Brutalist icon skilfully revitalised

Among the most significant cultural establishments on the South Bank area on the southern banks of the River Thames is the National Theatre, constructed in 1976 in line with architect Denys Lasdun's design. In 1983, Lasdun completed his vision on the neighbouring with the construction of the IBM Marketing Centre. The two buildings impress as a late Brutalist ensemble with balanced symmetry, horizontal lines, rough exposed concrete surfaces and imposing concrete structures. To prevent its partial demolition after IBM moved out, the City of London granted the former IBM building listed status in 2020, as it had the National Theatre in 1994. The architectural practice AHMM revised its conversion concept and promised the retention of 80% of the original fabric of the building.

The asymmetric building structure of the old complex featured offset storeys to the north and south, which created wide terraces. Brown bricks were applied beneath podium level, while in the upper storeys the continuous ribbon windows and exposed aggregate concrete spandrels matched the horizontal lines of the adjacent theatre. Plant towers with a pure concrete appearance formed sculptural elements on the roof. For the strategic development of the project by Stanhope PLC, the project now known as “76 Southbank” provided all the key aspects for a site remodelling geared towards sustainability: retention of the existing structure and value enhancement through renovation, as well as revitalisation and reinvention of a building steeped in history in accordance with listed building requirements, with major benefits for urban renewal.

The new concept from AHMM envisaged a sensitive modernisation. Following a low-carbon core renovation and energy efficiency upgrade, the floor space was to be increased by 11,000 m² by adding a new storey on top and by extending out to the south and east, creating new highly efficient, flexibly designed office spaces. To meet the exacting sustainability targets, the embedded carbon emissions in the existing building and the amount of waste generated during gutting needed to be reduced as much as possible. To do this, all of the construction materials from the existing structure and for the newbuild were subject to a comprehensive assessment with regard to their ecological footprint, with some extensive environmental compatibility tests being carried out if there were no EPDs available.

Despite gutting and dismantling the basement and ground floor, it was possible to retain 80% of the concrete structure and therefore prevent carbon emissions that would have been caused by demolition. Over 200 façade units made from concrete or granite were dismantled and either reused in the project or elsewhere; as were 27,360 floor tiles, 95 tonnes of paving stones and 71 tonnes of bricks. New foundations were laid and concrete supports were installed, with ground granulated blast furnace slag sand replacing 50% of the cement. Recycled steel beams and supports weighing were installed and recycled steel was used for the cavity flooring in the offices. The Ultra Low Carbon aluminium from Schüco has saved over 100 tonnes of carbon emissions when compared to standard aluminium. The annual carbon savings are equivalent to 425,000 m² of native forest.

The new façade played a major role in meeting sustainability targets, as it accounts for a considerable proportion of the embodied carbon in the project. Schüco supported Dane Architectural during the early analysis of the existing building by providing project-specific EPDs via SchüCal and, in doing so, enabled the precise analysis of the carbon footprint. Another focus of the collaboration was the use of recycled materials on the project. “We met the sustainability requirements with our Schüco ULC aluminium profiles,” explains Stephen Newell, National Specification Manager. “The profiles have a GWP value of less than 1.99 kg CO₂ e per kg of aluminium and are manufactured from at least 75% recycled post-consumer material.” The façade of 76 Southbank was constructed using the Schüco FWS 60.SI mullion/transom system in the version with surface-mounted cover strips. The ULC aluminium delivered by Schüco in accordance with the allotment process contributed to a saving of 100 tonnes of CO₂ in the carbon footprint.