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Thread: DWV System - Need advice

  1. #1
    DIY Member techinstructor's Avatar
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    Question DWV System - Need advice

    My husband and I are building a new house. Some of the work we've contracted out and other parts we are doing ourselves. After getting the revised estimate on having someone plumb the house, we decided that we could save a bunch of money and do it ourselves. Four years ago, DH re-plumbed all the supply lines in our current home with PVC and I assisted as a go-for, running to Lowes to get pipe, fittings, etc. so we've had some experience. And of course, I've always heard the that about all there is to know about plumbing is "Cold on the right, hot on the left, and sh!t don't run uphill." ; )

    Well, now that I've been educating myself on drain, waste, vent systems and reading lots of plumbing codes, I've learned that there is a WHOLE lot more to it than is indicated by that statement! So I've been reading this and other forums, articles, books and as well as the code to try to learn how to properly design a drain, waste, vent system that will both meet the NC state building code as well as work properly.

    I've drawn a plan using my CAD program and I would very much appreciate feedback from those of you who are experienced as to whether or not I have it right or if there is a more effective way to design the system.

    Here is the floor plan. The fixtures that are shown will actually be on the main floor above the pipes and are only shown on this plan for reference. All pipes and fittings will be schedule 40 PVC. The brown pipes are the waste lines and the green ones are the vents.


    Here is a section that shows the following from left to right:
    washing machine, lavatory, bathtub, vent, and toilet



    The 3" branch drain runs from the toilet to the 4" soil stack where it exits the house (picts of that to follow).

    Questions:

    • Is 3" the proper size for the branch drain (the total DFU for the house is 14)?
    • Is the vent coming from the bathtub drain necessary since it is only about a foot away from the vent for the branch drain?


    This section shows the branch drain again under the kitchen where it will connect with the soil stack. It shows one of two sinks we are installing.


    Questions:

    • Is 4" the proper size for the soil stack?
    • Is the vent tee in the correct place on the vertical stack (below all other tees)?
    • Do I need the cleanout where the soil stack turns to exit the house?
    • Once outside, the pipe will have another long sweep to before it runs to the septic tank. Do I need a cleanout there as well?
    • I don't think NC requires a house trap but do you think one is needed? I'm assuming it would go on the line outside of the house.


    **deleted picture to add one in a reply**

    The shows the same area but looking through the exterior wall.
    You can see where the sink vent exits the back of the cabinet and crosses over to join the vent stack. This is supposed to be placed 6" above the flood rim of the fixture, according to code, but because of the height of the counter and the windows, it may be a little short (I haven't actually measured it on site.). Any suggestions?

    Lastly, here is the second kitchen sink.
    **Sorry - had to delete the picture because I was over the limit of 4**
    My contractor suggested using an air admittance valve or studor vent here. Is it acceptable to install the AAV under the sink?
    After reading about AAVs on this forum, I think I may opt to run the vent pipe through the wall to connect to the vent stack that comes off of the soil stack. It's doable since the walls are all open.


    Lastly, the slope I used for all waste and vent lines is 1/4" per foot, the waste lines sloping down and the vent lines sloping up. I'm curious as to how that will work with fittings. This is such a small slope, and it seems like if the fittings are not sloped that it will affect it.

    Thank you in advance for sharing your knowledge and expertise. If anyone wants to see more of the house project you can view it on my blog at: http://cooperhomestead.blogspot.com/
    Last edited by techinstructor; 04-29-2009 at 01:36 PM.

  2. #2
    Plumber jimbo's Avatar
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    AAV are trouble, but are legal some places. What code are you on?

    You have an S trap on the tub or shower in the middle, NO GO!

  3. #3
    DIY Member techinstructor's Avatar
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    I'm in North Carolina. AAVs are allowed but if they are prone to failure I'd rather add the vent pipes instead.

    As for the S trap, I'm not sure how I can do it any differently.
    Is the problem created by the short length of the horizontal pipe coming off of the p-trap?

    If so, how long does that pipe have to be for it to not be classified as an S-trap?

    If that is considered an S-trap, then wouldn't the drain under the kitchen also be an S-trap?

    Sorry, I just don't understand. I thought an S-trap occurred when the drain curved directly off of the trap and wasn't vented, as both of these are.

    Thank you for your help and your patience.
    Last edited by techinstructor; 04-29-2009 at 01:33 PM.

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    Plunger/TurdPuncher kingsotall's Avatar
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    If it was an isometric drawing I might be able to follow the pipes better. Personally, I don't see an s-trap at the shower, it is vented. The sink trap can be offset with a 45 but any 90 degree change of direction must be 6" above the flood rim.
    I just post cuz I like to see my avatar.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default s trap

    The length of the pipe is immaterial as far as a "S" trap is concerned. The fittings used make it an "S" trap, and because of the disjointed drawings we cannot be sure if everything else is correct or not. The sink trap will either be a legal "P" trap or an illegal "S" trap depending on which fitting you use in the vertical pipe. In some of the drawings it appears you have pipes which are not doing anything, and in others pipes may be missing. IF you have an exact depictation of how you are going to install the piping, I can tell you that few plumbers, with even minimal experience, would install the piping the way you show it.

  6. #6
    Master Plumber Redwood's Avatar
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    On the shower change the wye and 1/8 bend to a sani-tee.
    That will fix the s-trapping.

  7. #7
    DIY Member techinstructor's Avatar
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    Quote Originally Posted by hj View Post
    The length of the pipe is immaterial as far as a "S" trap is concerned. The fittings used make it an "S" trap, and because of the disjointed drawings we cannot be sure if everything else is correct or not. The sink trap will either be a legal "P" trap or an illegal "S" trap depending on which fitting you use in the vertical pipe. In some of the drawings it appears you have pipes which are not doing anything, and in others pipes may be missing. IF you have an exact depictation of how you are going to install the piping, I can tell you that few plumbers, with even minimal experience, would install the piping the way you show it.
    Sorry about the drawings. Yes, it's hard to get the whole picture from them. Under the sink, there is currently a 1/4 bend coming off the top of the sani-tee. I'm going to try to change that to a 1/8 bend. The same thing was done at the tub.

    Would it be ok to run the tub drain over to the branch vent (between the tub and toilet) and let that vent serve both fixtures? That is a 2" vent that exits at the roof.

    Thank you to everyone for your critique. I'm still learning and appreciate your advice. I'll post more when I get my modifications done. I'll see what I can do to improve the images.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default dwv

    I guess part of the question is why the pipes, such as the sink, are coming up through the floor UNDER the fixtures, instead of the normal way of being a straight pipe up inside the wall? Unless there is an overriding reason for it, you are making the installation much more complicated than necessary. I also hope in your reading that you have discovered NOT to use PVC for the water piping. If that is really what your DH used 4 years ago, then you lucked out if nothing went bad in the interim.

  9. #9
    DIY Member techinstructor's Avatar
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    Quote Originally Posted by hj View Post
    I guess part of the question is why the pipes, such as the sink, are coming up through the floor UNDER the fixtures, instead of the normal way of being a straight pipe up inside the wall? Unless there is an overriding reason for it, you are making the installation much more complicated than necessary. I also hope in your reading that you have discovered NOT to use PVC for the water piping. If that is really what your DH used 4 years ago, then you lucked out if nothing went bad in the interim.
    Yes, I've learned that there are better things to use and also that the glues used in the PVC fittings can fail after about 20 years. We are planning to use either Uponor or Viega Pex for the supply lines - hoping to use a homerun system with a manifold.

    Yes, I realize that I'm complicating things by not running to the walls but I don't like the idea of a joint being in the wall because if it should fail or leak, then it would be hard to get to and cause more damage. Vents in the wall are no problem for obvious reasons.

    I have a full basement with 9-4" poured concrete walls. I just realized that the main branch drain, which runs parallel to the exterior wall and through a sleeve in the concrete interior wall, is most likely directly under a joist. DUH! (The house site is about 1 hour away from where I live so I can't just go look at it.) This means that I will have to change the way the toilet drain enters the branch. Can it join the branch drain at a 45 degree angle, created by offsetting the wye? Oh boy, what fun!

    I've always been a DIY and so has DH, but I will say that in learning how to do the things for this house, I have developed a new found respect for all of you in the trade. Of course the advantage to doing it yourself, if you can get it right, is that you understand the systems and you'll be better equipped to deal with any problems that should arise in the future.

  10. #10
    Plunger/TurdPuncher kingsotall's Avatar
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    Joints in the wall are going to be inevitable.
    I just post cuz I like to see my avatar.

  11. #11
    DIY Member gmrules's Avatar
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    At least they did not call u a moron as they did me and tell me to enter contest for being the idiot of the week.


    I guess I mad a mess of my single sink creating s trap I do appreciate the fact that they even take the time to help idiots like me

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default Moron

    Don't take offense to being called a moron, one of the writers in a national plumbing magazine says EVERYONE who does things differently than he does them IS a moron imbecile, or idiot. If you assemble the plumbing correctly you have very little to worry about with drains in the wall. The number of walls I have had to open in the last 55+ years because of leaks could be counted on your fingers and toes.

  13. #13
    Master Plumber nhmaster's Avatar
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    Quote Originally Posted by gmrules View Post
    At least they did not call u a moron as they did me and tell me to enter contest for being the idiot of the week.


    I guess I mad a mess of my single sink creating s trap I do appreciate the fact that they even take the time to help idiots like me
    Someone called you a moron? who called you a moron? Why I'll ......... let me at em....

    It wasn't me was it?

  14. #14
    Forum Admin, Expert Plumber Terry's Avatar
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    A pipe in a wall has less chance of being used for a coat hanger rod, or a place to lean a bike.

    There is very little that can happen to a pipe in a wall.

  15. #15
    Plunger/TurdPuncher kingsotall's Avatar
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    Save for thoses installing crown molding and hanging pictures and others I can't think of who have posted here.

    Then theres the call we went on where the DirectTV dude drilled right through a 3" soil stack and somehow got his cable line all the way through it. I wouldn't be able to do that if I tried even on a good day.
    I just post cuz I like to see my avatar.

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