A socio-ecological approach to investigate the perception of green walls in cities: A comparative analysis of case studies in Turin and Lisbon

New urban greening practices are increasingly adopted to contrast and mitigate critical issues of urban areas. These strategies involve nature-inspired solutions to increase sustainability and restore natural processes in cities. In this framework, green walls play a pivotal role to reintroduce nature and provide both environmental and socio-cultural benefits in high densely cities. Despite green walls contribute to increase the aesthetic value of buildings and people's consideration of the area, methodologies to effectively assess their social benefits are still lacking. This study proposes a place-based approach to investigate the Restorative capacity of two outdoor green walls: a modular living walls system covering two facades of a public university building in Turin (Italy) and a plastic planter boxes based living wall located in an inner courtyard of a cultural centre in Lisbon (Portugal). Firstly, the two living walls were characterised through direct observation considering technical, spatial, and social aspects that influence the fruition and the biophilic perception of these public spaces. Then, a self-rating questionnaire based on the Perceived Restorativeness Scale model was given on-site to participants to investigate the influence of green walls on people's cognitive perception and well-being. The novel Green Wall Perceived Restorativeness Scale consists of 17 items that evaluate individuals' perceptions of green walls, emphasising their attractiveness, integrative role in the environment and contribution to the overall appeal and comfort of space. Similar results between sites suggest that common features such as development at maximum building height, symmetrical disposition, element repetition and plant variety are drivers of citizens perception of green walls. Outcomes support the recognised link between citizens aesthetic appreciation of green walls and their perceived sense of comfort and mental relief, related to the Being away factor. The spontaneous social gathering and citizens resting near both green walls creates evidence of the attractiveness of this nature-based solution as a landmark in the urban environment. These conclusions demonstrate the pivotal role of urban biophilic design to combine natural and artificial elements in architectural and landscape design creating an opportunity to increase the use of green walls to contribute to citizens well-being in urban settings.