Solution for challenging floor levels and

Modern heritage management is about as old as the Nationalmuseum in Stockholm, which was completed in 1866. The first principles of restoration theory were formulated in the second half of the 19th century, provoking heated debate. The Nationalmuseum’s major refit included the use of modern CLT boards to preserve the original appearance.

text Stina Hagelqvist photo Sweco the question of how the cathedrals and the Vasa castles, especially Gripsholm Castle, should be managed for the future was first raised back in the 1890s. Should the building be restored to its ideal state or should its historical narrative be respected? The 20th century restoration debate oscillated between these different poles, posing further questions: Should the renovations be hidden or made visible? Should new or old techniques be used and should so-called modern or traditional materials be used? this makes the Nationalmuseum a chronicle of the restoration ideologies from different eras, having been rebuilt and repainted internally several times since its construction, and each change was modern at the time. In today’s Nationalmuseum, the windows boarded over in the 1910s have now been uncovered, and the 1960s additions – an auditorium, storage room and exhibition room that effectively obscured the façades of the southern courtyard – have been removed.

Each restoration of our listed buildings has been preceded by detailed discussions about objectives, necessary considerations and the possibilities available, while precision and professionalism have defined the implementation – be it humble log cabins or proud stone buildings, such as cathedrals, castles or, for that matter, the Nationalmuseum, which became a listed national monument in 1935. The restoration of national monuments thus requires not only the largest budget, but also interest in the latest ideas and technical solutions.

The lighter grey colour palette of modernism has been replaced by more vibrant colours, based on architect Friedrich August Stüler’s colour scheme from the 1860s and unearthed during the latest restoration. The museum now showcases a whole range of renovation methods, from antiquarian conservation and almost archaeologically exposed surfaces to reconstructions and new additions using old techniques combined with some new technologies. There is no universal solution, and today each restoration project is recognised as unique, with specific challenges that require specific solutions.

In addition to the modern requirements for accessibility, climate and safety, there are inherent limitations in terms of strength, load-bearing capacity, geometries and dimensions. In the case of the Nationalmuseum, the challenges were even greater because of the stringent requirements for climate control and ventilation in the exhibition halls on the one hand, and the preservation of the structure and existing floor levels on the other. The designers at Sweco had only 60 millimetres at their disposal when they came to fit a new load-bearing subfloor between the existing brick vaults below and the top layer of flooring. few materials other than the chosen CLT panels could have satisfied both the design requirements and the small dimensions allowed by the building. The boards replaced the previous wooden planks and were laid like a puzzle on the short brick columns that transfer the loads from the floor to the vault,