AbstractGreen roofs are becoming common practice in building new public buildings and are considered the roofs for the future since they address the issue of energy and environment simultaneously, providing social, environmental and economic benefits. Despite these benefits, retrofitting an existing building with a green roof is not widely practiced. Undergoing such a project is no small task since it requires a thorough investigation of existing building's constraints, functional, material, and technological to even begin considering design options. Therefore, this process requires specific, case-sensitive approach, especially with the aim of improving the building’s energy performance. This paper presents a methodological approach and design proposals of a green roof retrofit project, through a case study of Belgrade’s “City Housing” building. This retrofit project presents an interesting research topic since it incorporates three distinct roofs, of all of different types, different ways of accessibility and levels of privacy, varying top-to-bottom from a simple extensive roof through a semi-public semi/intensive roof garden to a ground-level public park with trees and intensive vegetation. Also, since this building provides socially significant services, it is frequently visited by general public which presents a potential for introducing educational and demonstration elements in the retrofit project, not only the functional and technological ones. That way, this project can be a showcase example, promoting greening the roofs of Belgrade’s existing public buildings as a way of improving their energy performance.