DURALARCH - suitability of selected coloured coniferous heartwoods of different origin for their use in outdoor applications

For outdoor above-ground applications with high demands on biological durability, there are only a few softwoods available that also have high density and strength characteristics. One of the most important timbers with these material properties is Siberian larch (Larix sibirica, Larix gmelinii), which is available in sufficient quantities due to its large distribution area. Imports of Siberian larch from Russia to numerous countries have therefore been established over decades exclusively for many areas of use, e.g. in structural frame construction as well as for terrace decks, windows and external cladding. As a result of the war in Ukraine that Russia started in 2022 and the resulting sanctions, the trade with Siberian larch came to an almost sudden standstill and the remaining stocks were used up within a few months. The German wood trade is currently trying to close the bottlenecks that have arisen while demand is high with different alternative woods. While the wood of the European larch (Larix decidua) or Douglas fir (Pseudotsuga menziesii) grown in Germany can be used for applications in which the biological durability of the wood is not crucial, other areas require wood with higher durability and sometimes also higher density and slow-grown wood, as is characteristic of Siberian larch. Among others, Canadian larch (Western larch, Larix occidentalis), Western red cedar (Thuja plicata), and Oregon pine (Douglas fir) from western North America and Dahurian larch (Larix gmelinii) from northern China are imported. Individual woods from the group of softwoods with coloured heartwood described here have already been examined in the past with regard to their biological durability. However, a comprehensive comparative study that also includes Siberian larch is still missing. Therefore, DURALARCH project aims at investigating different species of larch as well as Douglas fir and western red cedar of different origins. In addition to laboratory and field studies on biological durability, density and extractive content are determined and the sorption and moisture behaviour of the wood is characterized. In this paper, we provide an overview about the project and first results related to the moisture dynamics of the different conifers.