SSDA 2026: Climbing the stairs

Inspired by a Leonardo da Vinci design, the Double Helix Staircase at Fortnum & Mason comprises two flights of stairs that appear as one single structure, wrapping around the centre of the building’s atrium like twisting strands of DNA, creating a centrepiece for the recently completed refurbishment. 

Tom Athron, CEO of Fortnum & Mason, says: “It is the first time in over two decades that Fortnum’s has unveiled a project of this scale and ambition at Piccadilly, and we are immensely proud of the result.

“The staircase, designed by Ben Pentreath, is more than a feat of engineering; it is a work of art and a restoration of architectural integrity.”

The project required advanced structural engineering and digital modelling with traditional materials, bespoke detailing and a considerable amount of refined craftsmanship to produce the stunning staircase.

Translating this ambitious concept into a structurally workable solution required its geometry, proportions and visual symmetry to be maintained, while creating a structure capable of spanning considerable distances within the new atrium.

“Using structural steelwork was the only practical solution due to both the complexity of the Double Helix structure and the client’s requirement for an exceptionally shallow, slender stringer profile,” says Patrick Murray, Quantity Surveyor at Portview Fit-Out. 

“Steelwork’s strength and adaptability allowed the stair elements to remain visually light, while providing the required structural performance.” 

Curved steel stringers form the primary structure and establish the continuous double-helix geometry, while the completed staircase brings together timber treads, GRG soffits, hand-forged balustrade panels and bespoke brass fittings inspired by Fortnum & Mason’s tea leaves.

Guaranteeing the required strength and stiffness of the staircase, the long spans and slender elements required advanced digital analysis and optimisation. 

The design also had to account for forces transferred into the existing building and the interaction between movement in the staircase and the surrounding structure. Resolving these considerations without introducing visually intrusive supports was central to the design.

The store remained operational throughout the installation works, which required the construction activity to be managed in order to minimise disruption. Much of the installation was undertaken outside trading hours, with strict controls on noise and other activities while the store was open.

Piccadilly’s Central London location created further logistical constraints. Deliveries were made during limited road-closure windows, after which every component was distributed internally through the historic building. Access was restricted to an opening approximately 1,500mm wide and 2m high, limiting the size of individual elements and influencing how the staircase was divided for transportation and assembly.

A series of bespoke lifting frames and internal gantries were designed to move and install the steelwork safely within the building. The installation sequence was coordinated with the timber, balustrades, soffits and decorative finishes to maintain progress and avoid damage to completed work. These arrangements had to operate without large-scale lifting equipment normally available on a new-build project.

Produced by BCSA and Steel for Life in association with Construction Management.