Medieval Fortress Finds Future as Modern Rooftop Park

Comturey-Keller green roof, by ZinCo and Thomas Steinmann, in Mainau Island, Germany. Even though green roofs have existed in architecture for centuries, their proliferation is a rather new trend in today’s world. More and more innovative solutions in green roof systems are being found, from succulent rooftops to full-scale gardens placed on top of buildings. Looking at all of these fantastic designs, we may think it is almost impossible to come up with a project that will surprise thousands of potential users. But let’s have a look at the Comturey-Keller green roof in Germany. Located on one of Germany’s biggest islands — Mainau Island — Comturey-Keller has had something unusual to offer its users since 2014. Originally a medieval fortress, the Comturey Tower has been redesigned and rebuilt to meet the needs of modern-day users. The tower has been turned into a one-story restaurant with a façade of 80 square meters overlooking Lake Constance. The former fortress is surrounded by countless baroque castle gardens, which amaze visitors with their floral splendor.

But the biggest attraction is the park located directly on its roof. With an area of approximately 1,500 square meters, the park is definitely a surprise among the historical gardens of the Mainau Island. The rooftop garden is accessible directly from the ground on three sides. The park becomes a metaphorical junction between the historical gardens surrounding the building and the tower’s new, contemporary design. This also gives the impression that the restaurant is fully made up of greenery, which only adds to the delight of the view before us. Recommended Reading: 

• The Green Roof Manual: A Professional Guide to Design, Installation, and Maintenance by Linda McIntyre
• Green Roof Construction and Maintenance (GreenSource Books) (McGraw-Hill’s Greensource) by Kelly Luckett

Thousands of Plants, Thousands of Possibilities

With plenty of places to sit and even lie down, the park has been designed in such a way as to meet the needs of its modern-day users to the fullest. With more than 12,000 plants and upward of 200 species, the roof of the Comturey-Keller blends in seamlessly with its floral surroundings.

Parasol-like trees give an all-day supply of shade, which can be a life-saver on hot summer days in Germany. Perennials marking the pathways flow freely from one side of the roof to another, continuing the “hydrangea-path” on the ground below.

Connecting to the Historical Context

Even though the park has a contemporary design, the carefully thought-out use of plants in the project connects the restaurant with its historical surroundings. Despite its strictly geometrical features in the forms of platforms and sitting areas, we do not get a sense of detachment from the whole of Mainau Island. Also, several wooden podia have been constructed on the front edge of the roof, which can be used for admiring the view of Lake Constance or for sitting.

Materials used in this project are mainly metal and wood, which can be associated with a modern design. But when we have a closer look at the park, its surroundings, and its use of planting, all of these elements fall together to make a beautiful and harmonic whole.

How Was It All Made Possible?

Being the world’s most famous green-roof constructor, ZinCo has yet again proven its genius in green-roof construction. In cooperation with Thomas Steinmann, ZinCo has made a green bridge connecting the historical past of the design surroundings with the modern trend of rooftop gardens.

Careful Calculations Allow for a World-class Design

The innovative construction of the rooftop has given the landscape architects a lot of freedom in their design process. With its maximum and minimum weight carefully calculated and with its construction and drainage system, the roof could be treated the same way as any other on-ground area. The special hillside location of the restaurant brought some unusual aspects into the design process; the green roof could not be too heavy or too light, so that it could withstand the slope pressure acting on the whole of Comturey-Keller. The newly built tower at the sandstone cliff has resulted in a narrow but very long roof with an approximately one-meter-high parapet going along the whole front side of the rooftop. This feature and the adjoining canopy are wood panelled, and both of these features have been designed without an incline, allowing the water-retention irrigation system to work properly.

But how do you build a full-scale park on top of a tower without its roof collapsing?

The most appropriate solution in this case was the use of one of ZinCo’s build-ups –“Roof Garden” — which was combined with a multi-layer construction of bituminous and waterproof roof membrane, protection mats, drainage, and water-retention elements. The last of these is filled with a crushed, mineral brick substrate that provides excellent water storage while allowing excess water to drain through the underlying channel system. On top of the construction lie filter sheets and substrate — partially humus and mineral.

The substrate depth has been increased to two meters in parts lying closer to the hillside, allowing better modeling of the landscape. All of these elements make up an extremely bearable and long-lasting system that allows users not only to walk on the roof, but also allows for small maintenance vehicles such as road sweepers.

Railings for Security and Good Looks

Being a part of a bigger whole, the Comturey-Keller roof needed to be equipped with an integrated system of railings, not only protecting users, but also in some places acting as trellises for some of the plants in the park. The railings were especially required in the most accessible area at the front edge of the roof, where users stop to admire the view of Lake Constance spreading before them.

Construction Details

The railing system has been directly integrated into the green roof build-up and is kept in place by the superimposed load of the roof construction. The load of the railings is evenly distributed by the use of plastic plates and underlying metal reinforcements.

So if you are ever in doubt about whether contemporary planning and historical surroundings go together, here is the answer: They definitely do. The Comturey-Keller is the best example to show us that landscape design today is much more than just trying to get all of the elements of a project and its surroundings in the same style. Landscape architecture now has no limits, and we can easily mix modern and historical in one design. And if you don’t believe me, come with me to Germany’s Lake Constance and let’s see the Comturey-Keller together. It is definitely a sight to see!

Full Project Credits for the Comturey-Keller green roof

Project: Comturey-Keller green roof, Mainau Island, Germany Construction Year: 2013-2014 Roof Area: approximately 1,500 m² Architect: Hein Architekten Landscape Architect: Thomas Steinmann Recommended Reading

• Landscape Architecture: An Introduction by Robert Holden
• Landscape Architecture, Fifth Edition: A Manual of Environmental Planning and Design by Barry Starke

Article by Joanna Łaska

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