How deep the drain pipe bury under the cement floor

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by jimi, Jul 31, 2007.

  1. jimi

    jimi New Member

    Messages:
    10
    Location:
    Kitchener, Ontario. Canada
    I am helping a friend to build a bathroom and toilet in a old house basement, Waterloo, Ontario. It is a low basement and we wanted to run the drain pipes under the cement floor.
    How deep shall we dig to lay the drainage pipes?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    I think the operative question here is how deep is the main sewer line? You need to run 1/4" per foot slope from where the pipe turns horizontal to where it connects to the main drain line outlet. Depending on where that is, how far you have to go, and how deep it is will somewhat determine.
  3. GrumpyPlumber

    GrumpyPlumber Licensed Grump

    Messages:
    1,404
    Location:
    Licensed Grump
    Code here requires 3" backfill (sand) all around drainage.
    That would equate to a depth of at least 3" from the top diameter of the pipe....here anyway.
  4. jimi

    jimi New Member

    Messages:
    10
    Location:
    Kitchener, Ontario. Canada
    If the PVC sewer pipe is 4" dia +3" cover= 7" deep.
    How about the "u" joint for the toilet? and the distance from the main approximate 10 feet away, the slop?

    I am afraid to dig too deep that might hit something, such as a gas line??
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,298
    Location:
    Yakima WA
    What is a "U" joint for a toilet? If you are thinking of a P trap, toilets have their trap built in, so that is not a consideration. Or are you thinking of the closet bend that connects to the flange? That is just a special type of elbow and require no extra depth. You have to add 1/4" per foot depth for the slope. If there is a gas main, the gas company will locate it for you, just call them. There should not be a gas main buried under the floor. Have you planned for venting this toilet? I wonder if you may be into something beyond your experience level. It might be time to have a plumber in to evaluate the job. It might save you and your friend a lot of time and money in the long run.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    As to the length, just take say that 10' x 0.25"/foot, and you come up with 2.5". In other words, the low end needs to be at least 2.5" lower than the higher end of the horizontal portion. As to how high a closet bend is, I'm not sure; I'd have to either measure one or find the spec. You still need to know the height where you can actually connect that new run into the main sewer line...hopefully, you have enough drop so you can maintain at least the minimum required slope.
  7. frenchie

    frenchie Jack of all trades

    If you have any concerns about hitting any utilities... you should be calling the utility companies before you start digging, get them to come in and locate / mark the locations for you.

    I've never heard of any utility running under a basement floor, though.

    Gas, electric, and water usually all come in through a basement wall somewhere. Find them before you start.
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