Recent findings suggest that rooftop greenhouses could be more efficient when combined with waste streams in buildings, but there is a gap in quantification of the combined performance of building integrated greenhouses. This paper addresses this deficit for school buildings in London, UK, where urban agriculture is of increasing interest. A building energy simulation (BES) of an archetype school building is developed in EnergyPlus and co-simulated with a validated greenhouse energy simulator (GES). The performance of different greenhouse-building coupling configurations is evaluated to estimate the potential for crop growth, heat recovery and reduction in ventilation demand, through a sensitivity analysis and parametric study. Our results show that a 250m2 greenhouse on the top floor of the school could produce 6t lettuce with half the energy demand of the same standalone greenhouse. Trade-offs across increase in humidity, yields, and energy efficiency indicate the importance of modelling to ensure optimal designs.