Over the last seven years an extensive research program has been underway in the Priority Research Centre for Energy at the University of Newcastle in conjunction with Think Brick Australia aimed at investigating the thermal performance characteristics of walling systems particularly in relation to housing. This is a full-scale study using four purpose-built housing test modules constructed with a range of walling types. The study has been supplemented by the construction and commissioning of a Guarded Hot Box apparatus to measure wall thermal resistance properties as well as the development of building simulation energy modelling software. This paper gives a brief overview of the project and explores the difference in the observed behaviour of the housing modules constructed with four different wall types with a range of thermal resistances (R Values). The walls were cavity brick, insulated brick veneer, insulated cavity brick and insulated lightweight. The internal conditions could be allowed to “free float”, or be controlled within a comfort range by a heating/cooling system with the energy consumption being measured. The results show that the use of the wall R-value as the sole parameter to define the thermal performance of a building is not sufficient, as the internal comfort levels and energy demands of the modules built with walls with similar R-values were significantly different due to the influence of other effects such as the thermal mass of the walling systems.