Food security in cities is an increasing concern due to the impact of climate change and the concentration of world population in cities. Urban agriculture (UA) aims at enhancing food production in urban areas, providing potential environmental advantages by reducing food transport, packaging and waste generation. Among UA alternatives, rooftop greenhouses (RTGs) are greenhouses built on top of urban roofs, in which mainly soil-less agriculture systems are used to produce food. When RTGs are integrated into the metabolism of their buildings, they exchange CO2, energy and water to improve their performance. This alternative is called integrated RTG (i-RTG). This chapter analyses the use of i-RTGs to improve buildings and cities’ metabolism and its particular application in the area of Barcelona. This analysis aims to define a new agricultural system from a technological and sustainability approach focusing on Mediterranean cities. Our research is based on the development and results of the Fertilecity project. A particular experimental analysis was conducted at ICTA’s i-RTG lab located near Barcelona. The main factors of interest are architectural and engineering requirements, urban integration, CO2 emissions management, energy consumption, food production, social integration and rainwater harvesting. This analysis has used different methods such as life cycle assessment (LCA), life cycle costing (LCC) and semi-quantitative assessments. Multiple integrated results were obtained both at the building and city scale. For example, we proved that the i-RTG and its flow exchanges with the building could help to save heating energy, waste generation, water consumption and CO2 emissions.

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