increasing fllor joists strengh for longer span

Discussion in 'Carpenters' Talk' started by Sean Nash, May 13, 2019.

  1. Sean Nash

    Sean Nash New Member

    Interesting, I have a layer of flooring then an layer of ply then a layer of flooring on top. I'll ask him will that be enough
     
  2. chippie244

    chippie244 Well-Known Member

    If you ply underneath as well it adds a lot to the strength, wether that passes BR I have no idea.
     
  3. Jimbo

    Jimbo Active Member

    It needs to be bonded to the joists. Since the plywood is basically incompressible, this resists the comprehension on the top surface (or stretching on the underside, as chippie244 mentions) so making the joist more rigid. And, if you used say 1" ply, that becomes an extra inch of web height as well.

    I had this done at a house with very over-spanned joists (and a masonry wall sitting on it for good measure) - the calculations showed to 2/3rds reduction in bounce in that case.
     
  4. Sean Nash

    Sean Nash New Member

    When you say bonded what do you mean? Just regular construction adhesive?
     
  5. chippie244

    chippie244 Well-Known Member

    Glued and screwed it becomes a torsion box, very strong.
     
  6. Jimbo

    Jimbo Active Member

    The structural engineer will specify the adhesive to use.
     
  7. chippie244

    chippie244 Well-Known Member

  8. Sean Nash

    Sean Nash New Member

    How about ibs2000 bridging system. Would that help me with the span?
     
  9. Sean Nash

    Sean Nash New Member

    Just to update
    I miscalculated a bit. The joists are on 12 inch centres and the span would be 14ft 2 inches. I'm assuming this will help matters
     
  10. kitfit1

    kitfit1 Well-Known Member

    I could be wrong here OP, so correct me if i'm wrong. I'm guessing you have a Georgian house that has a preservation order in place ? Asking this because if you have, i have got huge experience on this lol :D
     
  11. Sean Nash

    Sean Nash New Member

    Correct
     
  12. kitfit1

    kitfit1 Well-Known Member

    You might well not like my answer then lol. In the house i renovated in the 1980's the joists were actually 9"x3", as you already seem to have concluded the joists you already have are way too small. Going to bigger joists is almost certainly what a SE might recommend. Using bonded ply as already mentioned is absolutely an option nowdays. Either way, the floor has to raised or the ceiling lowered, there is no getting away from that.
    In my case in the 1980's i raised the floor. I took that option because of all the original plaster coving on the cielings.
     

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