Experimental investigation on the effect of detail design on wood moisture content in outdoor above ground applications

An essential part of a performance-based service life design format for wood exposed in outdoor applications is the effect of proper detailing in terms of avoiding moisture traps. Models for predicting degradation and non-performance caused by decay are functions of arbitrary climate history of combined moisture content and temperature. Therefore it is crucial to be able to predict the behaviour of different detailing in terms of moisture content exposed to outdoor climate. An experimental study was made with continuous moisture content measurements of different details. The different detail set-ups are selected to represent a wide range of sawn timber dimension details of non-treated Norway spruce. Hourly moisture content values are recorded by a wireless monitoring system and the climate is monitored using a weather station. A simple horizontal board with no detailing is chosen as reference detail. This is, apart from a vertical board and sheltered details, what can be expected to be a good detail in terms of not trapping water. The remaining details show higher moisture content levels. It was found that the ratio between moisture content in a detail and in the reference detail showed a reasonably constant value over time. Consequently the behaviour of an arbitrary detail can be estimated by scaling the behaviour of the reference detail up or down using a constant value. Depending on the design the constant will be higher for more water trapping details and vice versa. This is important information and input for evaluating and developing details with acceptable performance.