The install-day price isn't the whole bill
Our decking calculator's own sourced bands, treated pine $200–$280/m², merbau and other hardwoods $280–$420/m², composite $350–$550/m², all fully installed, are day-one numbers: materials, subframe and labour, nothing after handover. For a 12 m² deck that puts pine roughly $1,800 to $3,240 cheaper than composite to build. What that gap doesn't carry is what the deck costs to keep looking like a deck for the next ten years, and that's where timber and composite actually pull apart, not at the till.
What it actually costs
Same worked example as our decking calculator: a 4 m × 3 m deck, 12 m², fully installed.
| Option | What it includes | Cost |
|---|---|---|
| Treated pine, oiled on schedule | Install plus a re-oil roughly every 12–18 months, skip it and the timber risks cracking, cupping or warping, not just fading | $4,800–$7,680 over 10 years |
| Merbau hardwood, oiled to keep its colour | Install plus an annual re-oil to hold the honey colour, a full-sun deck needs it closer to every six months | $6,360–$10,440 over 10 years |
| Merbau hardwood, left bare | Install only, skipping oil doesn't risk the timber, just fades it to a silvery grey within a year or two | $3,360–$5,040 over 10 years |
| Composite | Install plus an occasional soapy-water wash, no oiling, sanding or staining, ever | $4,200–$6,600 over 10 years |
Oiling cost and frequency from a 2026 Melbourne trade pricing guide (wash plus two coats, $25–$45/m² per application); install prices from our own decking calculator's sourced bands. Figures assume a deck with typical sun exposure, not full-sun worst case.
Why pine has to be oiled and merbau doesn't
The two timbers aren't in the same maintenance boat, even though our own calculator groups them as "timber". Treated pine's chemical treatment protects it from rot and termites, not from the weather: left unsealed, a pine board dries unevenly in the sun and can crack, cup or warp, the same structural damage a coat of oil every 12 to 18 months is there to prevent. Merbau is a dense, naturally oily hardwood that doesn't carry that risk, skip the oil entirely and it simply weathers to a silvery grey, the same graceful ageing you'll see on an unmaintained hardwood jetty. Oiling merbau only buys back a colour; the timber underneath was never at risk.
That's the twist in the table above: bare merbau, at $3,360–$5,040 over ten years, ends up the cheapest option of the four, cheaper even than the pine most people buy specifically because it's the "budget" material. Composite sits in the middle once pine's real maintenance bill is counted, and the one deck that's guaranteed to cost more than its install price every single year is oiled merbau, the option that looks premium walking past it in the timber yard.
Common questions
Is composite decking actually cheaper than timber over time?
It can be. Composite's $4,200–$6,600 installed price for a 12 m² deck is higher than treated pine's $2,400–$3,360 on day one, but once pine's required 12–18-month re-oiling is added in, a ten-year total for pine ($4,800–$7,680) lands close to or above composite's flat $4,200–$6,600, since composite never needs oiling, sanding or staining.
Do you have to oil merbau decking?
No, not to protect the timber itself. Merbau is dense enough to weather safely with no oil at all, fading to a silvery grey over a year or two instead of the cracking or cupping unsealed treated pine risks. Oiling merbau is purely to keep its honey colour, and it's the most expensive of the four options here specifically because that colour has to be reapplied every 6 to 12 months.
How often does treated pine decking need oiling?
Roughly every 12 to 18 months for an average deck, closer to every 9 to 12 months if it's in full sun most of the day, and it can stretch to 18–24 months under a pergola or roofed area. Unlike merbau, skipping it isn't just cosmetic: pine left unsealed can crack, cup or warp.
Is it cheaper to build a deck yourself than to have it built?
On labour alone, yes, by a wide margin, whatever material you land on above. See our companion guide on DIY decking vs hiring a carpenter for the real numbers, plus the permit and footing checks worth doing before you start.
Sources
Oiling cost and frequency: Modernize Solutions, Deck Oiling & Restoration Melbourne 2026. Merbau weathering and colour maintenance: Austimber, Guide to Maintaining Your Merbau Decking. Treated pine cracking/cupping/warping risk from going unsealed: Australian Treated Pine, Guide to Common Timber Problems. Installed cost bands: same Bunnings/live-fetched sourcing as our decking calculator. All fetched July 2026.