Nature-Based and Solar Façade Systems for a Net-Zero Built Environment: A Structured State-of-the-Art Review and Preliminary Comparative Assessment

Green building façades are increasingly recognized as a key strategy for decarbonizing the built environment, addressing climate change, urbanization, and the urban heat island effect. This paper investigates two main façade approaches: nature-based solu-tions (NBS), such as green façades and living walls, and Building-Integrated Solar En-ergy Systems (BI-SES), including photovoltaic, solar thermal, and hybrid BIPV/T sys-tems. The building envelope is framed as an active interface for both energy efficiency and on-site renewable energy generation. Through a structured state-of-the-art review, the study compares these systems in terms of energy performance, environmental benefits, costs, maintenance, lifecycle implications, and adaptability across climatic contexts. Results show that NBS provide consistent benefits in thermal regulation and cooling-load reduction, while solar façades are strongly influenced by orientation, ge-ometry, and urban shading. To complement the qualitative analysis, a preliminary en-ergy–environmental assessment is conducted for three façade configurations (conven-tional wall, green façade, and combined green–PV façade) across three Italian climates (Milan, Rome, and Palermo). Results indicate that vegetation reduces heat losses and CO2 emissions, with further improvements in integrated systems. Overall, NBS and solar façades emerge as complementary strategies whose integration can enhance building performance and support the transition towards net-zero carbon environ-ments.