The Aquatics Centre for the Paris Olympics - a case study in sustainable architecture.

In last month’s blog I discussed carbon in the construction industry which accounts for around 40% of all global emissions. I identified the main reasons for this and pinpointed the materials that are the main emitters of embodied carbon (concrete and steel) in the construction sector.

This month, I'm focussing on timber, which is in essence a renewable resource and therefore largely regarded as one of the most sustainable construction materials due to its low carbon footprint. As governments and the industry in general are now looking at timber as a solution for reducing carbon output in construction, it is likely to be used on a much greater scale in future. In this article I will examine aspects of using timber as an environmentally-friendly construction material and dig deeper into the facts around sourcing of timber and carbon accounting taking the new state-of-the-art Aquatics Building for the Paris Olympics as a reference project.



Swimming pool Image by Markus Spiske from Pixabay; "Co2" by Pete Linforth from Pixabay; "Forest Sunbeams" by jplenio from Pixabay

Many countries signed up to the Paris Agreement, which aims to limit global warming to 1.5°C by the end of the century, and to achieve a decline of 43% by 2025 [10]. Coincidentally, the Paris Olympics will be held in July this year, and according to Etienne Thobois, Paris 2024 Olympic Games CEO, the aim is to make sustainability rather than monumental construction its main legacy [9].

In contrast to previous games in Athens or London, for example, where large tracts of the city were regenerated by buildings and structures subsequently used after the games, as little as possible will be built and 95% of the venues will either be made from existing facilities or dismantled afterwards [1].

The new Aquatics Centre is the only permanent building to be constructed for the major sports event, which begins on 26 July 2024 [7] so from a sustainability standpoint it strives to be a role model project. It is a case study on the large-scale use of timber in a monumental civic building which also reflects France’s aim to cut carbon in the building sector as the EU aims to achieve a 55% reduction in overall emissions by 2030 by retrofitting existing structures and using more wood in construction. Timber is widely regarded as a more sustainable eco-friendly material and is therefore now being used on a much wider scale nowadays, thanks to technological developments. It is now also used instead of concrete and steel to perform a structural role in bigger buildings such as high-rise apartments and stadium venues like the Aquatics Centre in Paris.

‘Mass timber’ is used nowadays as an umbrella term to describe a family of wood-based materials have been engineered to enhance their structural performance. Cross-laminated timber, also commonly referred to as CLT, consists of timber strips glued together in a cross-wise arrangement to give it omni-directional strength and stability as well as greater economy in mass (lighter without compromising on strength), glued laminated timber (GLT) and laminated veneer lumber (LVL) match and/or exceed the stability of steel and concrete [2].

Woodpile Image by Zoltan Matuska from Pixabay

As already mentioned above, this building will be the only built legacy of the 2024 games, it is worthy of discussion, not just on its architectural merits but also because it reflects the current trends and discussion and debate in the construction industry in relation to sustainable building and the desire of the French government to demonstrate its environmental credentials on every level: the spectator seats are made of locally recycled plastic, for example.
 

As a former architect, I cannot help marvelling at the architecture of the Aquatics Centre, which has so many wonderful tactile qualities and is sculpturally bold and beautiful. I could not find any images that were not protected by copyright but I sketched an abstract impression which hopefully conveys a feel of the building. For photographs, a quick Google search or click on the references and the end of this article will give you the reality. 

The building has a concrete plinth which connects the lighter 'superstructure' above to the ground and a bridge which links the building to the St Denis district. The base also contains the pool structure and plant areas. Many trees and shrubs have been planted round the building to promote a healthy climate.

Just how much concrete was used to make the base is anybody's guess, as this could generate a large embodied carbon footprint. The designers, on the other hand, would argue that the decision to build the roof and its supporting structure entirely of timber which also doubles the required minimum percentage of bio-sourced materials offsets the carbon output of the base.
 

The concave roof appears to hover above the continuous 'floating' horizontal timber elements of the ‘brise soleil’, which wraps around the external glass façade of the building and visually belies the physical reality of the huge vertical forces transmitted from the roof on free-spanning timber beams over the arena.

Internally the roof kicks up at the ends to accommodate the spectator tribunes and swoops down towards the centre. Besides creating a striking architectural silhouette in the urban landscape of St. Denis, this reduces the interior volume (and therefore heating/cooling costs) which further underscores the energy credentials of the building. It is also what the architects VenhoevenCS and Ateliers 2/3/4 claim to be “one of the biggest solar farms in France” and is expected to generate 20% of all the electricity required.



What about the bigger picture?

Forest Sunbeams Image by jplenio from Pixabay

The components for the roof were prefabricated at a factory in Alsace near the border with Germany and shipped to the site. According to Frank Mathis who runs the woodyard, timber is currently in short supply due to the war in Ukraine and dwindling supplies from Russia and other European producers diverting timber across the Atlantic where they can command higher prices [9]. As much as possible of the timber (30-40%), consisting mainly of Douglas Fir and Spruce, is being sourced from within France. Although it does not have an abundance of forests compared to say Germany and Austria, it has set itself the goal of sourcing 50% of its construction timber from forests inside France. A carbon footprint is certainly produced by shipping the 60% of the felled timber from other regions to the woodyard then for shipping the finished components of the roof structure to the site.

On the other hand, the components were assembled extremely rapidly on-site, which uses much less energy and therefore offsets the carbon footprint of transportation to the site to a degree.

...and how is the timber processed?

Logging requires energy. And then there is the machining, trimming and manufacturing work on glued laminated components such as those used in the roof in Paris where the beams are required to span 89m and hold up the solar installation above it. When the use of timber is ramped up to a much larger scale, the environmental impact of all of these processes would increase exponentially.

According to one article published by an organisation that advocates the use of concrete in the construction sector “the wood industry is in fact responsible or releasing more than 10% of recent global annual emissions of carbon dioxide” [11].

So the argument for and against the mass use of timber is clearly ongoing, with each sector of the construction industry doggedly arguing their respective corners.



How can we prevent deforestation, over-harvesting and depletion of natural wildlife habitats as a result of using much more timber in construction

How are the forests where this timber is sourced being managed? Here in the UK according to Friends of the Earth “… our demand for wood is having a devastating impact on the world's forests. Forests that give us everything from oxygen to medicines – and help combat climate change. 1 in 3 tree species harvested for timber are currently at risk of extinction" [4]. They also claim that UK timber imports are driving deforestation in Malaysia and the depletion of the Amazonian rainforest is well documented.

So we may well have buildings that on the surface are more ‘sustainable’ locally but not globally as the impact is felt elsewhere in the world.
 

Groups like the FSC and PEFC set standards for replanting and conservation and over the last 30 years in Europe the amount of land covered by forests has increased by 9%. So providing timber is sourced through responsible regenerative processes it can be used in construction projects.

The question of how sustainable timber is in construction also largely dictated by the complexities of forest management, over which many questions currently exist. It could be argued that whether or not using timber in construction projects is sustainable largely rests on how carefully forests are managed.

What will happen to the timber elements of the Aquatics Centre when it reaches the end of its useful service life and these Olympic Games have faded into the dim and distant past?
 

One of the biggest ecological advantages of using timber is that it naturally sequesters carbon. It is a well-known fact that trees store Co2 through a process called photo-synthesis, so when timber is used in construction, the building also becomes a permanent Co2 store. From this point or view therefore, large-scale use of timber in the construction industry would be extremely beneficial in terms of keeping carbon out of the environment.

However, this only holds true while the building is standing, what happens to the timber and sequestered carbon in it when the building is renovated, redesigned or demolished?

If the timber can be 100% reused or recycled then the carbon storage benefits are retained but if, on the other hand, timber is landfilled at the end of its useful life, analysis has suggested that the net emissions from a CLT framed building could exceed the life cycle emissions from a typical concrete framed building. When timber is landfilled it rots and releases up to 60% of the sequestered carbon back to the atmosphere as methane, which is 25 times worse than carbon dioxide in terms of global warming impact [3].