deck posts on joists ??

Discussion in 'Landscaping and Outdoors' started by gingerneil, Sep 12, 2015.

  1. gingerneil

    gingerneil Member

    Afternoon all.
    I'm planning out a 3x5.6m deck and have a quickish query. I've run a string line and lined up the edging bricks that I will use to partition the deck from the grass. They are a change to the current run of bricks that sweeps in from a curve from behind the photographer, straightens up into a line and then ends at the far post. I would like the deck edge to overlap these about where the string line is. This got me thinking... I was planning to set a few posts (100x100) along this edge to support the outer 150x100 timber. There will be a step up halfway, so the near posts will be low down, with the far posts supporting the higher section of the deck and therefore higher posts. Its going to be tricky to set the posts this close to the row of bricks. Accounting for a 32mm deck board on the side to dress, 100mm for the timber, the post edge needs to be only 132mm from this line. The hole for the post would likely come very close, if not come into the brick line. As a result, can i instead set what would have been the outer posts next to the brick line so that they support a joist at the same point instead, but a little further from the edge timber ? I'm planning 400mm spacing of 100x150, using joist hangers.
     

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  2. chippie244

    chippie244 Super Member

    I think you are asking how far can you run your decking past your last joist but I'm not sure.
    100x150 joists are mahoosive overkill.
     
  3. gingerneil

    gingerneil Member

    Almost what I'm asking, but also being a muppet. I meant 50x150 (6*2)!!
    I will have the joists running left to right on the photo, and want the support posts on the joist, not the outer bearer.
     
  4. chippie244

    chippie244 Super Member

    I think you need to put up a drawing with some dimensions on so we can see what you are asking.
     
  5. gingerneil

    gingerneil Member

    Here you go. The grey curve is the ground level brick edging - slate going in the space around the deck. Blue section is just about ground level (prob 5mm gap to the ground), darker section will be this + height of a 150mm joist with a step between the two faced with deck board. Squares are where I'm thinking the 100x100 posts will go (not decided if I'll bury concrete or fill a column with concrete and use metal stand off mounts - thoughts ??).
    The question above is whether or not the posts along the bottom are OK to be mounted on the joists and not the outer horizontal bearer thats over the brick - putting them on the bearer will be difficult due to the row of bricks getting in the way.
    Joists are going to be bolted or coach screwed to the posts, and attached to the outer frame using joist hangers. I'll also have 2 rows of noggins - not included in the drawing as it would start looking at little busy!
     

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  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Posts will be fine on the joists, say up to 12" back from the front bearer. For more support(if you thought necessary), you could add shorter posts that may stand on bricks.

    Mr. HandyAndy - Really
     
  7. gingerneil

    gingerneil Member

    Do the posts in the diagram look OK placed, and enough/too many?
     
  8. abbeybuild

    abbeybuild New Member

    Looking at the diagram I would say you will end up with a strong base (belts and braces). Your top boards will of course add extra strength. I prefer to use concrete, but that's just me. If you are going to use metal stand off mounts, i'd coat them with old engine oil. Just a tip I picked up years ago.
     
  9. gingerneil

    gingerneil Member

    I read so many contrasting comments on cementing the posts in. Some say it's the way to go, others say that they are guaranteed to rot as the cement holds water like a sponge that is drawn into the post..... I think I'll set the outer ring in or attached to concrete, and the inner ones on joists on a brick set in a smaller amount of concrete to make a sturdy base, but less digging! :)
    Any final comments on sinking or fixing above ground? If above ground, which fixings are best and how deep should the base go? Is postcrete still OK, but without the post inside!
     
  10. abbeybuild

    abbeybuild New Member

    Each person finds their own way of installing decking over time. I've heard about posts absorbing moisture before but in reality concrete holds very little water once set. A good preservative on the posts will give you many years of service. It's all about what works for you. All the methods you mention are tried and tested and will work fine. Postcrete uses 3/4 aggregate (I believe) this could be a problem if you wanted to drill for bolts.
     
  11. gingerneil

    gingerneil Member

    Maybe a layer of bitumen paint on each post, up to about an inch above ground? Burying is def the most straightforward approach vs screwing, fixing etc.
     
  12. abbeybuild

    abbeybuild New Member

    That would work. It will give you peace of mind for years to come.
     
    gingerneil likes this.
  13. gingerneil

    gingerneil Member

    I'll go with that then. Thanks for everyone's help... :)
     
    abbeybuild likes this.
  14. abbeybuild

    abbeybuild New Member

    Good luck. It sounds as though it will be a sturdy and lasting project. Hope to see a picture of the finished job.:)
     
  15. gingerneil

    gingerneil Member

    I'm taking quick pics as I go, may well write it up when I'm done.
    Tomatoes nearing their end, and those posts are just resting on bricks built by the previous owner!
     

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  16. abbeybuild

    abbeybuild New Member

    :eek: I hope there are at least five courses of brick work above the frame. If it's bolted to the wall, the flexing in high winds will play havoc with the bonding.

    Look forward to reading your write up. ;)
     
  17. gingerneil

    gingerneil Member

    That's someone else's house, so not planning to fix to it. Leaving a 10mm gap to the frame, but will overhang the deck board so there's no gap to see.... You can see the damp course line if you look closely. The deck will finish a few bricks below due to the different levels of houses. Posts are fixed to wall higher up, and to concreted fence posts, just not ground!
     
  18. gingerneil

    gingerneil Member

    Went with upside down pots from Poundland, buried, cut off the top, add some hardcore from the old deck footing, then postcrete and a standoff bracket. Easy, and cheap - almost the same cost as the savings on the 4x4 posts that would otherwise have to be longer to be buried! :)
     

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  19. KIAB

    KIAB Super Member

    Do like the flan tin edging.:)
     
  20. gingerneil

    gingerneil Member

    Mud pie anyone!? :)
     

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