-P612-422-4-x-3-PVC-DWV-Double-Wye

 

[Sponsor]

 

[Jeff H Young]

we put 2 inch in to all wash machines and 2 inch showers so those 1 1/2 branches going both directions id scrap that idea, the 3 inch going up to the wall mount toilet should function ok but Id want a vent coming off the santee in the wall above and go up and revent or continue 2 inch out roof 1 1/2 is ok too in your area I think

 

[wwhitney]

My comments:

- 2" is better for laundry, kitchen sink, and shower. If the 1-1/2" is existing and not to be changed, I'd install 2" for the current scope of work so that in the future the rest could be upsized to 2".

- The bottom gray fitting with the cleanout should be a combo. No real point in any 4" inside the house, so it could be a 4x4x3 combo.

- The kitchen sink, laundry, and lav will all require venting elsewhere (above the floor), so the 2" vent is not useful where it is. If you keep it, it should attach to the 3" WC drain.

- The shower may be wet vented via the vented lav drain if the wye shown connecting them is within one trap diameter of fall (1-1/2" if you are using a 1-1/2" trap) from the trap outlet. Otherwise, it will need to dry vented within that distance from the trap outlet.

- The combined shower/lav drain can wet vent the WC by joining the 3" WC drain, eliminating the need for any vent connection in this area.

- I'm unclear on venting for the toilet ejection pump, but it would be elsewhere if required.

Cheers, Wayne

 

[Ron Benchetrit]

we put 2 inch in to all wash machines and 2 inch showers so those 1 1/2 branches going both directions id scrap that idea, the 3 inch going up to the wall mount toilet should function ok but Id want a vent coming off the santee in the wall above and go up and revent or continue 2 inch out roof 1 1/2 is ok too in your area I think

2” to the shower makes sense, to the laundry too, but the laundry is already plumbed behind walls in another room. Vent on the 3” for the toilet makes sense too, thanks!

 

[Reach4]

Vent on the 3” for the toilet makes sense too, thanks!

Can you join the lavatory+shower drainage to the 3-inch before the double-wye? I think you could use a 3x3x2 santee.

I think your 2-inch vent to roof does not do anything for you as far as meeting code. Kitchen+laundry and lavatory should have been vented before this.

 

[Ron Benchetrit]

My comments:

- 2" is better for laundry, kitchen sink, and shower. If the 1-1/2" is existing and not to be changed, I'd install 2" for the current scope of work so that in the future the rest could be upsized to 2".

- The bottom gray fitting with the cleanout should be a combo. No real point in any 3" inside the house, so it could be a 4x4x3 combo.

- The kitchen sink, laundry, and lav will all require venting elsewhere (above the floor), so the 2" vent is not useful where it is. If you keep it, it should attach to the 3" WC drain.

- The shower may be wet vented via the vented lav drain if the wye shown connecting them is within one trap diameter of fall (1-1/2" if you are using a 1-1/2" trap) from the trap outlet. Otherwise, it will need to dry vented within that distance from the trap outlet.

- The combined shower/lav drain can wet vent the WC by joining the 3" WC drain, eliminating the need for any vent connection in this area.

- I'm unclear on venting for the toilet ejection pump, but it would be elsewhere if required.

Cheers, Wayne

2” for laundry makes sense, but laundry is already plumbed behind walls in another room.
“No real point in any 3" inside the house” - Did you mean no 4”? A 4x4x3 combo would make connections easier for sure.
Yes, kitchen/laundry/lav/ejector pump all have their own vents so my vent could be moved to the WC instead.
One trap diameter of fall would be 6ft. In this case right? But using 2” pipe to the 3” sounds like a better idea.
Thanks for the tips, I’ll revise my diagram and post again.

 

[Reach4]

https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf page 12 at the bottom shows bathroom group wet venting. The lavatory can wet-vent the shower, and the combo can wet-vent the toilet, as long as you can upgrade to 2 inch after the lav.

 

[wwhitney]

2” for laundry makes sense, but laundry is already plumbed behind walls in another room.

Hence my suggestion of just using 2" for the current scope, and you can change over to 2" for the rest if ever exposed.

“No real point in any 3" inside the house” - Did you mean no 4”?

Yes, fixed, thanks.

Cheers, Wayne

 

[Jeff H Young]

Good Idea to ditch the san tee on back and go with a 4x4x3 combo as mentioned , Your sewer ejector pit and the bathroom it serves im assuming are adequately vented the drainage off the pump dosent get vented . it should tie in to stack with a wye fitting so your looking good

 

[Ron Benchetrit]

Hi all, I've drawn up a new design based on all the great feedback (hopefully I absorbed it all correctly). The new design is a bit shorter and easier to implement. Thanks for any further tips!

 

[wwhitney]

Looks good to me. The "new 2" vent to roof" may be omitted, the lavatory can wet vent the WC. I take it the shower is dry vented elsewhere?

Also, if you want things more compact, you can use a 3x3x2x2 double wye. Or if that's hard to fine, 3x2 bushings (rather than reducer couplings) with a 3" double wye.

Cheers, Wayne

 

[Reach4]

If both lavatory and shower are dry-vented, you are OK.
If shower is to be wet-vented by the lav, the line from the lav santee should be upped to 2 inch, and the shower p-trap output should come in on the horizontal rather than from above.

 

[Ron Benchetrit]

Omitting the current wc vent to roof would be great. So if I increase the lav drain to 2" then can a 2" vent (from the lav) handle (wet vent) all 3 of wc/lav/shower? (I currently have no vent on the shower, only on the lav)

btw, do you recommend adding cleanouts anywhere in the system?

"shower p-trap output should come in on the horizontal" - got it, thanks.

 

[wwhitney]

So if I increase the lav drain to 2"

For wet venting, if the lav is a single lav (just one trap), not required by the IPC to upsize to 2".

then can a 2" vent (from the lav) handle (wet vent) all 3 of wc/lav/shower?

Yes, or a 1-1/2" dry vent at the top of the lav san-tee, under the IPC.

"shower p-trap output should come in on the horizontal" - got it, thanks.

More specifically, for the geometry you drew, the crotch of the wye (where the branch intersects the straight run) needs to be no more than 2" lower than the outlet of the 2" shower trap. That limits your run to 8' horizontally if you make the shower trap arm at the perfect minimum allowed slope of 1/4" per foot.

Cheers, Wayne

 

[Reach4]

https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf page 12 has a diagram of a big IPC horizontal wet vent system vented by a 1-1/2 inch dry vent.

For wet venting, if the lav is a single lav (just one trap), not required by the IPC to upsize to 1-1/2".

Are you saying that if the lav trap is 1-1/4 the line from the lav santee to the wye could be 1-1/2 inch if there is only one lav? Or something else?

 

[wwhitney]

Are you saying that if the lav trap is 1-1/4 the line from the lav santee to the wye could be 1-1/2 inch if there is only one lav? Or something else?

Typo, I meant upsize to 2" as you suggested in post #13.

Just to be clear, for wet venting, size of the lav trap arm is immaterial. For the IPC and a singe lav, a 1-1/2" dry vent from the lav san-tee (assuming that is the vent connection method) is sufficient, and the portion of the wet vent carrying only the lav drain may be 1-1/2". For the UPC, the wet vent has to be 2", and if the wet vent is wet venting a WC, the dry vent also has to be 2".

Cheers, Wayne

 

[Ron Benchetrit]

Image update 3 - I've added in the lav drainage, traps and vent pipe since they are now integral to venting of all fixtures.
btw, I'm not sure why I had the shower pipe and trap as 2". 1-1/2" should be sufficient right?

 

[Jeff H Young]

sewer ejector tie in is too small only 2 inch IPC might allow 3" upc 4 inch min so check your code ( i think you are ipc ) but also you need to enter from a wye on its back