Published 15 June 202612 min readREn art. 14 · OCEN · IDCAudit · Strategy · SubsidiesUpdated June 2026
The IDC audit imposed in Geneva: obligations, content and action plan
In Geneva, an IDC above 125 kWh/m²·yr (450 MJ/m²·yr) is no longer merely an energy balance: it is a legal trigger. The OCEN sends a letter, orders an audit — and beyond the works thresholds (222 kWh/m²·yr / 800 MJ/m²·yr to end 2026, 180 kWh/m²·yr / 650 MJ/m²·yr from 2027 to 2030ge.ch: « 222 kwh/m2.an (800 MJ/m2.an) depuis 2022 jusqu'au 31 décembre 2026 ; 180 kWh/m2.an (650 MJ/m2.an) dès le 1er janvier 2027 jusqu'au 31 décembre 2030 ; 153 kWh/m2.an (550 MJ/m2.an) dès le 1er janvier 2031 ».République et canton de Genève — OCEN — Que faire selon le résultat IDC de votre immeuble2025-06-20 · accessed 2026-08-29, 153 kWh/m²·yr / 550 MJ/m²·yr from 2031) a 36-month deadline to start the works (REn art. 14). This dossier sets out what that means in practice, what a compliant audit contains, and how to turn an imposed constraint into a chosen renovation plan.
The OCEN letter: what it requires, and what it leaves out
The IDC — heat consumption index measures a building's actual heating and hot water consumption, related to its energy reference area. It is reported annually to the cantonal energy office (OCEN) by the energy distributors — SIG for most of Geneva. It is not a theoretical calculation but the building's real energy bill, declared from the meters.
The obligation to calculate is not confined to large buildings: the regulation exempts only residential buildings served by a single heating plantREn art. 14A para. 7: exemption from the calculation duty for residential buildings « alimenté par une seule centrale de chauffe et comprenant moins de 5 preneurs de chaleur » whose three-year average IDC is ≤ 125 kWh/m².yr.République et canton de Genève — rsGE L 2 30.01 — Règlement d'application de la loi sur l'énergie (REn)accessed 2026-08-29 and with fewer than 5 heat consumers, provided their three-year average IDC is already at or below 125 kWh/m²·yr (REn art. 14A para. 7). Houses and small blocks above the threshold are therefore covered. Where the IDC exceeds the thresholds set by the REn, the OCEN writes to the owner — and the obligations triggered are legally binding.
Situation
IDC threshold
Obligation
Deadline
Audit threshold
> 125 kWh/m²·an (450 MJ/m²·an)
Mandatory energy audit + improvement measures to be proposedREn art. 14 paras. 3 and 4: the department « ordonne la réalisation d'un audit énergétique et l'exécution de mesures d'amélioration aux frais de la personne propriétaire », to be implemented « dans un délai de 12 mois à compter de la notification ».République et canton de Genève — rsGE L 2 30.01 — Règlement d'application de la loi sur l'énergie (REn)accessed 2026-08-29
12 months
Mandatory works (until 31/12/2026)
> 222 kWh/m²·an (800 MJ/m²·an)
Mandatory energy renovation works
36 months
Mandatory works (2027–2030)
> 180 kWh/m²·an (650 MJ/m²·an)
Mandatory energy renovation works
36 months
Mandatory works (from 2031)
> 153 kWh/m²·an (550 MJ/m²·an)
Mandatory energy renovation works
36 months
Target of the renovation
< 125 kWh/m²·an (450 MJ/m²·an)
Threshold to be reached after the works
—
Source: REn art. 14 (Geneva energy regulation, L 2 30.01). Values checked on 12 June 2026. The IDC is a multi-year average, corrected for climate against reference degree-days (Cointrin station) — an exceptionally cold winter alone does not trigger the obligation.
125
kWh/m²·yr (450 MJ/m²·yr): audit threshold — exceeded by most Geneva buildings predating 1980
222 → 180 → 153
kWh/m²·yr (800 → 650 → 550 MJ/m²·yr): mandatory-works threshold, tightening at the end of 2026 and again from 2031
kWh/m²·yr (450 MJ/m²·yr): target to be reached after the renovation (REn art. 14)
What the letter contains — and what it leaves unsaid
The OCEN letter states the IDC found, the reference period, the threshold exceeded and the corresponding obligation. It is factual. It does not explain how to renovate, which measures to prioritise, or which subsidies to apply for. It sets a deadline and an obligation — not a roadmap. Building that roadmap is for the owner and their adviser.
Who is the letter addressed to?
To the owner recorded in the land register — an individual, a property foundation or another legal entity. Where the building is managed by an agent, the agent generally receives a copy or is informed in parallel. Legal responsibility lies with the owner; the managing agent is often the first point of contact and has to alert the client and coordinate the steps. Agents who take on that role proactively build lasting trust with their clients.
Anticipate rather than endure
An unrenovated building from the 1960s–1980s frequently exceeds an IDC of 180 to 250 kWh/m²·yrSource to be established — unverified figure. The order of magnitude is consistent with the Geneva building stock but was not taken from published statistics.Source to be established — unverified figure (650–900 MJ/m²·yr). Waiting for the OCEN letter means enduring the timetable and often ending up in the 36-month rush. Commissioning an audit before the letter — or as soon as it arrives — allows the strategy to be chosen, the phasing optimised and the available subsidies combined. Time gained translates directly into money saved.
02 — Regulatory content
What a compliant audit must contain
An IDC audit compliant with the REn is more than a CECB diagnosis. It analyses the building as a complete system — envelope, systems, use — and produces quantified recommendations. Here are the components of an audit that meets the OCEN's requirements while providing a useful basis for the renovation strategy.
Part 1 — Envelope analysis
Thermal condition of walls, roof, floors and windows
Survey of the constructional characteristics: wall type, existing insulation thickness (often none or insufficient), joinery, structural thermal bridges — continuous slabs, balconies, spandrels. Calculation or estimate of current U-values per building element. Analysis of available drawings and, where appropriate, a thermographic visit during the heating season.
Part 2 — Energy systems
Heating, domestic hot water, ventilation
Condition and age of the heating plant, fuel type (oil, natural gas, district heating), boiler efficiency, distribution network (flow temperature, controls), emitters (radiators, underfloor heating). Hot water production: central, storage tanks, solar thermal where present. Presence or absence of mechanical ventilation — and its type. REn art. 12G requires heat recovery above certain airflow thresholdsREn art. 12G paras. 2 and 3: balanced ventilation systems must have heat recovery; extract systems serving heated rooms must too, above 1,000 m³/h and 500 operating hours a year.République et canton de Genève — rsGE L 2 30.01 — Règlement d'application de la loi sur l'énergie (REn)accessed 2026-08-29.
Part 3 — Actual consumption
IDC data over at least 3 years, climate correction
Analysis of energy bills over at least 3 years, climate correction against Geneva reference degree-days (Cointrin station), recalculation of the corrected IDC. Comparison with the Geneva building stock. This part identifies whether the problem lies mainly with the envelope, the systems, or how the building is used (overheating, settings, behaviour).
Part 4 — Quantified recommendations
Prioritised measures with estimated gains, costs and subsidies
A list of possible renovation measures, each with an estimate of the gain in kWh/m²·yr, the cost of implementation and the applicable subsidies. Measures must be presented individually and in combination, so that portfolio effects can be analysed and different phasing scenarios simulated.
Part 5 — Demonstrating that the target is met
The resulting IDC drops below 125 kWh/m²·yr (450 MJ/m²·yr)
The report must demonstrate — with figures — that the chosen programme of works reaches the legal target of less than 125 kWh/m²·yr (450 MJ/m²·yr). That is the condition for the OCEN to accept the file. An audit that does not demonstrate this is not compliant.
CECB versus IDC audit: two complementary but distinct tools
The CECB assesses a building's theoretical performance from its constructional characteristics — it is a classification (A to G) and comparison tool. The IDC audit starts from actual measured consumption and produces a quantified, decision-oriented action plan. A building may have a CECB of D and an IDC of 200 kWh/m²·yr (720 MJ/m²·yr): both are useful, but they answer different questions. In Geneva the CECB is compulsory for property transactionsSource to be established — not verified during this pass. To be tied to the LEn or the REn at the next pass on the CECB dossier.Source to be established — unverified figure; the IDC audit is triggered by the OCEN letter or commissioned proactively.
An audit done to the regulatory minimum produces a list. A strategic audit produces a plan. The difference lies in the quality of the auditor — and in the questions the client puts before work begins.
03 — Reading it strategically
Reading the recommendations strategically
Most audit reports list measures without clearly prioritising them or spelling out the interdependencies. Reading a report properly means identifying what conditions what — and cross-checking that against the available subsidies and the schedule of upcoming maintenance work.
Prioritise: envelope first, systems second
The fundamental rule: reduce demand before sizing the systems. A heat pump sized to compensate for a poor envelope will be oversized after renovation — degrading its coefficient of performance and its service life. Here is the energy priority order in a typical Geneva renovation:
Priority 1 — Best gain-to-cost ratio
Roof and loft
Roof losses often account for 25 to 35 % of the thermal balance of an unrenovated block. Insulating the loft is the energy measure with the best return: easy access, short works, minimal disruption to tenants, no risk of a thermal bridge with the windows.
Priority 2 — Decisive for the IDC target
Façades (external or internal insulation)
A heavier investment, but indispensable in most cases to reach the 125 kWh/m²·yr (450 MJ/m²·yr) target. The future position of the windows within the wall must be decided here — before any joinery is ordered. Doing the façades before the windows avoids avoidable thermal bridges.
Priority 3 — After façade insulation
Windows and joinery
Replace the windows after the façade insulation, positioning the frames in line with the insulation. Windows fitted before external insulation end up as a thermal bridge in the future insulated wall — a structural defect that is difficult and expensive to correct.
Priority 4 — Size after demand has been reduced
Systems (heating, hot water, ventilation)
Size the new heat generation on actual demand after the envelope has been renovated. In Geneva, moving to non-fossil heating is unavoidable: an air-to-water heat pump on a low-temperature circuit, or connection to the district heating network where it exists. Balanced mechanical ventilation completes the renovation where the performance level justifies it.
Combining subsidies: GEnergie/SIG and the Buildings Programme
In Geneva two main channels fund IDC renovation works — and they can be combined where the conditions are met:
GEnergie / SIG (Geneva)
Geneva's utility company offers grants for efficient thermal equipment (air-to-water heat pumps, district heating connection, solar thermal) and for certain envelope measures under cantonal programmes. Amounts and conditions change: up-to-date information at sig-ge.ch/genergie. To be combined with an HPE or THPE application where the performance level reached justifies it.
Buildings Programme (Confederation + Geneva)
Available for renovations achieving an improvement of at least 2 CECB classes. In Geneva it is measure M-10 of the GEnergie schedule that pays this support: CHF 60.– to CHF 390.– per m² of energy reference area depending on use and the number of classes gained2026 rate schedule, sheet M-10: single-family 150/230/390 CHF/m² ERA, multi-family 90/140/210, other uses 60/90/150, for +2, +3, +4 or more classes.République et canton de Genève — OCEN — Barème des subventions GEnergie 2026, applicable dès le 1er février 20262026-02-01 · accessed 2026-08-29, the label improving the least setting the amount. Imperative condition: file the application before the works start. Information: programme-batiments.ch.
The golden rule of subsidies
Never start the works before the grant application has been confirmed. Most programmes require a prior favourable decision2026 rate schedule, point 4: the application must be « réceptionnée par l'OCEN avant le début des travaux faisant l'objet de la demande de subvention […] mais au moins 14 jours avant le début des travaux ».République et canton de Genève — OCEN — Barème des subventions GEnergie 2026, applicable dès le 1er février 20262026-02-01 · accessed 2026-08-29 — works started before confirmation are no longer eligible. Losing 15 to 30 % of the funding for the sake of speed is a common and costly mistake. This timetable belongs in the preliminary design.
An audit report that does not mention the available subsidies is incomplete. Reducing demand and optimising public support belong to the same profitability calculation.
04 — From constraint to control
From an imposed audit to a chosen renovation plan
Receiving a letter from the OCEN can feel like an administrative imposition. That framing is understandable — but counterproductive. A building with an IDC of 200 kWh/m²·yr (720 MJ/m²·yr) consumes three to five times more than a well-renovated one. Its heating cost weighs on service charges, its property value suffers, and its exposure to energy price swings is at a maximum. The OCEN letter is a signal — not a punishment.
A multi-year renovation plan is not an administrative document: it is a management tool. It sets milestones, priorities and budget — and gives the owner control of the timetable rather than having to endure it.
The four questions behind a well-built plan
What? The measures chosen, ranked by energy priority and constructional coherence — roof before windows, envelope before systems.
In what order? Intelligent phasing takes account of upcoming maintenance: a façade refurbishment planned in 3 years is the moment to add external insulation; a roof due for replacement is the moment to insulate the loft. You do not redo a roof twice.
With which subsidies? Buildings Programme, SIG/GEnergie, specific OCEN grants — each phase must incorporate the subsidies available when it is carried out, with applications filed before work starts.
For what result? The expected IDC trajectory after each phase, until the target of under 125 kWh/m²·yr (450 MJ/m²·yr) is reached — with a margin for climatic variation and implementation risk.
What Geneva case files show
Three recurring findings: the quality of the audit report determines how quickly the file is processed; a well-prepared file with subsidies built in from the outset cuts the owner's share by 15 to 25 %Source to be established — unverified figure. These orders of magnitude come from practical experience, not from published statistics.Source to be established — unverified figure; and final performance is largely decided during the design phase, before the first contractor's quotation.
HPE and THPE: Geneva's double opportunity
If the renovation reaches HPE (high energy performance — equivalent to Minergie® Renovation or CECB C/B, LEn art. 15 para. 1 and REn art. 12B) or THPE (very high energy performance — in renovation, Minergie®-A or Minergie®-P, or CECB Plus B/AREn art. 12C para. 3: renovated buildings « au bénéfice du label Minergie(r)A, Minergie(r)P ou de tout autre label équivalent »; para. 4 let. b: class B/A on the CECB Plus.République et canton de Genève — rsGE L 2 30.01 — Règlement d'application de la loi sur l'énergie (REn)accessed 2026-08-29, REn art. 12C paras. 3 and 4), specific cantonal grants are added to the federal subsidies. The THPE label is mandatory for new public buildings in Geneva (LEn art. 16 para. 1)LEn art. 16 para. 1: buildings of public authorities « conçues et maintenues de manière à satisfaire à un standard de très haute performance énergétique ». For renovation, HPE suffices (para. 2).République et canton de Genève — rsGE L 2 30 — Loi sur l'énergie (LEn)accessed 2026-08-29. For the private sector it opens a floor-area ratio bonus (LCI art. 59 para. 1: 25 % raised to 27.5 % with HPE and 30 % with THPE)LCI art. 59 para. 1: 25 % of the plot area, « portée à 27,5% lorsque la construction est conforme à un standard de haute performance énergétique, respectivement à 30% […] très haute performance énergétique ».République et canton de Genève — rsGE L 5 05 — Loi sur les constructions et les installations diverses (LCI), art. 59 — Rapport des surfacesaccessed 2026-08-29 — a significant value argument in a Geneva market under land pressure.
In French-speaking Switzerland outside Geneva
The IDC thresholds are specific to the canton of Geneva (REn art. 14)The legal bases on the ge.ch IDC page are cantonal: LEn art. 6 para. 8 and art. 15C, REn art. 14 and 14A. No other French-speaking canton applies an equivalent index.République et canton de Genève — OCEN — Que faire selon le résultat IDC de votre immeuble2025-06-20 · accessed 2026-08-29. The other French-speaking cantons (Vaud, Valais, Fribourg, Neuchâtel) have their own energy obligation regimes, generally based on the CECB and MoPEC 2014 — with no equivalent to Geneva's IDC. The federal Buildings Programme is available in every canton. If you manage a mixed portfolio across GE + VD or GE + VS, the analysis of obligations must distinguish between cantonal regimes.
05 — Common pitfalls
The mistakes that cost dear
The same mistakes recur in practice — usually for want of an overall view, under pressure to act fast, or because the interdependence of measures is underestimated. Here they are, with their real consequences.
Critical mistake
Windows before façade insulation
The new windows are set into the not-yet-insulated wall. When external insulation arrives 3 to 5 years later, the frame ends up as a structural thermal bridge. Either the windows are refitted (double cost) or permanently degraded performance is accepted — and any certification abandoned.
Critical mistake
Piecemeal works with no overall plan
Each phase is decided independently, with no overall view. The result: measures whose effectiveness is curbed by lack of coordination, untreated junctions creating thermal bridges, and an HPE or THPE certification that turns out to be unobtainable at the end — even though the level could have been reached.
Critical mistake
Replacing the boiler before renovating the envelope
A heat pump sized for 200 kWh/m²·yr will be oversized after the envelope is renovated (target < 125). Oversizing degrades the coefficient of performance, raises the electricity bill and shortens the equipment's life. The right sequence: envelope first, systems second.
Common mistake
Commissioning a "bare minimum" audit without setting objectives
The audit produces a list of measures with no analysis of interdependencies or of the subsidies that could be mobilised. The owner ends up with a compliant document that is unusable as a basis for strategic decisions — and will have to commission a second study to build the action plan.
Common mistake
Starting the works before the subsidies are confirmed
The Buildings Programme and GEnergie/SIG require a favourable decision before works begin. Works started — even partially — before that confirmation can invalidate the application. Losing 15 to 30 % of the funding for the sake of speed is an avoidable mistake.
Watch point
Neglecting airtightness
A building renovated without addressing airtightness can retain 20 to 30 % of its infiltration losses, even with excellent wall insulation. Airtightness is not a site detail — it is a work package in its own right, and it also governs how well the ventilation works.
06 — Questions from managing agents
What managing agents and owners ask
Who receives the OCEN letter — the owner or the managing agent?
The letter is addressed to the owner recorded in the land register. Where the building is managed by an agent, the agent generally receives a copy or is alerted in parallel. Legal responsibility lies with the owner; the agent is not the addressee of the obligations — but is often best placed to alert the client, coordinate the audit and follow the steps. Agents who take on that advisory role proactively stand out lastingly.
Is the audit mandatory if the IDC lies between 125 and 222 kWh/m²·yr (450 and 800 MJ/m²·yr)?
Yes. Any IDC above 125 kWh/m²·yr (450 MJ/m²·yr) triggers the audit obligation (REn art. 14). The distinction concerns the works: the mandatory-works thresholds (222 to end 2026, 180 from 2027, 153 from 2031) additionally trigger the duty to start works within 36 months. Between 125 and the applicable works threshold, the audit is mandatory and measures must be proposed — the owner has some latitude over the timetable, within the limits set by the OCEN.
What happens if the 36 months pass without the works starting?
The canton has legal means of enforcement. The OCEN sends formal reminders which can lead to administrative sanctions. Substitution procedures — where the administration has the works carried out at the owner's expenseSource to be established — unverified figure. The enforcement routes were not found in any text opened during this pass.Source to be established — unverified figure — exist in Geneva law, even if they remain rare in practice. The risk is real. And 36 months pass quickly once you factor in the audit, the preliminary design, the tendering, the building permits and the works themselves: there is no slack to waste.
Can the cost of the works be passed on to rents?
Under Swiss tenancy law (CO art. 269a), value-adding investments may justify a rent increase2026 rate schedule, general conditions: « L'octroi d'une subvention exclut définitivement l'application du supplément de hausse de loyer, justifiée par la baisse prévisible des charges énergétiques du locataire (BPC) […] art. 6 al. 3 et 9 al. 6 LDTR ».République et canton de Genève — OCEN — Barème des subventions GEnergie 2026, applicable dès le 1er février 20262026-02-01 · accessed 2026-08-29, subject to cantonal rent control rules — stricter in Geneva (LDTR). Insulation works reducing heating charges may be partly passed on, but the mechanism is regulated and documented evidence is required. It is advisable to consult a specialist lawyer or the relevant associations before any decision.
Can the IDC calculated by the OCEN be challenged or corrected?
Yes. The IDC is calculated from data supplied by the distributors. Errors are possible: a wrongly recorded energy reference area, a neighbouring building's consumption charged in error, unheated premises counted in the reference area. If your IDC looks inconsistent with the actual bills, ask the OCEN for the calculation details and provide the corrective evidenceREn art. 14A para. 4: absent a calculation by the owner, the department performs it, « laquelle peut déposer une réclamation auprès du département dans un délai de 30 jours dès notification ».République et canton de Genève — rsGE L 2 30.01 — Règlement d'application de la loi sur l'énergie (REn)accessed 2026-08-29. An experienced auditor knows how to identify and document such anomalies.
How should an auditor be chosen?
A good auditor understands the building as a system, knows the Geneva regulatory constraints, factors subsidies into the analysis and produces a report usable as a basis for decisions — not merely as an administrative document. The audit itself is a matter for a qualified professional recognised by the OCEN. NRG positive does not carry out IDC audits.
Sources and references (17)
Every figure and every claim in this dossier links back to its source. Hover or tap a footnote marker to see it.
Source to be established — unverified figure Source to be established — unverified figure. The order of magnitude is consistent with the Geneva building stock but was not taken from published statistics.
Source to be established — unverified figure Source to be established — not verified during this pass. To be tied to the LEn or the REn at the next pass on the CECB dossier.
Source to be established — unverified figure Source to be established — unverified figure. These orders of magnitude come from practical experience, not from published statistics.
République et canton de Genève — rsGE L 2 30 — Loi sur l'énergie (LEn)(accessed 2026-08-29) LEn art. 16 para. 1: buildings of public authorities « conçues et maintenues de manière à satisfaire à un standard de très haute performance énergétique ». For renovation, HPE suffices (para. 2).
Source to be established — unverified figure Source to be established — unverified figure. The enforcement routes were not found in any text opened during this pass.
An imposed obligation becomes a chosen renovation.
Once the audit is done, everything remains to be decided: the sequence of works, the performance level targeted, the trade-off between standards. Those are the choices we advise on.