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Green Roofs of Plenty in Stuttgart, Germany

A visit with International Green Roof Association (IGRA) Director Wolfgang Ansel

After visiting Stephan Brenneisen in Basel Switzerland, I traveled to Stuttgart, Germany where I met with International Green Roof Association (IGRA) Director Wolfgang Ansel. Wolfgang lives with his family on an old farm property in a Stuttgart suburb; he's lived there his entire life and his ancestors settled the land some 400 years ago! Wolfgang welcomed me into his home and quite graciously spent a day taking me to a number of green roofs. It was a great opportunity to learn about the policies and programs that promote green roofs in Germany.

Wolfgang Ansel with Stuttgart, Germany in view.

The emergence of modern green roof design and installation in Germany has its origins in the growth of the environmental movement in the 1970s. Today some estimate that about 10% of all German roofs now have green roofs. Stuttgart has been a clear leader in implementing policies encouraging and requiring green roofs since 1986. As Wolfgang explained, the legal framework for this progress was established in the Federal Nature Protection Law and Federal Building Codes. Both create the mandate for environmental improvement and mitigation for which green roofs are one solution. However, a mix of regulatory policies and incentive programs at the municipal level that has been instrumental in fostering the green roof building boom in Stuttgart and elsewhere in Germany.

Wolfgang summarized this mix of policies as follows:

1. Direct financial subsidies by government in the form of start-up grants can amount to 10-20 euros per square meter of green roof. The grants motivate some owners of private or commercial properties to voluntarily install green roofs. These grants must be value-added and not fund green-roofs for which are required as a condition of development. In recent years funding for green roofs have also come from federal funding to reduce CO2 emissions and reduce energy consumption, two of the benefits of green roofs. In Stuttgart, city staff provide free consultation for green roof development and interest and demand is high; in May of 2009 there were funding applications pending for 4,000 m² of green roof.

2. Reduced stromwater fees are provided to those who install a green roof. Depending on the prevailing fee, this can amount to savings of 1 euro per square foot of green roof. Over an average 40-year lifespan of a green roof, this in many cases this is enough to pay original installation costs.

3. The Federal Nature Protection Law includes provisions for ecological compensation that require that new greenfield development replace greenspace and associated environmental values lost to development. Ecoroofs are often a cheaper option than greenspace protection in the hinterlands and provides multiple social, ecological, and financial benefits in greater proximity to the original environmental impacts. Yet some local governments have set up banking or eco account systems similar to wetland mitigation banking wherein ecological compensation credits for green roofs can be pooled and leveraged for greater public benefit.

4. Local regulations in many larger German cities like Stuttgart require the installation of green roofs as a condition of development where technically feasible. In most cases that means roof with a gabled roof angle of less than 20 degrees. These requirements apply to a lesser and greater degree to current building construction and to larger urban planning zones. Stuttgart has provisions for new urban planning areas that call for over 1.5 million square meters of green roof.

Wolfgang showed me an example a new urban planning area at our first stop, a residential subdivision were many if not most rooftops were green. Unfortunately the vast majority of these roofs were out of view from the street. So the photos below show carports and outbuildings where the green roofs were visible. However as we toured around the subdivision, one could see tufts of grass and other vegetation emerging from just over the roofline of all the larger buildings with gently sloped roofs.


Wolfgang emphasized that a mix of tools- regulatory and non-regulatory- has been key to Stuttgart's success. The number and size of green roofs in Stuttgart grew quite slowly until the 1990s when planning mandates and regulations were added to enhanced incentive programs.

The impact of this policy change was illustrated in our second stop at a solitary hill outside of Stuttgart rising some 400 feet above the valley floor. The hill was partially forested and topped with a single tri-blade wind turbine typical of those found throughout Northern Europe. Apparently the hill was a former landfill some time ago but had since become a popular local natural area (I could not help to be reminded of Portland’s own St. Johns Landfill that now provides important open meadow habitat for Streaked Horned Larks and Meadowlarks). The decision to build the wind turbine on this former-landfill had been quite controversial because some people felt it- the wind turbine- would despoil the natural landscape. It was oddly comforting to know that Europeans are also capable of mistaking an artifact of human history for the product of nature.

But Wolfgang took me to the top of the hill to illustrate a different point relating to the more intentional cultivation of nature by humans. From the top of the hill we looked south across a large commercial- industrial area flanked by farmland, arterial streets, and rail lines. With the sun shining in our faces, the mix of warehouses and office buildings initially looked like any other you might see in the United States excepting for the speedy commuter rail that served the area. But looking closer, I could see that all the buildings to west of a certain point and a good portion of the newer ones to the east were topped with red and green-tinged roofs. At closer inspection I could see- to my astonishment- that these were green roofs.

A view from the hilltop outside of Stuttgart.

Wolfgang pointed out that the older buildings to the east that lacked green roofs were built before the adoption of Stuttgart’s requirement that all new buildings with roof angles less than 20 degrees install green roofs. Most the others had been built with green roofs since.


The view from the hill in Stuttgart is an amazing demonstration of the local governments success in implementing green roofs. Germany clearly has exceeded spectacularly in increasing the volume of green roofs in their urban landscapes.

To his credit, Wolfgang did not just show me all the success stories. He also shared a site, at our next stop, where project design and installation fell far short of its original aspirations. The public parking garage we visited (the name and location I won’t reveal) had originally been plan to compensate for development of some local farmland with commitments to build an expansive, intensive green roof that could also serve as a public greenspace. However the project faced huge cost over-runs and eventually gave way to a more immediately lucrative plan to build photovoltaics that displaced much of the roof vegetation. Unfortunately the lack of clearly defined goals and cost over-runs, led to a poor design and the needless trade-off between solar power and a fully functional green roof. The project stands as an monument of how not to plan and build a green roof, so in that sense is not entirely useless. Also while touring the site, we spotted a couple of peregrine falcons:).

Peregrine falcon near Stuttgart, Germany.

By all indications, Germany has demonstrated clear success in building an astounding quantity of green roofs, to date and making green roof design and installation a mainstream building practice. However, it seemed less clear that Germany has made the same progress of Basel or London in promoting biodiverse green roofs. Wolfgang admitted that the lack of clear design criteria and uncertainties about installation and maintenance costs held back the widespread development of biodiverse green roofs in Germany. Also, despite the benefits of making green roofs a professional and mainstream building practice, I did not get the impression that Stuttgart was encouraging ordinary citizens to install green roofs on their homes, carports, and out buildings, at least as energetically as I witnessed in London.

That said, our last stop at Naturschutzzentrum Schopflocher contradicted both these initial impressions.

Naturschutzzentrum Schopflocher is the Nature Center for the Swabian Alb Biosphere Reserve located outside of Stuttgart. There we met the director Dr. Wolfgang Wohnhas and toured two green roofs on site, including a marvelous 13 year-old roof atop of an equipment shed, built with volunteers as a demonstration.

Wolfgang and me on the green roof at Naturschutzzentrum Schopflocher.

Wolfgang Wohnhas and Wolfgang Ansel.

The equipment shed roof was really quite lovely even in mid-December, having a diversity of mosses, lichens, herbaceous plants, forbes, and wildflowers. The colorful photo below was taken in the spring. Both Wolfgangs insisted that the roof is really as stunningly colorful and diverse as portrayed here. How many homeowners in Portland would love to have one of these on their property?


All in all, the visit with Wolfgang Ansel in Stuttgart left me impressed by what is achievable in terms of green roof development with the right set of public policies. Portland and other cities in the United States have a lot to learn from the German experience in promoting the development of green roofs.

Previous posts:

Some green & gritty rooftops in Basel, Switzerland

London's Dusty Gedge and Ecoroofs for Biodiversity

Posted by jim.labbe 08:09 Archived in Germany Comments (0)

Some green & gritty rooftops in Basel, Switzerland

Stephan Brenneisen and Basel's Biodiverse green roofs

In September I visited Dusty Gedge, toured some green roofs in London, and learned about the latest in U.K. designs that promote biodiversity. December 8 thru 11, I visited Stephan Brenneisen in Basel Switzerland and Wolfgang Ansel in Stuttgart Germany.

Basel and Stuttgart are two of the green roof hotbeds on the European continent. To put this into perspective here's some estimated green roof areas in Basel, Stuttgart, Dusseldorf (another green roof rich city), London, Portland, and Chicago:

Basel, Switzerland: ~700,000 m² in 2007 (estimated by Stephan Brenneisen).
Dusseldorf, Germany: 730,000 m² in 2008 (according to a detailed inventory)
Stuttegart, Germany: >1,000,000 in 2009 (entire metro-area estimated by Wolfgang Ansel)
London, England: 500,000 m² (estimated by Dusty Gedge)
Portland Oregon: 62,000 m² in 2009 (according to Amy Chomowicz)
Chicago, Illinois: 49655 m² in 2008 (according to Green Roofs for Healthy Cities)

Basel is purported to have the highest per-capita area of green roof in the world. This is in part because the city has had local regulations for over a decade that require all new development to incorporate green roofs where technically feasible.

Stephan Brenneisen on the new Stucki Shopping Center Greenroof

But quantity should not be the only measure in green roof progressiveness. That was abundantly clear from my visit with Stephan Brenneisen in Basel Switzerland. Stephan is head of the Green Roof Centre of Competence at the Zurich University of Applied Sciences Wädenswil where he conducts research and advises on green roof policies and designs. Stephan did his PhD studies on how different green roof substrate depths influence biodiversity and continues to actively promote the design of green roofs for biodiversity. For a sample of his writing in English see this recent paper in Urban Habitats: Space for Urban Wildlife: Designing Green Roofs as Habitats in Switzerland."

Stephan's efforts are clearly a factor in Basel's leadership in green roofs. He is actively involved in developing and refining green roof policies in Basel and was instrumental in helping develop and adopt new, cutting-edge mandates that require all green roofs to incorporate design features which promote biodiversity.

Stephan took me to three green roofs in the Basel-area and gave me the information for a self-guided tour of three additional sites. December is probably the worst season of the year too tour green roofs but I have found some spring and summer photos of the sites I visited to better capture some of Basel's rooftop beauty. Many of the biodiversity-friendly roofs that Stephan shared had design features I encountered in London- varied substrates and topography to promote habitat diversity- but there were some interesting differences too.

Stucki Shopping Center Green Roof

One example of this is the relatively new Stucki Shopping Center Greenroof just installed in September (2009). The Stucki Shopping Center roof is 35,000 m² (roughly half the size of all the greenroofs in Portland) and is covered by mix of substrates ranging up to 12 cm in depth.

Stephan has been promoting green roof designs that use local or native soils from disturbed greenfield development sites. At the Stucki Shopping Center, the substrates include cobble, gravel, silt-clay soils, and some organic material some of which was gleaned from surface soils at a local mining site. As you can see, the roof is only four months old but already has substantial plant growth, atleast where the substrate is deeper.

Stephen on the Stucki Shopping Center roof.

Varied substrates and different depths and vegetation growth on the Stucki Shopping Center roof.

December bloom on the Stucki Shopping Center roof.

Beds on the roof perimeter provided rooting soil for green wall vegetation on the building exterior.

Stucki Shopping Cennter from the air (Photo from Architectural Review).

Perhaps because of the longer history of green roof installation in Switzerland, a number of Stephan's projects have involved ecological enhancement of existing green roofs originally designed for other purposes. Stephan has been involved in several projects that installed new substrates, varied topography, and/or organic material (from grass cuttings to woody debris) into existing green roofs in order to better promote biodiversity values.

Basel Main Exhibition Hall (Messehalle Basel) Green Roof

One spectacular example of this is the 8,000 m² Basel Main Exhibition Hall Green Roof. The roof was originally installed in 2000 with 7cm of volcanic substrate and planted with sedums.

The Basel Main Exhibition Hall Green Roof is purportedly the largest greenroof in Switzerland. I think this photo predates the biodiversity enhancements co-designed by Stephan.

In 2008 Stephan worked with local artists and the Exhibition Hall owners to add organic matter and woody debris to a roof to enhance biodiversity functions.


The early winter photographs I took don't do really this green roof justice, so here's some spring or summer photos I snagged from the greenroofs.com website:


The Exhibition Hall green roof includes PVCs that produce 215000 kwh/year and whose efficiency is improved by the cooling effect of roof vegetation.


Cantonal Hospital Greenroof

The 3000 m² Cantonal Hospital Greenroof was installed over 30 years ago as an aesthetic enhancement for hospital patients in recovery. In 2003 Stephen helped redesign the roof for a biodiversity. The soil is sand loam and gravel ranging from 8 to 25 cm deep, intended to stimulate river terrace and dry meadow habitats.

Varied substrate depth and vegetation.
The Cantonal Hospital green roof is visable from the patients' rooms.

I spent the afternoon walking in and around Basel visiting some other accessible green roofs that Stephan recommended I see. Below are some photos I took along the way.

Okay this roof looks like an airduct coming out of a vacant lot but it is actually atop the Restaurant Rypark next to the Rhine River where it mimics river terrace habitat.

I encountered this rural green roof atop barn just outside of the suburb of Pratteln.

Here's a volunteer green roof. Who says green roofs are high maintenance?

I had a delightful and engaging visit with Stephan. Apart from all the green roofs, I also had the pleasure of meeting his partner Barbara and their very adorable children (ages 6 and 8, I think) which gave me a very special window into Swiss home life during the Christmas season.

For a great short video of Stephan and Basel's green roofs see Amy Wong's World Radio Switzerland report, Green: Basel's green roof initiative.

Next stop: Greenroofs of Plenty in Stuttgart, Germany.

Earlier post:

London's Dusty Gedge and Ecoroofs for Biodiversity

Posted by jim.labbe 09:51 Archived in Switzerland Comments (1)

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