This paper analyses the current state of simulations and proposes ways to reduce the costs and to increase the reliability of building performance analysis. Functions in machine-code can be used to generate automatically simulation models for numerous simulation environments. Simulations models are proposed which adapt their accuracy and can therefore be used from very early up to late stages of the planning process. BIM based on semantic technologies can provide more flexibility and make it easier to find the right components. A semantic international product data base is planned to make it easier for practitioners to identify most suitable product.