Cutting cast iron vent stack


Getting ready to cut a cast iron vent stack to put in a new vent, now I know that I must support the weight of the stack and brace it from side movement I will be renting one of those chain type tools for snapping the pipe. I am concerned since I never did this, what is going to happen since the weight of the stack is still there all though supported from dropping how is it going react, I really don’t want this pipe to crack the wrong way. Any one who has done this and can let me know what to expect would be appreciated.
Thanks
Joe
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Joe wrote:

How big, how tall, how supported? Nowhere near enough information to be able to tell anything about your particular installation.
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dpb wrote:

I'm with Joe on this. And it can be risky.
Whatever the weight/height, you need to "preload" the support system so that when the cut is made, the stack doesn't drop at all. That's especially critical in the case where there are connections above where you are cutting (likely) since movement of any joints (or the roof terminal) will lead to failures later.
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know
movement
am
weight
one
appreciated.
5" diameter pipe, about 10' above cut no branches to roof, supported by using existing framing and building a clamping device off of the framing about two and three feet above the cut (hub about three feet above cut), and about 15' below cut to concrete floor several branches comming off.(tub, toilet, sink) Thanks Joe
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note replacing with plastic will add noise of water running thru pipe......
cast iron can also be cut easily with sawzall metal blade
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Joe wrote:

That will be 4" trade size pipe. Probably looking at around 100 Lbs weight above you. Wedge a brace at an angle under the support you have so you can pretension it. You will need to lift that weight in any event after you make the cut.
If the current framing doesn't support the lower part of the stack from moving sideways, nail some blocking down to keep it from shifting.
When the job is done, keep an eye out for roof leaks where the penetration is.
Jim
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