Moisture and Mould Challenges Within Low-Rise Timber-Framed Residential Wall Systems in Temperate Climates

Insulated timber-framed structures are quite common in many temperate climates, where there is a mixed demand for interior heating and cooling, a greater reliance on natural ventilation, and a regulatory context for intermittent interior conditioning. In these climate types, the development and application of hygrothermal specific building regulations is generally on a different trajectory from those developed in cool climate locations. Until the addition of greenhouse gas focused Australian building regulations in 2003, most new residential buildings had little thermal insulation and were not well air sealed. Since 2004, there have been regular building envelope thermal performance enhancements to the national building regulations. The most prevalent construction typology for residential buildings in Australia is low-rise timber-framed single dwellings. The building envelope focused energy efficiency regulations have required increased amounts of external wall insulation and improved airtightness. By 2008 some academic and industry representatives had raised concerns about the lack of hygrothermal guidance and by 2013, the increased presence of surface and interstitial moisture and mould was becoming evident in new homes. The development of hygrothermal guidance initially focused on regulatory developments in other countries, followed by non-transient simulation (2014) and transient hygrothermal simulation (2017). During the process of completing more than 10,000 simulations for south-eastern Australia, the research increasingly identified the need for well-considered and designed interior and exterior water vapour control to ensure the durability and health of timber-framed structures and an adequate indoor environment.