Quantifying the thermal performance of green façades: A critical review

• We reviewed the scientific literature on the thermal performance of green facades.
• Studies were prone to research design problems.
• Few studies investigated the influence of plant morphology and physiology on facade performance.
• We propose an approach to standardising the measurement of green facade parameters.
• Inputs from plant biology, ecology, horticulture and soil science are needed to progress this emerging field.

Green façades are climbing plants grown either directly against, or on support structures affixed to, external building walls. Like other forms of green infrastructure, they are increasingly being considered as a design feature to cool internal building temperatures, reduce building energy consumption and facilitate urban adaptation to a warming climate. To develop a better predictive framework for green façade thermal performance we reviewed the scientific literature – a literature currently dominated by the disciplines of architecture and engineering, and lacking inter-disciplinary input from plant biology, ecology, horticulture and soil science. We found that many of the studies were prone to research design problems; the small number of experimental studies lacked replication and provided insufficient information about the microclimate parameters measured, while the assumptions of modelling studies were not always delineated or justified. Few studies considered the influence of climbing plant characteristics, and fewer still investigated the impact of green façade design components (support structures, growing media, plant containers and irrigation systems) on green façade thermal performance. As a framework for future green façade research, we propose that standardised methods be adopted, and to this end, set out the minimum microclimatic data required to enable comparative assessment of green façade performance. Furthermore, we stress the need for research on the interaction between climbing plant parameters and building energy balances, as well as on the influence of green façade design elements on thermal performance. Without this shift in approach, unrealistic expectations of green façade performance and their climate change adaptation benefits will persist.