WC Venting Question

[NOLAcorn]

Question about proper venting here.

I live in Southeast Louisiana in a raised one-story house (3 ft crawlspace) that's about 110 yrs old. As you'd expect the plumbing is a bit 'interesting'. When we bought it, the house already had Sched 40 PVC for wastewater everywhere except for this bathroom and the main stack, which was cast iron. We knew there was a crack in the CI about an inch above the Tee for the toilet, so eventually it was going to have to go. I always wondered why the toilet was a full 2 ft from the wall on its right and almost touching the vanity to its left. When I ripped up the old floors I found it was probably because a large girder (which they notched anyway, but that's a separate project) was blocking it from being any further from the vanity and closer to the wall. I was planning to leave the sink plumbing as it was and just replace it with PVC. However, I want to move the toilet to the other side of the girder, but I see no way of doing that with a Tee off the main stack the way it was originally plumbed. I had an idea for an alternate plumbing route for the toilet, where the run from the closet elbow to the 90 deg turn is ~5 ft and another 1 ft from the turn to tie it into the rest of the house. I wasn't sure if:
A) would this be allowed according to code? and
B) is there a better way to vent the toilet?

I was able to create some diagrams in sketchup.

Old plumbing diagram

https://ibb.co/N7SpVxF

Proposed plumbing diagram

https://ibb.co/m5BY9MK

https://ibb.co/7krdYzX

w/ girder

https://ibb.co/p1VjNTJ

https://ibb.co/DVttVjc

I appreciate any feedback and suggested improvements.

 

[Terry]

It looks like your proposed plumbing ins going backwards at times.
Any fitting for waste on the horizontal should by a wye fitting, pointing the waste downstream.

 

[Sponsor]

 

[NOLAcorn]

Thanks for the feedback. I assume you're referring to the 3x3x3 Tee where the toilet line joins the one that comes from the rest of the house. Could what you're talking about be accomplished with a long turn Wye like this?

 

[wwhitney]

If it's a dropped girder (below the floor joists), can't you route the toilet drain over the girder between the floor joists?

Cheers, Wayne

 

[Reach4]

I presume the white pipe coming in has vented waste. If you can join that in below the new toilet connection, you can wet vent the toilet (no separate toilet vent needed). If it is a tub or shower that has not been vented yet, that changes things.


I don't get the big picture, since I did not look at all of your pictures. A rear-exit toilet could be useful potentially, to get the toilet waste to bypass the girder. But that is not necessary. There are probably other things that could work.

 

[NOLAcorn]

@wwhitney I could go over the girder but then I'd have to drop down and turn like stair steps and wasn't sure if that would be allowed, because the vent stack is sandwiched between two joists that I would have to go under.

@Reach4 I was trying to avoid tying into the cast iron pipe because it's buried underground and code here says you can't bury those flexible couplings, so I think I'd have to replace a lot more pipe.

 

[wwhitney]

@wwhitney I could go over the girder but then I'd have to drop down and turn like stair steps and wasn't sure if that would be allowed, because the vent stack is sandwiched between two joists that I would have to go under.

For a normal trap arm, you have to keep it horizontal until you vent it. But a toilet siphons on purpose and refills its own trap. So the toilet fixture drain can go vertical before being vented.

So you could go: closet flange, vertical pipe, closet elbow with outlet parallel to joists and just above girder, pipe over girder, long turn 90 rotated down 45 degrees from flat to get under the joists, (probably street) 45 to get back horizontal, pipe segment, sanitary tee in 4" stack. [Possibly the two instances of the number 45 could instead be 22.5, but that might not fit in the joist bay.]

Cheers, Wayne

 

[NOLAcorn]

For a normal trap arm, you have to keep it horizontal until you vent it. But a toilet siphons on purpose and refills its own trap. So the toilet fixture drain can go vertical before being vented.

So you could go: closet flange, vertical pipe, closet elbow with outlet parallel to joists and just above girder, pipe over girder, long turn 90 rotated down 45 degrees from flat to get under the joists, (probably street) 45 to get back horizontal, pipe segment, sanitary tee in 4" stack. [Possibly the two instances of the number 45 could instead be 22.5, but that might not fit in the joist bay.]

Cheers, Wayne

Here's a pic with what you proposed with joists in and the plastic sheeting where the ground is. I certainly like your idea better, way easier, I just thought you couldn't go vertical and stair step like that bc of the whole 1/2" per foot slope rule.

Sorry realized you said 45 to 45 to get to the Tee and not a single 90

 

[wwhitney]

As I mentioned, a toilet is different from everything else because the vent isn't to protect the trap seal on a toilet. So it is allowed. You can find some threads on here discussing it, or perhaps someone else will chime in to agree.

Also, you've shown it with a 90 before the san-tee, but you could use a 45 or possibly a 22.5, by rotating the upper 90. Less stair-steppy.

Cheers, Wayne

 

[James Henry]

If you can tie the toilet drain under the beam and into the stack with a Santee, looks like a textbook vertical wet vent.

 

[Reach4]

@Reach4 I was trying to avoid tying into the cast iron pipe because it's buried underground and code here says you can't bury those flexible couplings, so I think I'd have to replace a lot more pipe.

I am not saying you want or need to dig, but most places underground is pretty much the only place the unshielded flex couplings would be allowed. But even so, you can use shielded couplings underground anywhere AFAIK.

Regarding slope, minimum drop for 3 inch is 1/8 inch per foot with IPC. LA code is based on an earlier IPC version. In UPC it is 1/4 inch per foot. No max for a toilet as wwhitney pointed out. No max for anything else after it's vented.