Coated Accoya Cladding – West Lodge Primary School

Accoya wood is produced through a modification system that enhances the durability and dimensional stability of timber. This enables it to be used be used in situations where previously we may have relied upon durable tropical hardwoods or plastics such as uPVC.

Accoya cladding, decking and glulam boat house Norfolk

Evolution of the technology

75 years after the start of research into the modification of timber by acetylation the process is now a commercial reality, but why has it taken so long when the benefits of improved performance and durability are so pronounced?

Increasing scarcity and concerns over the traceability of durable tropical hardwoods from sustainable forests along with tighter legislation around the use of toxins in existing preservative treatments have helped drive the commercialisation of processes to improve the performance of timber. Accoya wood is produced by a modification system that enhances the durability of timber so that it achieves Class 1 durability and so can be used in situations where previously we would have had to rely predominantly on durable tropical hardwoods.

Enhanced durability without toxicity

Accoya wood is a modified wood system based on acetylation, a process which alters the cell structure by transforming free hydroxyl groups (containing oxygen and hydrogen) within the wood cell walls into acetyl groups (containing oxygen, hydrogen and carbon).  This is achieved through a patented system involving vacuum treatment of kiln dried timber with acetic acid – essentially just vinegar.  Transforming these free hydroxyl groups is key to improved durability and stability as it is to these sites within the cell wall that water can be absorbed and released as climatic conditions change thus leading to expansion and contraction of the timber.  Acetylation improves stability by 80%.

Dimensional stability

Increased stability of Accoya wood not only means that warping, bending and twisting are reduced or eliminated it also has benefits for surface treatments as cracks and fissures are smaller so paint finishes are not disrupted thus increasing their life span and reducing maintenance cycles. The modification process also ensures that timber is treated right the way to the centre – so there is no need to treat cut ends on site.

Accoya wood is increasingly being chosen by clients who recognise the positive contribution this material can play in their projects.  Accoya provides a highly durable and stable cladding finish backed up by a 50-year warranty and Class 1 durability.  Improved stability also means that maintenance is reduced as surface treatments such as stains and paints last 3 to 5 times longer.  Striking facades can be created with appealing aesthetic features of warmth, natural textures or bold coloured paint finishes while at the same time its high performance and FSC certification can contribute to improved BREEAM ratings for buildings.

Finally, what happens to Accoya wood at end of life?  Because only carbon, hydrogen and oxygen, have been added in the acetylation process, chemicals which are all present naturally in timber before modification, Accoya wood can be treated in exactly the same manner as any unmodified wood and so it is 100% recyclable.