The Tour Bois-le-Prêtre, north of Paris, was a seventeen-storey social housing tower built in 1961 and slated in the 2000s for demolition and replacement. Anne Lacaton, Jean-Philippe Vassal and Frédéric Druot put a counter-argument to the municipality: demolition destroys both embodied carbon and a settled community, and the same budget spent on improving the existing building yields more.

The solution was direct. The building's narrow concrete façade was removed and a three-metre-deep layer on a light steel structure added outside it: first a winter garden for each flat, then a balcony. Flats grew by about sixty per cent on average; the winter garden works as a thermal buffer in winter and as shade in summer, lowering energy use. Most importantly, the work was carried out while residents stayed in their homes — façade elements were prefabricated and craned into place, and no family moved.

The cost was roughly half that of rebuilding the same number of dwellings. The team repeated the method on the 530 dwellings of Grand Parc in Bordeaux, which won the Mies van der Rohe Award in 2019; the Pritzker Prize went to Lacaton and Vassal in 2021. The citation records a change in architecture's criterion: not to make something new but to make what exists better for more people. In a period when construction accounts for roughly a third of global carbon emissions, not demolishing is not an aesthetic preference but the result of a calculation.