Recent enhancements to energy efficiency regulations, combined with exterior water control layers and minimal changes to decades old external wall system construction for stand-alone and multi-residential buildings in Australia has led to an apparent increase of interior and interstitial condensation and mould. Since 2014 researchers from the university of Tasmania have been utilizing non-transient and transient calculation methods to provide forensic analysis of existing buildings and to provide guidance on changes that should be considered for the design and construction of external envelope elements for Australian dwellings. This paper discusses recent research conducted for the State of Victoria, Australia, that has included traditional hygrothermal and bio-hygrothermal simulation of 6 Star and 7 Star building regulationcompliant external wall systems.