Clerkenwell Close - a celebration of structural stone

Features: 15 Clerkenwell Close

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The mixed-use six-story building with a loadbearing stone façade designed by Groupwork + Amin Taha in collaborations with Webb Yates Engineers was one of the nominated for the RIBA Stirling Prize 2021.

15 Clerkenwell Close, which was included in this year's six-strong Stirling Prize shortlist despite not being one of this year's RIBA National Award winners, was hailed by the jury as “brave, ambitious, highly innovative and bespoke, where risks have been taken and have paid off, resulting in a truly imaginative, intriguing and astonishing work of architecture”.

What may appear at first glance as a traditional concrete frame clad in stone has a little surprise in store for the keen eye. A closer inspection of the columns will reveal ammonoids, drilled wedge holes and saw grooves indicating that part of the story has not been told. In fact, concrete columns and clip on stone have been rejected in favour of a simple system of solid stone load bearing columns.

Traditionally, a building’s structure is hidden from view with cladding and other purely aesthetic elements. Webb Yates Engineers innovative approach is to express and utilise a structure efficiently. If heavy elements (brick or stone facing, for example) are required for visual purposes, why not omit the concrete and make the whole column out of masonry or stone, making the aesthetic and structural elements one and the same?

At 15 Clerkenwell Close we concentrated on the efficiency of the façade, and with the introduction of the load bearing stone façade we achieved many benefits:

  • The loads on the slab perimeter were reduced which minimised the need for edge beams and ensured clean soffit lines were achieved.
  • The interface between architectural and structural elements was simplified. This brought the architect into the structural domain leading to greater collaboration and knowledge sharing.
  • Secondary framing elements required to support any cladding were reduced.
  • The amount of different trades on site was reduced, resulting in just a concrete frame contractor, stone mason and curtain wall fabricator.
  • The elimination of time-consuming finishes installation and simplified construction process resulted in a significant improvements to the overall programme.

As well as being innovative and efficient in terms of structural design, the construction process for Clerkenwell Close presented many great benefits. The construction of the façade was faster and more economical than traditional building techniques. Stone itself is much more environmentally friendly than steel, concrete or masonry, with only a tiny fraction of the embodied carbon associated with its manufacture.

Our work with stone is one of many vindications of our approach. After working on our first stone project over ten years ago we have become one of the UK’s top stone engineering consultancies.

Stone isn’t an unusual material to find on a construction site by any means. In fact, people respond to it well as a natural and innocuous material that embodies geological time and human history. Of late, it has been the unfortunate victim of a major flaw in the modern construction industry, which has relegated it to a solely decorative material, rather than one with its own inherent structural properties.

This first occurred to us when we began to collaborate with The Stonemasonry Company, over 10 years ago. They found that their repertoire in stone staircases was becoming limited by only being able to build traditional cantilever stairs affixed to load-bearing walls. Freestanding stone structures were out of the question for them at the time, and so they asked us to collaborate on something much more complex, beginning what has become a long partnership in stone innovation. With The Stonemasonry Company we began looking into post-tensioned and reinforced stone as a concept and together built progressively more adventurous structures, culminating in the Formby Stair, a freestanding staircase which sweeps 320 degrees from one floor to the next. The philosophy behind these designs is to use a material as both the skin and the bone of a structure, creating something both rational and elegant. Through this collaboration the team has built up a range of techniques allowing us to analyse structures and test the limits of the material and, rather than stopping at stone staircases, we began applying these techniques to structures of a much larger scale.

Our collaboration with Groupwork + Amin Taha and The Stonemasonry Company has resulted in not only the Clerkenwell Close scheme, but in many completed projects using stone structurally as well as The New Stone Age exhibition at the Building Centre in 2020.

Click here to find out more on how you can use stone as structural material.

Click here to watch the film about 15 Clerkenwell Close.