The Directive 2002/91/EC of the European Parliament requires member states to calculate the energy performance of buildings with the overall goal of reducing their energy consumption. Existing tools for the calculation of building energy efficiency provide good results in calculating the energy level of a given building but fail to support the user in the subsequent step – the identification of strategies on how to improve the building’s energy efficiency. The manual identification of the optimal building configuration is not only tedious but very costly for the user and, therefore, exacerbate improving building energy efficiency. This paper gives an overview of a new decision support system called SEMERGY that enables stakeholders to efficiently identify potential building configurations with regard to (i) environmental impact, (ii) energy consumption for operating the building, (iii) energy used for the production and distribution of building components, (iv) financial constraints, (v) building component compatibility, and (vi) legal requirements. The provision of computational support for the buildings’ design phase benefits the AEC (Architecture, Engineering, and Construction) stakeholders in view of cost reduction, energy efficiency, and occupants’ comfort and productivity and, thus, facilitates the design of energy efficient buildings.