The RE2020 has shifted the focus: the carbon footprint of a building over its entire life cycle now counts as much as its energy performance during use. Building an eco-friendly house today means making choices between materials with traceable carbon footprints and technical systems that reduce consumption without sacrificing comfort. Here, we detail the concrete points of vigilance that generalist guides overlook.
FDES and PEP: reading the carbon map of construction materials
Since the implementation of RE2020 in January 2022, every material choice must be justified by standardized environmental data. The Environmental and Health Declaration Sheets (FDES) for construction products and the Product Environmental Profiles (PEP) for electrical equipment are the two references to consult. They are hosted on the INIES database, supplied by manufacturers and verified by third-party organizations.
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A biosourced insulator labeled “eco-friendly” can have an unfavorable carbon balance if its transport or transformation consumes a lot of energy. Only the FDES allows for the comparison of two products based on identical criteria: global warming potential, water consumption, waste production. We recommend systematically requesting the FDES reference from any supplier before validating a batch.
In practice, an architect or a thermal engineering firm integrates these sheets into the regulatory calculation. However, the project owner should understand the logic: a material that performs well in insulation can be disqualified by its embodied energy. Wood, cellulose wadding, or wood fiber perform well on this criterion, provided the origin and manufacturing process are verified.
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To deepen the supply chains and site feedback on these materials, resources like uneautremaison.com allow for cross-referencing technical approaches and field testimonies.
Bioclimatic design: technical choices regarding orientation and walls
The orientation of the building and the distribution of glazed surfaces determine a significant part of the energy balance, well before choosing the heating system. A poorly calibrated bioclimatic design negates the gains of effective insulation.
The principle is known: maximize passive solar gains in winter, limit overheating in summer. Implementation, however, requires fine-tuned decisions.
- The glazing/living space ratio on the south facade must be sized according to the thermal inertia of the interior walls. A lightweight wooden frame without thermal mass (concrete slab, heavy partitions) will overheat as early as spring if the south glazing is too generous.
- Fixed solar protections (overhangs, sunshades) are calculated based on the project’s latitude. An effective overhang in Toulouse will be insufficient in Perpignan. The angle of solar incidence in summer varies enough to render standard sizing inappropriate.
- Natural cross ventilation remains the most underestimated lever. Placing openings on opposite facades, with a height offset, creates thermal draft that reduces reliance on active air conditioning.
We observe that many projects neglect dynamic thermal simulation (DTS). The regulatory RE2020 calculation relies on a simplified calculation engine. A DTS, performed by a thermal engineer, models the actual behavior of the building hour by hour over a year. It costs a few thousand euros, but it avoids design errors that will cost decades in heating or cooling bills.
Insulation and air tightness: the area where mistakes are costly
External insulation (ITE) remains the most effective solution to eliminate structural thermal bridges, particularly at floor/wall junctions. In new eco-friendly construction, ITE with wood fiber combined with a breathable rain screen offers a good compromise between thermal performance, moisture management, and low carbon impact.
Air tightness is the most discriminating control point. RE2020 requires a permeability test (blower door test) at the end of construction. A poor result indicates implementation defects: poorly connected waterproofing membrane, untreated duct passages, poorly installed joinery. Every undetected air leak degrades the actual performance of the building compared to the theoretical calculation.
The choice of a dual-flow mechanical ventilation system (VMC) is essential in this context. By recovering heat from the extracted air, the dual-flow VMC limits losses associated with air renewal. Its efficiency directly depends on the quality of the air tightness: in a leaky building, air enters through defects rather than through vents, and the system’s efficiency collapses.
Real cost increase and return on investment of an eco-friendly house
Eco-friendly construction incurs an initial cost increase compared to conventional construction. Field feedback places this difference between ten and twenty percent, mainly related to biosourced materials, enhanced insulation, and renewable energy production equipment (solar panels, geothermal heat pumps).
The amortization depends on the energy item being replaced. A passive house, with nearly zero heating consumption, radically reduces energy bills. According to documented projects, the return on investment is between fifteen and twenty-five years, a duration consistent with the lifespan of a building.
The real financial lever remains property valuation. An energy performance certificate (DPE) in class A or B, backed by durable materials and verifiable bioclimatic design, positions the property at the high end of the resale market. As regulatory constraints tighten on thermal sieves, the value gap between a high-performing building and a standard building will only widen.
Water management also deserves mention: rainwater harvesting for non-potable uses, water-saving fixtures, treatment through phytoremediation in areas not connected to the grid. These systems reduce potable water consumption and lighten the load on collective networks, a criterion that is increasingly important in responsible projects.
Building eco-friendly in 2025 is primarily about mastering the technical decision-making chain: verifying FDES, simulating actual thermal behavior, ensuring air tightness, and accepting an initial cost increase whose yield is measured over the building’s lifespan. The tools exist, regulations are pushing in this direction, it remains for each project owner to surround themselves with the right interlocutors from the design phase.