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National treasure

The historic Treasury building in Whitehall is undergoing a £128M refurbishment under an ambitious PFI scheme. Margo Cole reports.

Corridors of power really exist - but not for much longer at the Treasury. The 100-year old building is undergoing a major transformation that will see walls torn down and open plan offices introduced as sweeping changes are made in working practices at the Whitehall department.

Bovis Lend Lease is undertaking the refurbishment and reconstruction project as contractor to Exchequer Partnership, which has been granted a 35year concession to operate the building and lease it back to the Treasury. The work - financed by £128M in bank bonds - started in July 2000 and is scheduled to take 25 months.

The 100,000m 2building sits squarely at the southern end of Whitehall, its Portland stoneclad walls forming the entire north side of Great George Street. Treasury staff have been moved into the east side while 48,000m2 of space on the west side is rebuilt in this ambitious PFI project. When they move back, Exchequer Partnership - a joint venture of Bovis Lend Lease, Stanhope and Chesterton - will look for finance to refurbish the other half, and find another government tenant.

Government Office Great George Street (GOGGS), as it is known in Whitehall, was built in two phases at the turn of the 20th century. A 10-year gap between the two was taken up with delicate negotiations to persuade the ICE to move out of its newly built headquarters and relocate to the other side of the road. The first phase was built using load bearing masonry walls and clinker concrete floor slabs, while the later construction made use of newly discovered structural steel technology. Up to six floors of offices surround a square courtyard, with a further three basement levels below.

By ripping out walls and bringing existing light wells into use, Bovis is creating an extra 40% of space within the west half of the building. Bovis project director Julian Daniel describes the building as a doughnut, with the courtyard as the hole in the middle. Offices around the outside are being kept intact but from there to the courtyard, everything is being opened up.

Before work started the building was a maze of corridors, offices and small enclosed spaces - so much so that, according to Daniel, many of the 1,100 staff rarely ventured outside their own areas for fear of getting lost. The new scheme will make circulation easier, as well as turning the previously unused courtyard into a garden to create a 'focal point'. All services will be replaced, new lighting installed and a natural ventilation system introduced to improve environmental performance.

Light wells clad in traditional white glazed bricks penetrate the building, but currently offer little light. In the new scheme they will be roofed over to turn them into usable space for facilities including a library, kitchen and auditorium. One large light well at the west end will be incorporated into a new full height entrance and reception area, which will feature glass lifts (above right).

New light well roofs will be made of lightweight ETFE - the material used for the biomes at the Eden Project in Cornwall - to ease the load on the structure.

However, the total load is actually being reduced because so many solid masonry load bearing walls are coming down.

In all, Bovis is demolishing 12.5km of wall, some up to 6m high, and replacing them with an open plan layout based on a lightweight structural steel frame and concrete floors. However, it is not just a case of ripping everything out, propping up the facade and starting again.

The building is Grade II* listed, so nothing can be done to the external appearance, and English Heritage has to approve all internal work.

Walls and floors have to be preserved if they can be incorporated into the new layout. So while some sections have been demolished from floor to roof, in other areas individual walls and floors are being propped as part of extensive temporary works.

Some old walls also have a structural function. While planning the job the project team value engineered out all piling with a design that involves springing the new lightweight steel internal structure off the load bearing masonry. This saves money, but increases the amount of temporary works - predominantly a system consisting of steel 'goal posts' and intermediate props which can be removed systematically as the new floors are built back up.

Demolition contractor Griffiths McGee's £7M contract includes design of the temporary works, but the firm is working closely with structural steelwork contractor Rowen to ensure the new steel can be taken through and fixed into place.

Bovis has close relationships with the key package contractors, says Daniel: 'We've partnered 70% of the job and negotiated contracts with the firms. They're all friends.'

This is essential on what he describes as 'a builder's building. All the solutions are here, ' he explains. 'People say the devil's in the detail - and on this job you've got to understand the detail to understand what the risks are. If you take a superficial view you'll come unstuck.'

Design and buildability are completely interlinked, so the project team - which includes architect Fosters and consulting engineer Watermans - must be flexible enough to adapt to changing circumstances as demolition uncovers new problems.

A special feature of the Treasury building is the 'detonation slab' - a concrete slab between 1.75m and 3.5m thick that was installed beneath the ground floor slab when World War II broke out. Eight hundred workers were reputedly brought over from America for the slab's construction, as pumped concrete was still new in the UK at the time. The high strength slab, which contains 90N concrete and is reinforced with trams lines, was designed to withstand a bomb attack and allowed the government to relocate to the basement and sub-basement levels of the building for the duration of the War.

One third of the area beneath the slab is now occupied by the Cabinet War Rooms museum, which will be extended once the refurbishment is complete. For the most part, the slab is being left intact, but in some places sections have to be cut out, for example to give additional headroom in the basement, to install a new lift pit in the entrance and to create new wheelchair access.

In the circular east court the edge of the slab was visible in front of the building, and is being removed as part of the refurbishment. Specialist firm Robore has a £1M contract to cut the lumps of concrete out using a diamond wire cutter.

A core is drilled on either side of the section to be removed, so that the wire can be fed through it. The wire is attached to two arms of a hydraulically operated machine, which rotates, slowly bringing the arms closer together so the wire slices through the concrete.

The project is just six months old but already much of the demolition is complete and sections of permanent steelwork are in place. The last few corridors are about to disappear.

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