The paper describes the Zero Net Carbon (ZNC) modelling tool developed by Energy Efficient Strategies for Sustainability Victoria, and discusses approaches to upgrading Victorian houses to achieve zero net emissions over a year, based on their household energy consumption and electricity generation from rooftop PVs. The ZNC tool is highly flexible and allows both a ‘base’ and an ‘improved’ house to be modelled for various combinations of house size, building shell efficiency, climate, occupancy, fuel source, appliance mix and efficiency, rooftop PVs and battery storage. Hourly energy consumption over a full year is modelled for both the base and improved houses, as well as the electricity generation of any PVs present, and the interaction between the battery, PVs and electricity consumption. Outputs are provided for each house in the form of energy, greenhouse gas emissions, energy bills, in both annual and daily profiles. The tool calculates the additional cost of the improvements, the energy bill savings over a specified period, and the NPV and benefit-cost ratio. It also calculates the size of the rooftop PV system required to achieve a zero net carbon status for the improved house.