Does this drain layout look OK. Any advice?

[Zimm0who0net]

Does this drain layout look OK?

So my wife and I are building a guest house and we're trying to do just about everything ourselves. We're about to start framing and I figured I'd throw my drain layout here and see what you guys think. Here's a 3D view of the house:

Here's the layout:

Some items to note:

1. This is the 2nd floor. Joists are green. Interior walls are 2x4 in red. Lower basement (concrete/ICF) walls are the thick ones (also in red/white). Blue is a big steel beam to supoort the 2nd floor.
2. Joists are 16" OC I-Joists (14" depth). I think I've got enough depth to keep the whole thing inside the joist bay. For the toilet I'll figure a 4"x3" closet bend with a Souix Chief 884 flange that fits inside the vertical.
3. 3" ABS from toilet to the stack. Everything else is 2" ABS
4. IPC codes (Tucson, AZ).
5. Only cleanout is up by the laundry/vanity, and at the bottom of the soil stack.
6. The bar sink is problematic because of the steel beam right below the wall. I'll probably come up beneath the cabinet. Then I'll run into an S-trap (just kidding!). But seriously, I'll probably use an AAV there inside the cabinet because there's a wide window above the sink and an AAV seems like a decent option when you're coming up from the bottom of a cabinet. (plus it's allowed here)
7. I'm worried about fitting those pieces that run to the shower after the framing is complete because it'll be really hard to get them in there, so I'll probably cut the holes and stick the pipe through as I'm framing.
8. The concrete basement wall actually comes all the way up to the bottom of the subfloor (I hate that, BTW, but it's what the engineer wanted). I have a small chase through that wall roughly where the 2" drain goes to the laundry cleanout. I don't have a lot of wiggle room there. Any farther toward the bottom of the image and I interfere with the steel beam pier. And farther toward the top and I interfere with the lintel for the doorway below.
9. Is my 2x4 laundry/vanity wall thick enough? Do I need to go to 2x6 instead?

So, does this look OK? Is it to code? Would you guys do it differently? At this point I have a lot of flexibility about where the joists layout and other items.

 

[Reach4]

So, does this look OK? Is it to code?

I am not a plumber. Plumbing looks good. If you joined the laundry waste after the shower and use 2 inch for the shower vent, I think you could eliminate the toilet vent. Eliminating the toilet vent is probably not a big savings.

Any provision for a water softener?

 

[Sponsor]

 

[Zimm0who0net]

So something like this:

Eliminating vents is a plus. I'm trying to cover the roof with solar so I'd like to eliminate as many penetrations as possible. Of course I can always route all the vents together, but the fewer I have to deal with, the better. (plus it's a flat roof with only 12" depth and I'd like to maximize roof insulation (it's pretty hot in Tucson))

As for softened water, this is a guest house. The main supply comes from a manifold at the main house. That has a provision for a softener (although one is not there yet). I'm actually running two supply lines to the guest house. One is "un-softened" water for hose bibbs and the other is for the in-house softened water.

Actually, if you want to get technical, there's a 3rd line because I'm going to harvest rainwater off the roof and the 3rd line will bring that water (under pump pressure) back to my irrigation system near the main house.

 

[Reach4]

So something like this:

Yes.

I'm actually running two supply lines to the guest house. One is "un-softened" water for hose bibbs and the other is for the in-house softened water.

Good move.

 

[Zimm0who0net]

OK, now for the supply. For something this size would a trunk and branch work fine or would you go with a manifold/homerun system? If trunk, 3/4" with 1/2" branches? I'm not super concerned about the fixtures shown in the drawing, but I've also got a remote basement bath and an outdoor shower next to that and I'm worried that with 3/4" I'll have to wait a half hour to get hot water. Here's the walkout basement floor plumbing plan so you can see what I'm talking about.

 

[Zimm0who0net]

Could someone fill me in whether the 3" stack on the right side of my two drawings needs to be vented? I seem to be getting different answers depending on where I look. It would seem that all the fixtures on the 2nd floor are properly vented, so I can dive into the top of the stack with a 90 and be done, but elsewhere I've seen that people always vent the main stack. (again, IRC here for code reference)