Endless stair is an enthusiastically named, experimental wooden structure. Responding to a design challenge, dRMM architects investigated the potential in using tulipwood panels to produce a sculptural installation. Endless stair is the result. It’s on show in London and is an experiment in the use of cross-laminated hardwood.

Usually, cross-laminated timber (CLT) makes use of relatively cheap soft wood. American tulipwood is a hardwood, making the CLT panels used here very special. The designers present the project as 15 interlocking staircases that are interlinked like something out of an Escher drawing. The project was designed by de Rijke Marsh Morgan Architects and was engineered by Arup.

The Endless Stair project consists of a series of timber flights, some of which veer to the right, and some to the left. This gives the public different ways to explore the structure. The top flight stair leads, after 187 wooden steps, to a viewing platform at around 8 m above the ground. Alex de Rijke of dRMM decided early on to use stairs for the project: “On stairs people interact, they pass each other, they are always interesting places with spatial and social potential … Stairs are sculpture’s gift to architecture.”

Endless Stair is intended as both a sculpture and as a research project to advance the knowledge of timber technology and sustainability. Several design decisions reflect this. The steps and the balustrades on one side are manufactured from identical elements of CLT, all equivalent in size. These are stacked up with a spacer element between them, which shifts the staircase either to the right or to the left, depending on the position of the balustrade. The CLT that makes up the tread and balustrade panels is built up from three equal layers, each of which is 20 mm thick. The panels are connected with zigzag joints and sturdy bolts perpendicular to the joint.

The flights of stairs act as arching elements that transfer loads via the stiff balustrade elements and through the treads themselves down to the ground. The overall structure is stable when the flights are all joined together to form the overall sculptural form.

The project is a result of the collaboration between the London Design Festival and the American Hardwood Export Council.