Can you get on the roof? If you do this replacement you will probably need to replace the boot.

If the roof and boot is accessible - do the whole thing. Note: Cast Iron pipe is HEAVY.

You will cut it out with a metal blade on a sawsall. Connect the PVC with Fernco coupling.

Hi Jake, yes, I can. The roof was replaced a few years ago, they put a new boot on it; but yes, I can access it. I have had to cut those pipes under the house before, you are right, they are heavy! I'm concerned about getting the old pipes out, may have to make smaller sectioned to fit out.

Regarding the new pipe, I was thinking of using a 45 angle on both sides; but I'll have to do additional measurements.

Yeah, I was considering leaving it up there. The house will go on the market in the late spring.

What part of the country are you in?

SE Georgia, USA

Ok, because the insulation is a little light... you are going to sell though...

yes, it is. Not planning on doing anything with that. Several other projects; but this pipe was leaking... priority!

If you have decent access to the pipe, I have found that an angle grinder with a metal cutting wheel works much faster to cut cast iron pipe. If its hard to reach one side of the pipe, I cut as far as I can on both sides with the grinder, and then finish with the sawsall.

If you support the pipe properly you can use the all-rubber Fernco couplings, but I prefer to use the ones that are covered by the metal bands (similar to this one https://www.homedepot.com/p/4-in-EPDM-Rubber-Shielded-Coupling-P3000-44/100372288) , since they hold everything in place better.

Bruce

One additional question. There are a few different kinds of 4" PVC pipe. The first Lowes I stopped by had some that seemed pretty thin and had sewer/drain on it. What kind needs to be used to replace the current pipe? I am planning on replacing everything above the ceiling.

Schedule 40 DWV PVC should do it... It's common and I don't think you will go wrong with that. You should be able to use solid or foam core since it's non pressurized