Comparative studies on the moisture performance and durability of wooden facades

IRG/WP 12-20492

T Bornemann, C Brischke, J-M Lück

Wooden claddings are traditionally used in many parts of the world. Also modern structures are frequently made from timber and timber engineering panel products. However, wood has to compete with other cladding materials and its durability needs to assure sufficient functional and aesthetic service life. Besides many other factors the durability of a wooden facade is dominated by its moisture performance on the one hand and the occurring moisture loads on the other hand. Within this study continuous wood moisture content measurements were conducted on three different test objects: 1. Combined facade-decking elements made from eleven different wood species relevant for the European market were exposed to the South and to the North in Hannover, Germany. Material-specific moisture performance was evaluated and compared with climatic parameters. 2. Three-years of measurements were carried out on the walls of a timber-made test house at the same test site. Measurements were made in different wood species, at different distances to the ground and in all four compass directions. 3. The effect of different roof overhangs on the moisture load of a wooden facade made from Norway spruce was studied on a test assembly in Tåstrup, Denmark. In addition to the moisture content measurements, wood temperature was recorded daily and relevant weather parameters were collected from meteorological stations nearby. To assess the respective moisture performance of the various materials and construction related parameters, the number of wet days was determined and a performance model was applied to all data sets. Based on a model for above ground decay the expected service life was calculated for different exposures, materials and design details. The highest moisture loads were found on the West facade, which is the weather side in Central Europe, followed by the North facade, where re-drying was inhibited due to limited solar irradiation. Furthermore the splash water zone was clearly identified, where moisture loads were increased and re-drying reduced due to lower wind speeds close to the ground. Finally, the moisture performance of the various timber species differed significantly. Thus, a wide range of service life estimates was deviated from the data sets.

Keywords: eave, facade-decking element, moisture monitoring, roof overhang, service life prediction

Conference: 12-05-06/10 Kuala Lumpur, Malaysia

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