P trap height too low?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by joek, Dec 24, 2008.

  1. joek

    joek New Member

    Messages:
    6
    I'm doing some remodeling in my bathroom and we set the height of the 1.5" PVC fitting that enters the wall(the part that the p trap would connect to) at 13" AFF. After reading some more on the internet it looks like standard height is 16" AFF, so I'm wondering if I am going to run into issues and if so what type of issues with a P trap that is 3-4" lower then the standard height. Will the height the water has to drop from the sink evacuate the P trap, or are there any other issues you can think of?

    PVC is already glued so I would have to cut it with a hacksaw and replace a few fittings.

    Thanks,
    Joe
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,298
    Location:
    Bothell, Washington
    13" will work too.
    Depending on your counter height, it may be something like 18 or 20.

    It takes more distance than that before you need to worry.
    Last edited: Dec 24, 2008
  3. joek

    joek New Member

    Messages:
    6
    Thanks,
    Can you clarify what the 18 or 20 inches you were talking about is referring to? Is that the drop from the top of the sink to the trap?

    As long as 13" above the finished floor will work, I guess I'll leave it and test once the sinks in place before the sheetrock goes up on the other side of the wall.
    Last edited by a moderator: Dec 24, 2008
  4. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Trap height is not determined by finished floor. It is determined by the fixture outlet (drain). With that being said, the maximum distance between the fixture outlet and the trap weir is 24" so it sounds like you will be in good shape.
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,298
    Location:
    Bothell, Washington
    For a bathroom counter at 32", I stub out at 20"

    If you have it at 13", you will just need an extension for the tail piece.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,049
    Location:
    Cave Creek, Arizona
    trap

    Too low is seldom a problem, unless the cabinet has a high floor and you have to cut a hole for the trap to hang through it.
  7. Basement_Lurker

    Basement_Lurker One who lurks

    Messages:
    668
    Location:
    Victoria, BC
    If you roughed out at 13" above the finished floor you should be ok like everyone else is telling you. Standard vanity cabinets have a toe kick dimension of 4", which basically makes it a 6" dimension from the floor to the top surface of the inner cabinet base shelf. So you are left with roughly 7" to play with, and since a p-trap generally drops about 5", you will be cutting it close, but you can still make it work.

    They way I rough in lav/kitchen drains and supplies, the drain center ends up being 18.25" off of the rough floor.
    Last edited: Dec 26, 2008
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,049
    Location:
    Cave Creek, Arizona
    drain

    18.25" above the floor? Does that mean 18.325" is an error and too high. Most of us would be satisfied if it came within + or - one or two of the longer marks on the ruler.
  9. Basement_Lurker

    Basement_Lurker One who lurks

    Messages:
    668
    Location:
    Victoria, BC
    heh, wiseass.

    Like I said, 18&1/4 is what my drain center rough-in works out to be the way I rough in my supplies and drain for a sink...so I don't meet the 16" above the finished floor measurement that the poster found on the internet either.
  10. srdenny

    srdenny Plumbing Contractor

    Messages:
    361
    Location:
    SF Peninsula
    Generally, as stated above, low roughed in wastes can be attached with tailpiece extensions. Problems arise when you have to notch cabinet floors or shelves to fit the trap. On some pedestal lavs the porcelain on the pedestal is not hollowed out all the way to the floor. With a waste line below a certain point with such a ped the trap cannot be hooked up and requires a saw with a diamond blade to remove the offending porcelain or wall surgery to raise the stub out.
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