Massive timber as effective thermal mass in Australian contemporary housing

Since 2003, in an attempt to reduce the use of energy and subsequent greenhouse gas emissions in Australia, the Building Code of Australia has gradually increased thermal performance requirements for residential and non-residential buildings. To meet these requirements has included the selection improved glazing systems, increased insulation levels to subfloor, walls, ceiling and roofing, and a reduction of infiltration losses. However, these measures do have limitations and in many cases the inclusion of appropriately sized and placed thermal mass may provide a more efficient and effective thermal performance outcome. This study comparatively explored, through the use of a NatHERS approved house energy simulation program, the use of massive timber elements within the built fabric of a selected group of contemporary house designs. The simulations required the establishment of a base built fabric model for each case study house. Each house was then simulated with different built fabric systems in flooring, external wall lining, internal partition walls and ceilings. The built fabric systems included standard lightweight insulated timber framing, clay brick, concrete block and solid softwood and solid hardwood systems. Additionally, the study also included the assessment of these interventions in cool temperate, temperate, hot and dry, and hot and humid Australian climates. The results and analysis of the simulations reveal that the use of massive timber elements, as thermal mass, provides a comparative thermal performance improvement of up to 24% in all houses in all climate types. Additionally, the research identified benefits from the different types of thermal mass relative to the location within the built fabric of each house. Furthermore, the research has started to inform a thermal mass diagram for Australia, which indicates a climate-based delineation for the use of softwood or hardwood massive timber systems as thermal mass.