RE2020: low-carbon LCA redesigns architectural conception

France's RE2020, in force since 1 January 2022, lives its second wave of tightening. The Ic Construction threshold — the carbon impact of the construction phase across the whole building lifecycle — falls from 640 kg CO₂eq/m² in 2022 to 530 kg in 2025, then 415 kg in 2028. For an architecture firm delivering collective housing, this is no longer an administrative compliance topic — it is a design constraint that redefines material, envelope and structural-system choices.

What LCA at concept stage really changes

The Life-Cycle Assessment (LCA) defined by RE2020 requires computing the building's carbon footprint over 50 years, summing: construction (materials, transport, on-site work), operation (consumed energy), maintenance (forecast renovations), and end-of-life (demolition, recycling). Environmental and Health Declaration Sheets (FDES) act as the database — supplier product sheets validated by the INIES program.

The moment when LCA becomes decisive is no longer DCE (tender phase), it's APS (preliminary design). At APS stage, the architect makes structural choices (concrete, wood, hybrid, steel) that drive 40-60% of Ic Construction. When LCA is calculated only at DCE, it is too late to reverse without redoing the plan.

The silent problem: missing FDES

On a typical project, 60-80% of materials find their FDES in the INIES base. The rest — hardware, specific finishes, rare equipment — has no dedicated FDES. RE2020 provides a "penalized default value" (DED) mechanism that heavily penalizes the calculation. Result: a project that would have passed the threshold with precise FDES gets rejected on default values, and the architect must tweak around the edges to fit.

Thermal engineering offices that subcontract LCA bill on average 8-15 person-days per collective-housing project, and this load grows because BET firms are saturated. For agencies that internalize, the stake is to avoid running 3 LCA calculations during a project (one for APS, one for DCE, one for DOE).

Three levers few agencies exploit

Structural reuse

RE2020 recognizes reuse with a near-zero carbon coefficient (only transport and re-installation are counted). On a refurbishment project, keeping an existing structure rather than demo-rebuild can save 100-200 kg CO₂eq/m². But this requires a resource diagnostic done upstream by a specialized firm, and that step isn't in the standard architect contract.

The E+C- label as a head start

The experimental E+C- label (positive energy, carbon reduction) preceded RE2020. Many agencies have E+C- C2-level references — exactly the Ic 2028 level. The competence already exists in some teams, but it isn't tracked as a commercial advantage in tender responses.

Valued bio-sourced carbon

Wood, straw, hemp store carbon during the building's life. RE2020 values this storage in the LCA (simplified dynamic method). A timber-frame project can show a negative Ic Construction — a strong argument for public clients who have their own CO₂ targets (local authorities, social-housing operators committed to CSRD).

The 2026-2028 scenario for firms

The 2025 Ic Construction threshold (530 kg) is passable with low-carbon concrete and an optimized envelope. The 2028 threshold (415 kg) tips most projects toward integrating wood or bio-sourced materials on a significant share. Agencies that want to stay competitive on public tenders and private development will need to: (1) integrate LCA from APS, (2) build an internal library of validated FDES, (3) track design choices by their carbon footprint, and (4) document variant comparisons.

What changes the profession is that the architect no longer just "delivers" a compliant project — they document their carbon reasoning, and that reasoning becomes a piece of the DOE.