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Newbie Deck Design Height? Materials?

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  1. #1
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    Default Newbie Deck Design Height? Materials?

    Hi all i'm new here but have seen some great work and hopefully i can get some help with my deck.

    I'm a first time deckie but enthusiastic DIYer. The deck i'm currently planning is 7m x 4m across the back of my rumpus room. I have put in a new back wall on the rumpus with French Doors.

    Materials:
    11 x 3m RHS 100 x 100 x 6 (it was free) for Posts and Bearers -
    Posts: Qty: Suggestions
    Bearers: 1st @ 500mm, 2nd @ 2000mm, 3rd @3500mm.
    Timber or RHS for Joists?
    Joists: Qty 16 @ approx. 450mm centres +/-
    Decking: Merbau 90mm

    Problem 1: Looking at Rumpus Room Land is sloping Right to Left. RH corner has about 100mm clearance to ground and LH about 250mm.
    Q1:Should I excavate so I have minimum 300mm clearance plus drainage (crushed rock) to doors off Rumpus? I read somewhere this is the minimum height (also, is that too the deck or bearer?)

    Problem 2: Need to start 1st bearer 500mm out from house due to existing gutter/drain around perimeter which works well. Therefore Deck is independant from the house.
    Q2: Is it okay to finish on overhanging joists?

    Problem 3: Materials Posts, Bearers & Joists
    Q3's: How many Posts would you use with the RHS?
    Bearers are currently max. 3000mm weld or extra posts to join 1000mm length? (i.e. 7m = 2 x 3m, 1 x 1m RHS)
    Joists: use Timber (seeing bearers are steel termite risk is minimised!) or Steel what size(s)? Benefits, etc.
    Finally, Best hardware for fastening the whole thing together? post to bearer, bearer to joist, etc.

    Apologies for the long post and newbie Q's I am trying DIY but any hints or suggestions are greatly apprecioated as I do like to overcomplicate things.

    Thanks

  2. #2
    Resigned SilentButDeadly's Avatar
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    You really need this book


    Which is available from Bookshop
    Joined RF in 2006...Resigned in 2020.

  3. #3
    Apprentice (new member)
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    Default

    Thanks SBD.... as stated i do overthink to overcomplicate and am just looking for advice. Especially due to the mix materials (steel & timber) i doubt will be in the book.

    Also, have noticed a lot of people on this site aren't putting in 300mm clearance is it necessary?

  4. #4
    Senior Member
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    Default

    Allan Staines book is great but doesn't address using steel. Would still be a very useful read anyway

    Q1:Should I excavate so I have minimum 300mm clearance plus drainage (crushed rock) to doors off Rumpus? I read somewhere this is the minimum height (also, is that too the deck or bearer?)
    This minimum height relates to termites i.e. access to see termite activity. This requirement varies from council to council and I think Nillumbik (Eltham) is 400 mm from bottom of bearer


    Problem 2: Need to start 1st bearer 500mm out from house due to existing gutter/drain around perimeter which works well. Therefore Deck is independant from the house.
    Q2: Is it okay to finish on overhanging joists?
    You can cantilever (overhang) joists, but to go 500 mm you will need at least 120x 35 (read the span table sticky) Cantilevered is usually okay as it is at an edge and not many people stand, however outside a door it may be noticeable as you step onto it. It won;t bounce much but you probably feel some movement
    It would be better to to put a ledger on the wall (Bearer bolted to wall)



    Problem 3: Materials Posts, Bearers & Joists
    Q3's: How many Posts would you use with the RHS?

    The problem with steel as bearers and joists is span tables. I have not been able to find a single one.
    I would weld up the 7 metre length. I would join the posts and bearer by welding.

    How do you join timber joists to steel bearer? either bolt down through the 2. Problem being is the bolt may be in the way of your decking fixing. Weld flat bar as tabs up one side of the joists and bolt through that
    .

    Read through some of the other "Low deck" posts recently and there have been some good answers.

  5. #5
    Senior Member
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    Default

    Just for info bunnings stock the Allan Staines series of books in their DIY section.

    Cheers

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