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    Ashcat81's Avatar
    Ashcat81 Posts: 3, Reputation: 1
    New Member
    		  
    #1

    Jul 15, 2010, 07:57 AM
    Can you replace a 4 inch cast iron soil stack with 3 inch pvc?
    I recently purchased a home built (I'm guessing) in the early 1900's. I noticed a leak in my basement coming from the old 4 inch cast iron soil stack running from my second floor bathroom to the basement. There is water dripping down the pipe to the basement. Three plumbers have come out to diagnose the problem. The first plumber removed the commode and cut a bigger hole in the floor to try and find where the pipes begin and end. There was also a hole cut in the floor on the other side of the wall (in the closet in the hall around the corner from the bathroom) to follow the pipes from the bathroom leading to the soil stack which then travels down through my kitchen/dining room wall to the basement. There is a lot of deterioration in my pipe at the second floor level (several holes are visible) but that is not where the leak is. Several of the plumbers believe the cast iron is cracked in the kitchen/dining room wall. The entire pipe needs to be replaced/upgraded. The plumber is thinking of putting 3 inch pvc instead of 4 inch because the 4 inch (fittings-I'm not sure?) will be a difficult fit. Is that okay to do?
    Milo Dolezal's Avatar
    Milo Dolezal Posts: 7,192, Reputation: 523
    Plumbing Expert
    		  
    #2

    Jul 15, 2010, 05:38 PM
    There is always a way to connect 4" PVC to 4" Cast Iron and we do exactly that on everyday basis. If you post a photo of the proposed PVC to C.I. connection, I will tell you exactly what fitting to use.

    Back to you... Milo
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
    Eternal Plumber
    		  
    #3

    Jul 17, 2010, 06:53 AM

    I am replacing all the old cast iron with PVC. The cast iron is 4 inch, but the PVC that will be replacing it is only 3 inch. I just wanted to make sure there wasn't any plumbing code that says it should be at least 4 inch.
    Check with your Building Department. Different areas have different restrictions, Example!
    Then county I live in allows 3' above the pour and a 3" toilet branch under the slab connecting to a 4" house main but while the county just south of me mandates toilet branches under the slab be 4" to the main. I think you'll be OK with 3" above the slab but if you're replacing anything under the slab I'd check first. Good luck, tom
    massplumber2008's Avatar
    massplumber2008 Posts: 12,832, Reputation: 1212
    Senior Plumbing Expert
    		  
    #4

    Jul 17, 2010, 07:16 AM

    Hi all...

    In my area if you start 4" in the basement you MUST continue that 4" up and through to the roof.

    Your plumber isn't suggesting sticking 3" pipe inbetween the 4" headed to the basement and the 4" that goes up through the roof is he? If so, I am sure the plumbing code would not allow that... OK?

    As Tom said, talk to your local plumbing inspector... he'll have most accurate answer for you!

    Mark
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