•Expert system supports selection of heritage friendly urban level energy strategies.•Method allows an incremental decision-making that can be automatized through a DSS.•3D urban model with categorisation tool offers a data-conscious approach for baseline.\•The method and the DSS have been implemented in Santiago of Compostela.•Energy retrofit scenarios can be designed that are respectful with the historic values. European Historic Urban Environments (HUEs) are highly appreciated by their inhabitants and visitors and they can be considered as one of the most valuable collective achievements of the European culture. The preservation of our urban heritage requires the protection of the social context as well as the preservation of the authenticity and integrity of its physical materiality. That means improving the quality of life of their inhabitants as well as the sustainability of the historic districts. This paper proposes an incremental decision-making methodology that allows the modelling of the historic city and the selection of the best strategies. An application of this model is demonstrated through a case study using the historic city of Santiago de Compostela in Spain that was declared a World Heritage Site by UNESCO in 1985.