For architects, working on existing buildings can be exciting, but it can also be quite challenging. Apart from technical imponderables, it’s important to ensure ideas brought to the table work in harmony with things already in place. Reichel Architects have succeeded in bringing buildings owned by the Evangelical Bank in Kassel in tune with modern times – not only in terms of design, but also when it comes to energy use.

Existing buildings play an important part in sustainability. As well as portraying the identity of the locations they stand in – which applies just as much to buildings dating back to the years of rapid industrial expansion in Germany, as it does to buildings from the post-war modern era – preserving existing buildings offers tremendous potential to save energy, especially hidden or so-called grey energy. The challenge is to renovate what’s already there, do so responsibly and, if necessary, find new uses for existing features. Refurbishments carried out on the Evangelical Bank on the outskirts of Kassel city centre show how it’s done. Architect Prof. Alexander Reichel and his colleagues have succeeded in merging two somewhat run-down buildings to form a combined edifice that now also blends harmoniously into its urban surroundings.

Client, architect and planner – all on the same wavelength

It’s the year 2016. Reichel Architects have just emerged as the winners of a business pitch. Their task: a total refurbishment of two office blocks. The first is a building located on a road called Ständeplatz. Erected in 1949 during the post-war era and extended in 1981, the building is subject to a preservation order. Next to it stands the second building, an extension completed in 1981. It would be an exaggeration to claim the two buildings add anything worth mentioning to the area, and they really don’t look like they belong together. The aim now was to create a distinctive and cohesive ensemble of buildings, a complex that welcomes employees, customers and visitors alike, marrying tradition with innovation in ways that mirror the identity of the bank. One given from the outset was that the existing building should be developed sustainably. This aspect is central to a commitment made in all areas of corporate management by the Evangelical Bank, subsequent to its certification under the European Environmental Management System EMAS.

“We’ve been working on existing buildings at our architecture firm for more than 20 years, and we’ve successfully implemented projects of all sizes. The unpredictability of this particular task demands a high degree of flexibility from everyone involved in the building project. But I’m always happy to take on this kind of challenge,” says Alexander Reichel, explaining his intentions for the project. Reichel has been lecturing on the subject of sustainable building and design since 2010 in his role as a professor at Darmstadt University of Applied Sciences.

A further factor in safeguarding sustainability was the involvement of consulting and architectural firm ina Planning from Darmstadt. In the course of the project, the client decided to submit the development for DGNB certification. Also working on the project, and responsible for the certification process, were Joost Hartwig, CEO at ina Planning and his colleague Isabell Passig, who are also both DGNB Auditors. As for the DGNB certificate: the project achieved gold.

Summarising his approach to projects involving existing buildings, Hartwig says, “Continuing to use the very fabric of an existing building, translated into contemporary design, is sustainable in the best sense of the word. Compared to a new building of the same size, reusing the shell of the building alone offers tremendous savings in carbon emissions. This was scored positively for the bank project in the DGNB certification section covering the life cycle assessment.”

Taking what’s there already, changing the set-up and extending it

The central building on Ständeplatz stands six storeys high and was renovated in keeping with the preservation order. This contrasted with the extension, which – subsequent to a detailed survey – was stripped down entirely to leave just a concrete skeleton, the three basement storeys, which included a natural ventilation system, and the kernel of a staircase. A testimony to former times, the other staircases were left as they were, complete with original materials. According to calculations, in comparison to building from scratch, this saved 4000 tons of CO₂ in grey energy. That’s not a small number given that it takes 75,000 birch trees to sequester 1000 tons of carbon for a year.

To provide more office space and develop the public area around the buildings, a reinforced brick-lined framework of concrete was placed around the existing structures to create a building envelope, offset by approximately five metres. The pale limestone facade now forms a visual link to the main building, a recapitulation of the new setup of the building ensemble. Inside, plenty of space has been put aside to allow enough flexibility for floor plans, not only to enable agile working methods to be adopted, but also to allow the area to be used in different ways. Thanks to high-insulation masonry, only minimal technical equipment is required to air-condition the office areas. To round off the concept, solid materials such as concrete, stone and wood have been used, also conveying an air of naturalness. The section on the ground floor now houses a restaurant and a retail outlet to integrate the building complex into the public area.

The glass extension now forms a link between the existing buildings, offering a central meeting point for approximately 350 employees at the bank © Constantin Meyer

To complete the picture painted by the complex in its urban environment, the new glass-covered entrance hall acts as a centerpiece for the reorganised complex, forming a connection between the two buildings. As well as offering a lobby for visitors to arrive and gain their bearings, the three-storey-high hall also acts as an event venue. A wooden construction has been added with a translucent shell to act as a ‘Room of Tranquillity’, also providing a reference to the heritage of the bank.

The Room of Tranquility in the reception area © Constantin Meyer

Smart solutions and plenty of perseverance

© Constantin Meyer

One of the challenges you face when working on existing buildings is to find solutions that don’t necessarily adhere to norms. This is because any new plans you contemplate will have to consider what’s already in place. One problem with the bank was the required technical cabling. The standard approach – running cables under suspended ceilings – would have reduced the ceiling height to under 2.2 metres, which isn’t permitted. This is the point where lots of people would argue that the building should be torn down. But not in Kassel – oh no. A decision was made to integrate most of the technical equipment into the walls. This made it possible to preserve the ceiling height of around 2.75 metres. The new systems fitted inside wall panels are also removable, which once again allows for flexible use of the rooms. A solution was also found for a further problem: unlike new buildings, with old buildings there are often considerable differences within the building grid. The wall cladding on the building facade now conceals this, producing a uniform appearance inside the building.

As the concrete ceilings are no longer shrouded, they are now being used to store passive thermal energy. Certification also requires , and this proved helpful when planning the ventilation systems. Individual fans positioned on the outer facade are used to regulate indoor air and surface temperatures. Conversely, the same devices work in harmony with passive thermal energy to cool the building at night.

Special lighting systems were developed in collaboration with a manufacturer of luminaires. To add structure to open areas, lighting and sound insulation panels have been fitted, also delivering plenty of illumination and pleasant room acoustics. Although born of necessity, overall a number of novel and innovative solutions have emerged.