Green Building rating systems are the main vehicles for commercial application of ecologically sustainable design for buildings. Using less materials, modular design for deconstruction, long life structure, using recoverable materials are emerging concepts to reduce environmental impacts and increase the resource and economic efficiency of buildings. It has been argued that because of recent emergence of these concepts, Green Building rating systems do not fairly recognise the environmental benefits gained. This paper quantifies the impacts of the building reuse concept on the environment and the Green Building rating system scores and compares this with the energy category. It was found that lifecycle embodied greenhouse gas emission of approximately 20 kg CO 2-e/m 2/annum could be saved, if 80% of the office building components (structure, façade, wall, floor and roof) were reused in Australia. A second finding was that the current BREEAM 2008 and LEED 2009 tools do not provide fair recognition of the potential lifecycle embodied greenhouse gas emission reduction of building reuse compared to operational greenhouse gas emission reduction.