How to build a deck over concrete?

rbouadjenek

Hi everyone,

I'm planning to install a deck in my backyard and have drawn up a plan. The dimensions of the deck are 518 cm by 732 cm, and I plan to put the joists on the concrete elevated from ground with a Macsim Fasteners. The joists will be spaced 40 cm apart as depicted in the plan below.

I've attached a diagram of the plan for reference. Can anyone provide feedback or suggestions on the design? Specifically, I'm looking for advice on:

Whether the joist spacing are appropriate.
The recommended size for the joists to ensure proper support and safety.
Any tips or considerations I might have overlooked.

Thanks in advance for your help!

JacobZ

Hi @rbouadjenek,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Unfortunately, due to the size of the deck, you will need to contact your local council for building approval prior to construction. In most areas, any deck over 10 square metres in size requires building approval.

I would suggest you start by enquiring with your local council what their requirements are before delving too deeply into the planning.

I'm happy to help further once you're aware of your local councils' requirements.

Jacob

MitchellMc

Hi @rbouadjenek,

I thought I'd also add the link to our guide on How to build a low-level deck, which I trust you'll find useful. Since you are in the design stage, I'd also encourage you to check out our Top 10 most popular deck projects for inspiration.

Mitchell

rbouadjenek

Hi @JacobZ and @MitchellMc ,

I just checked with my local council about their requirements, which are as follows:

A building permit is not required if:

The height of the decking is not more than 800mm (mine is lower than that).
The decking is set on a concrete slab (which is the case for mine).
The decking is at least 1m away from the fence (which is the case for mine).
The decking is not attached to the dwelling (mine will be bolted to the concrete ground).

If you comply with these conditions, then your decking is considered landscaping and does not require a building permit.

So, I believe my plan is valid. I just need recommendations on its design and engineering. Any suggestions?

@MitchellMc : I have reviewed all the plans and projects you shared, which were very useful. I drew inspiration from them when designing my plan above.

Thanks, guys, for your support and help.

Cheers,

reda

MitchellMc

Hi again @rbouadjenek,

Your plan looks rather solid. My only suggestion is that you could push the joists out to 450mm centres (as that's adequate) and remove half of those noggins, as they are not necessary. Just remove every other one from your design.

90 x 45mm is what most of our member use for their joists.

Please let me know if you have further questions.

Mitchell

rbouadjenek

Thanks a lot for your feedback @MitchellMc

I have updated my plan based on your suggestions. Could you please double-check it?

I have one question: Can I use 70 x 45mm joists instead of the 90 x 45mm size you suggested? The 90mm joists seem too thick, as the gap between the concrete slab and the door entry is only 11cm.

EricL

Hello @rbouadjenek

Using 70x45 should still work with your proposed plan. Although I concur with Mitchell regarding using 90x45 as it will make your frame robust. But since you are using a great deal of noggins your decking frame should still come out rigid.

My best advice is to place a 6mm gap between your deck panels to provide maximum allowance for moisture to escape under your deck. I also propose checking the water flow on your concrete base. Make sure that water flows away to your garden and does not pool in the middle of your concrete base.

If you have any other questions we can help with, please let us know.

Eric

rbouadjenek

Thanks a lot for your advice @EricL ! There should be no water issues, as the entire area will be covered by a waterproof pergola.

Then I will go with 70x45 joints