1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Decking - Joist Span

Discussion in 'Off-Topic Discussion' started by Freddy, Oct 4, 2018.

  1. Freddy

    Freddy Miserable git, well known for it

    Joined:
    Jul 15, 2007
    Messages:
    8,322
    Gender:
    Male
    Occupation:
    Lazy slave
    Location:
    Bristol
    Ratings:
    +9,440
    Hello me ol’ chums :)

    Got a project, making a seating area. To this end, I’m going to construct some decking. I’ll be sinking/concreting some posts to attach the floor joists. I’m using 4 x 2 for the joists. These joists will be around 3m long. Question is, will I need additional posts to support this span? (I’m thinking I will)

    Cheers...Freddy
     
  2. hoofy

    hoofy Gardener

    Joined:
    Sep 4, 2018
    Messages:
    51
    Gender:
    Male
    Location:
    Lancashire
    Ratings:
    +39
    You can always put bricks/flags etc under the joists to take the weight. You won't see them when the deck boards are in place and you have put boards round the sides.
     
    • Like Like x 1
    • Freddy

      Freddy Miserable git, well known for it

      Joined:
      Jul 15, 2007
      Messages:
      8,322
      Gender:
      Male
      Occupation:
      Lazy slave
      Location:
      Bristol
      Ratings:
      +9,440
      Not a bad idea. I’d be a bit concerned though, as I’d be laying onto topsoil?
       
    • hoofy

      hoofy Gardener

      Joined:
      Sep 4, 2018
      Messages:
      51
      Gender:
      Male
      Location:
      Lancashire
      Ratings:
      +39
      You're already sinking some posts into the ground, just dig a few extra holes while you're at it and do a few more.

      People do put bricks and flags under joists to save them having to put posts in, but it is the lazy way.

      You also have to consider what the deck is going to be used for. If there's likely to be a group of people dancing on the decking, then you obviously need to build the frame to accommodate all that bouncing around. If it's just one person walking to a seat, then the strains on the frame are much less. It's your call.

      You could also drive stakes in next to the joists and when the stake won't hammer in any further, screw the stake to the joist and cut the top of the stake off, level with the top of the joist.
       
      • Like Like x 1
      • pete

        pete Growing a bit of this and a bit of that....

        Joined:
        Jan 9, 2005
        Messages:
        25,638
        Gender:
        Male
        Occupation:
        joinery
        Location:
        Mid Kent
        Ratings:
        +23,292
        Not a structural engineer.:biggrin::biggrin:
        So in such cases I usually over compensate.
        Can you up to 6x2 with maybe one central support, 16 inch centres on the joists.
         
      • Freddy

        Freddy Miserable git, well known for it

        Joined:
        Jul 15, 2007
        Messages:
        8,322
        Gender:
        Male
        Occupation:
        Lazy slave
        Location:
        Bristol
        Ratings:
        +9,440
        Hiya Pete.
        I’ve already got the 4x2, thought that was ok?
         
        • Like Like x 1
        • pete

          pete Growing a bit of this and a bit of that....

          Joined:
          Jan 9, 2005
          Messages:
          25,638
          Gender:
          Male
          Occupation:
          joinery
          Location:
          Mid Kent
          Ratings:
          +23,292
          To be honest @Freddy , if it feels solid enough when the joists are in place I wouldn't worry too much, If you need extra support you can bed a paving slab under and either brick up to the underside of the joists or cut lengths of 4x2 to bear on the slabs, screwed to the sides of the joists.
          I assume you are using pressure treated timber and normal decking boards on top.
           
          • Like Like x 1
          • hoofy

            hoofy Gardener

            Joined:
            Sep 4, 2018
            Messages:
            51
            Gender:
            Male
            Location:
            Lancashire
            Ratings:
            +39
            4 x 2 is ok, it's just that with 6 x 2 you might not need to put a post in the middle.
             
            • Like Like x 1
            • Agree Agree x 1
            • Freddy

              Freddy Miserable git, well known for it

              Joined:
              Jul 15, 2007
              Messages:
              8,322
              Gender:
              Male
              Occupation:
              Lazy slave
              Location:
              Bristol
              Ratings:
              +9,440
              Yes, pressure treated. I’m going for composite decking.
               
            • pete

              pete Growing a bit of this and a bit of that....

              Joined:
              Jan 9, 2005
              Messages:
              25,638
              Gender:
              Male
              Occupation:
              joinery
              Location:
              Mid Kent
              Ratings:
              +23,292
              Gotta be honest I know absolutely nothing about composite decking, sound like plastic?:smile:
               
            • Freddy

              Freddy Miserable git, well known for it

              Joined:
              Jul 15, 2007
              Messages:
              8,322
              Gender:
              Male
              Occupation:
              Lazy slave
              Location:
              Bristol
              Ratings:
              +9,440
              It’s a mixture of wood (dust I think) and recycled plastic.
               
              • Informative Informative x 1
              • hoofy

                hoofy Gardener

                Joined:
                Sep 4, 2018
                Messages:
                51
                Gender:
                Male
                Location:
                Lancashire
                Ratings:
                +39
                I know enough about it to say that the time is coming when sky news run a report showing a whale with a 4.8 length of composite decking stuck out of it's blow hole.:yikes:

                Thing is with composite, people don't know enough about it and what it will do over time like they do with wood. Ok, it might last longer than wood, but it might last too long, longer than people might want. What happens in 25 years when it looks tired and you want to take it up, how are you going to dispose of it?
                 
              • Freddy

                Freddy Miserable git, well known for it

                Joined:
                Jul 15, 2007
                Messages:
                8,322
                Gender:
                Male
                Occupation:
                Lazy slave
                Location:
                Bristol
                Ratings:
                +9,440
                Like I said, it’s recycled plastic. I’ll probably be past caring about it in 25 years :biggrin: Seriously though, I imagine it will be recycled again.
                 
              • pete

                pete Growing a bit of this and a bit of that....

                Joined:
                Jan 9, 2005
                Messages:
                25,638
                Gender:
                Male
                Occupation:
                joinery
                Location:
                Mid Kent
                Ratings:
                +23,292
                Well it should last, not sure of its strength, But I guess it has similar strength to timber of the same proportions but lighter and probably more rot resistant.
                Also it wont move like normal timber when it gets wet and dry.

                Probably a good move, but the deck is only going to be as sound as its framework underneath which will eventually rot . One day.:biggrin:
                 
                • Agree Agree x 1
                • Freddy

                  Freddy Miserable git, well known for it

                  Joined:
                  Jul 15, 2007
                  Messages:
                  8,322
                  Gender:
                  Male
                  Occupation:
                  Lazy slave
                  Location:
                  Bristol
                  Ratings:
                  +9,440
                  A workmate has it. He brought a piece in for me to look at, I’d say it’s heavier than wood. It doesn’t get slippery when wet, unlike timber. Seems a good product, if a bit pricey. I just want something to put down and forget about, just a clean now and then.
                   
                  • Like Like x 1

                  Share This Page