First Steps

ACME completes a prototype cross-laminated timber stair for its own London office


Ed Reeve

Architect ACME has completed a cross-laminated timber (CLT) staircase that links two floors of its London office while requiring minimal alteration to the building fabric – a solution that it regards as a potential prototype for future projects in similar settings. The massive timber stair was manufactured offsite – CNC-cut in Switzerland – in four weeks, and constructed in just five days.

The existing building had no usable stair between the ground and first floors. Cutting a hole in the first-floor slab revealed that it had no further load capacity, so the new stair is designed as a free-standing cantilever, with no connection to the floor above. ACME’s adoption of CLT for the project both provided sufficient counterweight for the cantilever and minimised the carbon-footprint of the addition to the fabric.


Each of the 20 steps is made from six timber elements. Once the interlocking pieces for one step are assembled, they are fixed with screws to the step below. The stair was designed to be self-supporting during assembly, to ensure it can be build without scaffolding or temporary works, and all elements were designed to be light enough to be assembled directly by the designers. To keep the cost of the stair low, the shape and the resulting timber cutting list was carefully optimised to achieve minimum wastage.

“The bifurcating twin spiral form of the staircase serves a number of functions”, explains the architect. “The shape creates its own structural integrity, the bifurcation allows people to make destination choices on the stair, the widening of the stair provided a place to stop and converse, and the inward rake of the upper steps provides stability and functions as a handrail”.

Inspired by Coco Chanel’s mirror stair in 31 Rue Cambon in Paris – which allowed the designer to keep an eye on all levels of her studio – ACME’s stair is clad with mirror on two sides, creating visual links between floors.


“The stair is a prototype to show how very humble elements of solid timber, simply fixed together, can form an interesting sculptural solution to the everyday task of going up and down, and solve a complex structural problem with an intelligently engineered solutions and an interesting use of timber technology”, says ACME director Friedrich Ludewig. “Simple structures can be simultaneously beautiful, economical and practical, and help to create inspiring spaces in which to live and work”.

Additional Images


Structural engineer
Blumer Lehmann


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