Advice on decking frame

Discussion in 'Carpenters' Talk' started by Allan1981, Apr 13, 2020.

  1. Allan1981

    Allan1981 New Member

    Looking for a little advice on building frame for composite decking. Previous built decking on concrete base but this one will be raised due to ground not being level.

    The decking i want to build is 8.4m wide x 3.6m. The decking comes in 3.6m lengths so this is why i plan on having the decking this size to save on wastage.

    I was thinking about 7 posts along front and back at 1.2m a part. Along the sides putting one in the middle. Is this enough?

    The joists have to be 300mm apart and I planned to use 2 x 6 for the joists. Can anybody tell me how many posts I will need to place to support the joists? Without counting the outer frame there will be 11 rows of joists.

    Would you recommend using joist supports or just use old fashion nails?

    Thanks
     
  2. furious_customer

    furious_customer Screwfix Select

    That is one big deck.

    So the joists will be running down the 8.4 length then I assume?
    I think the post spacing you mention would work but I think you would want a supporting joist running from post to post across the 3.6 span?

    I am just about to build a deck of pretty much the same size, but have opted to run the joists across the width because it will require less timber (I think - it certainly seems simpler).

    I would say you only need joist hangers if one or more sides will be attached to the house.
    If it's free standing and you have enough access from all sides then just secure them with coach screws.
     
    Last edited: Apr 14, 2020
  3. Severntrent

    Severntrent Screwfix Select

  4. Jord86

    Jord86 Screwfix Select

    300mm centres for deck joists is huge overkill. 450mm is fine, and divides into a 3.6m length.
     
  5. Severntrent

    Severntrent Screwfix Select

    My thoughts to but OP said joists have to be 300 apart so I assumed that is what the composite decking suppliers have speced?
     
  6. furious_customer

    furious_customer Screwfix Select

    Great deck! So does it have supporting pieces under the joists along the width?
     
  7. Allan1981

    Allan1981 New Member

    Apologies, it should have read 1.4 apart. Also thinking of putting 2 at the sides at 1.2 apart, counting the two front and back that makes 4 on the 3.6m length. Then putting the same with a joist running front to back at 2.8 & 5.6. Do you think this too much?
     
  8. Allan1981

    Allan1981 New Member

    It has to be 300mm as per the Composite Decking manufactures guidance
     
  9. Severntrent

    Severntrent Screwfix Select

    What lengths of 6 x 2 have you got to work with in the 8.4m direction
     
  10. Allan1981

    Allan1981 New Member

    They would be 4.8m but cut down to join at the 4.2 post.
     
  11. Severntrent

    Severntrent Screwfix Select

    Then I'd go for my original suggestion of 5 posts at 2.1m ( could be 2.4m with 1.2m make up piece at the end or middle) in the 8.4m direction and 4 posts in the 3.6m direction. This gives 20 posts, your idea gives same number but suggestion means all 3.4m cross members have more support as theses are the members with most load acting on them. Actual allowable span taken from building regs floor joists tables gives an allowable span of the 150 x 50 supporting your decking boards spaced a 400 centres as 3.5m, so even if youhave 4 posts at 2.8m in the 8.4m direction it would be acceptable. Choices,choices,choices!!! How high off the ground is your decking
     
  12. Allan1981

    Allan1981 New Member

    The decking will be about 300mm off the ground. Do you have any recommendations for screws to attach the joists to the posts? I was thinking of using Coach screws
     
  13. Severntrent

    Severntrent Screwfix Select

    Used 1/2" coach bolts on mine but posts were free standing and deck 600 off ground so did not want any sway. If you are setting posts in ground every thing will be rigid and coach screws should suffice Used 6" nails to connect joists to each other
    IMGP1146.JPG
     
  14. Allan1981

    Allan1981 New Member

    Are your post 100 x 100? Also I guess you countersunk the bolts
     
  15. Severntrent

    Severntrent Screwfix Select

    95 x 95 smooth, bolts not countersunk just tightened up to crush in so side decking laid flush
     
  16. Allan1981

    Allan1981 New Member

    Sounds like a better plan to save me from extra work. Did you use washers?
     
  17. Severntrent

    Severntrent Screwfix Select

    On nut side? Yes
     
  18. Allan1981

    Allan1981 New Member

    Thanks for the advice. Just need the company to come back with a quote for me now for all the stuff.

    have you ever done a picture frame round the decking before? Just saw some pictures of it and thought I might do that.
     
  19. Severntrent

    Severntrent Screwfix Select

    No, but looks straight forward enough, stuff on utube.
     
  20. Allan1981

    Allan1981 New Member

    Yeah that’s where I got the idea of doing it.
     

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