Skyscrapers made of wood? That now looks a realistic possibility across the world’s cities.
An increasing number of urban planners are swapping steel and concrete for timber as a more sustainable, durable and cost-effective building material.
While the share of wood in total construction varies between countries and regions, data shows the number of mass timber buildings constructed in the US annually is doubling every two years. It's on track to reach at least 24,000 by 2034, at which point the construction industry would be storing more carbon it emits.
Today, advances in technology and changes in regulation are paving the way for wood to feature in all types of construction, from sprawling office complexes to high-rise buildings, or “plyscrapers”.
“The switch to timber is being led by Europe but also gaining traction in the US, which is one of the world’s biggest real estate markets,” says Clark Binkley, Managing Director at International Forestry Investment Advisors in Portland, Oregon.
“This could be pivotal in reducing the carbon footprint of buildings and contributing to a sustainable transition.”
Wood, reimagined
Timber is a traditional building material used in structures for centuries across the world thanks to its durable and resilient properties and the relative ease of material sourcing and construction.
Built in 607AD, Horyuji Temple near Nara, Japan is the oldest surviving wooden building in the world which uses hinoki, or Japanese cypress, while Britain’s oldest door in London’s Westminster Abbey, made of oak, dates back to 1050AD.
In recent decades, however, this renewable material has fallen out of fashion in the face of concrete and steel, which are considered more durable, rot resistant and easy to mass produce.
Typically, residential buildings in Europe use around 20 per cent of timber in their frames; this number drops to just 5 per cent for commercial counterparts. In the US, the contrast is even bigger with nearly 90 per cent for houses and less than 10 per cent for commercial spaces.
“All in all, there’s significant room to ramp up the use of wood in construction, especially as a climate crisis intensifies pressure on the building sector,” says Binkley.
The world’s buildings are responsible for 40 per cent of global carbon emissions, to reduce its environmental footprint.
The good news is innovative technologies are changing the way we build with wood.
One of the most promising products is cross-laminated timber (CLT), a building panel made of sawn, glued and layered wood. Developed in Europe in the 1980s, CLT is a low-carbon material that is as strong as concrete but five times lighter.
Some of the high-profile projects for timber-based towers and expansive structures in the US testify to engineered wood’s potential as a viable sustainable building material.
Tech giant Microsoft used CLT to build its Silicon Valley campus in what is the largest mass wood structure built to date in the US.
The use of timber, along with other sustainable materials, is contributing to the firm’s goal of cutting its operational carbon emissions by 75 per cent by 2030.
The Ascent building in Milwaukee, Wisconsin is the world’s tallest mass timber building at 25-stories high.
To satisfy the building codes, the hybrid tower used CLT, glued-laminated (glulam) timber columns and beams, as well as reinforced-concrete cores.
A wood innovations programme at the US Department of Agriculture Forest Service provided grants for engineering and design work and supervised fire testing.
The market for CLT is expected to grow to a USD2.5 billion globally by 2027 from USD1.1 billion in 2021, an annual increase of some 15 per cent.
Some experts reckon it could grow even more rapidly. This is because revisions in regulations are making it easier to build with wood in the US, says Binkley.
Until recently, in most American cities, the height limit for wood buildings was 85 feet, or about seven stories. But the recent landmark revisions to the International Building Code (IBC) in 2021, a model building code which establishes minimum requirements for building systems, took the threshold up to 18 stories.
What has stalled the take-up of timber is rooted in the idea that wooden constructions pose a serious fire risk. Yet those views are in need of revision.
Safety tests show advances in production and building methods have increased timber’s resistance to burning.
When the external layers of a timber beam char, they protect the core from damage for longer periods.
Newer technologies such as CLT, meanwhile, produce a stronger and fire-resistant weave which can outperform unprotected steel structures in fire safety.
What is more, if wood materials can be sourced from overpopulated forests, this might reduce the risk of wildfires, which globally cost USD25 billion in losses with the southwest US being one of the worst affected areas.
Low impact, high benefits
Using more wood in construction can yield considerable environmental benefits.
In one influential study, scientists have found that increased wood use in non-residential construction could reduce emissions by 870 million ton of CO2 equivalent over 50 years – the amount of pollution generated by 233 coal-fired power plants in one year.
The same study also found that, compared with traditional buildings, plyscrapers’ carbon footprint is smaller during their construction phase – which is typically the most polluting period of a project because it involves extraction of raw materials, manufacturing, transportation, installation and disposal of waste.
Known as embodied carbon (EC), these construction-phase emissions originate in the first couple of years of a construction project and account for as much as 45 per cent of total emissions of an average life of a building. Timber-based buildings can reduce the median value of EC by 18-50 per cent, bringing the EC of mass timber buildings to 157-315 kgCO2e/m2 of floor area, the analysis showed. Buildings using engineered wood, meanwhile, can achieve a reduction of 16-44 billion tonnes of CO2e emissions globally compared with concrete and steel materials by 2060.
A reduction of this magnitude would be equivalent to removing 3.5 to 9.6 billion passenger vehicles from the road in one year. Global warming potential infographic
Timber’s environmental credentials are not limited to emission reductions. Thanks to their excellent thermal properties and warm visual appeal, timber buildings are expected save energy not just during construction, but also throughout their lifetime operations, according to Binkley.
Next-generation technology and improving regulations should help timber buildings to grow taller and become more numerous in the coming years.
“Timber can be a heavyweight in our fight against climate change,” Binkley says.
