Hamburg green roof strategy. To reach the city´s target of planting a total of 100 hectares of green roofs, this program offers financial incentives of up to 60% of the investments in installation costs. Building owners adhere voluntarily to the program. Costs in this program are divided by the city and building owners, who benefit from not only the reimbursement given by the city but also lower maintenance costs, reduced energy bills (thanks to the insulation effect provided by green roofs) and abatements in rainwater fees. From the city´s perspective, the water retention properties of green roofs are expected to have a positive impact on the costs related to rainwater drainage.