The AICB publishes a white paper on the performance of biobased materials for summer comfort and opens the debate on improving RE2020 calculators

Its objective: to present in a factual manner the performance of biosourced materials for summer comfort and to open the debate on the limits of RE2020 calculators, which do not yet take into account all the criteria that influence summer comfort.

Promoting the performance of bio-based materials in improving summer comfort

In this 24-page white paper, the AICB addresses summer comfort as a key issue in RE2020 and presents the factual responses to biosourced materials, derived from plant biomass (wood, hemp, straw, grass, etc.). , animal (sheep's wool) or recycling channels (paper, textiles) in the thermal comfort of buildings. The performances detailed in this white paper are supported by examples of achievements, feedback from professionals (architects, design offices, local authorities) and testimonials from users.

“If the priority has long been winter comfort, climate change brings with it a new challenge: guaranteeing thermal comfort all year round, and also during hot and scorching episodes, says Olivier Joreau, President of the AICB. . Through their intrinsic properties, biosourced materials have many advantages in meeting the challenges of summer comfort, within the framework of the new RE2020 regulations.”

Performances acclaimed by professionals, as evidenced by the global market share of biosourced insulation, which has almost doubled, going from 6% to 11% in less than 10 years. Today, 1 in 5 attics is insulated with biosourced insulation.

The advantages of bio-based materials to guarantee summer comfort

Most biobased materials share common and specific characteristics, which give them an advantage over traditional materials in improving summer comfort.

Thermal inertia

Thermal inertia plays a key role in summer comfort, as it helps to mitigate indoor temperature variations and maintain a stable temperature throughout the day.

The thermal inertia depends on the effusivity (ability to absorb heat) and the diffusivity (ability to transmit heat slowly) of the material, themselves linked to three factors: the density, the specific heat capacity and the thermal conductivity.

Long phase shift and good damping

The phase shift refers to the time it takes for a heat wave to cross a wall. Complementary to the phase shift, damping measures the ability of a wall to dissipate a thermal wave and to attenuate its intensity.

Bio-based materials have on average a longer phase shift time and better damping than traditional materials (bio-based materials have phase shifts of 6 to 10 hours and amplitude attenuations of up to 80%), which allows to keep a stable temperature during the hottest hours, but also to evacuate the excess heat by opening the windows in the evening and at night, when the temperatures go down again.

Good hygroscopic properties

A “hygroscopic” material helps to dampen variations in the humidity level of a room: it absorbs excess humidity, stores it and releases it when the atmosphere becomes drier. A good level of humidity in the air (40 to 60%) brings a feeling of thermal comfort to building users.

“Most biosourced materials have a very efficient hygrothermal behavior, compared to non-porous materials that are impermeable to water vapour. Thus, they promote summer comfort and limit the use of air conditioning, which is a considerable environmental advantage”, explains the President of the AICB.

Towards an improvement of the RE2020 calculators?

In its white paper, the AICB opens the debate in favor of a consultation of all building design professionals to improve the RE2020 calculators and take into account more criteria in the evaluation of summer comfort.

“Today, although the RE2020 calculators integrate the concept of summer comfort, they do not yet take into account all the characteristics of the materials which directly influence this phenomenon. They do take into account the specific heat capacity of the materials, but the accuracy of the calculation depends on the type of method used by the design office (lump sum, by point or detailed), develops Olivier Joreau. The phase shift of the walls and the capacities of water regulation, for example, are not taken into account, whereas their impact on summer comfort is significant. If we refined the calculation methods, we could build in a more virtuous way in France. »

The AICB white paper is thus intended to be a working basis for discussions with institutions and members of the profession in the context of improving RE2020 calculators.

The white paper "Summer comfort: the advantage of biosourced products" is available for free download on the AICB website: www.batiment-biosource.fr.