The four towers of the Haardau II Housing Estate have shaped the cityscape of the City of Zurich since their construction in 1976-1978. Proportions and placement and the sculptural façade reduced to a few elements make the ensemble designed by Mr. Max P. Kollbrunner a witness of architectural value. The comprehensive renovation of the façade of the residential towers will ensure the continuity of the estate for the next forty years. In a separate project, the old people’s apartments in the low-rise building to the west are also being renovated. While the work in the retirement apartments is planned in an unoccupied state, the façade renovation will take place during occupation. The first major challenge is therefore to ensure that the construction process is as conveniently as possible. When renovating the concrete element façade, the different condition of the building components must be taken into account, with correspondingly different depths of intervention. Since all the windows have to be replaced by modern and thus draught-free windows, a ventilation concept is also required that continues to enable the airflow. Above all, the project goal is to preserve the architectural quality and density of the complex. All buildings and the outdoor facilities are included in the inventory of protected objects of communal importance and are being implemented in close cooperation with the city’s monument preservation agency.