Endless Stair was the highlight of the 2013 London Design Festival. Designed by de Rijke Marsh Morgan Architects (dRMM) and engineered by Arup, it is a towering Escher-like structure that was erected outside Tate Modern for a month. Made from American tulipwood CLT, it was a magnificent and daring piece of architecture and engineering that also pioneered the use of a new material, and acted as a research project.

Endless Stair is a temporary sculpture designed to be endlessly reconfigured. Each flight of stairs is built from standard elements and can be re-used and relocated either in part, or as a whole. Alex de Rijke, Co-Founder of dRMM Architects and Dean of Architecture at the Royal College of Art, has described timber as ‘the new concrete’, predicting that it will be the dominant construction material of the 21st Century.

Tulipwood is a plentiful and sustainable American hardwood export, composed here for the first time as cross-laminated timber (CLT). CLT, which is usually made from softwoods, is an engineered timber solution that can form buildings quickly, efficiently and sustainably. Endless Stair pioneers the use of American tulipwood CLT, introducing an exciting new dimension to timber construction. The elegance of the steps in Endless Stair is only possible as a result of tulipwood’s superior structural properties.

Endless Stair is the first structure made for the London Design Festival with a full life cycle profile. The results are documented in this app along with photo galleries, videos, design and technical information about the project.

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Genesis of the design

Faced with the challenge from the American Hardwood Export Council to produce a sculptural installation using slender tulipwood CLT panels, Alex de Rijke of dRMM settled quickly on an idea involving stairs; “On stairs people interact, they pass each other, they are always interesting places with spatial and social potential. We thought a staircase would be a good vehicle for exploring structure, space and making a sculpture. Stairs are sculpture’s gift to architecture.”

An early decision was to design and manufacture the steps and the balustrades on one side from identical elements of CLT, equivalent in size. These are stacked up with a spacer element between them, creating the flights which, as a result of the stacking process, then veer either to the right or to the left, depending on the position of the balustrade.
The structural importance of the tulipwood CLT is showcased through the project's design. The CLT that makes up the tread and balustrade panels is built up from three equal layers and is 60mm thick in total. The use of other timbers would doubtless have increased the size of individual elements and arguably not concluded in such an elegant solution. Arup’s timber specialist, Andrew Lawrence comments, “The idea that we can now create huge wooden CLT panels from small trees is very exciting. Tulipwood CLT offers the potential to combine the advantages of CLT with the strength and appearance of tulipwood. It’s a great addition to the pallet of wood based materials.”

The installation has been designed to be interactive and people will be encouraged to climb the stairs. The sculpture therefore is safe to use, while not compromising the overall aesthetics of the design.