Is it ever permissible to have a waste piping system without a vent through the roof of the home? I recently saw a job where the only “vent” appeared to be an AAV in the attic - that doesn’t seem right to me. TIA
There is no AAV that I am aware of that is rated for the main stack.
Actually, there are.
As long as the jurisdiction allows AAV’s, this is not an issue.
Jeff, are they relativly new? Have any info on them? Didn’t find any on a quick Google search.
I probably saw my first one in 2003 or 2004. They are just “large” AAV’s. I’ve seen them in 3" and 4" sizes used in attics.
The State of CA does not allow AAV’s, but there are jurisdictions throughout the state where they are allowed. I include this statement when the main-line vent is equipped with an attic-terminated AAV.
The drain-waste-vent system (DWV) employs a mechanical vent, also known as an air-admittance valve or AAV. This application may have been approved by this local jurisdiction, however, you should be aware that this type of system is not recognized by California Building Officials as an approved vent system. Although they may function as intended, AAV’s are a mechanical component, and as such, they are subject to failure over time. Failure of these mechanical vents may allow sewer gases to escape into the attic which could result in potentially hazardous and unhealthy conditions. If, at any time, you notice an odor consistent with waste or sewage within the residence, you should immediately contact a qualified plumber to evaluate the AAV.
Thanks for the info Jeff. I’ve only seen them up to 2.5". Guess it’s time to visit the local plumbing supply.
Well, in the backwoods of the rural county in which I was inspecting, there is no inspection at all, so I guess I could not say it is not premitted ! 
Thanks
Many mobile homes have no vent stack. AAVs are used under the sinks