Biosourced materials: solutions applicable without additional cost to low -height buildings

The Low-Carbon Specifiers Hub has deciphered the bio-sourced materials sector from the perspective of carbon neutrality. And delivers some key messages.

Caption: The insulation of timber frame walls is made of wood wool, manufactured by Isonat in Mably (42), after defibration of softwood offcuts from sawmills or slash from Haut-Beaujolais forests.©Herrgott & Farabosc

After an initial brief on the concrete sector as well as an innovation book, the hub of low-carbon prescribers* has chosen to decipher the bio-sourced materials sector from the angle of carbon neutrality.

Recent arbitrations of the RE2020 have put biosourced materials at the forefront: what will be the place of biosourced materials in construction by 2030? What will be the availability issues? Which sectors and products are already mature enough to be deployed on a large scale?

So many questions to which the members* of the hub have tried to shed light, with first a brief, based on the key messages of the biobased, and secondly, the results of a call for innovation .

First message from the Hub, wood currently occupies around 8% of the construction market share in France. Which is low in view of the stakes since the wood-forest sector is targeting 20 to 30% of construction by 2030. We will therefore have to modify practices, build and operate differently. It is above all a question of not dividing the materials but of responding to a plural approach, in particular to meet low carbon objectives.

Two effects to take: substitution and carbon sequestration

What are these low carbon objectives? The SNBC (National Low Carbon Strategy) sets a collective horizon of carbon neutrality by 2050: it involves dividing our CO2 emissions by 6 and doubling carbon sinks.

To achieve this, the SNBC has opted for a massive mobilization of wood energy and biosourced materials in the building industry, summarizes the Hub of Low Carbon Prescribers. And the new environmental regulations, RE 2020, applicable to housing from January 1, 2021 have resumed their arbitrations.

Remember that wood stores approximately 1t C02e/m3 and that two phenomena must be taken into account: substitution effects and sequestration effects. Carbon sequestration is indeed made possible thanks to four major reservoirs: oceans, forests, wetlands and grasslands.

Be careful, warns the Hub: the carbon gain varies according to the resource, the use of the materials and the time horizon studied. This implies respecting 4 main criteria to optimize the interest of the biosourced: the preservation of the resource, its sustainable management, the lifespan of the biosourced materials (which must be long), and finally, the virtuous end of life of the materials. (via recycling).

Depending on the hub, a building that is part of an SNBC trajectory will store in 2030 on average between 60 and 70 kgCO2e sequestered per m2 built in collective housing and offices.

Sustainable management of the resource is an essential condition for optimizing the interest of bio-sourced construction, (here spruces), recalls the Hub.

Bio-based: an indisputable significant gain by substitution effect

Second important key message delivered by the Hub: the use of bio-based materials is a source of beneficial carbon gain. "Without considering the sequestration effect and even retaining an unfavorable LCA calculation method, we can say that the use of bio-based rather than a conventional material (substitution effect) brings significant gains in terms of carbon" underline the authors of the Brief.

Why? Few construction processes use as little energy (which would release CO2) as biobased. In this sense, bio-based materials are clearly the lowest carbon materials, asserts the Hub. And the distance in supply has very little impact on this benefit! Example: to become more carbon-intensive than stone wool produced on average at 460 km, wadding/straw or hemp insulation will have to travel 3400 km and wood wool, 900 km. Ditto for the parquet which even by traveling 2500 km does not lose its benefit compared to the other coatings.

The Hub puts forward a general order of magnitude of a 60% carbon gain with biosourced materials. This is the case for wooden windows (-26% i.e. between 20 and 40 kgCO2e/UF), or wooden coverings such as parquet floors (-44% i.e. between 10 and 15 kgCO2e/UF), wooden floors (-95 % i.e. between 80 and 100 kgCO2e/UF) or insulation (e.g. flax fiber-hemp wool in ITI: - 79%, i.e. between 1.2 and 1.7 kgCO2e/UF).

Integrating bio-based materials into construction sectors

Third message: it is now possible to integrate biosourced products into construction sectors thanks to multiple applications. The Hub considered four main segments and possible uses:

It's Asthma Awareness Month! Learn how to recognize the signs of an asthma attack in yourself and in your children… https://t.co/gPwiN64blu

— MIPA Thu May 09 17:00:09 +0000 2019

Plant insulation has a mature, industrial sector and is well advanced in terms of regulations. Here Gramitherm (grass-based insulation) which is one of the three winners of the call for innovations launched by the BC Specifiers Hub. The other two winners are Vicat hemp blocks and BB tiles and floors (for concrete wood).

Sufficient available resources to support

Fourth message: the availability of resources was taken into account in the reflection and reveals that it is necessary to support their development even if they are sufficient.

Thus, wood and derivatives benefit from resources since France represents the 3rd largest forest resource in Europe. Downside: wood uses in the Building industry favor the use of softwoods, whereas French forests are made up of hardwoods (three quarters). Imports mainly concern composite wood such as glued laminated wood, CLT or engineered wood. An effort to promote French forests will require structuring the sector around hardwood in addition to softwood.

On the vegetable fiber side, on the other hand, the resource does not pose any problem. It is a co-product, almost unexploited, and France is the leading producer of fiber plants. Example: out of the 22 million tonnes of straw available per year, Buildings can mobilize around 4 to 6 million tonnes (i.e. several tens of thousands of m3 of straw bales). But the sector will have to be structured and managed in order to meet the new challenges of biosourced.

Optimizing costs with the cost-carbon equation

Fifth message: to optimize the cost-carbon equation, it will be necessary to assimilate new practices. Indeed, most bio-sourced insulation represents an additional material cost compared to conventional insulation.

This additional cost (supplied-installed) at the scale of the building represents 0.2 to 1.6% (due to a lower thermal performance which generates an extra thickness and a loss of surface). But this additional material cost must be weighted with the carbon gains, up to - 7kg CO2e/m2 ​​Ghab and the other specificities of the insulators (including hygrothermy), underlines the Hub. And to avoid extra thickness, you might as well use distributed insulation, recommends the Hub.

As regards construction systems, the structural work footprint represents 30% of the carbon footprint of the building, the optimization of the carbon weight is a major lever in the decarbonization of buildings. A building with a concrete, mixed or all-wood structure is not designed in the same way, in order to take into consideration the technical characteristics of its different materials (technical resistance, fire behavior, acoustics, etc.). The carbon gains will strongly depend on the specificities of the building (technical, environmental, urban planning, etc.).

The low-carbon specifiers hub observes that a concrete structure generates 199 kgCO2/m2 SDP, and a wooden structure, 80 kgCO2/m2 SDP

Bio-sourced solutions adapted to low-rise buildings

The low-carbon specifiers hub observes that a concrete structure generates 199 kgCO2/m2 SDP, a terracotta masonry structure, 133 kgCO2/m2 SDP, a mixed wood-concrete structure, 145 kgCO2/m2 SDP and finally a structure wood, only 80 kgCO2/m2 SDP. The cost-carbon equation will therefore depend on the types of buildings, since some of the biosourced solutions remain particularly suitable for low-rise buildings. Examples with:

However, the costs in tertiary buildings are difficult to extrapolate, given the diversity of the projects and their emblematic characteristics that do not allow generalizable rules to be identified, concludes the Hub.

*The hub is a collaborative platform supported by the French Institute for Building Performance (IFPEB) in partnership with Carbone 4, intended for contractors in the construction sector (property companies, investors, developers, companies general...).

Source: batirama.com/ F. Leroy