Brut strength on the South Bank: refurbishing London’s IBM building

How Multiplex is remodelling, refurbishing and extending London’s brutalist IBM Building – while retaining 80 per cent of the existing structure

The buildings lining London’s South Bank are some of the best-known examples of brutalist architecture in the UK. The moniker derives from the French term béton brut or ‘raw concrete’ – it has nothing to do with being brutal. And there is an extensive amount of béton brut on display at 76 Upper Ground, the former marketing headquarters of tech firm IBM.

The IBM Building, completed in 1983, marked the end of the architectural career of Sir Denys Lasdun, who also designed the nearby National Theatre. The then poet laureate John Betjeman felt compelled to write a letter of praise to Lasdun for the design of the latter. However, the defining features of brutalism – rough surfaces, exposed concrete, imposing mass and stark lines – are loathed and loved in equal measure.

Plans for the renovation of 76 Upper Ground were submitted in February 2020, and the building was granted Grade II-listed status four months later. It was on Lambeth Council’s list of notable buildings, but the council planning officer had no issues with the plans.

“We walked through the main individual from Lambeth who was on site for about two minutes, said ‘great’, then walked off. They are usually a lot more specific,” says Matthew Price, project director at Multiplex, the project’s main contractor.

The building is being remodelled, refurbished and extended, while retaining 80 per cent of the existing structure. The original building comprises  20,000 square metres of internal floor area over five floors, with two three-storey cooling towers and a basement. The result is set to be a flexible, low-carbon office space, according to Multiplex.

Extended floor slabs hosted in new extensions to the south and east plus a brand new sixth storey on top will add around 11,000 square metres of new floorspace. The project is also raising the sustainability credentials of the building. Multiplex is aiming for BREEAM Outstanding for office and Excellent for retail space, WELL v2 minimum Gold rating and a NABERS five-star rating.

Foundations, columns and cores

Keltbray stripped out the ground floor and basement and installed 300 new mini piles to support the existing foundations. Then pile caps were connected to the existing and additional drainage that was cut into the ground and basement slabs. Notably, the 69 additional backward raking (driven diagonally) piles were added to support and reinforce the original vertical piles. A mini piling rig was used by Kilnbridge (subcontractor to Keltbray) to complete the 90 raking piles and vertical piles within the building due to restricted head heights. A rotary piling rig used for 15 rotary board external piles. As the site sits just 15 metres away from the National Theatre, the project coordinators had to take steps to not be a nuisance neighbour. Keltbray avoided all noisy works on Wednesday afternoons to avoid disrupting matinee performances.

More than 4,000 cubic metres of concrete were poured into the new slabs, slab extensions and slab infills. The new slabs were dowelled into existing slab edges, and coupled reinforcement to the top mat layer.

Of the 680 existing reinforced concrete columns, 216 were strengthened to help support the weight of the increased floor plate, with loading calculations provided by structural engineers from HTS. These were bolstered by the addition of a further 252 new columns.

By way of top-down demolition, concrete cutting, and hydro demolition, Keltbray Demolition broke down slabs and the existing core structures. It also deconstructed the existing ramp and former lobby using cut-and-lift techniques. More than 1,000 cubic metres of concrete was poured with a concrete pump and boom to jumpform two new cores, which sit in former lightwells to the south and north of the building’s centre. Sandwiched between them, a new lift shaft and feature staircase have been added, enveloped by glass. Around 33 reclaimed beams and columns weighing a total of 42 tonnes (eight 356x368x177 and 25 254x254x73) were used to create the frame for the lift shafts.

The process began with structural engineering firm Heyne Tillett Steel (HTS) assessing the stock available and matching it to the design specifications. The lab results and aesthetic quality of the steel were then verified. The installation of reusable steel saved approximately 102,000 kilograms of carbon.

The north and south cores host risers for ductwork, pipework and electrics, and goods lifts plus staircases, but only the north core has firefighting lifts. The feature staircase, which Price describes as “massive”, had to be made offsite in several pieces then bolted together on site using powder coated mild steel.

The painted steel staircase was dropped into place with a chain winch held from temporary lifting beams on the underside of the roof slab. The finished stairs will include terrazzo stone step infills and timber battens.

The roof between the north and south cores will house plant pipework and plant-feeding ventilation systems. It will be a sedum roof, planted with different species of flora including succulents and grasses. The green roof will also see the installation of 300 square metres of photovoltaic cells.

Due to working in tight confines, it has been difficult to get supplies, equipment and machinery into the South Bank, which is mostly pedestrianised. Price says this has been overcome by using just-in-time deliveries and prefabrication. “We try and get all the big pieces of kit prefabricated, before we get it delivered to the site,” he says.

Electrical and multi-services risers were prefabricated and placed in the riser openings. TClarke then wrapped and hoisted the electrical risers to the relevant floors and put them in place with a forklift. In contrast, GBE lifted the multi-service risers by tower crane and dropped them in place. Washrooms have also been prefabricated using pods and are “literal plug and play”, according to Price. Fully fitted-out washrooms are moved into place, the ventilation, power and water are plugged in and “it’s good to go”, he says. Price says this way of doing things leads to less mess and avoids a backlog of deliveries.

Prefabrication also makes a project more efficient and removes some of the health and safety risks, as it is harder for elements to be mislaid, lost or cause an accident if they are already contained in the final unit, he adds.

Sustainability

Another material that has increased the sustainability of the project is ground granulated blast slag (GGBS), a byproduct of steel production that has become more popular in the UK over the past decade.

Calum Greer, site manager at Multiplex, explains: “We’re using a significant amount of GGBS in the concrete. The new columns, 50 per cent of the cement in them has been replaced by GGBS.” He also says that the cement in the concrete used to strengthen the old columns is 40 per cent GGBS.  According to the Cementitious Slag Makers Association, Portland cement CEM I with up to 50 per cent GGBS has similar strength to Portland cement CEM I after 28 days.

Multiplex is retaining 80 per cent of the original structure’s concrete to minimise the CO₂ emissions that would be generated by demolition.

As the building is listed, materials have to be retained for reinstallation. Keltbray salvaged 120 pre-cast concrete or granite cladding panels, ranging from 3 to 10 tonnes. Keltbray was also able to salvage 27,360 floor tiles, 95 tonnes of paving blocks and 71 tonnes of bricks. This equates to an emissions saving of 210,240kg of CO₂e (carbon dioxide equivalent weight). Furthermore, 62 listed facade panels and 20 listed core facade panels were retained by Keltbray, saving 88,068kg of CO₂e.

The raised access floor, created from Kingspan’s RMG600+ panels, is also carbon friendly as it is created in an electric arc furnace. The kiln is powered mainly by solar energy and the resulting steel incorporates at least 90 per cent scrap metal.

Blockwork masonry contractor Lyons & Annoot used cement-free mortar in new infill walls to create washrooms on slabs within the new cores.

Matchmaking

For the new precast aggregate panels to match the look of those from the 1980s, facade contractors Dane, OAG and Octatube are using Midlands-based Evans Concrete Products to hand set the pieces of aggregate. “It was a process done 50 years ago on the originals, and they’ve gone back to the same mine to get that aggregate,” says Price.

Price says that the facade system also led to a significant carbon saving. Dane fabricated and installed the office floor facade glazing system, while Schuco manufactured the terrace door systems. The doors were subsequently installed
by Dane.

While the IBM sign may have gone, the building is on track to retaining its imposing grandeur.