Implications of green façades on historic building materials

Urban environments are subjected to various climate stressors, e.g. elevated temperatures and air pollutions levels, impacting public health and city resilience. As a result, historical buildings, crucial components of urban environments, experience accelerated degradation and sustainability challenges. To mitigate the urban environment, cities are increasingly implementing nature-based solutions (NbS), such as ground-based green façades, well-known for its small footprint while covering large areas with vegetation. Despite the proven benefits of green façades, their implementation on historical buildings, often located in dense city centres, is limited due to concerns about their impact on material durability and structural integrity, which is currently poorly understood.  Our research investigates how green façades affect the degradation processes of historic building materials, unlocking the co-benefits of greening built heritage for both urban environment and heritage conservation. Therefore, we analyse the interaction of green façades with stone-built heritage in both outdoor and controlled environments to better understand the compatibility of green façades with historic building materials.The findings highlight the potential of green façades to reduce the risk of common degradation processes affecting built heritage. By reducing incoming solar irradiation and moisture accumulation on wall surfaces, green façades can lower the risk on biodeterioration. The presence of green façades also lowers the maximum surface temperatures by providing shade and tempers relative humidity fluctuations, thereby reducing the likelihood of salt crystallisation. Evergreen vegetation enhances resistance to freeze-thaw cycles by maintaining higher minimum surface temperatures through thermal blanketing and reducing moisture accumulation on wall surfaces.This research offers valuable insights in the behaviour of green façades on built heritage, exploring the potential of green façades as a preventive conservation strategy for stone-built heritage. A deeper understanding of this interaction can support the implementation of green façades in urban environments, contributing to mitigate climate stressors while ensuring  the resilience of stone-built heritage.