Vent in attic

[Sem Sem]

Few things-

We moved to a new house and here is what I was told in the inspection report
5 (2) The plywood sheathing is stained as a result from a leak around the gable vent above the hall bath

Based on the second picture, it looks like the house already has at least one vent that goes through the roof. Question Can I cut this pipe down a little and add an AAV?

 

[Reach4]

I think WA code does not permit AAVs

Plus you need a vent to atmosphere for the house, even in places that allow AAVs.

You can tee into another vent in the attic, presuming the vent sizes are sufficient.