Green roofs in Vienna, Austria | Natural Water Retention Measures

General

National Id

Austria_03

Site name

City of Vienna

Summary

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?

In-depth

The in-depth description of the case study

cs-at-2-final_version.pdf

NUTS Code

Wien

RBD code

AT1000

Transboundary

Data provider

Sabine Tutte, ACTeon

Source(s)

„Logisch gedacht ist ökologisch bedacht" Ein Leitfaden für die Dachbegrünung

dachgrün

NWRM(s) implemented in the case study

Green Roofs

Longitude

16.373819

Latitude

48.208174

Site information

Climate zone

cool temperate dry

Mean rainfall

500

Mean rainfall unit

mm/year

Average temperature

11,5

Mean runoff

300

Mean runoff unit

450 - 600 mm

Type

Case Study Info

Average slope range

1-20%

Vegetation class

Depends on the individual project for intensive green roofs. Extensive green roofs consist of mosses and grass.

Monitoring maintenance

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

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.

Design & implementations

Application scale

City

Installation date

2003

Lifespan

Performance timescale

< 1 year

Area (ha)

1,6

Area subject to Land use change or Management/Practice change (ha)

1,6

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.

Constraints

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 "green roof" to find information. The public don'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	Name	Comments
Other	Other	1. Wiener Umweltschutzabteilung (city†™s authority for environmental protection)	Initiation of the project, subsidies for house owners
Other	Other	2. die umweltberatung	Facility of Vienna†™s adult education center. Consulting office for a near-natural life style. Publicity and information material
	Other	3. Verband fí¼r Bauwerksbegrí¼nung (Association for greening buildings)	Austrian section of the European Federation of Green Roof Associations
	Other		Publicity, implementation of green roofs, certification system for green roofs, Creation of technical standards

Lessons, risks, implications...

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

Financing type	Comments
Local funds	Subsidies of the city of Vienna.
Private funds	Fortune of the house owner.

Barrier

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
Other	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

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.	View

Policy, general governance and design targets

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

Socio-economic

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.

Biophysical impacts

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