Construction engineering to transform the composite frame of YY London

30 South Colonnade was a 13-storey composite framed office building, completed in the early 1990s as part of the first phase of London's Canary Wharf redevelopment. Between 2020 and 2023 it was refurbished to become YY London, a highly sustainable modern workspace. A key aspect of the project has been retention and reuse of much of the existing structure, dramatically reducing the new development's embodied carbon impact. This paper describes the way the composite steel-framed building's original structural configuration was developed to accommodate the move to on-screen share trading in the 1980s. It then outlines the reasons that change why change was needed for the 2020s. A key feature of the construction engineering was demolition that disconnected several bays of the original bracing from the surrounding slab, requiring staged construction of temporary stability, and complicated by an unusual decision by the original designers. UNSDG 12 Responsible Consumption and Production is stimulating architect, engineers, and clients to propose more extensive reuse of structures and their embodied carbon. This paper describes the construction engineering challenges that these schemes generate for contracting teams, and some of the solutions that can be implemented to preserve and reuse the embodied carbon of composite buildings.