NEWS     |    BLOG    |    EVENTS     |    JOBS    |     MARKETPLACE     |     INDUSTRY     |     PROJECTS    |    TV     |    GREENROOFS101   |     DIRECTORY     |    VIRTUAL 
Back to Sky Gardens - Archives

Sky Gardens ~
Travels in Landscape Architecture

By Linda S. Velazquez, ASLA Associate, Publisher

October 2003  Sky Gardens ~

German Flag

Stuttgart, Germany.  My first glimpses of greenroofs were in 1998 upon final approach into Stuttgart, a valley city nestled within an already verdant countryside.  So imagine my surprise as I viewed greenroof after greenroof adorning the tops of rather humble farmhouses, barns and sheds.  The blending of architecture within the landscape caught my fancy, and I have been hooked since.  Of course, the idea of ecological design was already engrained in my head as a student of Landscape Architecture at the University of Georgia, but I had never come across, let alone heard of, these dachbegrünungs, or greenroofs.  My "discoveries" led to many more sophisticated municipal, corporate and industrial greenroofs found in the area.

ZinCo Stuttgart Greenroofs ZinCo Extensive Greenroof with Solar Panels

ZinCo Extensive Green Roofs in Germany - Left: Stuttgart-Weilimdorf;
Right: Unterensingen; Courtesy ZinCo

Thus began my independent research, eventually leading to this website devoted to "The Earth Friendly Technology of Organic Architecture."  I had visited other German cities before but now I started paying attention and looking for greenroofs in every day situations, and found them - especially extensive ones, in particular over garages and small houses.

Sttutgart Panorama from

Stuttgart City Panorama from - Note the Greenroofs at Right

City Background

City of Stuttgart Herald

Stuttgart lies in the midst of a valley and ranks among the greenest large cities of Europe even though it is also one of the strongest industrial regions.  Stuttgart is the state capital of the Federal Republic of  Baden-Wuerttemberg with about 600,000 inhabitants.  This energetic metropolis of southern Germany is known for its beer and wine and mix of historical and modern architecture. Attractions abound as varied as ancient castles, vineyards, mineral water, opera, ballet, the automakers Mercedes Benz and Porsche, international sporting events, museums, markets, forests, parks and gardens. Stuttgart possesses one of the largest mineral water sources in Europe with over 250 marked wells in the city supplying 22 million liters daily from different sources.  Palace, botanical, Chinese, English and Japanese gardens are just a few examples of the numerous lush gardens to visit and enjoy.  (Explore the city with Virtual Stuttgart here.)

Stuttgart Japanese Gardens Stuttgart Pin Church

Left: Japanese Gardens; Right:  Stuttgart Pin Church; Source:

Stuttgart town planning and urban redevelopment go hand in hand with integrated green area planning, which includes protected open green space.  Diverse ecological initiatives include the program of "places, parks and panoramas."  Strict tree protection statutes cover the city center districts, parks and greenbelt, ensuring a green environment for human recreation and nature.

Left:  Public Mineral Well & Fountains; Right: The Lovely Countryside;

"Gruene U"

The Green U Map, Stuttgart, Germany
Gruene U, or The Green U Layout;  Source:

Citizen concerns for monument protection, nature conservation, and care and preservation of the city's historical landscapes led to the "Gruene U."  The "Green U" is just that - an eight kilometer (five mile) greenbelt enveloping the city roughly in the shape of a U, extending from the Palace Gardens to the Killesberg Elevator Park.

The goal of combining various city parks and gardens into an interconnected public park space had started in the 1920's and was completed with the 1993 International Horticulture Exhibition.  Bridges and bars connect the Palace Garden, the Mansion Mountain Park, the Rose Stone Park, the Wilhelma, the Leibfried Garden, the Waiting Mountain and the Killesberg Elevator Park to a large park commons landscape.  The individual areas reflect their respective garden history, culture, and character, and is a beautiful place to spend the day.

Stuttgart Gruenes U

Gruene U Stuttgart City Greenbelt; Source:

The Mercedes Benz Factory

Stuttgart Daimler Chrysler Mercedes Benz Factory

Stuttgart Daimler Chrysler Mercedes Benz Factory

The administrative centers of the Daimler Chrysler company are in Stuttgart Moehringen and the museum and premises can be visited on a tour.  The complex is famous for its architectural integration into the landscape and is considered a landmark in Stuttgart - notice the many greenroofs.

Pioneering Greenroof History in Germany

Greenroofs have existed in Germany in various forms in the last century and have evolved from the testing of materials, development of industry standards and codes, and trial and error.  The acceptance in the marketplace came when systems were enhanced and designed with a reliable root barrier and a sophisticated build up that could guarantee safety and a long lifespan.  In this regard much of the credit goes to the German greenroof companies optima and Bauder as the pioneers of modern greenroof technology, in particular with regard to root resistant bituminous waterproofing.  For example, the GENO-Haus bank building greenroofs in Stuttgart, seen below, were originally installed in 1969.  Experiments had entailed using a modular system made of Styrofoam, but the necessary technology to protect the membrane from the roots had not yet been perfected.  After the renovation of the roof membrane in 1990 the 48,000 sf of three greenroofs on the 11th floor were reinstalled with updated technologies by landscape architect Peter Philippi and the greenroof system manufacturer, optima.

Designed by Peter Philippi and optima; Photo Courtesy Peter Philippi Courtesy Peter Philippi

The GENO-Haus bank building in Stuttgart designed by Peter Philippi and optima;
Courtesy Peter Philippi

True modern greenroofs - backed by study and testing of materials - were introduced in Germany in the early 1970's.  Gerda Gollwitzer and Werner Wirsing, and Hans-Joachim Liesecke are credited with being the early individual pioneers, followed by Kolb, Professor Hans Luz and Dipl. Ing. Hans Kienle, landscape architect Bernd Krupka, Professor Penningsfeld and his successor Dr. Peter Fischer.  More popular thought holds Liesecke, Kolb and Krupka as the initiators, but according to the report in The International Green Roof Journal, No. 1, 2002, Gollwitzer and Wirsing outlined modern greenroofs in their 1971 book, Roof areas inhabited, viable, and covered by vegetation.  And Professor Hans-Joachim Liesecke outlined the basis for intensive greenroofs in his 1972 report Dach und Terrassengärten - Roof and Terrace Gardens.

By the end of 1970’s, optima had two franchisees within Germany with Paul Siegert of optima-North and Rudolf Harzmann of the then optima-South (now Optigrün).  Jürgen Große-Wilde represented Technoflor, Walter Zink started ZinCo and a handful of well-known local architects also contributed to the greenroof industry with smaller businesses.  Uwe Harzmann of present-day Optigrün says the idea of greenroofs were imported from Switzerland in 1972, with the first optima projects completed in Stuttgart and Munich in 1974.  He also credits Mr. Ackermann, Stuttgart City Building Director, as a greenroof proponent.

According to Heidi Eckert of the present ZinCo International, although greenroofs - in one form or another - had existed in Germany for decades, the real start of the modern day greenroof movement was in the early 1980's.  The Stuttgart market itself started in 1986 as a result of government subsidiaries and incentives.

A lot of German Greenroofs

Design & Installation by Peter Philippi

Greenroof by and Photo Courtesy Peter Philippi

Greening roofs is a strong industry in Germany representing approximately 7% of all new roof construction.  Penn State's Dr. Dave Beattie states that by late 2002, 15% of all of Germany's flat roofs are now greenroofs, and 22% of Stuttgart's roofs are greened.

Heidi Eckert of ZinCo says it can be estimated that 50, 000 M² (over 500,000 sf) have been subsidized by municipal agencies in Stuttgart alone, although a lot more has been simply mandatory.  In Germany, she estimates that approximately 75 million M² (over 800 million sf) of roofs have been greened overall to date, representing over 4,000 individual greenroof projects at various stages  - and of varying size - managed by ZinCo at any one time.  (Note:  Some estimates are lower - National Geographic News reported in 2002 that Germany had 140 million sf of greenroofs.)

Optigrün's Uwe Harzmann estimates over 4,500 greenroof projects are projected within all of Germany within the next 26 months.

Dr. Michael Marrett-Foßen of optima Dachbegrünungs GmbH estimates five million M² (almost 54 million sf) is the total roof area greened by optima in Germany over the last 25 years.  optima is based in the north but has plans for expansion within southern Germany.

Widespread Industry Support

Since 1996 there have been over 80 cities in Germany that offer incentives for greenroofs - through direct and indirect subsidies, reduction of stormwater utility fees and ordinances.  According to Optigrün's Uwe Harzmann, currently over 120 German cities are on the incentive list, and possibly more.  In 1989 Stuttgart included the requirement of greenroofs on all flat-roofed industrial buildings in their construction codes.  For more information, please visit Industry Support.

The Stuttgart Greenroof Market

Stuttgart is not only home to many examples of greened roofs but also of two of the world's leading greenroof manufacturers:  ZinCo and Optigrün.  These area leaders are followed by optima, Bauder (as a producer of bituminous membranes who also sells green roofs) and ReNatur.  Numerous smaller roof greening companies coexist and vie for greenroof projects as the greenroof industry is a growing one (although the construction industry in general has been somewhat flat).

Optigrün Headquarters Visit

Optigrun Kreissparkasse Biberach

Optigrun Kreissparkasse Biberach,

Optigrün is the previous southern Germany partner or subsidiary of optima, located in the north.  Originally they were one company with two headquarters and test stations in Toresch (close to Hamburg),  and Krauchenwies (close to Stuttgart).  Optigrün and optima have been in business for more than 35 years, and annually both companies install greenroofs valued at over $40 million.  Currently, Optigrün estimates they are responsible for over 250 greenroofs in the Stuttgart area.

The companies split ways in 1999 and are now two totally distinct entities.  Optigrün currently partners with Roofscapes, Inc. of Philadelphia.  Both companies have long-range goals and services with large design and engineering expertise, holding patents on many of their systems and maintain the world’s largest private database on the performance of greenroofs.

Otigrun Test Greenroof Facilities;

Optigrün's test facility in Krauchenwies

I had the opportunity of visiting optima's offices in March of 1999 and the Optigrün headquarters and the test facility station in July 2001, where I was graciously attended. I took the accompanying photos of their test facilities.

Optigrün's test facility has a weather station to measure rainfall amounts, temperatures, and wind speed.  They measure water retention and runoff rates in varying greenroof systems, soil depths, growth media, and plant types with flat panels and panels with slopes from 0° to 15°.  Optigrün maintains several control panels, i.e., gravel, tile and concrete, as you can see below.  They developed their RWS Computer Simulation Program after extensive monitoring at this site for over a three year period.  For example, based on rainfall from 1990 through 1992, the average three year water retention amount on a 4.72" (12 cm) greenroof is 73.5%, or about 31,000 cubic yards (26,600 m³).

Optigrun Control Panels Optigrun Flat Grasses & Herbs Test Panel

Optigrun Tree Volunteer on Flat Panel

Optigrun Extensive Sloped Test Panel

Optigrün test facilities near Stuttgart; Photos by Linda S. Velazquez, 2001

ZinCo GmbH

Greenroof by ZinCo GmbH

ZinCo Sloped Greenroof; Source:

ZinCo was my first source of greenroof information on the web in English in 1998; the website is available in eight languages. I recently met Heidrun Eckert (Heidi), Landscape Architect and International Sales Engineer for ZinCo GmbH in Chicago this past May at the Greening Rooftops for Sustainable Communities 2003 Conference, and she invited to visit them, so I look forward to seeing ZinCo's campus next time I visit Stuttgart - look for a Feature coming soon.

The ZinCo headquarters are located in Unterensingen, Germany, close to Stuttgart, and they also have test and research facilities within their office complex.

NOTE:  I did visit the large ZinCo campus in September, 2004.  Read my Sky Gardens article about that visit and the International Green Roof Congress hosted by ZinCo (among other German industry leaders) here.

ZinCo Semi Intensive Greenroof at ZinCo headquarters in Unterensingen, Germany

ZinCo GmbH
has been in the extensive and intensive greenroof market for over 30 years with many projects completed throughout North America, Europe and Asia.  Their motto is “Changing the ‘dead’ roof into a living landscape,”  and also hold patents on many of their innovative greenroof build up components including growth media,
Floradrain® drainage products, and more.  American Hydrotech is ZinCo's North American representative in the greenroof market here.

ZinCo Int'l Extensive Greenroof ZinCo Extensive Greenroof

Extensive Greenroofs by ZinCo; Source:

Peter Philippi

Peter Philippi is one of the many independent German landscape architects in the greenroof field with over 20 years experience, and graciously contributed to my column.  Peter has a company specializing in designing, constructing and maintaining greenroofs in Sindelfingen, near Stuttgart, and has previously worked with optima on many occasions.  He is responsible for the design of the GENO-Haus bank building above, as well as some of the representative projects below.  He feels the U.S. and Germany have approached and driven the concept from different perspectives and sensibilities.  When greenroofs started out in Germany the motivation was quite different from what he perceives is the case in the States.  The organic form of greenroof architecture greatly appealed to the German sense of amenity and aesthetics.  "The benefits for the building, the environment and the community where known, but only an added value. In the States it seems to be just the other way around," says Peter.

Philippi Extensive Greenroof Stuttgart Greenroof by Philippi

Landscape architect Peter Philippi's work in the Stuttgart area

Stuttgart is truly an enjoyable city with many natural and man made places and spaces to enjoy leisurely.  Perhaps their greenroofs are not held in as high regard as their excellent mineral water, beer or wine, but they should be.

For additional information regarding greenroofs in Stuttgart and Germany, please contact the following people:

optima Dachbegrünungs GmbH: Dr. Michael Marrett-Foßen, at or visit;

Optigrün international AG: Uwe Harzmann, at or visit

Peter Philippi:

ZinCo International: Heidrun Eckert, Landscape Architect, International Sales Engineer, at or visit

To learn more about Germany, click on the following books:

Lonely Planet Germany

Fodor's 2002 Germany

Event Landscape? by Federation of German Landscape Architects

Next month I will be exploring the beautiful and ecological city of Portland, OR, co-host of next year's Greening Rooftops for Sustainable Communities 2004.  Portland is one of the major U.S. leaders in sustainable design in general and greenroofs - or ecoroofs - in particular.

Back to Top