The use of timber as a sustainable structural building material: is it possible for tall buildings? Sukriye ‘Rae’ Robinson of SOM reflects on our latest webinar.

The exploding urban population in cities around the world creates an increased demand for tall buildings but as the effects of climate change continue to be felt more acutely and the industry pursues new ways to decarbonize, are sustainable tall buildings even feasible? Drawing upon lessons learned through a series of projects located around the world, the panellists agreed that using timber to realize tall buildings can broadly offer a solution to this challenge. However, this isn’t as simple as black and white; there are shades of grey that must be considered if the industry wants to go further in the pursuit of realizing timber tall buildings at scale.

First up, Liz Dailey from Pilbrow & Partners presented EDGE London Bridge, a 27-storey multi-tenant office building that integrates a demountable, engineered-timber ‘village’ directly beneath a structurally independent office tower elevated on columns on the ground. The use of CLT as part of demountable timber sections in the building’s upper volume floors means that the building is designed to be adaptable and responsive to the needs of new tenants in the future. Working for a client with an international reputation in realizing highly sustainable projects, Liz also talked about timber as a contributing factor to the well-being of the building’s occupants, providing an inspiring and healthy work environment.

Eckersley O’Callaghan’s Toby Ronalds also spoke about a hybrid timber tower, the Atlassian Central project in Sydney. Once complete, the building – measuring 180 meters tall - is due to be the world’s tallest hybrid timber tower with a reduction in embodied carbon of up to 50 per cent. Toby described some contextual challenges: a site with a retained heritage building that limits the touchdown of the building, the local climate and natural humidity, and working to local building regulations which limit timber buildings to lower than 25 meters tall. The resulting structural design essentially consists of small independent timber buildings sitting within a steel exoskeleton, organized by transfer floors made of steel and concrete with every three out of four floors made of CLT.

To end, Dmitri Jajich, Principal in Structural Engineering at SOM based in the firm’s London office, presented SOM’s decades-long investigation into timber towers. Dmitri made the case that whilst there are efforts underway globally to realize innovative mass-timber projects, these are exceptional and the reality of building these at scale is limited. To make the greatest impact across a wide range of typologies and budgets, Dmitri advocated for the industry to embrace hybrid timber towers and, in particular, look to impact where most of the concrete is in a structure. Identifying that nearly half of a building’s embodied carbon is in its concrete structure and two-thirds of structural concrete in the slabs, Dmitri shared SOM’s work into developing a timber-concrete composite slab that halves the amount of concrete typically used, reduces construction time, increases off-site manufacturing in addition to being applicable to a wide range of buildings.

This led to a panel discussion, chaired by the NLA’s Emily Gabb, where the previous speakers were joined by Nigel Burdon, Technical Director of Building Structures at AECOM. Based in Melbourne, Nigel agreed that the hybrid approach for tall buildings offers the most promising approach for the future and whilst there are significant disparities in regulations between Australia and the UK, the challenges of using timber in construction are universal, particularly with regards to cost and lack of data around its performance. It was interesting to hear Nigel speak about the journey that the local construction industry and builders have had to go on in realizing timber buildings; the labour force has skilled up in response to the growing application of timber and is feeling the benefits of a more time-efficient way of building. This highlighted the importance of architects and designers thinking about the specificity of the local markets where they are working and ensuring that the necessary skills to realize complex or new construction technologies exists.

There were interesting discussions about other sustainable materials beyond CLT and timber and how embodied carbon measurements are different according to where materials are sourced from. The conversation felt like it could have easily continued, demonstrating the nuances and many possibilities afforded by tall timber buildings!