Faced with the challenges posed by global warming and the depletion of fossil fuels, all the actors in society (individuals, industries, communities, and governments) are led to find ways to reduce their energy consumption. As residential buildings contribute significantly to the overall energy consumption, a particular effort is requested from buildings occupants to reduce their energy consumption without having to compensate on their quality of life. The energy behaviour of buildings is directly influenced among others by the behaviour of their occupants. This paper describes a new approach based on historical data to sensitize occupants for their actions' impact on building energy comportment without the need to develop a physical model thanks to case-based reasoning (CBR). We report on an experimental evaluation of the approach based on real-world data collected from an office building including two years of historical data.