Feedback on venting

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PhilT

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I am currently designing a DWV system for a small cabin and, since I'm new to this, I would like feedback on the approach. I'm in the boonies so no inspection is required but still want to make sure I follow best practices.

I made a mockup of the bathroom group (shower, WC and lav) with my proposed sizing on the diagram. There's also a kitchen sink with its own AAV discharging in the main drain further downstream (not on diagram).

As you see, I'm planning to use wet venting for the lav and shower and use an AAV instead of going to the roof. I'm trying to reduce the amount of piping required due to limited space in the wall.

Will this work? Is the pipe sizing adequate? Are there things I should be doing differently?

Thanks

Phil

wet vent proposal.png


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wwhitney

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It should be like the drawing below, as far as AAV location and order of fixtures. In particular:

- The lav and shower trap arms need to be vented before they fall more than one pipe diameter.
- So the lav needs a dry vent at its elevation, which the AAV provides (can be under the sink)
- And the lav wet vents both the WC and the shower.
- But one of the wet vented fixtures has to meet the lav drain before the other can, i.e. they can't be both be upstream of the lav. I drew the WC hitting the lav, and then the shower joining, but it could be the opposite: the shower hitting the lav, and then the WC joining.
- 2" is better for a shower and lets the trap arm be up to 8' long if you achieve the exact minimum slope of 1/4" per foot.

Cheers, Wayne

wet vent proposal.png
 

Terry

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The AAV should be on the lav, run with 2", not 1.5", and the fitting dropping into the 3" is a wye or combo fitting, no santee there.
The 2" shower arm also comes off of a wye. Showers are 2" and so are their drains.
 

Reach4

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Codes require at least one atmospheric vent. This prevents pressures from building up. Imagine your septic tank with gas-forming bacteria, but no place to relieve the pressure (other than from your indoor drains).

Also, imagine you flush your toilet, and a slug of water+solids tries to move toward the septic. That could be fighting pressure.

If you propose an outside vent, but not thru the roof, that could function. Maybe it would be in the yard, close to the septic tank. It would not meet code, but you may not be subject to code.
 

PhilT

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Codes require at least one atmospheric vent. This prevents pressures from building up. Imagine your septic tank with gas-forming bacteria, but no place to relieve the pressure (other than from your indoor drains).

Also, imagine you flush your toilet, and a slug of water+solids tries to move toward the septic. That could be fighting pressure.

If you propose an outside vent, but not thru the roof, that could function. Maybe it would be in the yard, close to the septic tank. It would not meet code, but you may not be subject to code.
Thanks. I had not thought about that pressure build-up aspect. I assume that this outside vent has to be far away from or above the cabin roof (ie I could not just T off the main drain under the cabin to relieve that pressure)? How big does this vent pipe need to be?
 

Reach4

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Depends on how you want to follow codes. 1.5 inch and 2 inch would be your common size.

Under IPC, and if I read correctly, if you run 3 inch to the septic tank, then 1.5 inch. If you run 4 inch, then 2 inch.

Table 906.1 of https://codes.iccsafe.org/content/IPC2018/chapter-9-vents gets more involved.

This assumes you are not in some really cold part of Arkansas.
 
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