Often being modular in design, lightweight prefabricated mass timber building systems are easily assembled, provide thermal benefits, and are well-suited to energy-efficient construction and the standards of net-zero-ready design.
Mass timber design is a sustainable solution that can cut as much as 75 per cent of embodied carbon emissions compared with conventional steel and concrete designs, and enables buildings to be constructed 25 per cent faster than with concrete while requiring 90 per cent less construction traffic.
It also provides aesthetic and design flexibility, as wood can be altered and cut as needed and has many avenues for recycling. Moreover, various studies have shown timber designs can create marked physiological and psychological improvements in humans, improving job performance by reducing stress, fatigue,anxiety, and absenteeism.
Products used in mass timber structures consist of multiple solid wood panels nailed or glued together to provide strength and stability, and can be used as a load-bearing structure or as an interior finish material.
These include cross-laminated timber (CLT), glue-laminated (glulam) beams, laminated veneer lumber, nail-laminated timber, and dowel-laminated timber.
Mass timber can also reduce the global warming potential of the built environment by up to 26.5 per cent, as trees absorb carbon throughout their lifecycle, as well as drastically reducing construction material waste.
Research published in the journal Nature has predicted that using mass timber for 90 per cent of new urban buildings could prevent about eight billion tonnes of carbon dioxide emissions by 2050.
A Council on Tall Buildings and Urban Habitats (CTBUH) tall timber audit undertaken in 2023 counted 162 mass timber buildings around the world with eight storeys or higher, and either proposed, under construction or completed.
Europe accounts for most of the total with 92 buildings (61 complete, 26 proposed and five under construction), while North America has 46 (10 complete, 26 proposed and 10 under construction) and Oceania 17 (seven complete, six proposed and four under construction).
Five projects were in Asia (two complete, three proposed) and one proposed project each for South America and Africa. Looking at only the 99 mass timber projects under construction and completed, 63 of them were residential, 23 office, 11 mixed use, and two were institutional in function.
The prominent use of mass timber in residential buildings correlates with the material’s well-reported benefits, such as its aesthetic appeal when the structure and panelling is exposed within units or common areas.
Of the 99 projects, 66 are in Europe, 20 in North America, 11 in Oceania and two in Asia. Broken down by structural classification, 46 of the 99 are all-timber, 31 are concrete-timber hybrids, 12 are steel-timber hybrids, and 10 are concrete-steel-timber hybrids.
Notable timber buildings in Australia include the Adina Apartment Hotel at 55 Southbank in Melbourne, the world’s tallest mass timber vertical extension. Completed in 2020, 55 Southbank hosts a 220-room serviced apartment complex, with the extension more than doubling the building’s previous height.
The existing building was originally designed to allow for an additional six-storey vertical extension using concrete-framed construction, but this did not provide enough floor area to make the apartment complex commercially viable. As CLT is five times lighter than concrete, its use allowed an extension of 10 storeys, as well as resulting in lower transport costs, while offsite prefabrication – such as the prefabricated modular hotel bathrooms – significantly reduced the time spent on site.
The 72-metre-high building used about 1,850 CLT panels weighing about 1,730 tonnes, while also sequestering about 2,800 tonnes of carbon dioxide or the equivalent of the annual carbon emissions of 130 homes. Architects Bates Smart said the design complemented the curved architecture of the existing building without overtly expressing the timber, as was typical in many CLT buildings.
The studio said: “A large recessed balcony helps celebrate the corner and the building’s new height – it also gives guests a place to take in expansive Melbourne skyline views. “Curved walls also distinguish the space, and work in accordance with the curved façade and sinuous lines of the new extension.”
Another significant project is the proposed C6 tower in South Perth, which received developmental approval late last year and at 183 metres would be the tallest mass timber building in Australia. The 50-storey, $350-million hybrid timber tower will also become the country’s second carbon-negative building after the Atlassian tower in Sydney, through an embedded power network with wind and solar power, and a biophilic design featuring 3,500 square metres of floral, edible, and native gardens.
Featuring both CLT and glulam, the tower’s hybrid structure was carefully designed to make the best use of each material, according to Reade Dixon, Director of Fraser & Partners, architect for the project. Dixon said: “We relied on the hybrid structure model, using concrete where it was the most efficient and required for gravity loads and lateral stability at this height – in the core and the columns – and using timber where it was more efficient than using concrete, the horizontal structure being the floors and beams.
“At this height, typical superstructure design was used, such as concrete outrigger walls at three different locations in the tower to deal with lateral loading and reduce core and column sizes. “A steel diagrid was also used to further assist with bracing requirements. “All these elements combined together to allow this new benchmark in height for mass timber.”
According to the developer, the building’s core will sequester more than 10.5 million kilograms of carbon dioxide compared to a similarly-scaled traditional concrete structure. All of the necessary 7,400 cubic metres of timber required to build the apartment floors, columns, and beams will be able to be regrown from just 580 seeds.
Robert Svars, General Manager of mass-timber specialist firm Vistek Engineers, which is conducting C6’s timber structural engineering, said the building would be a beacon for others to follow. Svars said: “When you mix materials, you have issues about concrete and wood behaving differently over time, with shrinkage rates and so on. “Design must have constructability at the front of mind and take a holistic look and the structural engineer must be hands on – timber calls for integration with the architects.”