Drain Waste Vent options — the good, the bad, the ugly.

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wwhitney

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OK, so some more information is needed: first, a floor plan showing the floor joists and the "existing drain" and the "existing cast iron stack," along with the wall below that is the next bearing point for the floor joists . Also, what size are the floor joists? And the existing cast iron stack, is it the vent for any fixtures on the floor below, or is it just a drain for second story fixtures? Your photos show a cast iron san-tee in the floor system.


Cheers, Wayne
 

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OK, so some more information is needed: first, a floor plan showing the floor joists and the "existing drain" and the "existing cast iron stack," along with the wall below that is the next bearing point for the floor joists . Also, what size are the floor joists? And the existing cast iron stack, is it the vent for any fixtures on the floor below, or is it just a drain for second story fixtures? Your photos show a cast iron san-tee in the floor system. Cheers, Wayne

Here's the general joist layout. It's the second floor, living room below, attic above. Floor joists are 1.75 x 9.25 x ~13'. It's balloon framing, joists are nailed to studs on outside wall (left side of diagram) and sit on a load bearing plate on the interior wall (right side of diagram). The cast iron stack currently services the main bath (tub, toilet, lav) on the other side of the wall.

Framing Layout
7Es7HjL.png


Original idea for layout
drz1Gww.png
 

wwhitney

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The perspective view is cool looking, but an actual 2D projection (plan view) would be easier for this purpose.

Looks like you'd have to cross 2 floor joists to get the toilet fixture drain to the 3" PVC, or 4 floor joists to the toilet fixture drain to the cast iron stack?

I assume you don't like any layouts where the toilet flange is in the same joist bay as either the 3" PVC or the cast iron stack? Because that would be the simplest solution, and may be the only reasonable solution.

Cheers, Wayne
 

wwhitney

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On first reading, this looks like a reasonable solution to drilling a 2x10 with a 4" hole for a 3" pipe (3.5" OD):

https://joistrepair.com/products/2810hr

I'd be inclined to send the toilet to the 3" PVC, so that you only have to reinforce 2 joists. Then the lav would wet vent it. Whether it's better to send the tub and shower to the lav drain upstream of the toilet, so they are also wet vented by the lav drain, or instead send them separately to the cast iron stack, I don't have an opinion.

Cheers, Wayne
 

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I assume you don't like any layouts where the toilet flange is in the same joist bay as either the 3" PVC or the cast iron stack? Because that would be the simplest solution, and may be the only reasonable solution.Cheers, Wayne

That is an option, but not one of the favored layouts since it puts the toilet floating out near the door and, given the new position of the vanity, would reduce its possible size from 6' to 42". It may end up being the direction I go though, since it would solve the joist issue (as well as help me avoid having to move the radiator :D)

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On first reading, this looks like a reasonable solution to drilling a 2x10 with a 4" hole for a 3" pipe (3.5" OD):

https://joistrepair.com/products/2810hr

I'd be inclined to send the toilet to the 3" PVC, so that you only have to reinforce 2 joists. Then the lav would wet vent it. Whether it's better to send the tub and shower to the lav drain upstream of the toilet, so they are also wet vented by the lav drain, or instead send them separately to the cast iron stack, I don't have an opinion.

Cheers, Wayne

Yeah, I would likely try to get everything sent over to the PVC since that will help me avoid cracking into the cast iron multiple times.
 

wwhitney

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Well, the vanity location in your last rendering makes wet venting easier (closer to shower/tub, so easier to bring the vanity in between the shower and tub).

How deep is the jog at the chimney (I think that's what that is)? Have you considered putting the vanity against that, and extending it towards the (current) radiator, with a deeper counter in that area? Just a thought. The shower/tub might need to get swapped, not sure.

Cheers, Wayne
 

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Well, the vanity location in your last rendering makes wet venting easier (closer to shower/tub, so easier to bring the vanity in between the shower and tub).

Trying to read back through your other guidance to understand what you are saying here... I think what you mean is that with this layout, the lav could be at the end of the waste run over to the PVC drain, and I could run a vent over the cast-iron — like this?

7UGRFwy.png


How deep is the jog at the chimney (I think that's what that is)? Have you considered putting the vanity against that, and extending it towards the (current) radiator, with a deeper counter in that area? Just a thought. The shower/tub might need to get swapped, not sure.
Not a bad thought. That was one of the versions I tried, but with the vanity over there, it encroaches on the toilet, so the toilet would have to move back to the placement where the joist drilling would need to happen and at that point, I would just move the radiator and tuck the vanity into that wall space.
 

wwhitney

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Yeah, like that, except with only one horizontal 90 in the floor system. I'd put the lav san-tee off center towards the shower, then start in the floor system perpendicular to the joists, pick up the shower before the 90 degree turn, and pick up the bathtub either before or after turning.

BTW, if you want the toilet near the 3" PVC, it doesn't have to be centered on the PVC. You just need to be able to install a closet flange with the outlet in the correct joist bay. I think that should give you a 10" left-right range of options, FWIW.

Cheers, Wayne
 

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Yeah, like that, except with only one horizontal 90 in the floor system. I'd put the lav san-tee off center towards the shower, then start in the floor system perpendicular to the joists, pick up the shower before the 90 degree turn, and pick up the bathtub either before or after turning.

So run it horizontal over towards the shower drain so that it can run by the shower drain? Never pulled that move before...

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BTW, if you want the toilet near the 3" PVC, it doesn't have to be centered on the PVC. You just need to be able to install a closet flange with the outlet in the correct joist bay. I think that should give you a 10" left-right range of options, FWIW.

Yeah, the way it's there now is that it's virtually right on top of the PVC stack, so it's really tight. I may try to offset it a bit.
 

wwhitney

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No, I was trying to describe the layout below. The jog at the shower drain is just what you get from the p-trap, to make it easier for the downstream combo to fit in the joist bay.

Cheers, Wayne

157Draft.png
 

wwhitney

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How about a top down view with joists of your preferred toilet location? Personally, if I thought that was a better arrangement, I wouldn't hesitate to drill two joists for the 3" toilet line, using those reinforcement brackets I linked to earlier.

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How about a top down view with joists of your preferred toilet location? Personally, if I thought that was a better arrangement, I wouldn't hesitate to drill two joists for the 3" toilet line, using those reinforcement brackets I linked to earlier. Cheers, Wayne

In this scenario, with the lav already down near the drain, that would be back to one of your earlier suggestions where the drain comes out of the lav where the bath connects, then the shower, then the toilet and then to the stack, yeah?

Here's the top down view:

lVxK2Pq.png
 

wwhitney

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A couple options for your consideration based on the last overhead view. Green is vent, red is drain, and orange is alternate drain path.

With the shower drain so far from the lavatory, I don't see how you could reasonably wet vent the shower using the lav. I assume you're doing a monoslope shower with a trench drain at the end, that's why the drain is so close to the wall? You can take advantage of the proximity to the wall to dry vent the shower fairly easily. The shower then wet vents the tub and the toilet. I drew the lav san-tee very closet to the chimney, but in this plan there's no need for that, it can be anywhere you want left-right.

157Draft2.png
 

wwhitney

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And if you are interested in moving the shower drain to the entrance side of the shower, then I think you'd be close enough to reach the lav for a wet vent. The orange is an alternate "cut the corner" path if necessary to stay under 8' trap arm length. For the two wyes in one joist bay, you'd want to use a street wye for the upstream one (and possible the downstream one, depending on where a long turn 90 (rather combo) puts you and whether you can poke the hub end of it through the joist without an excessively large hole).

Cheers, Wayne

157Draft3.png
 

Jeff H Young

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you can always move the stack , run a new one up etc. put everything where you want .
 

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With the shower drain so far from the lavatory, I don't see how you could reasonably wet vent the shower using the lav. I assume you're doing a monoslope shower with a trench drain at the end, that's why the drain is so close to the wall? You can take advantage of the proximity to the wall to dry vent the shower fairly easily. The shower then wet vents the tub and the toilet. I drew the lav san-tee very closet to the chimney, but in this plan there's no need for that, it can be anywhere you want left-right.

View attachment 68896

Yes, shower is curbless and pitching away from the main floor area and tub. This layout makes sense, but this means there are two vents that need to be tied into the cast iron, right?
 

wwhitney

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Yes, shower is curbless and pitching away from the main floor area and tub. This layout makes sense, but this means there are two vents that need to be tied into the cast iron, right?
Sure, but they can combine with each other before tying into the cast iron. So the difficulty at the cast iron stack should be the same either way.

How are you going to achieve the curbless shower pitch without chewing up your joists? While somewhat unusual, a pitch towards the entrance would mean that you are building up rather than sloping down. Could be tricky to get the details right, but one advantage would be moving the drain closer to the lav, which I think would make wet venting everything via the lav feasible.

Cheers, Wayne
 

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How are you going to achieve the curbless shower pitch without chewing up your joists? While somewhat unusual, a pitch towards the entrance would mean that you are building up rather than sloping down. Could be tricky to get the details right, but one advantage would be moving the drain closer to the lav, which I think would make wet venting everything via the lav feasible.

Plywood is being lowered to be level with joists while the surround subfloor will be bumped up a bit.

I ended up having my plumber come over for a consult. After we checked out the condition of the cast-iron, it was pretty clear it wasn't something I should try tapping into, so I'm proceeding with a new PVC vent out the roof and a layout similar to your recommendation:

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