The ICTA-ICP Rooftop Greenhouse Lab (RTG-Lab) is a research-oriented RTG situated in the UAB Campus (Bellaterra, Barcelona). In contrast to current RTGs, the RTG-Lab integrates energy, water and CO2 flows into the building’s metabolism. This integrated RTG (i-RTG) is an eco-innovative concept that will enhance the sustainability of both systems involved while producing high-value crops and maintaining indoor comfort in buildings with lower energy inputs. The RTG-Lab, within the Fertilecity project, aims to demonstrate the feasibility of producing vegetables in i-RTGs in the Mediterranean context and to quantify the environmental and economic performance of the metabolic integration between the greenhouse and the building. To do that, experimental crops (lettuce and tomato) in soil-less culture systems (perlite) will start on Fall 2014. Preliminary data of the metabolic integration is described in this contribution. First, the residual heat from the building will be introduced in the greenhouse to maintain crop temperatures. Moreover, the airflow from the building will help the ventilation of the greenhouse in hot episodes. Second, the rainwater collected in the rooftop of the building will be used for the irrigation of the crop, leading into a 100% water self-sufficient crop. Third, the airflow from the building has a higher CO2 concentration than the greenhouse air. This CO2 will be used by the crop when supplied to the greenhouse, as in current CO2-injection techniques in industrial horticulture.