The European standard EN 350-2 classifies Douglas fir as moderately resistant to fungal decay on the basis of standardized laboratory and field tests. However, the lifespan expectancy of outdoor structures such as cladding, decking and elements of wood construction carpentry may also vary according to environmental conditions (climate, exposure to weathering), maintenance and design. An investigation of approximately thirty wooden structures made of Douglas fir and installed in various locations in France over the period of several decades was performed and their performance in terms of resistance to decay was studied. The results show that outdoor above ground structures made of Douglas fir seem to be less susceptible to fungal decay than could be deduced from its natural durability classification. The evidence provided by this study proves that both the sapwood and heartwood of Douglas fir perform better in real outdoor use conditions than predicted by standardized tests, promoting its use without any preservative treatment for a wide range of outdoor purposes. Furthermore, it makes a valuable contribution to the ongoing French and European studies investigating the possibilities of applying recently developed service life prediction methodologies.

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