DECoRuM is a tool that estimates baseline energy use and carbon emissions from residential buildings and predicts emission reductions from various measures. It was developed to help local authorities track and reduce emissions. The tool was applied to a case study of 318 homes in Oxford, estimating current energy use, emissions and costs. Various carbon reduction strategies were analyzed, finding that solar water heating and photovoltaic systems could achieve over 60% reductions at relatively low cost compared to other approaches. DECoRuM can help local authorities and homeowners identify cost-effective ways to cut emissions from the domestic housing sector.