How to Build a Floating Deck in Australia: A Step-by-Step Guide
A floating deck, also called a freestanding deck, is a low-level platform that sits on the ground without attaching to the house. Because it is independent of the building structure, it is simpler to construct than a traditional attached deck.
Floating decks are popular in Australian backyards for good reason. They can be placed anywhere in the yard. They usually do not need deep concrete footings. And in many cases, they do not require a building permit.
This guide walks through every step of building a standard 3.6 m × 3.6 m floating deck using composite boards on a treated pine subframe.
Table of Contents
Before You Start: Rules and Permits in Australia
Floating decks are simpler than attached decks, but they are not exempt from all regulations.
- Building permits: In most Australian states, a deck does not require a building permit if it is under 10 sqm in area and less than 600 mm above the ground. A 3.6 m × 3.6 m deck is approximately 13 sqm, so it will likely require a permit in most jurisdictions. Rules vary by council. Always check before you start.
- Setbacks: Most councils require structures to be set back a minimum distance from property boundaries. This varies, typically 900 mm to 1,500 mm for side boundaries. Check your local planning scheme.
- Railings: Under the Australian NCC (National Construction Code), a deck more than 1,000 mm above ground requires a balustrade at least 1,000 mm high with gaps no wider than 125 mm. Most floating decks sit well below this height, so railings are optional.
- Termite management: In termite-prone areas (most of mainland Australia), any timber in contact with or close to the ground should be treated pine rated to H4 or above. Composite deck boards are not susceptible to termites, but the timber subframe is.
Tools You Will Need
- Circular saw or mitre saw
- Cordless drill/driver
- Drill bit set (including 3 mm pilot bits)
- Speed square
- Framing square
- Tape measure (metric)
- Builder’s line and line level
- Spirit level (1,200 mm)
- Hammer
- Socket wrench set
- Safety glasses and hearing protection
- Shovel and rake
Materials List (for a 3.6 m × 3.6 m Deck)
| Item | Size | Quantity | Approx. Cost (AUD) |
|---|---|---|---|
| Concrete deck blocks (pier blocks) | 400 × 400 × 200 mm | 9 | $12–$18 each |
| Treated pine bearers (H4) | 90 × 90 mm × 3.6 m | 3 | $25–$40 each |
| Treated pine joists (H3) | 90 × 45 mm × 3.6 m | 9 | $12–$20 each |
| Composite deck boards | 138 × 23 mm × 3.6 m | 26–28 | Varies by product |
| Rim joist boards (treated pine, H3) | 140 × 45 mm × 3.6 m | 2 | $15–$25 each |
| Joist hangers (galvanised) | Suit 90 × 45 mm | 18 | $3–$5 each |
| Structural screws (galvanised) | 10 × 65 mm | 1 box (100) | $25–$35 |
| Hidden fastener clips | Suit board profile | 1 kit | Varies |
| Fascia / skirt boards | Suit deck profile | 4 lengths | Varies |
| Drainage gravel (20 mm) | — | 0.5 cubic metre | $50–$80 |
| Landscape fabric | — | 15 sqm | $20–$30 |
Estimated total material cost: AUD $1,500–$2,800, depending on board material (treated pine at the low end, composite at the high end).
EVODEK composite deck boards offer excellent water resistance and termite resistance. Use the EVODEK Decking Calculator to estimate exact board quantities for your deck dimensions.
Step-by-Step Installation
Step 1: Prepare the Site
Choose a flat, well-drained area. Remove grass, weeds, and topsoil to a depth of approximately 50–75 mm across the entire deck footprint plus 300 mm on each side.
Lay landscape fabric over the cleared area to suppress weed growth. Spread a 50 mm layer of 20 mm drainage gravel evenly over the fabric and compact it with a hand tamper.
Tip for sloping sites: If the ground slopes more than 100 mm across the deck footprint, you will need to level the site by adding extra gravel on the low side or digging down on the high side. For slopes greater than 300 mm, consider using adjustable post supports instead of deck blocks — or consult a builder.
Step 2: Position the Deck Blocks
Place nine concrete deck blocks in a 3 × 3 grid. Space them at 1,800 mm centres in both directions. This creates support points for three parallel bearers.
Use a string line and spirit level to check that all nine blocks are level with each other. Add or remove gravel underneath each block to adjust the height. Take your time here — accurate levelling at this stage prevents problems later.
Step 3: Lay the Bearers
Place the three 90 × 90 mm treated pine bearers across the deck blocks, running in the same direction. Each bearer sits in the channel or notch on top of the deck blocks.
Check that the bearers are level along their length and level with each other. Use plastic packers (shims) between the bearer and the block if needed.
Measure the diagonals of the bearer layout. If both diagonal measurements are equal, the frame is square. If not, tap one bearer sideways until the diagonals match. A difference of less than 5 mm is acceptable.
Step 4: Install the Joists
The joists run perpendicular to the bearers. Space them at 450 mm centres. This is the standard maximum joist spacing for most composite decking products, including EVODEK boards. Tighter spacing (e.g., 300 mm) may be required for diagonal board patterns or heavy-load areas.
Fix each joist to the bearers using galvanised joist hangers and 10 × 65 mm structural screws. Position the first and last joists flush with the outer edge of the end bearers.
For a 3.6 m span with 450 mm centres, you will have 9 joists in total (including the two outer joists).
Step 5: Attach the Rim Joists
Cut two rim joist boards to the full width of the deck (3.6 m). Fix them to the ends of all joists using structural screws — two screws per connection.
The rim joists close off the frame and stiffen the structure. They also provide a fixing surface for fascia boards later. After installing the rim joists, check the frame for square one more time by measuring the diagonals.
Step 6: Add Blocking
Install short blocks (noggings) between the joists at the midpoint of the span. Cut treated pine offcuts to fit snugly between each pair of joists and fix with screws driven through the joists into the block ends.
Blocking prevents joists from twisting over time and adds rigidity to the frame. Stagger the blocks slightly (offset by 20–30 mm) so you can drive screws in from both sides.
Step 7: Lay the Deck Boards
Start laying boards from one edge of the deck. Place the first board flush with the rim joist and fix it using the manufacturer’s recommended fastening method.
For composite boards with hidden fasteners: Insert the clip into the groove on the board edge. Screw the clip into the joist. Slide the next board onto the exposed clip edge. Repeat across the deck. EVODEK boards use a hidden clip system that leaves no visible screw heads on the surface.
Leave expansion gaps. Composite boards expand and contract with temperature changes. Leave a 6–8 mm gap between each board (the hidden clip automatically sets this gap on most systems). Leave a 10 mm gap at each end where the board meets the rim joist or fascia.
Cut the final board to the width if needed. Measure the remaining gap, subtract 10 mm for the expansion gap, and rip the last board to fit using a circular saw.
Step 8: Install Fascia and Skirt Boards
Fascia boards cover the exposed rim joists and board ends. They give the deck a clean, finished appearance.
Cut fascia boards to length and fix them to the rim joists with screws. If using composite fascia, pre-drill all screw holes to prevent splitting.
For decks that sit slightly above ground level, add skirt boards below the fascia to close the gap between the deck edge and the ground. This keeps leaves, debris, and animals out from under the deck while still allowing airflow.
Step 9: Add a Step (If Needed)
If the deck surface is more than 200 mm above the surrounding ground, add a single step for comfortable access.
Build a simple step frame from treated pine. Two stringer boards (200 × 50 mm) support one or two treads. Fix the stringers to the rim joist using galvanised brackets. Attach the tread boards to the stringers with screws.
Under the Australian NCC, the maximum riser height for a step is 190 mm, and the minimum tread depth is 240 mm. If the deck height requires more than one step, a handrail may be required — check your local council requirements.
Step 10: Final Checks
Walk the entire deck surface. Check for any boards that are not sitting flat, any loose fixings, or any excessive gaps. Tighten or adjust as needed.
Sweep off all construction debris. If you used composite boards, wash the surface with warm soapy water to remove any installation marks or dust.
Why Composite Boards Suit Floating Decks
Floating decks sit close to the ground. This means limited airflow underneath. Moisture from the soil can rise and sit against the underside of the boards.
Timber boards in this environment are prone to moisture absorption, warping, and mould growth on the underside. Treated pine resists rot but still absorbs moisture and needs regular sealing.
Composite boards handle this environment better. The plastic content prevents moisture absorption. The co-extruded cap layer (on products like EVODEK) seals all four sides of the board, including the underside. This makes composite boards a strong match for floating decks, where ground-level moisture exposure is the primary concern.
EVODEK composite boards are FSC-certified, tested for slip resistance, and backed by a 25-year residential warranty. Order free samples to compare colours and textures before you buy.
Summary
A floating deck is one of the most accessible DIY deck projects. It does not require deep footings, wall attachments, or complex engineering. With basic tools, a helper, and a weekend, most homeowners can build one.
The key steps are proper site preparation (remove turf, lay fabric, add gravel), accurate levelling of the deck blocks and bearers, correct joist spacing (450 mm for composite), and careful board installation with the right expansion gaps.
For a floating deck that handles Australian conditions with minimal upkeep, composite boards are the practical choice. They resist ground-level moisture, require no sealing, and will not warp or rot against a damp gravel base.
Frequently Asked Questions
Do I need a building permit for a floating deck in Australia?
It depends on the size and height. In most states, decks under 10 sqm and less than 600 mm above ground do not require a permit. Larger or higher decks typically do. A standard 3.6 m × 3.6 m deck is approximately 13 sqm, so check with your local council before starting.
How much does a floating deck cost to build?
For a 3.6 m × 3.6 m (approx. 13 sqm) floating deck, expect to pay AUD $1,500–$2,800 for materials if you build it yourself. Using composite boards costs more than treated pine but eliminates ongoing maintenance costs. Professional installation adds AUD $1,500–$3,000 in labour.
How long does it take to build a floating deck?
A handy DIYer with a helper can build a simple floating deck in one to two weekends. Day one: site preparation, blocks, bearers, and joists. Day two: deck boards, fascia, and finishing. Adding a step or complex design extends the timeline.
Can I put a floating deck on grass?
It is not recommended. Grass trapped under the deck will die, decompose, and create moisture problems. Always remove the turf, lay landscape fabric, and add a drainage gravel base. This prevents moisture buildup, weed growth, and uneven settling.
What joist spacing should I use for composite decking?
Most composite decking manufacturers recommend 450 mm maximum joist centres for standard straight-lay patterns. For diagonal patterns (45°), reduce the spacing to 300 mm. Always check the specific product’s installation guide.
Will a floating deck shift or move over time?
A properly built floating deck on level ground with compacted gravel is very stable. However, on soft or expansive clay soils, some movement is possible over time. To minimise this risk, compact the gravel base thoroughly and consider using screw-in ground anchors on the deck blocks in exposed or windy locations.
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