Abstract Energy retrofit of the facade of condominium buildings may be a difficult task because thermal bridges such as those due to balconies, common elements in the architecture of many countries, are often arduous to correct by added insulation due to several constraints. An alternative retrofit approach is therefore analyzed, easy to implement and relatively inexpensive. It consists in changing a balcony into a ventilated sunspace during the cold season, exploiting solar gains to compensate heat loss. More specifically, transparent plastic roll-up sheets are installed along the balcony perimeter, removable in the hot season, to enclose the volume between two superposed balcony slabs. The obtained sunspace is then used as a pre-heating chamber for a single-flow ventilation system that ensures the air changes required indoors. Heat gain to the indoor environment can thus be increased with respect to a simpler sunspace without ventilation, and possibly modulated along the day by proper control of the flow rate. In this work, the proposed approach and a small-scale physical model are presented. The model will serve to validate analyses aimed to forecast and optimize the performance of ventilated sunspaces built around balconies.