The new Calwer Passage building in Stuttgart is taking shape. The green building complex will house modern offices with a mix of retail and innovative gastronomy. On the roof above the sixth floor, tree planting has already begun for the mini mixed forest. Black pines, English oaks, Swedish mealy pears and hornbeams up to ten metres high have been planted for the pioneering project of green urban development in Stuttgart and, together with the green façade, are to make an ecological contribution to a better urban climate. Florian Starz, Project Manager Facade Engineering at Werner Sobek AG, provides here answers to questions about the construction and the choice of plants of a green facade.