Minimum vertical distance from tub bottom to p-Trap inlet?

Discussion in 'Shower & Bathtub Forum & Blog' started by bagdanoj, Oct 20, 2009.

  1. bagdanoj

    bagdanoj New Member

    Oct 16, 2009
    The title is the crux of my question, but here's more information if you need it:

    I am doing a bathroom remodel. The old bathtub (already removed) was installed on a 7-inch platform (also, already removed) in order to accomodate the drain plumbing that had to be installed above the floor (the inlet to the p-trap is about 3 inches above the subfloor and must stay that way). I am preparing to rebuild the platform to accomodate the new tub, and I was just told by a plumbing contractor's estimator that I will need to build the platform so that the bottom of the tub is a full 7 inches higher than the p-trap inlet (to accomodate the drain and overflow assembly, with sanitary tee and 3-inch tailpiece).

    But this doesn't seem right to me. The specs for the Kohler drain/overflow assembly I want show a total of 5 7/8" from the top of the drain shoe to the bottom of the included 3 inch tailpiece. And the installation instructions explain that 1-2 inches of the tailpiece actually extend into the p-trap inlet. Basic math tells me that the bottom of the tub would only need to be about 4-5 inches higher than the inlet.

    Any ideas where the estimator might be getting the additional inches? Are there additional parts required by code that's not sold in these standard kits? I've asked for clarification from the estimator, but he hasn't really explained it. I'd hate to build a 10-inch platform when a 7-inch platform would do just fine (as was there before). 10-inches is a big step up and would bring the tub way too close to what's already a low, sloped ceiling. Also, I'd hate to buy an drain/overflow kit that doesn't meet plumbing code for some reason.

  2. dcelite

    dcelite Plumber

    Oct 5, 2009
    Los Gatos, CA
    As far as I know, the vertical distance between a fixture outlet and the trap weir shall be as short as practicable, but the tailpiece from any fixture can not exceed twenty four inches in length. (section 1001.4 tailpieces). Sounds like you can go as short as you like.
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