A hygrothermal analysis of international timber frame wall assemblies tested under temperate maritime climatic conditions

As the use of timber frame construction increases it is important that the assemblies specified have sufficient drying capacity to withstand any moisture loads that may occur over the life of the structure since decay is heavily dependent on the presence of moisture. The purpose of this study was to assess the hygrothermal performance of common timber frame wall assemblies under temperate maritime climatic conditions. Four timber frame wall assemblies were simulated using WUFI 2D. An additional moisture source was modelled to simulate wall performance under the presence of a construction defect. The results show that under normal conditions all four wall types behave in a similar manner. However once the moisture source is added, relative humidity in two of the wall types exceed thresholds above which the risks of mould growth are high. This effect is the result of the location of the OSB sheathing on the external side of the timber frame, which limits the escape of moisture from the wall assemblies. Wall types where the OSB is on the internal side have greater drying rates due to the increased rate of moisture mass transfer through the wall. This drying capacity is important in humid climates where the probabilities of high moisture loads are greater.