An evaluation of methods to determine the water vapour diffusion resistivity properties of solid-wood plantation timber commonly used in construction

Understanding the water vapour diffusion resistivity properties of elements used in the external envelope of buildings is a key input for transient hygrothermal analysis of energy efficient buildings. For the last three decades, solid-wood and engineered wood products have been increasingly used in the external envelope of Australian buildings. Previous hygrothermal research has identified that water vapour diffusion resistivity properties for Australian grown timber was not available from international databases and may not be known. Solid wood elements adsorb moisture, and under the right conditions support mould growth, leading to mould spores and structural decay. This research focuses on evaluating the water vapour diffusion resistivity of Australian plantation grown softwood and hardwood. The timber materials will include solid wood, solid wood with glue and engineered solid wood elements. This paper includes an assessment of laboratory based and ‘in-building’ evaluation methods. The review identified the need to adopt relative humidity dependent wet- and dry-cup laboratory test methods to ascertain the water vapour diffusion resistivity properties for Australian solid wood and engineered wood products.