Sawmilling SA: Taking timber to new heights

Taking timber

to new heights

A report by global design, engineering and architecture firm Arup, Rethinking Timber Buildings: Seven perspectives on the use of timber in building, states that global carbon dioxide emissions have increased by almost 50% since 1990, with the global construction industry alone producing around 15% of these emissions. Furthermore, an estimated two billion square metres of new building stock are needed every year between 2019 and 2025, especially for housing.

When you consider the findings of the more recent Intergovernmental Panel on Climate Change Assessment Report which states that climate change is widespread and rapidly intensifying, the built environment holds the mantle for sustainable and swift climate action. How? By using more wood.

For many years, wood has been viewed as an inferior building material reserved either for the very poor or engineered for the ultra-rich. It’s been labelled a fire hazard, weak or the cause of deforestation.

Aiming high with a lower footprint

Many people associate wood with rudimentary shelters or ‘wendy’ houses; for some it’s a luxurious log cabin nestled on a hillside with a view of the ocean. But for professionals and architects who are drawn to the wonders of wood, the sky is quite literally the limit.

The presence of wood even makes us feel better due to ‘biophilia’, a hypothesis popularised by biologist and author Edward Wilson. As humans, we have an innate tendency to seek connections with nature and other forms of life.

The world’s tallest mass timber building is the 18-storey Brock Commons Student Residence in Vancouver, Canada. In 2018, Sumitomo Forestry announced its plans to build a 70-storey hybrid timber skyscraper to mark its 350th anniversary in 2041. Dubbed W350, this lofty tower of lumber reflects a growing global trend to take wood to new heights in the built environment.

Green cred

But mention of timber buildings, and most people think ‘deforestation’. Roy Southey, Executive Director of Sawmilling South Africa, says: “There is no doubt that concrete, steel and stone are good building materials, but it takes something special to match wood’s environmental credentials.”

South Africa has 1.2 million hectares of farmed trees, and only 10% is harvested and replanted with new trees each year. This makes sustainably produced wood a renewable resource. The consumption of sustainable wood can actually help combat deforestation and local plantations are managed to stringent environmental criteria, especially in terms of water and biodiversity impacts.

Sustainable forestry maintains trees in an active growing phase, optimising carbon storage. By harvesting small tracts at the right age, there is reduced risk of releasing carbon back into the atmosphere due to disturbances such as disease, decay and fire. Carbon is stored for longer when the trees are harvested and used for the production of wood products.

Some 0.9 tons of carbon are sequestered by one cubic metre of wood throughout its lifetime. With a timber to steel ratio of 9:1, Sumitomo’s timber titan of 185 000 cubic metres will be a vault for 166 500 tons of carbon.

Timber ticks the boxes

Engineered wood types, such as glued laminated timber (glulam) or cross laminated timber, can match well with concrete and steel, with their competitive strength-to-weight ratios.

“Along with design flexibility, longevity and superior insulating properties, timber structures are often prefabricated off-site and lighter to transport, reducing both construction times and associated costs,” points out Southey.

Wood, of course, is a natural product and is thus susceptible to biological degradation. Biological degradation can occur

either through fungal decay when exposed to higher moisture conditions, or attack by wood destroying insects like borer beetles and termites.

According to Bruce Breedt, Executive Director of the South African Wood Preservers Association, the importance of using pre-treated timber to prevent degradation is critical to retain the benefit of timber in construction.

Sustainable supply

“Locally, we have enough forestry and timber resources to build more than 55,000 houses a year,” states Dr Philip Crafford from Stellenbosch University’s Department of Forest and Wood Science who co-authored a study with Dr Brand Wessels. This study revealed that our local log resource is sufficient for a sustainable wood residential building market.

Despite this, South Africa is far behind the curve when it comes to using timber as a mainstream building material. Currently, only 1% of new houses in the country are wood-based, compared to more than 90% in countries such as the United States, Canada and Australia.

“Structural timber does, however, have a long history here in the form of roof trussing,” says Southey, adding that it is widely accepted as the preferred method of construction for residential and medium-sized commercial roof structures.

Collaborative construction

Timber buildings are well-suited for public and private sectors invested in mitigating their environmental impact. From timberbuilt low-cost dwellings, staff housing and public buildings to high-end luxury homes, citizens, business and government could tap into the unique potential of wood.

As the Arup report rightly asserts: “The use of timber alone will not solve our many challenges, but it could form a vital component of how we choose to design and build and underpin a more resilient built environment.”

By working in tandem with other construction industries, and not in opposition, the timber sector can not only rethink how it creates living and workspaces but act against climate change and create a greener building economy using one of the oldest, most intelligent and beautiful materials known to humankind.

Untitled-3 1 2013/10/25 12:00 PM Timber buildings bring tremendous returns to all players along the value chain, from the timber grower to the homeowner while also serving to mitigate environmental impact. Photo by Roger Jardine

Believe in Better Building, Osterley, UK. Photo by B&K Structures The four-storey-tall timber cassette cladding panels on this timber office building for Sky UK comprise internal and external wood facing panels separated by timber webs. Insulation occupies the spaces between the webs, and internal and external membranes control the passage of any moisture that may appear in the insulated cavity. With integrated assemblies like this, rigorous building physics analysis is important to give confidence in the thermal and moisture performance of the system.

The timber sector is working to change perceptions in South Africa when it comes to using timber as a mainstream building material.