What is Accoya wood?
Accoya is a modified timber made by treating radiata pine (Monterey pine) with acetic anhydride in a process called acetylation. This process chemically alters the cell walls of the wood so that it can no longer absorb moisture. The result is an extremely durable, dimensionally stable timber with a service life of over 50 years above ground and 25 years in ground contact.
How does acetylation work?
During the acetylation process, the hydroxyl groups (OH groups) in the wood cells are replaced by acetyl groups. These groups do not attract water, which means the wood:
- Barely moves — minimal swelling and shrinkage with changing moisture levels
- Does not rot — fungi no longer recognise the wood as a food source
- Resists insects — wood-boring insects avoid the material
- Retains its strength — the acetylation process does not damage the wood fibre
Application
Accoya is used where high durability and dimensional stability are required:
- Windows and doors — ideal because the minimal movement means they won’t stick or warp
- Cladding — Accoya cladding requires minimal maintenance
- Decking and boardwalks — durability class 1 (the highest class)
- Bridges and lock gates — resistant to permanent water contact
- Garden furniture — long-lasting resistance to weather
| Property | Accoya | Tropical hardwood | Pressure-treated softwood |
|---|---|---|---|
| Durability class | 1 | 1–2 | 3–4 |
| Dimensional stability | Very high | High | Moderate |
| Service life (exterior) | 50+ years | 25–50 years | 10–15 years |
Related terms
- Timber
- Timber species
- Durability
- Window frame
- Cladding
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