The paper numerically models the thermal behaviors of multi-layer living wall. The aim of this study is to identify the most efficient wall configuration according to indoor and outdoor climate conditions by using a new simulation tool developed using Matlab and Simulink. The simulation tool is created to evaluate both conventional facade systems and those integrated with phase change materials (PCMs). The model is validated using experimental results from the literature for the multi-layer PCM-enhanced wall. The ventilated cavity wall model is also verified using TRNSYS "TYPE36", a well validated and respected model for simulating thermal storage wall. The location within the wall assembly, the orientation and the optimal thermal properties of PCM's are then analyzed using the tool. The validated multi-layer wall system is further integrated with a full-scale building model with a genetic algorithm optimization method. The results show that an optimized active multi-layer living wall system can allow 27-38% of reduced heating energy consumption while avoiding thermal discomfort. (C) 2015 Elsevier B.V. All rights reserved.