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With its current housing programme and the development of commercial sites, the Senate of the Free and Hanseatic City of Hamburg is setting new standards. The goal is to build at least 10,000 apartments and develop new commercial areas every year. As a result, the city will become more dense and there will be noticeable effects on the sealing of surfaces, the climate and the amount of open space. Hamburg‘s roofs have a great potential to mitigate these consequences. Hamburg‘s green roof strategy is pursuing the goal of developing new open space on rooftops and of taking advantage of green rooftops as a resource for rainwater storage and climatic comfort. This publication deals with the economic dimensions of green roofs in Hamburg. By looking at the creation of nearly a dozen green roofs in the Hanseatic city, it considers the investment and maintenance costs involved as well as the economic benefits and effects. Everyone involved with the planning of buildings and the cost issues of green roofs is addressed here, and property owners and other decision-makers will find convincing arguments for investing in green roofs. The results of this study show that an investment in green roofs is all the more worthwhile, the earlier and more consistently the topic is made a part of the planning process. The cost of building a green roof amounts to about 1.3% of a building‘s overall construction costs. In multi-storey residential buildings this share can sink to as little as 0.4 % of overall construction costs. When considering life-cycle costs, both black roofs (i.e. without greening) and green roofs have similar costs over a 40-year period.