Green fagades and walls greatly contribute to reducing solar gains and dispersion through the building envelope. This implies a lower energy load for both heating and cooling and the mitigation of thermal conditions in outdoor areas. Despite this, more studies are needed regarding the influence of these systems on the thermal behaviour of insulated fa ades. In this manuscript, we report the results of experimental research carried out on a vertical green wall in a continental Mediterranean climate. The main goal of the research is to establish a thickness above which the behaviour of the green facade becomes isothermal and its performance do not improve. To this end, we analyze and evaluate the effect of insulation thickness on the energy performance of a green wall using a new methodology called green faade optimization (GFO). Comparing the simulations to experimental data, collected in a full-scale experimental box during the summers of 2011 and 2012, allowed the model to be validated. The results show that a green wall acts as a passive cooling system when the faade is moderately insulated, up to an insulation thickness of 9 cm, above which more insulation becomes redundant and inefficient. (C) 2017 Elsevier B.V. All rights reserved.