What is the alternative to a plumbing roof vent?

The alternative to a Plumbing roof vent is an AAV. This is an Air Admittance Valve, a simple spring loaded ABS fitting that serves exactly the same function as a roof vent, except that it does not penetrate the roofing. I used 4 of these while re-plumbing my mobile home, three under countertops and one in the wall behind toilet. I'm very happy with their performance and even happier at having less holes in the roof.