Decking in Sydney: What to Get Right Before the Boards Go Down

A deck is the cheapest room you will ever add to a Sydney house, which is exactly why so many of them are built badly. The boards are the part everyone looks at and the part that matters least. What decides whether a deck is still solid and level in fifteen years is what is underneath it, how water leaves it, and whether the height and the site were properly thought about before anyone ordered timber.

Start with what the deck is actually for

There is a real difference between a deck you walk across to get to the yard, a deck you put a table and eight chairs on, and a deck that exists to give you a level surface off the back door on a sloping block. They want different sizes, different shapes and sometimes different materials.

The most common regret is a deck that is too small for the furniture that was always going to go on it. A table and chairs needs room to push back and walk around, and a deck sized to the plan rather than to the furniture ends up as a walkway with a barbecue on it. Mark it out on the ground with string and put the actual furniture in the space before you commit.

Height off the ground changes everything

A low deck sitting just above ground level and a deck a metre or more in the air are different builds with different rules, different costs and different failure modes.

As decks get higher, balustrades become a requirement rather than a choice, the footings and the framing have to carry more, and the structure becomes more visible and so has to be built to be looked at. Height also affects whether the work needs approval: in NSW, low decks under a certain height and within setback and size limits can often be built as exempt development, and the figure commonly cited is around one metre above ground level, but the exact thresholds depend on your land, your zoning and your council. Confirm it with your local council before you build rather than after.

Low decks have their own problem, which is ventilation. A deck built tight to the ground with no airflow underneath holds moisture against the framing, and that is where rot starts. Clearance and cross-ventilation under the deck are not optional details.

Hardwood, treated pine or composite

There is no single right answer here, only tradeoffs worth understanding.

• Australian hardwood (spotted gum, blackbutt, merbau and similar) gives the best looking deck and is hard wearing and durable. It needs oiling to keep its colour, it will grey if you let it, and it moves with the weather. Left alone, it does not fail, it just stops looking new.

• Treated pine is the budget option and it works, particularly for a deck that will be painted or that is largely functional. It is softer, marks more easily and needs the treatment level to suit its exposure and ground proximity.

• Composite boards do not need oiling and do not splinter or grey, which is why people choose them. They cost more up front, they can get noticeably hot underfoot in full Sydney summer sun, and cheap ones can look plastic. Quality varies more in this category than in any other.

• Whatever goes on top, the framing underneath is normally treated softwood or steel, and it has to suit the exposure and the ground conditions.

A fair way to decide: if you like the look of timber and do not mind an oil every year or two, use hardwood. If the idea of maintaining it is the reason you have been putting the deck off, buy a good composite and stop thinking about it.

The substructure is the deck

Footings, bearers and joists are what you are really paying for. Footing size and depth depend on the load and on what the ground is doing, and a lot of Sydney sits on reactive clay that moves with moisture, or on sandstone that turns a simple post hole into a coring job. Either one changes the price, and neither can be assessed over the phone.

Joist spacing is set by the board you are using, not by habit. Boards spanning too far between joists is the reason a deck feels springy underfoot, and it cannot be fixed later without lifting everything. Termite protection and adequate ground clearance also belong to this stage, because after the boards go down the substructure is effectively sealed off.

Where the water goes

Decks fail at the wet spots. The places to get right are where the deck meets the house, where water runs off the boards, and what happens to the ground underneath.

Boards should be laid so water drains off rather than pooling, gaps between boards have to be appropriate for the material and left clear of leaf litter, and the junction with the house wall has to be detailed so water cannot sit against the building or get behind the cladding. Under the deck, the ground should fall away rather than collecting water, and a dark permanently damp cavity under a low deck is a maintenance problem waiting to happen.

Pool decks

A deck around a pool brings the pool barrier rules with it. The barrier height is measured from the finished surface people can stand on, so building a deck up beside an existing pool fence can reduce the effective height of that fence and put a compliant barrier out of compliance.

The non-climbable zone applies too, so a deck, a step, a bench or a planter near the barrier can create a foothold. Slip resistance is worth thinking about on a wet pool deck, and composite and timber behave differently underfoot when wet. Requirements vary with the age of the pool and the site, so confirm yours with your local council or a registered pool certifier before the deck is designed, not after it is built.

Fixings and finish

Top-fixed screws are quicker and cheaper and leave a visible, regular pattern of fixings, which many people are perfectly happy with. Hidden fixing systems give a cleaner surface with no screw heads, cost more in both product and labour, and make individual board replacement a little more involved.

Near the coast, use stainless fixings of an appropriate grade. Ordinary fixings in a salt-air position stain the timber around every screw within a couple of seasons, and once that starts there is no tidy fix.

On a new hardwood deck, let the timber weather briefly before the first oil rather than sealing it immediately, then keep to a schedule. Most Sydney decks want re-oiling every one to two years depending on how much sun and rain they take. A north or west facing deck with no cover works much harder than a sheltered one.

Where decks fail early

• Framing too close to damp ground with no ventilation underneath.

• Joists spaced too far apart for the board being used, so the deck flexes.

• Footings sized for the ground someone assumed was there rather than the ground that is.

• The connection to the house not detailed for water.

• Non-stainless fixings in a coastal position.

• A pool deck designed without checking what it does to the barrier.

What drives the cost

We do not publish square-metre prices, because a deck quote that has not seen the site is a guess. What moves the number is the board you choose, the size and shape (curves, angles and multiple levels cost more than a rectangle), the height off the ground and whether balustrades and stairs are needed, the ground conditions under the footings, access for materials and machinery, and whether anything has to be demolished or the ground re-levelled first.

If you are thinking about a deck, have a look at our decking services, the Sydney areas we service, or get in touch for a site visit. A Cut Above Landscaping & Carpentry holds NSW Contractor Licence 484384C in Structural Landscaping.

Also worth reading: Retaining Walls in Sydney, since a sloping block often needs one before a deck is practical, and our pool fencing compliance guide if the deck is going in beside a pool.