Green walls and green roofs are innovative construction technologies involving the use environmentally friendly materials. In addition to their aesthetical and environmental benefits, green walls have significant thermal effects on buildings and heat islands within high-density urban areas. In this paper, we study the impact of an innovative green wall system on building energy performance. These green walls have specific composition and particular geometry that can lead to higher thermal performances and therefore more significant impact on building energy performance. The development, validation and prior integration of a hygrothermal green wall model in a transient building simulation tool make possible the assessment of the energy performance of buildings when covered by green walls. The used model was adapted to be the particular forms and composition of the studied green walls. In parallel, this type of green walls has been installed on a one tenth building mockup to be experimented. The aim of the experiment is to measure the thermal effects and to calibrate some parameters of the numerical model. The results highlight the thermal benefits of this kind of green walls in summer condition. They reduce annual energy demand of building up to 37% for hot climates.