Kwila is one of the most common timber choices for decks across Christchurch. Walk through any established Canterbury suburb, from Fendalton to Halswell, and you will spot it: a deep reddish-brown hardwood, often weathered to silver-grey, holding up year after year against southerlies, frost, and the occasional 30-degree nor’wester. If you are weighing up kwila for a new deck or replacing an old one, here is what actually matters on the ground in Christchurch.
What kwila decking actually is
Kwila (botanical name Intsia bijuga, also sold as merbau) is a dense tropical hardwood sourced mainly from Indonesia, Papua New Guinea, and the Solomon Islands. It is naturally Class 1 durable, which means the heartwood resists rot, insect attack, and fungal decay without chemical treatment. That natural durability is the reason kwila has held a strong share of the New Zealand decking market for the better part of three decades.
A few defining characteristics:
- Density: around 800 kg/m³ when dry. Heavy to handle, which matters if you are building a raised deck or working alone.
- Hardness: roughly 1,925 on the Janka scale. It will not dent under a chair leg or a dropped tool the way pine will.
- Movement: low to moderate. Expansion and contraction across Canterbury’s wet-to-dry seasonal swing is manageable if the boards are laid with appropriate gaps.
- Colour: rich reddish-brown when fresh, fading to silver-grey within 6 to 12 months if left untreated.
The trade-off is that kwila is a tropical hardwood, which raises both sustainability questions and price. We will get to both.
Kwila decking cost in Christchurch
Pricing moves around with shipping costs and exchange rates, but the current Christchurch range as of mid-2026 looks like this:
- Kwila decking boards, 90 x 19mm: around $14 to $18 per linear metre, including GST.
- Kwila decking boards, 140 x 19mm: around $22 to $28 per linear metre, including GST.
- Fully built deck, supplied and installed: roughly $480 to $700 per square metre including GST, depending on height off the ground, substructure complexity, balustrades, and access.
For a typical 25 square metre back deck in a Christchurch suburban section, you are looking at $12,000 to $17,500 all up. A larger 40 square metre deck with steps, a small pergola post or two, and stainless balustrade wire will sit closer to $22,000 to $30,000.
These figures assume standard H3.2 treated pine framing underneath, galvanised joist hangers, stainless steel decking screws, and standard ground conditions. Christchurch’s mix of TC2 land, sandy coastal soils in places like New Brighton, and the heavier clays out west all influence the substructure work, so site visits matter.
How kwila handles Canterbury weather
Canterbury throws four full seasons at a deck, often in the same week. The relevant stresses are:
- UV exposure: high summer UV breaks down surface oils and pulls colour out of the timber.
- Freeze-thaw cycles: frosts down to -5°C in winter, repeated dozens of times across June to August.
- Nor’west drying winds: low humidity drying events that shrink boards.
- Easterly moisture: salt-laden air for coastal suburbs (Sumner, Redcliffs, Brighton).
Kwila handles all of this well, but two issues come up locally that are worth flagging.
Tannin bleed. Fresh kwila leaches a deep red-brown tannin for the first 6 to 12 months. Rain washes it onto whatever sits below: concrete patios, white weatherboard, light-coloured pavers. In Christchurch this matters because so many homes have light Oamaru stone, white Linea, or pale concrete around deck areas. The fix is straightforward: hose the deck down weekly for the first two months, or pre-soak and rinse the boards before laying. A pre-oiled finish also slows the bleed substantially.
Board cupping. Kwila is laid bark-side up (the growth rings curving down). Laid the wrong way, boards cup and trap water on the surface, which accelerates surface checking under our UV. Any builder familiar with kwila will know this, but it is worth confirming if you are getting quotes.
Kwila vs the alternatives in 2026
The decking market has shifted in the past five years. Here is how kwila stacks up against what else is being installed across Christchurch.
Vitex. A New Zealand-favoured tropical hardwood, paler honey-brown colour, similar durability to kwila, less tannin bleed. Around 10 to 15 percent more expensive supplied. Good option if tannin staining is a concern.
Garapa. Brazilian hardwood, golden colour, very stable, expensive (often 30 percent above kwila). Less common but growing.
Thermally modified pine (Abodo, Accoya). New Zealand-made or European, treated with heat or acetylation to give Class 1 durability without tropical hardwood sourcing. Light brown or honey colour. Pricing sits 20 to 40 percent above kwila supplied. Strong sustainability story.
Composite decking (Trex, Futurewood, Ekodeck). No oiling required, 25-year warranties common, $90 to $140 per linear metre supplied for premium ranges. Total installed cost often within 10 percent of kwila once you factor in zero maintenance over 15 years. Heat retention in direct sun is the main downside in Canterbury summers.
H3.2 treated pine. Cheapest at around $5 to $8 per linear metre, but expect to replace boards within 10 to 15 years. False economy for most permanent decks.
For most Christchurch homeowners building a deck they want to last 25-plus years, the real choice in 2026 is kwila, vitex, or a quality composite. Price is similar across all three once installed. The decision usually comes down to look, feel underfoot, and how much weekend maintenance you are willing to do.
Oiling and ongoing maintenance
A kwila deck needs oiling. There is no version of this where you skip it and still get the rich brown look.
The standard Canterbury schedule:
- Initial oil: 4 to 6 weeks after installation, once the tannins have flushed and the boards have stabilised. Hose, scrub with deck cleaner, dry for 48 hours, oil two coats.
- Annual top-up: every spring, typically September or early October before the harsh summer UV hits. One coat is usually enough if the previous coat is intact.
- Full strip and re-oil: every 5 to 7 years if you want to keep the deep colour. Otherwise let it silver naturally and just clean it.
Decking oil options that work well locally include Dryden WoodOil, Cabot’s Aquadeck, and Sikkens Cetol. Budget around $80 to $150 per 4 litres, which covers roughly 30 to 40 square metres per coat.
If you let kwila silver naturally, you still need to clean it annually with a deck wash to prevent mildew and lichen, especially on shaded south-facing decks.
Sourcing and sustainability
This part is worth thinking through. Kwila is a tropical hardwood and a portion of global supply has historically come from poorly managed forests. The relevant certification to look for is FSC (Forest Stewardship Council). Most reputable timber merchants in Christchurch (PlaceMakers, ITM, Carters, Mitre 10 Trade) now stock FSC-certified kwila as their default. Ask for the certification when quoting. If the merchant cannot tell you the source, walk away.
There is a growing case for switching to vitex (mainly from PNG, often FSC) or to thermally modified New Zealand pine (Abodo) on sustainability grounds. For a deck that will be there for 30 years, the embodied impact of the timber is worth a conversation with your builder.
Practical tips before you build
A few things that get missed on Christchurch kwila deck projects:
- Confirm board orientation with your builder (bark side up).
- Specify stainless steel fixings, not galvanised, for kwila. The tannins corrode galvanised screws and you will see black streaks within two years.
- Leave a 4 to 6mm gap between boards in winter installs, 2 to 3mm in summer. Boards swell when wet.
- Sub-floor ventilation matters. Low decks in Christchurch need 150mm minimum clearance and end-to-end airflow, or the boards cup from underneath where moisture cannot escape.
- Check council requirements for decks over 1 metre high or attached to the dwelling. Christchurch City Council requires a building consent for most attached decks over 1m. Your builder should handle this.
A well-built kwila deck in Christchurch should give you 25-plus years of solid use, fade gracefully whether you oil it or not, and add real value to the property. The decisions worth getting right are sourcing, fixings, oiling cadence, and substructure ventilation. Get those four right and the deck looks after itself.