Building-integrated agriculture: Are we shifting environmental impacts? An environmental assessment and structural improvement of urban greenhouses

Urban and building systems are awash with materials. The incorporation of green infrastructure such as integrated rooftop greenhouses (iRTGs) has the potential to contribute to buildings’ and cities’ circularity. However, its greater sophistication than conventional agriculture (CA) could lead to a shift in environmental impacts. One of the key elements for greenhouse building-integrated agriculture (BIA) and CA to achieve high levels of environmental performance is their structural design, which largely impacts the economic and environmental life-cycle costs (by up to 63%). In this context, the study assessed iRTGs life-cycle material and energy flows and their environmental burdens at structural level (m^-2y^-1) within life cycle assessment (LCA), based on a case study in Barcelona. A structural assessment following European standards allowed the identification of key design factors to minimize the environmental impacts of RTGs’ structure within improvement scenarios. The assessment revealed that a steel structure in a business-as-usual (BAU) scenario contributed from 31.5 to 67.3% of the impact categories analyzed, followed by the polycarbonate covering material (from 21.8 to 45.9%). The key design factors responsible for these environmental impacts were ground height, ventilation design, building integration and urban location. The improvement scenarios compensated for additional steel inputs by up to 35.9% and decreased environmental impacts that might occur in the BIA context by 24.1% compared with the BAU scenario. The assessment also revealed that urban environments do not imply shifting environmental impacts per se, as greenhouse BIA structures can benefit from their advantageous characteristics or be compensated by optimized greenhouse structures.