I am working on our upstairs bathroom and plan on moving some of the fixtures around to a different side of the room. This means I need to make changes to where the drain comes into the stack (I want to bring it in lower than it is now).

How do I go about replacing a section of 85 year old cast iron pipe? Can I just replace the section I want to change with PVC and tie back into the original cast iron above and below it? Or do I have to replace everything above it with PVC as well (it runs up through the attic and the roof)?

I hope I don't have to replace the entire stack with PVC (I am not sure the new PVC pipe would even fit inside some of the walls as I think the PVC flanges are larger than my cast iron pipe's).

1 Answer 1


85 years old. The biggest problem is that cast iron is heavy. By removing a section of the piping you might end up inadvertently messing up the mounts for the old pipe. If it is at all possible I would replace it with PVC, otherwise, I would leave it alone.

  • I guess I will replace it from where I need to add the new drain and everything upwards. Leaving the old pipe below.
    – auujay
    Commented May 15, 2011 at 21:03
  • 1
    Adding some extra strapping (or other mounting) to the part of the cast iron you plan on leaving in there would also be a good idea. Just in case the upper section of iron was holding the whole thing up. Good Luck. Commented May 16, 2011 at 0:49

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