The natural durability of important European wood species has been tested on 3970 specimen in field trials. The wood was exposed at five test fields in Germany with different climates at each site in European hazard class 4 and 3 (with and without soil contact). Within EHC 3 it was distinguished between tree different expositions (end grain sheltered, unsheltered and with water trap). The test is now running for 3 years. The results have shown that the type of exposition (EHC 3 or EHC 4) has a strong influence on both: the decay activity and the durability determined as the quotient of decay of tested species and of decay of Scots pine sapwood. The test site had a strong effect on decay activity and time to failure, whereas the effect on durability was minor. Up to now it is not yet possible to calculate the final durability classification, but so far the field tests in soil confirmed the natural durability given in EN 350 (with the exceptions of Quercus robur and Robinia pseudoacacia, both were less durable than said in the standard). Whereas so far the above ground tests revealed a higher durability for all softwood species with coloured heartwood (heartwood of Larix, Pseudotsuga and Pinus) than classified in the standard EN 350. It is obvious that the current classification of natural durability is only valid for use in soil contact. Future amendments of the standard EN 350 seem to be reasonable. It is proposed to list durability class separately for in ground and for above ground use in the future.

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