Is that the only vent in the home? IPC calls for one vent that is half the size of the building drain which in most cases is going to be 1 1/2" to vent through the roof so it may well be to code.
Huh? 1.5" isn't enough to vent even 1 toilet. Pretty sure you need at least an equal total area of venting as drainage, so for a 4" stack, you need a 4" vent, or a 3" and a 2" (I think, not looking at the equivalents right now), or some other combination. Also, I don't think you're allowed to reduce a vent like that... maybe if the total venting load on the line is less than the allowable fixture units for a 1.5" vent, but again, that wouldn't even allow there to be a toilet on this line.
I stand by my recommendation to get a REAL plumber to come check all of this out. Whoever did this mess is a hack, even if they're licensed.
There's no way what the OP described is legal under ANY plumbing code. There are fittings in his pictures that are illegal. No doubt the venting is all wrong too. You know you're tradesmen are screwing you when they cut off a stack in the attic so they don't have to flash around it. What a crock that is.
I don't know what Tom is talking about, we don't use IPC, but if what he's saying is true, don't follow IPC. Those requirements are a joke, and definitely will cause problems in your area. I'm fairly certain neither the IRC or the IBC will allow anything he said. You want a minimum of a 3" vent, you do not want all those AAVs (if the old system was vented, why the heck would they take them out and put in AAVs? Thats ridiculous and not at all acceptable if there is a way to vent them properly), you certainly don't want an AAV in the attic on the top of a stack, the list goes on.
This is awkward, but...
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