States establish ambitious policies and important measures to achieve targets for the energy upgrade of buildings but although some important barriers prevent their implementation in space, they are rather overlooked by research. In this paper, it is argued that extensive multi-ownership (MO) and weak performance of the real estate market in degraded urban areas impede the mass energy retrofitting of multi-owner buildings (MOBs), which are an important part of the urban building stock A deprived area of central Athens (Greece) that serves as a case study. With a pluridisciplinary approach based on extensive field surveys, cadastral data analysis and cases of energy renovation of buildings through a public–private partnership financing scheme as well as ways to overcome the MO issue were explored, according to the provisions of the Greek legal framework. The integrated urban regeneration approach is promoted as a means to encounter the MO issue and enhance the functioning of the real estate market by the generation of surplus values that will render the energy retrofitting of buildings more attractive to investors and thus achieve the deep renovation of MOBs towards the sustainability of the urban environment. This paper ultimately advocates the integration of energy planning with spatial planning.