Retrofitting existing buildings: the added value

On the outskirts of Aarhus, a port city on the east coast of the Danish peninsula, lies a small single-family house from the 1960’s. Its architectural features draw on a local functional tradition, defined by yellow brick walls, large areas of glazing and a gable roof with eaves. The building was among the first big-scale prefabricated housing produced in Denmark for the rising middle-class, serving a post-Second World War generation who built and owned their own houses in the suburbs. Perceived as ordinary, their typology has not been subjected to heritage protection.

As the houses welcome a new generation of owners, many of them are extensively renovated and gutted of their original features. In this case, the new owners of the house wanted energy optimization. CJ Arkitekter, a Danish company, suggested removing a recent 18-square-metre extension and restoring the original floor plan and facades, contradicting a general tendency of adding more square metres to family houses. The building was insulated, old windows were replaced with energy efficient ones, and original details were preserved or repurposed when possible. Restoring the original architecture by subtraction, rather than addition, resulted in an optimized home with a better indoor climate and lower energy consumption.

This is an example of the application of the theoretical field of tectonics in renovation and restoration. A tectonic approach begins with the structural design of a building but takes into account its material and immaterial dimensions as well. A building’s architecture and history are seen as a meaningful contribution to society, collective memory and everyday life. Analyzing and understanding the historic intentions of a building enables architects to transform it in accordance with its original constructional principles and its layers of cultural meaning. 

In July 2023 in Copenhagen, Denmark, the UIA World Congress of Architects concluded with the presentation of the “Copenhagen Lessons” consisting of ten principles of conduct needed for the built environment to reach for the United Nations 17 Sustainable Development Goals. Among them, lesson three states that “existing built structures must always be reused first”. This principle aligns with the Intergovernmental Panel on Climate Change (IPCC) report on the climate crisis mitigation potential of retrofitting existing buildings in the western world.

Adaptive reuse, renovation and reconstruction as well as rebuilding offer broad fields of alternatives to the demolishing of existing buildings that fail to deliver to current needs. After decades marked by a rapid rate of demolition and construction, the emergence of transformative new technologies and global reckoning with environmental urgency, proponents of heritage practice are backed by a number of arguments. 

Over the past 20 years, around 150,000 housing units have been demolished in France, with the aim of replacing worn-down modernist projects with contemporary ones. This is a costly strategy with a significant environmental impact. In comparison, improving the pre-existing architecture can bring significant environmental and economic benefits. The Grand Parc case from Bordeaux, France, shows how adaptive reuse was achieved by analyzing the existing structure, its problems, the original intentions, as well as the people occupying it. 

The Grand Parc is a mass housing complex characteristic of 20th century architecture, a concrete construction erected at scale and vilified as the symbol of social challenges. Such modernistic apartment buildings were originally built to address housing shortages after the Second World War. Unfortunately, the construction techniques of the time had multiple negative consequences for the indoor climate and viability of the constructions, resulting in social pressure and stigma in many of these housing areas. 

The architects in charge of the project created a strategy based on respecting residents' appreciation of an otherwise overlooked building. Big balconies with sliding doors and reflective, insulating curtains, known as the winter gardens, were added to the building's south façade, therefore extending the living room area of each flat. The northern façade was insulated to provide the existing structure with an improved energy performance.

In this case, adaptive reuse was done on the basis of the analysis of the existing structure, its problems and original intentions, as well as the community inhabiting it, solving this with passive energy approaches and modern technologies. The approach consisted of working with the strengths of the structure while improving its performance and real estate value.  

Another example comes from the German capital of Berlin, where the Kapelle der Versöhnung was built in 2000 as part of a larger memorial complex. The chapel narrates the history of a 19th-century church that was situated in the borderland between east and west when the Berlin Wall was raised. It stood unused until 1985 when it was demolished. When the Wall fell, only rubble remained. 

Longing to rebuild a united city, the modus operandi of the Berliners was to remove as much evidence as possible of the division of Berlin, but the parish decided to reuse the rubble. A rammed earth chapel was rebuilt on the site. Red brick rubble from the old church was used as an aggregate for the earth construction. In this way, the parish was able to deliberately use the tectonics of the new building to take back the ownership of history and narrate the complex story of a societal trauma.

These examples of retrofitting have in common that the initial assessment was based on the tectonics of the building by linking design, materials, construction methods and structural logic with a sense of place, purpose and identity. Not only is this approach more sustainable, but it also enables architects to enhance the tangible and intangible values of a building and the community it is situated in. 

A building can thus be transformed in accordance with its original construction principles and its layers of cultural meaning. This approach has the power to bring out the meaningful contribution of a building to society, to the collective memory and to everyday life.