Construction potential of biobased materials

Extraction and transformation of materials, intensive construction, energy-greedy activities and performance... in France and worldwide, the building construction industry (see below) is a key source of pollution. According to the French Ministry of Ecology, Sustainable Development, and Energy, this industry is responsible for 43% of the country’s annual energy consumption and 23% of its greenhouse gas (GHG) emissions. The construction and demolition phases engender the highest energy costs and are responsible for 60-90% of the total carbon footprint of a building with a 50-year life span. “Yet, these figures do not take into account the impacts of material extraction, transport, and processing”, underscores Laurent Arnaud, head of the Sustainable Construction Department at the French Centre for Studies on Risks, the Environment, Mobility, and Urban Planning (CEREMA). Cement production alone emits nearly one billion tonnes of CO₂ because raw materials such as clay and limestone are transported thousands of kilometres and must be heated to 1,450°C during cement creation.

A shift in regulatory focus

In 1974, the French government passed its first regulations related to thermal standards in occupied buildings, which sought to limit energy usage tied to heating, air conditioning, water heating, and lighting. As of January 1, 2022, new regulations (RE 2020) are in place that focus on environmental impacts: attention is now paid to the GHG emissions resulting from building construction, which are estimated using a life cycle analysis (LCA) of the materials used. This shift thus strongly encourages manufacturers to opt for lower-emission materials. For example, hemp concrete could serve as a green alternative to conventional concrete, with its energy-intensive production and large carbon footprint. With this recent legislation, the French government is pursuing the environmental transition objectives of the country’s Climate Action Plan¹, which is aiming for carbon neutrality by 2050. 

Biobased materials, a promising alternative

The French government has a three-pronged strategy: lowering energy consumption, billable energy costs, and carbon footprints for existing and future buildings. The goal is to promote the more frequent use of wood and biobased materials, which store carbon over a building’s lifetime.
Taken directly from the living world, biobased construction materials have various forms. They may be the fibres used in insulation or the granules with which mortar is made. The source material may be wood, hemp, cork, or flax, to name a few examples.
INRAE researchers have been exploring these and related topics for over 15 years. “Such materials, and especially their fibres, could serve as simple replacements for petroleum-based materials”, explains Monique Axelos, INRAE’s Scientific Director of Food and Bioeconomy. “However, they also present their own advantages, such as lightness and strength, and can thereby contribute to the circular economy, boosting sustainability and regional development.” These materials have tremendous potential, since LCA shows that they can help drastically reduce GHG emissions. They can even store carbon. “A 1-m², 30-cm-thick hemp concrete wall can store 32 kg of CO₂ over its lifetime”, comments Laurent Arnaud. Another advantage of this approach is that it makes use of “waste”, plant matter that is generally discarded, such as straw mulch or rice hulls (i.e., the protective coverings of rice grains). Furthermore, it can be procured at a low cost almost anywhere in France. 

Facilitating progress

At first glance, such materials would appear to be an easy sell. However, as Philippe Léonardon, an engineer in ADEME’s Construction Department, explains, “At present, only 10% of insulation materials on the market in France is biobased.”
He clarifies that what is lacking is political commitment because the necessary technical knowledge already exists. Indeed, Philippe Léonardon highlights that the new legislation does not require construction companies to use biobased materials. In his view, the regulations only indirectly encourage the use of such materials because the underlying calculations are complex: “Each construction product, piece of equipment, and service, such as the supply of energy or water, is assessed from the perspective of a specific environmental objective. Overall GHG emissions are determined using 27 indicators, which include the relative contribution to global warming, consumption of fresh water resources, and elimination of radioactive waste. Thus, while biobased materials can help meet environmental objectives, they are not specifically named.”
France is the leading producer of hemp in Europe and can therefore reliably develop hemp-based construction materials. Such will not be the case for other countries that do not have consistent access to this crop. While biobased materials are a promising source of solutions, we must carefully consider how to scale up their production to ensure that the entire value chain is sustainable. Monique Axelos warns that we must be wary of certain unconscious biases. For example, people might not value biobased products because the latter are assumed to be biodegradable, given that they are natural. She comments, “To optimally utilise resources, we need to manufacture long-lasting, reusable materials.” It is also essential to assess the impacts of harvesting plant residues, which naturally fertilise soils, and to maintain reasonable transport distances. Furthermore, resources must be managed so as to avoid competition among industries. For example, grain straw already serves as animal bedding and is used to produce biogas via anaerobic digestion and second-generation liquid fuel in biorefineries. 

1. Launched in April 2022, the Climate Action Plan is a set of official economic and budgetary measures intended to guide French industry through the environmental transition (read it here in French).