In this case study four 7 m long Douglas fir crossbeams were investigated regarding the remaining metal and moisture content. The crossbeams were replaced from a timber tower after 10 years of service in the Black Forest region (South Germany) due to fungal decay. From each of the crossbeams five stem discs were taken and relevant parameters (density, moisture and remaining metal content) were determined at four points (3, 6, 9, and 12 o’clock position). The results confirm the hard treatability of Douglas fir sapwood. Remaining metal content correlates with the performance of the logs, whereby following ranking was found: Eastern crossbeam > Western ≈ Southern > Northern crossbeam Beside this, the results revealed that the highest remaining metal content was determined in discs taken close to the end-grain and -in general- in lower segments (6 o’clock position) of the discs. Furthermore it was found that the applied chromium-copper-ratio can be a useful tool for the interpretation of the remaining metal content vs. metal release. The investigation of the discs enabled the conclusion that the fungal infection started in the transition zone between sap- and heartwood due to core cracks, in combination with a longer period of internal wetness. Afterwards the infection expanded predominantly in a horizontal direction. In order to avoid an early failure of the new installed crossbeams, it was suggested to protect the upper side of the logs by means of stainless steel u-profiles against weathering. A first visual inspection of the covered beams did not show any signs of damages after three years.

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