Climate change is having a significant impact on European forestry, particularly on the softwood species used for window frames. This study investigates potential replacement tree species for spruce (Picea abies), the predominant material for window frames. We evaluate Douglas fir (Pseudotsuga menziesii), Scots pine (Pinus sylvestris), thermally modified poplar (Populus nigra) and discarded silver fir (Abies alba) in laboratory and field tests. The laboratory tests included artificial ageing, various coating treatments, exposure to decay and soft rot fungi and the factor approach for estimating the resistance dose (DRd). In the field tests, large scantlings of the tested wood species were exposed to outdoor conditions at three different locations, with real-time moisture monitoring using resistometric sensors. Our results emphasise the superior performance of Douglas fir, which outperforms spruce in terms of decay resistance and mechanical strength. The acrylic/polyurethane coating significantly improved the DRd of all wood species, but the long-term performance needs further investigation. The oil coating offered a minor advantage. Discarded silver fir, while comparable to spruce in its basic properties, exhibited lower mechanical strength and cohesive weakness, leading to delamination in field tests. The real-time moisture data from the field tests provided valuable insights into material performance and potential structural defects. To summarise, Douglas fir is a promising alternative to spruce for window frames due to its inherent resilience, mechanical properties and compatibility with protective coatings. This study emphasises the importance of researching climate-resistant wood species and conducting real-time monitoring to achieve optimal window frame performance.

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