Hi,
Newbie here & need some advice on a recent bathroom re-model. When the walls were opened up, the 4" cast iron vent stack was badly corroded & replaced with about 10' of pvc going into the attic. Instead of going all the way through the roof with pvc, the guy doing the job connected the pvc to the old cast iron piece that goes through the roof. (about a 5' section which was in fine shape) I'm concerned about the weight of this top cast iron section being supported in part by the pvc below it. I do want to replace the cast iron iron & was wondering if this is something that needs immediate attention, or should it be OK to leave as is till Spring when the weather is better. Just wondering if there are any potential problems that could/might crop up if it isn't changed now. Thanks in advance.

How much cast pipe sits on top of your bnew piece of PVC? If its only 3-5' I would not worry about it. Did he add any strapping to the PVC as it passes through the ceiling rafters?

How much cast pipe sits on top of your bnew piece of PVC? If its only 3-5' I would not worry about it. Did he add any strapping to the PVC as it passes through the ceiling rafters?

The cast iron section through the roof is close to 4' long. I forgot to mention the pvc is 3'', versus the 4" cast iron. He connected both pieces with a rubber collar/boot that has 2 stainless straps at each end. There's no kind of support strapping, if that's what you're referring to.

You should not reduce from 4" to 3" and then go back to 4".

As said above, structurally, I would not worry about it. Even though I would use Shielded couplings in place of Flex Seal coupling he used.

OK, thanks very much guys. I do appreciate the input. As long as it should be OK for now, I'll leave it alone and replace the cast iron in the Spring. (or sooner if weather permits)
Thanks again... great forum here!

Next time use shielded metal couplings. They are more ridged then the neoprene couplings. Good luck, Tom

Will do Tom. Thank you.