National Id
Site name
City of Vienna
Since 2003 the city of Vienna supports financially the implementation of green roofs with 8-25 € per m². The maximum subsidy can be 2200 €. Until 2010 16000 m² roof were transformed and 150 000 € invested.
Light or indepth?
The in-depth description of the case study
RBD code
Data provider
Sabine Tutte, ACTeon
NWRM(s) implemented in the case study
Climate zone
cool temperate dry
Mean rainfall
Mean rainfall unit
Average temperature
Mean runoff
Mean runoff unit
450 - 600 mm
Case Study Info
Average slope range
Vegetation class
Depends on the individual project for intensive green roofs. Extensive green roofs consist of mosses and grass.
Monitoring impacts effects
Monitoring location
Edge of Field/Plot
Monitoring parameters
During the project the retained amount of rain water was measured. Moreover, the pollutants removal was documented as well as the composition of plant and animal population. The temperature was recorded in the surroundings of the green roofs
Performance impact estimation method
Catchment outlet
Performance impact estimation information
Collection of the runoff from a green roof and a traditional roof during a precipitation event.
Application scale
Installation date
Performance timescale
< 1 year
Area (ha)
Area subject to Land use change or Management/Practice change (ha)
Design capacity description
The water retention capacity of a green roof depends on several factors such as: intensity of a precipitation event, annual precipitation, and amount of precipitation events. Moreover the individual design of the roof (plant composition, soil type and thickness of soil layer) determines the water retention capacity.
Green roofs can be installed up to a slope of less than 45°. Intensive green roofs require an adaptation of the statics of the roof.
Favourable preconditions
Lack of land, increasing sealing and thus in creasing amount of rain water.
Contractural arrangements
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Design consultation activity
Activity stage Key issues Name Comments
Implementation phase
in general the publicity for the project is not sufficient. It is criticised that people already have to know the term &quot;green roof&quot; to find information. The public don&#039;t know about the manifold advantages of green roofs. It is just reduced to a garden
information material
Design land use change
Land use change type
Design authority
Authority type Role Responsibility Name Comments
1. Wiener Umweltschutzabteilung (city†™s authority for environmental protection)
Initiation of the project, subsidies for house owners
2. die umweltberatung
Facility of Vienna†™s adult education center. Consulting office for a near-natural life style. Publicity and information material
3. Verband fí¼r Bauwerksbegrí¼nung (Association for greening buildings)
Austrian section of the European Federation of Green Roof Associations
Publicity, implementation of green roofs, certification system for green roofs, Creation of technical standards
Key lessons
Green Roofs are able to provide a lot of benefits such as climate regulation, water retention, or "island habitats" for plants and animals. These advantages have to be communicated more intensively to the public.
Green roofs cause only little additional costs compared to a traditional flat roof. These costs are often compensated by the longer lifespan of the roof and energy savings
Success factor(s)
Success factor type Success factor role Comments
Attitude of relevant stakeholders
secondary factor

Many firms specialised on the construction of green roofs. They organised together with architects on national and european level to support the implementation of green roofs

Attitude of decision makers
main factor

Adaptation of the building code, information of the public.

Existing technical standards
main factor

Legal framework for the construction of green roof and liabilities of firms, architectures and house owners.

Financing possibilities
secondary factor

The local authorities support the construction of green roofs with 8-25€/m² and with a maximum of 2200€.

Financing type Comments
Local funds
Subsidies of the city of Vienna.
Private funds
Fortune of the house owner.
Barrier type Barrier role Comments
Expected maintenance needs
main barrier
House owners are often afraid that the installation of a green roof is combined with high costs. However this is not the case for extensive green roofs and the additional costs are often balanced by energy savings and the longer life span of the roof
main barrier
Lack of communication. Citizens are not sufficiently informed about the many advantages of green roofs. The majority thinks, it is just another kind of garden
Missing regulatory support
secondary barrier
Architects/planners are liable for 30 years for the construction of a green roof. Since there is the risk that they aren't leakproof, architects partly refuse to consider green roofs in their plannings
Driver type Driver role Comments
Legal obligations
main driver
Technical standard for building green roofs. The technical code of Vienna gives the legal framework for green buildings.
Availability of subsidies
main driver
The local authorities support the construction of green roofs with 8-25€/m² and with a maximum of 2200€.
Organisation committed to it
main driver
Both organisations inform the public about the advantages of green roofs. Moreover the Verband für Bauwerksbegrünung is composed of planers, architectures and specialised firms. They developed a certification system for green roofs and consult house owners and planners.
Financing share
Financing share type Share Comments
Private funds
This depends on the individual roof.
Policy description
The more people are moving to cities, the more surface needs to be sealed and green areas are disappearing. In Austria 15 to 25 ha of usable ground get sealed every day. However green areas are important for recreation, mood lifting and health. Green roofs are a possibility to regain green areas and offer a manifold of advantages. A cadastre of potential roofs was developed. It proved that 20% of Vienna's roofs could become green roofs.
Policy target
Target purpose
Runoff control
Peak-flow reduction
Groundwater Recharge
Pollutants Removal
Improved Biodiversity
Oher Societal Benefits
Policy pressure
Pressure directive Relevant pressure
Policy area
Policy area type Policy area focus Name Comments
Policy impact
Impact directive Relevant impact
Policy wider plan
Wider plan type Wider plan focus Name Comments
Policy requirement directive
Requirement directive Specification
Direct benefits information
Energy savings and a longer lifespan compared to a traditional flat roof. Savings meet the additional costs of implementation and maintenance.
Costs investment information
0,31 Euros/m2 for extensive green roof with a slope less than 10° on a multi-family house with 7 floors.
Costs capital information
0,31 Euros/m2 for the implementation of the green roof, without potetntial adaptation of the roof's statics.
Costs land acquisition unit
€ (total value)
Costs operation maintenance
0,19 Euros/m2 for an inspection twice a year, removal of growing trees, cutting grass.
Costs total information
0,5 Euros/m2
Compensations annual information
Financial support given by the city's authorities only once: 8-25€/m² up to 2200€.
Ecosystem improved biodiversity
Information on Ecosystem improved biodiversity
Green roofs can act as bridge between different habitats and populations. Birds find there material for building nests. Some observations even document that some ground breeding species take green roofs as new habitat. Insects find new food/habitat resources with the green roofs.
Ecosystem provisioning services
Information on Ecosystem provisioning services
Intensive green roofs can serve as garden and deliver fruits and vegetables.
Ecosystem impact climate regulation
Impact on GHGs (net emissions and storage) including soil carbon
Information on Ecosystem impact climate regulation
Vegetation stores CO² by photosynthesis. The increased evapotranspiration enhance dust adsorption, leads to an ambient temperature in the underlying rooms and takes up the summer heat of a city.
Information on retained water
The microclimate improves. That means: the increased evapotranspiration leads to an ambient temperature. The underlying rooms profit from this "natural air condition".
Water quality overall improvements
Positive impact-WQ improvement
Information on Water quality overall improvements
Rain water is filtered by the vegetation.
Information on Water quality Improvements (N)
Reduction by more than 90%.
Information on Water quality Improvements (Cu)
Reduction by more than 90%.
Information on Water quality Improvements (Zn)
Reduction by 16%.
Soil quality overall soil improvements
Not relevant for this application