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Giving identity to a skyline

Architect Jürgen Engel talks about the Central Business Tower and other high-rise buildings in Frankfurt

Jürgen Engel and his architectural firm KSP Engel have left their mark on the skyline of Frankfurt am Main like few other architects. The 18 high-rise projects realized in Frankfurt alone include the WestendDuo, the WinX, the Jumeirah Hotel, the 160 Park View, the Maintor Porta and Primus, the Nextower and the refurbishment of the GardenTower. Currently, KSP Engel is realizing the Central Business Tower and the Canyon in downtown Frankfurt. One of his office’s most significant international projects is the Algiers Grand Mosque, completed in 2020, which is not only the third-largest mosque in the world, but also Africa’s tallest skyscraper to date with its 265-meter minaret. He has also received a wide variety of awards for cultural buildings, such as the Documentation Center of the Bergen-Belsen Memorial and the Chinese National Library in Beijing. But the architecture of everyday life is also one of the topics for which the unpretentious architect and urban planner is committed and finds architecturally convincing solutions.

The SKYLINE ATLAS met the internationally award-winning architect and spoke with him about his current high-rise project, the Central Business Tower, Frankfurt’s high-rise development plan, other high-rise locations in the east of Frankfurt, the ideal city of the future and his international mega-projects.

SKYLINE ATLAS: Dear Mr. Engel, thank you for taking the time to speak with SKYLINE ATLAS today. Your architecture practice’s design won the competition for the Central Business Tower back in 2001 and then planning juddered to a halt for 20 years owing to ownership issues and 9/11 2001. As an architect do you need special endurance and to always be an optimist, or did you at some point also doubt whether the high-rise would ever be realized?

Jürgen Engel: We never had doubts. Never. We felt certain that the CBT would be built at some point in time. Throughout those years we kept working away on the project. That said, you always need a bit of luck, too. Our client, the Helaba, has very strong foundations and a lot of endurance as well. In the end, the Gordian knot got cut and construction work started immediately.

We won the competition in 2001 because we had developed a very interesting solution for the footprint that ensured the building was a highly cost-effective home for all manner of office types. We devised the Central Business Tower such that it was completely flexible. That is a basic prerequisite for the long-term use of a tower. The footprint was derived from a sculptural idea: two tower halves are juxtaposed to each other such that the façade, which is staggered toward the middle, causes a twist in the building. This dynamic shape of the building responds to the form of the urban ground plan at the junction of Neue Mainzer Strasse and the Wallanlagen, the ancient ramparts.

Jürgen Engel – Managing Partner of KSP Engel Architekten

The construction site of the Central Business Tower in Neue Mainzer Straße

SKYLINE ATLAS: The CBT will feature a photovoltaic plant that will have 3,800 photovoltaic panels that can generate a total of as much as 158,000 kilowatt hours a year. Added to which the flat roof will be greened, and rainwater will be processed into water for irrigation. That said, the glass façade will also require permanent cooling by an air-conditioning system. How sustainable will the CBT actually be and to what extent can the planned measures cover the entire building’s energy requirement?

Jürgen Engel: The CBT is a highly sustainable high-rise and a pilot project as regards generating energy with the photovoltaic panels we have integrated into the facade. The tower functions like a vertical ‘solar power plant’. The use of remote heat and the energy from the photovoltaic panels mean the tower requires about one third less energy than a conventional high-rise powered by natural gas. The photovoltaic panels generate about 158,000 kilowatt hours (kWh) a year, which on sunny days considerably reduces the energy required to cool the (office) areas in the skyscraper. We have geared the technical facilities to operate with ‘green’ electricity and thanks to our on-building sourcing of power are making a crucial contribution to sustainability. With the double-skin façade we have designed we will in fact be more than fulfilling the regulations for heat protection in summer. Not to forget that it enables wind and weather-proofed sun protection and natural window ventilation.

The façade has a very open feel to it thanks to the double-shell structure with the box-type windows. However, only about 55 percent of the frontage can actually be opened. In combination with the photovoltaic elements that we have likewise integrated into glass panels level with the ceilings of the respective stories we have succeeded in giving the tower a very open, transparent appearance overall.

Central Business Tower - Frankfurt - Jürgen Engel - KSP

The Central Business Tower (CBT) in Frankfurt

SKYLINE ATLAS: The Central Business Tower as an office high-rise combines public and private usages, as it also houses the satellite of Weltkulturen Museum and hospitality. The museum and the restaurant with its open-air terrace, café, and wine-bar will spread across four stories. How will the CBT open out onto downtown at the level of the ramparts of Wallanlage and will the CBT be offering Frankfurt citizens a new high-grade leisure-time space?

Jürgen Engel: It was important to us to mastermind a new space for Frankfurt locals on Neue Mainzer Strasse, which has to date not possessed any real leisure-time appeal. And we have succeeded in this with the CBT. The public arcade with the café allows you to stroll from Neue Mainzer Strasse through to the Wallanlage ramparts and in the direction of the LRT stop. Moreover, on the ground floor there is a day-time bar and a restaurant with a terrace that has a great view of the park. The arcade also leads you to the museum lobby, meaning all in all the CBT will always be filled with life.

“The identity of Frankfurt’s skyline is created by the totality of all skyscrapers”.

– Jürgen Engel

The Central Business Tower (CBT) in Frankfurt

The CBT as seen from the Opera Square

Interior view of the CBT

SKYLINE ATLAS: As an architect in the course of the last 20 years you have been involved in no less than 18 high-rise projects in Frankfurt and the vicinity (Eschborn), including the high-rises 160 Park View, Garden Tower, High Lines, Nextower and Jumeirah Hotel, Maintor Porta and Primus, Solid Home, Taunusanlage 11, WestendDuo and WinX, to which we should add another 13 high-rises in Germany and 14 in other countries – which spells a grand total of 45 towers. Some of them are currently at the planning stage, others under construction – such as the CBT and Canyon Towers, two huge construction sites in downtown Frankfurt. Is it safe to say that Frankfurt has been shaped by your architecture?

Jürgen Engel: The identity of Frankfurt’s skyline is the product of all the different skyscrapers. Put differently, with our high-rise projects we make a strong contribution to this identity, albeit always in connection with others. What is unique about Frankfurt is the cluster of high-rises in a minimum of space. To what degree our projects shape the face of the city of Frankfurt is for others to say. However, I believe that good architecture always does its bit toward people feeling good in a city and therefore identifying with it.

WestendDuo - KSP- Jürgen Engel

WestendDuo in Frankfurt

SKYLINE ATLAS: Your international office with 300 employees at seven locations stands for diversity and is very broadly positioned, from interior design to urban planning, as a service provider and consultant for all types of real estate. What goals and values in architecture does KSP Engel stand for?

Jürgen Engel: Our office stands for resilient, modern and at the same time timeless architecture. Through our restrained and rational formal language, which does not submit to any fashion, we create distinctive, elegant buildings that speak for themselves permanently and are aesthetically convincing.

In addition, we are also very interested in the technical aspect. In order to develop technically intelligent and sustainable solutions, we work in interdisciplinary teams. The WestendDuo in downtown Frankfurt is a project in which we collaborated at a very early stage with a specialist engineer for building services and a structural engineer. The project was implemented in 2006 according to our plans and produces 40 percent less heat and energy consumption than a conventional high-rise building. In addition to these technical issues, we are interested in tasks where innovation and design come together and we can deal with architecture holistically – from the high-rise to the door handle.

SKYLINE ATLAS: In Algiers in 2020, your office built the world’s third-largest mosque on a 26-hectare plot of land, with a large prayer hall that can accommodate up to 35,000 worshippers. Which of the international projects you have realized, and also in Frankfurt, are you particularly proud of?

Jürgen Engel: Among the buildings I would like to highlight in Frankfurt are four high-rises: the WestendDuo on Bockenheimer Landstrasse, the 27-story Parkview residential Tower on Grüneburgweg, the Maintor WinX office Tower and the CBT Tower on Neue Mainzer Strasse, which is currently under construction.

Nationally, the Documentation Center of the Bergen-Belsen Memorial, which was awarded the Lower Saxony State Prize for Architecture, is one of the office’s most important buildings. Even though it is not a large building, it was a very important milestone for us. We tried to do justice to this extraordinary place in a sensitive way with a very reduced and monolithic architecture.

On the international front, we are particularly proud of three major projects in China. The National Library in Beijing, which is one of the 13 most important buildings in Beijing according to a Chinese survey, is one of them. Completed in 2008, it is the third largest library in the world. The second project is the Meixi Urban Helix, built in 2017 in Changsha, a city of seven million people in southeastern China. It is located as an approximately 30-meter-high lookout point on the lake and is connected to the land via a long bridge. The promenade and observation tower form a place where people can stay and experience events. The location on the lake and the landmark character of this structure make the Urban Helix a very special place.

Third, we are currently building a large cultural complex with a museum and library in Shenzhen, which will be completed this year. The central idea of the design was to create a public place here in this metropolis of 12 million people that combines art, culture and urban space.

But the Great Mosque in Algiers is also one of the projects of which we as an office are very proud. In addition to the sacred part with a prayer hall and the 265-meter-high minaret, the project includes other facilities such as a conference center, a library and a theological college. As the new landmark of the city, it is the new religious and social center of Algiers and catalyst for a new future urban expansion.

Maintor WinX Frankfurt

Bergen-Belsen Documentation Center

Great Mosque in Algiers

Art Museum in Shenzhen

Meixi Urban Helix  in Changsha

SKYLINE ATLAS: What does the ideal urban district of the future look like to you? And what do you think the attractive city center of the future will look like? More green, more culture, fewer cars?

Jürgen Engel: For the urban neighborhood of the future, I think it’s very important to create neighborhoods with a 15-minute radius. These are mixed neighborhoods that offer all facilities for daily needs within a 15-minute walking radius: from shopping, leisure activities, schools to cultural offerings. In Frankfurt, we already have this, because you can walk through the entire city center in 15 minutes. In addition to the actual city center, there are many districts with their own neighborhood centers, such as in Bornheim, Sachsenhausen or Bockenheim.

The solution for a more attractive city center is the 24-hour city. Monofunctional shopping miles like the Zeil, on the other hand, are only busy between 10 a.m. and 8 p.m.. Today, many people no longer find that attractive. Life after closing time is missing, because no one lives there. Cafés and restaurants could be placed on the first floors of the department stores so that people can sit outside in front of them. This would improve the quality of stay on the Zeil. In the middle of the Zeil there should be a lane for cyclists, electric scooters and cabs. Then pedestrians and cyclists would not constantly get in each other’s way – while pedestrians should have absolute priority. This permeability and a mix of uses would, in my opinion, be of great benefit to the city center and would improve safety and social control on the Zeil.

The Zeil in Frankfurt

SKYLINE ATLAS: Do you assume that less office space will be needed in the future because the world of work is changing due to digitalization and home office? In addition, new office space is currently being created in line with modern New Work or sustainability standards.

Jürgen Engel: I don’t think that office complexes in inner-city areas will reduce dramatically. The office workplace will continue to be important, because it is also a social place where I can meet people and build contacts. There will certainly be some industries where the home office will continue to be practiced and will also have advantages. But I’m convinced that in many areas, working in the concentrated space of an office with quick exchanges among colleagues works better.

SKYLINE ATLAS: What will happen to the old high-rises and office complexes?

Jürgen Engel: We must preserve the existing buildings and continue to tap the “grey energy”, meaning the energy what was inputted and used to build them in order to lower CO2 emissions. We are currently converting a whole series of office high-rises into hotel and residential towers. In these buildings, open types of work with open-plan offices are definitely possible as the high-rise ground plans are highly flexible.

Vacancies arise if a property cannot be used cost-efficiently. I consider vacant buildings to be a great opportunity. Areas for retail will be concentrated on the lower floors: on the ground and first floors and in the basement. The floors above should be used for apartments, offices, and cultural facilities – even in the case of department stores. That would be a highly beneficial development for our inner cities. However, the legislative must create the conditions to enable this to happen. We need a law that prioritizes the conversion of existing builds and facilitates planning in this field. Submission of applications for building permission should be simplified and we architects should be granted more free scope in designing and replanning existing buildings. These are exciting tasks and a challenge for all us architects.

SKYLINE ATLAS: The new edition of the High-Rise Development Plan is scheduled to come out this year after being postponed several times. Quite a few years ago the city authorities declared that the skyline should only be allowed to grow very circumspectly. What is your take on this?

Jürgen Engel: With the new high-rise development plan, the city should designate new sites that are relevant for the next 50 years and focus more on Frankfurt’s east. Because it offers a great opportunity to give the overall picture of high-rise buildings in Frankfurt a completely different dimension once again. I still see great potential for more high-rises in the vicinity of the ECB, i.e. around the Ostbahnhof and in the Osthafen area. The last major high-rise development took place when Martin Wentz wanted to convert the area around the main train station. That was a great idea. However, such large high-rise developments at designated sites can only be realized if there is a political will and the city pursues a common urban development goal.

“I still see a lot of potential for more high-rises around the ECB.”

– Jürgen Engel

SKYLINE ATLAS: The city wants to designate new sites in the banking district, the station district and the Ostbahnhof/Osthafen area, thus enabling about a dozen new high-rises. What is your opinion on this?

Jürgen Engel: With the new high-rise development plan, the city should designate new sites that are relevant for the next 50 years and focus more on Frankfurt’s east. Because it offers a great opportunity to give the overall picture of high-rise buildings in Frankfurt a completely different dimension once again. I still see great potential for more high-rises in the vicinity of the ECB, i.e. around the Ostbahnhof and in the Osthafen area. The last major high-rise development took place when Martin Wentz wanted to convert the area around the main train station. That was a great idea. However, such large high-rise developments at designated sites can only be realized if there is a political will and the city pursues a common urban development goal.

SKYLINE ATLAS: How can Frankfurt hold its own when competing with metropolises like Paris, Amsterdam or Milan, or do you think urban development that emphasizes a lot less traffic to be a move in the wrong direction?

Jürgen Engel: Frankfurt’s major advantage is the sheer density of the high-rises and the fact that urban infrastructure is also concentrated in a central location. As a result, downtown coincides with the conglomeration of towers. Now that is not the case in the other cities, if we think or Paris and Milan, for example. And precisely this is Frankfurt’s real advantage. It is a city where everything is close at hand, where there is very close and easy communication between the individual buildings. I believe promoting that trend is absolutely the right way to go.

Moreover, for Frankfurt it is also key that urban life that is not related to work per se is more strongly fostered and supported. After all, it is urban coexistence, namely the combination of different offerings when it comes to culture, housing, restaurants, stores, plazas, and green zones, meaning attractive outdoor spaces, that really goes to make up the urban life in our inner cities that we all want to see.

Many thanks for your time, Mr. Engel.

In the center of Paris, car traffic is to be further restricted so that residents and tourists can travel more freely on foot or by bicycle.

About the person: Jürgen Engel

Jürgen Engel studied architecture at the Technical University of Braunschweig, the ETH Zurich, the RWTH Aachen and the Massachusetts Institute of Technology (MIT), Cambridge, USA. From 1982-1986 he worked for Schneider-Wessling Architekten in Cologne, and from 1986-1989 for O. M. Ungers in Frankfurt as office manager. In 1990 Jürgen Engel started his own business as a partner, and since 2009 he has been managing his architectural practice KSP Engel as a managing partner. With around 300 employees from 40 nations, it is now one of the largest in Germany and has offices in Berlin, Braunschweig, Frankfurt, Hamburg and Munich, as well as offices abroad in Beijing and Shenzhen.