Today, simulation tools are widely used to design buildings because their energy performance is increasing. Simulation is used at different stages to predict the building's energy performance and to improve the thermal comfort of its occupants, but also to reduce the environmental impact of the building over its whole life cycle and lower the cost of construction and operation. Simulation has become an essential decision support tool, but its reliability should not be overlooked. It is important to evaluate the reliability of simulation and measurement as well as uncertainty so as to improve building design. This work aimed to evaluate and order the uncertainty of the simulation results during the design process. A three-step methodology was developed to determine influential parameters in the building's energy performance and to identify the influence of parameter uncertainty on the building performance. This methodology was applied at the INCAS experimental platform of the French National Institute of Solar Energy (INES) in Le-Bourget-du-Lac to identify and measure the uncertainty in a simulation hypothesis. The method can be used during the entire design process of a building, from preliminary sketches to operating phase. (C) 2012 Elsevier B.V. All rights reserved.