Best drain routing for tight space in basement bathroom

[MrHappy]

Hi all, located in MN which follows 2018 UPC for the most part.

Working on renovating an old bathroom. The old plumbing was done wrong (no vent for shower, trap is higher than the drain) and I am swapping the positions of toilet and lav during the renovation. Currently still digging out the old cast iron, but had some questions with regard to drain routing.

I sketched a quick drawing of the proposed layout and proposed drain using all wet venting from the lav. This would mean the lav drain goes in towards the shower to meet the 5ft rule, then bends back around ~135 degrees towards the main stack, picks up the toilet, then meets the stack and exits the house. I'm not sure if having all the bends is a bad idea from the lav. This minimizes above-ground protrusions but if it is going to cause clogs or other issues I would of course prefer to do it differently. The tape measure in the pic is extended to 5ft for reference

2nd idea (not sketched) is to dry vent the shower with a rolled 45 to the wall, and have the toilet wet vent off of that. The lav would be separately drained/vented all above ground. This would require framing a 2x3 or 2x4 wall to accommodate the vent piping which I'd like to avoid (but don't mind if idea 1 doesn't work).

Another question I was wondering is how to deal with the tie-in to the cast iron. For some reason they put a cast iron wye directly under the footing. The old bathroom branch comes in horizontal and I will just be cutting the pipe and capping. The other side receives the main stack, but it comes in from above at a 45 degree angle. I was planning on having this be where I tie in and transition to PVC. Will it be difficult to get a 3" donut in and a 3" pvc 45 elbow hammered in? Is there a better way to go about this? The space between the toilet and main stack, then main stack to sewer exit is pretty tight

 

[wwhitney]

On the wet venting, the 2" kitchen/laundry drain needs to be kept separate from the bathroom group. So rather than join the shower, run it separately until it can tie in after the WC joins the shower/lav. Also, while the lav trap arm can be 1-1/2", it needs to hit a 2x2x1.5" san-tee for the vent takeoff, i.e. the wet vent needs to be 2".

As to the lav wet vent rounting, I don't think adding one extra LT90 so that the wet venting works is a problem. The wet vent can come out from the lav wall going to the right on the page, then LT90 to go up the page, and then combo into the shower trap arm going to the left on the page.

Cheers, Wayne

 

[Sponsor]

 

[MrHappy]

On the wet venting, the 2" kitchen/laundry drain needs to be kept separate from the bathroom group. So rather than join the shower, run it separately until it can tie in after the WC joins the shower/lav. Also, while the lav trap arm can be 1-1/2", it needs to hit a 2x2x1.5" san-tee for the vent takeoff, i.e. the wet vent needs to be 2".

As to the lav wet vent rounting, I don't think adding one extra LT90 so that the wet venting works is a problem. The wet vent can come out from the lav wall going to the right on the page, then LT90 to go up the page, and then combo into the shower trap arm going to the left on the page.

Cheers, Wayne

Playing around with the configuration more I think I'm going to separately vent & drain the lav all above ground, then vent the shower/toilet together. Would I be able to use a double wye 3x2x2x3 to join the toilet, shower, and kitchen/laundry drain together if i"m using the shower section as a wet vent for the toilet?

I don't have the space for 2 wyes butted up next to each other unfortunately.

 

[wwhitney]

Would I be able to use a double wye 3x2x2x3 to join the toilet, shower, and kitchen/laundry drain together if i"m using the shower section as a wet vent for the toilet?

Using a double wye with the barrel horizontal is problematic. If you think about a line (the barrel) pitched at 2%, and then add in the two side inlet lines themselves coming off at 2% and 45 degrees to the barrel, that shape is not planar. But a double wye is planar.

It is doable if you pitch the barrel at 3%, and ensure that the two side inlets are dead level with each other (which puts each of them at 2.1%), but it's really a very last choice option.

If the WC is coming in the 3" inlet, and one 2" inlet carries a dry-vented shower, and the other carries a non-bathroom drain, does that count as wet venting the WC? I don't think that's exactly addressed in the plumbing code, but it seems to me that it should.

I don't have the space for 2 wyes butted up next to each other unfortunately.

Even if one of the wyes is a street wye?

Cheers, Wayne