Pole Barn Rough In - is it wrong?

[MacksCustoms]

Hi all,

I’m in the process of preparing to pour the slab for my pole barn. I’m adding a 4x7 bathroom in the back corner, with toilet and lav. On the other side of the wall from the lav (offset to one side, not back to back), there will be a utility/laundry type sink. The two sinks cannot be back to back, as I am planning for a 2’ wide workbench to run along the back wall of the building and run into the bathroom wall.

Please take a look at my rough in fittings laid out as I plan to install them and let me know what you think. The forum won’t let me upload them directly so I’m sharing them in a google drive folder: https://drive.google.com/drive/folders/1YcEUwZwvgSmagFgtU8H7BkGH7D3QHVly

The plan is to come in with 3” main line (existing main septic line being tied into is 3”) and have a 3x2 san tee to run vent through exterior wall to roof. Then, combination and closet flange obviously. Coming out of the combination for the toilet, I’m planning to drop down to 2” line for about a 4.5’ run. Then, a 2x1.5x1.5 wye will branch out the lines for the two sinks, which will turn up into the wall with long sweep 90s.

My question is, is there anything WRONG with this setup???

I fully understand that there’s more than one way to run this, and my idea of doing it this way is that I can avoid drilling so many large holes in my studs to tie the two sinks together inside the wall. The way I have it laid out, I will only have to pass a single 1.5” pipe through a stud to vent the two sinks together. I will either install an AAV on the 1.5” line in the wall or run it up and across the ceiling to tie back into the 2” stack at the exterior wall.

My dad, who is helping me with this entire building, is trying to convince me that the 2” and 1.5” lines are too small, and that I should run the single 3” line all the way up into the wall where the sinks will go, then tie each in inside the wall. I see this as an extra expense and a considerably larger hole through the bottom plate for no reason, as the two sinks should only equal 3 DFU which is well under the capacity of 2” pipe.

Let me know what you think.

 

[WorthFlorida]

https://www.co.lincoln.or.us/DocumentCenter/View/961/2015-Plumbing-Guide-PDF

 

[Sponsor]

 

[wwhitney]

Under the IPC, you could do (starting at the upstream end):

1.5" vent through the roof
2x1.5x1.5 san-tee for both lavs (1.5" sink trap arms combine, each trap arm individually must be at most 1.5" fall)
2" lav drain/wet vent
3x2x3 combo for the WC
3" line exits the house

That is, the san-tee for a vent downstream of the WC is superfluous, the 2" lav drain will wet vent the WC.

Now if one of the sinks is a utility sink or laundry, then it can't be part of a horizontal wet vent as it's not a bathroom fixture. In which case you'd either need to check out circuit venting or the like, or dry vent the WC. The way to do that is similar to what you proposed, except starting at the WC the pattern would be

closet flange
closet bend
3x3x2 combo for the vent takeoff (or san-tee on its back)
3x3x2 wye for the 2" drain line from the sinks to join in

That is, the WC dry vent takeoff should happen before the WC fixture drain joins any other drains. You'd also want a 2" cleanout-tee below the san-tee(s) for the sink. [If the utility/laundry sink has a lower trap than the lav, best to just use two stacked san-tees, with the lav san-tee on top.]

Cheers, Wayne

 

[MacksCustoms]

the WC dry vent takeoff should happen before the WC fixture drain joins any other drains.

Looking at IPC, it says that I must have one vent that runs outside at some point in the system. This is why I added the 3x2 tee at the exterior wall. I do not have access to vent through the roof at the wall where the sinks are going. In order to vent outside from there, it would have to 90 over at top of wall and run horizontally about 8’ back through ceiling until it reaches exterior wall, then 90 up again. If this is okay, then I could do that.

So with that setup, WC and lav are wet vented via 1.5” pipe running through ceiling back to the exterior, and I need to eliminate the 3x2 tee at the exterior wall? And then run a separate 2” line all the way back to the utility sink and tie it in downstream of the combination for the WC? Will the utility sink also be able to vent off the same exterior vent pipe, considering I tie that in above the connection for the lav?

Forgive me if I sound dumb. I work in the water distribution field and have done plenty of plumbing on water supply pipes of all kinds but never drainage. This is my first time dealing with plumbing code or actually doing any DWV at all. I’m having quite a time figuring out how to apply all the rules of IPC into this tiny 8’ straight run of drain pipe.

 

[MacksCustoms]

Ok, what if I were to flip this entire setup around and start from scratch? Please see the extra photo I have added, here’s the link again - https://drive.google.com/drive/folders/1YcEUwZwvgSmagFgtU8H7BkGH7D3QHVly

After further investigation, looks like this will create an illegal venting situation on the WC, so I may have to scrap this idea. I’m starting to think that simply running that extra 2” line for the utility sink to tie in all the way behind the WC is probably the route to take. I just want this to be as simple and cost effective as possible, while also being sure I’m going to pass inspection and get my slab poured next week.

For now, ignore the placement of the 3x2 tee and the 2” pipe coming off the back. Both of those would get cut out in this scenario and relocated/removed. Also excuse my hideous primer spills.

What if I place the 3x2 tee in the wall uphill from the WC, vent it back across the ceiling as mentioned earlier to the outside. On the uphill side of the tee, I could add a piece of 3” pipe and turn it up to a clean out in the floor.

Then, down the line from the WC, add in the utility sink with a 3x2 wye, then at the exterior wall, 3x2 combination to tie in the lav. I assume that the lav vent would shoot straight up and tie into the vent headed outside, and the utility sink would also tie into said vent inside the wall behind WC.

 

[wwhitney]

Now if one of the sinks is a utility sink or laundry, then it can't be part of a horizontal wet vent as it's not a bathroom fixture. In which case you'd either need to check out circuit venting or the like, or dry vent the WC

I see rereading the OP that one of the sinks is a laundry sink. So another option is to just keep its drain separate from the lav drain, and the laundry sink drain would join the WC/lav downstream of where the lav joins the WC. That would let the lav wet vent the WC and you wouldn't need a dry vent for the WC. The only dry vents would be for the lav and the laundry sink. Those two vents could combine into a single vent at any elevation at least 6" above both flood rims.

Cheers, Wayne