Buildings have direct and indirect impacts on the CO2 emissions. This paper presents a study on the impact of wall systems and cladding materials on the CO2 emissions and aims to analyse the performance of those systems in order to provide designers with reliable technical data. The studied systems include stucco, masonry veneer, aluminium siding, vinyl siding and the exterior insulation and finish systems (EIFS). To evaluate the economic performance, environmental performance and embodied energy, green building modelling system was used, while to estimate the impact of operational energy, a simulation model was first used and then simple bottom-up model constructed. A sensitivity analysis was conducted in order to determine the relative influence of each system on a representative educational building. It was found that some cladding materials reduce the direct CO2 emissions, but provide a moderate reduction in terms of operational energy, and vice versa. Others positively impact the embodied energy and environmental performance and can optimise the operational energy performance. Therefore, a careful evaluation should be carried out in selecting wall cladding systems and finishing materials in order to reduce the CO2 emissions effectively. (C) 2009 Elsevier Ltd. All rights reserved.