Preserving suspended structures with light façades (1960-1980).Architectural study and retrofitting proposals

Nowadays, the energy efficiency of the existing building stock is internationally accepted as a topical issue. Energy retrofitting is encouraged, improving the thermal performances of buildings, but often altering the historical image of our cities. Attention should be paid to preserve not only environmental, but also cultural resources. Accounting for almost 45% of the existing stock, the architecture of the second half of the 20th century is seen as the main target, a vulnerable category in spite of its heritage values. Invasive renovations, exclusively aiming to energy savings, are becoming increasingly common, with minor concerns about preservation. In this context, suspended architecture constitutes one of the most threatened building types. Suspended buildings are characterized by the brilliant combination of hanging structures and light curtain walls, features that make of preservation an absolutely challenging practice. Historically, suspended architecture mainly developed between the 1960s and the 1970s. After the 1980s, cable-supported solutions were progressively abandoned and hanging construction was almost forgotten, even by contemporary historiography. Thus, the first aim of the present thesis is the knowledge production, starting to fill a recognized gap in the field of construction history. The phases of suspended buildings' development are retraced, from rise to fall, with a focus on engineering, technologies and building components. The recognition of hanging architecture's qualities allowed to assess suspended buildings' heritage value. At the same time, the lack of shared retrofitting guidelines in modern heritage preservation made it clear the need to develop a cohesive method, capable of integrating thermal improvement and architectural conservation. Assuming as a starting point the 15-years-long research developed by the TSAM lab at the EPFL, the second aim of this thesis is to outline a methodological approach to preserve the cultural values of modern buildings, while fulfilling the main energy standards. In this sense, a multidisciplinary methodology is defined, consisting in a step-by-step process, including historical and architectural research, heritage preservation, building technology. The proposed method has been tested on three buildings: the BP tower in Antwerp by L. Stynen and P. De Meyer (1961-1963); Chauderon administrative complex in Lausanne by Atelier AAA (1970-1974); the Olivetti Corporate Building in Florence by A. Galardi (1969-1972). Starting from the archival documentation and crossing multiple sources, the construction history of each building is presented. Several intervention scenarios are proposed and compared; detailed redrawing allowed to understand specific architectural design and building technologies; while dynamic models permitted to simulate the energy consumptions. The final results are encouraging, reducing the energy consumptions for heating by more than 70%, always respecting the original materiality. The two issues of architectural preservation and energy improvements - sometimes a priori opposed - appears in this way reconciled. It is also assumed that the technologically extreme suspended building type can constitute the basis for a wider scale application, covering more common cases. An alternative way towards future architectural retrofitting is thus outlined, opening up towards a stimulating debate in the field and capable to better address today's needs of society.