Ok to use a sanitary cross in a wet vent?

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peeks

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I'm wet-venting my shower drain. The wet vent will consist of the shower drain pipe connecting to the drain pipe coming from the sink. There is a vent from the sink up through the roof. I've checked with the local inspector to make sure all the pipe sizes are correct, but I forgot to ask him about the correct fitting to use when connecting the the shower drain pipe to the sink drain pipe. Ideally I'd like to use a sanitary (waste) cross placed upright, as it's supposed to be. Put the shower drain pipe into one side of the cross and the sink drain pipe into the other side. Then cap off the top of the cross with a cleanout fitting, and connect the bottom into the waste stack.

I'm guessing the sanitary cross is the fitting I want to use here, but I thought I'd check with folks that know more about it.

Thanks in advance!
 

Terry

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That won't work.

You can't use an "S" trap on the lav.
The trap arm for the lav should be 18" to 22" from the floor.
The trap arm for the shower will be below the floor.

A wet vent would nomally be a 2" santee for the shower and a 2"x1.5"x1.5" santee for the lav. The vertical between the two is one pipe size up, therefore the 2" vertical up to the the lav santee.

It's ok to increase the vent beyond that too. You never get into trouble doing things better.
The smallest vent you can use on top of the lav santee would be 1.5"

dwv_b1.jpg
 

peeks

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cross in a wet vent?

Terry,

Thanks for your comments although I don't know if I understand fully why it won't work. Here's a diagram of what I described in my original post:

My local inspector already approved this design (in fact he suggested it) - with the exception of the sanitary cross fitting. He used a wye in his sketch because all the piping was going to be horizontal. However the location of the drain tie-in has changed a little since then so I was wondering about substituting a cross for the wye. I don't see the problem with that substation so long as the wye remains vertical.

So I'm confused - are you suggesting that the use of the cross fitting is bad, or are you suggesting that the entire wet-venting design being employed here is flawed? If the entire design is flawed, what would you suggest be done to

fix it so it meets code?

Thanks!
 

Terry

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Well..........Not the UPC Plumbing code.

That's a strange way of doing that.
No inspectors I know would let me do that.

If you can't wet vent it right, it should be done the standard way.
Each trap gets a vent, and then tie the two vents together at 42" above the floor.

I don't know why you wouldn't want to spend $10 more and get it right.
 
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peeks

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sanitary cross in a wet vent?

Terry,

Ok - if you don't think it's to code then I believe you. There must have been a miscommunication between he and I. I better go check with him again.

Can you do me a favor and please tell me what piece(s) of the proposed design are flawed?

Thanks!
 

Jimbo

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A recent post on another forum discussed problems the owner was having with an installation involving a cross. One arm was the toilet, and solid waste was flowing over into the other arm and then sitting there, causing slow drainage. The solution was to use a double wye to ensure that waste from both arms went DOWN into the stack. So, codes and inspectors may allow one or the other, but I hope this explains the rationale for recommending against the cross.
 

hj

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cross

It is a "dumb" way to do it. If the line beyond the cross ever gets plugged, and it will someday, there is no way it could be snaked without the snake going across into the shower trap, or across and up the sink drain, depending on where you started. And if you use a "Y", or double "Y", you create an "S" or 3/4 "S" trap for the shower which is also illegal. If you are going to do it that way, and I would try something better first, then a sanitary tee for the shower with an elbow on top going to the sink would be a better solution.
 

peeks

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sanitary cross in a wet vent

First thanks very much everyone for your comments. I checked with the inspector and he advised me not to use the cross fitting just like everyone here did. Ok fine, so that's eliminated. He said that if a wye is substituted then it should be fine. So here's what I've got now:

wet_vent_line_drawing.JPG


How does this look? There was some discussion previously about an "S" trap not being allowed on the lav. I'm not sure what this means since I don't use an S trap - I have 2 P traps. Is it a simple matter of 2 P traps in the same wet vent = 1 S trap and that's a code violation?

Looking at Terry's wet vent drawing above, it seems like I'm doing the same thing in my design except that in Terry's drawing a toilet is always used as the 2nd fixture off of the wet vent rather than using both a lav and a shower. Is this the (critical) difference?

Thanks in advance for any hints/tips/explanations/suggestions,
 

peeks

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sanitary cross in a wet vent

Wait, I think I may have just had a breakthrough in understanding this. I just Googled "illegal s-trap" and came up with the following definition:

"A trap having its weir installed above the inlet of the vent connection."

an interpretation of the above that I also found is:

"the pipe going out of the trap to the drain pipe cannot drop downward until it is past a vent source."

So this was violated in my original drawing, since the drain came before the vent. However in my latest drawing above I don't think I have an illegal S-trap configuration since the branch drain from the shower ties right into the wet vent section.

Is this interpretation correct or am I still way off?

Thanks again!
 

Terry

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Getting there

If you roll off with a wye and a 45 to the lav, that could work.
You would treat the lav line as a vent for the shower.
Flat vents are rolled higher slightly than the flow line of the pipe it serves.
Thus, if you tilted the wye and ran toward the lav with the raised end, it would keep that section of pipe clear.
 

hj

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vent

If your drawing is accurate, then you have the ""Y" in reversed. You do not give distances, but if it is within 5' from the sink riser to the shower "P" trap, put a sanitary tee in the sink riser and run from that to the "P" trap. Or put it in the riser before the first 90, and then go to the "P" trap. You are trying to make this much more complicated than it really is.
 

peeks

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sanitary cross in a wet vent?

Right, it looks like my wye is reversed in the diagram. I should have drawn it so the shower p-trap is on the left side of the drain line.

Thanks to everyone for their comments! - it looks like I have a workable solution now.
 
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