Located directly on Lake Zurich, an administration building from the 1970s was renovated. The architects came up with a remarkable solution for the façade – we asked project manager Natalie Adelhoefer about it shortly before the building was completed.
You are now reading an interview from our September 2024 issue, when the building was not yet finished. Now we want to show you the final result.
A vacant administrative building from 1974 in a prime location directly on Lake Zurich was not demolished, but transformed into a modern, sustainable office building. It meets the Swiss Minergie-A standard. Its new façade also provides more light in the interior, energy generation through photovoltaic panels and shading for the workstations. A newly inserted atrium connects the office and rental office units to form a communicative whole.
Baumeister: Ms. Adelhoefer, why was demolition out of the question for the client?
Natalie Adelhoefer: It would have been possible to demolish and rebuild on the site, but a new building would not have been possible with the current volume and overall height of the existing building. In other words, the client would have been allowed to build significantly less usable space in the new building than could have been retained with the renovation.
B: Does your office work a lot on preserving existing buildings?
N A: Our office has a broad portfolio and we work with all typologies and programs. In our one hundred years of company history, we can also boast a number of refurbishments. Building in existing buildings, especially transformation projects, is a very important topic, particularly with regard to conserving resources, reducing CO2 and achieving climate targets. And will become increasingly important in the future. In other words, we want to work with more refurbishments and transformations in the future.
Sustainability is a natural parameter in all phases of planning in our office. C.F. Møller Architects has set itself the goal of making sustainability an integral part of all new projects in order to motivate every client to include sustainable components in their building projects. At the beginning of a project, a simple and comprehensible “screening” is carried out based on the client’s ambitions and objectives, and compared with the firm’s knowledge and experience in order to formulate a common objective.
Working with existing buildings from the 1970s, such as Bellerivestraße, offers great potential in terms of achieving climate targets. However, it also entails challenges: in the Bellerivestraße project, the phase of pollutant remediation was significantly extended, as far more asbestos and other pollutants were found than originally assumed. Some of the concrete quality of the ceiling spires, to which the new canopy construction and façade were attached, also had to be upgraded. After the dismantling phase, the existing façade grid turned out to deviate from the planning, and the building had also settled in one area. Working with existing buildings is complex and involves a number of fixed framework conditions; the architect’s freedom is not limitless, it is not a blank sheet of paper on which to start writing.
B: Nevertheless, the effort was obviously worth it …
N A: At Bellerivestrasse, we managed to convert and renovate an existing building in such a way that it can continue to be used as an office and meet sustainability standards. Our aesthetic goals, our vision of a pavilion in the park, have been realized with the more modern building envelope and a new transparency and openness. The tenants feel comfortable in the new old building, and our client is pleased that he was able to preserve and upgrade the existing building. Our goals as architects to create a green building in addition to the aesthetics were also achieved. We were able to preserve around 86% of the existing concrete and the BIPV energy generation covers the majority of the building’s own electricity requirements. The green terraces help to retain water during heavy rainfall.
B: What role does solar energy play in your office?
N A: You could perhaps go so far as to say that we specialize in working with BIPV in our projects. In any case, we have ten years of experience in this field. One of our first projects with a focus on solar energy, building-integrated photovoltaic modules (BIPV) in façade design, is the Copenhagen International School in Copenhagen (2013 – 2017). Around 12,000 solar panels were installed here, covering around half of the annual electricity consumption. This corresponds to the energy consumption of around 70 single-family homes.
Since then, we have been investigating the possibility of working with solar energy in all our projects.
One of our current projects with BIPV, which is currently under construction, is the new headquarters of Hyp Bank in Berlin. As with Bellerivestrasse, you will only see at second glance that the façade has integrated photovoltaic panels. At the Federal Ministry for the Environment – another of our Berlin projects – the integration of PV in the façade is also being investigated.
B: You found an outstanding solution to combine solar shading and energy input …
N A: Thank you, we are very pleased with the positive feedback we have received so far for this solution. We already had the idea of the surrounding cantilevered canopies, which generate energy on the sloping upper side and at the same time provide effective external solar shading with their depth of 1.8 meters to the façade, during the competition phase. This concept proved to be good in the further course of the planning and building physics analyses. Thanks to the slope, we were able to generate around 20 percent more surface area for the PV panels compared to a vertical covering of the ceiling ends with PV panels. There was no need for any additional external solar shading, which would have been difficult given the location and wind speeds over Lake Zurich. Internal glare protection was sufficient here.
B: Were there any hurdles in the development of the façade?
N A: The development of the BIPV concept for the Bellerivestrasse project was not without its hurdles, but we had a constructive dialog with our clients and the right specialists on board. The development of PV technology is rapid, and in a planning process lasting several years, it is uncertain what possibilities will open up as a result of new developments. A lot happens in PV development during a calendar year.
For this project, we wanted to use a structured glass on the top side (glass-glass PV modules), which refracts the light and generates a floating effect. This was to echo the shimmering on the water surface of Lake Zurich. However, the irregular surface of the textured glass means that dirt tends to accumulate, increasing the cleaning effort and reducing the efficiency of the PV. In addition, we architects wanted to work with a uniform color concept, i.e. the top and bottom of the canopies were to be kept in the same color palette as the façade elements. The color also reduces the efficiency of the PV panels. Overall, we are talking about a reduction in electricity generation of around 20 percent compared to conventional black solar modules. All in all, as architects, we had to do a lot of convincing to stick to the holistic color and design concept of the new building envelope. To make matters worse, the desired textured glass was not available and we had to find an alternative, which we ultimately succeeded in doing.
In the process of developing the new building envelope, it should also be mentioned that façade mock-ups were created in two rounds: with the aim of testing colors, surface textures and technical execution details, finding decisions and being able to determine the direction for the execution on a large scale. The mock-ups were an important and target-oriented method in the development and decision-making process for the new building envelope. The mock-up was also inspected by the authorities and helped to assess the aesthetics that were being sought on site.
Fortunately, we met with approval from the client for our choice of trapezoidal canopies. The steel construction of the canopies proved to be more expensive than the actual 1,700 PV modules that were attached to the substructure.
B: Your office builds all over Europe. Is there a lack of good examples of successful solar architecture in Germany, for example?
N A: The situation is improving, as most state building regulations now stipulate PV for new buildings, so this is now also on the agenda for large construction projects.
Up to now, the bureaucratic hurdles in the construction and operation of BIPV have been an obstacle, especially for large projects. However, we see a positive development here in the medium term. In one of our projects in Hamburg, the issue of the subsequent administration of the PV systems was a major stumbling block. This mainly relates to tax problems during the rental period.
PV quickly becomes unattractive for developers if it is too expensive to operate. There are now companies that specialize in this area and offer to take over this part for the building owners and operate the BIPV separately. This case alone shows how much bureaucracy there is behind PV systems in Germany. Another bureaucratic hurdle in Germany is the approval of PV modules in façades, which is a sensible location for PV in high-rise buildings in inner-city areas, such as our project for Berlin Hyp in Berlin, due to the limited roof space available, which also competes with biodiversity requirements, technical and other uses.
Every component requires approval in Germany. For BIPV panels, there is no general approval for façade PV, especially in the area of the high-rise directive. This means that approval is required for each individual facade system. These approvals are complex and take time. This makes it unattractive for most companies, international PV companies shy away from it and do not submit offers, it simply does not pay off.
This thins out the German market for PV in the facades. The companies then prefer to bid on projects outside Germany, as the process is much simpler and less bureaucratic in other EU countries.
B: Do you also build here in Munich?
N A: There were similar hurdles with our projects in Munich. Here, we were also unable to install conventional PV systems due to the green roof. Here, we proposed enclosing the technical areas with PV on the roof as a solution. The vertical PV panels are classified as a façade component, which is the same case as the Berlin project: approval is required.
BIPV still appears to be a niche market in Germany. Demand is gradually growing, but there are not yet many German manufacturers. The amortization of the systems does not always add up either, especially when the installation of PV modules is accompanied by a complex substructure.
The questions were asked by Sabine Schneider.
