The installation of small and medium-size wind turbines on the rooftops of high buildings has been often suggested by architects and project developers as a potential solution for achieving sustainable energy in building design. In such locations, however, because of the presence of buildings and other adjacent obstructions, wind is normally turbulent, unstable and weak, in terms of direction and speed. The use of wind turbines in the built environment poses challenges to overcome, including energy yield reduction due to lower mean wind speeds in urban areas, and environmental impacts because of their close vicinity to people and property. There is a need to understand the inflow wind conditions for a small wind turbine in the built-environment. A resource assessment of the potential wind turbine site in the built environment can determine the wind characteristics including zones of wind acceleration, recirculation, blocking and channelling. This knowledge is crucial for input into the design process of a small wind turbine to accurately predict blade fatigue loads and ensure that it operates safely, and performs optimally in the environment. Computational Fluid Dynamics (CFD) is a useful method to model wind flows in order to perform a resource assessment for the application of small wind turbines in a manner that requires less time and investment than a measurement campaign. This paper presents the results of research using a CFD code to model wind flows over the roof of a building and assesses the possibility of combining a CFD package with wind atlas software to form a wind energy resource assessment tool for the application of small wind turbines on the roof of a building. Experimentation with the model shows that the results are particularly sensitive to building height and shape, roof shape, wind direction, and turbine installation height and location. The results will be used to help develop a recommended practice of wind resource assessment in the built environment, in an international collaborative effort via the International Energy Agency Task 27. (C) 2013 Elsevier Ltd. All rights reserved.