Hardwood decking joist spacing

Discussion in 'Carpenters' Talk' started by Norv, Apr 21, 2016.

  1. Norv

    Norv New Member


    I'm in the middle of decking one side of my garden, 10m x 3.5m between my house and next doors garage. I have laid a 4x2 frame with 600mm joist centres and supports to the ground every 1m with noggins to suit.

    The decking I am now looking to use is Yellow Balau decking boards 21mm x 145mm in 3.5 metre lengths so no butted joints, the boards will run away from the house in the 3.5m lengths cut to suit.

    Everywhere I have read has said joist spacing would be best at 400-500mm centres, but I have now finished the framing.

    Would you say that 600mm spacing is too much and I risk warping the boards? Is my only option to take apart the framing and rebuild it with 400mm centres? Or are there any other solutions to this problem?

    I've looked into 40mm thick cedar boards but they don't suit the look I am going for.

    Any help gratefully recieved!
  2. KIAB

    KIAB Super Member

    If the boards were thicker like 28mm - 32mm then 600mm would be ok just, as your boards are only 21mm, then I be looking 400mm ideally, 500mm at a push.

    You can get Yellow Balau in either 25mm & 32mm x150mm size, grooved or reeded.

    Let see what others say though, before deciding.
    Last edited: Apr 21, 2016
  3. Phil the Paver

    Phil the Paver Screwfix Select

    Agree with KIAB, at 25mm 600mm is to far apart, even when I lay 32mm I set 500mm centres.
    KIAB likes this.
  4. Phil the Paver

    Phil the Paver Screwfix Select

    You will only have to remove every other one and replace with two at 400mm centres.
    KIAB likes this.
  5. KIAB

    KIAB Super Member

    Beat me to that.:p

    Will give a much firmer deck with no deflection.
  6. chippie244

    chippie244 Super Member

    You could call it sprung decking :)
    KIAB likes this.
  7. Norv

    Norv New Member


    This is my frame. Would there be a way of just running in additional joists which aren't supported on the ground? Maybe notch the joists and noggins so they can just offer support? Or would the noggins only having 2x 3" nails end nailed through the joists not be strong enough?

    Every other joist certainly sounds the better option! Does that look like it would work with the way I have constructed my frame? Would you modify the frame to accomadate the balau or would you look at thicker alternatives like cedar (which doesn't look as nice) or any others you might know of?

    Thanks for the input, very much appreciated.
  8. Norv

    Norv New Member

    Haha, sprung decking! I can't see that catching on. Think I will do the 400mm centres unless any nice looking hardwood decking comes in thicker boards to suit 600mm centres and doesn't cost the world! Asking a bit too much there I'm sure.
  9. Phil the Paver

    Phil the Paver Screwfix Select

    That's doesn't look level, have you built in a fall on purpose.

    Also I don't like plates bolted to the walls, i always leave a gap for the joist and the decking to try and eliminate damp problems.

    As for spacing just fit another joist in the middle so your at 300mm centres, packing it along the way to stop it springing.
    KIAB likes this.
  10. wiggy

    wiggy Screwfix Select

    As its for yourself I wouldn't worry about it, yellow balau is a fairly stable wood, pre drill it and fix it with a good stainless steel screw about 25mm from the edge.
    I laid 19mm ipe in my garden at 580 centres and it hasn't moved a bit.
    The only thing I would do looking at your framework is move your noggins so they fall under the boards, there is nothing worse than a line of noggins falling right on the gap, they just collect crud, a small detail but it makes all the difference, I wouldn't have bolted to the walls either, I would have built it as a free standing unit, bit late for that now mind.
  11. KIAB

    KIAB Super Member

    At least then you can still use exsisting noggins cut in half,saves waste.
  12. Phil the Paver

    Phil the Paver Screwfix Select

    Wiggy, does it not bounce when walked on.
  13. dwlondon

    dwlondon Active Member

    Unfortunate. For it to be put right means a lot of work and/or waste of materials. Equally if your finished height only allows 21mm you are stuffed for heftier decking.

    Also I always throw down some black 1000 guage dpm to stop any weeds taking root under the deck.
  14. Phil the Paver

    Phil the Paver Screwfix Select

    Yes and he only need 5 more joists so no real expense and will be solid.
  15. Norv

    Norv New Member

    Thanks for the input. It's got a fall of 1 in 100 to aid drainage. 18mm on a 6 foot level. It is pretty much level, those pics probably dont do it justice.

    Would the frame being bolted to the walls (bolted to the house and the walls except the neighbours garage) be a potential problem that I should try and alter now? Or live with it? I have put some DPC between the wood and any brickwork.

    The noggins under the board joints is a good point, I'll bear that in mind. Would you line them up and secure the noggins as you go along with the boards or mark them all out and fix them before hand?

    I have some weed membrane to put down, it was gravel underneath with no major weed problem, so that should be enough to keep them at bay.
  16. wiggy

    wiggy Screwfix Select

    Not at all phil, the spacing for decking joists is more about stoping the wood twisting.

    I made the mistake years ago of using 600mm centres on iroko, which in itself would have been ok, it was a nice 22mm thick board, but I forgot the customer wanted the boards at an angle, so that increased the span to about 700 from memory, which was still ok for the bounce but it twisted like a pig.

    If the OP wants to add some more joists (which I personally wouldn't) I would rip the whole thing up, dig another 6inchs out for air flow, take the timbers off the wall, as phil says its not a good idea, it will be damp the whole time, and I would set the noggins to fall under the boards.

    To be honest there is nothing that bad there that will drastically reduce the life of the decking, just soak that frame in creosote or similar
  17. chippie244

    chippie244 Super Member

    Which way are you laying the decking?
  18. wiggy

    wiggy Screwfix Select

    For the noggins, from your first board measure from the centre of that board every 145mm (or whatever your width is) and mark it until you get to where you want a noggin, using 4x2, every 1200/1400
  19. Norv

    Norv New Member

    Decking boards will be 3.6m so will be laid across the joists with no joints.
  20. wiggy

    wiggy Screwfix Select

    I think chippy meant, smooth or grooved.
    Yellow balau I am guessing grooooooooved
    Joe95 likes this.

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