What Is Accoya?
Accoya is Radiata Pine that has been acetylated — a non-toxic modification process that permanently changes the wood at a cellular level. Acetic acid (the same acid found in vinegar) replaces the hydroxyl groups in the wood cells, making them unable to absorb water. The result is timber that does not swell, shrink, crack, or rot, even in sustained ground contact or full weather exposure.
Unlike pressure-treated timber, which relies on chemical preservatives that leach over time, acetylation is a permanent structural change. The wood itself becomes naturally resistant to decay and insect attack — not because of added chemicals, but because fungi and insects cannot digest the modified cell structure.
Accoya vs Other Timbers for Windows
| Property | Accoya | Engineered Redwood | Sapele Hardwood |
|---|---|---|---|
| Rot guarantee | 50 years | 30 years (with treatment) | 25–30 years |
| Dimensional stability | Exceptional — 75% less swelling | Good | Moderate |
| Paint retention | 2× longer between repaints | Standard | Standard |
| Sustainability | FSC, Cradle to Cradle Gold | FSC available | FSC available |
| Weight | Light (515 kg/m³) | Medium (560 kg/m³) | Heavy (640 kg/m³) |
| Cost premium | +30–40% vs redwood | Baseline | +15–25% |
Why Accoya Makes Sense for London
London’s climate is uniquely punishing for timber windows. Rain, humidity, pollution, temperature swings between seasons, and the occasional frost cycle all conspire to break down conventional timber. South-facing windows in particular take enormous UV and rain exposure. Accoya handles all of this without complaint because the wood physically cannot absorb enough moisture to support fungal growth.
For Conservation Area properties, Accoya is increasingly the specification of choice among architects and conservation officers. It meets every aesthetic requirement of a traditional timber window while offering a maintenance cycle that is half as frequent as conventional softwood.
Paint and Finish
Accoya holds paint and stain significantly longer than untreated softwood. Independent testing shows paint coatings on Accoya last twice as long before requiring a maintenance coat. We factory-spray every Accoya window with Sikkens or Teknos microporous coatings — the same systems used by the National Trust on their historic properties.
Colour options include our full range of 140+ Farrow & Ball colours, RAL colours, and dual-colour schemes (different colours inside and out).
Pricing
Accoya sash windows start from approximately £1,060 for a standard 600×900mm window — roughly 30–40% more than engineered redwood. Over a 50-year ownership period, the reduced maintenance and zero rot risk typically make Accoya the more economical choice. Use our 3D configurator to compare timber options and see prices instantly.
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