Feedback on venting

Users who are viewing this thread

PhilT

New Member
Messages
3
Reaction score
0
Points
1
Location
Arkansas
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


index.php
 
Last edited by a moderator:

wwhitney

In the Trades
Messages
6,532
Reaction score
1,822
Points
113
Location
Berkeley, CA
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

The Plumbing Wizard
Staff member
Messages
29,946
Reaction score
3,460
Points
113
Location
Bothell, Washington
Website
terrylove.com
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

Well-Known Member
Messages
38,795
Reaction score
4,413
Points
113
Location
IL
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

New Member
Messages
3
Reaction score
0
Points
1
Location
Arkansas
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

Well-Known Member
Messages
38,795
Reaction score
4,413
Points
113
Location
IL
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.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks