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

    Hi,
    I have an old property that has 6x2 floor joists on 16 inch centres. The complete span of the house is 21ft. There is a steel beam in the centre of the room that I want to remove and relocate further back at around 15ft.
    So the longest unsupported span would be 15ft and then the rest would be 6 ft.

    Now I know i should be going deeper and wider with my joists but I don't want to affect the ceiling height below or raise the floor above.
    Could I add more 6x2 joists to spread the load?
     
  2. Severntrent

    Severntrent Active Member

    In theory yes, but how many and at what spacing would need a structural calculation as normal span tables don't cater for spacings of less than 400mm. The defection of the joists would probably be the limiting factor more so than their structural strength.
     
  3. Sean Nash

    Sean Nash New Member

    Thanks, yeah thats what I cant find. I guess if I paced them beside the existing joists it would in effect create a 6x4 and I could work my load bearing from that
     
  4. Pollowick

    Pollowick Well-Known Member

  5. KIAB

    KIAB Well-Known Member

    Easi joists may be another option.
     
  6. Pollowick

    Pollowick Well-Known Member

    Another thought ... what size is te steel? and any reason why it cannot be lifted and installed IN the ceiling with joists notched into it?

    Again, subject to SE approval?
     
  7. KIAB

    KIAB Well-Known Member

    Just thought the same.:)
     
  8. Sean Nash

    Sean Nash New Member

    The building has a preservation order on it and as such I can't alter the existing beams. Plus the nearest point to Instsll a beam to get the desired look is 15ft (if that makes sense)
     
  9. Sean Nash

    Sean Nash New Member

    Are they stronger than their equivalently sized completely timber joists
     
  10. KIAB

    KIAB Well-Known Member

  11. dobbie

    dobbie Well-Known Member

    Using rule of thumb calculations the 6x2 joists you have at the moment are undersized.I think a calculation by a structural engineer is required to calculate new joist sizes for the job you want to carry out.
     
  12. Sean Nash

    Sean Nash New Member

  13. Sean Nash

    Sean Nash New Member

    Yeah I noticed that alright, I'll be making sure the SE takes a look but I want to be armed with some info
     
  14. KIAB

    KIAB Well-Known Member

    Quite a few firms around who do metal web joists, I'm a bit out of touch with them now.
    Think around 196mm is standard starting depth for them,but do check, Dobbie has already mentioned your joists are under sized for exsisting span.

    http://www.huwsgray.co.uk/shop/building-materials/timber/easi-joist.html

    http://www.haldane-fisher.com/timber/engineered/posi-joists/

    http://www.donaldsontimberengineering.co.uk/timber-engineering-open-web-joists.php

    https://www.wolfsystem.co.uk/find-a-manufacturer.aspx
     
    Last edited: May 13, 2019
  15. dobbie

    dobbie Well-Known Member

    I was actually talking about the span you have at the moment,not when you move the rsj,a ten and a half foot span should be bigger than 6x2.
     
  16. Sean Nash

    Sean Nash New Member

    Yep, they would only really be capable of a 9ft span. It's part of the reason I'm allowed to add extra joists as it's underspeccified for the current span
     
  17. Sean Nash

    Sean Nash New Member

    From initial calculations I'm not gaining anything by using them. They still specify nealry 9 inches for the posi joists
     
  18. stevie22

    stevie22 Active Member

    The joists at present appear to be OK but I don't think you'll do it with extra joists if you move the beam: you'll be looking at nearly solid wood.

    An additional steel set into the floor depth at the middle of the 15 foot is probably the best option.

    I assume you want the beam you're moving where it goes for aesthetcs?
     
  19. Sean Nash

    Sean Nash New Member

    Correct. Unfortunately I can't set a steel into the floor. I might just have to add 8 inch joists and drop the ceiling height.
     
  20. Jimbo

    Jimbo Active Member

    Change the floorboards for screwed and glued plywood, a structural engineer can confirm how much the sag will be reduced by, it may well be enough.
     

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