Accoya timber for heritage windows
Many homeowners haven't heard of Accoya, yet it's become one of the best timbers for new heritage windows and doors. It looks and works like traditional painted joinery but lasts far longer, with much less movement and maintenance.
What Accoya is
Accoya is a modified timber. It starts as fast-growing radiata pine from sustainably managed, FSC-certified forests. It's then treated through a process called acetylation, which changes the structure of the wood itself. The result is a softwood that behaves more like the most durable hardwoods. No toxic chemicals are added, and the wood remains fully recyclable.
Why it suits heritage joinery
- Exceptionally stable. Ordinary timber swells and shrinks with the weather, which is why old sashes stick in winter and rattle in summer. Accoya moves far less, so windows keep opening smoothly and joints stay tight.
- Very long lasting. Accoya is rated Durability Class 1, the highest rating for timber, and is backed by the manufacturer's 50-year warranty above ground.
- Paint lasts longer. Because the wood barely moves, paint doesn't crack and flake in the same way, so redecoration is needed far less often.
- Ideal for fine detail. It machines cleanly, so mouldings, glazing bars and putty-line profiles can match historic windows precisely.
- A sustainable choice. It comes from responsibly grown timber, lasts for decades and can be recycled at the end of its life.
Accoya and vacuum glazing
Accoya's stability makes it an excellent partner for vacuum glazing. A frame that barely moves protects the glass seal and keeps the window draught-free, while slender sections and fine glazing bars keep the traditional appearance. See vacuum glazing in new heritage windows.
Is Accoya acceptable in a listed building?
Accoya is widely used for painted heritage joinery, and once painted it looks just like traditional timber. For a listed building, the conservation officer is mainly concerned with design, proportions, profiles and finish, so a well-detailed Accoya window to the right pattern is usually acceptable. A few officers prefer a specific traditional timber for certain buildings, so state the timber clearly in your application and be ready to explain why it was chosen.
How I can help
I can help you decide whether Accoya is right for your windows and doors, and make sure your Listed Building Consent application explains the choice clearly.
More guides
These guides are general information for England and don't replace advice specific to your property or your local planning authority.