Which timbers perform best outdoors — and which leave the lightest carbon footprint?
This paper from Factory Furniture (dated 17 Sept 2025) compares 10 timber types for outdoor use in the UK. It focuses on durability, lifespan, cost (£/m³ as of April 2025), and CO2 emissions (kg CO2e/tonne from cradle-to-gate). The timbers are evaluated for 70mm sap-free, uncoated sections with good drainage. Key factors include origin, treatment, transport and environmental impact.
Longevity and Sustainability of Timber in External Environments
Timber basics
Hardwoods: From flowering trees (eg Oak, Sapele); often from temperate/tropical areas.
Softwoods: From conifers (eg Redwood, Douglas Fir); make up 80% of global timber; can be modified for better durability (eg Kebony).
Durability classes: High (>10 years), Moderate (5-10 years), Low (<5 years).
Availability classes: X (high >1,415m³/year), Y (medium, 355-1,415m³/year), Z (low <355m³/year).
Life Cycle Analysis (LCA): Tracks timber from forest to end-of-life, including carbon storage, emissions and recycling.
Timber comparison table
Summary of the 10 timbers
Timber |
Origin |
Durability |
Longevity |
Cost (£/m³) |
CO2e (kg/tonne) |
|---|---|---|---|---|---|
Tanalised Redwood |
Northern Europe |
Moderate |
15 |
500 |
250 |
Douglas Fir |
British Columbia–CA |
Moderate |
40 |
1000 |
350 |
Abodo |
New Zealand |
Moderate |
40 |
1700 |
600 |
Accoya |
New Zealand |
High |
60 |
1800 |
550 |
European Oak |
France/England/Germany |
High |
70 |
1800 |
200 |
Sapelle |
East Africa |
Moderate |
40 |
1100 |
450 |
Iroko |
West Africa |
High |
70 |
1300 |
400 |
Opepe |
Tropical Africa/S. America |
High |
90 |
1500 |
420 |
Cumaru |
Northern S. America |
High |
90 |
1800 |
380 |
Kebony Clear |
Norway (from NZ pine) |
High |
60 |
1000-1200 |
500 |
CO2 emissions notes
Lowest: European Oak (200, local sourcing), Tanalised Redwood (250, nearby + efficient).
Highest: Abodo (600, long transport + modification), Accoya (550, similar).
Emissions rise with distance (eg NZ timbers ship 18,000km) and treatments (eg chemicals add 20-50 kg/tonne).
Longevity helps offset emissions by storing carbon longer.
Design and treatment details
Timber |
Moisture Content |
Drying Method |
Chemical Treatment |
|---|---|---|---|
Tanalised Redwood |
18% |
Kiln |
Tanalith |
Douglas Fir |
12% |
Air |
None |
Abodo |
7% |
Heat |
None |
Accoya |
3-5% |
Kiln |
Acetic Acid |
European Oak |
15% |
Kiln |
None |
Sapele |
14-16% |
Kiln/Air |
None |
Iroko |
14-18% |
Kiln/Air |
None |
Opepe |
12-18% |
Kiln/Air |
None |
Cumaru |
15% |
Kiln/Air |
None |
Kebony Clear |
4.6% |
Kiln |
Furfuryl Alcohol |
Transport: closest = Tanalised Redwood/European Oak (500-2,000km); farthest = NZ-based (18,000km). All shippable; some truckable.
Environmental impacts: chemical risks (eg leaching in Tanalised); high transport emissions for distant woods. Tropical ones (Iroko/Opepe "Near Threatened"; Cumaru regulated) risk deforestation if not FSC certified, causing biodiversity loss and soil erosion. FSC helps via sustainable practices.
Key insights
Longevity: Best = Opepe (90 yrs), European Oak/Iroko (70 yrs), Accoya/Kebony (60 yrs); worst = Tanalised Redwood (15 yrs).
Cost vs durability: Budget pick = Tanalised (£500, short life). Best value = Opepe (£1500, 90 yrs). Premium = European Oak/Accoya/Cumaru (£1800, long life).
CO2 vs cost/longevity: Graphs show European Oak as top for low CO2 + high durability. Tanalised is cheap/low CO2 but short-lived. Abodo/Accoya high in both cost/CO2 but durable.
Recommendations
Low cost/low CO2/short-term: Tanalised Redwood.
Long-term/moderate CO2: Opepe, Kebony Clear.
Sustainable/durable (higher CO2): Accoya, European Oak, Cumaru.
Lowest CO2/high durability: European Oak.
Choose based on budget, needed lifespan and carbon goals. Prioritise FSC-certified to avoid environmental harm.
For full details/references, check the original paper (eg sources on wood databases, sustainability reports).
