An office building of more than 1,000 m² consumes an amount of energy each year that its owner must now declare, track, and reduce according to a precise schedule. The tertiary decree, officially named the Eco Energy Tertiary device, sets this energy reduction trajectory with deadlines in 2030, 2040, and 2050. In 2026, the companies concerned will face a concrete step: the declaration of 2025 consumption on the OPERAT platform, managed by ADEME.
Traceability of energy data: the real challenge of the tertiary decree in 2026
Most articles on the subject detail the thresholds and deadlines. The problem that companies face daily is different: the reliability of the data declared in OPERAT.
Declaring an annual consumption seems simple. In practice, a tertiary building may have multiple occupants, several meters, and areas that change usage during the year. It is necessary to reconcile the declared consumption with actual invoices, verify the utilized areas, and document the periods of occupancy.
Do you occupy an office floor shared with two other companies? The distribution of consumption between occupants and owner becomes a governance issue, not just a counting one. As the legal information on Décideur specifies, responsibility is shared between the owner and the tenant according to the terms of the contract.
This traceability is all the more delicate because declaration errors can distort the entire reduction trajectory. An incorrectly reported reference year or an inaccurate area compromises the comparison from one year to the next.
Energy reduction targets: relative method or absolute value
The tertiary decree offers two ways to achieve the set targets. Understanding the difference between the two avoids choosing an unsuitable trajectory for one’s building.
Relative method: starting from one’s own consumption
The company chooses a reference year (after 2010) and commits to reducing its final energy consumption compared to this starting point. The milestones are as follows:
- 40% reduction by 2030 compared to the chosen reference year
- 50% reduction by 2040
- 60% reduction by 2050
This method is suitable for buildings whose starting consumption is high. The higher the starting point, the more accessible the margin for improvement seems.
Absolute value: a threshold set by activity category
The other option is to reach a defined consumption level expressed in absolute value, measured in kWh per square meter per year, depending on the type of tertiary activity carried out in the building. A retail space does not have the same threshold as an office or an educational institution.
Each company can choose the most favorable method between the two. The OPERAT platform performs the calculation and indicates the trajectory to follow.
OPERAT declaration 2026: timeline and scope of affected buildings
In 2026, the obligated parties must declare the consumption for the year 2025 on OPERAT before September 30. This deadline allows several months to collect invoices and verify data, but multi-site companies often underestimate the time required.
All buildings, parts of buildings, or groups of buildings housing at least 1,000 m² of cumulative tertiary activities are concerned. The threshold applies cumulatively: three floors of 350 m² in the same building trigger the obligation.
Some categories are exempt from the device: temporary constructions, places of worship, and certain buildings related to national defense. For all others, the annual declaration is mandatory, and administrative penalties are foreseen in case of non-compliance.
Change in the electrical conversion factor in 2027: anticipating the impact
One technical parameter deserves attention right now. The electricity conversion factor will change from 1.9 to 1.7 on January 1, 2027 in energy performance diagnoses (DPE) and audits, according to a statement from the Ministry of Ecological Transition dated August 31, 2026.
This change does not directly alter the obligations of the tertiary decree. However, it influences energy performance diagnostics and audits that often serve as the basis for companies’ action plans.
Specifically, a building heated by electricity will see its DPE recalculated with a more favorable coefficient. DPEs and audits conducted before December 31, 2026, will remain valid and can be updated for free in 2027 through the ADEME DPE-Audit Observatory.
Why does this matter for the tertiary decree? Companies preparing their reduction trajectory based on an audit conducted in 2026 will need to check if the conclusions change with the new coefficient. An audit conducted at the end of 2026 could overestimate the primary energy consumption of an electric building.
Concrete levers for reduction in tertiary buildings
Achieving the objectives of the tertiary decree does not rely on a single lever. Actions are divided into three categories:
- Works on the building (insulation, replacement of joinery, sealing), which reduce heating and cooling needs
- Replacement or optimization of technical equipment (LED lighting, heating regulation, building technical management)
- Adaptation of usage by occupants (temperature settings, turning off equipment when not occupied, raising awareness among teams)
The first two categories require investments. The third produces results without budget but requires regular monitoring. Combining the three approaches is the only realistic way to achieve a 40% reduction by 2030.
The decree also provides for possibilities to adjust the objectives in certain situations: technical or architectural constraints of the building, disproportion between the cost of works and the expected benefits, or change of activity. These adjustments must be documented and justified in OPERAT.
The tertiary decree is not a one-time declarative exercise. It is an energy management system over several decades, where the quality of data and the coherence of actions matter as much as meeting deadlines.
