Adding a second vanity sink

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Shros

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I am in the process off remodeling a bathroom and am converting what was a single vanity to a double. While I am not a plumber, I usually know enough to get by with a little here and there when it’s not worth calling one in on my projects. However figuring out how to properly drain and vent this one has me a bit stumped and I’m looking for ideas. I am not concerned about it passing inspection(no permit) I just want it to work properly. As you can see in the picture I am tying into galvanized pipe, not only with the drain but with the water lines as well. With the way I have it now I am unable to bring a vent back over to the stack mostly due to lack of room-(circled in red) the galvanized water lines go all the way up and don’t really allow enough room for 1 1/2” to make it thru the studs above my drain line and below is an outlet that takes also up too much space. The only places there is room for 1 1/2” ABS is where I have it running now below the outlet along the bottom plate. Also, this is in a basement-so concrete floors. Other than running the pipe as I have drawn in blue(which I don’t think works because of flood rim level) the only other idea I have is putting an AAV on at least the trap on the left if not both. Any ideas or advice is appreciated, thanks.

AD77FB6C-8932-4720-A0CA-51871788D426.jpeg
 
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wwhitney

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Your lav trap arm can't turn down before it is dry vented. More specifically, the vent has to come off before the trap arm falls one trap diameter. Plus under the UPC, which I understand ID uses, a 1-1/2" trap arm is limited to 42".

What size is the galvanized stack? If it's 1-1/2", do you know what size the horizontal pipe under the slab it connects to is? A 1-1/2" vertical drain is good for 2 lavatory traps (2 DFUs) but a 1-1/2" horizontal drain is only good for 1 DFU. So if the galvanized is 1-1/2", it needs to connect to a 2" horizontal drain; if it's 2" already, no problem.

Will the lavatories drains be more than 30" apart? If not, then you have the option to use a single trap and plumb it like a kitchen double sink. Then you just need one trap arm in the wall. That would also be only 1 DFU I believe, so it would work with a 1-1/2" horizontal under slab pipe.

If the left hand trap will be no more than 42" from the galvanized stack, including the length of the trap arm outside the wall, then you have the option to cut open the galvanized stack and put in 2 san-tees, one on top of each other (the top one could be a street san-tee). You'd need 2 holes in that first stud, so it might bear reinforceing.

Otherwise, you'll need to add a san-tee behind the left hand sink, open up more wallboard, add two san-tees to the galvanized stack, one below the existing for the new drain, and one above the existing (and at least 6" above the flood rim level) for the vent to tie back in. The right hand lav can be served by a san-tee at the existing location. If that means converting more of the galvanized water lines to PEX so you can route them out of your way, that's what you'd have to do.

Cheers, Wayne
 

Shros

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Your lav trap arm can't turn down before it is dry vented. More specifically, the vent has to come off before the trap arm falls one trap diameter. Plus under the UPC, which I understand ID uses, a 1-1/2" trap arm is limited to 42".

What size is the galvanized stack? If it's 1-1/2", do you know what size the horizontal pipe under the slab it connects to is? A 1-1/2" vertical drain is good for 2 lavatory traps (2 DFUs) but a 1-1/2" horizontal drain is only good for 1 DFU. So if the galvanized is 1-1/2", it needs to connect to a 2" horizontal drain; if it's 2" already, no problem.

Will the lavatories drains be more than 30" apart? If not, then you have the option to use a single trap and plumb it like a kitchen double sink. Then you just need one trap arm in the wall. That would also be only 1 DFU I believe, so it would work with a 1-1/2" horizontal under slab pipe.

If the left hand trap will be no more than 42" from the galvanized stack, including the length of the trap arm outside the wall, then you have the option to cut open the galvanized stack and put in 2 san-tees, one on top of each other (the top one could be a street san-tee). You'd need 2 holes in that first stud, so it might bear reinforceing.

Otherwise, you'll need to add a san-tee behind the left hand sink, open up more wallboard, add two san-tees to the galvanized stack, one below the existing for the new drain, and one above the existing (and at least 6" above the flood rim level) for the vent to tie back in. The right hand lav can be served by a san-tee at the existing location. If that means converting more of the galvanized water lines to PEX so you can route them out of your way, that's what you'd have to do.

Cheers, Wayne
Thank you for your informative response. So the stack is 2”, the sinks are around 32” making the left sink right around 42” front the stack. So if I understand correctly it sounds like I could get away with a double sink trap(which I’d rather not do because of what I’d have to do to the cabinet) or bring two San-tees off the stack. Just to make sure I’m on the same page is the picture below what you mean? Or do both have to have a running back to the stack? Also do you see anything wrong with my idea of using an aav on the left? Thanks again
 

Shros

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Thank you for your informative response. So the stack is 2”, the sinks are around 32” making the left sink right around 42” front the stack. So if I understand correctly it sounds like I could get away with a double sink trap(which I’d rather not do because of what I’d have to do to the cabinet) or bring two San-tees off the stack. Just to make sure I’m on the same page is the picture below what you mean? Or do both have to have a running back to the stack? Also do you see anything wrong with my idea of using an AAV on the left? Thanks again

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wwhitney

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Does ID allow AAVs? The base UPC doesn't, but I don't know what amendments ID may have.

Basically each lav trap needs a vent, and the part that is missing from both your drawings is that the vent takeoff has to occur at an elevation that is at most 1-1/2" lower than the 1-1/2" trap outlet. So the trap arm can't go down before the vent takeoff.

If your run (with 1/4" per foot slope) from the left hand sink trap, into the wall, and horizontally across to the 2" stack is 42" or under, then you can use the stack to vent your left hand lav (assuming there's no drainage coming down the stack from above). In that case you could also use the stack to vent your right hand lav, by running a separate trap arm above or below the left hand sink trap arm, to a separate san-tee on the stack.

If it's longer than 42", then you have a couple options, The AAV would work for the left hand sink if it is allowed, with the right hand sink vented by the stack. In that case the left hand sink drain could turn down after the AAV (right at the wall is fine, if the AAV is under the sink as is common), then turn back horizontal and connect to the stack below the existing san-tee.

Or you can open up the wall more and use a separate san-tee behind the left hand sink to vent it. The new vent would rise to at least 6" above the lavs, then run to the right and connect to the stack. The stack would have 3 connections on it, from top to bottom they would be left hand sink vent, right hand sink vent and drain, left hand sink drain.

Cheers, Wayne
 

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Does ID allow AAVs? The base UPC doesn't, but I don't know what amendments ID may have.
Basically each lav trap needs a vent, and the part that is missing from both your drawings is that the vent takeoff has to occur at an elevation that is at most 1-1/2" lower than the 1-1/2" trap outlet. So the trap arm can't go down before the vent takeoff.

If your run (with 1/4" per foot slope) from the left hand sink trap, into the wall, and horizontally across to the 2" stack is 42" or under, then you can use the stack to vent your left hand lav (assuming there's no drainage coming down the stack from above). In that case you could also use the stack to vent your right hand lav, by running a separate trap arm above or below the left hand sink trap arm, to a separate san-tee on the stack.

If it's longer than 42", then you have a couple options, The AAV would work for the left hand sink if it is allowed, with the right hand sink vented by the stack. In that case the left hand sink drain could turn down after the AAV (right at the wall is fine, if the AAV is under the sink as is common), then turn back horizontal and connect to the stack below the existing san-tee.

Or you can open up the wall more and use a separate san-tee behind the left hand sink to vent it. The new vent would rise to at least 6" above the lavs, then run to the right and connect to the stack. The stack would have 3 connections on it, from top to bottom they would be left hand sink vent, right hand sink vent and drain, left hand sink drain.

Cheers, Wayne
Does ID allow AAVs? The base UPC doesn't, but I don't know what amendments ID may have.

Basically each lav trap needs a vent, and the part that is missing from both your drawings is that the vent takeoff has to occur at an elevation that is at most 1-1/2" lower than the 1-1/2" trap outlet. So the trap arm can't go down before the vent takeoff.

If your run (with 1/4" per foot slope) from the left hand sink trap, into the wall, and horizontally across to the 2" stack is 42" or under, then you can use the stack to vent your left hand lav (assuming there's no drainage coming down the stack from above). In that case you could also use the stack to vent your right hand lav, by running a separate trap arm above or below the left hand sink trap arm, to a separate san-tee on the stack.

If it's longer than 42", then you have a couple options, The AAV would work for the left hand sink if it is allowed, with the right hand sink vented by the stack. In that case the left hand sink drain could turn down after the AAV (right at the wall is fine, if the AAV is under the sink as is common), then turn back horizontal and connect to the stack below the existing san-tee.

Or you can open up the wall more and use a separate san-tee behind the left hand sink to vent it. The new vent would rise to at least 6" above the lavs, then run to the right and connect to the stack. The stack would have 3 connections on it, from top to bottom they would be left hand sink vent, right hand sink vent and drain, left hand sink drain.

Cheers, Wayne
So it is exactly 42” from the left to the stack. Is there any reason I could leave it the way it is and do an aav on the left trap(under sink inside cabinet)? That outlet is in my way to do it as you described. I can move it up if need be but aside from the extra work it’s plaster so it’s not much fun to mess with.
 

wwhitney

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So it is exactly 42” from the left to the stack.
Is that 42" within the wall? The measurement includes the portion outside the wall, so if it's 42" within the wall, it's definitely over the allowable length once you add the plumbing under the sink.

Is there any reason I could leave it the way it is and do an aav on the left trap(under sink inside cabinet)?
As far as I can easily tell (via a minimal web search), ID does not allow AAVs in bathrooms. I've given you a number of code compliant options; the current configuration is not one of them.

If you need to open up more plaster, you can get away with just opening the stud bay with the galvanized water lines, and the stud bay with the stack. That will let you rearrange the galvanized lines and tie a new vent back into the stack at 6" above the vanity flood rim or higher. You could put a new san-tee for the left hand sink on the left edge of the stud bay with the galvanized lines.

Cheers, Wayne
 

wwhitney

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If you need to open up more plaster, you can get away with just opening the stud bay with the galvanized water lines, and the stud bay with the stack.
E.g. as in the drawing below, where the purple is the new plastic DWV, and the circles are where the stub outs turn out of the wall with LT90s.

Cheers, Wayne

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Shros

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Does ID allow AAVs? The base UPC doesn't, but I don't know what amendments ID may have.

Basically each lav trap needs a vent, and the part that is missing from both your drawings is that the vent takeoff has to occur at an elevation that is at most 1-1/2" lower than the 1-1/2" trap outlet. So the trap arm can't go down before the vent takeoff.

If your run (with 1/4" per foot slope) from the left hand sink trap, into the wall, and horizontally across to the 2" stack is 42" or under, then you can use the stack to vent your left hand lav (assuming there's no drainage coming down the stack from above). In that case you could also use the stack to vent your right hand lav, by running a separate trap arm above or below the left hand sink trap arm, to a separate san-tee on the stack.

If it's longer than 42", then you have a couple options, The AAV would work for the left hand sink if it is allowed, with the right hand sink vented by the stack. In that case the left hand sink drain could turn down after the AAV (right at the wall is fine, if the AAV is under the sink as is common), then turn back horizontal and connect to the stack below the existing san-tee.

Or you can open up the wall more and use a separate san-tee behind the left hand sink to vent it. The new vent would rise to at least 6" above the lavs, then run to the right and connect to the stack. The stack would have 3 connections on it, from top to bottom they would be left hand sink vent, right hand sink vent and drain, left hand sink drain.

Cheers, Wayne
Or if I have to do the aav the way you described does the lav arm on the right need to have a vent running back to the stack or are you saying the stack acts as it’s vent (hope that makes sense)
 

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In case it would be easier for some reason, here's another option:

The left hand sink is dry vented and wet vents the right hand sink. Purple now means 1.5" and Green means 2". In the stud bay with the galvanized water lines, you'd need an upright 2x1-1/2x1-1/2 combo for the vent to come off, followed by a horizontal 2x2x1-1/2" combo for the right hand sink stub out (you can't use a san-tee horizontally as in your picture, it needs to be a combo).

[In the previous drawing I didn't show sizes, but all the purple could be 1-1/2", except the stack on the right would stay 2".]

Cheers, Wayne


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Shros

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In case it would be easier for some reason, here's another option:

The left hand sink is dry vented and wet vents the right hand sink. Purple now means 1.5" and Green means 2". In the stud bay with the galvanized water lines, you'd need an upright 2x1-1/2x1-1/2 combo for the vent to come off, followed by a horizontal 2x2x1-1/2" combo for the right hand sink stub out (you can't use a san-tee horizontally as in your picture, it needs to be a combo).

[In the previous drawing I didn't show sizes, but all the purple could be 1-1/2", except the stack on the right would stay 2".]

Cheers, Wayne


View attachment 81159
So I think I’m going to go with the last option you sent but I realized today that the stack actually does drain 1 vanity sink from above. The single vanity above is also supposed to be converted to a double vanity…
 

wwhitney

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So I think I’m going to go with the last option you sent but I realized today that the stack actually does drain 1 vanity sink from above. The single vanity above is also supposed to be converted to a double vanity…
Then you need to separate the stack into two stacks (each could be 1-1/2" if you are talking about only 2 lavatory upstairs, 2 lavatories downstairs). One side is the drain from upstairs, the other side is the vent from downstairs. The two stack could combine once they are both vents (i.e. 6" above the upstairs flood rim) and also once they are both drains (i.e. below the downstairs vanities.

Cheers, Wayne
 

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For example, like the right side of the drawing below. This assumes stacked walls, and I duplicated your downstairs picture to stand in for upstairs. Avoiding having the vent stack cross the upstairs drains could be tricky, in the example I put one of the upstairs lavs on the other side of the existing stack to make that simple. The exact details would depend on the relative placements of the upstairs and downstairs lavs along the stacked wall line, assuming the walls really are stacked.

Cheers, Wayne


D3A5F8BB-A5DB-4C4F-9BC7-7D70666D5E5D.jpeg
 

Shros

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For example, like the right side of the drawing below. This assumes stacked walls, and I duplicated your downstairs picture to stand in for upstairs. Avoiding having the vent stack cross the upstairs drains could be tricky, in the example I put one of the upstairs lavs on the other side of the existing stack to make that simple. The exact details would depend on the relative placements of the upstairs and downstairs lavs along the stacked wall line, assuming the walls really are stacked.

Cheers, Wayne


View attachment 81180
Sorry, another question for you. Does the vent have to be in between the two stub outs or can I have a t with a 90 to the left of the left stub?
 

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Sorry, another question for you. Does the vent have to be in between the two stub outs or can I have a t with a 90 to the left of the left stub?
Also, the bathrooms are basically duplicates on top of each other. So I will have to do almost the same thing upstairs but also need to keep this vent out of the way of not only the plumbing but also electrical/lights etc. so that stud bay on the left is going to be my best best-hence hoping to run it to the left of the lav. I can obviously run it back over that way but would hope to be able to take it straight up from a 90
 

wwhitney

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Sorry, another question for you. Does the vent have to be in between the two stub outs or can I have a t with a 90 to the left of the left stub?
A dry vent can't be horizontal until 6" above the fixture flood rim. So you can't use a combo horizontally with the straight entry for the dry vent takeoff. If a combo with the straight entry bent up at 45 degrees existed, you could use that to do what you suggest, but it doesn't exist.

Since you said the bathrooms are basically stacked, here's one last drawing for you. Brown is wood framing, with 2x members rendered as a line, but the floor framing as two lines. Purple is 1.5", Green is 2". It keeps the 2" stack in place (although given that it's galvanized, it would probably be wise to replace it with plastic at this time). The upper right lav could be plumbed like the lower right lav instead, if you'd prefer to put one 2" drain through that stud, instead of (2) 1.5" drains through that stud.

Also, this whole discussion is predicated on the idea that the other bathroom fixtures are properly vented elsewhere. Often the lav drains are useful for wet venting the other bathroom fixtures, so it's a bit unusual to have a stack just for lavs.

Cheers, Wayne

Option.jpg
 

Clay033

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A dry vent can't be horizontal until 6" above the fixture flood rim. So you can't use a combo horizontally with the straight entry for the dry vent takeoff. If a combo with the straight entry bent up at 45 degrees existed, you could use that to do what you suggest, but it doesn't exist.

Since you said the bathrooms are basically stacked, here's one last drawing for you. Brown is wood framing, with 2x members rendered as a line, but the floor framing as two lines. Purple is 1.5", Green is 2". It keeps the 2" stack in place (although given that it's galvanized, it would probably be wise to replace it with plastic at this time). The upper right lav could be plumbed like the lower right lav instead, if you'd prefer to put one 2" drain through that stud, instead of (2) 1.5" drains through that stud.

Also, this whole discussion is predicated on the idea that the other bathroom fixtures are properly vented elsewhere. Often the lav drains are useful for wet venting the other bathroom fixtures, so it's a bit unusual to have a stack just for lavs.

Cheers, Wayne

View attachment 81188
 

Clay033

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Hopefully someone can answer a question for the last plumbing configuration posted by Wayne. When vertically locating the first floor auxiliary vent pipe (also referred to as revent pipe) above the horizontal branch on the second floor, what is the minimum vertical distance that can exist between the auxiliary vent pipe and the horizontal branch below it? Is it required to be a minimum of 6" above the flood level of the fixture attached to the horizontal branch or a greater distance? Thank you, you guys are awesome for the guidance and experience you freely share!!!
 
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