I decided to replace the cast iron portions of my waste lines from a double vanity sink to the waste line. Previously a plumber had replaced the accessible portions with PVC so I have quite a mix. Now that I have opened up the wall, I see that I have a cast iron vent stack / hub (see pics: ) that the two sinks drained to and then cast iron down to the floor. In the crawl space the plumber had tied into the cast iron where it exited the floor and it is PVC to main wast line that goes to the septic system.

My problem / question:

I got ahead of myself and cut the vent stack just above were it enters the hub. I was going to replace all of this with PVC but it has not occurred to me that the weight of the cast iron stack will be too heavy for the PVC to support. This is a single story ranch so the vent stack is pretty simple. There is nothing above. Are there hanger systems to support the cast iron when coupled with PVC? Any advice on how to proceed?

Short of running PVC all the way to the roof, ( that's what I would do) you can purchase a raiser clamp to install on the stack and cut a couple of 2 X 4 jacks to hold the clamp and the stack up. Good luck, Tom