The support team of the 'Covenant of Mayors - Demonstration Projects' summarized the experience of the demonstration projects and identified the most frequent and common defects in different thematic sectors. This guideline aims at all technical experts who are involved in the construction works process e.g. construction companies, site supervisors, project managers, etc. The guide provides basic information on the technical defects but not limit all possible deviations from the suggested technical solutions, required standards and installation practices.