Nature Based Solutions - Implementation Models Database

Green roofs

Green Roof Strategy in Hamburg

A short description of the NSB

In response to climate change, one of Hamburg’s objectives is to become greener ‘in the city and on the roofs’. In this regard, Hamburg becomes the first German city to have developed a comprehensive Green Roof Strategy which goal is to plant a total of 100 hectares of green roof surface with plants and flowers in the metropolitan area by 2020. In particular, new residential constructions provide a 44 hectare green roof potential over 5 years and new business constructions provide an additional potential of 66 hectares. The city’s ambition is to have 20% of the green roofs on new buildings to be made available to residents or employees for recreation, in the form of sports fields and parks, or as gardens in shared use by the housing community. By promoting green roofs, the city aims to encourage space efficient leisure areas, improve the city’s rainwater retention capacity, increase biodiversity and reduce extreme temperature effects (i.e. reduction of the heat island effect). The strategy is characterized by a broad instrumental approach covering the range of instruments that are available to the public sector: creating (financial) incentives and providing good examples, communicating about the positive aspects of green roofs and stipulating the greening of rooftops where necessary. These instruments are encapsulated into four action points: 1. Promotion: with an incentive programme the city is providing subsidies until 2020 for each owner (private or public) voluntarily deciding for a green roof. The subsidy will be paid both for refurbishing the roof as well as green roofs in new buildings. 2. Communication and dialogue: the incentive programme is communicated strongly with a city-wide awareness campaign “On Your Roofs, Get Set, Green!”. Using posters, brochures, press articles and internet promotion, the green roof benefits are shared with Hamburg inhabitants and visitors. The greening of public roofs is an excellent promotional example. A full-time communication officer in the Hamburg Ministry of Environment and Energy is in charge of all communication actions. A dialogue is necessary with local politicians, authorities, architects, engineers and economists. 3. Policy and regulation: embed the Green Roof Strategy in urban landscape planning. The Strategy aims to incorporate or enhance green roofs into legally binding instruments such as the Hamburg Building law, the wastewater law, planting regulations on structural systems and land-use plans. Scientific support: the HafenCity university is providing scientific support to the Green Roof Strategy. Scientists at the university are evaluating international findings on green roofs, developing their own recommendations for Hamburg’s green roof construction, and collecting data on water retention and the water management effectiveness of green roofs especially with severe cloudbursts (the latter to convince sceptics that question the green roof’s water retention capacities of large roofs). In fact, the city of Hamburg and the HafenCity university want to develop guidance for the promotion of green roofs which other cities can then use to create their own measures for climate change adaptation. The scientific work is partly funded by the federal government of Germany as a part of the “Measures to Adapt to Climate Change” project.

NBS Implementation context
Location Hamburg (Germany)
Status (from - to) Ongoing (since 2012)
NBS Scale Object (building) Neighbourhood City
NBS Impacts scale Object (building) Neighbourhood City
Urban density/ Soil consumption High (dense city center, etc.)
NBS Typology

NBS Uban Challenges
Climate Issues Climate mitigation
Climate adaptation
Other 0
Urban water management and quality Urban water management and quality
Flood management
Other 0
Air Quality Air quality at district/city scale
Air quality locally
Other 0
Urban Space and Biodiversity Biodiversity
Urban space design
Urban space management
Other 0
Urban Regeneration and Soil Air quality at district/city scale
Other 0
Resource efficiency Food, energy and water
Raw materials
Other 0
Public health and well-being Acustic
Quality of life
Other 0
Environmental justice and social cohesion Environmental Justice: Recognition
Environmental Justice: Procedural Justice
Environmental Justice: Distributional Justice
Environmental Justice: Capabilities
Environmental Justice: Responsibility
Social Cohesion
Other 0
Urban planning and governance Urban planning and form
Governance in planning
Other 0
People Security Control of crimes
Control of extraordinary events
Other 0
Green economy Circular economy
Bioeconomy activities
Direct economic value of NBS
Other 0
NBS Stakeholders & Governance

Hamburg is using a wide range of networks and cooperation with other cities to present itself as a climate action centre at regional, national, European and international level. When developing the incentive programme for green roofs, Hamburg involved other cities in a search for good practice and soliciting for feedback on draft versions of the incentive programme. Based on this interaction with other cities Hamburg decided to have their financial incentive program based on surface and thickness of the green roofs instead of water retention capacity as is the case in most other programs in other cities. This decision led to constructors not only focusing on water retention but also considering other benefits that green roofs may have such as in the context of biodiversity and space utilization. Within the city a stakeholder group is established including housing estate companies, constructors, landscape architects and urban planners. Parallel to the dialogue with other cities this group is involved in defining the incentive programme. The group remained active since and during its bi-annual meetings; the Green Roof Strategy is evaluated by the working group. Finally, Hamburg seeks to raise awareness among the general population about all aspects of climate change and protection. It is systematically building up and expanding the range of easy-access information for the general public.

Initial actors (Leaders) Governments Local government/municipality (Hamburg municipality)
Involved actors Governments Local government/municipality (Hamburg municipality) Semi-government organizations / institutions (HafenCity university, Housing estate companies),Market Private sector ( landscape architects and urban planners)
Ecological scale Local scale green area City scale green networks
Governance model CLUSTER 5: Network Governance Collaborative governance
NBS Financial aspects

Green roofs are an investment with clear future returns: a green roof can create a more pleasant building climate and help to save on heating or cooling costs; it insulates in winter and cools in summer resulting in energy savings varying from 2-44% depending on roof insulation measures separate from the green roof; it also protects the roof water proofing from weathering effects so that green roofs last up to twice as long as conventional flat roofs; plants and substrate on green roofs retain a large amount of rain water, which results in additional savings of 50% on rain water fees for the owner in Hamburg. Hamburg’s Ministry for Environment and Energy invests. €500.000 of its own resources for the implementation of the overall Green Roof Strategy, including efforts in all four areas of activity: promotion/support, dialogue and communication, scientific support, and policy/regulation. It also includes a full-time employee based at the Ministry. In addition, Hamburg’s Ministry for Environment and Energy and the Harbour City University receive €300.000 in federal grants on expenditure basis from the German Ministry of the Environment under a funding programme supporting local activities for the adaptation to climate change. This federal grant on an expenditure basis is used to pay a full time communications officer and a part-time HafenCity researcher for 2-3 years. The Green Roof Strategy’s incentive programme has € 3 million at its disposal until the end of 2019. This amount includes the total remuneration to be provided under the financial incentive programme implemented via Hamburg’s investment and development bank (IFB), which handles all applications and transactions for the Green Roof incentives programme. Of the total € 3 million, € 2 million are sourced from the ‘implementation and service’ budget line of the Ministry responsible for city development and environment; the other € 1 million stems from the innovation fund of the Senate Office. The general approach taken is that financial incentives are available to those that voluntarily decide for a green roof before 2020. After that date Hamburg plans to have green roofs are compulsory by law. In particular, until 2020 building owners can receive subsidies to cover up to 30-60% of construction costs for the greening of their roofs. The multi-functionality of green roofs is reflected in the subsidy system supporting the Green Roof Strategy. A basic subsidy creates incentives to build a basic green roof while additional funding encourages more specialized, sustainable measures. Optional additional subsidies are then provided for: constructing high quality rooftops (root penetration protection and improving load bearing capacity for existing roofs), sustainable urban develop (inner city roofs, a green roof in combination with solar energy generation, and/or space utilization area) and an extra flood prevention by reducing rainwater discharge (improving run-off delay). Private owners with a 20-100sqm green roof who live themselves in the building receive a 40% subsidy on the total construction cost, including materials and contractor, and even up to 60% on material cost if the constructors are trained (professionals) either in architecture, roofing, landscaping or gardening thus ensuring high quality in construction. For all other owners with a >20sqm green roof - commercial, private, public - an owner receives a basic financial incentive ranging from € 14/sqm meters (on 8cm substrate soil thickness) to € 56/sqm (on 50cm substrate soil thickness) net vegetation area (maximum can be achieved via additional subsidy of € 1/sqm of net vegetation area per additional centimetre substrate soil thickness (rooting layer thickness)).

Global (estimated) cost of the project 1M€- 5M€
Financing mechanism CLUSTER 2: Financial institutions Municipal Green Bonds
NBS Business Models Archetype
Technological Substitute with renewables and natural processes
Social Adopt a stewardship role
Organisational Re-purpose the business for society/environment Develop scale-up solutions
NBS Success and limiting factors
Process enablers
Knowledge Generation of evidence Research on benefits Research on cost effectiveness, Information accessibility and sharing Knowledge platforms, Awareness Climate Change
Governance Co-creation and participation Involvement of urban government Tools to build a common vision
Economy De-risking Public de-risking strategies, Government support Provisioning of incentives to attract private investment
Process inibitors
Knowledge Uncertainty Operational unknown Performance unknown
Governance Participation and awareness Perception Lack of participation
Economy Risk perception
IM Keywords
  • Collaborative governance

  • Local scale green area

  • City scale green networks

  • Municipal Green Bonds

  • Substitute with renewables and natural processes

  • Adopt a stewardship role

  • Re-purpose the business for society/environment

  • Develop scale-up solutions

References 18/Session4/Bornholdt_-_Green_roof_strategy_Hamburg.pdf Sustainable Built Environment Conference 2016 in Hamburg : Strategies, Stakeholders, Success factors, 7th - 11th March 2016 ; Conference Proceedings. Available at: