Wood is predominantly degraded by organisms. Thus, compared to other building materials, service life of wooden material is influenced by many more factors, which are divided into direct and indirect factors. Climate, geographical position, and construction criteria count to the indirect decay factors. Besides material inherent properties (natural durability, wood preservatives), wood temperature, wood moisture content, and the presence of certain species of wood degrading organisms are the strongest direct factors influencing service life of wooden building components. On this account an experimental set up was developed to quantify these direct decay factors: Field tests were performed in European Hazard Class 3 (EHC 3) to determine the influence of macro and micro climate on decay progress and decay factors such as temperature and moisture content of wood. Therefore Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) have been positioned in double layer test devices since 2000. Thirty-two sites in Europe and the United States representing preferably different climatic conditions were chosen for exposure of the test devices. For all sites, data on climate were available since they were located next to an official meteorological station. This way all relevant climatic factors (precipitation, air temperature, relative humidity, sunshine duration, wind) are correlated with MC and temperature of the samples to be measured once a minute and logged once a day. Furthermore the samples were evaluated respecting to decay and discolouration every year according to EN 252 (1990). Preliminary results concerning the influence of macro and micro-climate show that this approach will provide a sufficient data base for a better understanding of the most important factors determining decay.

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