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Willmott puts Plymouth's maritime history in a box

Plymouth’s Museum and Art Gallery is being transformed through a project featuring everything from new build and asbestos strips to heritage carpentry and stained glass restoration.

Project: ‘The Box’ Plymouth
Client: Plymouth City Council
Contract type: JCT Traditional
Contract value: £23m
Region: South-west
Main contractor: Willmott Dixon
Start date: June 2017
Completion date: September 2019

Plymouth is a city packed with maritime history.

A major port for the British navy, it was also a stopping off point for the Pilgrims’ voyage to America aboard the Mayflower, as well as the location of Sir Francis Drake’s famous game of bowls before the rout of the Spanish Armada.

So it is easy to see why a city brimming with historical significance is investing more than £30m in a new history and art centre.

‘The Box’, as the completed scheme will be known, features the complete transformation of the city’s Museum and Art Gallery building, which sits opposite the towering campus of Plymouth University on North Hill. It will become the focus for the city’s ‘Mayflower 400’ commemorations in spring 2020.

The Grade II-listed structure is being refurbished and remodelled inside with a new extension added at the rear. An outdoor plaza and exhibition space will link this extension to another indoor gallery and lecture area, which are being created from the former St Luke’s Church on Tavistock Place.

From heritage to new build

“This is a high-profile project for Plymouth and we are grateful that the city council has the trust in us to make sure the project is delivered,” says Willmott Dixon senior building manager Kristian Cartwright.

“It is a fantastic scheme to work on. It has all the elements of construction – new build to heritage work and pretty much everything in between.”

The Box Plymouth Willmott Dixon Plymouth City Council 9467

The Box Plymouth Willmott Dixon Plymouth City Council 9467

He’s not wrong. Work on the original building has included the full demolition of an unsympathetic 1960s extension at the rear, as well as a full asbestos strip. Heritage carpentry, plaster, stained glass and masonry restoration work is needed throughout both the museum and the church buildings, while the new reinforced concrete extension to the main building provides the bulk of the new build. The paved plaza offers plenty of scope for the landscaping team to extend themselves too.

Since taking over the building in March – and once Plymouth City Council had finished moving out the exhibits and books – the team has been focused on clearing the building and preparing the ground for the main section of new build. This will form the box after which the completed project will be named.

Unwelcome surprise

Following the demolition of the existing 1960s rear extension, which originally housed the main library, operatives began digging out to the foundation level of the new building.

“As soon as we started the demolition work we realised the extent of the chrysotile asbestos”

Steve Killer, Willmott Dixon

But the floor slabs that passed through from the original building into the extension had an unwelcome surprise for the team. An early underfloor heating system had been installed through the 200 mm-thick floor slabs, with the pipework encased in asbestos.

“Basically, that section of the building has been cut out and now we are digging through the underlying rock to foundation level,” says Willmott Dixon assistant building manager Steve Killer. “As soon as we started the demolition work we realised the extent of the chrysotile asbestos. We needed to seal off the rooms and then start breaking through section by section. It took three to four weeks in the middle of June to clear it all.”

He admits the team was fortunate that it was the height of summer when the asbestos was found. “We lost some time over that, but you can’t afford to take any risks with asbestos, you have to work through it carefully and systematically. Thankfully we were able to catch up some of that lost time thanks to it being the middle of summer.”

The main section of the new build is the reinforced concrete box that will host the city’s main archive, spread across the fully waterproofed basement and the four floors above. It will tower 10 m above the roof height of the original building and be clad in Alucabond aluminium facade panels.

Tough shillet

The building is founded on shillet – a tough slate-type rock typical of Plymouth that has been difficult to break out. In one plane the material can be almost picked out by hand, but where the layers of rock have been twisted and lie in a different angle, it is proving very difficult to excavate. This has seen the team using hydraulic peckers fitted to the excavators to break out the shillet piece by piece.

“It is proving incredibly tough – it’s like trying to break through reinforced concrete,” Mr Killer says. “We need to dig through to formation level, but it is difficult to do that.”

The strength of the shillet has not stopped the team from installing a row of piles along the line of Tavistock Place at the rear. This piled wall is acting as a temporary measure to retain the road fill from the basement excavation.

“We had to be very careful when excavating around those services and used vacuum excavation”

Steve Killer, Willmott Dixon

The 273 mm-diameter steel encasement piles are drilled and then push through to a rock socket. Operatives then drop the steel reinforcement cage into that socket and cast the pile, with a capping beam formed along its length. The piled wall doglegs into the existing building where it retains the fill beneath the library. Here the team has installed 65 Odex piles.

“The road is full of ducts and services,” Mr Killer explains. “There is a 90 mm gas main that runs along its line with four fibre optic cables, water sewerage and a mains electricity cable. We had to be very careful when excavating around those services and used vacuum excavation to make sure we didn’t damage anything.”

Stained glass conundrum

Across the other side of Tavistock Road, the Willmott Dixon team is concentrating on the refurbishment and remodelling of the Grade II-listed St Luke’s Church into a high-specification exhibition space and gallery. When complete, the space will link to the Art Gallery on the other side of the road and Tavistock Place will become a pedestrianised / access-only throughfair.

The main floor has already been cleared away, with the footings to the original ornate cast iron columns that support the upper congregational tier strengthened with new 750 mm cubic concrete pads.

The Box Plymouth Willmott Dixon Plymouth City Council 9481

The Box Plymouth Willmott Dixon Plymouth City Council 9481

The church features 18 stained glass windows, each of which are to be fully cleaned, re-leaded and repaired. Finding skilled tradesman capable of working on the windows has been difficult, but a specialist from Yeovil has stepped in to strip the stained glass.

“They are so big that we don’t have the lay-down space on site to store them all and work on them here,” Mr Killer says. “They will be taken down and taken off to our specialist subcontractors one by one. We estimate it will take two weeks [of work] per window to fully refurbish them.”

In the main building the bulk of the work will be focused on the timber parquet floors, decorative plasterwork and mechanical and electrical installation that will continue into the new extension.

Demanding sequencing

In one section, however, the roof has been removed from the main building. This section features steel roof trusses that will be refurbished and strengthened with new material cut into the frame. Here the team has installed a temporary roofing frame that was initially launched from the old library – the very building the team demolished.

The sequencing of work has required a careful eye to develop the final temporary work design. “We knew we would have an issue with the scaffolding and temporary roofing system, but our experience enables us to solve those sorts of problems,” Mr Killer says. “That is why these projects are interesting and exciting.”

The main building is shrouded from the Plymouth public by a hoarding and scaffolding system that is heavily kentledged at the front. This takes over half of the pavement along one of the main thoroughfares for thousands of Plymouth University and College of Art students. Managing those students and the rest of the public that pass around the project has seen the team introduce full 24-hour security around the site.

The Box Plymouth Willmott Dixon Plymouth City Council 9465

The Box Plymouth Willmott Dixon Plymouth City Council 9465

“There are lots of bars and clubs around here,” Mr Killer points out. “We have been working through freshers’ week and needed to make sure we kept everyone safe on off the site. Managing the interface between the public and the project is very important.”

If everything continues to go well, the project the team should be handing the completed scheme over to the client in time for the September 2019 intake of students.

With the following spring set for an influx of tourists to celebrate the 400th anniversary of the Mayflower’s sailing, The Box will provide a fitting backdrop to commemorate Plymouth’s rich history.

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