Vertical greenery systems: A systematic review of research trends

Expansion of modern cities reduces green areas, especially within city centres where the urban heat island has become a significant problem. In an attempt to increase greenery in cityscapes and to provide passive cooling, vertical greenery systems (VGS), an old practice of covering building facades with plants, are receiving attention from architects, engineers, building planners and researchers. This paper systematically reviews available publications on VGS and classifies them according to 13 distinct themes. Research into VGS has increased over recent years and the trend shows the approach to this field of research is changing. Thermal research remains the most prevalent theme compared to others, representing almost half of all publications (76 out of 166), with the top three most highly-cited articles all related to thermal properties of VGS. Nevertheless, the systematic review shows a strong trend of diversification into cross-disciplinary research. The proportion of VGS papers reporting on two or more themes has grown from 25% in 2011 to more than 60% in 2017. The review has revealed that among the limiting factors to VGS are cost and maintenance. The outcomes of this systematic review allow recommendations to be made to architects, designers, planners and owners of VGS regarding the need to account for maintenance in the overall design and operation of these systems. On the basis of this review, future research into VGSs will be increasingly multidisciplinary and will need to consider the interconnected dimensions of the system and how they determine both its cost and effectiveness.