Tub support?

Discussion in 'Shower & bathtub Forum & Blog' started by Nate R, Oct 3, 2007.

  1. Nate R

    Nate R New Member

    Messages:
    472
    Location:
    Milwaukee, WI
    When a standard bathtub is filled with a person and water, where is the weight carried in the house? By the studs it's nailed to, or by the floor? Or is it some of both?

    I'm wondering about floor deflection beneath a tub. Seems to me a tub could easily exceed 40lbs per sq ft, so I'm assuming the walls bear some load. But is it almost all the load, or is it shared with the floor?
  2. statjunk

    statjunk DIY Senior Member

    Messages:
    542
    The floor should carry the entire load. The connection to the wall is for level only.

    Tom
  3. Nate R

    Nate R New Member

    Messages:
    472
    Location:
    Milwaukee, WI
    But that seems to clash with this:

  4. patrick88

    patrick88 Plumber

    Messages:
    836
    Location:
    Webster Ma.
    If you look under one of those tubs you will see the
    So the tub doesn't touch the floor. The frame hold the tub so the frame takes the weight, but if a customer asks I would say
  5. no. The frame is an inbetween thingie that transfers all the weight to the floor. So although nursedoe said it holds the tub up off the floor, it still puts all the weight on the floor, and doesn't mean anything in terms of reducing the total weight of the tub by making use of the walls, no.

    A bed frame under the boxspring and mattress holds the bed off the floor. But all the weight still goes into the floor.

    The thread also explains why SOME manufacturers say no to mortar. Because they are scared of bad installs that will get blamed on the tub, they just say NO, without any nuance.

    When I ask about insulating my electric WH, they say, "No need" and I say well what if i want to, and they avoid Answering the Question, because some weirdo just might go too far and insulate it too well and the circuitry melts... or whatever unknown and unexpected thing could happen. It's not their purview, not their bailiwick, not their responsibility, to help me do better. They have enough on their hands just keeping their liability down to a reasonable level.



    David
  6. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I believe the reason for the instructions on the americast is that the resin substrate needs to be able to expand and contract with temperature. If it was locked into a mortar bed, it could not move.
  7. Nate R

    Nate R New Member

    Messages:
    472
    Location:
    Milwaukee, WI
    I guess I was really wondering how much the floor JOISTS take load from the tub.

    I have balloon framing, so the wall is seperate from the floor. I'm hoping that the tub doesn't bear too much weight on the joists. I suppose if the tub does rest on the floor, it adds weight to the wall hung portion as the joists deflect under load.
  8. Livin4Real

    Livin4Real New Member

    Messages:
    192
    Location:
    Indianapolis, IN
    If your balloon framing is the same as this balloon framing then your joists should still bear all the weight since they rest on the same bottom plate as the walls. Was there not a tub in the spot before where you plan on putting this one?

    [​IMG]
  9. Nate R

    Nate R New Member

    Messages:
    472
    Location:
    Milwaukee, WI
    Hmm, I guess I again left out details. My tub is on the 2nd floor. And it's the 2nd floor joists I'm concerned about. Yes there was a tub in the same place. But, because of sagging joists, it's tremendously off level. If you took a shower, you had to kick some of the water to the drain because it would sit in the side of the tub. But this tub wasn't even connected to the studs at all on the long side. It may be in the front, as I don't have that wall off yet. The back is open. (It's from the 1940s or so.)

    My only concern is that the joists would deflect too much to the point that the weight would then bear on the studs the tub is connected to. I can't see a fiberglass tub flange being able to support that much weight without shearing around the screws that would hold it in.
  10. statjunk

    statjunk DIY Senior Member

    Messages:
    542
    If the joists are sagged and you can see them you'll need to sister up some new joists and if possible use hangers. I guess I was taught how to do this stuff by an old schooler but I wouldn't buy a tub that said I couldn't put it in a morter bed. Sounds wrong to me.

    Tom
  11. Livin4Real

    Livin4Real New Member

    Messages:
    192
    Location:
    Indianapolis, IN
    ahhh, gotcha, didn't think to consider it was on a second story. In that case, I would think the wall studs would bear a good amount of the weight and adding sister joists would just increase the load on the wall studs, if it is old school balloon framing where the wall studs go all the way from the bottom sill to the top sill of the second story. I don't suppose there's an area on the first floor under the bathroom that's hidden where you could add a screwjack (like the ones used under beams in basements, etc.)? This is a good dilemma for a structural engineer to figure out.
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