Brett Field
Yes. You can build a timber or composite deck on a concrete slab, as long as the frame sits on battens, packers or pedestals rather than flat on the concrete, and water can drain away underneath. That is the advice of the Australasian Timber Flooring Association (ATFA) and decking makers such as ModWood.
Below is how it is done, the rules for timber and for composite, how low the deck can go, whether it needs approval on the Gold Coast, and what it costs. These are market prices from cost guides and suppliers, checked on 5 October 2026. They are not a quote from us.
How do you build a deck on a concrete slab?
You fix a low frame to the slab and lay the boards on that. There are three common ways to build the frame:
- Battens on packers. Timber or composite battens are anchored to the slab, sitting on small plastic packers so water can run under them (ATFA).
- Low bearers. Timber Queensland says bearers can sit straight on a concrete base if they are in-ground Durability Class 1 hardwood or H5 treated pine, and do not block drainage.
- Adjustable pedestals. Stands that sit on the slab and wind up or down, so the deck sits level even though the slab slopes.
Whichever you pick, the slab has to drain first. The ATFA says the concrete needs a fall, and no hollows where water can pond. Its test is simple: hose the slab and watch where the water goes. High spots can be ground down, and low spots filled with an outdoor levelling compound.
The slab replaces the footings a normal deck stands on. If you are comparing the two, our guide to deck footings covers what a deck needs on bare ground.
What are the rules for a timber deck on a slab?
The ATFA's industry recommendations set out how a timber deck over concrete should be built.
| Part of the deck | ATFA recommendation |
|---|---|
| Timber battens | Raised at least 5 mm off the slab on plastic or similar packers |
| Packers | No more than 450 mm apart |
| Batten size | At least 70 x 45 mm, on edge |
| Height from slab to top of the boards | At least 95 mm |
| Batten timber | Durability Class 1 hardwood (sapwood treated to H4) or H4 treated pine |
| Fixing to the slab | Mechanical anchors within 100 mm of each batten end, no more than 900 mm apart |
| Decking boards | No wider than 90 mm, with gaps of at least 5 mm |
Source: ATFA, Residential Timber Decks, version 2 (April 2020), checked 5 October 2026.
The packers let the underside of each batten dry out, and let water pass under it. That matters most where battens run across the fall. Composite battens laid in the direction of the fall need no packers, the ATFA says. Narrow boards and wide gaps help because a deck this low stays damp for longer. Our guide to decking board spacing has the gap rules for every kind of deck.
Can you put composite decking on a concrete slab?
Yes, but never straight onto the concrete. Every maker we checked wants a frame underneath.
| Maker | What it says about slabs |
|---|---|
| ModWood | Battens at least 50 mm high. At least 50 mm clearance over concrete (300 mm over soil). The frame should not touch the slab, must be fixed down rather than floating, and the edges must stay open. Boards need 6 mm gaps when they sit less than 150 mm above the slab. |
| NewTechWood | At least 40 mm clearance over concrete. Frame fixed to the slab with dynabolts and brackets. Boards must "never be glued directly to concrete". |
| Trex (Australia) | Can go over a solid surface only "when using a sleeper system". |
Sources: ModWood's guide to fixing over concrete (April 2017) and fixing chart (September 2021), NewTechWood and Trex Australia, checked 5 October 2026.
ModWood adds that battens should run in the direction of the slab's fall, so they do not hold water under the deck. NewTechWood says gluing boards down removes the expansion gaps and airflow the boards need, and voids its warranty.
How low can a deck on a concrete slab be?
It depends on the material. For timber, the ATFA says the top of the boards should be at least 95 mm above the slab. For composite, ModWood asks for battens at least 50 mm high, and NewTechWood for at least 40 mm of clearance. So a composite deck can usually sit a little lower than a timber one.
Any deck this close to the ground gets extra rules. WoodSolutions and Timber Queensland both treat a deck less than 400 mm off the ground as close to the ground. WoodSolutions says these decks need more airflow, better drainage and more durable timber. A deck on a slab always falls in this group.
Keep the edges open, too. Timber Queensland says the perimeter of a low deck should be kept open for airflow. ModWood says not to seal off the deck ends with garden beds, trees or solid objects.
What about termites when the deck meets the house?
Leave a gap, or make it easy to inspect. The National Construction Code 2022, which Queensland still uses, treats a deck as an "attachment" to the house. Part 3.4 asks for either a termite management system on the deck or an inspection zone between the deck and the house.
For low decks, WoodSolutions recommends a gap of at least 40 mm between the house and the deck, for pest inspection and airflow. The ATFA gives three options: a 40 mm gap, removable panels so someone can check the termite barrier, or extra chemical treatment to AS 3660.1. In Queensland, chemical termite work needs a QBCC licence at any value.
The City of Gold Coast lists "termite protection to adjacent buildings" and "durability when close to ground" as things to consider on any deck.
Does a deck on a slab need council approval on the Gold Coast?
It depends on its size, and on how your certifier sees it. The City of Gold Coast's approval page does not mention slabs. It says a deck, "an elevated platform supported off the ground at any point", needs building approval unless it is under 10 m2, under 1 metre high and meets all building requirements. Landscaping timber laid on natural ground, with no posts or supports, does not.
A deck on battens over a slab sits between those two, so ask a building certifier about yours. Even with no approval, the deck must still meet the building code. Our guide to council approval on the Gold Coast covers who gives approval and what happens if work is done without it.
Separately, any deck job over $3,300 (labour and materials) must be done by a QBCC licensed contractor.
How much does a deck on a concrete slab cost?
We could not find a cost guide that prices a deck on a slab as its own job (checked 5 October 2026). What you do skip is the footings.
| Item | Price | Source |
|---|---|---|
| Concrete footing (not needed on a slab) | $200-$400 each, installed | Sparky, Brisbane (September 2026) |
| Screw pile (not needed on a slab) | $150-$300 each, installed | Sparky, Brisbane (September 2026) |
| Composite battens for decking over concrete | $40-$60 per m2, parts only | Brite Decking, supplier (2026) |
| Buzon adjustable pedestals | $3.66-$15.46 each, parts only | Adheseal, supplier (October 2026) |
The boards, fixings and labour are still part of the job. Our deck cost guide for the Gold Coast has prices per m2 for each type of decking.
We build timber and composite decks across the Gold Coast, from pool decks to deck stairs and landings. You get a timeline with your proposal, before any work starts. More on what we build is on our deck building page.
Where do these figures come from?
Checked on 5 October 2026: the ATFA's Residential Timber Decks industry recommendations (version 2, April 2020); ModWood (Fixing over concrete, April 2017, and fixing instructions, September 2021); NewTechWood (laying composite decking over concrete); Trex Australia (FAQ); Timber Queensland Technical Data Sheet 13, Decks Close to or on the Ground (revised February 2014); WoodSolutions Technical Design Guide 21 (revised October 2020); Sparky (Brisbane decking costs, September 2026); and supplier prices from Brite Decking and Adheseal. Rules from the City of Gold Coast, the QBCC and the NCC 2022 Housing Provisions Part 3.4. We will check the prices again every three months.
See our decks and patios work, or check what your job will cost.
