Cost Benefit Analysis of Simulated Thermal Energy Improvements Made to Existing Older South Australian Houses

Abstract Since 2010/2011 changes to the national construction code require newly constructed houses to perform at a minimum Nationwide House Energy Rating Scheme (NatHERS) energy rating of 6 stars (or BASIX equivalent in NSW), which determines the predicted thermal energy a house requires to maintain thermal comfort, given its location. This initiative aims to improve the energy performance of new housing stock in the residential sector, however, many existing houses were built before the introduction of these regulations. These houses account for the vast bulk of the nation's housing stock and are shown by studies to achieve low star ratings and can require significantly higher amounts of thermal energy to maintain occupant thermal comfort. This paper investigates the likely impact of various renovations for six existing houses in South Australia mainly within the Adelaide climate zone representing a range of typical housing stock constructed before the adoption of NatHERS based energy regulations. These houses were built between the 1930's to 1990's, are sited on individual allotments, and are modelled in NatHERS rating software from an existing base case and then for a variety of both minor and more significant building shell and fabric upgrades; extensions to floor areas or major structural modifications are not considered. The costs associated with the upgrades is presented together with the thermal energy improvements, which bring older houses up from star ratings of 1-3 to the current minimum performance of 6, which reduces the demand for and greenhouse gas emissions of heating and cooling devices, for material and labour costs of $15-25k. Further analysis identifies the types of renovations that are the most cost effective.