Bouncy floor advice

Discussion in 'Engineers' Talk' started by NJ Rider, Jan 29, 2022.

  1. NJ Rider

    NJ Rider Member

    We have moved in to a house built in 1989. All the floors seem to be bouncy all over the house. The floor joists are 2" by 8" 600mm apart. The flooring is some form of Chipboard P5 22mm nailed to the joists at 50mm intervals.

    The pervious owner seems to of tried to fix the problem by adding counter beams in the floor below which are against the plasterboard and not the joists so they look to do nothing.


    Is there a simple solution to eliminate the bounce? It's bouncing at the centre of the rooms. Two worst rooms are 5m by 7m wide. So large spans. With the joists running the 5m direction.

    I'm planning on removing the P5 and replacing with pine 9" T&G boards.

    Is there a simple solution such as bolting additional joists to the current joists. Bolting steels to the joist and flooring? Putting Ply board over the joists before the pine boards?

    This wasn't flagged in the structural survey so I'm guessing it's not a structural problem. It's not something I've come across in older houses.

    We can't place ornaments in display units as they bounce right out when someone walks from one side to the other. I can't see any damage or cutouts.
  2. Jord86

    Jord86 Screwfix Select

    It is a structural problem/issue, the joists are undersized for their span. Double them up by inserting new 8x2's alongside the old ones and screw them both together with 90-100mm timberlok screws.
  3. stevie22

    stevie22 Screwfix Select

    2x8 at 600crs are way overspanned at 5m.

    It is a structural problem but I don't have a lot of faith in surveys personally so not surprised it wasn't picked up.

    You need to lift the floor boards and sister the joists. If you go with C24 2x8 fixed to each joist I think you'll find a bit of a difference. You don't need to cut the new joists into the wall, just up to the face.
  4. NJ Rider

    NJ Rider Member

    Thought that might be the case. Can the counter beams come out as they don't look to be actually doing anything? They're taking up valuable headroom in the lower floor and not resting on the underside of the current joists. I'll slap joist hangers on the c24 and sister them in.

    What's this about ply board sub layers also helping reduce bounce? Is it worth doing this at the same time as I'm swapping out the flooring?
  5. stevie22

    stevie22 Screwfix Select

    You don't need hangers, just fix the joists together. Probably easiest to run a couple of good beads of construction adhesive and drive a rake of screws in.

    Yes to losing the cross beams.

    I would also make sure there were at least 3 lines of nice tight blocks in there as this will help stiffen the floor.
    NJ Rider likes this.
  6. Severntrent

    Severntrent Screwfix Select

    If you bother doing it with joist hangers you could just set the new joists central between the existing joists i.e. 300 centres, and forget the faff of sistering . Achieves the same results but gives less chance of floorboards flexing (not that it would be an issue). Noggins at 1/3 and 2/3 span as per TRADA tables whichever way you go for
    Abbadon2001 and NJ Rider like this.
  7. NJ Rider

    NJ Rider Member

    Thanks I'm having a bit of earache from the Mrs. over messing up with her lounge. I'll see which option is best suited when I rip the basement ceiling down and get a good look at the joists. She doesn't want the furniture moved out the room so I was planning on doing the floor boards in stages and moving it from one side to the over. I'll see if I can slot the new joists in or clamp and sister them. Both are equally painful with the floorboards still in place.
  8. stevie22

    stevie22 Screwfix Select

    Garage below? Drop the ceiling and work from underneath. Done as oner and the cost of a few sheets of plasterboard vs the wrath of SWMBO is a no brainer.

    Shove some insulation in while your at it as I'll take a bet that is below code/non existent.
    NJ Rider likes this.
  9. NJ Rider

    NJ Rider Member

    To be fair to the guy, he had stuffed 100mm of rock wool between the joists. Definitely not enough, but I'll sort that out too as I want to sound proof it.

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