Building the Zero Carbon city: what materials are needed to achieve carbon neutrality?

During the second round of “Building the Zero Carbon City” lectures, four construction industry specialists addressed how construction materials can contribute to achieving low carbon building targets.

Zéro Carbone matériaux

After the initial meeting in which the challenges were discussed along with the subtleties of measuring a building’s carbon footprint, this second event in the “Building the Zero Carbon City” addressed another defining issue for all new construction projects: the choice of materials and their carbon impact.

We brought together four experts to compare the advantages of the main materials used by the industry: Nathalie Mehu and François Cussigh, respectively head of sustainable solutions and concrete expert at VINCI Construction France, Anne-Sophie Perrissin-Fabert, director of Alliance HQE-GBC, and Mathieu Desaubliaux, a pre-project engineer at Arbonis, a VINCI Construction subsidiary specialising in timber buildings.

The entire conference can be watched on our YouTube channel (in French only).

The materials that determine a new building’s carbon balance

Upcoming regulatory changes will see a shift in practices and how we approach a construction project. On 1 July 2020, France’s Environmental Regulations (the so-called RE 2020), will replace the current RT 2012 regulations. RE 2020 will require the overall impact of a construction to be examined at all stages in the building’s life: from the choice of raw materials through to its demolition, including the building’s use. Reducing a building’s energy consumption is no longer enough. It will now be necessary to analyse the global impact of the construction on the environment. For the materials, the carbon balance in this life-cycle analysis (LCA) will include all impacts from the manufacture of the constituent materials and all of a building’s equipment.

In this respect, Nathalie Mehu pointed out that 60% of a building’s admissions are attributable to its construction phase, with the materials used for the structure accounting for as much as 40%. The equipment (lifts, heating, distribution ducts, electric wiring, etc.) make up the rest of the construction emissions. An accumulation of small components that are far from being mere incidentals. As a result, building contractors’ habits will have to change: they will have to decide very early in the project stage what previously was decided much later (e.g., what floor coverings to use, what type of flashings, etc.), to reduce the impact of these materials.

Nathalie Mehu Anne-Sophie Pérrissin-Fabert

Anne-Sophie Perrissin-Fabert, from Alliance HQE-GBC, raised the point that the choice of materials is not the only area in which the carbon footprint can be reduced. It is also important to look at optimising the use of space. Sharing and maximising usage of square meterage can also reduce a building’s carbon balance. For example, how might office carparks only used in the daytime and left vacant at night be better used? Perhaps one solution would be to pool these carparks with a neighbouring building so that its residents could use them?

Timber vs. concrete

When asked about the impact of concrete on a building’s carbon balance, François Cussigh advised that it would be compatible with the future regulations. This essential building material has many advantages: it is multi-facetted, improving and potentially has a long life. Moreover, it is often manufactured locally thereby being responsible for very limited greenhouse gas emissions for its transport.

In fact, it is the cement – the bonder – that has the highest emission levels in concrete. There are a growing number of experiments for developing concrete without cement or recycled concrete, and new types of concrete with lower emission levels while still retaining the same strength. All avenues are worth exploring by testing new compositions with lower emissions (geopolymers, clays, concrete made using clinker from steel industry waste etc.), as well as looking to the past with its concrete made from a mixture of lime and volcanic ash developed by the Romans.

François Cussigh et Mathieu Desaubliaux

And in the other corner, wouldn’t timber be a better alternative in order to reduce a building’s carbon impact? This is an attractive avenue, especially given that one cubic meter of timber represents one tonne of CO2 absorbed by the tree and stored until it is burned.

Mathieu Desaubliaux believes that it is above all transport that has the highest impact when building with timber. This points to the need to use local timber to reduce the carbon footprint. For many years, builders have looked to Northern Europe for their supplies of the softwoods that make up the majority of species used by this industry. In a bid to reduce this line in the emissions balance, Arbonis is conducting tests with hardwoods which make up the majority of French forests, for example, beech or poplar glulam, oak CLT, and so forth. If these tests prove positive, the carbon balance of timber constructions will be significantly improved.

The discussions will continue on 29 January with a final round of lectures devoted to the comparative benefits of zero carbon construction and zero carbon renovation.