Case studies and guidelines for energy efficient communities : a guidebook on successful urban energy planning ; [IEA EBC Annex 51 Energy Efficient Communities: Case Studies and Strategic Guidance for Urban Decision Makers ] What are the barriers that prevent us from achieving our long term energy goals in cities or more generally in our built environment This Annex 51 wants to give answers based on the evaluation of over 20 Case Studies carried out within the 10 participating countries and elaborated in the form of this guidebook on successful local energy planning.