An empirical measurement of Eucalyptus Nitens water vapour diffusion resistivity

The quantification of moisture transport through building envelope materials plays a vital role in ensuring durability, thermal performance, and indoor air quality. For effective moisture control, accurate hygrothermal modelling, and mould growth prediction, reliable data on the water vapour diffusion resistivity of construction materials is essential. Internationally, limited data exists on the water vapour diffusion properties of solid wood species. In Australia, despite the growing use of plantation timber over the past three decades, key hygrothermal properties remain undocumented. This lack of empirical evidence restricts the development of moisture-resilient design strategies, weakens simulation accuracy, and increases the risk of building failures due to mould and material degradation. This study starts to address this knowledge gap by experimentally measuring the water vapour diffusion resistivity of Eucalyptus Nitens, a plantation-grown hardwood increasingly used in Australian construction. Sawn and kiln-dried samples were provided by industry collaborators to reflect real-world applications. Each specimen was carefully sealed and monitored for mass changes over time, enabling the evaluation of water vapour diffusion. In this first stage of the research, the samples were placed in a controlled room with temperature of 23°C, and a relative humidity of 35%. Results show that the water vapour diffusion resistivity of Eucalyptus Nitens varies significantly subject to material density. This variability has critical implications for envelope design in climate-responsive construction. The next stages of the research will measure the water vapour diffusion properties under three other relative humidity conditions to ascertain a relative humidity dependant water vapour diffusion resistivity dataset.