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    Rough plumbing in slab - drain and vents

    Asked Apr 9, 2008, 08:58 PM 5 Answers
    I'm having a difficult time finding a plumber for a small rough plumbing job and may be tasked with this project myself. I see a lot of great info on this site. I've attached a drawing of my floor plan (small garage apartment) and I'm looking for some advice on it. I've laid out my drain and vent lines but I'm not real sure about the placement. For the kitchen sink, I'm thinking of using the small mechanical cap type vent so I don't have to penetrate the metal roof twice. Any advice is appreciated.
    Thanks,
    Ron

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    massplumber2008's Avatar
    massplumber2008 Posts: 11,871, Reputation: 1114
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    #2

    Apr 10, 2008, 03:42 AM


    Hi Ron.

    OK... you need to install a 4" main drain cleanout just as you enter the building or just outside the foundation (brought to just above grade)...then install a 4"x2" wye for shower (1.5" vent as you have), then install another 4"x2" wye for the kitchen sink waste (mechanical vent), then install another 4"x2" wye for the bathroom sink... run this to bath sink and continue it full size 2" out through roof (1.5" shower vent connects into this vent)... this 2" bath sink vent/drain acts as a WET VENT that vents toilet as well as vents and drains the bath sink. Then end your run with a 4 " elbow directly to toilet.

    At kitchen sink, need full size 2" DANDY cleanout (see pic.) under sink. If bath sink is vanity, install a 2" cleanout there, too.

    On all underground waste lines use 22.5 degree fittings, 45 degree fittings, and LONG SWEEP 90s when need to come up and out of ground (at sinks) and when need to turn 90 degrees (a long sweep can be made by cementing a 45 and a street 45 together). Add a 1" foam liner or similar around toilet pipe stub up so can cut pipe and install toilet flange at finish time.

    A mechanical vent is not always allowed in every state... check with local codes enforcement to see if allowed in your area... if so, install under the kitchen cabinet about 6-12 inches higher then the trap... if not, will need to continue that kitchen sink vent 1.5" to just below the roof and then increase to 2" and penetrate the roof (18-24" tall pipe).

    That should get you started. Any questions, let me know... Mark

    If this helped please RATE THIS ANSWER. Thank you

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    ronmvdb's Avatar
    ronmvdb Posts: 3, Reputation: 1
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    #3

    Apr 10, 2008, 08:00 PM
    Thanks so much for the info! I've redone my drawing. Hopefully it's close to what you described. How deep do the drain lines need to be? It will be a 4" slab with 12" footings. I'm thinking my kitchen side can be right below the slab and with the 1/4" per foot slope, the bathroom side will be about 6" below the slab. Do I just cover the pipe with dirt up to the top? Any suggestions on supply lines? That seems pretty straight forward. Thanks again for the great info.
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    massplumber2008's Avatar
    massplumber2008 Posts: 11,871, Reputation: 1114
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    #4

    Apr 11, 2008, 04:28 AM


    Looking good!

    You also have the pitch figured properly.

    Fill just needs to be clean dirt (absolutely no rocks) or crushed pea-stone... tamp dirt around and especially under the pipe (I actually use a 2"x4" piece of wood and "TAMP" the dirt tight ). Cover pipe completely and just be sure that the kitchen drain does not end up in concrete in any way.

    The supply lines... you mean water lines here... yes? I would go with a 3/4" PEX pipe for hot and cold water supply (3/4" PEX is like 1/2" copper pipe) There are a few types of pex out there. I am a big fan of VIEGA Pex (look up online)... but each area seems to carry a specific brand so will need to check with a local plumbing supply house to see what they carry, see what tools needed (not expensive tools, but necessary tools).

    PEX will save you time and money compared to copper... and not a little either, great stuff!

    Let me know how it goes along... Mark

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    ronmvdb Posts: 3, Reputation: 1
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    #5

    Apr 12, 2008, 06:15 AM
    Thanks, Mark. One more thing I can't see to grasp. How would I go about connecting the shower to the wye? I have very little room to come off the wye and get to the shower drain. Don't I need to have a p-trap below the shower? I doesn't seem like I can come off the wye to a p-trap and still end up close to my shower drain which is 12"x12" from the wall. Thanks again for all your help.
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    massplumber2008's Avatar
    massplumber2008 Posts: 11,871, Reputation: 1114
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    #6

    Apr 12, 2008, 07:06 AM


    Yes, you need a ptrap and vent off that wye... need to take the 4"x2" wye and install it further away... and then turn back to shower, installing fittings as required. That make sense..
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