Distance between toilet and soil stack and venting

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NewPlumbingStudent

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I have tried to search for an answer to this question, both here and on Google, but I am not able to find a definition answer to what I am trying to do, but perhaps I am not understanding the terminology correctly. I am trying to pipe a new second floor addition which will add 3 more bathrooms. A rough-in diagram is attached based on what I am thinking to pipe. The main problems I am facing are

1. Venting of the water heater.

2. The bathroom on the top left-hand corner which is very far from the main stack which is sitting close to the right-hand side (the thickest vertical line on the right).

The 3 bathrooms and kitchen should all be fine because the furthest fixture is still within 10ft of the main stack, so the worst case, as far as I can tell, is that I will use a 4in PVC pipe to connect to the main stack, both top for vent and bottom for drain.

Regarding venting of the water heater. The location of it remains the same, but since there is currently no second floor (not even attic), the existing vent goes up directly and out of roof. One option is to continue to extend the same pipe going through second floor, attic, and out of roof, but this will go through the bathroom directly above in the middle. Can I use 2 90-degree PVC elbows to bring the vent into the wall, go all the way up to attic, another 2 90-degree elbows to bring the pipe inside, and then go straight up out of roof? Or potentially is there another way to tie this into the main venting/drain stack system so I don’t need to have another hole on roof? Either utilizing the newly added attic space or through walls/joists?

Regarding the bathroom on the top left-hand corner, the solution to this may be tied to water heater vent if the best solution is to have a separate vent for water heater going straight up. Ideally, I would hope to tie this bathroom into the main stack on the far right (see the copper color line named option 1). However, I don’t know if the fixtures being about 30ft away from the main stack is a problem. Option 2 is the blue line which is have another opening on top for venting. Draining will still be connected to the main stack (see the red line).

I have seen posts saying that if a toilet is within 6ft of soil stack, then 3in PVC is fine. If 4in PVC is used, then the distance can be as far as 10ft. In this particular case, toilet is about 34ft away from the main stack. Is this going to be a problem even if I use a 4in PVC pipe for draining? I am not too worried about the slope because the draining PVC pipe will go through floor joists which are 12in in height. With ~34ft, I only need to have a height differential of ~8 inches to have enough flow in the drain PVC pipe which should be okay as far as the holes on the joists are concerned.

The thing I am confused is whether the 6ft (3in PVC) or 10ft (4in PVC) distance requirement is for venting (which I am okay to add a separate vent pipe shown in blue up) or for draining (which means there is no solution unless I redesign the floor plan and move the bathroom), or for both.

We are in New Jersey.
 

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wwhitney

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Since you are in New Jersey, your plumbing code is the NSPC, which is available here:
http://epubs.iapmo.org/NSPC/NJ2018/index.html
So what you read about the IPC or UPC may not apply to you.

Your diagram is a bit confusing, as you are using up and down on the page to both mean vertical (the 2 different floors) and to mean horizontal, perpendicular to left-right (the diagrams within each floor).

NSPC allows up to (4) WCs on a 3" horizontal branch drain, so I see no reason that you would have to use 4" horizontal drains. The distance from a fixture to its vent under the NSPC is limited to 10' for 3" pipe sloped at 1/8" per foot. That distance has no bearing on the distance from fixture to drain stack or vent to drain stack.

3" horizontal lines may be sloped at 1/8" per foot under the NSPC. For a 36' horizontal run, that would be 9" of fall at 1/4" per foot, which plus the 4" OD of a 3" hub, would be 13", so too much to fit within the 11-1/4" height of a 2x12 (or even 12" if you are using engineered joists). So you'd need to use 1/8" per foot slope, unless you add a stack on the left side of the page to reduce the horizontal runs.

With 1/8" per foot slope, the drop would be 4-1/2", which allows for a total vertical interval of 8-1/2" with 3" hubs. For 2x12s, holes may be drilled only in the central 7-1/4" of the joists, which means your 3-1/2" OD pipe can only fall 3-3/4". Meaning that the first and last holes could be only 30' apart. I.e. you'd have to arrange that enough of the run at the beginning or end is parallel to the joists. [If you have engineered joists, you can check the allowable hole locations, you will likely have more flexibility.]

As for venting, the minimum number of dry vent takeoffs allowable for all the fixtures in your drawing would be 6. That's 1 each for the 4 lavatories, the washer, and the kitchen sink. Each lav dry vent can horizontally wet vent the other fixtures in its bathroom subject to certain rules. So there would be no need for any dry vent takeoff directly on the 3" horizontal drain in the bathrooms.

That should be good for a start.

Cheers, Wayne
 

NewPlumbingStudent

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PlumbingDiagram_2.jpg
As for venting, the minimum number of dry vent takeoffs allowable for all the fixtures in your drawing would be 6. That's 1 each for the 4 lavatories, the washer, and the kitchen sink. Each lav dry vent can horizontally wet vent the other fixtures in its bathroom subject to certain rules. So there would be no need for any dry vent takeoff directly on the 3" horizontal drain in the bathrooms.

Thank you very much for the comments, but I am still not very clear with what you are saying regarding dry and wet vent. However, I believe I understand why you felt my drawing was confusing (I was entirely thinking from an electrical circuit point of view so there is really no up/down concept).

Here is the updated drawing based on my understanding of the suggestions. I am assuming the followings:

1. I will likely be using TJI and, if needed, can bring the furthest fixture in the bathroom on the left hand side within about 22 feet so I have enough space in my joist to let the pipe go through. Based on the feedback, I believe I will need a separate vent pipe for this bathroom since I won't be able to tie it to the main vent stack on the far right.

2. I believe I do need a dedicated vent pipe (4"?) to vent the water heater. This means, including the two vent pipes for bathrooms and kitchen, and a furnace, I will have a total of 4 pipes sticking out of roof.

3. Just a little clarification on this new drawing:
a. I am adding a section between floors to indicate joists.
b. At the very bottom, the cast iron drain pipe goes into concrete slab which I assume goes out to the city sewer system.
c. I am not able to see how the drain pipes are connected to the cast iron pipe because I assume they are under slab. The draining pipes that I am unsure of are dotted black lines. The draining pipes that I will be adding are solid black lines. The red solid lines are the vent pipes.
 

wwhitney

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The water heater vent has no relation to DWV vents, other than that they are both roof penetrations and conduct gases. It needs to be run and installed according to a different set of rules, and doesn't really belong in this discussion. Other than possible competing for space (and it may need a certain minimum distance from combustible, depending on the type of water heater and type of vent), it doesn't really belong in this discussion.

You've drawn every single plumbing fixture as dry vented. That's fine, it's just more work than wet venting; wet venting would allow you to connect a dry vent only to the lavatory in each bathroom group, and not have to take dry vents separately off each WC, shower and tub.

Your dry vent takeoffs can recombine as you've drawn as long as every joint is 6" above all the flood rim levels of all the fixtures being vented. That means that if you want you can run the left hand bathroom group vent through the attic (or the attic floor joists) to meet up with the other combined DWV vent, and have only a single DWV roof penetration.

Vent sizing I'm not so familiar with under the NSPC, the rules differ between the UPC and IPC, and the NSPC is probably somewhere in between.

Cheers, Wayne
 

NewPlumbingStudent

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Thanks Wayne! Glad at least I have created something that works, but probably not efficient like you have pointed out. Thank you for responding this late. Would you mind to take a look at this drawing as I have attempted to create wet vents for 3 out of the 4 bathrooms (except the one on the lower right hand corner and I will explain why I left it out shortly).

The bathroom on the lower right-hand corner is an existing one and I cannot tell where the draining and vent pipes are really going. Given the house was built in the 50s, I don't even know if there were proper vent pipes built in. Since I do not want to break up the slab for this, is there any harm that I still build a dry vent for each of the 3 fixtures in this bathroom, even if there could be a vent built in elsewhere? In other words, can I have, say, 2 vent pipes for a, say, toilet?

It is much cheaper to waste a few feet of PVC pipe and maybe a couple more hours of work than breaking up the concrete slab.
 

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wwhitney

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The drains under the slab could be camera'ed. But there's no harm adding a dry vent takeoff, as long as it's vertical (on the upper half of the drain, and rises at a slope of at least 45 degrees above horizontal) until at least 6" above the fixture flood rim.

The washing machine should have a vent.

Cheers, Wayne
 
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