Partial Stack Replacement Question

Greetings,

I am renovating a second floor bathroom and, as part of this job, recently had to replace a sevaral foot section of the old cast-iron stack with PVC to tie in the new toilet location.
My question relates to my longer term renovation plans for the house. Specifically, I plan to put in a powder room on the first floor and tie the fixtures into the same cast-iron stack. This will likely involve another PVC sleeve in the stack to accommodate the new drains/vents.

Question: Is it ok weight wise to have two PVC sections in an existing cast-iron stack, or will this make it unstable where I have cast iron sections sitting above the PVC? I'm particularly concerned about the portion of the stack that sits above the PVC connection on the 2nd floor, as it is heavy cast-iron running another 8 feet up to the roof.

For background, the house is 100 years old, but the existing cast iron stack is still in very good condition.

Thanks !

Just my opinion from working on our house built in 1926 - knock that crap out and go back with schedule 40. You're already in the wall, go the extra mile and you won't have to worry about it later. I'm in the process of removing the last of iron pipe from our house drains. A few blows with a 2 lb hammer makes quick work of it. 8' of iron is about 50 lbs I'd guess, because I just carried a piece that size around to the back of the garage.

I agree - you're already in the wall...but if it is not accessible easily that's different.

You can do what you're planning - but you better darn well put some riser clamps in place on that stack.

At the minimum, ensure proper support clamps are above each section so it doesn't cause injury when cut. This will also take the load off of the pvc sections you insert.

In addition, adding bathrooms means you cannot use the same stack that vents fixtures to drain other fixtures. You need separate vents.

Thanks for the quick responses to my question.
I did not mention, but probably should have, that my preference is to not knock down the whole stack because of an access issue.
But I appreciate the advice on the riser clamps. I will go that route and make sure it is well supported

Thanks again, Mark

stack

Unless that upper portion of the stack is hanging in mid air, it is already supported by the piping attached to it that is going through the walls or floor.