In the light of increasing energy prices and declining fossil resources, energy efficient design is an important aspect of building construction planning. Software application BauOptimizer supports the planner in calculating, monitoring and optimizing both energy demand and cost aspects from the very first planning phase until the final architecture improving economic and ecologic properties of the building design. Furthermore the number of required planning phases is reduced as normative limits are kept considered right from the beginning. Costs for building hull creation and expected energy costs for the next decades are linked together as efficiency measure and all planning variants applicable for a concrete construction area are automatically evaluated, covering different material at different thicknesses, the window ratio, roof modality, and many more aspects. Within this full construction variants coverage, the planner optimizes his architectural design and building physics aspect to approximate efficiency optimum with respect to economy and ecology.