Spotted gum vs merbau vs composite decking in Canberra

Published 21 September 2026 · Updated 13 October 2026

What Canberra's weather does to a deck

Canberra is hard on outdoor timber in two directions. Winters bring frosty mornings, and the Bureau of Meteorology and CSIRO's ACT climate guide notes that Canberra's frost risk has typically ended by the last week of October. Summers are hot and dry: the same guide reports an average of seven days a year above 35 °C over 1989 to 2018, up from about four in the three decades before.

For a deck, that means boards that dry out and check (fine surface cracks) in summer sun, take up moisture from frost and dew in winter, and move a little between the two. Low decks close to the lawn also see less air underneath, so the frame stays damper. None of the three boards below is ruined by that, but each copes with it differently.

Spotted gum

Spotted gum is an Australian hardwood from New South Wales and Queensland forests. The Queensland Government rates it durability class 1 above ground ("life expectancy more than 40 years") and class 2 in-ground, resistant to termites, at a density of about 1,010 kg/m³. That weight is why spotted gum boards feel solid underfoot and why they need pre-drilling near the ends.

Its colour runs from pale grey-brown to dark brown in the same pack, which suits a natural look. Left unoiled, it weathers to silver-grey within a season or two in full Canberra sun. Oiled, it keeps its colour longer and checks less.

Merbau

Merbau is an imported hardwood, mostly from South East Asia and Papua New Guinea. WoodSolutions marks its natural durability as more than 40 years above ground and lists it as resistant to termites, with a seasoned density of 860 kg/m³: a little lighter than spotted gum.

Merbau is an even reddish-brown, which many people like for a uniform deck. It's known for bleeding a dark tannin stain for its first months outdoors, which can mark pavers, concrete and render below the deck, so plan the run-off or let the boards weather and clean them before oiling. Our deck oiling guide covers that first coat.

Composite decking

Composite boards are a mix of wood fibre and plastic, made to a consistent size and colour. They don't need oiling, don't split or splinter, and the colour holds better than bare timber. The trade-offs are the board price, a surface that gets hot underfoot on a 35 °C afternoon in full sun (darker colours more so), and that each brand has its own clips, gaps and joist spacing that must be followed.

Composite also expands and contracts with temperature, and Canberra's range between a frosty morning and a summer afternoon is wide. That's why the maker's end-gap and fixing rules matter more than they would on the coast.

The frame underneath is the same for all three

Whichever board you pick, the posts, bearers and joists under a low deck are usually treated pine. The NSW EPA's hazard-class chart lists H3 for outside, above-ground uses such as decking and framing, and H4 for in-ground posts. Posts set in the ground need H4; posts on stirrups above the ground, H3.

The frame decides how long the deck lasts more than the boards do: good drainage, ventilation under the deck and joists spaced for the board you choose. Some composite boards need closer joist spacing than hardwood, which adds timber and labour to the frame.

What each costs installed in Canberra

We found two Canberra-area businesses that publish deck prices per square metre. Their figures are below as published; don't add them together or average them.

Installed decking prices per m², Canberra

Published by a Canberra deck builder (MS Decking & Repairs, page published October 2024 and updated August 2025) and a composite decking supplier that installs across the ACT (Compotech Solution, 9 March 2026), checked 8 October 2026. Neither says whether GST is included. MS Decking doesn't say whether its hardwood figure includes installation. Compotech's figures are for composite only and it sells the boards. A deck's own price is set after seeing the site: height, steps, access and the timber change it.

Neither source publishes a separate spotted gum figure; MS Decking's Australian hardwood range ($200 to $350 per m²) is the closest. Height, steps, access and the old deck coming out move a job within these ranges. The deck cost guide goes through each, plus the ACT fees that only apply when a deck needs approval.

Choosing for your deck

• Want the look of real timber and don't mind oiling once a year or so? Spotted gum or merbau.
• Want an even red-brown colour? Merbau, with the tannin run-off planned for.
• Want an Australian hardwood with colour variation? Spotted gum.
• Want the least upkeep and can cover the higher board price? Composite, keeping darker colours out of full afternoon sun where bare feet go.
• Block near bushland? A Bushfire Attack Level can limit materials for a deck attached to the house, so check before choosing.

Questions about decking timber