Northacre aims for stability in an uncertain environment
Client/developerNorthacre/Minerva joint venture
Construction manager Woolf Shell and core contractor Coinford
Structural and civil engineerConisbee
Demolition and temporary worksKeltbray
Project value £100 million
Completion date December 2010
Spending £100 million reconstructing a single residential development might not seem the smartest move, given the current climate.
But if it’s turning a run-down 1970s hotel in London’s Bayswater into 77 luxury apartments – and you are a developer whose homes still sell for millions of pounds – there is money to be made.
Northacre, the firm in question, specialises in transforming dilapidated historic buildings in London into premium properties. Its latest project is The Lancasters, a seven-storey, Grade II-listed mid-19th century terrace on Bayswater Road.
Currently at the demolition stage, the project will become flats which have been designed so that through the windows they will look like period homes.
The building’s character will be kept by retaining the original stucco and brick facade.
At 124 m-long and 26 m-high at the front of the building, it is thought to be one of the largest facades in Europe.
What is effectively a new building will be constructed behind the facade. And almost 24,000 cu m will be excavated in front of the facade to help create 31,000 cu m of underground car park and plant rooms. This will have gardens planted on top.
David Charlwood, project director at Woolf, which is managing the project, says that 500 tonnes of steel is being used to temporarily restrain the facade during the demolition of most of the rest of the building.
Walers support the flat front of the building facing Bayswater Road and a series of flying buttresses support the back of the building, which is stepped.
A mini bore-piling rig was driven in through the building to put piles in for each of the flying buttresses.
“After piling, we dropped in stanchions using a tower crane, through openings broken out in the floor slabs and through the roof. Then the beams and braces, supporting the flying buttresses, had to be constructed within the existing building while trying to keep it watertight as best we could,” Mr Charlwood explains.
Lattice beams run through the flying buttresses on the outside of the building. Then to support the building while the floors come down, flying shores were put in through the windows, above and below each floor.
“As soon as we put a flying shore in at the top and bottom of the top floor we could remove that floor. We worked our way through the building taking all the floors out as we went,” says Mr Charlwood.
“You end up with a huge great open space with the flying shores keeping up a 26 m high existing brick and stucco facade.”
But flying buttresses could not be used on the front of the building because there would be excavations going on for the garden and underground car park.
So the facade on the front was stabilised using walers which run across its entire width.
“The walers were put through at the same time as the buttresses, and sit outside of the building. They are fixed on by cantilevered brackets attached to the flying shores. So it’s keeping it one place,” says Mr Charlwood.
Demolition is due to finish early next month. The team is reconstructing at the same time, starting with two swimming pools on the west end of the building. As the floor plates go in, the flying shores will come out and then the buttresses.
The facade is constantly monitored for any movement and at one point the site was closed for two days as faulty equipment suggested the facade could fall off.
The existing walls have also been underpinned. Mr Charlwood says that this was done because the lower ground floor had to be lowered to make way for an acoustic floor to absorb vibrations and noise from the London Underground central line, which runs almost parallel with the building.
The hotel had got around this problem by putting ballrooms and conference rooms on the lower floors.
“Reducing the level of the existing floor would have meant we compromised all the existing foundations,” he says.
“We extended the existing walls down by about a metre and used a concrete stem and a pad foundation and then drypacked in between.”
It is a laborious task: there are nearly 700 underpins and the process has been going on since December last year – but it is due to finish soon.
The excavations for the garden at the front of the building are monitored carefully as they are closest to the Underground tunnels, and 12 m contiguous piles form a perimeter retaining wall around the garden. The piles are outside the exclusion zone set by Transport for London and the most they have moved is 10 mm.
“Before we started digging the garden box we contiguously piled all around it. There are 318, 750 mm diameter piles with props in between,” says Mr Charlwood. Groundwater is not an issue because of the area’s impermeable London Clay.
The garden zone is being worked on from east to west because of logistics. But the building will be constructed from west to east, because the most expensive homes are at the far west of the building, at number 75 and 76 and are about 10,000 sq ft each.
The idea is that they will be sold first to release capital – the developer would not be drawn on their asking prices.
“The challenge for us is to complete the whole of the garden zone before we get completion of the building – we need all the concierge finished, a fully live occupational building and the garden to be completed at the same time,” says Mr Charlwood.
As the building has been tinkered with over the years, various discoveries have been made, including quite a lot of timber.
“The facade is made up of brick piers which take most of the load from the party wall from the floor and the spandrel panel in between. They are then dissected with embedded timbers, so one of the things we found was that most of the openings had existing timber lintels in them which have been replaced over the years, some with steel and some precast. We are now replacing them all with precast,” Mr Charlwood says.
There is also embedded timber in the protruding cornices and balconies – some are being kept in place.
Chris Gaylord, a director at Nilsson Architects, whose founder Klas Nilsson has a 20 per cent stake in developer Northacre, adds that timber was much relied on in the 19th century.
“Wood was an important part of the construction. They used the long spans as tension members to try and hold the whole thing together. The bricks were piled on top of them and they became very strong because they are clamped into place. We opened up a lot of them and they were fine,” he says.
The building will have a concrete structure, the walls are precast in Germany and then slotted in.
“The frame contractor Coinford put the idea forward and there was a huge advantage in terms of time and site logistics. one of the big problems is where to keep the concrete,” Mr Gaylord says.
“Structurally it would have been easier to do an in-situ concrete building.”
Access to the site is tight with it being in central London. “We are using every square inch here,” says Mr Charlwood.
“We’ve got two tower cranes up. Everything that comes in has to be offloaded from Bayswater Road so we’ve got no storage, it’s all just in time deliveries.
Normally we have 70 to 80 traffic movements in terms of muckaway lorries. We close Leinster Terrace every day at 8 am and reopen it at 6.30 pm.”
Control is tight. All parties are contracted directly to Northacre and many have worked with the developer before.
Building services and fitout contractors are being procured at the moment and it seems there is no shortage of companies wanting work.
“There are a lot of people available for work, it’s just how many understand the ethos of what we produce,” Mr Gaylord says.
FROM THE CRIMEAN WAR TO TODAY
The terrace was built originally as 15 grand houses overlooking the north side of Hyde Park.
Woolf project director Dave Charlwood explains that the original 120 m long building probably took 10 years to complete when it was originally built in 1855.
“It was the Crimean War, a housing slump was straight after where no one wanted to build because it wasn’t worth it – things don’t change really. Henry Austin, the developer, went bust eventually. So let’s hope we don’t repeat the saga,” he says.
The first five homes were built with elaborate, barrelled roofs and the rest were simpler, the original developer changing the specification in line with what it could afford.
Then in the 1920s the homes were divided up into flats, and in the 1970s it became a 400- bedroom hotel.
“It was a bit of barbarism, they put a huge central corridor through the middle of it to form one of the longest hotel corridors in Europe, but it did nothing for the character of the building,” says Mr Charlwood.
A concierge area was added in the middle in the 1980s, which meant that all the party walls were taken down. Then a transfer slab was created at ground floor level, which was all reinforced concrete and transfer columns and beams going back down to the lower ground floor.
Some of the original cornices and fireplaces will be preserved, along with balconies and two cantilevered staircases. The party walls are being cut down by hand and brickwork repairs to the facade are done but the staircases were too fragile to remove so everything had to be demolished around them.
And while the area may be the preserve of mid-market tourist hotels, there is still a dose of aristocracy. Lord and Lady Kennet are close neighbours and can see what is going on from their first floor window.