Space cooling and heating in residential sector is significant contributor to energy consumption in Australia. Therefore, it is important to reduce the cooling and heating requirements. The selection of a good walling system helps to save energy by homes. This research compared the thermal efficiency of a modern house (constructed using brick veneer walls with concrete floor slab) with an old house (constructed using fibro cement walls raised timber floor) using the AccuRate simulation tool. A standard house with two living rooms, one kitchen, one laundry and four bedrooms are simulated in a Sydney Suburb in Australia. It was found that modern house showed lower inside temperature variation than the old house all year around. The results also showed that the modern house has a lower energy consumption for space heating and cooling than the old house. The annual energy use for space heating and cooling in both the modern house and old house were 5197 kWh and 15,712 kWh respectively. Moreover, the annual energy costs were found to be $1,403 and $4,242 respectively for modern and old houses. The modern brick veneer house saved about 33 % of energy compared to old old house. When the net present value of the energy cost for f both houses over 50 years is computed, the energy cost of modern house was found to be $25,629 while it of old house is was $77,488 for the old house.