Assessing Indoor Climate and Mould Risks in Energy-Efficient Australian New Homes: A Comparison of AIRAH DA07 Continuous and Intermittent Conditioning Approaches

Energy-efficient building design has emerged as a key strategy in addressing the global climate crisis. However, growing evidence suggests that such buildings can reduce indoor climate resilience, particularly due to interstitial moisture accumulation and mould growth. Transient hygrothermal and bio-hygrothermal simulations can inform building envelope design to mitigate moisture and mould related risks. To support the development of hygrothermal simulation methods, Australia has drawn upon international standards, which prescribe continuous indoor conditioning regimes with stable temperatures and relative humidity levels. However, this assumption does not reflect typical Australian conditioning patterns, where the mix of climatic and cultural factors has led to intermittent heating and cooling practice. This study explores this discrepancy by comparing continuous conditioning with intermittent conditioning regimes and their impact on hygrothermal and bio-hygrothermal simulation results. This article reports on the results for timber-framed and compressed fibre cement sheet clad external wall systems within three climate types. The results reveal that intermittent conditioning can frequently lead to prolonged periods where indoor relative humidity exceeds 70% and indoor air temperatures are often below 20°C, depending on room type, orientation, and outdoor climate. The results indicate substantially higher risks under intermittent conditioning scenarios, with indoor mould growth predominantly occurring in bedrooms and open-plan kitchen-living areas. Mitigation confirmed under continuous conditioning was found to be inconsistent and generally less effective. These findings underscore the importance of developing locally calibrated indoor climate assumptions to improve the accuracy of simulation outcomes and better safeguard occupant health in Australia.