Mass timber construction: Building for the better

Sarah Hicks and Scott Jackson

Photos courtesy ZAS/BMCEA

Construction, maintenance, and demolition of the built environment are a leading source of the world’s carbon dioxide (CO2) emissions. In the face of climate change, exponential population growth, and urban densification, it is imperative society develops sustainable building solutions to meet growing housing and infrastructure needs without accelerating climate change.

The building industry must be empowered to tackle these challenges with every possible tool. The industry cannot improve by doing things the way they have always been done, and small incremental changes over time will not be enough. New products, systems, and ways of thinking must prevail. This understanding of the need for a radical shift in our thinking is fueling a mass timber revolution in the construction industry. Environmentally responsible development requires high-performance buildings that pay greater attention to both embodied energy and operational impact. Mass timber construction provides an avenue for delivering sustainable buildings of the future.

We now know for a certainty mass timber is a strong and fire-safe construction option. There is ample empirical evidence proving this from building material research scientists in Canada and around the world. There are also thousands of mass timber buildings already in service that demonstrate this to be true. Nevertheless, mass timber construction has, until relatively recently, been a niche market.

That is about to change, thanks to the industrialization of the construction process. The shift from site-built developments to offsite manufacturing, enabled by building information modelling (BIM) and computer numerical control (CNC) fabrication, is gaining momentum. Mass timber is perfectly suited to this form of construction.

Prefabricated mass timber components have the potential to transform the construction process and the built environment while simultaneously reducing its carbon footprint. Canada’s forest management practices are recognized among the best in the world with more third-party certified lands than any other country. The country has the natural resources and intellectual capital needed to be a world leader in green construction technology and sustainable development if the industry can be transformed to unlock the potential of mass timber builds.

Forests as carbon sinks

The Toronto Region Conservation Authority’s (TRCA’s) new four-storey administrative office building in Toronto incorporates numerous sustainability features, including a mass timber structure.

Although the creation of artificial carbon sinks has been explored, no major artificial system has been developed to remove carbon from the atmosphere as effectively or at the scale forests do.

Wood is not simply our only major renewable building material, but also the most environmentally friendly option with respect to the construction and development sectors. Wood uses less energy to produce than alternatives, results in less water and atmospheric pollution, and perhaps, most importantly, represents the best opportunity we have to mitigate the impacts of climate change.

As trees grow, they remove CO2 from the air. On average, 50 per cent of an 80-year-old tree’s dry weight is made up of carbon.

However, when it comes to carbon sequestration, all trees do not perform equally. The amount of CO2 removed from the atmosphere is directly related to the incremental growth of the tree (i.e. the more weight a tree puts on in a given year the more carbon dioxide it removes from the air). Small trees may double in size quickly, but their overall growth is relatively small. Conversely, older (or larger) trees will eventually stop growing. As a result, while larger trees may represent big storehouses of carbon, they do not typically remove additional carbon dioxide from the air (i.e. no net gain). In fact, elderly trees can act as carbon sources as they senesce and decay. Older forests are also more susceptible to some natural disturbances, such as fire, which can result in large stores of carbon being returned to the atmosphere in a relatively short period of time. The frequency and severity of fires are expected to increase in the face of climate change, potentially exacerbating this concern. In Ontario, Crown-managed forests (the publicly owned area that is actively and sustainably managed for forestry operations) are currently net carbon sources, in part due to an older than natural age structure. Ultimately, middle-aged trees provide the greatest rate of carbon sequestration.

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