Discussions about sustainability in architecture have been present since the seventies and today architects are becoming increasingly aware of sustainability in their work and also in communicating these issues, as it is for example seen through exhibitions. In Denmark the discussion about sustainability is mostly focused on the energy consumption during operation, which is also reflected in the building regulations and with the increasing interest in developing passive houses in Denmark where different pilot projects are currently seen. It is within this context that my approach to sustainable architecture is located. This increased focus on energy consumption requires the architect or design team to be able to utilize knowledge about relations between the architectural form and sustainable issues – basically meaning recognizing and using the fact that the technical issues have an impact on the architectural form and using that knowledge to help develop the ideas as seen in the Integrated Design Process. Research shows that it is important to address such issues early in the design process as this is where the impact of decisions are biggest, but it is also seen that the use of the different assessments, especially digital tools are mostly limited to the later stages of the design process and that the tools developed to make these simulations are difficult to use in earlier stages, making it more difficult for architects to utilize them in what could be described, as the crucial early stages of the design process where the initial and intuitive ideas based on previous experiences needs to be tested against the constraints of the brief and legislation. This problem is the point of departure for this PhD that draws on the developments in performance based simulations and Building Information Modeling (BIM) as well as knowledge about the design process. It focuses on how knowledge about the design process and the parameters that affects them in relation with new digital tools can help the design team to address issues about especially energy consumption during the early stages of the design process as research show is important.