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How to optimise the structural frame for deck?

Hi Workshop Community,

I am attempting to build my biggest deck to date, and wish to seek some advice on how to optimise my framing (and therefore, effort) for the deck. Deck will be low height (approx 500mm above the ground). Refer to the frame layout below

Large Deck Plan.png

Purple - 90x90 H4 Treated Pine Posts -> fixed into full stirrups embedded into concrete foundations

Orange - Bearers, 140 x 45m H3 Treated Pine, fixed to the posts with 2 M10 bolts per post

Green - 90 x 45 H3 Treated Pine Joists, 450mm centres, sitting on top of the bearers and attached using metal joist straps

Finished Surface - 89x19mm blackbutt to match already completed decks

I have access to the AS Span tables and have used them to set out my frame to date, but not sure if my plan is overkill. Looking for any possible optimisation, as mentioned earlier

Also looking for some advice regarding joining bearers together. Obviously I aim to keep the bearers as long as possible, but a joint is unavoidable. My current thought is a butt-joint and a plate joining the members? Something like this https://www.bunnings.com.au/dunnings-200-x-35mm-m10-galvanised-bracket-plate_p1076799?srsltid=AfmBOoqiLhZ3V1nJjX_m7qlGXImoZ-t61Ug2KLahX6j_eC-2E0QoAINE

There is a set of stairs to build in the middle, but I'm leaving that for another day/post 😋

Seeing some other posts, I have already checked council standards and don't need any permits etc. to do this, given the low height.

Thanks in advance
Bob

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Comments

EricL

Hello @bob17

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your decking frame.

I don't think your design is overkill, you've designed it very well and are within the span limits of the timber pieces you are using. However, I'm just a little bit worried about maxing out the span on the bearers 140mm x 45mm. I propose either adding more posts in between your existing posts or changing your bearer to 190mm x 45mm for a much stiffer frame. In regards to the joint, I suggest looking at doing a lap joint along with a support post at the bottom.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/51236#Comment_51236

Good Evening @bob17

Looking at your drawing I am a little worried about the span between posts, I would have a shorter span as you dont want any flex in the deck at all.

A few extra posts overall is a small cost/time to make sure its solid. I did a whole bunch more then that on mine 🙂

I am thinking 1.8m to 2m apart for the posts at the max. (When you load up a deck you want it to be fine for that dance party 🙂 )

A lap joint is also what I would be doing, I just like them structually, they "feel" stronger when built that way. They are satisfying to do and really not hard to complete.

Dave

Nailbag

Hi @bob17

Terrific detailedplans and thought process. A slightly shorter span with a lap-join will be structurally required. It's obviously going to be a very expensive build. So, unless you know a registered builder (my go-to on major builds as braintrust) I think it might be worth getting some advice from a local draftsperson. For what I would consider a small investment would be worth it in gaining accurate information relative to your project.

Nailbag

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