Raise the roof with mass timber to bring down carbon emissions

The built environment is already responsible for almost 40% of global carbon emissions. And the problem grows bigger every day – in fact, the world adds buildings equivalent to the size of Paris every five days, says Johanna Pirinen, SVP, Sustainability and People & Culture, Wood Products Division, Stora Enso.

Making a meaningful move towards sustainability requires addressing the whole life carbon emissions of both new and renovated buildings. Whole life carbon considers emissions from operating buildings such as lighting and heating, as well as the emissions that are embodied in the production of building materials, the construction and the renovation processes. Sustainable materials, like mass timber, can reduce whole life carbon emissions but adoption is not as rapid as it could be.

All of which is to say, we need to get a grip on emissions emanating from the built environment. This will require a host of mindset shifts throughout the complex web of stakeholders involved – from architects and developers to insurers and occupants – but to start, let us focus on just three.

Shift 1: Rebalancing operational and embodied carbon
First, the good news: there has been tremendous progress in addressing the emissions of buildings in operation. Few people will now be surprised to see solar panels on roofs or heat pump compressors on walls, and the benefits of LEDs over incandescent light bulbs is well-established.

This is excellent, but it represents only one side of the coin. The other is the embodied carbon – the emissions caused by manufacturing the materials that comprise the building, and the emissions released in the process of building it. In this regard, progress has been much slower. The go-to ‘modern’ feeling materials for architects and designers are steel and glass, built on a concrete structure. In fact, concrete, steel and aluminium production worldwide account for 23 per cent of global emissions today.

Unlike operational emissions – which can be reduced over time – these emissions are effectively locked-in from the design table onwards. That makes it even more time critical to address, yet we are only just beginning to.

Shift 2: Rethinking materials
With concrete, steel and aluminium causing such a significant proportion of emissions, the natural question is – how can we improve on that?

And in fact, there are great concerted efforts from those industries to lessen their footprint, including by investing in new technologies such as electric arc furnaces and carbon capture. However, these trends are in their infancy and remain expensive – we remain a way off widespread adoption.

For many applications however – including structural ones – we can look to other materials instead, namely mass timber.

Mass timber – or engineered timber – refers to specifically manufactured wooden elements that replicate many of the structural advantages of what we assume to be the gold standard materials – concrete and steel. However, if sourced from sustainably harvested forests, timber can be not only lower in carbon than these materials, it can be carbon negative. This is because carbon captured from the air during a tree’s growth remains in the wood for the duration of the material’s lifecycle and is only released if the timber is allowed to rot or be burned. Timber can still be recycled and reused for purposes such as furniture, packaging, and paper after its initial use as a building material, thereby prolonging the period before the carbon is released.

It’s not just the embodied emissions of the materials production where mass timber stands out, its lightweight durability allows for the delivery of a higher volume to site with a single delivery, saving on emissions across transportation.

However, certain outdated perceptions of mass timber remain, which, for today’s mass timber elements, are very far from the truth.

Shift 3: Whole-life thinking
A building may stand for 50-100 years. Therefore, it is tempting to leave the question of dismantling and disposal to future generations. Tempting, but unjustifiable. Every day, old materials find their way to landfill, with only minimal reuse. It doesn’t have to be that way – elements can be designed for reuse, either in new buildings or in other sectors.

The move towards circularity backed by life cycle assessments (LCAs) seeks to address this, calculating the environmental impact of products throughout their life cycle, from cradle to grave. Producers are therefore incentivised to extend that life cycle to attain better performance, whether through extended longevity or designed-for reuse.

This is true of all materials of course, but mass timber lends itself especially well to whole-life thinking. The natural first choice is reuse as a building element, but failing that it can be repurposed for another sector. Today, the extensive industrial infrastructure for mass reuse and repurposing does not exist, but studies are ongoing that we can hope will address this by the time the buildings we erect today reach end of life.

Shifts in action
However, we are not starting from square one. There are pockets of progress where these mindset shifts are already well underway. For example, in 2020 the French government introduced a law known as RE2020, which came into effect in 2022. These rules mandate the use of LCAs, and put an explicit focus on embodied carbon in addition to energy use. RE2020 is explicitly focused “on three pillars: low-energy design, use of low-emission materials, and reuse,” says Laurent Petit, Director of Engineering at real-estate developer WO2.

The French government also proposed a groundbreaking law the same year, which would have mandated that 50% of all new public buildings to be made of wood or other biomaterials. Sadly, this was dropped, however the passion for mass timber construction remained.

In France, these mindset shifts are well underway. In some of the Nordic and German-speaking countries, they have also been underway for some time. However, progress must be made on a global scale to keep whole life carbon in focus and make important progress in reducing the built environments contribution to global emissions.

Mass timber presents itself as powerful means of contributing to sustainability and climate mitigation efforts however, there remains a way to go before we see developers everywhere raising the roof – and their climate ambitions.

If you would like to read more stories like this, then please click here