A Guide to Choosing Decking Material: Natural Timber, Composite, Bamboo, and Accoya

By James Chong | Published on 8 October 2025

Thinking of refreshing your deck — or simply done with scrubbing, sanding, staining and re-oiling it every summer? You’re not alone. New Zealand’s mix of strong sun, heavy rain, salt-laden coastal air, and local building standards all influence the best choice of decking materials.

This guide compares the four most common options used in NZ — natural wood (treated pine and hardwoods), composite decking, engineered bamboo, and Accoya (acetylated wood). We evaluate each for properties, advantages and disadvantages, initial cost, installation cost, maintenance cost, durability, appearance, and sustainability, and conclude with a ranking of their likely carbon footprint in NZ conditions.

In short: If you want low-maintenance decking in coastal or humid NZ environments, Accoya or BRANZ-appraised composite boards are the easiest options. If you prefer a true timber feel with the lowest raw embodied carbon — and are willing to maintain it — locally sourced certified timber remains a strong choice. Engineered bamboo can also be an eco-friendly alternative, provided you choose a proven, high-quality product.

NZ realities that matter

• Durability rules: The NZ Building Code B2 requires external elements (including decking) to meet minimum durability periods (decking and associated fixings typically need a 15-year durability level unless an alternative solution is justified). NZS 3602 is the timber standard commonly referenced for meeting those durability expectations.

• Corrosion & fixings: Coastal salt spray increases the need for stainless or appropriately coated fixings and correct detailing.

• Local product appraisal: Several composite and alternative decking products are BRANZ-appraised for NZ conditions — that matters when you want confidence they’ll handle our sun and rain.

1. Natural wood (Treated radiata pine & durable hardwoods)

What it is

Local radiata pine (pressure-treated to H3.2 for exterior use) and a range of naturally durable hardwoods (e.g., garapa, kwila). Proper treatment and installation to NZS 3602 are essential.

Properties & behaviour

• Timber stores biogenic carbon and feels warm and authentic.

• Softwoods move more (shrink/swell/cup); dense hardwoods are more dimensionally stable and more rot resistant.

Pros

• Beautiful, traditional timber look; can be sanded and refinished.

• Low embodied energy for local radiata; good sustainability when FSC/PEFC certified.

Cons

• Highest routine maintenance (washing, sanding, re-oiling or staining every 1–3 years depending on exposure).

• Shorter service life for softwood in exposed/coastal conditions unless detailed & maintained well.

  
  

Typical NZ costs (approximate ranges)

• Material (board only): radiata pine $60–$140/m², common hardwoods $150–$350/m² depending on species and grade. (region/supplier dependent)

• Installation (labour & fixings): $80–$180/m² typically (site complexity, joist spacing, railings, stairs all add cost).

• Total upfront (material + installation): $140–$520/m² (low-end softwood up to premium hardwood).

• 20-year maintenance cost: High — expect periodic sanding, oiling/staining and board replacement; budget roughly $1,000–$3,500+ over 20 years for a typical 25 m² deck depending on how often you re-coat and any replacements.

  
  

Durability in NZ

• Treated radiata: ~10–20 years in exposed conditions (can be longer with careful detailing).

• Durable hardwoods: 20–40+ years when well installed and maintained.

  
  

Appearance

• Real wood grain and natural ageing (can silver if left uncoated). Many owners love the authenticity.

  
  

Sustainability & carbon

• Good if timber is locally grown and certified (FSC/PEFC). Lower embodied carbon per m² than plastics; frequent replacement or heavy maintenance increases lifecycle emissions.

2. Composite decking (wood–plastic composites & capped boards)

What it is

Engineered boards combining wood fibre with plastic (often recycled) and sometimes a polymer cap. Several brands have BRANZ appraisals for NZ performance.

Properties & behaviour

• Low moisture uptake, dimensional stability, and high resistance to rot and splitting.

• Colours are manufactured into the board — you can’t easily sand back to a fresh look.

Pros

• Very low maintenance (wash occasionally — no oiling or staining).

• Long warranties and consistent performance in NZ’s sun and rain when BRANZ-tested.

Cons

• Higher upfront embodied carbon (plastic + manufacturing), though recycled content reduces this.

• Typically more expensive up front than softwood; heat retention (gets hot underfoot in sun) can be an issue.

  
  

Typical NZ costs (approximate)

• Material: $140–$240/m²

• Installation: $100–$200/m² (comparable to timber when using hidden-fix systems)

• Total upfront: $240–$440/m²

• 20-year maintenance cost: Low — mainly cleaning; budget $200–$800 over 20 years for a 25 m² deck (cleaning and minor repairs).

  
  

Durability in NZ

• ~25–30+ years for good quality, BRANZ-appraised systems.

  
  

Appearance

• Wide range of wood-look finishes; can look very convincing but lacks the ability to sand/refresh like timber.

  
  

Sustainability & carbon

• Higher raw embodied carbon per m² than responsibly sourced timber. However, long life and recycled content mean the per-year carbon can be competitive in some cases. Always check the product's Environmental Product Declaration (EPD).

3. Engineered bamboo decking

What it is

Densified/thermo-treated bamboo boards or bamboo composites. NZ suppliers now stock higher-density bamboo surfaces designed for outdoor use.

Properties & behaviour

• Bamboo is a grass that grows fast — engineered boards can be very hard and dimensionally stable if processed correctly.

Pros

• Renewable resource with quick regrowth cycles.

• Attractive, uniform look and good hardness for wear resistance.

Cons

• Performance depends on manufacturing (adhesives, density, heat treatment). Poor product choices can delaminate or swell in NZ’s wetter climates.

• Typically imported — shipping adds to embodied footprint.

  
  

Typical NZ costs (approximate)

• Material: $130–$200/m²

• Installation: $90–$180/m²

• Total upfront: $220–$380/m²

• 20-year maintenance cost: Moderate — periodic oiling and inspection; budget $500–$2,000 over 20 years for a 25 m² deck.

  
  

Durability in NZ

• High-quality products claim 25+ years under appropriate conditions and install methods; verify product test data and warranties.

  
  

Appearance

• Warm, consistent grain; contemporary aesthetic.

  
  

Sustainability & carbon

• Potentially low embodied carbon because bamboo regrows fast, but adhesives, heat processing, and transport significantly affect the actual footprint. Request Life Cycle Assessment (LCA) /Environmental Product Declaration (EPD) from suppliers.

4. Accoya (acetylated wood)

What it is

Radiata pine (commonly) chemically modified by acetylation to change the wood’s cell chemistry. The modification is full-section (not a surface treatment) and greatly reduces moisture uptake and decay. Accoya has strong warranty backing globally and is widely used in NZ.

Properties & behaviour

• Exceptional dimensional stability (very low shrink/swell), high decay resistance, and excellent paint/oil retention.

Pros

• Very low maintenance relative to untreated timber — minimal movement reduces gaps, cupping and split repairs.

• Long warranties — 50 years above ground in many markets (manufacturer data).

• Can be finished like timber; recyclable and non-toxic (no heavy metal preservatives).

Cons

• Higher upfront cost and often higher than many hardwoods.

• Processing adds embodied energy (acetylation), but long life tends to offset that.

  
  

Typical NZ costs (approximate)

• Material: $200–$320/m²

• Installation: $100–$200/m² (similar to hardwoods; better stability usually simplifies finishing)

• Total upfront: $300–$520/m²

• 20-year maintenance cost: Low — occasional cleaning and minor re-coating; budget $200–$800 over 20 years for a 25 m² deck.

  
  

Durability in NZ

• ≥40–50+ years above ground when installed and finished correctly; backed by manufacturer testing and case studies in NZ projects.

  
  

Appearance

• Real timber look; accepts oils and coatings well; boards remain straighter and more stable.

  
  

Sustainability & carbon

• Strong lifecycle case in NZ when made from certified plantation radiata: higher processing energy is offset by much longer life and lower replacement frequency. Ask for EPD for project-level verification.

Quick NZ comparison table (at a glance)

Material	Typical total upfront (mat + install)	20-yr maintenance estimate (25 m²)	Typical NZ life	Best for	Carbon note
Treated radiata pine	$140–$260/m²	$1,000–$3,500+	10–20 yrs	Budget, local feel	Low embodied; replacement risk raises lifecycle emissions
Durable hardwoods	$280–$520/m²	$800–$2,500	20–40+ yrs	Premium look, durability	Good if certified; imports transport impact
Composite (BRANZ options)	$240–$440/m²	$200–$800	25–30+ yrs	Low maintenance	Higher embodied carbon; recycled content helps
Bamboo (engineered)	$220–$380/m²	$500–$2,000	15–30 yrs (product dep.)	Eco look, renewable	Low potential carbon but check Life Cycle Assessment (LCA) & origin
Accoya	$300–$520/m²	$200–$800	40–50+ yrs	Long life, stability	Excellent lifecycle carbon when local radiata base used

(Price bands are indicative NZ 2025 ranges — always get local quotes; labour & site conditions can swing numbers.)

Ranking by Carbon Footprint (NZ-centred lifecycle view)

(Lower = better for overall lifecycle carbon when amortised over realistic service life)

1. Accoya — long guaranteed life + local radiata base generally gives lowest kgCO₂e per year.

2. Certified local timber (radiata / responsibly managed hardwoods) — very low embodied carbon when locally sourced and maintained.

3. High-quality engineered bamboo (with Life Cycle Assessment (LCA)/ Environmental Product Declaration (EPD) — fast growth helps, but shipping and adhesives matter.  

4. Composite decking — often the highest embodied carbon per m²; long life and recycled content can narrow the gap but typically ranks worse raw.

   
   

Note: these rankings use a service-life perspective (kg CO₂e per year of useful life). Raw embodied carbon per kg or per m² can tell a different story — always ask suppliers for EPDs / LCAs to compare products directly.

Practical tips before you buy

1. Match material to exposure. Coastal or very humid sites: favour Accoya or BRANZ-appraised composite or a highly durable hardwood. Softwood needs excellent detailing.

2. Use correct fixings. Stainless or appropriate galvanized fasteners are essential in coastal zones.

3. Ask for EPDs and BRANZ appraisals where available — these give you verified environmental and performance info for NZ conditions.

4. Design to avoid trapped water. Good fall, ventilation under joists, and clearance to ground drastically extend deck life.

5. Get at least three local quotes. Labour and detail differences often explain more cost variation than material prices.

Final thought

If you’re fed up with the endless routine of clean → sand → oil → repeat, choose a low-maintenance system that suits your exposure: Accoya gives you the real timber feel with far less fuss, while BRANZ-appraised composite boards give truly low maintenance if you accept a manufactured finish. If climate-friendly materials top your list and you’re prepared to maintain them, certified NZ timber or proven engineered bamboo remain great options.

Disclaimer: The views expressed in this post are my own and do not represent the opinions of any organization or employer. The content is for general information only and should not be taken as professional advice.