In Europe, the concept is that buildings should use less and less energy in the future. The clocks appear to go backwards in only one respect: most concrete ceiling slabs today are considerably thicker than 20 years ago, technical building systems are becoming ever more complex and insulation itself is becoming thicker. The energy required for their manufacture is thus also increasing. The embodied energy used for manufacturing, maintaining, repairing and disposal is becoming an increasingly important factor in buildings. In the case of passive houses, this can account for more than a third of the total primary energy that a building needs in the course of 50 years. In zero-energy buildings, only the embodied energy has a negative effect on the energy balance. This poses new questions about building planning. How can the use of energy and resources be minimised as early as the construction phase? And what reliable decision-making criteria are there for the selection of ecological materials?