About face: 15 Clerkenwell Close, London

What an astonishing, and controversial, building. An invigorating conversation with architect Amin Taha about his 15 Clerkenwell Close development veers widely and vividly to take in everything from Norman abbeys to Spanish pilgrimages, the Dissolution of the Monasteries, French post-war architect Fernand Pouillon and the minutiae of stone dressing.

Although without Taha at hand to explain it would be impossible to understand the full range of reference, detail and nuance, this most singular construction can’t help but draw a response from all that see it. Not for Taha the over-polite and bland anonymity that would have saved his building becoming embroiled in a post-construction planning dispute with Islington Council that could, shockingly, result in its demolition. Taha is contesting an enforcement notice to take the whole building down. 

Rich in detail with an extraordinary limestone exoskeleton, the 2400m² building houses Taha’s practice Groupwork at ground and lower ground level with five floors of flats above, including Taha’s own at the top.

He bought the site in 2011 and took a good few years to really explore and understand the site context, deep in London’s Farringdon in a quiet road opposite St James Church, and ‘getting to know people who live and work here who could inform me of histories that might not be written’. Once a Victorian match factory, the building had been altered over the years and suffered fire damage before ending up as a gallery and offices. Site constraints included two party walls. 

Taha’s response was informed by the site’s history as part of the larger curtilage of a long-gone Norman limestone abbey. After exploring several superstructures for his redevelopment including CLT and steel, the final design met the conservation officer’s challenge of employing locally used materials and also Taha’s preference for avoiding a clad structure.

‘Any material should preferably be either its internal finish and superstructure or external finish and superstructure...what you see is how the building is put together,’ he says.

After extensive research into stone construction, his solution was a structural limestone column and lintel exoskeleton set in front of a glazed envelope and tied back to the inner structure. Fortunately the stone superstructure option turned out to be highly economical – coming in at 25% of the cost of a comparable stone-clad steel or concrete structure. Combined with the thermal envelope, the overall cost of the dry shell and core was about 50% of the equivalent using concrete or steel. 

For Taha, choosing stone meant not only understanding its physical structural properties but also its tactile and visual qualities that ultimately, he says, give a poetry that’s not skin-deep but is ‘utterly fundamental’ to the building.

After discounting Portland stone because it couldn’t sufficiently guarantee strength for load-bearing use, Taha chose limestone from a quarry near Lyon in France, adding that some of the better listed buildings in the Clerkenwell area also use load-bearing limestone. 

Structurally, the building has a concrete core with a reinforced 200mm deep concrete floor slab spanning 8m to the perimeter without columns. This gives a flexible interior well-placed to accommodate future changes in use. The underlying exoskeleton column grid is spaced 3200mm centre-to-centre. At ground floor level, the columns are wider at around 800-900mm depending on their position in the load path, reducing to 250mm further up.

The connection between the limestone exoskeleton and the floor slab is achieved through bolted connections between the stone and a galvanized 10mm, mild steel end plate. In addition, a galvanized steel strap is fixed from the universal beam into the limestone lintel using countersunk galvanized bolts. The UB is then bolted into the back of the floor slab through a cast-in 20mm fixing plate and a 40mm nylon thermal separator. A window system designed by the architects was used for the full height glazing that runs between the exoskeleton and inner structure – the stone exoskeleton provides shading that enabled the use of double rather than triple glazing.

A key part of the design composition is the range of stone finishes on the exoskeleton. This enabled Taha to use the superstructure to ‘tell a story’. Visiting the quarry, he chose to include a variety of stone dressings to express the marks of the processes of extraction and subdivision. There are three main types. The most distinctive are those in a roughly textured ‘as found’ state, in some cases with fossilized coral and ammonites, where no attempt has been made to smooth away irregularities.

‘An interesting way of dressing it is leaving it with its innate, intrinsic beauty,’ says Taha.

The other two finishes reveal the banded effect of hand-drilling used at the quarry to subdivide the masterblock, and the smoother finish created by saw cutting in the mason’s yard. Taha combined all three in a facade composition that aimed to appear organic without repetition or pattern – the last thing the architect wanted was an unattractive, accidental rhythm. 

However, achieving this multi-finish composition was a leap of faith, since it was only when each consignment of limestone blocks arrived on site from the quarry that the architect could inspect them and finalise the exact composition in time for the construction of that part of the exoskeleton. 

Taha concedes that while the practice found the uncertainty of the process ‘quite exhilarating’, the result was ‘dramatically alien to what people have seen before’. 

The combination of finishes is certainly rather unsettling and a little jarring, especially when first glimpsed from afar. A number of smoother, saw-cut faces are clustered to create a lighter patch across the stone exoskeleton. Choice blocks with particularly impressive contours or fossils and quartz are located approximately one per floor where they could best be appreciated. On either side of the vehicular access gate at ground floor level, blocks have been polished to bring out the fossils better and in doing so, allude to idea of the gate being burnished over time by carriages passing through.

This is a building full of moments of drama and poetry. The entrance to the studio is via a charming flanking garden of stone cobbles that alludes to the cloisters of the long-gone nearby abbey. This is adorned with seating formed from more of the limestone blocks, some carved and gilded by apprentice stonemasons. At the front, another of these appears as if fallen at the foot of the building to help reinforce the romantic idea of a ruin. Once inside, it’s only after crossing the wood clad bridge and descending the folded metal stairs to the lower basement that you realise that a glass meeting room is dramatically balanced on a huge I beam projecting forcefully across the studio. Above the studio is a total of eight enviable apartments, their plans freed up by a clever redistribution of the 1.8m-wide smoke shaft as a slither around the top of the stair and lift core.

And while the stone elevation will inevitably continue to grab the attention and divide opinion, it’s just one aspect of a deeply considered design full of detail and delight, from the shells incorporated into the gate to the glint of a single gilded metal support plate on the edge of the main elevation designed to attract and intrigue the eye. 

Already, climbing plants inhabit the stonework and soften the initial shock of its design. It is bedding in, and hopefully, unless Islington Council prevails, can take its own place in Clerkenwell’s rich architectural pot-pourri.