Bovis Lend Lease and demolition contractor Griffiths McGee are halfway through a complex deconstruction job on an iconic Grade II-listed block on the banks of the Thames.Paul Thompson reports
PAUL Sims, Bovis Lend Lease project director on the redevelopment of a listed office block in central London, has no doubt that, despite working on some of the capital's most prestigious projects in recent years, his current one has the potential to be the most taxing.
'It is not only an extremely challenging project technically, but it's also historically very interesting, ' says the affable Mancunian.
'What we are doing is taking the traditional home of a major corporation and revitalising it, bringing it up to date as a functional, attractive place for the corporation's employees to work.'
Unilever House, standing on the north side of Blackfriars Bridge, across the river Thames from many other landmark buildings, including the Oxo Tower, and within a stone's throw of St Paul's Cathedral, has been the headquarters of consumer product company Unilever for the better part of a century.
Now contractor Bovis Lend Lease and developer Stanhope are helping the building reclaim its former glory by giving it an update without disturbing its Art Deco facade.
Throughout its history Unilever has held the happiness of its staff in high regard. So, when it was reluctantly agreed that the layout of the grand old building and its less sympathetic north wing - added in the 1980s - were not exactly 'worker-friendly', much thought was given to its restoration.
'It just did not work particularly well for staff in the building.The links between the original structure and the north wing meant that staff had difficulties getting around the building. It was a bit of a maze, ' says Mr Sims.
The curved frontage overlooking the river is Grade II listed by English Heritage and its demolition was never likely to get past city planners or the heritage body, not that its total demolition ever crossed the minds of anybody working on the project team.
'The Unilever staff are incredibly proud of the building and feel a huge amount of ownership over the whole project.There is so much history in the building, not just its structure but its fixtures and fittings too, that everyone wants to try and preserve as much of the original as possible. It is an ideal that has spread through everyone working on the site, ' says Mr Sims.
Tony McAree, construction manager for Bovis Lend Lease, agrees.He has worked alongside Mr Sims for many years on huge projects, such as the Paternoster Square redevelopment not far from the current project.
'It is a fantastic building to look at and work on.
Like most redevelopment where much of the original building is being retained, the whole project is technically demanding, ' he says.
Which is why, before demolition contractor Griffiths McGee even stepped foot on site, representatives from Bovis Lend Lease, McGee, Unilever, Stanhope and architect Kohn Pedersen Fox ran through every demolition option on a computer screen, working out when and where the most difficult points on the project timetable would be to avoid unnecessary hold-ups.
A three-dimensional model of the whole site, including the original Unilever House, north wing and surrounding access was built. Computer analysis tools were used to work out the best sequence of deconstruction and dismantling for the project in a process that took eight months to complete.
'The building had probably been demolished a dozen or more times on a computer simulation programme before the final method was agreed, ' says Mr McAree.'They were just various engineering changes to the method but, put it this way, we were on revision 'K'when the plan was finalised.'
The McGee demolition team were on site for some 18 months before the final site start in October 2004, confirming general background surveys and working out the strategy for carrying out the extensive temporary works that help shore up the curved facade while work continues behind it.
'Around the 1930s, when Unilever House was built, there was a general rule of thumb for structural engineers that, if the building was as wide as it was tall, then it could be deemed stable.
'Obviously, we have moved on since then and we needed to be sure of a few details before we could start on the temporary works, ' says Andrew Stevens-Cox, project manager for demolition contractor Griffiths McGee.
For Mr Stevens-Cox that meant the digging of trial pits around the site and exposing the existing piled foundations.More than 1,800 steel-cased, reinforced concrete, 300 mm-diameter Raymond piles up to 12 m deep litter the site and these had to be accounted for so that Mr Stevens-Cox could prove his temporary work system.
There was also a dangerous legacy of asbestos to think about.
Despite an asbestos survey and strip carried out in the 1980s, when the north wing was built, some material was still left on the project.
'It is not that the original asbestos strip had been carried out poorly or the contractor had hidden some of the material but more that the asbestos stripping industry has moved on and become - like most of the demolition sector - more efficient.We just cleared the asbestos using the technological advances available to us today, ' says Mr Stevens-Cox.
This allowed his team to get on with the temporary works without fear of any unwelcome surprises.
And in those temporary works more than 300 tonnes of steel help support the frontage of the building.At the building's highest point, nine levels stand above the ground floor with a further three levels below that.
These are supported by a network of 305 mm universal beams that cross each level and help support and tie the facade into the remainder of the floor slab that will be left in-situ following demolition.
Three 'fingers' of the 1930s building that ran across the site between the main facade and north wing have been demolished as has half of the north wing itself (the other half houses the project offices and site welfare for all of the workers on the scheme) but at the front of the building, most of the original slab is being retained.The redesign has called for a more effective use of floor space in keeping with the demands of a 21st century office but as Mr Sims puts it: 'There is no point demolishing what you do not have to.'
Nevertheless, gone are the small individual offices that run along the perimeter of the building and in their place will be one huge, open-plan office on each floor.
The main lift and stairwell in the centre of the building is currently being demolished, which will help the final layout of the scheme.
But as each level is demolished the floor below has had to be propped to ensure they are strong enough to hold both the plant being used to take the building down piecemeal and the loading from the rubble itself.
The old clay hollow flooring is just not strong enough to take the combined loads from plant, debris and temporary works without a forest of props supporting its from beneath.
The demolition is carried out from top to bottom with nothing being smashed down. Steel beams are cut by a worker wielding an oxy lance and are then lifted out by machine.
Eventually a hole is made in the floor slabs and the assortment of specialist grabs, dumpers and 360s are lifted through to the storey below ready to start again.
'If we do not prop the floors then the whole thing could be demolished a lot quicker than we wanted it to be, ' says Mr McAree with a smile.
And with accident statistics revealing no reportable injuries on the project in more than 25,000 man hours, this is one scheme at least where safety will not be compromised by speed.
THROUGHOUT the project, Bovis Lend Lease and client Unilever have gone to extraordinary lengths to make sure that as much of the original building as possible has been reused or reclaimed.
Bovis Lend Lease even went as far as negotiating to ship the building's original boiler to India before the move foundered in red tape. Even the lifts have been rescued by elevator producer Otis, according to Paul Sims of Bovis Land Lease.
'Unfortunately, we failed on the trip to India but Otis lifts came in to take some of the equipment for use as spares on other projects, ' says Mr Sims.
The old oak panelling in the boardroom at Unilever House has found a new home at a new educational facility on the Isle of Wight and one fireplace that weighed in at six tonnes will be cleaned and reinstated.
'English Heritage was insistent on keeping some of the fixtures and fittings, but Unilever was also keen to try and keep as much of the original building as possible, ' says Mr Sims.
One of the prime finds on the project though was the 6,000 sq m of wooden parquet flooring that was found hiding, unloved, under an old carpet. Shipped off to a restorer in Aberdeen and stripped back to its former glory the floor will be reused in the new Unilever building.
Six tonnes of stone cladding, stripped from the walls of the building, will also be reused as floor surfacing.
'It is more labour intensive to work like this but we have found lots of opportunities to recycle and reuse.This is controlled deconstruction rather than demolition and it has helped in the reclamation of material, ' says Mr Sims.
McGee piles in
NOT content with looking after the demolition of Unilever House, Andrew Stevens-Cox, project manager at contractor Griffiths McGee, is also overseeing some of the construction work for the new building.
The contractor has the responsibility for excavating by hand the 14 new piles that will help support the structure.
With the ground being as poor as it is, some will go down as far as 22 m and, at 2.5-m diameters, this is no simple task.
'There are some programme benefits in us carrying out the piling work at this stage.
'The floor slabs above us give the pile workers protection against the demolition going on above, it means we can continue with both areas of work continuously, ' says Mr Stevens-Cox.
Looking after the workers
THE REDEVELOPMENT of Unilever House to help improve the building for its staff is not the first move by the company to benefit its workers.
As long ago as the mid-1880s, William Hesketh Lever determined that he should make an effort to provide workers at his soap factories with decent housing and schools.He became tired of paying high port fees and rent for his factory buildings resolved to buy a suitable site for a new factory and workers' village.
He settled on a 23 ha site on the Wirral alongside the river Mersey and opposite the then thriving port of Liverpool.With almost 40,000 tonnes of his main product, Sunlight soap, selling each year Mr Lever called his model village Port Sunlight. Its construction began in 1889 and by 1900 more than 400 houses had been built and more land acquired until the model village reached its current size of 130 acres and 800 houses.
Two large schools, a technical college, library, museum and open air heated swimming pool were also built for the benefit of the workers.
Project value: £70 million - shell and core
Joint venture alliance: Bovis Lend Lease/Stanhope
Demolition and piling contractor: Griffiths McGee
Demolition and piling package value: £6.5 million
Steel frame contractor : William Hare
Structural engineer: Arup Structures
Facade engineer: Arup Facades
Architect: Kohn Pedersen Fox