Down by the Riverside

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The five innovations that transformed a dowdy 60s block into a thameside attraction, all under the watchful eye of the HSE

The grand projects aren't all brand spanking new, writes Peter Kernan. A £38m refurb of Riverside House on London's Bankside has turned an ugly duckling office block into a steel-and-glass swan. More than just a makeover, the refurb stripped the building back to its frame before bolting on a whole new structure. It has also earned Bovis LendLease project director Chris Howcroft a place in the finals of 2003's Construction Manager of the Year awards.

Starting point for Howcroft was a drab 1960s office block with little appeal and less function. "Once the drab precast concrete cladding was off, the hundreds of closely spaced concrete columns in the building left us with something that looked like a jail," he says.

Then the developer decided to knock down neighbouring Bear Wharf and extend Riverside House. But getting an old building to line up with a new one is a tricky business. "The old building was all over the place," says Howcroft.

Points of View
The solution was to clamp a steel exoskeleton to the old concrete frame. By transferring the building load onto the steel support, Howcroft was able to remove many of the view-restricting columns. It also let him put in a spinnaker (a huge sail-like bulge in the facade), offering each floor big open-plan views over the Thames to St Paul's and the City. At its furthest point, the spinnaker extends 6.5m from the building. Bolting a new steel frame to the outside of the block and extending the floorplates up to it also increased floorspace by around 10%.

Another problem was headroom. Rather than lose another 0.2m or 0.3m from the already limited 2.7m headroom (0.1m had to go to put in the raised access flooring standard for cabling), Howcroft ran the lighting and the sprinkler system through multi-service chilled beams 3m apart rather than a suspended ceiling.

The whole refurbishment took two years and was completed under the interested gaze of 800 pairs of eyes from the nearby HSE offices. Everyone on the site, says Howcroft, got used to being at the centre of attention. "The building's lit up at night by huge blue spotlights," he says. "It was like working on the Starship Enterprise. Boats would come in at night to wave at the construction crew."

1 Drylining

With half of Riverside House a new-build and the other half straight refurbishment, drylining the offices helped establish a common identity. The lift shafts and stair cores were covered with fire-rated plasterboard. Enquiry number 207 (British Gypsum)

2 Flooring

The flooring was a real headache because the old floor screed had been hacked off to gain a bit more floor-to-ceiling height. Whereas most new offices put in a raised access floor some 150mm to 200mm off the subfloor to run telecoms and computer cabling through, most of the underfloor voids in Riverside House are considerably lower, at 100mm, to give the required headroom. The shallowness of the void made it difficult to install a dead-level floor over a subfloor that went up and down like a ploughed field. Over 2500 600mm by 600mm steel-encased wood-core flooring panels were delivered on a just-in-time basis. Enquiry number 208 (Access Flooring Services)

3 Cladding

Riverside House is clad in glass, aluminium and yellow terracotta. For cleaning purposes, the use of a window-cleaning cradle is superfluous because each storey-height window has its own walkway or balcony that gives access . All other windows are tilt-turns that can be cleaned from inside the building. The 1.8m wide floor-to-floor cladding panels were assembled offsite. It was an international affair: the aluminium was imported from Austria, the terracotta from Germany. Terracotta handrails wrapped around a reinforcing steel tube on the external window-cleaner walkways offer sufficient solar shading to dispense with blinds. Enquiry number 209 (GIG Facades)

4 Steel

Around 1400 tonnes of steel went into Riverside House and its new-build extension. Attaching the steel to the old concrete structure required 70m3 of grout and took up 10 weeks of the programme. Steel supplier Rowecorde also engineered the spinnaker’s six vertical arms (each made up of curving steel tubes joined to each other by a single pin), bolting them at the top to one of the building’s two massive concrete cores to prevent the whole thing toppling over. “I wanted a company that could think it through,” says Howcroft. “You only get it right once.” Reader enquiry 210 (Rowecorde)

5 Service beams

The building contains around 3350m of multi-service chilled beams supplied by Trox. Delivered pre-plumbed and pre-wired in 3m lengths, the 80cm wide by 20cm deep beams were suspended 8cm below the ceiling. Six risers on the outside of the building channel the services through internal bulkheads. Reader enquiry 211 (Trox)