Extra vent required?

I'm installing a new shower into an existing washroom, however the vent stack for the existing drainage is located across the open room, which will end up being more than 6 feet away from the shower drain. However, where the shower drain is joining the drainage system is in between the down pipe and the vent stack. In the diagram included, I've added an auxiliary vent by the shower which would by vented by an AAV in the attic, but I'm wondering whether or not I need that since the pipe its joining is already vented.

Any comments on the diagram in general appreciated. Thanks!

Instead of the AAV, run a vent line horizontally in the attic to connect to the real vent.

Here, we increase the vent size before penetrating the roof as a 2" vent is more likely to become obstructed with snow/ice in the winter. I don't know what the your code says about this.

What's with the s-trap on the left side of the double lav.
Why isn't that run with a double fixture fitting?
There is no way that would work here, it's going to siphon the trap.

Ah, the lavatory work is somewhat guess work, as that's existing plumbing and behind the wall. There may be another vent hooked up there. I'm only adding the shower part.

About attaching it to the vent in the attic, it would have to run over about 10' in the attic which only has about 1 foot of clearance on that side of the house. I'd much rather add another vent if I needed to, but since this vent is only meant to allow proper drainage, I thought that an AAV would be acceptable.

In the end though, it sounds like a vent would be needed for the shower considering its > 6 feet from the vent shaft, despite the fact that the drain line is already vented. Am I right?

I hope your drawing is NOT accurate, because you cannot use 1 1/4" for the lav drain lines and the left one is not vented. The distance for the trap is from the trap TO a vented connection, (which is the Y/combo at the drain line). and if your inspecor allows the lavatory vent to service the shower then you do not need an additional vent. Doing it the way you show would create a horizontal vent and that would be marginally better than no vent.

Alright, taken some good points here and removed specifics that I'm not actually changing and just guessing about

I've removed the vent stack and will take this to the inspector and look to see if he needs a vent there.

Thanks for everyone's feedback!

Now all you have to do is make sure you use the "correct" fitting to connect the shower to the drain line.

So after opening the floor, it turns out that the drain going downwards is a 3" not a 2", and the drain is coming from my toilets. So the new picture is attached.

The question I have now is.. Is there any problem hooking the drain from the shower into the main 3" toilet drain stack? If there isn't, is the correct fitting something like a long turn tee wye 3x3x2?

Thanks