Horizontal wet venting bathroom code question

[Jeff S.]

Sec. 908.2.1.2 ...The wet vent shall be not less than 2" in diameter for four DFU or less, and not less than 3" in diameter for five DFU or more...

Does this mean that if I've got a lav, shower and w/c, that the entire wet vent needs to be 3", or just the part with 5 or more DFU on it, i.e., after the w/c? I don't actually have to have a 3" drain for the lav, and then on to pick up the shower trap arm, do I?

Also, Sec. 908.2.1.3...The vent pipe opening from the horizontal wet vent...shall not be below the weir of the trap.

Where is the "vent pipe opening from the horizontal wet vent" in this set-up? Is it where the wet vent becomes a dry vent? Apologies in advance for my ignorance here. The language confuses me.

Thank you.

 

[Terry]

A 2" will vent a bathroom group. And I don't know why anyone would wet vent be

908.2.1.3 Trap Arm. The length of the trap arm shall not exceed the limits in Table 1002.2. The trap size shall be in accordance with Section 1005.3.3. The vent pipe opening from the horizontal wet vent, except for water closets and similar fixtures, shall not be below the weir of the trap.

That means a santee on the vertical, or you can use a combo on the horizontal. The vent can't be below or the trap will siphon. If you are pulling the shower off the 2" line going to the lav, and it's being wet vented horizonally, you would use a wye fitting. If the shower pulls off the vertical, you use a santee.