Accoya

Accoya is an excellent choice for high-end architectural laminated beams or posts because its unmatched dimensional stability and class-leading durability ensure straight, flawless structures that will not twist, rot, or degrade.

Architects, high-end builders and carvers favor it for structural and aesthetic glulam applications.

Why Accoya excels for laminated beams & posts

• Zero twisting or warping: The acetylation process prevents the wood from absorbing water. Laminated beams remain completely straight and stable over time, which is critical for maintaining precise architectural lines.

• Flawless, long-lasting finishes: Because the timber does not shrink or swell (Accoya absorbs up to 80% less water than normal pine), any applied coatings, paints, or translucent stains do not crack or peel. Maintenance intervals for expensive architectural finishes are extended by up to two standard cycles.

• Invisible, ultra-strong glue lines: Wood movement is the primary cause of checking and delamination in laminated beams. Accoya’s stability places minimal stress on adhesive bonds, ensuring the structural integrity of the lamination remains permanently secure.

• Ground-contact durability: It achieves a Class 1 durability rating. This makes it highly resistant to rot, decay, and insect attacks, allowing architectural posts to be placed directly into the ground or exposed to harsh weather without degradation.

• Non-toxic and sustainable: Unlike traditional pressure-treated timber, Accoya contains no heavy metals or toxic chemicals. It is fully sustainable and safe to handle, aligning perfectly with modern green building certifications.

The science that gives Accoya its stability

Accoya timber resists water absorption because it undergoes a molecular modification process called acetylation, which replaces the wood's water-loving hydroxyl groups with water-repelling acetyl groups. This process permanently alters the cellular structure, reducing the wood's ability to absorb moisture by roughly 80%.

The science:

• Unmodified wood: Ordinary wood naturally contains an abundance of "free hydroxyl groups" within its cell walls. These molecules are hydrophilic (water-attracting), which causes wood to absorb moisture, swell, shrink, and rot.

• The acetylation process: Accoya (commonly sourced from Radiata Pine) is treated with acetic anhydride (a highly concentrated, non-toxic form of vinegar) under specific heat and pressure.

• The chemical reaction: The acetic anhydride chemically reacts with the hydroxyl groups, transforming them into acetyl groups.

Because water molecules cannot bind to acetyl groups, moisture is unable to penetrate the cell walls. This keeps the timber highly dimensionally stable meaning it won't swell, shrink, or warp. Additionally, fungi and insects no longer recognize the modified wood as a food source, which provides exceptional rot resistance.

For more information, visit Accoya NZ website