The physical function of a cladding is to protect the interior construction. Under normal circumstances the performance requirements can be met for a very long time, meaning that the technical service life of a wooden cladding can be very long. Since the cladding is a major part of the facade, it also has visual requirements that may define the aesthetic service life, and often it is much shorter than the technical service life. The visual changes that occur during weathering may be colour changes, abrasion or wear, blistering, flaking, and even cracks in the wood or coating, but more often growth of mould and blue stain fungi. A field test with claddings was established in southern Norway to study the variation in moisture content in the cladding, the material temperature and the ambient microclimate. The aim of the field test is to provide data that can be used to estimate aesthetic service life of claddings based on material properties, surface treatments, and climate. One of the primary objectives is to identify conditions that are critical for establishment and development of mould and blue stain fungi. The field test will also be used for preference studies in order to identify critical levels of visual changes. Claddings were made of Norway spruce (Picea abies (L.)) from two sites with different growth conditions. It includes both heartwood and sapwood, and both juvenile and mature wood. Selected boards were crosscut into four pieces, of which three were treated with different paints, and one was left untreated. The samples are exposed in an open environment, facing either north or south. Relative humidity and temperature is measured in air close to surfaces, and wood temperature and moisture content are measured in the claddings. Moisture content is calculated by measuring direct current resistance across grain, and corrected for temperature. Mould growth and blue stain fungi, as well as mechanical changes on the surface of the claddings were evaluated visually according to the EN 927-3 standard. Results from the first year are presented. It shows differences in moisture content and material temperatures depending on colour and exposure, whereas the differences in mould growth are minor so far.

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