Assessing the environmental performance of plastic-based and felt-based green wall systems in a life-cycle perspective.

With the remarkable growth of cities and the increase of built-up areas, mitigation of urban heat island effects has become one of the most crucial challenges in social and environmental sustainability with significant impacts on public health. This has led to an increasing development of urban green infrastructure. Among those nature-based solutions, green wall systems have been receiving a growing attention, being a passive technology with their ability to reduce greenhouse gas emissions, adapt to climate change, improve air quality and reduce the heat island effect in urban environments. Despite that growing interest in studying the functions and features of such green systems, and the various types of living walls nowadays available, most studies evaluate their energy efficiency and performance only during the use phase. This study aimed to assess the overall environmental performances of two types of green walls in a life cycle perspective, considering the embodied energy, greenhouse gas emissions, materials and energy consumption, and embodied carbon. After collecting inventory data related to all components and processes of each system, a life cycle assessment with cradle to gate approach has been performed to compare the performances of a felt-based system without organic growth medium and a system based on plastic modules with organic growth medium. The main impacts have been detected in the production stage and materials used in systems structure. By comparing the results achieved in the 16 impact categories analyzed, the felt-based system showed the highest overall impact, with the use of fertilizers and aluminum components playing a crucial part. Polypropylene used to produce the panels, water used for plant irrigation and potting soil composition are the main environmental impact contributors in the plastic-based system. The results pointed out the importance of accurate choice of materials for the design and production of green walls.