Leading timber research institute, BM Trada, tested the stability of Accoya wood against other widely used engineered wood siding materials by cyclic exposure of coated boards to wet and ambient conditions.
BM Trada found that Accoya wood had exceptional stability and stated that Accoya used for siding boards could increase from standard 150mm wide profiles to 200mm when used externally. This increased width specification board shows Accoya wood’s design flexibility and superior performance when compared to western red cedar, larch and thermally modified pine.
Leading timber research institute, BM Trada, was commissioned by Accsys to perform a series of exposure trials. The trials using the same coating began in February 2007 in
Buckinghamshire, England and tested Accoya siding board’s resistance to natural weathering and splitting in comparison to Pine and Siberian Larch.
This test, using a translucent black coating for maximum radiant heat build is a particularly difficult situation for wood products.
After 3.5 years, Accoya wood was found to outperform the competing siding boards in a number of ways – showing excellent coating performance. Pine siding boards showed severe levels of fissuring, resin exudation, end fissuring, paint peeling over fissures, shelling, surface checking and board distortion; whilst Siberian Larch was found to have extensive surface checking and burst resin pockets.
Accoya wood, however, had a flat surface with no grain raising, virtually no shelling, cracking, checking or fissuring. External dirt was easily cleaned off revealing a sound clean surface with no coating issues.
This harsh test proves that Accoya wood has superior coating performance compared to many competing materials.
Though BS EN350-2 does not strictly speaking apply to modified timbers such as Accoya, the BRE have made an assessment that the durability class 1 rating achieved by Accoya wood in trials is equivalent to class 1 of natural timbers. Therefore service life statements attributed in BS 8417 are applicable to Accoya wood. Under BS 8417, only siding made from timbers of durability class 1 are suitable for situations where there is a desired service life of 60 years.
