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The Barbican Centre in London is architectural Marmite – visitors either love the bold geometric shapes, bush-hammered concrete and chunky brass fittings, or they hate the confusing layout, elevated walkways and murky 1970s colours. But the construction team working on the refurbishment and residential conversion of Frobisher Crescent, a dramatic nine- storey curve in the heart of the complex, has found that the Barbican’s charms grow over time.

It’s partly because contractor United House and architect TP Bennett have found themselves working in an authentic construction time-capsule. Site manager Mick Wade was at technical college in Doncaster when the Barbican was under construction, and remembers it being used as a teaching example. ‘The quality here’s exceptional,’ he says. ‘Today, all the trades are using lasers.

But if you look at the concrete parapets on the towers, they’re all in perfect alignment. You have to admire the craftsmanship of that era.’

Phil Baxter, a director of United House, has found that the quality of the original specification has made its job significantly easier. ‘We were surprised how durable the original windows and sliding doors are – the original mechanisms still worked after 30 years. We also found the original ironmongery on the doors, and steel Crittall windows. Everything was obviously well designed and considered at the time.’

For Chris Bennie, principal of TP Bennett, it was the resonance between the aspirations of the original design team and today’s thinking on sustainability, mixed-use development and efficient design that made Frobisher Crescent fascinating to work on. ‘While I wasn’t a fan before, my appreciation of the Barbican estate grew the more I began to understand it. As an example of dense urban living, it has real relevance again now,’ he says.

Completed in 1982 and listed along with the rest of the complex in 2001, Frobisher Crescent was the final building in the Barbican Centre, a pioneering mixed-use arts and residential complex built by the Corporation of London on a site left vacant by bomb damage in the Second World War. It was designed by architect Chamberlin Powell & Bon in the 1960s and 70s as a brave new architectural world.

The crescent was originally designed as a series of wedge-shaped flats with the topmost floor enjoying generous ceiling heights under a barrel-vaulted roof. But at some point during construction, the Corporation changed its mind, and the building was re-purposed as offices. Lower floors were – and still are – occupied by admin teams for the Barbican and the London Symphony Orchestra, while the three top floors became teaching space for the Cass Business School, part of City University.

The latter’s decision to move out created the opportunity to return the upper part of Frobisher Crescent to its intended use. The Corporation selected developer/contractor Untied House, partly because of its strong reputation in refurbishing residential blocks while the occupants are in situ. The Barbican complex also includes more than 2,000 flats, and the new scheme will add another 69, split between space-efficient studios and one- and two-bedroom flats.

But the mix of uses created an unforgiving environment for the team. Frobisher Crescent is situated directly above the Barbican’s Concert Hall, a location that placed tight restrictions on noise. United House has also had to share a single loading bay with the rest of the complex – which also includes conference space, a theatre, a gallery, cinemas, and a reference library – and take all materials in and out via a single hoist.

As a result, the main challenge has been managing noise, demolition and deliveries. In a given week, the client only allows noise-making activities on certain days or part-days (when the LSO wasn’t rehearsing). ‘The rest of the time we’ve got to be practically silent. But we’ve worked out the programme to accommodate that and increased the labour at the times we need,’ says Baxter.

During demolition, United House deployed a team on each floor to spend the entire day breaking things out, then two days loading rubble onto pneumatic trolleys. Where there was a need to break out the concrete to create new internal openings, a small ‘nibbler’ was used to bite away small pieces. ‘There were additional costs, but we had virtually no complaints,’ says Baxter. The noise limit set by the client was 75dB, but the team kept within a 50-60dB range.

In the site office, a constantly-updated plasma screen keeps everyone informed of activities in each part of the site, and also alerts the team to the approach of a delivery truck. Sub-contractors are notified to make sure their site operatives are there to meet it. Baxter says that the system has been ‘an absolute boon’. ‘It tracks everything, so there’s never any arguments about when something was delivered. Yes, it cost money, but it’s enabled us to deliver what we said we’d deliver.’

The flats were designed with underfloor heating running on hot water supplied by the Barbican’s district heating system – a combination that any sustainability-conscious contractor today would surely recommend. But in an era overshadowed by the 70s oil crisis, the power source for the district heating system was electricity, which was assumed would be cheap and plentiful as the UK entered the nuclear age.

United House opted against updating the underfloor heating, which would have meant breaking out 150mm of floor screed in each flat. The district heating system was replaced with a new communal boiler, and the individual flats are heated by radiators. Insulation has been added to all internal and party walls.

The flats originally featured back doors that opened outwards onto the outer walkway. ‘In the event of escaping a fire, you’d be likely to knock your neighbour over the balcony!’ comments Baxter. However, the contractor was able to remove the door-sets, refurbish them, then re-hang them to open inwards. In some cases, damaged doors were replaced by originals from elsewhere in the building. At the same time, steel Crittall windows to the partially-glazed outer walkways were stripped and refurbished.

Sliding French windows at the front overlooking the Barbican’s Sculpture Court also provide access to the curved inner walkway. Again, United House was able to re-use some of the originals, complete with their lever handles, although some duplicates had to be commissioned. The original single glazing in the windows was also replaced with double glazing.

On the inner curve of the crescent, solar shading to the flats is provided by banks of tilting wooden louvred screens. These were stripped and refurbished and fitted with a mechanised opening system.

‘The quality of the original fittings and external joinery was so good, it’s hard to know which were new, and which were original,’ says Bennie. ‘It shows you don’t need to use plastic or powder-coated metal for durability – it was a real lesson.’

A further problem was that the original service runs were encased in concrete and United House had to be creative in finding routes to thread new vertical risers and horizontal distribution. Overhead bulkeads now carry services along the outer walkway, while newly-built risers deliver water to each flat.

In the uppermost floor, the flats under the vaulted roof have double-height living space overlooking the Sculpture Court to the front and a mezzanine sleeping platform to the rear. The barrel vaults themselves had originally been coated in spray-applied insulation, which was found to be flaking off in patches.

The contractor retained the original look and feel of the rough-cast texture, but applied a spray-on hardener. ‘We could have chipped it all off, but that would have meant lorryloads of rubble and wet trades on site,’ says Baxter. ‘We managed to track the manufacturer of original material, who supplied the new coating.’

When the construction team leaves the site early next year, it will have the satisfaction of knowing that the upper floors have been restored to their original planned use with their original features and in the original spirit of space-efficient urban living. As a parting gift to a building that has provided so many bonuses and insights, United House will make a donation towards the renovation of the under-used Sculpture Court.

Accommodating conversion

The conversion will deliver 19 flats on the 7th floor, 24 on the 8th floor and 26 double-height flats with mezzanines on the 9th floor, all accessed by three stair and lift cores.

Rather than re-instate the original Chamberlin Powell & Bon designs, which featured duplex flats with concrete internal staircases, United House has re-thought the layouts and created a mix of studios and flats.

The concept of good use of space is continued with fold-down beds in the studios and mezzanine platforms in the top-floor flats.