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Thread: Newbee: help with drain on slab foundation

  1. #1

    Default Newbee: help with drain on slab foundation


    I will be doing a slab foundation on my next house and I noticed some homes have drains in the washer/dryer room as well as the water heater.

    Question: From a plumbing perspective, should the area where the drain's are to be located on the slab be recessed 3-1/2" ? also do these drains also require a breather pipe to the roof?



  2. #2

    Default Forgot to ask

    Forgot to ask.

    I have also noticed many new homes have the water lines running through the slab foundation vs. up in the attic. These lines are wrapped in plastic covers. Is there an advantage to doing this? If a line breaks in the foundation, how will you know and how do you fix it if its in the slab?

    Thanks again for any info. and tips.


  3. #3
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
    Join Date
    Nov 2005
    Central Florida


    Here in Florida, almost all plumbing is under-slab. Most codes now require wrapping copper, don't know about CPVC, but I think they do it anyway for thermal insulation. They wrap copper, if they use it at all anymore, because some soils here eat the stuff and cause pinhole leaks.

    You know there's a leak because your water bill goes up. If you're paranoid, you can turn off the main valve at the curb and see if your house's plumbing holds pressure.

    In my case, I noticed the well pump was coming on for no good reason, and eventually tracked it down to an under-slab leak on the hot-water side. You can fix it either by tearing into the slab at the point of the leak and fixing it conventionally, but then it's usually only a matter of time before another leak pops up. The fix of choice is to re-plumb the entire house overhead.

    Don't know much about lowering the floor in those areas, but it sounds like a good idea. I stole 7' from my garage for a "formal" laundry area, and it was already 3 1/2" lower. Water heater is also in the garage.

    As far as I know, anything connected to the waste system has to have a trap and be properly vented.

  4. #4


    Thanks for the info Mikey.
    My neck of the woods is south texas- Mcallen. Humidity is high, pretty darn hot and dry year round.

    Actually, I will be building a new home in a few months with slab foundation and I've seen the plumbing run through the slab, fairly new here in my area, the majority of homes have all supply lines in the attic.

    My dilemma is that I have placed the water heater, in the plans, in the middle of the house in a small closet that's 2'6 x 2'4 and I would like to "recess" the foundation and install a drain in this little closet. Is this something that is pretty common from a plumbing perspective? Any complications to doing this install in a slab foundation?



  5. #5
    Plumber Winslow's Avatar
    Join Date
    Dec 2005


    you shouldn't tie these drains into the sewer if it can be avoided. If it is tied into the sewer then you need to do something to keep the traps primed, otherwise the water will evaporate and sewer gas (and roaches) will enter the house.

  6. #6


    Winslow, thanks for the tip. I did have that concern.
    My floor will be a foundation slab so I won't have any crawl space.
    DO you know if code requiers these type of floor drains be hooked up to the sewer? (texas) sewer will run to septic tanks.

    What are the alternatives?


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