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Endless Stair, a towering structure of 15 Escher-like interlocking staircases made from American tulipwood, was conceived as a sculptural work and research project. Created originally for the 2013 London Design Festival, the structure pioneered the use of hardwood for cross-laminated timber, which is typically made from softwood, and demonstrated the real potential for tulipwood, an abundant, light and strong American hardwood.
Endless Stair is a publically accessible temporary sculpture designed to be endlessly reconfigured. A key objective for dRMM was to make the project environmentally friendly, with as little waste as possible in construction, and with the ability to re-use and relocate the modular design either in parts, or as a whole.
Technical/Structural Properties - Faced with the challenge from the London Design Festival to produce a sculptural, landmark ‘lookout’, dRMM settled quickly on ideas involving stairs. Stairs are sculpture’s gift to architecture, where people experience space, pass each other and interact. This project served as vehicle for exploring structural and sculptural possibilities of tulipwood, donated by the American Hardwood Export Council, who were closely involved in the research and design process. The whole team worked collaboratively to overcome the challenges and complexities of the project within the time available. Expert academic and product supplier advice was taken. The University of Trento was central to understanding the essential rolling shear properties of the CLT, whilst the adhesive manufacturers helped specify the right type of glue to meet the manufacturing constraints and external use of the panels.
One of the earliest decisions was to make the steps and balustrades on one side from identical connected pieces, equivalent in size. These are stacked up with a spacer element between them, creating the flights which, as a result of the stacking process, can step either to the right or to the left.
The project was an opportunity to explore the properties of engineered hardwoods and understand the potential presented by cross laminating the material. This spanned the full process of design, manufacture, construction and re-use at the structure’s ‘end of life’. Investigations included material properties, the manufacturing process; design requirements for an accessible temporary art installation, and how Endless Stair could be built in front of the Tate Modern and one month later, de-constructed. A Kit of Part - The interlocking stair design is a three-dimensional demonstration of composition, structure and scale. Within this prefabricated construction, each piece is an essential part of the additive structure, indispensable within the load transfer path. Endless Stair is a fast and dry construction, easily demountable, and able to be entirely recycled on another site. This was recently demonstrated with a new, cantilevered composition, using seven of the original fifteen flights at the FuoriSalone 2014 exhibition in Milan.
A wider aspiration remains knowledge and experience gained from the series of reconfigurations of this engaging sculpture can inform the debate on higher performance timber structural design, and the mainstreaming of hardwoods as an efficient engineered timber material.
Material - Tulipwood is a plentiful and sustainable temperate hardwood manufactured in this case as cross laminated timber (CLT). The client’s aspiration was to advocate and demonstrate opportunities to use lower grades of hardwood, in this case tulipwood, for higher performance engineered timber products. The client supported the geometrical experimentation using tulipwood and undertook testing to identify its impressive material properties.
Sustainability - Throughout the Endless Stair project there was a major focus on efficient use and reuse of materials. The word ‘endless’ refers to the structure’s continuous re-use. This includes the fifteen interlocking flights being separated and installed into existing or new buildings. CLT is an inherently efficient use of wood. Each sheet is built up from a number of planks so any local weak areas such as knots have relatively little effect on the overall strength. This makes it possible to use lower grades of timber than are traditionally considered for construction, without any loss of quality in the finished product. Moreover, the lightness of this species of timber minimises foundational carbon.
The CLT production method allows for the incorporation of timbers of a range of lengths and widths and the design ensured that panel thickness matches that which is most readily engineered from the raw materials available, minimising the need for cutting and waste during fabrication. Endless Stair is composed of 23m3 of CLT panels manufactured from 54m3 of kiln dried tulipwood lumber. The conversion process generated 14.1 tonnes of excess wood material, of which 4.2 tonnes were reused for animal care and panel products and 9.9 tonnes was used for energy production. The carbon footprint of Endless Stair, including all processes involved in its realisation, was 13.1 tonnes of CO2. It is estimated that about 14.5 tonnes of CO2 is stored in the structure.
In addition, the structure was designed to be very transportable, fitting into three lorries as all the parts nest together as a very compact load. Although the timber was transported from the U.S, 6000miles by ship is the equivalent of 600miles by lorry in terms of carbon footprint of the transport process.
Endless Stair takes inspiration from the compositional and social possibilities of the staircase, and from the Tulip Tree. Tulipwood is a plentiful American hardwood export, composed in this project for the first time as cross-laminated timber. dRMM designed a temporary sculpture which could be endlessly reconfigured. For its first iteration, it was sited on London’s Southbank, outside Tate Modern. It was a 3D exercise in composition, structure and scale – a prefabricated construction, each piece an essential part of the bigger structure, transferring load in unison. The second site was the Ca’ Granda, the main venue in the FuoriSalone 2014 event in Milan, Italy. Scale Infinite – the next iteration in the life of Endless Stair – once again harnessed the possibilities of user interactivity through varying levels, joints, and possible routes. This play on perspective allowed users to experience the courtyard from unique points of view, reaching dramatic culmination on the topmost stair.
