With urbanisation growing at a greater rate than population, one architectural firm looks to make skyscrapers sustainable, by making them out of wood. Simon Frost reports.



In a bid to cater for population growth in a sustainable way, the American architectural firm behind New York’s One World Trade Center has developed a structural system that could see wood-framed skyscrapers sprouting up in cities around the world.

Skidmore, Owings and Merrill (SOM) completed the Timber Tower Research Project in 2013, using its 42-storey Dewitt-Chestnut Apartments building, built in 1965, as a concrete benchmark for the prototype. The structure consists of solid mass timber for the primary members, such as the floor panels, columns and shear walls, which are connected with steel reinforcing through concrete joints. The floors would use cross-laminated timber panels of around 200mm thickness, spanning between the central shear wall core and columns at the perimeter of the building, with the ends of the panels restrained from rotation by the concrete joints and vertical structure (see diagram).

The Timber Tower is expected to be the world’s tallest wooden building, standing at 127m, offering 10,000m2 of space and, SOM claims, up to 75% carbon savings compared with traditional materials.

Skyscrapers are built almost exclusively from steel and concrete, which have higher material strengths than wood and more straightforward conformance to building codes. But the Timber Tower would comprise as much as 80% wood, which would greatly reduce the carbon cost compared to energy-intensive steel and concrete production. The structure would require supplementary steel-reinforced concrete, mostly for the highly stressed connecting joints. The foundations up to the first floor would also be concrete, to protect against moisture and allow for the large open space expected in entrance areas.

However, further research and physical testing are necessary to overcome scepticism and verify the system’s performance – especially with regards to fire. Speaking at the Timber Expo event in Birmingham, UK, in October, Dmitri Jajich, Associate Director at SOM, said, ‘The fire resistance of timber is more a perception issue than a technical problem. When mass timber burns, it creates a charring layer, so it actually takes a long time to fail.’ It is hoped that flammability tests of exposed timber elements will show that fires will self-extinguish, and extensive component, assembly and full-scale fire tests will also be carried out in addition to physical testing.

Jajich made reference to similar obstacles met by the world’s first reinforced concrete skyscraper, the Ingalls Building in Cincinnati, Ohio. When it was built in 1903, it provoked opposition from both the public and the engineering community, as concrete was still considered an unsafe material at such great heights. One journalist camped opposite the building overnight when the supports were removed so that he could be the first to report its collapse.

SOM is confident that its structural system is technically feasible, and could revolutionise skyscrapers – but it needs to prove this before the research can become reality.