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Floor drains for concrete slabs

dmdurham | Posted in Construction Techniques on July 14, 2008 05:41am

New here-

I’m wondering if anyone has any advice on how to install floor drains in a concrete slab.  Thinking about round drains installed in three-car garage and also for 40’x60′ metal building.  Any special considerations, like P-traps, how to set-up before time to pour slab?  I’m thinking about just draining to outside on ground. 

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  1. Marson | Jul 14, 2008 06:00am | #1

    How about a trench drain? For example: http://www.basementsystems.com/basement_waterproofing/waterproofing_products/basement_waterproofing_system/trenchdrain.php.

    P trap is not desirable in a garage because of freezing, and unneeded if it drains to daylight. The ones I've put in, just have been staked in place with rebar until the pour.

    1. dmdurham | Jul 14, 2008 06:23am | #2

      Thanks. Sounds like it may be simpler than I'm thinking. 

    2. dovetail97128 | Jul 16, 2008 04:52am | #12

      Trench drains that connect to a sanitary sewer system need to have traps and vents.
      They can't get your Goat if you don't tell them where it is hidden.

      1. Marson | Jul 16, 2008 02:14pm | #13

        Obviously. That's why where I live, plumbers daylight them. It gets cold here, and a trap would freeze even in an attached garage.

        1. User avater
          BillHartmann | Jul 16, 2008 04:49pm | #16

          A waterless trap won't freeze..
          .
          A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          1. Marson | Jul 16, 2008 07:59pm | #17

            That's a new one on me. How does it work?

          2. User avater
            BillHartmann | Jul 16, 2008 08:33pm | #18

            http://www.trapguard.com/
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

  2. User avater
    CapnMac | Jul 14, 2008 09:26am | #3

    how to set-up before time to pour slab? 

    Well, you need to string the location in, so you can get the elevation set to most of right, whci often meand either cheating the drain to the nearest rebar, or cheating a bar to the drain.  Usually, the hardest part is screeding the slope to the drain.

    I'm thinking about just draining to outside on ground.

    Now, some jurisdictions will not permit that for a car-storage type building, on the theory that leaking POL for the vehicles can be become "unrestricted runoff," if I remember the term-of-art correctly.  Some places just want a box trap at the daylight exit.  Others want other things.

    Occupational hazard of my occupation not being around (sorry Bubba)
    1. jrnbj | Jul 14, 2008 08:11pm | #6

      Grease trap, this neck of the woods....

      1. MFournier | Jul 17, 2008 04:43am | #19

        Depends on the code in your area.here is a link to the City of Howard Lake Ordinance Establishing Specifications for Garage Floor Drains but it is based on the national code. Most states and cities are adopting the national code.http://www.herald-journal.com/government/howardlake/ord1710.htmlRemember Gas can also leak and gas in a liquid trap is a hazard. Can you say under slab pipe bomb :)

        Edited 7/16/2008 9:46 pm ET by MFournier

  3. McMark | Jul 14, 2008 02:48pm | #4

    Something else that works well is to "block out" your location.  Run the pipe, and set the drain, trap, and trap primer as applicable.  But form a box of about 2'x'2' around the drain location.  This can be poured latter with sack-crete.  I like this method on occasion because it gives  room for error and adjustment of the drain.  It is also a little easier for the concrete guys, especially since they now have a strong and firm form to screed to. 

    If you trap the drain in the initial pour, you better have the elevvation dead on, and really isolate the drain from hits and smacks it may take in the pouring process.  You would be wise to do much of this yourself.  A proper plumber would not want to be responsible for setting the entire elevation of your slab

  4. User avater
    BillHartmann | Jul 14, 2008 04:25pm | #5

    You can use Trap Guard in place of the P traps.

    It is a "mechanical" trap and thus you don't need to worry about it drying out.

    .
    .
    A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
  5. woodturner9 | Jul 14, 2008 10:17pm | #7

    I'm thinking about just draining to outside on ground. 

    Can't do it, legally - it's a plumbing code violation.  Garage drains have to be tied into the sanitary sewer system to be legal.

    1. dmdurham | Jul 15, 2008 02:48am | #8

      Curious.  Seems like there'd be no difference between rainwater (or anything else) running/dripping off of a vehicle if its in a garage or sitting out in a driveway/on the lawn.  I have a buddy who washes his vehicles in the garage, rain or shine.  Don't think his drains go to the septic system.

      1. woodturner9 | Jul 15, 2008 03:03pm | #10

        Seems like there'd be no difference between rainwater (or anything else) running/dripping off of a vehicle if its in a garage or sitting out in a driveway/on the lawn.

        The rationale for including this requirement in the national plumbing code (according to the plumbing inspector) is that vehicles often leak oil or drip oily water after a rainstorm and salt from the roads in the winter.  These chemicals can be treated through the sewer system, but are harmful to the environment if discharged to daylight.

        You are right about sitting in the driveway vs sitting in the garage - but once the car is in the garage, it is inside a building.  I  think that is really the issue - the code says that all interior drains must be tied to the sewer.

        I think this is a fairly recent change, though, and there are certainly a lot of "grandfathered" exceptions in my area.

    2. Marson | Jul 15, 2008 05:08am | #9

      Perhaps it's in the plumbing code, but it isn't enforced where I'm from. How would you keep a trap from freezing?

  6. Clewless1 | Jul 16, 2008 02:47am | #11

    How about just slope the slab to drain toward the door. More even slab (no multiple slopes) and w/ minimal water on it, it's not much of a problem. Saves hassles and details of the floor drain.

    1. woodturner9 | Jul 16, 2008 03:49pm | #15

      How about just slope the slab to drain toward the door.

      That's what I did on my garage - works fine and complies with the plumbing code.

  7. GRCourter | Jul 16, 2008 03:03pm | #14

    Souix plumbing products makes a concrete floor drain with a p-trap, clean out, and ball system that stops water back up.  Put in 3 so far and 2 more to go

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