Regulatory calculations

Regulatory calculations refer to all the official models required by French regulations to demonstrate the energy and carbon compliance of a project (new build or renovation). For new builds, the RE2020 regulation mandates verification of factors such as Bbio, Cep/Cep,nr, Ic energy, Ic construction, and DH (summer comfort) using an approved calculation engine. For renovations, the existing building regulations (RT Existant) are applied (by element or as a whole) with performance requirements for the building envelope and systems. These calculations result in certifications (for building permit applications and upon completion) and are prerequisites for accessing certain funding or labels.

Regulatory calculations: definition and scope

In practice, the regulatory study is based on plans (architect), a technical description (building envelope, joinery, HVAC/DHW/ventilation systems), reference weather data and standardized usage assumptions.

Depending on the circumstances, the following is checked:

• RE2020 (new):

- Bbio (bioclimatic need) ≤ threshold;

- Cep / Cep,nr (primary energy consumption, including non-renewable portion);

- Ic energy and Ic construction (carbon indicators);

- Summer comfort via DH;

- PC & completion certificates with consistency check.

• Existing RT (renovation):

- By element: each component (U of the walls, system efficiency) reaches a regulatory minimum;

- Overall: the renovated building must reach a calculated level of performance.

Typical deliverables: calculation note, regulatory files, summary tables, points of difference and optimization strategies (solar protection, inertia, water law, system substitutions, etc.).

Advantages, limitations and precautions for regulatory calculations

Interests

• Compliance: securing the permit and the receipt (official certificates).
• Guided design: early arbitration envelope ↔ systems to hold Bbio/Cep/Ic.
• Low-carbon trajectory: energy and carbon visibility from the initial sketch.
• Access to aid/labels: technical basis for CEE, labels, green lease, etc.

Boundaries

• Standardization: conventional assumptions do not always reflect actual usage.
• Limited scope: some auxiliaries or behaviors are not fully covered.
• Iterative: several adjustment loops may be necessary (study delays/costs).

Points to be aware of

• Reliable input data: wall resistances, thermal bridges, certified performance (Uw, ηs, COP, etc.).
• Summer comfort: aim for external protection, thermal inertia, night ventilation to reduce DH.
• Carbonation: materials and FDES (Ic construction) chosen from the APD stage.
• Coordination: architect ↔ HVAC design office ↔ electrician (reservations, BMS, water law).
• Traceability: keep product sheets, test reports, installation photos (air tightness, insulation).
• Site post: check at the end that the constructed = calculated (discrepancies to be documented).

Anecdote — “The Bbio that found its shadow in Montpellier”

In Montpellier, a small office building struggled to meet the RE2020 energy performance standard (Bbio) due to its heavily glazed west-facing façade. Rather than increasing the insulation thickness, the team ran calculations on the following: external adjustable sunshades, a light-colored roof, and slight internal thermal inertia. The result after recalculation: the Bbio met the required standard, the energy density (DH) decreased, and the primary energy consumption (Cep) improved… without significant additional costs. The moral of the story: in regulatory calculations, a well-designed bioclimatic building is sometimes more valuable than an extra centimeter of insulation.