007 / Tall Timber
By Khaled Abou Alfa • Published July 2019
As a grand act of piety, the Emperor Shōmu began building as many Buddhist temples as possible. The epicentre of this work was the Tōdai-ji (Eastern Great Temple), in Japan’s Nara province. This project was at such a grand scale, it would nearly bankrupt Japan. The material he sought to use for these temples was not stone or steel or marble. It was wood. When completed, around the 8th century A.D, Tōdai-ji was home to the world’s largest wooden structure. It had to be rebuilt twice. The first time was due to the direct action of waring clans, while the second was the result of an earthquake. The current incarnation was rebuilt and completed in the 1700s. Although the height remained the same, the Great Buddhist Hall was constructed to around 60% the size of the original. Even at this reduced size, Tōdai-ji was to remain the largest wooden structure in the world until 1997.
By the early 1900s wood as the primary construction material was about to fall out of favour globally. Making way for concrete and steel, this would relegate wood and timber to the fringes. A material predominantly used on a domestic scale. The extent to which this material has fallen out of favour is best captured by the fact that in the past five years, 17 buildings taller than seven stories exist worldwide. This number is a function of factors such as regulation and alternative ‘modern’ materials. Which in turn diminished market acceptance and all but extinguished research and development.
As we look again to using timber as the main source of material for construction we have to aim higher, both figuratively and literally. In this new era of timber, we should aim to not only meet current life safety standards but exceed them. We must develop new practices and varied approaches. Practices that are considerate of the impact on forests and the environment. Practices that reflects the commercial realities of the world. Practices that allows us to better connect with nature, where this connection has been severed. Of course, there are many technical and societal challenges that we will need to overcome first.
The biggest breakthrough for the use of timber in more ambitious construction, began with the introduction of Cross Laminated Timber (CLT). Developed in Austria and introduced into the European market in the 1990s, CLT would spread globally. A traditional CLT panel consists of several layers of kiln-dried lumber boards stacked in alternating directions, bonded with structural adhesives, and pressed to form a panel. With the established Glued Laminated Timber (Glulam), these two timber products would lead to the creation of mass timber panels and open the door to the use of timber in larger projects again. Encouragingly, development of the technology continues, with the introduction of dowel-laminated timber panels that do not require glue or nails.
As our awareness and responsibilities to the Earth increase, we must reassess our needs and methods. What we may have considered as the only sensible or viable way, will need to shift and to accommodate the challenges ahead of us. Populations, and the need for new housing, will rise. We need to address the struggles of the 900 Million people who are living in slums. Timber will not solve all our issues, but it has a key role to play in our transition to a more sustainable and harmonious built environment.
Our populations will continue to grow for the foreseeable future (see graph in issue 005). As our populations move away from the countryside and into cities 1, our daily connections to nature erode. These connections are important in promoting a more harmonious society. There are numerous studies that have documented the impact that natural elements have on both our physical and mental health. From this study:
This makes the link between the presence of wood and physiological manifestations of stress very clear. That is, wood prevents us from becoming more stressed by our environment.
While architecture evokes a wide range of emotions, reducing stress is an unsaid rule. How many architects strive to make their creations stressful? This reduced stress then manifests itself as improved social integration, reduction in crime and increased local investment. Bringing these natural elements within our buildings, in the form of exposed structure, finishes and furniture will only contribute to these well-being benefits.
Sustainability & Carbon
The combined CO2 emissions from both cement and steel industries account for around 12% of all global emissions2. While both industries are trying to address these shortfalls, recycling or reusing these materials is the rare exception. Furthermore, currently these practices offer limited returns. By contrast, timber offers a compelling third option. Timber is one of the few renewable materials. For trees to grow, CO2 is removed from the atmosphere and ‘stored’ in the wood itself. That difference in CO2 is then further compounded when the energy for processing and transportation is accounted for. While not negative, timber requires less energy to process than cement or steel. By considering the gifts that nature has bestowed upon us we will strive for a more sustainable future that is in actual equilibrium with the resources we use.
The story for the use of timber in taller structures, replacing a world dominated and reliant on cement and steel, will touch upon a plethora of thorny subjects, which include:
|Market Acceptance||Earthquakes||Water Damage|
While each subject deserves considered attention, we will only review the first two on the list.
Codes, Regulations and Fire
This era of reintroducing timber as a significant material in construction comes with considerable scrutiny as building codes and safety regulations take centre stage. While the regulations vary from country to country, broadly the height restriction is around the 7 storey mark3. These requirements are changing, as taller structures are being considered and approved. Both the environmental and even commercial considerations will help push these regulations forward. Regulators (and politicians) will be keen to tread carefully into a situation similar to that caused by the widespread use of aluminium composite panels.
For all its advantages there is one unavoidable fact: timber, by its nature, is a combustible material. Manipulating timber constructions in a manner that allows them to perform suitably in a fire is a crucial requirement to increase the use of this material. Tragedies such as Grenfell Tower will continue to plague us, an unfortunate indicator that even in the most advanced countries we still have a great deal to achieve when it comes to fire safety. The task of realigning public understanding around the properties of timber structures and their capabilities against fire will be a long and hard fought battle.
Considering that the regulations either limit the heights or require that all exposed timber parts are encapsulated in a fire rated construction (which defeats the purpose), more research and a better understanding of how cross laminated timber (CLT), as a compartment, reacts in a fire will help us develop the products in more suitable and meaningful ways.
Of particular interest is how timber reacts in fires once de-lamination (or char fall-off) occurs. The char layer provides protection to the unburnt timber behind it, while the new exposed timber will cause a fire to continue or grow. Keeping that char layer in place throughout the fire is an important obstacle to overcome. Engineering a solution to this property (through adhesives or constructions that do not allow delimitation to occur will solve a major concern for the use of CLT.
Deforestation account for over 15% of all global carbon emissions, as we lose 18.7 million acres of forests annually. The main reason for this loss comes from agriculture, although urbanisation and prized consumer products contribute to the issue. This list doesn’t need the addition of major construction as another incentive. A world where timber becomes a material that is more readily used over cement and steel may seem like solving a problem in one area while creating one in another. Managing our forests will become a significant indicator of how successful we are. Sourcing timber from sustainable and certified sources, such as those certified by the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC) will pave the way. Additional incentives and checks will be required to help our forests thrive into this future.
Waiting for the moment
In his 2013 TED talk, architect Michael Green talked about an ‘Eiffel Tower’ moment. This moment has not arrived yet and so the vision and promise of tall timber has not been realised. Many of the technical and societal challenges have yet to be tackled. In some respects, Michael Green’s path mirrors that taken by Zaha Hadid in the 1980s. Many of her designs considered unbuildable at the time (some may still remain unbuildable), indicated a destination. A destination that the rest of the construction industry would reach many years later.
Incremental steps towards a new reality will start taking a hold as the technologies, our understanding and the market shift. It’s time for wood to take a more central role in our future construction practices and reclaim some of its former glory.
The IBC (International Building Code), 2012 and 2015 versions allow for timber framed construction around 6 storeys or 25m (85 ft). For many years, the UK Building Regulations limited the allowable height to 3 floors. ↩︎