The HarWin (Harvesting solar energy with multifunctional glass-polymer windows) FP7 project focuses on the development of innovative windows and their integration in buildings. These innovative windows aim at improving significantly the energy efficiency of windows and buildings and performing environmentally well on a life cycle base. The improvements are based on reduced material usage and weight, reduced thermal conductivity and energy consumption and hence, reduced environmental life cycle impacts. The innovation lays in the integration in the window of intelligent phase changing materials and novel glass-polymer composites with wavelength management capability. As windows are multi-component and multi-functional systems, an appropriate Life Cycle Environmental Assessment (LCEA) method is needed. Based on an evaluation of best available methods and tools for LCEA an adapted method for windows is proposed. This paper furthermore discusses how the method proposed can be used efficiently during the development process of the innovative window.