Candidate – Germany

Submission by: Landschaftsarchitektur+ Holzapfel-Herziger & Benesch PartG mbB

Project name: Green Bunker St. Pauli

Link: www.l-plus.de/projekte/bunker-st-pauli

Short description

The former anti-aircraft bunker from WWII, one of the largest high-rise bunkers in Germany with a floor area of 75 x 75 metres, has been extended by five pyramid-shaped storeys to a height of 58 metres. A 560 metre long green mountain path leads up to the roof via ramps and stairs. In total, more than 7,600 square metres of public and communal green areas have been created, with an additional 3.200 square metres of façade greening. In this pioneering landscape architecture project the green roof and façade have an identity-forming effect for the entire complex, which includes a hotel, event locations, rooms for social and cultural projects, a memorial site and much more. The project sets new standards for building greening in densely populated urban areas.

a) Social Cohesion
The usage concept and the design of the open spaces were developed in collaboration with the citizen initiative Hilldegarden e.V. Residents from the neighborhood were able to compile ideas in a concept book. The association is also actively committed to creating a memorial and information site related to the history of the building. Both inside the building and in the outdoor areas, spaces have been reserved for community activities. Events, exhibitions and urban gardening can take place there. The outdoor areas are freely accessible to the general public during operating hours. They offer a wonderful panoramic pathway upward, several outdoor terraces, and a rooftop urban garden. Additionally, our office, in collaboration with a school and a beekeeper, organized two planting activities with children and teenagers on the bunker. The children are expected to study how crocuses develop at different heights and in the substrate over an extended period of time.

b) Biodiversity
The planting plan focuses on a balanced mix of evergreen and deciduous plants with nectar-rich flowers and fruits for animals. The site conditions were challenging: frost, drought, summer heat, strong winds, and in some areas, very limited planting spaces. The design emphasizes robust coniferous and deciduous trees from alpine regions and northern German coastal areas. Key species include Pinus mugo, Amelanchier lamarckii, Acer campestre and Elaeagnus ebbingei. In some areas, fruit trees are also included, such as old northern German apple varieties. The trees are complemented by overhanging shrubs, climbing plants, and hedge plants. In total, around 4,700 woody plants were planted on the bunker, along with approximately 16,000 perennials and grasses. The design concept allows for a wild, dense growth of the plants, creating sheltered spots between the branches and leaves for animals. The planting of multiple generations ensures stable vegetation over a long period and allows for the loss of individual specimens without affecting the overall concept.

c) Economic factors
In earlier times, there were considerations to demolish this massive building. However, the impact of the detonation on the surrounding neighborhood would have been too great. Today, the St. Pauli bunker demonstrates how an existing structure can be efficiently repurposed for various activities and become an attractive destination for locals and tourists alike. This is an important factor for the city marketing of Hamburg to enhance the city‘s appeal. Since the construction and maintenance of the building and outdoor areas are financed by a private investor, there are no additional costs incurred by the city or taxpayers. It is being investigated whether the greenery has a positive impact on the building‘s operating costs for climate control.

d) Climate
A high number of natural plants on the St. Pauli bunker positively impact the microclimate in and around the building through the evaporation effect. Thick substrate layers up to 90 cm and retention boxes absorb large amounts of rainwater and additionally cool the air through evaporation. The drainage capacity is designed so that the majority of the precipitation remains on the roof surfaces. Any excess rainwater is collected in a huge cistern with a capacity of 500 m³ and can be reused for watering the vegetation. Smart drainage regulation anticipates heavy rainfall events and proactively releases water into the cistern before such events. Initial surveys show that the cistern water covers the majority of the irrigation needs, with only a small amount needing to be supplied from the public network.

As part of a research project about climate-friendly building by the Technical University of Berlin, more than 60 sensors are being used over several years to evaluate how the greenery affects building management and the climate in the long term. They measure, among other things, the temperature inside and around the building, humidity, soil moisture and irrigation amounts. In addition data about the energy used for cooling and heating the building will be collected and evaluated.

e) Wellbeing of visitors/users
What makes this project special is that the path to the top and the rooftop garden are open to everyone. Visitors can enjoy the view over Hamburg from a height of 58 meters or stroll among the trees. The trees provide shade, and thanks to the high retention volume of the substrate, a pleasant coolness is created. To protect visitors from strong winds, the plants on the top level were arranged in a circular pattern, serving as a natural windbreak. Hotel guests wake up each morning to fresh greenery outside their windows, offering them a green view despite residing in the heart of the city in a highly urbanized environment. Some athletic individuals even use the pathway upward for vertical running exercise.

f) Selection, origin and quality of used products
The materials were chosen from German and European manufacturers. A water-permeable Polyway surface was used on the upward-leading ‘mountain path.’ The high-quality Pentapanel slabs come from Denmark and were designed by the renowned design and architecture firm C.F. Moeller. Solid benches and a pergola made of wood sourced from sustainably managed forests were custom-made by a company from the Hamburg region. The trees and shrubs were supplied by the traditional nursery Lorenz von Ehren, also from the Hamburg region. Regional tree species, such as the North German apple variety ‘Finkenwerder Herbstprinz,’ were also selected for this project. Further emphasis was placed on selecting climate-resistant plants that can withstand the challenging conditions on the bunker.

g) Overall design
The design is derived from the concept of ‘Lost Places’ as well as the surrounding neighborhood. In Lost Places, nature reclaims spaces that have been abandoned by people. The bunker was no longer needed in its original function after the war. Now, nature is allowed to cover the building like a green cloak, bringing new life to this monstrous structure. The St. Pauli district also played a role in the design. St. Pauli is the heart of Hamburg‘s alternative scene, where May 1st demonstrations take place, and right next to the bunker is the football club with the skull-and-crossbones symbol. The people of this neighborhood see themselves as creative and unconventional. Therefore, parts of the greenery on the roof should appear wild and untamed as well. A new type of urban nature is to emerge here, one that can develop spontaneously and adapt over the years to the harsh conditions of its surroundings.

The architecture of the new construction deliberately reveals the historical structures to ensure the history is not forgotten. Old anti-aircraft gun positions were intentionally preserved, and a former bunker command post can now also be visited. These areas were previously not accessible to the public. The new uses are arranged around the historical elements.

The ‘mountain path,’ which leads up around the building, also features some greenery. However, since it also serves as an emergency escape route, the possibilities for planting were more limited and were realized with smaller planters and grass areas along the path. At the request of the Hilldegarden citizens’ initiative, there are areas with moss and boulders on the roof of the original bunker. This idea originated from the association’s concept book.

h) Impact on environment
The green roof of the St. Pauli bunker offers users a new place for walking or social gatherings. For animals, the roof serves as a stepping stone habitat between Planten un Blomen Park to the east and Wohlers Park to the west. Flowers and fruits provide food for many animal species. A study is being conducted on the bunker by Hamburg’s environmental authority. It evaluates whether beetles can independently settle on the bunker. Due to the high retention capacity of the vegetated areas, a large portion of the rainfall is retained on the roof, reducing the load on the city‘s drainage system. With the results of the research data, we will learn more about the development and impact of green roofs in northern Germany. We expect that the green roof will have a positive impact on the microclimate around the building. The goal is to derive planning recommendations for other construction projects based on the experiences gained.

i) Innovation value of the project
The Green Bunker St. Pauli project is unique in Germany and perhaps in all of Europe. It demonstrates how we can repurpose an old building without destroying its historical substance. It offers users a completely new quality of experience, with a public garden on the roof and a walking path leading upwards. In this way, the dimensions of the building become physically tangible on multiple levels. The greenery is extensive, with around 4,700 trees, hedge plants, and climbing plants, giving users a completely new perspective on the city of Hamburg and a positive effect on the microclimate of the building itself. But most importantly: The project opens up the discussion on how we can make rooftop spaces accessible to the public to address the growing population pressure in metropolitan areas.