A major concern for sustainable development is urban systems energy consumption. A possible way to gain additional whole system energy efficiencies is to integrate rooftop greenhouses (iRTG) on unoccupied roofs. This work presents actual environmental data (2015–2018) and calibrated energy modelling results to analyze the energy symbiosis between an iRTG and the host building. Simulation results illustrate that annually 98 kWh/m2 of heating energy is passively recovered (84% during night time) from the building by the iRTG. Conversely the iRTG insulating capacity resulted in annual energy saving of 35 kWh/m2 for the host building (equal to 4% of the building’s annual energy needs). When combined an overall 128 kWh/m2 of net energy savings and 45.6 kg CO2 eq/m2 of savings are realised via iRTG. On average, iRTG daytime temperatures can be 5.1 °C warmer (summer) and -4.3 °C cooler (winter) than the building. This presents major potentials for recovery and exchange of heating and cooling energy flows through integrating heating and ventilation air conditioning systems of the building and iRTG. Hence, iRTGs can provide a source of renewable energy as well as a sink for building exhaust air to improve energy efficiencies of urban built environment and urban agriculture. The authors are grateful to the Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya for the award of a research scholarship (FI-DGR 2018) to Joan Muñoz-Liesa; to the Universitat Autònoma de Barcelona for the award of a research scholarship (PIF-2017) to Martí Rufí-Salís; to the Spanish Ministry of Economy and Competitiveness (MINECO) for the financial support to the research project Fertilectiy II “Integrated rooftop greenhouses: energy, waste and CO2 symbiosis with the building. Towards foods security in a circular economy” (CTM2016-75772-C3-1-R; CTM2016-75772-C3-2-R). Authors also acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities, through the “María de Maeztu” program for Units of Excellence (MDM-2015-0552). This work was additionally enabled by the Càtedra JG Ingenieros – Universitat Politècnica de Catalunya and the UK Engineering and Physical Sciences Research Council grand EP/P001173/1. Authors also thank Oriol Baeza, Prof. Xavier Gabarrell, Prof. Joan Rieradevall and the ICTA-UAB staff for their very valuable supporting advise and help. Peer Reviewed