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help with the bearer and joist size

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  1. #1
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    Default help with the bearer and joist size

    Hi Guys I need some help with the bearer and joist size on a deck I'm planning on building - Please look at the pdf for a plan of what I'm thinking. I have done a lot of searching and reading in the this forum and have gotten a copy of Allan Staines book.
    Where i get stuck is , my joist continuous span is 5m and bearers 8.65 m and 1 run over 17m - Staines book doesn't go that big , has any one got AS 1684.2 that might be able to help ???? or explain how i can do this ????

    Also should note the height of the deck is around 17cm to the start of the slab of the house. I thinking of using 90x19mm Merbau for the deck , attaching to the house with ledgers and brick piers where i can , post spacing 1500mm x 1400 mm , I'm in melbourne (non cyclonic), The 8650mm x 5000 section of the deck is undercover - Al fresco.

    Any help would be greatly appreciated and if you require any more info or pics please let me know

    Thanks
    Attached Thumbnails Attached Thumbnails img_0108.jpg   img_0109.jpg   img_0110.jpg  
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  2. #2
    Old Chippy 6K
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    The extra run doesn't matter unless you are trying to maximise spacings - and why do that? I would close those spacings up a bit (say 1200 x 1200 roughly - just even according to you site) - the only consequence is another row of bearers and a couple of extra posts/ strirrups & holes.

    On the wall of the house you need only a ledger and it could be 70x45 so with 90x45 joists and 19mm decking there's your 17cm. Or you could use a 90x45 ledger and joist brackets so the top of the joists sit flush with the top of the ledger.

    Bearers are 90x90 (or 2 x90x45) joists at 400-450 - closer is what I use - again why skimp on what will be a couple of extra joists.

    I hate bouncy decks!

  3. #3
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    Thanks for the quick reply Bloss ! I dont mind closing the post spacings at all as i hate bounce on a deck so 1200 x 1200 it is . My major concern was the joist and bearer size with the limited space i have. Looking at the span tables in staines book , i thought i had to get something like 290x 45 for bearers & joists because the deck is large. I must be reading them wrong. How about post size 100 x 100 ok ? and stress grade F7 ??

    Thanks again

  4. #4
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    Just a note, If you have termite barriers at DPC level you could be bridging them with this deck & may have to have have some more termite protection added.
    regards inter

  5. #5
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    I was a bit worried about that , any suggestions ? Would using galvanised RHS and deck not attached to the house help ? or do i have to fork out on a reticulation sytem ?

  6. #6
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    If your DPC level is where the barrier is located just have the top of the deck 20mm below it, it may also depend on the system that has been used eg termimesh, graniteguard, whatever method you use it has to be compatable with the installation of the original system, In NSW the installers details are located in the electrical meter box
    regards inter

  7. #7
    Old Chippy 6K
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    Termites build tunnels to get where they need to go and need moisture to do so - good drainage away from the house is a must and no garden beds etc abutting the house. No bits and pieces of timber should be left lying around to rot etc. The deck is just one way termites might get into the house framing - not an issue to get out of proportion.

    The best protection is to be sure that regular inspections can be carried out and are done. Decks should be clear of the wall in any case and a 20mm gap allows inspection and also breaks the potential (low IMO) access via deck timbers. Any ledge should be attached to stand off the bricks and the decking too.

    See http://www.csiro.au/resources/Termites.html for info.


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