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Thread: Tub support?

  1. #1
    DIY Senior Member Nate R's Avatar
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    Default Tub support?

    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. #2

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

    Tom

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    DIY Senior Member Nate R's Avatar
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    But that seems to clash with this:

    Quote Originally Posted by nursedoe
    No, guys, the instructions says absolutely not to put the tub on a bed of mortar or any other bedding material. In fact, the warranty is void if that is done. I am not sure why the inexpensive Americast tubs are like that. The instructions says that the tub itself should not be touching the floor. It sort of has a frame that supports the tub part off the floor.
    nursedoe

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    Plumber patrick88's Avatar
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    If you look under one of those tubs you will see the
    It sort of has a frame that supports the tub part off the floor.
    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
    The floor should carry the entire load. The connection to the wall is for level only.
    I'm just starting to work with an old friend of mine to bring solar electric and hot water systems, wind turbines, Flex Fuel Boilers, batteries, hydroponic gardening, books, pellet grills and more. Also the parts for DIY installation.

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    Homeowner geniescience's Avatar
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    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

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    Plumber jimbo's Avatar
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    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.

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    DIY Senior Member Nate R's Avatar
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    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.

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    DIY Senior Member Livin4Real's Avatar
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    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?

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    DIY Senior Member Nate R's Avatar
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    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. #10

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    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. #11
    DIY Senior Member Livin4Real's Avatar
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    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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