Accoya acetylated wood has been used for years in Europe for decking as well as for other exterior projects, though until recently availability in the US has been limited. That could change, however, as the product has recently received ICC-ES evaluation report ESR-2825 providing evidence that it meets code requirements for resistance to termites and decay for both above-ground (AWPA use category UC3A, such as siding and millwork, and UC3B, such as decking, guard rails, and even docks) and also for ground-contact use (UC4A, such as deck joists and support posts).
Acetylation is a process that transforms wood’s cellular structure through a combination of heat, pressure, and acetic anhydride, replacing hydrophilic free hydroxyls within the wood with hydrophobic acetyl groups. The process can be used with a range of different hard and softwoods, though Accoya typically uses a species called radiata pine. According to its ICC-ES report, only stainless steel fasteners and hardware should be used with Accoya wood. The only other major supplier of acetylated wood, Eastman Chemical Co., which manufactured Perennial Wood, withdrew from the market back in early 2014 (click here to read more).