Heavy Tread

A stone staircase at the heart of a renovated London house serves both aesthetic and environmental ends, say architect Graham West and engineer Steve Webb

Words
Graham West, Steve Webb
Photos
Ben Blossom

Located next to the Regent’s Canal in north London, an early Victorian house that West Architecture has recently renovated had been neglected and altered in an ad-hoc way before being listed in the 1990s. Our task was to refurbish and extend the house within the constraints of the listed building consent.

The focal point is a stone staircase which replaces a timber one added in the 1980s. Designed in collaboration with engineer Webb Yates, it has a simple, legible structural conceit, being a half arch that leans from the lower ground to the upper ground. It is solid, unreinforced stone and was fabricated in three large sections. These were pinned together at clearly visible joints displaying the tectonics of the whole. Although Mirabell, a Portuguese limestone, is a low-cost, high strength-material, this format uses relatively little stone and the strength is less critical that the geometric equilibrium of the pieces. The shape is everything.

The Mirabell stone is used repetitively throughout the project for the structural elements, a series of monolithic basins and sinks and wall and floor surfaces. We opted for Mirabell due its colour, its character and its ability to work well in each situation. The final selection of stone and particularly the finish was made with our client at the stonemason’s yard in Coston, near Melton Mowbray. We were keen that the stone for the adjacent lintels and stair plinth would be rusticated to tectonically separate them and express their structural burden. We originally thought this would be achieved through a flamed finish, but in the end opted for a combination of a honed finished for the majority of the stone, offset by heavy sandblasted stone for the rusticated elements.

We decided to build the flight in three sections, rather than as individual treads, as this allows the grain or sediment of the stone to run uninterrupted from tread to tread. Each section of the stair charts several million years in its formation.

While the stair was being built it was supported on temporary blockwork walls, working from bottom to the top. The stair finally became a single self-supporting element when connection to the key stone – the top landing, in our case – was achieved.

The use of stone, here, isn’t a purely aesthetic choice but rather chimes with other exposed structural elements within the building on a ‘philosophical’ level. The load-bearing Victorian brickwork and the exposed floor joists tell a similar story. Although the idea of an architectural element being honest and having integrity is nothing new, it forms a key point in the narrative of this design.

During installation the stair was supported on temporary blockwork walls until the arch was complete and could support itself (ph: The Stonemasonry Company)

Honesty doesn’t necessarily signal virtue but here there is also a moral aspect to the choice. A more typical approach to a stair of this type might have been to build a reinforced concrete flight and over-clad it, but we would prefer to avoid concete where possible. The production of cement accounts for about 8 per cent of global carbon dioxide emissions. An average limestone would be three times stronger than a typical concrete, but only has a tenth of the carbon footprint. It is perverse to quarry competent stone, and subject it to various environmentally unfriendly industrial processes,only to make an inferior material. But how can we use raw stone in the way we use reinforced concrete?

We believe that using stone in inventive ways in high-end projects is a way of proving its continued worth and building its appeal to a wider market. In this case, a simple design shows how thousands of concrete stair flights might be swapped for stone every year – each one a step on the road to a glorious stone future.