I was just wondering if someone might be able to help me out. I am going to be re-plumbing a house's sewer lines and there's not a lot of room to work under the house. I have about 3 foot at the most under the house. I am replacing old cast iron that's about 50 years old or so and I was wondering what the best thing to do with the stacks are. I'd like to re-use the CI stacks, but I know as soon as I cut the pipe, the stacks are going to drop. Someone told me to get 2X4s and support it, but that sounds like a pain in the butt. I think I'm going to take the stacks out and go with all PVC, which is not a problem. The problem lies in where to cut the pipe. The best thing I can think of is to go into the attic and cut it and rest it on the studs in the attic until I can get on the house to pull them out of the roof. Do you think this might be the easiest way? Any suggestions that might make this go a little smoother for me? Thanks for your help.

Speedball1 will catch this tomorrow mornig and can post some pics. You need to add hjacks made for capturing the cast pie and carry the weight so you can make your cut. Then transition to ABS or PVC.

Are you sure the stacks are CI and not galvanized pipe?

Your cast irom stacks won't fall if you use raiser clamps,(see image) and 2 X 4 for jacks under the clamps to secure the stack while you're installing the main under the house. However,
he problem lies in where to cut the pipe. The best thing I can think of is to go into the attic and cut it and rest it on the studs in the attic until I can get on the house to pull them out of the roof. Do you think this might be the easiest way? Any suggestions that might make this go a little smoother for me? Not as easy as simply pulling it out the roof. You'tr going to hafta disconnect all the branches that connect to the stack before it can be moved. The toilet, lavatory, kitchen sink and bathtub. All have to be disconnected at the stack before you can even start to cut it up. Major job! Be easier to leave the cast iron stacks and just repipe the main. But, If I were going to chop those stacks up I would do it all in the attic. ( If you take it out the roof in one piece you will have to enlarge the hole in the roof to let the fittings get past and that's not good. I'd take that sucker out in pices. I would take two raiser clamps and two bumper jacks up in the attic plus a set of ratchet cutters,(see image, rent a set at your local Rent a Tool).
Take the bumper jacks,brace them on the rafters and move then down to the lowest point they will go. Place a raiser clamp on the bumper and take up a strain. Place the second clamp above the first one leaving enough room to slip the bumper jacks under it after you make the cut.. You may now take the ratchet cutters and cut the cast iron next to the upper clamp. Remove the piece you cut and place the clamp off the cut piece back on the piece you left above the first clamp. You can now proceed to jack the stack up and cut off a nother chunk. And so on. Hey! Removing a cast iron stack's major surgery! Noboby said it would be easy! Don't forget, you're still going to hafta connect all those fiixtures back that you disconnected. Still want to replace the stacks? That's the best I can do. Good luck, tom

Usually there is nothing wrong with vertical stack. You could replace only horizontal runs under the house and you should be fine.

Speedball,

How much clearance under the house will I need? Worse case, I can go under the house with a cut off shovel and dig it out. I have about 3 ft under the house. It looks like I only have one stack to worry about. I was shocked when I found out that the kitchen sink and washing machine don't have stacks. Not for sure how that passed inspection, but it did. The house was built back in the mid 60's. Thanks.

In our area crawl space is 16". We do lots of crawling. You say, you have 3 feet. You have lots of space to work with...