The Diamond Formation | Thorp Precast Remodel Commercial Site In Westminster
Embossed brick-faced cladding supplied by Thorp Precast has breathed new life into a mixed-use Westminster development.
Buckingham Green is a remodelled commercial site in the heart of Westminster, where one of the three blocks has been transformed using brick-faced cladding, creating an embossed, diamond pattern across the brick-clad façade.
The impressive detailing was created by precast specialist Thorp, which supplied 315 cladding panels on No.3 Buckingham Green, working with Fletcher Priest Architects and main contractor BAM.
The redeveloped site, which also includes a residential tower and a smaller office building, has been revamped to “reflect the area’s character with richly articulated red brick and a new public thoroughfare,” according to Fletcher Priest.
Block No.3 is a six-storey, steel-framed building, with 28,183 sq ft of office and retail space. The brick-faced cladding, chosen by the architect to complement the Victorian surroundings, covers over 2,000 sq m of the envelope, wrapping fully around the façade.
It folds seamlessly into the interior, where the brickwork provides a dramatic backdrop in the double-height reception.
“The brick-faced panels primarily used traditional construction, with spandrels and mullions fixing onto to the steel frame,” says Steve Morgan, technical manager at Thorp.
Some 214,000 bricks were used on the project in total. “Around 100 cut-brick ‘specials’ form the raised diamond pattern, using just 13 master bricks,” explains Morgan. “In some cases, we managed to get four finished cuts out of a single brick.
“As the pattern wraps seamlessly, the panel joint locations always had bricks missing from the precast units. These were handset into place on site, once all panels were installed, whether protruding or non-protruding. Each handset pocket allowed for movement and featured a weep tube.”
In Thorp’s factory, the brickwork was set out in the mould so the 25 mm protruding pattern sat on the mould floor, with the setback brickwork supported by a precise 25 mm build-up of plywood.
Windows were installed into the façade on site, between each mullion and spandrel interface.
“Three window types each had a differing angle return – this meant that the precast brickwork needed to run at an angle that was pre-set,” says Morgan. “Stencils were cut from plywood and used to set out the finished brickwork line and for cutting the bricks.
“This also allowed our pointing team to set the line of flush pointing, to help stop the ingress of water.”
One of the project’s biggest technical challenges was a Loggia feature, which required a major structural design rework using ultra high-performance fibre reinforcement concrete (UHPFRC).
“The Loggia area uses a four-faced, two-storey mullion, weighing 5,450 kg,” explains Morgan. “Our value engineering removed all primary structure, with internal and external cladding and the jigsaw of panel joints integrated to achieve the structural requirements.
“There were no structural members close to the panels here, so the UHPFRC mullion works as a structural element. The big corner column is traditional concrete construction, but using UHPFRC, we successfully engineered it down to a weight within the crane’s lifting capacity.”
The central structural member on the Loggia, weighing in at 6,800kg, was the heaviest precast unit on the project.
“Spandrel panels above locked the whole system together and were then restrained back to the main structural frame using bespoke brackets,” Morgan continues.
“As each unit was installed on site, we put in place a temporary works system, with props restraining and supporting each panel before the final piece was installed.”
The spandrels in this area were also used to run electrical services into the loggia area, with conduit tubes cast into the panels for the cabling, says Morgan.
“Though a major value engineering exercise, our Loggia solution retains the desired architectural intent of the façade,” he adds.
Thorp also used UHPFRC for precast parapet panels at roof level, balcony units and in two internal areas of No.1 Buckingham Green: the reception, and the loading bay on Caxton Street.
The reception contains the largest flat panel on the scheme, measuring 8,000 mm by 4,000 mm, but cleverly engineered to weigh only 6,300kg. “This panel was 75 mm thick overall, including the brick, with three
55 mm-thick ribs,” explains Morgan. “Using conventionally reinforced concrete, the panel would weigh nearer to 16,000kg and be around 200mm thick – so this was a really innovative use of UHPFRC.”
Both reception and loading bay also contain curved ceiling soffit panels, measuring up to 12,000mm by 4,000mm.
“These units were installed using a temporary propping system designed by Thorp,” says Morgan. “This allowed the structure to be built around the panels. We then tied them back to the primary structure.
“Other panels in these areas were split into handleable sizes that could be installed later in the construction programme. This was specified during the design process. These panels also featured structural ribs, meaning the majority could be thin, ensuring no issues with weight would hamper the installation.”
Given the complex shape, geometry and slenderness of the curved soffit panels, Thorp took additional precautions with the logistical arrangements to avoid any damage.
“We cut a series of polystyrene blocks to the same shapes as the panels and sent these to site prior to the units being transported to Buckingham Green,” says Morgan. “On arrival at site, the precast units could be safely sat down on these polystyrene blocks, ready for their installation at a later date.”
Buckingham Green was completed during 2018.