Perth Decking Cost Per m²: What You Actually Pay
Decking in Perth runs $190–$580 per square metre installed depending on the timber, with most builds averaging around $275/m². But the per-metre rate isn't fixed — it shifts with deck size, the subframe underneath, and how tricky your block is. Here's what drives the number.
Almost every Perth deck builder quotes by the square metre, which makes it the fastest way to compare jobs — as long as each quote is pricing the same thing. The catch is that the "same thing" varies a lot. A $300/m² quote with a light frame and a $450/m² quote with a properly engineered subframe are not the same deck, even if the boards look identical. This guide breaks the per-m² rate into its parts so you know what you're paying for.
The per-m² rate by material
| Material | Perth cost per m² (supply + install, inc GST) |
|---|---|
| Treated pine | $190–$370/m² |
| Merbau / hardwood | $315–$580/m² |
| Composite | $295–$580/m² |
| Perth average (all materials) | ~$275/m² |
These are full supply-and-install rates including the subframe, GST included, re-verified against 90+ sources for the Perth metro area. Material choice is the single biggest lever — typically 40–50% of the budget — but it's not the only one.
Why deck size changes the per-m² rate
Bigger decks are usually cheaper per square metre. The reason is simple: the fixed costs — site setup, delivery, the crew's mobilisation, the machinery — get spread across more area. A 12 m² courtyard deck carries all that overhead on a small footprint, so its per-metre rate sits at the top of the band. Stretch to 40 m² and the same overhead is diluted, pulling the per-metre rate down. As a rough guide:
- A 20 m² deck in Perth costs approximately $5,500–$11,000 depending on material and site.
- A 25 m² deck costs around $8,400–$16,800.
- Larger multi-level builds with stairs, balustrades and premium boards climb well beyond that.
The subframe: the cost you don't see
The boards are what you look at; the subframe is what you pay for. Joists, bearers, footings and the connection back to the house are often the biggest single component of a deck's cost, and they're where a cheap quote usually cuts corners. A deck is only as good as the frame under it — get the substructure right and merbau lasts 25–40 years, get it wrong and even the best boards will move, cup and fail early. When you compare quotes, ask each builder to spell out the joist spacing, timber treatment level (look for an "H" rating) and footing method. A quote that's vague on the frame is the one to be wary of.
What else moves the number
Site difficulty. A flat, clear, ground-level block is the cheapest scenario. Sloping ground, elevated builds, rock, or difficult access all add labour and can add $500–$3,000 in site preparation before a board is laid.
Height and structure. A ground-hugging deck is quick. Raise it up and you add posts, bracing, balustrades and, often, a council permit — most Perth councils require one once a deck passes a certain height or size.
Extras. Balustrades and railings run roughly $200–$400 per linear metre. Stairs, built-in seating, screening and lighting all sit outside the base per-m² rate and are quoted separately.
How to compare quotes fairly
Get three quotes and make each one price the identical deck: same board or timber species, same subframe spec, same footprint, same extras. When they're truly like-for-like, the per-m² comparison is meaningful. Leave a 15–20% buffer for the surprises that show up once the old deck comes off or the ground gets dug — and remember the cheapest per-metre rate is rarely the cheapest deck to own once maintenance and lifespan are in the picture.
Frequently asked questions
What's the average decking cost per m² in Perth?
Around $275/m² across all materials, with treated pine at $190–$370/m², merbau hardwood at $315–$580/m² and composite at $295–$580/m² — all supply and install, GST included.
Why is my small deck more expensive per square metre?
Fixed costs like site setup, delivery and crew mobilisation are spread over less area on a small deck, so the per-metre rate lands at the top of the range. Larger decks dilute those overheads and cost less per m².
Do deck builders quote per m² or as a fixed price?
Most Perth builders quote per square metre, but you can ask for a fixed price for clarity. Either way, make sure the quote specifies the subframe and timber species so you're comparing like with like.
Is the subframe included in the per-m² price?
It should be — the ranges here are full supply-and-install including the substructure. If a quote looks unusually cheap, check whether the frame is specified, as that's the most common place costs get trimmed.
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