The technical relationship between vertical greening and built heritage

Built heritage is rich in cultural and economic values and is an essential part of urban environments. These buildings are abundant in city centres that have been the site of development for several centuries. This has produced a dense environment, exhibiting strong urban heat island effects. Green initiatives are increasingly being implemented to mitigate current climate stressors and improve the health and well-being of residents. However, built heritage is often excluded from these approaches due to concerns about their impact on materials and structural integrity, which is poorly understood. This research scopes the technical compatibility of vertical greening with built heritage in an urban environment regarding the degradation of historic building materials. Vertical greening here is understood to include plants, rooted in the ground, growing along a vertical surface by either attaching themselves to the façade or trellising. Investigating the impact of vertical greening on the local microclimate by monitoring case studies, lab experiments and analysing current literature can help us understand how vertical greening affects common forms of degradation caused by salts, frost, bio-activity and air pollution. Each method has its own approach to understanding the relationship of vertical greening with built heritage and is complementary to the others. The lab experiments explore the three main factors impacted by vertical greening such as temperature and relative humidity, incoming solar irradiation and precipitation exposure. Temperature and relative humidity are inseparably connected with each other and therefore analysed together. The impact of vertical greening on the aforementioned environmental parameters is investigated separately to provide better insights into those microclimatic changes that determine the risk of weathering of historic building materials.