Is a 3" stack vent absolutely required?

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broddo

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Hi there! I'm in Ontario and I have an annoying situation. I'm doing a 2nd storey addition. My existing 3" stack is now located directly under a window on the new floor. This detail got missed by the architect. Moving the window at this point isn't really an option and space is pretty tight in that location anyway.

I've a couple of options - I'm just not sure which ones meet code.

Option 1: I can offset the stack in the floor. The photo illustrates this. You can see the top of the stack in the floor below the window. As space is tight, the vent portion would have to run horizontally for about 16 inches before going vertical. Then, when vertical, I would have to embed it in the 2x6 exterior wall which means notching that double top plate (could probably bore a hole but I don't know if this would be better). I don't know if code allows me to do this as the 3" OD is more than 50% the width of the stud.
So this option has two caveats: can I run the vent horizontally and can I cut into that support wall (maybe add some reinforcement)

Option 2: Don't vent the stack here at all - the attached photos illustrate this one. Instead add a 3" vent further upstream in the main bathroom ( works out about 6 foot away from the stack). The attached diagram illustrates my thinking here. This way, I don't have to worry about going through structural framing, however a portion of the vent probably has to go horizontal to get to where it needs to be.

Option 3: Do I need this 3" stack vent at all? If I properly vent every other fixture in the bathroom and connect them to a header in the attic before venting out the roof, would this work? The exit to the roof would have to be 3" anyway. The header could also be 3". I could also vent the stack using something smaller that wouldn't be so hard on the structural framing if that helped.

Can anyone tell me if any of these meet Canadian code and which option is best?
Many thanks!
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Reach4

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I don't know Ontario code.

What part of your drawing exists already? Is that everything outside of the dashed-line box? Your drawing is not the kind of thing that is normal wet venting.

How big is your existing TTR (thru the roof) vent? You may be able to join stuff in the attic. In cold areas, the TTR vent often needs to be larger than the vents in the walls need to be. That is to prevent the vent from getting iced up.
 

Breplum

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The UPC dictates only that total vent area must equal largest required building drain diameter area.
For many homes, that means, with a three inch drain that you can use any combination of smaller vents that comes to equal the area of three, like two 2" vents and one 1-1/2" vent.
 
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broddo

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I don't know Ontario code.

What part of your drawing exists already? Is that everything outside of the dashed-line box? Your drawing is not the kind of thing that is normal wet venting.

How big is your existing TTR (thru the roof) vent? You may be able to join stuff in the attic. In cold areas, the TTR vent often needs to be larger than the vents in the walls need to be. That is to prevent the vent from getting iced up.
The only part that exists so far is the vertical stack. All the rest is just ideas at the moment. The diagram leaves out a lot details so don't worry, I will vent those properly. However, the thing I wanted to point out mainly is if the 3" vent is ok being located upstream from the stack.

The TTR needs to be at least 3" so yes indeed I'd need to step up a 2" for icing. The original one was this size but it has been cut away now to make room for the new floor.
 

broddo

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The UPC dictates only that total vent area must equal largest required building drain diameter area.
For many homes, that means, with a three inch drain that you can use any combination of smaller vents that comes to equal the area of three, like two 2" vents and one 1-1/2" vent.

Thanks, I wasn't aware of this. This might help me navigate the Canadian NPC better.

Here are the 3 venting relevant statements from the NPC that I've found:
2.5.4.1 Stack Vents
1) The upper end of every soil-or-waste stack shall terminate in a stack vent

2.5.7.2 Size Restriction
1) The size of a branch vent, stack vent, vent stack or vent header shall be not less than the size of the vent pipe to which it is connected
2) Sanitary building drains shall be provided with at least one vent that is not less than 3 inches in size.
My reading of this is that I would need a vent extending vertically from the original stack, but that vent only needs to be 1 1/12 inches (totally doable).

It's the last clause that causes me problems - my read of that is I must vent that same stack with 3". I can't tell if that means 3" TTR and can be smaller elsewhere or of the vent must be 3" never reducing but that 3" could be anywhere.
 

Reach4

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I expect that 3 inches is thru the roof, and that it can be smaller at some point earlier. Whether that point is at a place that will not freeze, or somewhere higher than that, I don't know. But you may be able to figure that out from the wording.

Your drawing has a pipe coming in from the lower right, and that is labeled "To other bathroom." I expect you mean from other bathroom. Does that pipe already exist, and you will cut into it? Or is the other bathroom not yet built either.
 

broddo

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I expect that 3 inches is thru the roof, and that it can be smaller at some point earlier. Whether that point is at a place that will not freeze, or somewhere higher than that, I don't know. But you may be able to figure that out from the wording.

That’s encouraging. I can check the language surround freezing.

Your drawing has a pipe coming in from the lower right, and that is labeled "To other bathroom." I expect you mean from other bathroom. Does that pipe already exist, and you will cut into it? Or is the other bathroom not yet built either.

Correct, that should read as: from other bathroom. That bathroom doesn’t exist yet and either does that horizontal pipe so I won’t be cutting into anything - just adding on as I continue upstream.
 

John Gayewski

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Where all the vents connect to each other should be 3". You could have each bathroom vent with 2"then connect to each other via 3" common vent.
 
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