Benjamin Street - London

Figure A

This image shows the finished elevation of Benjamin Street, highlighting the combination of handmade brickwork and heavy, wet-cast stone panels. The technical challenge addressed by ACS occurs at the floor slab junction behind the façade at every floor level with only the column available to fix to.

All subsequent technical solutions; masonry support, stone restraint, and the downpipe integration, are concentrated within the cavity space behind the brick and stone at these congested locations.

Figure B

For this project, the masonry support, a core structural component located at every floor, required a tremendous amount of bespoke engineering.

Masonry support is the primary element for taking the load of the brickwork above and transferring it back to the structure. On Benjamin Street, to handle the significant forces exerted by the heavy stone and masonry piers, we engineered and manufactured a completely bespoke solution that met the load requirements while optimising material use to manage both cost and mass.

To achieve the required load, stiffening ribs were strategically placed and sized underneath the main support plate. This rib system prevented deflection or bending failure under the high stresses concentrated at the pier locations, ensuring the long-term structural integrity of the system.

Also, unlike traditional masonry support, this bespoke unit incorporates additional features and cleats designed to act as the attachment point for the large stone panels on either side, ensuring all load is consolidated and efficiently transferred back to the primary structure.

Figure C

The large, horizontal stone panels that frame the window were attached via a specialised restraint system. To facilitate easy, precise, and adjustable fixing on site, we supplied 31/21 cast in channel which was cast directly into the wet-cast stone panel during its manufacture. This foresight allowed for simple mechanical connections without the need for complex and time-consuming drilling into hardened stone on site.

Our bespoke support system was designed around this configuration, using our patented Alpha II adjustment system, which significantly simplified the on-site fitting process and ensured precise alignment.

The Alpha II system offers vertical adjustability to ensure the heavy stone panel is accurately located and aligned with the rest of the façade.

Figure D

A notable design element of Benjamin Street was the architect’s vision to conceal rainwater downpipes within the cavity wall. This approach, while contributing to the clean lines of the façade, presented a significant challenge to traditional cavity wall construction. Typically, the cavity is designed as an uninterrupted space to manage insulation, moisture and airflow, with services like downpipes running externally.

Integrating downpipes within the cavity, while giving the building a cleaner aesthetic, introduces a number of challenges for the ACS Technical Team to overcome:

• Obstruction of the Cavity: The pipes can impede airflow and moisture management within the cavity, potentially leading to dampness and thermal bridging issues.
• Support and Stability: Traditional masonry support systems are not designed to accommodate or support vertical pipes running through them.

Recognising that designing the downpipes through the masonry support, caused the potential for fire to spread between floors, ACS designed the support unit to include an allowance for a specialised fire barrier system within this central gap. We proactively worked with an external fire protection company to ensure that our bespoke masonry support design was fully compatible with their chosen fire collar product. This collaboration ensured that while our unit handled the structural load, the necessary passive fire protection measures could be integrated seamlessly, preventing the vertical spread of fire through the cavity.

Figure E

Benjamin Street features exposed aggregate polished concrete medallions, and intricate manufactured stonework. In order to support these we came up with more specialised systems.

First, the large, decorative stone panel that splits the brickwork panels was designed to break up the mass of the façade. To prevent this panel from falling, it required both robust support and effective restraint. The stone was installed on to the support below which included welded dowels, with pre-drilled holes on top, allowing capped dowels to be inserted, then securing back to the inner structure. This system provided multiple points of contact for restraint, ensuring the panel remained secure despite being located in a highly congested area around the main structural columns.

Figure F

The deep stone window cill required specific fixings to prevent the heavy unit from rotating downwards into the cavity. This was a critical safety concern, especially as any external load on the sill could cause an unbalance.

In order to secure the units in place we engineered bespoke, two-direction adjustable cleats that were fixed into cast in channel on the back of the cills. This system allowed the construction team to precisely align the stone unit, securing it against rotation while accommodating necessary tolerances and movement. This restraint, fixed from the back of the cill into the main structure, was crucial for the stability and safety of the stone elements that sit on top of the brickwork. As the bottom cleat was secured to carbon steel box sections, we also included prevention for bi-metallic corrosion.

Figure G

Once installed, the entire weight of the surrounding stone panel structure is transferred. The stone is bolted down onto its cleat, which is in turn attached to the main Pier Support Unit. This effectively means the weight of the two stone panels (one on either side) is collected and taken entirely through our central Pier Support Unit and into the floor slab. This configuration allowed the brickwork below and around the support to be built up afterward, using special cut bricks to coordinate around the cleats and ensuring a precise fill.

Figure H

This final image of the finished elevation demonstrates the seamless integration of our bespoke engineering solutions into the building’s complex envelope. The clean aesthetic, the goal of concealing the rainwater pipes, is achieved, and the intricate bond patterns and heavy stone elements are held securely in position by the systems detailed throughout this case study. The visual success of the façade is a direct result of the precise design, fabrication, and coordination of the masonry support, bespoke cleats, and dowel restraint systems hidden beneath the surface, confirming ACS’s ability to turn complex architectural visions into structural reality.