Secondary or 'alternative' hardwood timber species can replace traditional hardwoods and contribute significantly to satisfying the overall demand for hardwoods in the UK timber market. A selection of these 'alternative' hardwoods is currently being tested at BRE-WTC for natural durability both in ground contact (to EN252) at two field sites, and out of ground contact (as L-joints to EN330) at one site. The objective is to provide an assessment of the suitability of each species for future commercial application. Moisture movement has been monitored in the L-joint tenons showing in less durable timbers, such as rubberwood (Hevea brasiliensis), rapid in-depth wetting during rain. Other monitored features of timber failure in out-of-ground exposure, including surface mould, cracking, discoloration and rot, indicate to date clear species-based differences. Comparison of the test timbers, based upon responsiveness to moisture and degree of timber failure, classify calophyllum (Calophyllum spp.), Ghanaian teak (Tectona grandis) and niové (Staudtia stipitata) as most durable and least reactive to moisture. The results to date of the ground contact trials, when compared with archived durability data show that the archive records of ground contact natural durability remain valid, although some modern plantation-grown timbers, such as teak (Tectona grandis), appear less durable than material from virgin forest. The likely value and commercial application of some of the secondary hardwood timbers examined is summarised.

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