small Bath layout vent question

[SC5001]

I have an detached shop I working on plumbing a small bath in. It has already a small septic tank next to it tied in the the leach field. It is fairly compact so wasn't sure if the two vents I was planning to install were sufficient and maybe more then required. This bath is ont he wall the septic tank line come in from so all in a close area. This will be all under a slab when completed.

The picture if over head view.

I have a 3" line coming in from the tank. in a short space I will have a wye for a 2" vent up. Then two wyes back to back going different directions. Then straight a short bit to a toilet. Both Drain Lines of the 3" I was going to use 2" pipe. On the Left I was going to rough up to 2 sinks. The first I was going to vent up and tie in to the Main 2" vent up the wall. The other sink due to the lay was going to be hard to tie the vent in. I believe since its only a few feet away the first sink vent is sufficient. To the other side of the sinks I was placing a floor/shower drain with 2". does this line need a vent as well?

hope I explained it well. Thank you for any feedback.

 

[wwhitney]

Comments:

- The 2" dry vent in the middle of the drawing does nothing for satisfying the fixture venting requirements.

- Every trap needs a vent near the elevation of the trap, namely before the trap arm falls one pipe diameter. So if each sink turns downward before the drains join, each sink will need its own vent (dry vent or AAV). You could combine the two sink trap arms before either turns down, and use a single dry vent for both them, if you comply with certain distance limits. An elevation drawing would be better for explaining those requirements.

- You currently have the shower and the WC drains combining with each other, and then the sink drains coming in. If both sinks are lavatories, then they could wet vent both the WC and shower if you move the shower to come in downstream of the WC/lav joint, and if the shower trap arm (from the trap to that joint with the lav/WC drain) falls no more than one pipe diameter (2").

- If one of the sinks is a utility sink, then you can't use the combined sink drain to wet vent the shower or WC. However, if you moved the 2" dry vent that is currently downstream of all the fixtures to instead connect to the shower or WC drain, and kept the current connectivity pattern, it would dry vent that shower or WC, and that fixture could then wet vent the WC or shower, respectively.

Cheers, Wayne

 

[Sponsor]

 

[SC5001]

Thank you for the feedback. Yes the one sink far left will be a utility sink. I can move a vent over to the shower/WC portion. I was wondering if the center vent was needed given the layout. I was kind of thinking about it as if there was a main stack/vent I suppose. Thinking about it a bit more I can add a vent to the far left sink. just a little more work going around a widow and such if needed or use a AAV.

Thank you