Help with yet another bath drain configuration please and thank you.

Work has slowed so much, so long, I'm forced to work on my own house. Hopefully I can explain this clearly....

The first pic below shows the layout of my bath. The yellow area is the floorplan of the master bath which backs up to the hall bath. The circle with X marks the main drain. The others are as marked with the "tub drain" (outside the yellow) being from the adjoining hall bath. The distances from the main drain to the fixtures are:
Shower = 65"
Toilet = 20"
Tub drain = 40"
Vanity = 24"

The second pic is the main drain with a 3x3x2 fitting balanced on top. My thought was to fernco the pvc onto the main drain, put a 3x3x2x2 Y coming off the 3" side of the fitting and go from there to the toilet, shower and tub. Then the 2" on top of the fitting in the pic would 90 over to the back wall as a vent where it would also pick up the vanity coming in at the wall point. The vent would be able to travel into the attic and tie into another nearby vent or penetrate the roof on it's own but there would be no other vents for the fixtures mentioned.
If it's important, there's about 20" of space from where the bottom of the fernco would be to the bottom of the subfloor.

I'm sure this must read like one of those logic puzzles but hopefully the explanation is clear. What I'm unclear on is...
Do I need more venting for the shower and/or tub?
Is it OK to Y the shower and tub lines into the toilet line before they hit a vent or will that suction out the traps?
If I need to put another fitting above this one, can I cut the top off the cast iron and fernco onto the cut off top?

Does this look workable or am I way off base?

Thanks for all help!

Your description makes sense to you, but not to us. Draw the piping the way you hope to install it. From what I can decipher, however, you seem to be a vent or two short.

hj said:

Your description makes sense to you, but not to us. Draw the piping the way you hope to install it. From what I can decipher, however, you seem to be a vent or two short.

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I was afraid of that. I had tried to draw it out but it came out so bad I thought I'd do better with words...
But here are my impressionistic renderings of the pipe plan from above and a (sort of) elevation.

Here's the alternative idea I had which I alluded to in the original post. This would probably involve cutting the cast iron further down to make room for the fittings. Again, I hope this is comprehensible!

Neither of those, double wye or "V" as you called it, wont allow you to "roll" the fitting upwards for proper pitch, and shouldn't be used horizontal.

dlarrivee said:

Neither of those, double wye or "V" as you called it, wont allow you to "roll" the fitting upwards for proper pitch, and shouldn't be used horizontal.

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Hmmm, Actually my "V" was a poorly made Y but I'll start using wye now that I know.
I get what you're saying... should I be thinking more of a single wye, maybe 2x2x1.5 like this?

The hubs in plastic fittings allow you enough "slack" to install the pipes with adequate pitch, as long as it done before the cement joint hardens. The tub and shower would need individual vents if done according to the original drawing. IF done as per the last one, one of the two would have to be vented before they come together. The vent after their merger would be basically cosmetic. The vanity would also need its own vent connection.

hj said:

The hubs in plastic fittings allow you enough "slack" to install the pipes with adequate pitch, as long as it done before the cement joint hardens. The tub and shower would need individual vents if done according to the original drawing. IF done as per the last one, one of the two would have to be vented before they come together. The vent after their merger would be basically cosmetic. The vanity would also need its own vent connection.

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So if I had a vent in the shower line before the 2x2x2 wye it would be OK?

And the vent coming from the stack is no longer directly below a wall so it would have to horizontal (plus whatever rise "slack" allowed) over about 18". At that point it would turn vertical up the vanity wall and I figured the vanity could just tie into it pretty much as it did originally. That would put the lav drain only about 24" from where it hits a vent. Not OK?

Just so you guys don't think I came up with this design out of thin air, here's a pic of the original dwv lines from a top view. The biggest difference now is that the toilet has been moved to the same side of the waste stack that the tub and shower drains are. In the original, there was no separate venting for the tub or shower or lav. The vent was straight above the stack and went up thru the wall with the lav tying into it enroute. That's why I figured it would be ok to just have one vent for everything.

The other difference is that the shower has been moved back so that it is now further from the stack/vent. I think the drain would be about 65" from the vent. (maybe 5" too much?)

This system has worked fine since 1959. I realize codes have changed but I often can't understand the "why's" of the codes and I'm trying to follow common sense along with code.

Thanks again,
John

It worked because the pipes are large enough that it never filled with water to pull a siphon on the tub or shower trap. Simple as that. Combination waste and vent basically.

Hackney plumbing said:

It worked because the pipes are large enough that it never filled with water to pull a siphon on the tub or shower trap. Simple as that. Combination waste and vent basically.

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Sooo...is there any reason to think my slightly changed plan wouldn't work as well? PVC smaller diameter? Shower drain line too long? Or is it that even if it works fine, it's not code compliant?

LocalHero said:

Sooo...is there any reason to think my slightly changed plan wouldn't work as well? PVC smaller diameter? Shower drain line too long? Or is it that even if it works fine, it's not code compliant?

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If you want to comply with your local codes I would suggest calling an inspector and explaining your working on your existing personal residence and would like to purchase a permit and have a short discussion about the venting issue. He may approve an alternate system or he may make you install vents. Adding a vent may not be as difficult as you think. In some areas homeowners cant even pull permits for their own homes.

If you were asking us how a plumber would do it, that would be different then asking us to approve something that could perhaps physically work, but not typical of current plumbing codes.

Right now it looks like the lav would be S trapped, which I have never been allowed to do.

Well here we're required to have engineer-stamped plans for such work. I'd like to stick with code but I can't see paying an engineer for approval on the framing changes I already made two years ago when I re-did the hall bath.

Adding a vent would likely not be that difficult but so far from the discussion here I'm unclear on whether I'd need to add 1, 2 or 3 vents. Also, if I can't go with the "elevation" drawing in my second post of this thread, I dont' think the fittings will fit under the subfloor without cutting the collar off the cast iron sweep. That would make for a sketchier fernco attachment, I think (but I'm not sure). I was trying to avoid cutting the cast iron down at the horizontal level (it's right on the ground) but that might end up being the case....

Terry said:

If you were asking us how a plumber would do it, that would be different then asking us to approve something that could perhaps physically work, but not typical of current plumbing codes.

Right now it looks like the lav would be S trapped, which I have never been allowed to do.

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S trapped? (I'm looking this up...)

This is sort of what I'm looking to do. The vent stack would technically be a "wet vent" if I understand the terminology because the lav would be using it as both a drain and vent. Is that what you're saying?

If the waste ling going to the tub and the lav is 2", it would be wet vented.

Terry said:

If the waste ling going to the tub and the lav is 2", it would be wet vented.

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Dang it Terry, I thought I was going to understand your answer! Do you mean to say it wouldn't be wet vented if one or more of the lines were sized differently? And is wet venting the same thing as "S trapped?

The lav, since it "can" be run in 1-1/4" can be wet vented over the tub if you go up two sizes, or a minimum of 2"
Two pipe sizes up is 2"
Therefore, by using 2" for the tub, and then using a wye fitting to go up to the lav with 2", that makes it a legal wet vented section between the tub waste and the lav trap arm.

I really don't mind the work of venting the vanity but it would mean draining it back under the house which means adding another fixture to the stack (I think) which doesn't fit under the floor. Below is a pic of the iron I'm fernco-ing onto. If I cut the collar off the top of that iron, would I still be able to put a fernco on the cut off sweep? Is that commonly done or is it a bad idea?

Terry said:

The lav, since it "can" be run in 1-1/4" can be wet vented over the tub if you go up two sizes, or a minimum of 2"
Two pipe sizes up is 2"
Therefore, by using 2" for the tub, and then using a wye fitting to go up to the lav with 2", that makes it a legal wet vented section between the tub waste and the lav trap arm.

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The comprehension problem was mine... I thought you were saying wet vented was not OK but that's not what you were saying.

At what point would I need to switch to 2" coming from the lav? Directly from the lav so that the trap would also be 2" or somewhere else?