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Suspected Timber Joist Deflection

Discussion in 'Building' started by self builder 123, 21 Mar 2010.

  1. self builder 123

    self builder 123

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    Hi

    In my timber framed house there is one area of the upper floor which seems to creak when you walk across it - this area is around the stairs.

    The upper floor is constructed from regularised 47mm x 195mm C16 solid timber joists. The centres are at 400mm.

    In the area that moves the clear span is 4.2m. At one end the joists sit on a structural timber partition - at the other end they are attached to a flitch beam ( 2 x 47mm x 195mm C16 joists ) with joist hangers.

    At the edge of this area 2 x 47mm x 195mm C16 joists were used to form the trimmer.

    The joists are cross tied to each other using full depth off cuts of joists at regualar intervals.

    I have attached 3 photos.

    Photo 1 shows the construction. Photos 2 and 3 show the pipework in the same area which was later installed by the plumber.

    In Photo 1 you will see pipework up towards the top left hand corner of the photos. This the same pipe work as shown in Photo 3 which goes through the trimmer inside ( as I understand it ) the 0.25 to 0.4 span rule for drilling joists. I wonder if this is part of the problem ?

    In hind sight I wished we had installed the joists at 300mm centre spacings in this area or had opted for 220mm deep joists throuhout, however the house was built several years ago and BCO had no issue which the drawings.

    My question is can I fix this annoying joist deflection creak ?

    My thoughts are to drop the plasterboard on the underside of the joists and

    (1) ( Photo 2 ) add coach screws through the centre point of the trimmer to help strengthen it

    (2) secure a 5mm thick steel to one side of the trimmer right under the pipe work, which goes through the trimmer ( Photo 3 ) as I understand that the bottom of the trimmer is in tension.

    (3) ( Photo 2 - joist will black arrow markings ) fit 5mm thick x 100mm deep steel plate to either side of this joist and bolt the plates together through the joist. This would support the bottom 100mm of the joist where I believe that it is tension.

    We would need to notch out the cross supporting timbers so that the steel plate was continous - may not be able to use one section of steel plate due to length and handling but any individual sections would be butt jointed together.

    So in your opinion are my joists the problem and will the steel plates make them stronger thus stopping the deflection ? The plasterboard under this area is finished and painted, but shows no sign of cracking which it what I would have expected if the joists were deflecting, however the movement must be very small, but creates the cracking type of noise.

    Any help would be much appreciated.

     
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  3. joe-90

    joe-90

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    If it were me I'd be cutting a length of timber or using some kind of acro prop and temporarily support the floor from below and keep moving it around. Then nip upstairs until you can isolate where the deflection happens. Then think about how to achieve a permanent solution based on your findings.
     
  4. marsaday

    marsaday

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    your photo show compression joints for the plumbing. i thought this was a no no when piping is hidden out of the way?
     
  5. joe-90

    joe-90

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    they look like push fit to me.
     
  6. Deluks

    Deluks

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    Are you sure it's the joists? The spec sounds absolutely fine. Creaks and squeaks are usually floorboards. As you have osb as the deck I would imagine this would squeak in the same way that chipboard floors are known to do (notorious in fact!) If the deck is just nailed down then go over with 50mm screws every 200mm in each direction.

    Structural repairs seem a bit overkill and a waste of money. Fact is, timber will always want to move whatever the size and thus will make some form of noise.
     
  7. noseall

    noseall

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    I concur with Deluks.
     
  8. self builder 123

    self builder 123

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    Hi

    thanks for your replies.

    the osb was fitted then 50mm x 40mm timbers were screwed down to extend the joists so that UFH heating pipes and screed could be installed. The finished floor is 22mm oak flooring secretly nailed to the timber straps. No glue was used.

    Today I placed 3 acro props under the joist marked with the black arrows. This got rid of the deflection and all the noise.

    If I was to go ahead with a structural modification could I strengthen this joist using steel plate on both sides of the joist ?

    cheers
     
  9. big-all

    big-all

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    ok may have got this wrong
    you have a single joist going from left to right
    not only are the stairs hanging off it the gallery on the other side seem to be supported by it
    now as i am a bench joiner i could be wrong but should that joist not be a lot more substantial!!!

    ok looking at it again i see it has a"TRIMMER AGAIN" sistering it
    what is the span off that sistered joist and what size is the gallery area it supports!!!
     
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  11. Deluks

    Deluks

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    To reinforce it you may as well just bolt on some timber alongside, will be much cheaper than steel plate. However deep it is, match it with same depth, 50mm thick, either side.

    Re: BA's concern, hard to tell exactly what's going on from the pics, but from the description the stairs seem to be over the area where the flitch beam is.
     
  12. self builder 123

    self builder 123

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    Hi

    The sistered joist spans 4.2m from the structural partition at one end to the joist hanger at the other end.

    I have uploaded a snap shot from the drawing showing the plan view of the stairs.

    I take it that you can reinforce a joist without having to have the reinforcing timber hang from a joist hanger at either end ?
     
  13. Static

    Static

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    Joist size is inadequate, your looking at maybe 20mm delfection under worst case domestic load which will feel really bouncy and will probably cause cracking to ceiling finishes. Who from BC passed these?

    Your joists can span about 4m under normal domestic loads with no partitions on them. Sounds like someone saved some cash on joist sizes.

    Are all your floor boardings securly fixed with screws?
     
  14. Deluks

    Deluks

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    Yes, if the loading isn't enough to cause the end of the joist to shear. Unlikely in this case though, you are looking to stiffen so sistering additional timber should sort it.
    Although if you can get full length support then you should do so.
     
  15. self builder 123

    self builder 123

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    Cheers Deluks - Many thanks :D
     
  16. shaunassy

    shaunassy

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    Hi, having taken a look at your picture the problem is all your trimming joists around your stairwell ( opening) should of been double timbers bolted together. What you have done has put the aperture in stress and its twisting!
     
  17. catlad

    catlad

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    I have never seen it were they were not doubled up before.
     
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