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Written 5th November 2020

Project study seven

60 London Wall 

It is widely known that the greenest building is the one that already exists. As a practice we place retrofit and reuse at the heart of our approach and have extensive experience in the refurbishment of existing buildings. To create low-carbon structures capable of achieving the RIBA and LETI carbon targets, our approach for each project is to extensively research the site and its structure, creatively remodel, and sustainably repurpose.

Located in the City of London, 60 London Wall is a complex redevelopment of an existing post-modern office block. Alongside EPR Architects for our client CSHV 60 London Wall SARL, HTS is working on the structural design and delivery of the building. Previously a tired and outdated steel-framed building, the existing seven-storey structure has been retained and redeveloped and a five-storey extension has been added, increasing the building height to 11 storeys and the area to 46,238sqm.

To unlock the opportunities within the existing structure we exhaustively investigated archive information, drawings and photographs. Our understanding of the existing structure, gained from the research, enabled us to simplify the complex coordination of the steel frame with the new floor plates, optimising the construction process and minimising waste. Following the findings from the historic research, we undertook a series of material tests on site. The original columns and beams were surveyed and back analysed to ensure they could carry the additional loads of the extra five-storeys. Only 60 of the existing columns (equating to around 10%) needed strengthening with the remaining piles reused and proven. Resulting from thorough geotechnical investigations and analysis we were able to reduce the original Factor of Safety (FoS) of 2.6 down to 2.2. This enabled us to increase the ultimate load the existing piles could withstand and prove them for the new development.

The character of the building has been carefully reconsidered. At the heart of the building, a working atrium has opened up sightlines and increased natural light levels while the two pre-existing atria have been infilled, increasing the floor area. Designed for future flexibility, the building features large adaptable floor plates suited to a range of future uses and tenants.

Forming a series of new greened terraces, the floor plates step back from the façade line above the fifth floor. To achieve level finishes between the new internal and external spaces the slab and supporting steel structure have been dropped below the terrace areas and new steel transfer beams have been provided at each floor to accommodate the step backs.

To boost the building’s environmental performance, we worked closely with main contractor SKANSKA and EPR architects on each phase of works to accurately measure and significantly lower the building’s embodied carbon. This is an approach we have termed ‘Total Engineering’ and is one that we look to apply to a large proportion of our projects. By measuring everything from the strip out to practical completion and taking responsibility for as many phases as possible, the project has been delivered quicker, the cost reduced, and the embodied carbon levels lowered.

Our Total Engineering approach for this project included undertaking responsibility for the existing structure, connection design, demolition, temporary and proposed works. Through a holistic approach to the reuse of the existing structure, 8,600 tonnes of carbon have been retained, equating to planting 370,750m2 of forest area. The embodied carbon of the structural elements has been measured at 193 kgco2e/m2, sitting well within the LETI 2030 carbon target of 228 kgco2e/m2 and just above the RIBA 2030 target of 169 kgco2e/m2.