This paper describes the knowledge on building assessment, from the policy-maker standpoint. More specifically, the paper describes the key approaches to assess technological and non-technological potentials, then it reviews the metrics for setting political ambitions to explore these opportunities; further, it studies barriers to realisation of these ambitions and policies to overcome them. Finally, it reviews the approaches to policy impact evaluation and ways to diagnose the reason for a particular level of policy performance. The paper concludes with an identification of gaps in knowledge which constrain successful realisation of the energy efficiency potential in buildings.