Design question, back venting

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ArtStudent

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Hi Terry, if the vertical pipe is a 3 inch stack going to the roof, and an upstairs bathroom drops into the same main stack, is what I have designed here up to code and/or functional? originally it was just this one toilet on the ground floor, with a 2 inch vent extending up to the roof, that 2 inch stack was cast-iron and is rusted closed so I’m replacing it with a three, but wondering if it’s OK for the drainage upstairs to pass behind the toilet if it makes sense way out to the sewer.

* for the 90 I have a long wide sweep

64239462-AEC6-49CC-9466-0FEE633533EE.png
 

Terry

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When the upstairs toilet is flushed, it's going to displace water in the downstairs toilet. Venting the downstairs toilet prevents that.

dwv_b2.jpg
 

ArtStudent

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When the upstairs toilet is flushed, it's going to displace water in the downstairs toilet. Venting the downstairs toilet prevents that.

dwv_b2.jpg
Thanks for the reply Terry.
I’m confused though, because the 3 inch stack is going through the roof. Would I vent right beside into the same 3 inch stack or do I have to run a second vent right beside the main stack right up through the roof, so I have a 3 inch main stack plus a second vent beside it?

In your diagram everything connects to the main stack from a distance, but in this case the toilet is right on the main stack if that makes sense.
 
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Terry

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Vents can tie into other vents 6" above the flood level of the fixtures served. How that looks in my picture, is tying back in at 42" above the next floor.
Every home in North American has separate venting for plumbing that extends up through the roof. This is to prevent siphoning of traps and displacement of water in fixtures. An example in the video below shows how the air in front of the charging water will lift water in a toilet bowl, allowing water to fall over the high curve and then be lost down the drain.

 

wwhitney

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In other words, your downstairs WC vent needs a path through the roof through pipes that don't carry any drainage.

So the WC vent could rise alongside the stack, and at a height of 6" above the highest flood rim of fixtures that drain into that stack, the downstairs WC vent can be combined with the stack. Because at that height, both the stack and the WC vent will only ever see air, even if every connected fixture overflowed.

Cheers, Wayne
 

ArtStudent

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Thanks so much Terry for the second reply.
I guess I just can’t wrap my head around the physics. I’ll take your advice and plumb in the 2” vent from the 3” drain post toilet to the 3” stack above toilet. Nice video!
 

wwhitney

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I’ll take your advice and plumb in the 2” vent from the 3” drain post toilet to the 3” stack above toilet.
If the WC vent connects back to the 3" stack, that connection needs to be above the highest flood rim of all the fixtures draining into the stack. So if you had fixtures on the stack for 2 stories above, it would have to rise up 2.5 stories before connecting.

If that's prohibitive, then you can check if your plumbing code allows AAVs.

Cheers, Wayne
 

Reach4

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My recollection is that AAVs are allowed in Ontario, but they have to be 6 inches min above the flood plane.

Normally it is easiest to vent a toilet by using the lavatory drainage as a wet vent.
 

ArtStudent

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If the WC vent connects back to the 3" stack, that connection needs to be above the highest flood rim of all the fixtures draining into the stack. So if you had fixtures on the stack for 2 stories above, it would have to rise up 2.5 stories before connecting.

If that's prohibitive, then you can check if your plumbing code allows AAVs.

Cheers, Wayn
If the WC vent connects back to the 3" stack, that connection needs to be above the highest flood rim of all the fixtures draining into the stack. So if you had fixtures on the stack for 2 stories above, it would have to rise up 2.5 stories before connecting.

If that's prohibitive, then you can check if your plumbing code allows AAVs.

Cheers, Wayne
hwy thanks Wayne. Wow, so I have to have a vent running right beside the stack all the way up to above second floor fixtures? I guess that’s what I’ll do!
Thanks Whitney as well
 

ArtStudent

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Hey all, so here’s what I did yesterday: I tied a 2” vent from the downstairs WC into the stack about 6” above where the upstairs washroom drains from a 3” line. Looking at what Wayne wrote it looks like I should have gone higher (ie above flood like of upstairs sink.

How’s this look?
 
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