No joist to support the floor under the bath tub

Discussion in 'Carpenters' Talk' started by VictorN, Jul 1, 2019.

  1. VictorN

    VictorN New Member

    Hello all,

    My first post here, please be gentle ha

    I have lifted all floor boards on the first floor of my house to install sound insulation (the house is taken pretty much back to brick at this point). I have unfortunately discovered that the walls were built on top of floorboards and now I am left with the following dilemma:

    The wall between the bathroom (where the bath tub needs to go) and one of the bedrooms sits exactly on top of a double beam, leaving me nowhere to attach new underfloor to. On the bedroom side, I have screwed in 2x3 timber, which should do the job supporting floor under a bed or a wardrobe. I do not think this would do the trick to support a bathtub full of water with me and my missus in it.

    Any ideas?

    Thank you,
  2. sospan

    sospan Screwfix Select

    If you want to do it properly don't use 3x2 use the same thickness as your floor joist.

    It isn't a big issue to run noggins, struts, blocking between joists to strengthen a floor cut them slightly oversize and then fix them in with nails/screws. Alternatively you can use joist hangers
    VictorN likes this.
  3. Mr Rusty

    Mr Rusty Screwfix Select

    sounds exactly the same as my project house. I ran a 4x2 along the double joist and used substantial numbers of coach screws to provide a bearing for the ends of the floorboards. If you have access to both sides you could put some 10mm coach bolts through and bolt it all together. I also managed to cut my boards half way across the first of the double joist with a multitool so there was some bearing of the boards on original joist. My bath is at 90deg to the joists though.

    I think you may find that your wall is not fully resting on that double joist. Mine was actually a stud wall with brick infill. Had a sole plate and timber uprights secured to the ceiling joists.
  4. Martyn21uk

    Martyn21uk Member

    Just to note that the bathtub will never be filled with water, you and your missus all at the same time. To put 1 or in your case, 2 adults into a bathtub, a volume of water, the same mass as the human being(s) will be displaced.
  5. VictorN

    VictorN New Member

    I discovered today that mine were in fact stud walls with brick infill too. I just don't want to end up with a bathtub in the middle of my kitchen ha
  6. VictorN

    VictorN New Member

    Joist hangers sounds like a very plausible idea, especially since the ground floor ceiling is coming down tomorrow and I will be be able to attach them from below
  7. VictorN

    VictorN New Member

    That's true but you are still looking at approximately 300kg when used, just like being extra careful
  8. Dam0n

    Dam0n Screwfix Select

    It'll be displaced but it's not going anywhere so the weight is still there just the water is at a higher level.

    200kg of water plus two people at 150kg is 350kg. Unless you displace the water so much it drains away.
  9. Mr Rusty

    Mr Rusty Screwfix Select

    shear strength of a single M10 is a couple of tonnes+ - just bolt a sister joist alongside. It really won't go anywhere.
  10. Martyn21uk

    Martyn21uk Member

    For sure, I was just making the point that people often work out the capacity of their bath tub, and then add on the weight of one (or 2) people on top of that. But yes, if you are working it out taking into account you only half fill the tub with water and then add on the weight of people after that, all is great!
    Dam0n likes this.

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