NZ TIMBER EDITORIAL GUIDE
Pine vs Kwila Decking
Treated radiata pine and Kwila can both form a useful deck, but they create different buying, installation and ownership decisions. Pine is lighter and cheaper in the current reference data; Kwila is denser, darker and more demanding about sourcing, tannin management and fastening.
The decision matrix
| Decision | H3.2 radiata pine | Kwila |
|---|---|---|
| Upfront board reference | Lower in current catalogue data | Substantially higher |
| Appearance | pale/green-brown treated softwood; grade affects knots | dark red-brown hardwood with natural variation |
| Workability | lighter, easier to cut; soft surface marks more readily | denser and heavier; predrilling commonly required |
| Weathering | coating choice controls colour; treated-wet boards can shrink | weathers toward grey; new boards can bleed brown extractives |
| Fixings | must suit treatment and exposure | stainless and supplier-specific guidance commonly apply |
| Sourcing | NZ plantation product widely offered | ask for species and responsible-source documentation |
Upfront cost is only the first ownership year
At the site’s 13 August 2026 references, 90 × 19 pine is $2.52/LM and 90 × 19 Kwila is $7.77/LM. At an illustrative 95 mm installed cover, that is about $26.53/m² versus $81.79/m² before waste. A 20 m² model with 10% waste produces about $585 of pine boards or $1,803 of Kwila boards.
That gap does not decide the whole deck. Grade selection, random-length yield, screws, cleaning, coating and delivery also differ. The subframe should be priced separately and must satisfy the same design whichever surface is chosen, unless the selected board requires a changed joist layout.
What living with pine looks like
Radiata pine decking in New Zealand is commonly H3.2 treated for exterior above-ground use. Suppliers offer merchant, dressing and premium appearance grades; a low price may therefore include more knots or defects than an appearance-sensitive entertaining deck can accept. Treated-wet boards need correct seasoning and spacing because they can shrink as they dry.
- Best fit: budget-led deck where periodic cleaning/coating is accepted.
- DIY advantage: lower weight and generally easier cutting/driving.
- Watch: dents, splinters, wet-treatment movement and compatibility of coatings/fixings.
- Do not infer: H3.2 treatment is not a structural grade and does not define joist span.
What living with Kwila looks like
Kwila is a dense tropical hardwood with a dark red-brown appearance. BRANZ notes its high hardness, durability and stability, but also limited supply and the need to check source certification. New Kwila can release brown water-soluble extractives, staining adjacent concrete, plaster or paving unless runoff and cleaning are managed.
- Best fit: a prominent deck where the owner values a darker hardwood surface and accepts the premium.
- Installation: expect heavier handling and follow supplier instructions for predrilling, end distance and stainless fixings.
- Maintenance: decide whether to retain colour with a compatible finish or allow an even grey weathered surface.
- Sourcing: request species identification and responsible-source evidence rather than accepting ‘premium hardwood’ as a complete description.
Scenario recommendations
| Project | More defensible starting point | Reason |
|---|---|---|
| Budget family deck | H3.2 pine | Lower board reference and easier replacement; choose grade deliberately. |
| Premium visible entertaining area | Kwila | Dense hardwood appearance can justify cost if sourcing and tannin control are accepted. |
| Rental property | Pine with a documented maintenance plan | Lower capital cost; specify grade and make maintenance responsibility explicit. |
| Coastal property | Neither by label alone | Fastener grade, exposure, detailing and supplier documentation decide suitability. |
| First DIY deck | Pine often simpler | Lighter workability, but treatment moisture and spacing still require care. |
The correct conclusion is scenario-specific, not ‘both are good’. If the budget cannot absorb Kwila offcuts, stainless fixings and appearance selection, pine is the honest choice. If the visible hardwood surface is the reason for the project and sourcing can be verified, treating Kwila as interchangeable with pine misses the point.
Embodied decisions and sourcing evidence
Radiata pine is widely grown in New Zealand plantation forestry, while Kwila is imported from tropical forests. A responsible decision considers verified chain-of-custody or certification documentation, species identification, transport and expected usable life. Do not turn origin alone into an unsupported environmental score.
Ask suppliers for evidence applicable to the batch or product programme, not a generic sustainability logo on a website. Also compare usable yield: rejecting a large share of appearance-grade boards changes material use and cost.
| Evidence | Why request it |
|---|---|
| species/botanical identification | avoids vague 'merbau-style hardwood' descriptions |
| certification or chain of custody | supports sourcing claim |
| appearance grade rules | sets knot/defect expectations |
| length pack list | shows likely offcuts and joints |
| maintenance guide | makes ownership comparison concrete |
Sources and technical guidance
- BRANZ — slatted decking timber comparison (technical)
- Pukepine — radiata decking grades and treatment (technical)
- Timber Dealers reference data — checked 13 August 2026 (commercial)