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Deck plans, selecting size for bearer & joist

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  1. #1
    tinsmith
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    Default Deck plans, selecting size for bearer & joist

    To the timber Guru in the net

    I am building a deck on my house and this is new to me, so I donít know the spacing between the bearers and joists, (I assume the size of the members are part of this too)? How is this calculated?

    The other part of this problem was the shape, itís a wedge(ish) shape, and will this change the design? Or the supports? I have some old plans of house that have decks and I used these to draw up my plans but they are all square shape.

    Attached is two snap shots, one part of the plan view & the other the footings.
    (the deck is between 1 to 0.7m high)

    Bearers size @ ? distance
    Joists size @ ? distance

    Regards Joel

  2. #2
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    Im in the same boat, i am also drawing up my deck at the moment. I went to bunnings and in their book section there are a collection of Allan Stains Books. I have both the Decks and Patios and the Home Building. These books are used as reference materials in the TAFE architectural drafting course.

    They are pretty reasonable. The deck and patio book has a section with the TRADAC timber section details to suit bearers and joists selection

    G

  3. #3
    Im here now, Damn it! Zedd's Avatar
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    Hi,

    Not an expert but I seem to remember that posts should be at least 100x100mm H4 or 5 treated pine with centres 600mm max apart.

    bearers (i assume this is the name for the horizontals that the deck is nailed to) should be adequate size to support the decks weight - your deck looks pretty big so I would use say 200mm x 45mm at least. some of the more expert guys on this forum should be able to confirm this - perhaps journeyman mick or doorstop.....) each post should have its own bearers.

    in your drawings attached it looks like there are no posts along the triangular line of the edge of your deck so a fair bit of your deck as drawn will be unsupported (flexing) - I would redesign so that it has supports all the way to the edge of the deck for the entire length.


    I hope I'm making myself clear here - im not a tradie - just an amateur.

    good luck - Hope I havent led you astray...
    Religion is the bane of civilization, superstitious proleteriat controlling poppycock.

    Zed

  4. #4
    A Member of the Holy Trinity silentC's Avatar
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    If you get yourself a copy of the NSW framing manual, it will give you the minimum dimensions of the various members for different spans and grades of timber. Possibly overkill for a deck but I'd rather go up a size than have it bounce like a trampoline when you walk across it.
    "I don't practice what I preach because I'm not the kind of person I'm preaching to."

  5. #5
    Senior Member Eastie's Avatar
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    Have a look here: http://www.tradac.org.au/newsite/pub/free/4_decks.pdf

    Combine this with the the book mentioned by C3PO above should give you all the info you need.

  6. #6
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    Thanks for the reference material,Eastie.
    That will come in handy indeed.

    G

  7. #7
    Senior Member Eastie's Avatar
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    Just eating my lunch and looking at my old plans and my old deck tables.
    Donít use any of the following without looking at the current manuals (Timber Promotion Council/ TRADAC/Allan Staines) for yourself and working out the required dimensions as Iíve gone of rough dimensions Iíve come up with on the drawings Ė they may be ballpark or may be way off depending if Iím reading it the same way you are.

    Firstly that height isnít a big factor.

    Joist spacings take into account the deck board timber type/thickness. For 19 mm hardwood / 25 mm cypress 500 mm centres is standard. For 19 mm treated pine and cypress 400 mm centres. For 21 mm cypress or 22 mm treated pine 450 mm centres. No biggy really as the joist spacing tables generally take care of this.
    As you can see fromt he tables in the above link the bearer size will depend upon what timber you intend to use (and which areas will be single span and which will be continuous span/cantilevered). Once youíve made that selection and worked the layout you can work out the floor load width Ė FLW - and from this you can then specify minimum bearer sizes and then joist sizes. (the link in my above post does not give FLW = half distance between adjacent bearers for single span or for continuous span midpoint to midpoint from adjacent bearers (from the centre stump measure Ĺ way to each stump either side)

    Very rough calculations from your plans (from what I can make of them in relation to stump spacings = approx. 1.6 FLW) gives me the following bearer options:
    F5 seasoned treated pine 2x 140x45 mm (single or continuous span).
    F7 seasoned treated pine 190x45 mm.
    F8 hardwood 150x50 mm unseasoned (just sneaks in).
    F17 seasoned hardwood 120x45 mm
    F5 unseasoned cypress 200x50.
    F7 unseasoned Oregon 200 x 50 mm or 2x 125x38 mm

    Based upon 1.6m between bearers the following joists will give you an idea (again very rough as the drawing is not fully specíd and I may have the wrong picture of how youíre actually doing it Ė worked on continuous span):
    F5 s tp 120x35 @ 300 Ė 500 mm centres.
    F7 s tp 90x45 @ ďĒ
    F8 us hw 100 x 38 @ ďĒ
    F17 s hw 70 x 45 @ ďĒ
    F5 us cyp 100 x 50 ďĒ
    F5 us oreg. 100 x 38 ďĒ

    Hmm, I seem to have forgotten something here but for the life of me I canít put my finger on it? Anyway get the reference books/materials and get your design looked at and approved.

  8. #8
    Novice IanA's Avatar
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    Timber Promotion Council in Vic have lots of good publications including one on design and construction of timber decks. (Less than $20 inc postage.)

    Try their website www.tpcvic.org.au

    Tried to insert a clickable link, didn't work. Anyone able to enlighten me?
    Ian

  9. #9
    Novice IanA's Avatar
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    Looks like it did work. Strange!!
    Ian

  10. #10
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    Tinsmith,

    As per previous posts, Allan's deck & pergola book is the best DIY guide around. It has bearer and joists spacings for various timber sizes and shows how to work out floor load widths for non conventional shaped decks. Its available at Bunnies or through TRADC as posted previously.

    Before deciding on the spacing etc, you may want to decide which way / direction you want the decking to run and what species / size of decking to use. Rest will follow.

    Good luck.

    Regards,

    Theva

  11. #11
    tinsmith
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    this was the first time I have been at this forum,

    and simply..... it is great, thank you for your help.

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