Assessment of the environmental loads of green facades in buildings: a comparison with un-vegetated exterior walls

摘要

Green vertical systems have advantages in terms of building energy performance, but their environmental impact should be assessed in comparison to un-vegetated constructive systems. The aim of this paper was to evaluate the environmental loads of a green facade, which was compared to other building exterior wall systems. A Life Cycle Analysis approach was used to compare the green facade with constructive solutions commonly applied for enhancing the thermal insulation properties of the building exterior walls. The green facade and the other constructive solutions were characterised by an equivalent thermal behaviour. A green facade system prototype, realised with vegetation climbing on a steel frame, was used for the study. The comparison was carried out with exterior walls using insulation materials as expanded polystyrene, expanded cork and wood fibre. A double wall with an un-ventilated air gap was used as well. On average, the best environmental performance was recorded for the wall using cork as insulating material and for the double wall. The results highlighted the environmental criticalities of the green facade as the system having an environmental load among the most burdensome. Different scenarios of green facade with the use of alternative constructive solutions were hypothesized and compared by the life cycle analysis and life cycle impact assessment. The study showed that the adoption of a wooden frame in place of the steel one, as plant supporting structure, reduces the carbon footprint of the green facade by 58%. The environmental comparison was carried out also considering non-vegetated constructive solutions having an equivalent sun shading effect on the wall. The analysis showed that the green facade has the best environmental performance when compared with sun shading systems in aluminium or PVC.