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Discuss Cross joist waste for bathroom sink in the Bathrooms, Showers and Wetrooms area at

  1. Ian McGuire

    Ian McGuire New Member

    hi guys, I have a client that wants their sink moving to opposite side of the bathroom.
    After getting through the tiles, 1/2” of adhesive 10 mm ply with about a Million nails in I find the ropey old floorboards and realise that joists run typically 90deg to pipe plan

    I cannot drill and run a 32 or 40mm pipe through the joists as no way of getting pipe through even where permissible, not enough space outside either.

    Can I and this is where it gets interesting, use a y piece and run 2 15 mm pipesthrough the joist to another y that then tees into waste on external wall.

    In theory it seems ok, doesn’t contravene building regs regarding joists, will need to check wras but wondered whether anyone else has had to engineer a solution like this in the past

  2. Craig Watson

    Craig Watson Plumber GSR Top Contributor!!

    I'd give it a week tops before the pipes blocked :rolleyes:
    • Agree Agree x 3
  3. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Yeah soap scum is a pig. Can it drop into the room below
  4. Ian McGuire

    Ian McGuire New Member

    Ok so above floor piping it is then. Def need to move the basin as taps stop the window/fire escape opening
    • Funny Funny x 1
  5. king of pipes

    king of pipes Trusted Plumber GSR

    Hepvo flexible waste will get you out of trouble look at BES website , or run it above and box it in 15mm is a definite no no . Kop
    • Like Like x 1
    • Dislike Dislike x 1
  6. king of pipes

    king of pipes Trusted Plumber GSR

    What's to dislike ?
  7. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Why can’t you get a 32mm through the floor ?
  8. YorkshireDave

    YorkshireDave Plumber

    On other side of room, getting an appropriate fall would be an issue I suspect Shaun.
  9. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    agree but depends on length of the run upto 2m your fine on standard joists
  10. YorkshireDave

    YorkshireDave Plumber

    Of course also depends where its terminating :)
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