I found this yesterday. The kitchen sink vent runs up the exterior wall to the top of the cabinet where it passes out then sits horizontally above the cabinet.
Any issues with this, I don’t know if the AAV can be installed horizontally.
I do know it didn’t have to due this. This is only 1 of the issues here.
How do you like the modified Trusses?
Some (but not all) AAV’s are listed for both horizontal and vertical uses. . .
I’d call out the lack of shutoffs under the sink.
I would call the trusses “questionable framing” as in - What were they thinking? Is this place up for sale? 
John Kogel
www.allsafehome.ca
“funny” thing with the trusses, every attachment point is made with 1 (a single) screw:shock: 3 screws per 2X
I can’t believe noone mentioned the black tape - leak stopper. You know how expensive plastic nuts and washers can be. :roll: 
Some AAV’s can’t be horizontal, but usually says right on the package. Normally the vent goes all the way to the eaves and then comes out or is contained in a soffit. Also laying a Tee on it’s side like that promotes stoppage.