Durability by design – a case study of the performance of wooden decks after 9.5 years of natural weathering
M Kutnik, M Montibus
The service life expected for wood decking manufactured with poorly durable wood species, left untreated and exposed to severe environmental conditions such as high humidity and active biological agents, is usually assumed to be short (less than 10 years). The current classification of wood’s natural durability is based on EN standardised tests which do not fully reflect the real end-use conditions (such as outdoor decking or cladding), that might lead to underestimate the expected performance and service life of certain wooden commodities. In addition, design is known to play an important role in the performance of wooden elements over time, especially in the case of outdoor applications. With the aim of evaluating the positive impact of water-draining designs on wood’s service life, decks were manufactured using six wood species and up to six different designs, selected for their ability to generate or to avoid water traps through different design details. The decks were rated for fungal decay after 9.5 years of natural weathering in the city of Bordeaux, France. The results of the evaluation demonstrated that (1) significant difference in the ability of the decks to withstand decay over time exists depending on the design details used, the water-draining designs performing better than most of the water-trapping ones in the case of the non-durable spruce and poplar; (2) high variability in the resistance of the spruce and poplar deck boards against fungal decay was noticed for each tested design, but unexpectedly with a quite high percentage of boards of each type performing very well after such a long exposure to weathering; (3) the heartwood of larch, maritime pine and Douglas fir was found to perform very well after 9.5 years of weathering in decking application, with only slight differences observed between the selected designs, demonstrating that these species could be valued for decking applications despite their moderate natural durability.
Keywords: natural durability, service life, performance, design, natural weathering, decay