4x2 joist floor, fix bounce

Discussion in 'Carpenters' Talk' started by stuthorpe, Oct 15, 2021.

  1. stuthorpe

    stuthorpe New Member

    Hi everyone, I'm after some advice and thoughts please.

    I'm turning a large subvoid under my house into a games room / storage. I've taken a number of walls out (and replaced with steel) that supported the ground floor that is made of 4x2 timber joists at approx 400mm centres.

    Largest area has a span of 3.5 to 4m, with one end in a wall pocket and then supposted by two steels, mid and othr end. No noggins what so ever are located within the floor make-up. The floor is wedged up well on the steels and I've screwed the floorboards down into the joists.

    Ive still got some bounce / wobble on the floor in the largest area where the kids play.

    I was firstly going to just put noggins in, but from researching I'm not sure if this will reduce the bounce to what I want. Now I'm thinking of sistering each joist with the same size C24 4x2, coach bolting and glueing together. I don't intend to make the wall pocket larger at one end, so the new joist will be bolted straight on to the old. I will be abe to get the majority of the length in for each sister. I don't want to increase the joist depth because I'm already very tight on headroom.

    My question is, would this sistering approach work to reduce the bounce? Any thoughts greatly appreciated.

    Many thanks, Stu.
  2. Jord86

    Jord86 Screwfix Select

    4x2 is good to span up to 2m give or take, it's not surprising you have bounce. Noggins will do nothing, for a good job, whether you want to or not chop pockets out of the wall and fit new joists bearing onto each wall then coach screw them to the existing ones.
  3. Adamfya

    Adamfya Screwfix Select

    ive put noggins in on my suspended floor joists, and its definitely stopped some of the bounce in the floor. all more rigid than it was
  4. Severntrent

    Severntrent Screwfix Select

    Structurally not quantifiable
  5. Adamfya

    Adamfya Screwfix Select

    What rellevance is that?
  6. Severntrent

    Severntrent Screwfix Select

    That your noggins will have no effect on bounce
  7. Adamfya

    Adamfya Screwfix Select

    They do. They did in my place
  8. stevie22

    stevie22 Screwfix Select

    Sistering is the way to go. You don't need to open up the wall pockets: it will make no appreciable difference in the real world provided the joists are fixed together well.

    Structurally the noggins will make no difference to the deflection. They are more useful in deeper joists where there is a tendancy for the joists to twist under load (a phenomenon called lateral torsional buckling)
    stuthorpe likes this.
  9. stuthorpe

    stuthorpe New Member

    Hi Adam, what size joists are they on your house?
  10. stuthorpe

    stuthorpe New Member

    Thanks everyone for the replies.

    I wasn't very clear above, total length of my 4x2 joists is approx 3.5m, supported one end in a wall pocket, mid point on steel at 1.8m and other end also on steel.

    On reflection, I think I can only get about a 1.5 to 1.7m length in to sister because of other steels in the way. I've attached a plan for info. Any other suggestions would be greatly appreciated. Many thanks, Stu.

    Attached Files:

  11. Adamfya

    Adamfya Screwfix Select

    9x2 or old money equiv. I rekon...
    stuthorpe likes this.
  12. Adamfya

    Adamfya Screwfix Select

    The way i see it... chuck all the technical stuff out...
    Get a ladder and knock out a few rungs....see how that effects its strength and rigidity
  13. Severntrent

    Severntrent Screwfix Select

    But dont forget to fix each end of the ladder and fix floorboards across the rails all the way up and have a minimum of 2 ladders so that you are working across 4 rails.

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