Tertiary energy audit: diagnostics, savings and compliance

The tertiary decree (ELAN law, articles R174-22 et seq. of the Construction Code) requires any building over 1000 m² to submit an annual declaration of energy consumption on the dedicated regulatory platform. Three texts complete this foundation for French offices.

• Energy Code, article L233-1: mandatory audit every 4 years for companies with more than 250 employees or €50M in revenue, except where a certified energy management system is in place. It must cover 80% of energy bills and comply, for the acoustic aspect of buildings, with class B or A of the ISO/TS 19488:2021 standard, in line with article 8 of directive 2012/27/EU.
• EPBD recast in 2024 (EU directive 2024/1275): strengthened requirements for non-residential buildings, transposed via the DDADUE law.
• BACS decree extended in 2023 (decree no. 2023-259): obligation to install a class B BMS in tertiary buildings of more than 290 kW.

Consumption is distributed across three main areas: HVAC (40 to 55%), lighting (15 to 25%), office equipment (10 to 20%). The energy cost of an office is generally between 15 and 35 €/m²/year depending on the building’s initial performance.

Our reading differs from the prevailing industry view on one specific point: the penalty, capped at €7,500 per year, is often presented as negligible, leading to the conclusion that the regulatory risk is overstated. This is false for an Asset Manager: the real risk is not the fine, it’s the discount on resale of an asset that is not compliant with the -40% trajectory in 2030. Market studies show that a significant valuation gap separates assets with good EPC ratings from energy-intensive assets, which is particularly marked in the Paris market. The audit is not a CSR matter, it’s a matter of asset value.

The Kytom method, structured in 5 steps, deployed over 8 to 12 weeks following a building energy audit framework.

The audit unfolds in five structured steps, compliant with the normative framework applicable to tertiary buildings.

1. Data collection over 3 rolling years: bills, load curves, supply contracts, green leases. Scoping with the real estate department or the CFO.
2. On-site visit by an OPQIBI 1905 qualified auditor: thermographic readings, HVAC flow measurements, illuminance checks (target 300 to 500 lux), envelope inspection.
3. Dynamic thermal modelling (DTS): simulation of 3 to 5 renovation scenarios, integration of actual uses (open space, meeting rooms, remote working 2 to 3 days per week now firmly established in the tertiary sector).
4. Prioritised action plan: costing by lot (HVAC, DALI-controlled LED lighting, BMS, flat-roof insulation, joinery, AHU or heat pump replacement) with payback period, CO2 savings and impact.
5. Support: regulatory declaration by 30 September on the dedicated platform, selection of contractors or RGE-certified firms, preparation of EEC (energy savings certificate) files.

When this full method is not relevant: below 1,000 m² of tertiary floor area, the building is not subject to the obligation and a simplified audit is sufficient; for a building delivered less than 5 years ago with a class A BMS already commissioned, targeted commissioning is preferable to a full audit; if a sale is planned within less than 18 months, the audit should be reframed as energy due diligence.

For the CFO and the Asset Manager: tangible savings, controlled ROI and balance-sheet impact

On audits managed by Kytom, the savings observed on the energy bill are significant from the second year, with a return on investment generally achieved in less than 4 years depending on the scope of the works undertaken. By lot, measured over the same scope: DALI-controlled LED relamping generates significant savings on the lighting item with a fast return on investment, a class B BMS reduces HVAC consumption, flat-roof insulation lowers total consumption, and AHU or heat pump replacement optimises the HVAC item. Beyond the financial ROI, the audit secures the regulatory trajectory for reducing tertiary energy consumption and enhances the asset’s value: the correlation between EPC rating and the market value of a tertiary asset is now well documented, with better-rated assets consistently commanding a value premium over comparable energy-intensive assets.

Method

1. Document collection
   Gather 36 months of energy bills, up-to-date plans, HVAC maintenance contracts and occupancy data. This basis determines 80% of the diagnostic’s quality. Kytom provides a standard checklist validated over 150+ assignments.
2. On-site technical visit
   In situ measurements with a thermal camera, wattmeters, lux meter and analysis of BMS setpoints. Detection of drifts invisible on the bill: permanent lighting, compressed air leaks, over-ventilation. Half a day per 2000 m² block.
3. Modelling and simulation
   Construction of the building’s energy model, simulation of 3 scenarios (frugality, optimisation, major renovation). Each action is costed in CAPEX, annual savings, IRR and tonnes of CO2 avoided.
4. Reporting and COMEX decision-making
   1-hour presentation to the executive committee with a 2-page summary. Decision on the selected actions, validation of the schedule and identification of available financing (EECs, heat fund, green loans).
5. Energy declaration and monitoring
   Pre-filling with strategic selection of the reference year. Setting up monthly monitoring indicators to measure actual vs theoretical savings and adjust the trajectory.