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Thread: basement bath remodel, need some under slab and vent help

  1. #1
    DIY Junior Member kentd's Avatar
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    Default basement bath remodel, need some under slab and vent help

    Hi all!

    Recent lurker and first time poster here. I promised myself and my wife that we would save money on the basement remodel by leaving the bathroom alone...um...yea. In the end, I just couldn't leave it be. Plus, it would've looked out of place in the otherwise new basement, right? Actually, I decided to tear things apart when I couldn't figure out how the fixtures were vented. This concerned me. Sure enough, opening things up revealed that the plumbing was another hack job by the previous owner of the house. After doing some poking around this forum, I decided to seek some advice for how to put it all back together.

    Here is what the final layout will be.

    - The new shower is in orange. I haven't decided if I will do an offset drain or a center drain (both possible locations shown in black). I will probably purchase the kerdi shower pan, drain, and membrane for the shower build.

    - The existing main line is shown in green.

    - The toilet has a 30" opening.

    - The vanity is 24".

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    Here is a pic showing the existing plumbing. This is facing the new shower location. Notice the buried AAV and the double-trapped vanity! From what I know (which is very little), the AAV was doing nothing to vent the shower drain and toilet since it was installed above the under slab p-trap for the sink.

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    Here is a pic showing the 'west' wall with tape marking the new fixture locations. The old shower drain can be seen here (old shower was a big box cheapo corner enclosure).

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    This pic shows how the various fixtures hook into the main line.

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    This final pic shows how the main line comes into the vanity/shower wye and also the drain tile.

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    So that's what I have to work with. I'm fairly certain of the following basic plumbing principles:

    1. Each fixture needs its own vent line.

    2. The vent lines can tie together at either 42" above the floor or 6" above the flood rim of the highest fixture (whichever is higher).

    3. The toilet must be the last fixture to enter the main line.

    4. I think there might be restrictions on the maximum amount of turns between the drains and the main line. I think I read 135 degrees for a p-trapped fixture?

    Given all this, I can't quite figure out the best layout for my situation.

    Here are my questions right now:

    1. The 'west' wall where all of the fixtures will be located is a non-load bearing wall, so I think I can bore through the studs to route a horizontal vent line behind the fixtures. Is this the best place to put the 3 fixture vent lines?

    2. After the vents go up into the west wall and join into the horizontal vent header, I will route the vent line out the north wall into the adjacent furnace room. I plan to install a new AAV in the furnace room for venting all three fixtures. Is this okay or do I need to find a way to get to the attic and join into another vent?

    3. Is the existing vertical drain stack for the vanity and shower ok? (assuming I will correctly vent both the vanity and the shower before they hit the vertical drain)

    4. The output of the toilet combo wye is essentially under a foundation wall. In other words, it will be a pain to remove the toilet combo wye and replace it with something else. Is there any way I can leave that combo wye in place and get the lateral shift I need to get over to the new closet flange location?

    One final piece of info, the top of the main line is about 18" under the top of the slab.

    This forum is a great resource and I've already learned a lot from just the first page of threads! Thanks for making this a great site.

    Kent

  2. #2
    DIY Junior Member kentd's Avatar
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    Well, I had a plumber come in to work up a bid for doing all of the under slab work assuming I would do all the digging and backfilling and slab repour myself. He hasn't gotten back to me yet, but he did inform me of the code requirement to have a backwater valve for the basement fixtures. A backflow valve sounds like a good idea to me, but I have read on here about their limitations. Also, I would not really have a way to access it unless I would tear up a lot more concrete and put the valve in the next room over (my furnace room).

    I also don't like the idea of digging up my front yard in order to put in a backflow valve outside the foundation wall.

    Thoughts?

  3. #3
    DIY Junior Member kentd's Avatar
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    Still working on this under slab layout. I would appreciate any feedback you can give.

    I am considering breaking up more of the basement slab so that I can put the backwater valve in an accessible location in the adjacent furnace room. I would leave a hole in the repoured slab for access to the valve.

    Current questions I have include:

    1. Does code allow for the number of turns I have in the horizontal drain lines before hitting the main?

    2. Is the lavatory vent+drain providing a legal wet vent for both the toilet and the shower?

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  4. #4
    DIY Junior Member kentd's Avatar
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    Any help here on the 1 month anniversary of my thread?

    The line drawing in post #3 shows all of the under slab drain plumbing I am proposing. The only existing plumbing is the right-to-left running main line that goes to the street.

    Would an isometric drawing be helpful?

    Regards,
    Kent

  5. #5
    George the Plumber Gsalet's Avatar
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    Kent
    What you are proposing will work if you have enough grade. Most plumbers would not like it though. The most direct route is usually the best option, also if you have to open the check valve to clean it being outside is a plus
    george

  6. #6
    In the Trades Tom Sawyer's Avatar
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    It's one of those deals where having a plumber do the piping will probably save you money and surely save headaches.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  7. #7
    DIY Junior Member kentd's Avatar
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    Gsalet and Tom Sawyer,

    Thank you for your replies. I am starting to become convinced that I should pay a professional to handle the under slab work.

    One more question: Am I allowed to add a floor drain behind the backwater valve as shown in the revised pic? I would install a Flood-Guard device on the floor drain.

    Regards,
    KentName:  bath2.2.jpg
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  8. #8
    DIY Junior Member kentd's Avatar
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    Hi all! Here's how the plumbing turned out.

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    I have a few questions on the result:

    1a. The shower branch-to-main branch wye is on its side. I understand that this branch is wet vented. Would it still be properly wet vented if the wye was rolled away from the horizontal? For instance, either at a 45* angle or on its back?

    1b. Would it serve any purpose to have it rolled up? I am wondering if it would make any clogging material from the toilet or lav less likely to catch on or back up into the shower branch.

    2. Can I tie in a bar sink drain by inserting a santee on the vertical drain line below where the lav drain enters? The bar sink will have its own vent at the fixture as it will be some 20 feet away from this particular drain stack.

    3. The drain line from the toilet riser to its exit on the bottom of the picture is 3". Is this required to be at 1/4" pitch or can it be 1/8"?

    Thanks for the help,
    Kent

  9. #9
    DIY Senior Member dlarrivee's Avatar
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    I'm wondering why the 2" from the lav doesn't just tie into the 3" at the same elevation on a 45* angle?

    Is this all glued together already, you might want stub out the slab wit 4" for the w/c instead of 3", so your flange can slide inside it?

    No cleanout on the 2" vertical?

    I would leave the 2" p-trap for the shower out for now, and block out an area with 2x before pouring concrete, unless you're absolutely sure that is where you want the drain?

    Someone other than myself will have to chime in on whether or not you're allowed to have the w/c furthest upstream in this wet vented group... (Where I come from, the w/c MUST be furthest down stream for a 3-piece wet vented bath)
    Last edited by dlarrivee; 02-01-2012 at 05:32 PM.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    The shower is NOT wet vented, in fact it is not vented at all, and it CANNOT connect to the main drain without a vent if the toilet discharge flows past it, which yours does. IF its connection were not on its side the shower would be connected with an "S" trap which would be an additional violation. If you installed a floor drain the same would apply to it. Your statement #3 in the original posting was in error. The toilet can go ANYWHERE in the line as long as it, and everything else, is vented properly.
    Last edited by hj; 02-01-2012 at 05:49 PM.
    Licensed residential and commercial plumber

  11. #11
    DIY Senior Member dlarrivee's Avatar
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    So if kentd want to use the lav for a wet vent, would it not make sense to tie the w/c in furthest down-stream rather than furthest up-stream?

  12. #12
    DIY Junior Member kentd's Avatar
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    Well, some days you're the pigeon, and some days you're the statue. The work was done by a licensed plumber and it passed inspection.

  13. #13
    DIY Senior Member Hammerlane's Avatar
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    Quote Originally Posted by dlarrivee View Post
    I'm wondering why the 2" from the lav doesn't just tie into the 3" at the same elevation on a 45* angle?
    I was wondering the same also. That Wye(pointed to with yellow) should be rotated 90 degrees to the right and like dlarrivee said that would tie the lav drain into the 3" at the same elevation. The way it is set up now it appears that the 45(pointed to in red) coming off the Wye is making the lav branch drain travel uphill at that point.
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    Last edited by Hammerlane; 02-02-2012 at 04:25 AM.

  14. #14
    DIY Senior Member Hammerlane's Avatar
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    Hopefully Terry will chime in on the toilet and shower being vented via the 2" lav drain

  15. #15
    Moderator & Master Plumber hj's Avatar
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    As long as the lavatory is connected to the toilet BEFORE it reaches the point where it joins the main drain,(in this case that is "Y" fitting for the shower), it makes not difference where it is for the lav to be the wet vent. Many inspectors were contractors or journeymen who could not make it in the private sector so they became inspectors, and sometimes they just have a "cozy" relationship with the installing contractors. Here, the inspectors are rotated periodically to prevent that kind of buddy/buddy interaction. Any GOOD inspector would have rejected it, because it violaltes the "NO major over a minor" drainage rule.
    Licensed residential and commercial plumber

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