Timber reaches new heights

‘How tall’ is now the question facing those striving to build the tallest timber buildings around the world. Peter Wilson of Timber Design Initiatives explains that as the boundaries of engineered timber technology expand, the use of wood in buildings is soaring upwards.

Before the completion of the Stadthaus in the London Borough of Hackney in 2008, the development of timber construction in the UK was predominantly based upon platform frame technology, a construction method generally considered to be effective up to seven storeys.

The Stadthaus’ eight storeys of cross laminated timber (CLT) arranged in a honeycomb structure above a single storey masonry plinth changed this forever. Designed by Waugh Thistleton Architects and Techniker engineers, this residential building in a densely populated part of London ticked many boxes for the local authority, not least for its carbon credentials. Speed of erection, reduced deliveries, minimal waste generated and low noise during construction all added to its case.

Hackney has since become a world epicentre for dense, tall residential structures formed from CLT. The majority are within the 8-10 storey range, but the fact that they are there at all – in a city where the Building Acts are predicated on the 1666 Great Fire of London – is testament to how far the material has come in a relatively short period, a fact confirmed by the sheer number of tall residential CLT structures currently being built or proposed globally.

The next tallest timber structure to be completed was the 10-storey Forte Building in Melbourne (2012) which used imported CLT throughout. Moving beyond the 10 storey level (a height limitation invariably due to local building regulations rather than the ability of structural engineers to design taller buildings with new engineered timber products) has taken a little longer, but ever taller projects are now emerging. At 14 storeys, the Treet Building in Bergen, Norway (2015) is currently the world’s tallest residential timber building, but will be overtaken next summer when the University of British Columbia’s 18-storey Brock Commons Student Residence in Vancouver opens. The lead position in the race upwards has temporarily shifted to Canada, the result of determination within the forest and timber processing sector there to take advantage of a technological development that can incrementally increase the value of the country’s vast raw material resource.

In 2012 Vancouver-based architect Michael Green produced ‘Tall Wood’, a downloadable research report that pushed forward the possibility of commercial buildings up to 20 storeys in height being formed from hybrids of glulam and cross laminated timber. The architect has since followed up with proposals for 30- and 35-storey towers in Vancouver and Paris respectively, as well as designs for entire urban districts comprised of tall timber structures.

North American endeavour is not confined to Canada, however. The $2m Tall Wood Building Prize to Innovate Building Construction was launched in October 2014 as part of the Obama administration’s commitment to mitigating climate change in the US. This focused heavily on cross laminated timber and other emerging timber technologies. The campaign produced not one, but two winning development teams, with 12-storey timber towers now underway in Portland, Oregon and New York. There is also a bill in front of the US Senate to “accelerate the use of wood in buildings, especially tall wood buildings, and for other purposes” which, if and when enacted, will become the Timber Innovation Act of 2016. Elsewhere, architect SOM has redesigned a 42-storey reinforced concrete and glass tower it built in Chicago in 1964 using today’s engineered timber

technologies. The company’s comprehensive research study shows it can be done using a hybrid of solid timber and concrete connections, the latter for stiffness but also to provide the weight necessary to maintain the building’s stability in the Windy City.

In Europe, designs for a plethora of tall, engineered timber buildings are in process: four 20 storey apartment blocks for Stockholm’s waterfront proposed by Tham & Videgård Arkitekter, the 24-storey Ho-Ho tower in Vienna designed by RLP Rüdiger Lainer + Partner, and the 34 storey Västerbroplan residential tower in Stockholm by C.F. Møller Architects (as illustrated).

In each, the boundaries of timber engineering are being pushed ever further, but the example that takes this endeavour to a completely new level is the Barbican Oak tower in the City of London. This research project exploring the possibility of building up to 80 storeys in timber was initiated by PLP Architects in London, Smith and Wallwork Engineers in Cambridge and Cambridge University’s Architecture Department. Speculative and provocative, the project raises many technical and wood science questions, the responses to which will undoubtedly expand the boundaries of engineered timber technology and manufacture far beyond current understanding and industry capacity.

Time will tell just how far these technologies can advance, but the speed of transformation to date suggests Professor Alex de Rijke’s prediction that ‘timber is the new concrete of the 21st century’ is closer than ever before to being fulfilled.

Peter Wilson is managing director of Timber Design Initiatives.