A deck looks like a simple build. Four bearers, a grid of joists, a row of boards across the top. The detail that separates a deck you walk on for ten years from one that creaks and twists by the second summer is mostly in the decisions you make before you start.
Here is the short list, in the order a builder works through them.
1. Pick the right board for the climate
The board you choose is the single biggest decision. It controls the look, the maintenance and how long the deck lasts. The five board families that cover most South Australian backyards:
- Treated pine (clear grade). The most affordable hardwood-look option. Looks good for the first few years if you stay on top of oiling. Will silver out fast if you do not. Best for tight budgets or temporary structures.
- Merbau (Kwila) or Kapur at 90 mm width. Warm reddish-brown. Strong, dense, holds up to weather. The default choice on most jobs we quote. Bleeds tannins for the first six months (rain stains the concrete below) so plan for that.
- Blackbutt or Spotted Gum at 86 or 90 mm width. Australian hardwoods. Beautiful colour variation. A step up on price from Merbau but worth it for a finer finish that holds its colour with oiling.
- Merbau wide-board at 140 mm. Same timber, fewer joints, faster to lay, more contemporary look. Sits on top of joists at slightly tighter centres because the wider board moves more.
- Evalast Infinity, Apex or Pioneer (composite). Capped composite boards. Nearly zero maintenance, no oiling, no splinters, long warranties. More upfront cost but the lifetime cost is often lower.
If you cannot decide, here is the rule of thumb. If you want the best look for the next five to ten years of kids, dogs and the BBQ, and you do not mind oiling it, go timber. If you are planning fifteen years or more and want to never oil it again, go composite.
2. Height matters more than you think (and council cares above 1 metre)
Once any part of the deck sits more than 1000 mm above natural ground level, council certificate territory kicks in. In South Australia that means an application, an engineering check on the bearers, and a balustrade at one metre high.
A small step-down deck (around 350 mm off ground, our standard build height) is essentially permit-free. A raised pool deck or one stepping out from a sloping yard frequently lands over the threshold and needs the paperwork. Talk to your builder early about this. The council application cost and the engineering check together add a meaningful fixed amount to any raised deck build, so it is worth factoring in from day one.
3. Joist and bearer spacing
The structure under the board is what you will never see, and what makes the difference between a deck that feels solid and one that bounces.
A working rule for the standard board sizes we use:
- Bearers at 1800 mm centres
- Joists at 450 mm centres (boards under 100 mm wide can stretch a touch further)
- Joists at 400 mm under wide boards (140 mm) because the longer span between fixings flexes more
If you are building over an existing slab and your boards are running across the slab, you can drop bearer spans and skip joists altogether. Trade-off is more screws and a lot more bearers.
If you are framing on stumps or piers, drop the bearer span to around 1500 mm for wide-board composites which are notably heavier than timber.
4. Fixings, fascia and the small stuff that adds up
The least exciting part of the build, but the part that ages worst if done cheaply.
- Screws over nails, every time. Stainless steel for hardwoods, hot-dip galvanised for treated pine. Hidden-clip systems (Camo, Klever) look cleaner but cost more in materials and labour. Top-fix with two screws per joist is the standard.
- Fascia (the trim around the perimeter). Match it to the board where possible. A timber deck with composite fascia looks wrong. Our base spec always includes matching fascia.
- Underside. Most decks need some kind of skirting or screening so leaves and possums do not get under. Slat skirting (timber or composite) on the visible sides is a worthwhile add-on for any deck more than 300 mm off the ground.
- Gap between boards. 5 mm is the standard for timber to allow for expansion. Composite uses the manufacturer's clip system which sets the gap automatically (usually 6 mm).
5. Sun, wind and water management
The site shapes the build more than people think.
- Which way does the deck face? A west-facing deck cooks in late afternoon. Plan for shade (a pergola, sails or shadecloth) early or your investment will only get used three months a year.
- Where does rain run off the boards? A deck under a verandah catches water during a southerly. Make sure the deck has a fall of at least 5 mm per metre toward the open side so water sheds, not pools.
- Wind. Salt air on the South Coast is hard on fixings. Specify stainless on coastal builds, no exceptions.
6. Maintenance reality check
Be honest with yourself about how much maintenance you will actually do.
- Timber decks need an oil treatment every twelve to eighteen months to stay rich-coloured. If you skip it, the boards go silver-grey (which is fine as a look in its own right, but the colour shift is not reversible without sanding back).
- Composite decks need a wash with a deck cleaner once a year and that is it.
- All decks need a leaf-blow under the boards once or twice a year so debris does not trap moisture against the joists.
Here is what the planning above turns into on the ground. This Hindmarsh Island courtyard went from a dated tiled area to a wraparound entertaining deck:
When to call a professional
Decks in the 6 by 4 metre range at ground level (under 600 mm high) are within reach of a confident DIY weekend warrior with a circular saw and an impact driver. Anything above one metre, anything attached to the house with a ledger, anything involving a slope, or anything where the boards are wide and need a fastening clip system is faster, cleaner and warranty-backed if a licensed builder handles it.
We are a fully licensed building company (BLD319926) and we deck a lot of these every year on the South Coast. If you want to scope yours out, open the 3D Designer and sketch it in ten minutes, or get in touch and we will walk through it on the phone.
You can also browse our recent projects to see the materials and configurations in real backyards.
