Making buildings: The Scoop goes for Conical effect

The Scoop is an extension to a former music school now converted to an office in London’s Southwark by architect Corstorphine & Wright. It features a conical cut-out facade, sculpted to frame the circular window of the neighbouring 19th century listed church.

The cut-out enabled the existing building to be extended in front of the church to maximise its floor area. The semicircular cut-out is constructed in white glazed bricks supported on a bespoke stainless-steel frame built by Winthill Engineering.

David Crosthwait, director, and Henry Jones, associate, at Corstorphine & Wright and Tom Blakeman, engineering director at Winthill Engineering, explain how the scooped-out section was built.  

 

What was your brief for this project?

Henry Jones: Our client, THB Properties, bought this building, which had been home to a music school, to convert to a showpiece office space by extending the building as much as possible. We established that we could put an additional storey on the roof. We also looked at extending the building out into O’Meara Street in front of the church. Our first attempt at this completely blocked off the view of the church and its big circular window from Union Street. 

The window is its main architectural feature. It was an obvious focal point, so we used Grasshopper parametric software to establish a conical viewing corridor from eye-height on Union Street to the window.

Why form The Scoop out of a heavy material like brick?

David Crosthwait: The planners were incredibly supportive of the building but they were very keen that it was built using quality materials and they put conditions on that. We investigated every possible construction option before eventually deciding on brick. We would have taken an easier route if we could have achieved a similar aesthetic and build quality. 

Initially, we built the void’s compound curved brick wall virtually. We started with a flat vertical wall built from bricks laid with a stretcher bond. We then pushed each brick back horizontally by a slightly different distance to form the conical indent, which is how you get the brick-pixelated effect.

Why use white glazed bricks?

HJ: We developed a parametric tool using Grasshopper to create the conical form and then to push back the bricks to hug that form. Because the scoop flattens out at the top and bottom, you end up exposing more of the brick faces than would normally be the case. We chose glazed bricks because they are very dense and the glazing makes them more durable and weather resistant. 

We used Ibstock’s London White Glazed Brick. They are standard 215mm x 65mm in elevation but their depth varies. The principle when cantilevering a brick is one-third overhang, two-thirds bearing, so we had to have special, extra-deep bricks made. The bricks’ additional depth meant they developed a slight curve in the kiln which had to be accommodated on site by the bricklayers. Although we positioned each brick using parametric software we had to manually assign a brick type to almost every brick.

After we’d designed the form we did have discussions with precast brick panel companies about preassembling it in sections but they were not interested in a one-off so we ended up going down the site assembly route.

DC: We had expected to use a fully hidden support system but there was a liability issue from having such a big overhang at the top of the curve with the possibility of a brick failing and hitting someone on the head. So, from a health and safety position, we took the view that the bricks needed additional support. 

How are the bricks supported?

Tom Blakeman: Henry and David came to us with the digital model of the scoop. They had each brick positioned in three dimensions but floating, unsupported, in the air. We had to build a cantilevered structure capable of supporting every brick. 

We came up with the concept of placing each course of bricks on a horizontal shelf. These shelves are bolted to a series of giant 9.5m-high vertical ribs, which are set back out of sight behind the brickwork. The ribs transfer the loads imposed by the scoop to the main building structure.

How was the structure built?

TB: The entire supporting structure is built from stainless steel for its weathering properties and because of the structure’s height above ground. 

The scoop is a compound curve so each shelf is a slightly different shape. The shelves were precisely cut in a zig-zag profile from stainless-steel sheet by a plasma cutter using dimensions taken from the CAD drawings. The back of the shelf was then bent upwards into a lip to increase its stiffness. A number was then etched onto the back of the shelf to identify it and its location on the structure. Finally, an Oyster White powder coating finish was applied to the entire stainless-steel structure for additional durability and cohesion where the underside of the shelf is exposed beneath the bricks.

How was the structure put together on site?
TB: To simplify site installation, the 1.2m-long shelves were preassembled in a series of  cassettes in our workshop. This ensured accuracy of assembly and reduced assembly time on site. Each cassette contains between two and ten shelves. Additional plates were inserted between the shelves to increase the cassettes’ rigidity. On site, the cassettes were simply bolted to the ribs.

The giant ribs that transfer the loads from the scoop to the structure are each cut from a single 10m x 3m sheet of 20mm-thick stainless steel. The ribs incorporate small feet to attach them to the steel structure at each floor of the building. We were not responsible for installation but we were on site throughout to support the contractor.

 

Were any special bricklaying techniques used?

DC: We could not use normal bricklaying tolerances because of the shelf supports and the need to connect to the main steel frame of the existing building. In a normal building you could accept 10mm, 15mm or even 20mm tolerance, here the team had to do everything they could to keep within a 2mm to 3mm tolerance.

The white glazed bricks were meticulously laid by Grafton Brickwork. We did the setting out drawings for every brick course with every brick set back by a specified dimension from the adjacent brick.

HJ: What was interesting on site was that a very precise design process became more handcrafted to take into account the variations in the fired brick dimensions. There was a really good back-and-forth communication on site with the bricklayers, the steel frame installers and fabricators to ensure everything aligned. The bricks are held in position using a mixture of special adhesives and standard mortar. 

Is the scoop visible inside the offices?

DC: The giant structural ribs protrude inside the building so we had to infill between these using an insulated timber frame to form the interior wall. We used CNC-cut timber studs made from laminated plywood to shape the inside of the scoop to mirror its exterior curve. The windows punch through this internal wall in a series of steel-framed boxes.

How has this innovative solution been received?

DC: Feedback has been phenomenal. The thing I like the most is when pedestrians walking past the street, who would have otherwise not have given this building and the church a second thought, catch a glimpse of The Scoop out of the corner of their eye and then stop and take a picture.