What Are They?
Hardwood refers to timber from broadleaf trees — typically Meranti, Sapele, Iroko, or European Oak for window manufacturing. It's dense, strong, and naturally more durable than softwood. It has been the default choice for quality timber windows for centuries.
Accoya is radiata pine that has been acetylated — a non-toxic modification process that changes the wood's cell structure, making it extremely resistant to rot, insects, and moisture absorption. The result is a softwood that outperforms most hardwoods in durability tests.
| Property | Accoya | Hardwood (Meranti/Sapele) |
|---|---|---|
| Durability class | Class 1 (highest) | Class 2–3 (varies by species) |
| Rot guarantee | 50 years (manufacturer) | None (depends on maintenance) |
| Dimensional stability | Excellent — 75% less swelling than untreated timber | Good — but can move in extreme conditions |
| Paint retention | Excellent — coatings last 2× longer | Good |
| Weight | Light (510 kg/m³) | Heavy (600–800 kg/m³) |
| Sustainability | FSC-certified, fast-growing pine | Variable — check sourcing carefully |
| Cost premium | +15–25% vs hardwood | Standard |
| Workability | Easy — machines like softwood | Harder — blunts tools faster, can split |
Rot Resistance
This is Accoya's headline advantage. The acetylation process makes the wood inedible to fungi and insects. It achieves Class 1 durability — the highest possible rating — with a manufacturer-backed 50-year guarantee against rot.
Hardwood is naturally more rot-resistant than softwood, but it is not immune. Sapele and Meranti are Class 2–3, meaning they'll last decades with proper finishing but are vulnerable if paint breaks down and moisture gets in. European Oak is Class 1–2 but significantly more expensive and harder to work.
In practical terms: if your windows are well maintained (repainted every 8–12 years), both will last a very long time. If maintenance is neglected, Accoya is far more forgiving.
Dimensional Stability
Accoya absorbs 75% less moisture than untreated timber. This means it swells and shrinks significantly less with changes in humidity and temperature. For sash windows, this is important — a sash that swells even slightly can stick in the frame, making it difficult to open.
Hardwood is naturally more stable than softwood but does still move. In London's climate — wet winters, warm summers — hardwood sashes occasionally need adjustment. Accoya sashes almost never do.
Paint Retention
Because Accoya doesn't swell and shrink, paint coatings last roughly twice as long. Where hardwood might need repainting every 8–10 years, Accoya can comfortably go 12–15 years between coats. Over the life of the window, that's several fewer repaints — and significant savings in decorator's bills.
Sustainability
Accoya is made from radiata pine grown in FSC-certified sustainable plantations in New Zealand. The trees grow fast (25–30 years to harvest) and absorb significant CO&sub2; during growth. The acetylation process uses acetic acid — essentially vinegar — and is non-toxic.
Hardwood sourcing is more complex. Tropical hardwoods like Meranti and Sapele come from Southeast Asia and Africa respectively. While FSC-certified options exist, illegal logging remains a problem in these regions. Always verify the chain of custody. European Oak is sustainably available but expensive.
The Verdict
Choose Accoya if: you want the longest guarantee, minimal maintenance, the best dimensional stability, or you're concerned about sustainability. The 15–25% premium is worth it for the peace of mind.
Choose hardwood if: you prefer the weight and feel of a denser timber, you're on a tighter budget, or you're matching existing hardwood windows on the same property.
We manufacture in both. Design your windows in 3D or ask us for advice.
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