In a building’s life cycle, the construction phase represents the largest element of the carbon footprint (60%) compared to just 40% for its operation. Until recently, it was estimated that 60% of global emissions from a new building were from the materials used. While not new, the role played by biosourced products is increasingly recognised and the latest regulatory developments take this into account.
Which products?
Biosourced products for construction come from vegetable biomass (wood, hemp, flax, cereal straw, miscanthus), from animal biomass (sheep’s wool, goose down) and materials from recycling (paper: cellulose wadding, textile: cotton). For several years however, research has been progressing and new developments emerge, particularly in the domain of vegetable concrete (see below). As renewable raw materials, biosourced materials constitute an alternative to the use of fossil fuels or where supply shortages exist.
For what applications?
As the main biosourced product in construction, wood is used in carpentry, frameworks (beams, boards, joists, battens etc.), in panels, parquet floorings, panelling and frames. Some biosourced materials are also employed for insulation. It is further estimated that 11% of the French insulation market is based on vegetable fibre or wool, cellulose wadding, or wood. Straw bales may be used in construction. Some concretes and mortars contain vegetable elements (hemp, wood, rapeseed) to which a mineral binder is added: this is known as “vegetable concrete” (see box). Biosourced materials can also be composite materials (cladding laths based on wood or hemp). Meanwhile, in the domain of interior design a range of products or biosourced molecules are going into the make-up of paints, linoleums, underlays, coatings and more.
Vegetable concrete: new developments
A conventional concrete essentially contains cement (produced most often from clinker, a highly energy-intensive process), aggregates (gravel, limestone, granite), a fine particulate (sand), water, and chemical additives. Vegetable concrete, however, uses vegetable fibres instead of mineral aggregates. Most building materials producers offer these in their product range. While the first generations were primarily based on wood and hemp, combinations using miscanthus or flax are beginning to appear. In addition, research now underway is focusing on rapeseed, sunflower and maize stalk.
What’s the environmental performance like?
In addition to the limited energy they use in production, and their local sourcing, biosourced products of vegetable origin have a key role to play in carbon storage. They offer insulating and hygrothermal (humidity regulating) properties. They can also contribute to improving air quality and acoustic comfort.
Two methods exist for evaluating the environmental performance of a biosourced product: on the one hand, “life cycle inventory” (LCI) data coupled with the results of a life cycle analysis (LCA). Accordingly, a recent study conducted for the Record association was able to show, through LCI of thermally insulating floor coverings and concrete blocks, that there was indeed a reduction in the climate change impact (although it remained more cautious regarding other types of impacts). The authors also stressed that the origin of the particular biomass was a determining factor.
Another means of assessing the environmental performance of a biosourced product is the use of accreditations. By way of example, the “Produit Biosourcé” (Biosourced product) accreditation, launched by Karibati in 2017, identifies biosourced materials containing a significant proportion of biomass by accrediting their biosourced raw material content. A minimum threshold is set by product family (e.g.: 25% for vegetable concretes and 70% for insulations). A “Produit Biosourcé +” version was developed in 2021 to differentiate products with more than 80% biosourced content.
Acceleration through regulation
The use of biosourced materials in construction is not new in itself. The principal regulation concerning these is the Building Energy Performance Directive (Performance énergétique des bâtiments) which is undergoing revision. In France, most of these products are the subject of a technical evaluation document from the CSTB, an Acermi certification, a European technical agreement, or rules for their implementation (Documents Techniques Unifiés, or Unified Technical Documents), and as Ademe emphasises the many documents “required for the structures concerned to be insurable”. Numerous standards are also specific to biosourced products, which must particularly respect the requirements for technical performance (mechanical, thermal, acoustic, fire behaviour etc.) and for durability in accordance with the expected applications and usages. In 2010 the French Ecology Ministry launched a plan aiming to remove obstacles to the large-scale use of biosourced materials in construction. However, in recent years that’s really taken off: as well as Article 5 of France’s TECV law of 2015 (Energy Transition and Green Growth), the ELAN law of 2018 (Changes in housing, land management and digital technology) highlighted carbon storage and the use of renewable raw materials. More recently still, RE2020 – the goals of which are threefold (reducing the climate impact of new builds, getting a grip on energy consumption and improving thermal comfort) – highlighted low-impact materials, among them biosourced and geo-sourced materials (earth and stone). All this should help boost the sector.
Comfort in both winter and summer
At the beginning of June, the Industry Association for Biosourced Construction (AICB – Association des industriels de la construction biosourcée) published a White Paper aiming to present how well biosourced materials performed for summer comfort (where the tendency is to look only at comfort in winter)*. Among these performances is thermal inertia which helps provide some attenuation of indoor temperature variation via wall phase shift, which can be described as the time taken by a heat wave to cross through a wall: biosourced materials possess longer phase shift times (6 to 10 hours), enabling a stable temperature to be maintained during the hottest parts of the day. Additionally, because of their hygroscopic properties, biosourced materials allow variation in humidity levels to be cushioned: they absorb excess humidity, storing it and releasing it when the atmosphere becomes drier.
Learn More : Life cycle assessment (LCA), an essential tool for eco-design
