Published on August 1, 2026
10 min read
EnerPHit · Minergie-P Retrofit
IDC · Project strategy
Updated June 2026
Retrofitting in Geneva: IDC, standards and strategy
In Geneva, the IDC now triggers legal obligations for building owners — and a retrofit is first and foremost a matter of strategic choices. This dossier sets out the framework: IDC thresholds, the EnerPHit and Minergie-P Rénovation standards, project approach and phasing. Implementation — envelope, airtightness, systems — is detailed in the practical dossier.
01 — Context
Why retrofit to this level?
More than 60% of the Swiss building stock dates from before 1980 — built without significant thermal insulation, with heating consumption often exceeding 150 kWh/m²·an. Switzerland has set itself the target of carbon neutrality by 2050: this means deeply retrofitting most of this building stock, not just replacing boilers.
A superficial retrofit (replacing windows, a more efficient gas boiler) brings only a marginal improvement. Only a coordinated envelope + systems retrofit can divide consumption by 5 to 10 and achieve lasting thermal comfort.
Retrofitting to the passive standard does not mean sticking insulation everywhere. It is a comprehensive design approach that treats the existing envelope as a coherent system — with its own constraints and opportunities.
> 150
kWh/m²·an: typical consumption of a pre-1980 Swiss building before retrofit
≤ 25
kWh/m²·an: EnerPHit threshold (net heating demand after passive retrofit)
÷ 6 à ÷ 10
achievable reduction in heating consumption with a retrofit to the passive standard
40–60 %
of the Swiss building stock's CO₂ emissions come from buildings built before 1980
Subsidies available in French-speaking Switzerland
The Programme Bâtiments (Confederation + cantons) subsidizes retrofits that reach high performance levels. In Geneva, the OCEN offers specific grants for HPE (high energy performance) and THPE (very high energy performance) retrofits. Minergie®-certified works benefit from a bonus. Information: programme-batiments.ch and OCEN for the canton of Geneva.
02 — Geneva obligations
The IDC: what Geneva law requires of building owners
In Geneva, every heated building with 5 or more heat off-takers is subject to monitoring of its IDC — Indice de Dépense de Chaleur (heating expenditure index) : the actual heating and domestic hot water consumption, measured at the meters and expressed per unit of reference energy floor area. It is not a theoretical calculation — it is the building's real energy bill, declared to the OCEN.
This index is no longer just a monitoring tool: it triggers legal obligations for building owners.
> 125
kWh/m²·an (450 MJ/m²·an): above this IDC threshold, an energy audit of the building is mandatory
> 180
kWh/m²·an (648 MJ/m²·an): above this threshold, remediation works are mandatory from 2027 (222 / 799 MJ/m²·an until end of 2026, 153 / 551 MJ/m²·an from 2031)
36 months
deadline to begin the required works once the threshold is confirmed
1 kWh = 3,6 MJ
the IDC is often expressed in MJ/m²·an: 125 kWh ≈ 450 MJ, 180 kWh ≈ 650 MJ
In practical terms, for an owner or a property management firm
An unrenovated building from the 1960s–1980s frequently exceeds these thresholds. Waiting for the letter from the OCEN means being subject to its timetable; anticipating the audit means choosing your own strategy — which works, in what order, with which subsidies. This is precisely the difference between a retrofit imposed piecemeal and a planned retrofit that adds value to the building.
NRG positive coordinated IDC monitoring for a portfolio of buildings owned by the State of Geneva (Programme de Transition Écologique, OCBA, 2023–2025). This experience on the administration side makes it possible to anticipate the canton's expectations — and to turn a regulatory constraint into a coherent retrofit project. Let's talk about your IDC →
03 — Retrofit standards
EnerPHit and Minergie‑P Rénovation
Two main standards define "passive retrofit" in French-speaking Switzerland: EnerPHit (Passivhaus Institut, Darmstadt) and Minergie-P Rénovation. Their requirements differ in logic, but their shared goal is to reach a performance level close to new passive construction, while accounting for the constraints of the existing building stock.
PASSIVHAUS INSTITUT
EnerPHit
Heating demand
≤ 25 kWh/m²·an (PHPP)
or a component-based approach (U-values)
Airtightness
n₅₀ ≤ 1,0 h⁻¹
(vs 0,6 for new Passivhaus)
Key feature
Dual certification path: either the overall energy balance, or compliance with target U-values per component (a more flexible approach for phased retrofits).
MINERGIE®
Minergie-P Rénovation
Heating demand
≤ 90 % of MoPEC 2025 (cantonal model energy regulations) limit values for retrofits (SIA 380/1:2016)
(vs ≤ 70% for new Minergie-P — regulation 2026.1)
Airtightness
qE50 ≤ 1,6 m³/(h·m²) for retrofits
Key feature
Certification possible in stages (module by module). Requirements adapted for protected buildings (heritage sites, listed buildings). Official recognition by the Swiss cantons.
Take care when comparing the numerical thresholds: the reference energy floor area (SRE) is not calculated the same way between Passivhaus (PHPP reference floor area, PHI Darmstadt) and Minergie® (SRE per SIA 416). A "≤ 25" for EnerPHit and a "≤ 30" for Minergie-P Rénovation therefore do not refer to the same floor area — a direct comparison of the values is approximate.
EnerPHit's component-based approach: welcome flexibility
When it is not possible to reach the overall threshold of 25 kWh/m²·an (compact building, heritage constraints, phasing over several years), EnerPHit allows component-based certification: each renovated envelope element must meet specific target U-values. This approach allows for progressive certification, component by component, over a period of up to 10 years.
| Criterion |
Passivhaus New Build |
EnerPHit Retrofit |
Minergie-P New Build |
Minergie-P Retrofit |
| Heating demand |
≤ 15 kWh/m²·an |
≤ 25 kWh/m²·an |
≤ 70 % MoPEC 2025 |
≤ 90 % MoPEC 2025 |
| Airtightness * |
n₅₀ ≤ 0,6 h⁻¹ |
n₅₀ ≤ 1,0 h⁻¹ |
qE50 ≤ 0,8 m³/(h·m²) |
qE50 ≤ 1,6 m³/(h·m²) |
| Heating capacity |
≤ 10 W/m² |
— |
≤ 10 W/m² |
— |
| Phased certification |
— |
✓ Components |
— |
✓ Modules |
| Calculation tool |
PHPP |
PHPP |
SIA 380/1 |
SIA 380/1 |
| Protected buildings |
— |
⚠ Case by case |
— |
✓ Dedicated procedure |
Implementation, component by component
Envelope strategy (façades, roof, windows, thermal bridges), airtightness plane, ventilation and heating: the technical detail is covered in a dedicated dossier —
Passive retrofit in practice →
04 — Approach and phasing
How to run a passive retrofit project
A passive retrofit cannot be improvised after the fact: decisions made at the design stage determine 80% of the result. Here is the typical sequence of a well-run project.
Step 1 — Diagnosis
Energy and technical baseline survey
Full thermal audit: survey of existing U-values, initial Blower Door test, infrared thermography (winter), thermal bridge analysis. Identification of any heritage constraints. This diagnosis guides everything: without it, it is impossible to define objectives or cost the works.
Step 2 — Preliminary design
Defining the envelope + systems strategy
Choice of target standard (EnerPHit, Minergie-P, or an intermediate level). Construction system variants per component. Preliminary PHPP or SIA 380/1 calculation to check that targets are met. Cost assessment per variant and identification of applicable subsidies.
Step 3 — Detailed design
Detailed design of construction junctions
Drawings of all critical construction junctions (façade/slab junction, window/ITE junction, wall base). Thermal bridge calculation (Ψ). Definition of the airtightness plane with continuity details at every critical point. Sizing of the ventilation system and heat generation.
Step 4 — Construction
Quality control and intermediate testing
Site supervision with particular attention to the interfaces between trades (masonry/joinery/airtightness). Intermediate Blower Door test before closing up. Sign-off of construction junctions before they are covered. Training of tradespeople on airtightness requirements (the weak link is often a lack of awareness on site).
Step 5 — Handover and certification
Final Blower Door test, as-built calculation, certification file
Final airtightness test (n₅₀ ≤ 1,0 h⁻¹). Update of the PHPP or SIA 380/1 calculation with actual values. EnerPHit or Minergie-P certification file. Consumption measurements over the first heating season for verification.
Phased retrofit: planning for coherence from the outset
Many retrofits are carried out in several phases (windows one year, façade three years later, roof afterwards). This is often a financial necessity. But without an overall plan, each phase can compromise the next: windows replaced before the ITE will end up in the wrong position and create thermal bridges. The golden rule: design the complete project from the outset, even if execution is phased.
05 — Key questions
What building owners ask
How much does a retrofit to the passive standard cost?
Costs vary enormously depending on the building's initial condition, its geometry, the presence of structural thermal bridges, and the choice of materials. As a rough guide: for a 150 m² single-family home, a complete retrofit to EnerPHit level typically represents CHF 150,000 to 250,000 in envelope and systems works (excluding interior decoration). With subsidies from the Programme Bâtiments and cantonal grants, the net cost to the owner can be reduced by 20 to 40%. The return on investment is also measured in comfort, property value, and protection against energy price volatility.
Can a retrofit be done in stages without doing everything at once?
Yes — it is even the most common situation. The key is to design the project as a whole before starting the first phase, to ensure that each intervention is consistent with those that follow. The rule: start with the roof (the most cost-effective energy-wise), then the façades, then the windows (taking into account their final position within the insulated wall), then the systems. Never replace the windows before deciding on the façade insulation system.
What is the difference between a "Minergie" retrofit and an "EnerPHit" retrofit?
Both standards target a similar level of performance and allow a component-based approach. Minergie-P is more widely recognized in the Swiss context, with a well-established cantonal procedure and better integration into subsidy applications. EnerPHit is the Passivhaus Institut's international standard: it is recognized outside Switzerland and its PHPP methodology is very precise. In practice, building owners in Geneva or Vaud will often choose Minergie-P Rénovation for its administrative ease, while EnerPHit will be preferred for projects with strong technical stakes or an exemplary role.
A retrofit project — or an IDC to bring back into line?
Envelope strategy, critical review of the file, support and certification follow-up — let's talk about your building and its timeline.
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