Adding second floor bathroom, is this vent diagram ok?

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Cserman

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Please help. Can I vent these fixtures this way for the new second floor bathroom? I'm attaching a diagram. The toilet is using the main 3" vent without a separate vent. It is only about 12" from the stack. Any comments greatly appreciated.

Can the existing 1st floor fixtures remain as they are without individual vents?
 

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wwhitney

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No, you can't use a single 3" stack (vertical pipe between stories) as the vent for the downstairs bathroom and the drain for the upstairs bathroom. You'd need to run separate 3" pipes between stories. And the upstairs bathroom drain should join the downstairs bathroom drain downstream of all the downstairs fixtures, to avoid disrupting the wet venting in the downstairs bathroom.

Actually, the downstairs lavatory should have its own dry vent, either through the roof or an AAV, which is missing from your drawing. And then if the 3" stack is properly dry venting the WC (the way you've drawn it doesn't comply with the dry vent rules, as the dry vent is horizontal below the floor) and then wet venting the downstairs shower, the upstairs bathroom drain could join the 4" downstream of the downstairs shower.

Cheers, Wayne
 

Terry

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Can the existing 1st floor fixtures remain as they are without individual vents?

No vents on the first floor?


Venting goes up by itself, and ever fixture needs to be properly vented, not just a vent here and there thrown in.
The waste lines going down stays separate too.

dwv_b2.jpg
 

Cserman

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Thank you both Wayne and Terry, I very much appreciate your replies. Does this look better? I was not sure what you meant Wayne about the WC dry vent comment. Were you referring to the upstairs WC or the downstairs?
Terry, can I combine the upstairs drains into one 3" that connects downstream of the 1st floor fixtures?
 

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wwhitney

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I was not sure what you meant Wayne about the WC dry vent comment. Were you referring to the upstairs WC or the downstairs?
I was referring to the downstairs WC. In the first drawing you posted, if you just delete the upstairs bathroom completely, the dry vent path for the downstairs WC isn't correct. A dry vent has to come off the upper half of the drain, and it has to rise at least at a 45 degree angle until 6" above the flood rim level of the fixture. So the WC dry vent can't go horizontal under the floor to reach the 3" stack you have.

Your last drawing is fine; the 3" stack on the right has the same problem as far as dry venting the WC, but the dry vented shower (assuming its vent complies with the above rules) will wet vent the WC. In fact if you want to reduce the number of dry vent take offs, you could do it like in the drawing below. Upstairs the dry vented lav can wet vent both the upstairs shower and the upstairs WC. In fact downstairs you could eliminate the shower dry vent if you rerouted the lav drain to join the horizontal line between the shower and the WC; then it would wet vent both the WC and the shower. [The dry vented fixture wet venting the bathroom group can't be the third or later fixture, it has to be one of the two most upstream.]

Note that the vent takeoff for a sink or a shower (or anything with an external trap) has to happen before the drain (trap arm) falls more than one pipe diameter. On a wet vent, that vent connection is where the fixture drain joins the horizontal drain that is carrying the dry vented fixture.

Cheers, Wayne


Venting.png
 

Cserman

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I was referring to the downstairs WC. In the first drawing you posted, if you just delete the upstairs bathroom completely, the dry vent path for the downstairs WC isn't correct. A dry vent has to come off the upper half of the drain, and it has to rise at least at a 45 degree angle until 6" above the flood rim level of the fixture. So the WC dry vent can't go horizontal under the floor to reach the 3" stack you have.

Your last drawing is fine; the 3" stack on the right has the same problem as far as dry venting the WC, but the dry vented shower (assuming its vent complies with the above rules) will wet vent the WC. In fact if you want to reduce the number of dry vent take offs, you could do it like in the drawing below. Upstairs the dry vented lav can wet vent both the upstairs shower and the upstairs WC. In fact downstairs you could eliminate the shower dry vent if you rerouted the lav drain to join the horizontal line between the shower and the WC; then it would wet vent both the WC and the shower. [The dry vented fixture wet venting the bathroom group can't be the third or later fixture, it has to be one of the two most upstream.]

Note that the vent takeoff for a sink or a shower (or anything with an external trap) has to happen before the drain (trap arm) falls more than one pipe diameter. On a wet vent, that vent connection is where the fixture drain joins the horizontal drain that is carrying the dry vented fixture.

Cheers, Wayne


View attachment 88195
Thanks a ton, I think I got it now and am attaching the drawing again with the 1st floor lav wet venting the shower and WC. Now hopefully I can actually get this plumbing in! - Chad
 

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wwhitney

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Yes, that works. Bear in mind the limit on the fall of each shower and lav trap arm, while maintaining the minimum 2% slope.

A note on sizing: the IPC would allow a 1-1/2" vent for each lav, combining to a 2" vent through the roof if you have a 4" building drain. But if you are in a cold climate where the vent through the roof would frost over, you need to upsize the vent to 3" before it exits the thermal envelope of the building. So I'd suggest using 2" vents on the lavs, with 2" lav and shower drains, keeping the 2" vents in the thermal envelope, and combining them to a 3" vent through the roof. [Partially because my plumbing code, the UPC, would require those sizes.]

Cheers, Wayne
 

Cserman

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Yes, that works. Bear in mind the limit on the fall of each shower and lav trap arm, while maintaining the minimum 2% slope.

A note on sizing: the IPC would allow a 1-1/2" vent for each lav, combining to a 2" vent through the roof if you have a 4" building drain. But if you are in a cold climate where the vent through the roof would frost over, you need to upsize the vent to 3" before it exits the thermal envelope of the building. So I'd suggest using 2" vents on the lavs, with 2" lav and shower drains, keeping the 2" vents in the thermal envelope, and combining them to a 3" vent through the roof. [Partially because my plumbing code, the UPC, would require those sizes.]

Cheers, Wayne
Thanks Wayne.. I don't want to push my luck, but I'm also adding a bath and kitchen in a detached garage and there is a kitchen sink in the house which is the last to connect. Is this connection from the accessory dwelling unit ok to make at this point on the main line? I already have approval from the building department to connect to the house main but not sure if connecting here is ok?
 

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wwhitney

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Yes, that can work. You haven't specified the venting on the ADU bath and kitchen, but what is required there doesn't affect anything in your diagram.

Cheers, Wayne
 

Cserman

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Good evening Wayne. If the ADU connection was moved to the end where the cleanout is would that still be ok? It would allow for a much more direct line to the garage.

Best,
Chad
 

Cserman

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Sure, the order of the ADU vs the main kitchen doesn't matter.

Cheers, Wayne
Thank you Wayne. Can you please give one last look at the attached updated drawing showing the ADU? give one last look at the attached updated drawing showing the ADU? Do any major problems jump out at you?

plumbing with ADU.jpg
 

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wwhitney

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Thank you Wayne. Can you please give one last look at the attached updated drawing showing the ADU? give one last look at the attached updated drawing showing the ADU? Do any major problems jump out at you?
Yes, you have several problems with venting.

1) The upper left shower has a dry vent takeoff that is on the top of the trap arm, but it turns horizontal below the floor. It need to continue rising at least 45 degrees above level until at least 6" above the shower flood rim. I.e. to dry vent a shower you need to route the shower trap arm alongside or under a wall that your dry vent will rise up into.

2) Do I understand correctly that the right hand drawing is the ADU, and that the 4" horizontal on the right connects to the 4" horizontal on the left? In that case, to wet vent the left hand downstairs bathroom, you need to keep its branch drain separate form the 4" line until the wet venting is done. Which will also help you with the next issue

3) The downstairs left hand shower trap arm can't turn down before being wet vented. With a horizontal wet vent for the shower, the shower trap has to be at the same elevation (other than the 2% slope) as the horizontal wet vent. So add a 3" horizontal bathroom branch just below the joists, drop the shower trap to that level, as well as the lav and WC connections, and then the left end of the 3" horizontal bathroom branch can drop down into the 4".

4) On the right side, the washer drain has to join the bathroom drain downstream of all the bathroom fixtures to use wet venting for the bathroom fixtures.

5) The right shower trap needs to be lowered same as in (3)

6) The mop sink needs a vent, either connecting up to the vents through the roof, or an AAV.

Cheers, Wayne
 

Cserman

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Thank you Sir. Can I still wet vent the upper left shower using the lav vent? I believe you mentioned that would work before.

For your 5 other comments, please check the updated drawing, am I understanding you correctly?
PLUMBING V3.0.jpg
 

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wwhitney

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On your latest drawing:

- The right side laundry standpipe needs a dry vent, through the roof or AAV. The length of the standpipe is limited (42"?) and the trap is typically above the floor.

- The right side shower can be wet vented by the lav like that, but the trap arm includes all of the pipe between the trap and where the vertical lav pipe connects. That trap arm is limited to 2" of fall, so 96" in length if you keep it at perfectly at the minimum 1/4" per foot of fall.

- You're drawing your 3 way connections as square inside corner tees. They need to be combos or san-tees as appropriate.

- On the left side upper bathroom, that can work for wet venting. You show the lav and shower hitting the stack with the WC on top at the same elevation. Depending on how that looks in plan, you need to get the right 4-way fitting to do that. If there's some out of the page offset between the lav drain and the shower trap arm, it might be simpler to join the lav drain to the shower trap arm on the horizontal, and then the combined drain connects to the stack with a san-tee or combo.

Cheers, Wayne
 
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