23 Jan 2023 By Paul Thompson
With limited space, Gilbert-Ash is transforming a former multistorey car park site into a hotel, commercial and office space. Paul Thompson reports
Scheme: 68-86 Farringdon Road ‘Clerkenwell Hotel’
Client: Whitbread Group
Architect: Sheppard Robson
Main contractor: Gilbert-Ash
Overall construction contract value: £45m
Overall development value: £90m
Construction start date: March 2020
Construction completion of hotel: Spring 2023
Construction completion of offices: Summer 2023
Contract type: JCT design and build
The Clerkenwell area of London has seen quite an uplift in fortunes since Charles Dickens set his novel Oliver Twist in the area. In the 1837 tale, its squalid housing and the open sewer that was the River Fleet play a starring role, providing the base for Fagin’s criminal empire.
Since those days, the area has changed markedly. Now, global centres of finance sit alongside fine-dining restaurants and trendy bars. Even the fetid River Fleet has disappeared from view, culverted beneath Farringdon Road, which plots the Fleet’s ghostly course until it empties into the River Thames at Blackfriars Bridge.
At the northern end of Farringdon Road, hospitality business Whitbread Group is planning to tap into the area’s vibrancy with a new six-storey mixed-use development featuring a 180-room Hub by Premier Inn hotel, as well as office and commercial space.
“We have been interested in the area for a good few years now, identified this site and managed to acquire it,” says Whitbread project and programme manager Chris Walton. “The opening of the Elizabeth line and its close proximity to the city makes it attractive.”
Developing Whitbread’s latest venture is a challenging task for contractor Gilbert-Ash under its design-and-build contract, which includes the full fitout of the hotel and delivery of the offices to Category-A standard.
It is being developed on a 1980s-built former multistorey car park site on an awkward slither of land hemmed in by neighbouring residential properties and a busy road. The site is 24 metres wide, narrowing to about 20 metres, and 94 metres in length, with the new development set to fill the space completely.
The Clerkenwell railway tunnel, dating from Dickens’ era, splits the site, with its shallow crown sitting little more than 10 metres below ground level, as Thameslink trains pass within going to and from Farringdon and St Pancras stations.
“These constraints have meant we have been forced to work from north to south across the site and that has influenced the phasing of our work,” says Gilbert-Ash contracts manager Karl Jordan. “We split the site into three sections and that phasing – which included capping a Thameslink ventilation shaft – has continued across the build process.”
Demolition of the reinforced concrete car park that stood on the site was undertaken by Redhammer Demolition. Being in such close proximity to neighbouring residential properties and the Thameslink tunnel meant the work had to proceed at caution and under constant monitoring.
Consultancy Waterman carried out a ground-movement assessment to look at how the tunnel may be affected by the demolition and both the temporary and permanent construction works.
Waterman evaluated the vertical and horizontal ground movements during each stage, concluding that maximum displacement would be around 12mm so the risk of work damaging the tunnel was low to moderate. Nevertheless, the project team was at pains to mitigate any potential for movement throughout the process.
“We worked closely with the Network Rail engineers and monitored the tunnel for movement 24 hours a day,” Jordan says. To minimise ground heave, demolition was carried out using concrete crusher attachments with dust suppression rather than impact methods.
Most successful projects include a combination of detailed design ideas and elements that come together during the process, and the Farringdon Road scheme is a prime example.
The architectural team at Sheppard Robson worked tirelessly throughout the project’s feasibility, concept and final design stages to create a building that gives a nod to the site’s pre-car-park tenement-block past, without the impact of a monolithic development that would dominate the smaller-scale structures surrounding it. By breaking down the scheme into separate facade finishes, they have ensured the completed scheme does just that.
But as Sheppard Robson’s Matthew Allen admits, ground-borne vibrations caused by trains passing beneath escaped their attention until a fortunate coincidence pushed the subject up the agenda.
“We were at a meeting in an office further down Farringdon Road and became aware how intrusive those vibrations were. We realised we needed to develop a solution that would isolate the building,” he says.
That solution, from Lancashire-based TVS Group, is a 50mm-thick foam mat that sits on top of the ground beams and slab to isolate the building, with further anti-vibration mounts on the lift core and the structural steel at ground and first-floor levels.
“It added six weeks to the programme, but we have a building that is acoustically independent,” he adds.
From the project’s earliest stages the plan had been to reuse some of the car park’s existing piles and ground beams (see box, below), minimising potential clashes and disruption to the Network Rail asset and saving on installation costs. Many were proven to be capable of reuse, but where new 1.7-metre wide x 2-metre deep ground beams spanning 25 metres were needed, the team fixed three layers of 50mm-diameter reinforcing steel, pouring the concrete in 500mm increments.
“There is a huge amount of steel in the bottom mat,” says Jordan. “The foundations are certainly robust.”
The structural frame for the new offices and hotel is steel, above a 2.4-metre deep basement made from reinforced concrete. The basement slab sits on the ground beams, which bridge across from the piles sitting either side of the rail tunnel.
It has been waterproofed using a two-stage barrier injection process from specialist supplier Rascotec. Injection channels are installed prior to the concrete being cast to ensure the waterproofing grout injected through them once the structural concrete has cured is distributed evenly to create a waterproof barrier.
The building’s facade changes over its length, differentiating the hotel and office sections. Brickwork finishes were dismissed as too heavy. Instead, distinctive copper panels are being used to clad the front elevations of the hotel element, while zinc cladding is being used over the office development. Retail units and ground-floor levels will be glazed. At the rear of the hotel, powder-coated aluminium panels have been used.
“We want the copper on the front elevations to develop its own distinct patina over time. At the rear we have settled on an approximation of that likely patina on the PPC [polyester powder-coated] panels,” says Matthew Allen, associate partner at architect Sheppard Robson.
The panels are configured to offer some level of privacy to hotel residents and people in the surrounding offices and houses – a difficult
task in central London and one that gives the building its distinctive ‘saw-tooth’ look. Windows are secondary glazed to eliminate noise from the street.
But with many hotel residents attracted by Clerkenwell’s newfound vibrancy, will they be that bothered by a little hubbub?
Cutting down waste in construction has to be a priority if the sector is to make significant inroads into the reduction of its carbon footprint.
Project-wide waste strategies help to do just that, but at Farringdon Road the team is pushing a little further.
As part of the building’s design, wherever possible, the team is reusing existing piles and ground beams initially installed to support the original reinforced concrete multistorey car park, to bear the new structure.
Its lightweight design when compared to the original early 1980s car park has helped, but the team still followed a painstaking process to verify the integrity of each pile and ground beam being reused.
“Verifying and testing each pile provided a risk throughout the process,” explains Gilbert-Ash’s Karl Jordan. “If one pile failed it meant we would have to go back to the drawing board and redesign.”
Each of the existing piles was tested for loading and fracture. In all, 45 original piles were reused with 25 cut and removed because they couldn’t be verified or were in the wrong place. An additional 12 new 900mm-diameter piles were installed to 25 metres to complete the array.
Ground beams measuring 1.7 metres x 25 metres x 2 metres deep were also reused where possible. Those that were redundant were wire-cut at each end and lifted out to avoid any adverse load differential across the site.
“It was a very demanding process and one which was carried out in close collaboration with Network Rail engineers. The safety and integrity of the tunnel was paramount,” says Jordan.
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