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Soil Stack Vent Size Reduction

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  • #16
    Re: Soil Stack Vent Size Reduction

    Originally posted by Big Jim View Post
    I have no idea.

    Where's the Master when you need him.
    Probably in jail for beating up that
    plumbing inspector.
    I can build anything You want , if you draw a picture of it , on the back of a big enough check .

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    • #17
      Re: Soil Stack Vent Size Reduction

      Originally posted by toolaholic View Post
      Probably in jail for beating up that
      plumbing inspector.

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      • #18
        Re: Soil Stack Vent Size Reduction

        typically the cross sectional area of all vents would need to be equal to the building drain.

        so assuming the other vent is a 2'' then a 3'' combined would be slightly smaller than 4''.

        but in reality there is nothing that is going to happen by reducing the line to 3''.

        out here pre 1957 all toilets were 3'' or 4'' vents. now they're all 2'' and it's not uncommon to see a 4x2 reducer in what use to be a furred out wall or 2x6 wall for the old 4''.

        now i can't figure why he can't just continue with a 4'' line unless there is a stud right up there and it won't fit? but then that's what 45's are for.

        3'' is fine and 4'' would make the whole forum happy

        rick.
        phoebe it is

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        • #19
          Re: Soil Stack Vent Size Reduction

          Thanks for all the comments.

          My area follows the 2009 NSPC.

          The eave area where the 4" CI was terminated is very tight. It is actually a bump out so the main roof is not directly above it. I need to bring the vent in towards the center of the house and then go vertical to penetrate the main roof. It is a finished attic which also constrains where I can run it. It didn't make sense to me functionally to continue a 4" for such few fixtures and any reduction in size would make it easier to run. However, if it is code to continue the same size through the roof then I will stay with the 4". I don't want a future owner of this house to run into issues with something I did.

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          • #20
            Re: Soil Stack Vent Size Reduction

            If you reduce it to 3" you will not have sufficient cross section going through the roof. The cross section of all your vents have to equal the cross section of the main sewer. A 4" sewer has a cross section of 12.56. A 3 line is 7, a 2 is 3.14 and an 11/2 is 1.75. If you reduce it to 3 your cross section would only be 10.14 or 8.75, depending on the size of the kitchen/ laundry vent (most likely 1.5)

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            • #21
              Re: Soil Stack Vent Size Reduction

              There are a number of ways this could have happened without it originally being a code violation. For instance sometimes the roof gets changed and the newer rafters are higher and the vent fails to get lenthened to penetrate. Either way just because it is not done properly now isn't an excuse to fix it improperly.

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              • #22
                Re: Soil Stack Vent Size Reduction

                Originally posted by Big Jim View Post
                Alright, boys. Just calm down.

                Ratz, the OP didn't ask if vent reduction was allowed, he asked if he could do it.

                Now what does that mean? I don't know what his code is. Maybe it would be allowed

                in his situation. Tool, the purpose of a vent stack is for drawing air, not for drain

                cleaning. That's what clean outs are for. Granted, at times you have to snake from

                the vent, but in the absence of a c.o. you do what you can. All I'm saying is a 3"

                vent is more than adequate for his needs. I know the code exists for a reason, and

                most of them are necessary, and if he hired me to do the job I would do it to his code

                requirements, whatever they are, and charge an appropriate price. I just think he's

                interested in what's gonna work.
                The vent size is not based soley on the number of fixtures it serves, it also has to vent the main sewer, therefore the cross section of the vents have to equal the cross section of the main, regardless of the fixture count on the line. Therefore according to the code it will not work.

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                • #23
                  Re: Soil Stack Vent Size Reduction

                  Originally posted by winslow View Post
                  The vent size is not based soley on the number of fixtures it serves, it also has to vent the main sewer, therefore the cross section of the vents have to equal the cross section of the main, regardless of the fixture count on the line. Therefore according to the code it will not work.
                  And the code is therefore....wrong.


                  J.C.

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                  • #24
                    Re: Soil Stack Vent Size Reduction

                    Is always trying to get away with the smallest pipe possible a home owner thing?

                    I'm a home owner, and I don't understand it?

                    If somebody tells me my kitchen sink should be 2" instead of 1.5" and my shower should too, I'm going to use 2"... Do people really think they're saving themselves money by reducing pipe diameters everywhere they can?

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