This experimental project is to aim to acquire on the basis of the Kiel Towers in Antwerp as a case study, the necessary knowledge and experience to come in future renovation projects more (cost-) optimal energy-saving projects. The aim is to translate these insights and experiences to tools and guidelines that are widely applicable in the renovation of residential blocks, for both technical aspects, costing as comprehensive energy efficiency. There is worked out a method in which each step of the process is optimized, from audit of building shell over flow chart for hygrothermal risk, up to the determination of a cost-efficient optimum between architectural and installation procedures.