Green walls for advanced building envelopes: design optimization and analysis - A case study in Milan

The paper illustrates the potential use of green walls for advanced building envelopes. In the last years, several technological systems have been developed for green building envelopes. They can be categorised into two groups, according to their system and growing methods: green façades and living walls. Green façades are created by growing climbing plants up and across the façade itself, either from plants grown in garden beds at its base, or by container planting installed at different levels; they can be direct (i.e. self-clinging climbers, deciduous or evergreen, which adhere to the building exterior by means of adventitious roots) or indirect, where plants are kept away from the walls by continuous supporters and substructures. Living wall systems differ from green façades in the fact that they incorporate multiple ‘containerised’ plantings to create a vegetation cover rather than being reliant on fewer numbers of plants that climb and spread. Once decided to include vegetation into the building project, several questions may be asked. The first one is about structural stability and safety, as envelopes have to be designed to withstand very high dead loads. Another crucial safety aspect is the fire performance: vegetation could be considered a fire propagation medium ‘par excellence’, and the façade must be designed to assure that, in case of fire, its propagation is reduced as much as possible. Moreover, plants sustentation should be carefully considered, since they have to receive light and water to naturally live and grow; natural light supply depends on surroundings and building shape; water supply could be more problematic, because a system of water irrigation and disposal must be designed and integrated in the building envelope. If not properly designed, these aspects can lead to cumbersome and noisy drainpipes and to maintenance issues related to difficulties in inspections and replacement of the drainage components in case of damage Therefore, a very important aspect is maintenance, and maintenance schedule as well: plants need to be cut to keep them healthy, and excessive or abnormal grow has to be avoided. Maintenance system is a sensitive issue, and the designer should think about it since the beginning. This paper presents and details a case study of an office building in Milan with an indirect green façade: vine plants are located in special planters across the façade, and they are free to grow and develop along metal wires included in the curtain wall. Eventually, technical aspects are analysed and some guidelines on technological and construction aspects are given, in order to assure the optimal vegetation life.