Client:The Great Ropemaker Partnership, a joint venture between Great Portland Estates and BP Pension Fund
Structural Engineer:Heyne Tillett Steel
Orms has reinvented an unloved 1970s office block, expanding the workspace by 70% thanks to spare capacity in the structure
By 2013, 160 Old Street was looking decidedly out of place in London’s high-tech quarter. Built in the 1970s as offices for the Royal Mail, it was ripe for demolition, with dated interiors, low ceilings, inflexible layouts and wheezing systems. Fastforward eight years, however, and it has been granted an unlikely second life, swapping the humble postal service for 21st-century communications as the London base of satellite news giant CNN.
The building may look completely different, but in fact, 76% of the original concrete structure was retained. “Refurbishment is always our first port of call, because of the amount of carbon you can save,” says Simon Whittaker, director at project architect Orms. “And this building had good bones to it.” According to the Revit plug-in One Click LCA, this reduced life-cycle emissions by 2,850 tonnes.
The other constraints on redeveloping the site from scratch were the existing nine-storey structure’s under-reamed piles, which would have been impossible to excavate, and the surrounding buildings’ rights to light, which ruled out a new high-rise. Despite this, Orms and structural engineer Heyne Tillet Steel, were still able to increase the net lettable area of the building by 70%, pushing out the perimeter by 500mm, inserting strategic connections between the wings of the E-shaped plan, and adding three lightweight storeys to the top of the structure. “Part of the reason we were able to do that was that the concrete frame had such inherent capacity,” says Whittaker.
“We added 40% additional load to the frame without having to reinforce it.” The starting point was to understand as much as possible about the original structure. HTS managed to find about 260 of the original structural drawings, from which the team built a Revit model, using the original 1970s concrete codes. “This was one of the first projects that we as an office did in BIM,” says Whittaker. “We all collaborated on the model and that gave us a really good understanding of the structure very early on.”
As they began to strip the building down to the frame, HTS could then confirm their assumptions by taking core samples. “That verified the strength they were anticipating, but it also verified that the concrete had gained strength since it was poured, which was very useful.” The structure may have been in good repair, but it was still designed to house a very 1970s idea of what an office should be. Floor-tofloor heights were a slightly claustrophobic 3m and the unusual E-shaped plan meant there were no fewer than five cores, two with lifts and three with stairs. The floor was a clay pot slab, which was in good condition but restricted where ceiling fixtures could go – any damaged pots had to be repaired to maintain fire integrity.
All of this presented a challenge, as this was a speculative development and the client, Great Portland Estates, wanted an extremely flexible office space that could suit a variety of tenants. Orms’ guiding philosophy, however, was to work with the fabric of the building. The existing cores were kept, which resulted in the entrance moving onto the eastern elevation, away from Old Street. “Rather than making a new core with all the lifts in one place, we created this long pavilion-like reception area: you deliberately come in right in the middle of the two lift cores and are then directed to one or the other depending on what floor you’re going to,” says Whittaker.
It’s an intriguing example of form following a previous, defunct function: “Had it not been for the cores, the reception wouldn’t have been quite as generous and open as it is.” Embracing the original structure went as far as leaving a wall in one of the lift lobbies, right in front of a lift entrance. “Originally we said, ‘we’ve got to get rid of it, it’s not where you’d want to have this wall’, but because it was a shear wall it would have cost about £1m to remove it so we decided to expose it and make a feature of it. We grit-blasted and lit it, and it has become part of the experience of the building.”
Orms continued to expose the structure wherever possible. “We were quite conscious about how honest we wanted to be with the found elements in the building, and it was just about making the most of all these different things we uncovered.” The internal columns on the upper floors have been grit-blasted, while the soffits on the lower floors, once parking and storage areas, have been stripped back to celebrate their deep downstand beams. “It was a very dynamic space to turn into an office, with big structure and big spans,” says Whittaker. “They were the spaces that TBS [owner of CNN] took, because of those really interesting volumes.”
The columns in the reception area are just as striking. Originally external perimeter columns, these have been grit-blasted to expose the Halfen channels that once anchored the cladding, giving a steel pinstripe to the raw concrete. “We debated whether we should pull them out, but it provided a really good contrast to some of the more clinical finishes in the reception.”
The exposed structure also helped to solve the problem of achieving 2.7m-high ceiling heights with so little headroom for manoeuvre. The services are channelled through a metal raft system along the middle of each wing of the building. Beneath this raft zone, the floor-toceiling height is 2.4m, but the rest of the soffit is clear up to the structural slab, giving the extra 30cm. “Having multiple cores came to our aid here,” adds Whittaker. “We could serve the floor plates from both ends, halving the length of the ductwork, and reducing its depth.”
The result – after some suitably media-friendly fitting out – is an office that comfortably holds its own against the district’s best white collar factories, with flexible workspaces, new light-filled internal courtyards and external terraces on every floor. Occupants control the lighting and temperature of their desk space using a smartphone app, which is based on a digital twin that records and monitors the building’s performance. In time, it will also inform any future adaptations – which should ensure that tomorrow’s structural engineers don’t have to root around looking for 50-year-old drawings …