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How to build a low level deck over concrete slab?

I am an absolute novice and need some help to get started on a low-level deck to cover an ugly and cracked concrete slab.

The slab is 4.0 x 3.6 and I want to keep the deck a low as posable so I won't be able to do bearers and joists. The slab is not even and is open to weather so I need a way to level the deck and allow for water to run away.

I really need a design and a materials list. Help!

I'm thinking to build a rectangular frame from timber - I don't know what type or size - and then to 'fill in' the frame with more timber - again no idea about type or size or how to attach or space the timbers.

I'd like to level the frame with plastic pedestals to improve drainage, but I don't know what size or type or how many I would need. And also if I would need to attach them to the slab and how I would do that.

This is all before I even think about the deck surface. Thinking treated pine so I can paint it.

I'll take any advice you've got so I can get started. My Deck 2.jpg

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Comments

EricL

Hello @su51q

I suggest having a look at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. These guides will give you a general idea of how to plan a decking frame and what you need to take into consideration. I also suggest having a look at this featured project - Low-level composite deck over concrete and soil by @oninpena. It's an excellent example of a single level deck that is supported by angle brackets and pedestal feet.

As the decking frame can be adjusted before they are permanently fixed onto the angle brackets and pedestal feet there should be no worry in regards to the decks adjustability.

Please note that placing anything heavy on this deck such as a spa for example will need serious planning and I suggest engaging the services of an engineer to make your decking plan for you. So that it will be built safely and to code.

I also recommend having a look at Bunnings deck building guide:

How to plan out your deck
How to set out a deck
How to install stumps
How to install bearers
How to install joists
How to lay decking
How to add a step to your deck.

If you need further assistance, please let us know.

Eric

su51q

https://www.workshop.bunnings.com.au/discussion/comment/52921#Comment_52921

Thank you for that feedback. I have watched the videos and read the posts you have suggested.

Am I correct in concluding that I need to use 95 x 45 H3 treated pine for the bearers/joists?

- I need a double joist on each end = 4 x 3.6m

- I need joists evenly spaced at about 450 centres, that's an additional 7 joists to span the 4m stretch = 7 x 3.6m

- I need to put noggins in the double joist = 1 x 3.6m

- I need to put noggins between the joists at alternating 400 centres = about 4 x 3.6m

I will need to put a pedestal every 500? Do I need to use brackets to fix the bearers/joists to the slab?

TIA

EricL

https://www.workshop.bunnings.com.au/discussion/comment/88710#Comment_88710

Hello @su51q

The double joist assembly is only needed if you are planning to build your deck with a picture frame around it. Yes, 450mm spacing is used for joist centres, you'll need to share your plan with us in order for us to understand how you've placed the joist in the frame work. Yes, you'll need to put noggins to stiffen the framework of the deck. In regards to the pedestal footing, again we'll need to see your framework plan so that we can confirm its position. Because it is a free standing decking frame using brackets will fix the frame in place.

My best advice is to draw the decking frame on a piece of paper so that we will have a clear idea of what you are trying to build.

If you need further assistance, please let us know.

Eric

su51q

https://www.workshop.bunnings.com.au/discussion/comment/110064#Comment_110064

Thank you.

I have drawn a plan and it is attached.

Could you please advise about spacing for pedestals - how many and where - and if I need to sercure them to the concrete or should be using brackets to top the deck moving. If I use brackets, how menay would I need and where would I out them given that the slab is not level.

If I wanted to put a lazy boy inflatable spa on one corner, what change would I need to make?

Susan Screenshot 2025-06-08 at 1.42.10 pm.png

EricL

https://www.workshop.bunnings.com.au/discussion/comment/122399#Comment_122399

Hello @su51q (Susan)

On the condition you are using 90x45 framing timber I suggest using a spacing of 800mm per footing. The angle brackets come in various sizes, so you'll need to choose the one that allows you to adjust the level of the decking frame relative to the level of the concrete base. This is on the condition that only people will be standing on this deck, and no heavy items will be placed on it such as a spa.

Please, note that the general weight of a Lay-Z-spa is around 670kg++ when filled with water, if you include 4 possible occupants you are looking at a total weight of 900kg++. Your current decking plan will not be strong enough to hold that much weight. I propose engaging the services of an engineer in order for them to calculate and create a decking frame plan for you that can hold the weight of the spa along with people in it. This will include the proper footing for the deck and the size of deck framing timber to be used. This also guarantees that the deck will be safe, built to local code and council regulations.

If you need further assistance, please let us know.

Eric

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