The authors believe that to realize the potential offered by building simulation software, a new breed of DBSs (Decision Based Systems) is needed coupling existing simulation engines with formal optimisation methods through neutral data standards (BPM – building product models) for seamless integration. This paper first elaborates on the previous attempts at solving integration issues related to the design process and simulation; also attempts at finding the limitations. Secondly, formulation of design problems as optimisation has been discussed with reference to the different stages of design. Thirdly, for effective integration of activities among stakeholders and processes, the use of client/ server oriented building product model has been proposed to overcome the limitations of file-based prototypes. Analysis and discussions based on the above aspects form as justification for ArDOT, an Architectural Design Optimisation Tool under development at IRUSE, National University of Ireland, Cork. Combining all three aspects into one makes ArDOT unique, which is essentially an enhanced decision making tool for the design of energy efficient buildings.