Designed by Mies van der Rohe, the Neue Nationalgalerie (New National Gallery) in Berlin is an important piece of architectural history and forms part of the “Kulturforum”, a collection of cultural buildings. A team from David Chipperfield Architects has been renovating the museum since 2016 on behalf of the Federal Office for Building and Regional Planning (BBR). The building services, especially the ventilation and air conditioning technology, have been totally renewed. Now the project has been completed and this icon of modernism has been restored to its former glory with fresh sparkle.

1961 in post-war West Berlin: Ludwig Mies van der Rohe was commissioned to design an art museum. He created an architectural masterpiece, a temple of modernism based on the idea of “universal space”: the large, column-free entrance hall is surrounded by glass walls and is based on an unrealised design for the Bacardi headquarters in Santiago de Cuba. Just two columns on each side support the 1260 tonne steel roof, highlighting the clean lines of classic modern architecture. The larger basement, parts of which have no windows, forms a contrast. While the upper hall is predominantly made of steel, glass, granite and marble, Mies van der Rohe chose carpeted floors and woodchip wallpaper for the lower level. This contains the exhibition space where the museum’s collection has largely been displayed to date, as well as an adjacent sculpture garden and offices. The Neue Nationalgalerie is the only building Mies van der Rohe completed in Europe after emigrating to the USA. Due to ill health, he was unable to attend the opening in 1968 and passed away a year later. The building became a listed monument in 1995.

As impressive as the building is, the bold steel and glass structure had its weaknesses from the start. The main issue has been condensation on the uninsulated glass façade and the resulting damage from corrosion on the façade construction, as well as glass panes breaking due to the lack of expansion joints – all of which caused recurring problems after just a short time. Following more than 50 years of intensive use, a complete renovation was inevitable. All the building services had reached the end of their life and also needed to be replaced. David Chipperfield Architects were tasked with the refurbishment and proceeded with great respect and caution. The guiding principle was to preserve as much of the building fabric as possible and have minimal visual impact on the structure, i.e. to retain “as much Mies as possible”. To achieve this, almost every component was painstakingly dismantled, stored, restored or reconstructed before everything was then put back together. This is what happened with the granite floor slabs in the large entrance hall, for example. There is now a new underfloor heating and cooling system below them.

Replacing the ventilation and air conditioning technology required detailed, advance planning. Since exhibition spaces are subject to stringent conservation requirements, among other factors it is essential to maintain a stable ambient climate to protect the artworks. The two areas of the museum differ considerably in this respect. The lack of insulation on the outer façade of the large exhibition hall made the glass panes fog up and allowed condensation to form. This in turn caused damage and corrosion on the façade. As the building is listed, replacing the large panes of glass with insulating glass units was not an option. Instead, in future the new ventilation technology will largely prevent the glass panes from fogging up. For this purpose, a parameter study involving simulations of air flows and smoke tests was conducted on site before the refurbishment work commenced. It was important to identify how to shield the façade and to avoid condensation in the 8.4 m high exhibition hall, so that all international climate standards could be met.

The conservation requirements in the exhibition areas below ground are even more stringent: with a room height of four metres, stipulations on ambient air velocities need to be adhered to up to a hanging height of three metres. An extra complication was the need to retain the existing perforated metal plates due to the building’s heritage status. These cover the actual air diffuser and therefore affect the discharge characteristics. As part of the planning process, Kiefer carried out experiments in its flow laboratory to align the listed building requirements with conservation standards.

The existing ceiling in the basement was a modular system of a type previously unknown in Germany at the time of installation. Already in use in the USA, it formed the basis of Mies van der Rohe’s idea to give the exhibition space a flexible floor plan. In post-war Germany, it was only possible to approximately replicate this type of suspended ceiling. As part of the general renovation, this replication using square timbers and chipboard was removed and reconstructed as a new modular ceiling with the same look. Kiefer’s INDULCLIP ceiling air diffusers are installed behind the 60 x 60 cm modules. Based in Stuttgart, the company manufactured the front panels and the plenum boxes on the back using custom dimensions. Fixing these various components discreetly, including the decorative perforated metal plate, proved to be very complex in order to integrate the ventilation technology out of sight in the modular ceiling as required. Kiefer’s clip elements enable very high induction, so large differentials in temperature down to -12 K between the supply air and ambient air can be reduced very quickly. This achieves draught-free air distribution and keeps the ambient temperature and indoor environment perfect for visitors and exhibits alike. The Neue Nationalgalerie will reopen in summer 2021 with a new exhibition.