- Building from within
- Almost-ancient burial ground
- Room for a view
- Skanska’s Queen Square self-build
- Getting a Georgian building airtight
Swedish firm is not only main contractor but client, piling specialist and even M&E provider on a project to revamp a corner of Georgian Bristol.
Project: 66 Queen Square
Client: Skanska Development
Contract value: £14m
Main contractor: Skanska
Demolition subcontractor: Wring Demolition
Piling subcontractor: Berryrange
Piling subcontractor: Cementation Skanska
M&E subcontractor: SRW Engineering Services
Since it was first built on a marshy bog of land outside Bristol’s medieval city wall, Queen Square – named in 1702 following Queen Anne’s visit to the burgeoning port town – has had a colourful history.
Initially developed as an exclusive residential neighbourhood for Bristol’s growing population of rich merchant traders and maritime adventurers, it was the site of the first American Consulate in Britain and home to privateer Woodes Rogers.
Listed buildings abound and, with its frontage onto the square, the category A office building Skanska is creating boasts Grade II status.
And this clearly is very much Skanska’s creation, with the company’s various arms filling not only the main contractor role but also serving as client, piling specialist and M&E contractor (see box).
Sitting in the north-west corner of the square with King Street running behind, the new 66 Queen Square development retains the Georgian grandeur of five listed terraced houses.
An uninspiring 1980s office block that had filled in space to the west of the terrace has been completely demolished and rebuilt, replaced by a contemporary curved steel, stone and glass façade at the development’s entrance off Thunderbolt Square.
“There were some concerns about maintaining the stability of the two separate terraces. We excavated beyond their foundations and below road level. We had to be sure of our approach”
Ben Yates, Skanska
The King Street façade features a gabled and rendered frontage designed to nod at the historic buildings that surround it while a small section features a reclaimed rubble/brick façade.
On the Queen Square side though, the listed Georgian terraces have been fully retained.
Three of the five have been incorporated into the main section of the redevelopment while the remaining two - numbers 72 and 73 Queen Square - are being completely refurbished.
These will remain separate from the main 66 Queen Square development and will be offered as separate office space.
Building from within
Back in early 2013, before the enabling and demolition work was carried out, the building was little more than a derelict squat with a mish-mash of floor levels and a large central atrium.
The plan to transform this building has been to remove the existing 1980s frame and excavate to create a basement with plant room, car park and cycle store.
The new reinforced concrete frame is brought up through ground level to level three with post-tensioned slabs.
Rooftop penthouse offices at level four are of a smaller footprint and built using a steel frame that links into the curved, steel-framed atrium of the Thunderbolt Square entrance.
“It is a completely post-tensioned slab building other than in the steel frame corner section; the shapes through there just didn’t work with post-tensioning”
Ben Yates, Skanska
“We worked closely with our demolition contractor Wring Demolition,” says Skanska operations manager on the project Ben Yates.
“There were some concerns about maintaining the stability of the two separate terraces.
“The staircases from the 1980s frame had to be cut from them and then we excavated beyond their foundations and below road level. We had to be sure of our approach.”
Wring completed the demolition phase in September 2013, leaving the construction side of the team to look at the difficult task of bringing the new structure out of the ground.
“The basement is around 4 m below the water table,” Mr Yates explains.
“We needed to install sheet piles around it, creating a cofferdam and ring beam before we could start any piling work.”
Almost-ancient burial ground
Across the site more than 215 CFA piles have been installed.
The 600 mm-diameter piles pass through 2 m of made ground, which dates back to the 17th century when the area was marshland.
They then reach depths of 25 m below ground level where they socket into the underlying mudstone bedrock.
The sheet piles have been pushed to depths of 16 m.
The 300 mm-thick concrete basement slab is heavily reinforced to help prevent any cracking and water ingress.
The columns that launch from this are set predominantly on 9 m and 7.5 m gridlines, while 225 mm-thick post-tensioned concrete slabs make up the rest of the floor space.
“It is a completely post-tensioned slab building other than in the steel frame corner section; the shapes through there just didn’t work with post-tensioning,” Mr Yates says.
“We had to use it elsewhere to get the spans we wanted but also so that we could gain the floor heights that would fit in with the Georgian buildings and also give the feeling of openness and space we need in a category A office.”
That steel-framed corner section is actually a completely free-standing building that has been constructed alongside the existing listed buildings and the new concrete-framed section.
Somerset-based contractor William Haley Engineering has carried out the steel work.
“We knew the plant room would have to be in the basement because of planning issues. There is lots more ductwork because of that”
Ben Yates, Skanska
“It is quite a simple detail,” Mr Yates explains. “The steel building sits tight against the existing and new build concrete frame.
“There is a soft joint where the concrete frame is poured against the existing building.”
The team used a tower crane in the centre of the new concrete frame building to serve the site, pulling materials from the project’s small lay-down space at the corner of King Street.
A knockout panel was cast to infill the gap in the slabs.
Room for a view
Under planning restraints, the design called to keep the roofline as low as possible so that any increase had no impact on views from the Square’s central green.
This meant that the plant room was pushed down into the basement, complicating the layout of ducts and services.
“We knew the plant room would have to be in the basement because of planning issues but that makes the M&E installation – particularly the air conditioning – much more convoluted.
“There is lots more ductwork because of that,” Mr Yates explains.
Notwithstanding the ductwork difficulty, the building is well on course for completion later this year, ready for handover to tenants.
Accountancy and financial services firm KPMG has already tied up 85 per cent of the new office space on a 15-year lease – a sure sign the numbers add up on this latest addition to Bristol’s most famous square.
Skanska’s Queen Square self-build
If ever there was a project that highlights the benefit of being a multi-faceted company, then Skanska’s redevelopment at
66 Queen Square is it.
The client for the scheme is Skanska’s development arm, Skanska UK is the main contractor, Cementation Skanska is taking care of the piling and the M&E role is being filled by the firm’s SRW Engineering Services offshoot.
It is a deliberate move to help create revenue for the overall business, according to development manager Liam Coughlan.
“This arrangement has been tried elsewhere before, but we set up in the UK around three years ago,” he says.
“By using our own companies to develop,we get a double impact on the bottom line.”
The Queen Square project is one of two schemes the company has taken forward. Both were carefully planned and assessed before the development decision was taken.
“We need to be very careful about where we develop,” Mr Coughlan says.
“We want to use our own businesses, which means we can only develop where we have strong construction presence - we certainly have that in Bristol, but we also need to assess the economy within those areas and demand for real estate.
“We realised that by developing Queen Square everything would be coming together. This is the right development in the right place at the right time for Bristol.”
Getting a Georgian building airtight
With a contractual demand to achieve a BREEAM Excellent rating, the site team knew they were facing a tricky challenge.
Getting a Georgian terrace through stringent sustainability and energy efficiency checks can be difficult.
For the Queen Square team, that target has been offset mainly by installing photovoltaics on the roof, making the building as airtight as possible and using recycled and ‘green guide’ materials throughout.
“We knew that ‘Excellent’ would be achievable but only if we kept a very close eye on everything.
“We couldn’t let anything get away. This is a very thermally efficient building thanks to its airtightness.
“Even the photovoltaics have been compromised due to the planning demands to preserve the view of the roofline from Queen Square.
“They have to sit beneath the parapets, which means the installation isn’t quite as efficient as it could be.
“Fortunately we have been able to offset that,” Mr Yates says.