Of every ten homes renovated over the past five years in Suisse romande, perhaps two were done in the right order. The other eight started with windows because they were visible, or with heating because it broke down. These choices are not always wrong, but they are almost never optimal.
The order of energy renovation works has a direct impact on total cost, final performance, and the grants that can be unlocked. This is one area where an hour of careful thought can save CHF 20,000.
The principle: envelope first, systems second
The technical logic is simple. As long as a home is losing heat massively through its envelope (loft, walls, windows), any heating system installed will have to compensate for those losses. A heat pump in a thermal sieve consumes two to three times more than a heat pump in a properly insulated home.
Hence the standard order, validated by CECB+ assessors and most energy consulting firms:
- Loft or roof: the item with the best cost-to-benefit ratio.
- Airtightness and thermal bridges: often overlooked, but essential.
- Facade: structurally important, more costly, best combined with render work.
- Windows: useful for comfort, less impact than the envelope.
- Heating (heat pump): sized according to the renovated envelope.
- Photovoltaics: added as the crowning step once envelope and heating are up to standard.
- MVHR (double-flow ventilation): recommended when the envelope is highly airtight.
This order is not dogma. A CECB+ tailors the prioritisation to each building, and certain situations require departures from it. But as a general framework, it has proven its worth.
Why the loft is almost always the priority
In an uninsulated home from the 1970s–1980s, the roof typically accounts for 25–35 % of heat losses. An uninsulated roof leaks the equivalent of a radiator running continuously.
Indicative costs in 2026:
- Cold loft insulation (glass/hemp wool, 30 cm): CHF 6,000–12,000.
- Sarking insulation beneath the roof covering (major renovation): CHF 28,000–45,000.
- Finished loft insulation from the inside: CHF 12,000–25,000.
For a cold loft insulation at CHF 9,000, annual heating savings typically fall between CHF 600 and CHF 1,200. That gives a gross payback of 8–15 years, reduced to 5–9 years after grants and tax deductions. No other item has such a favourable ratio.
Windows: overrated in the popular imagination
This is the item that gets replaced most visibly, and starting with it is almost always poor timing.
In a standard uninsulated home, windows typically account for 10–15 % of heat losses, compared with 25–35 % for the roof. The cost per m², however, is very high: CHF 800–1,500/m² installed for quality double glazing, more for triple.
The cost-to-benefit ratio of windows alone is often less favourable than the loft — sometimes two to three times less.
Cases where windows become a priority:
- Single glazing still in place (very rare in 2026, but exists in older buildings).
- Rotten or failing frames (compromised airtightness).
- Severely degraded thermal comfort (cold surfaces, condensation).
- Aesthetics (full renovation of a home, old windows out of keeping with the rest).
In these cases, windows are treated as a priority, or even first. But in a home with 1990s double glazing in good condition, start with the loft.
The facade: structurally important but costly
External wall insulation (EWI) is the single operation with the greatest impact on energy class: it can alone gain two to three classes. But it is also the most expensive item.
Indicative costs in 2026, full EWI on a standard detached house:
- Simple facade (regular gables, no complications): CHF 35,000–55,000.
- Complex facade (projections, balconies, mouldings): CHF 55,000–85,000.
- Full render renovation (paint, finishes): add CHF 8,000–15,000.
The classic optimisation: combine EWI with a render that would have been needed anyway. The additional cost of insulation then covers only the insulation material and its fixings, not the full scaffolded project.
EWI is particularly justified when:
- The facade needs re-rendering (flaking paint, cracks).
- Thermal bridges are significant at floor-to-wall junctions.
- The home is aiming for an energy class B or A (generally impossible without EWI).
Heating: to be sized after the envelope
Once the home is properly insulated, the heating system is calibrated to the actual (reduced) needs. This changes the sizing, the cost, and the efficiency.
A concrete example. A 160 m² home from the 1980s, uninsulated: heat loss 12–14 kW. After loft insulation + EWI: heat loss 6–8 kW. Consequences for the heat pump:
- Heat pump sized at 12 kW (without envelope renovation): cost CHF 38,000–44,000.
- Heat pump sized at 8 kW (with prior envelope renovation): cost CHF 32,000–38,000.
Saving on the heat pump alone: CHF 4,000–6,000. Plus an additional operating saving of 30–40 % because the heat pump runs better within its optimal range.
The classic pitfall: replacing the boiler in an emergency (breakdown in winter) without insulating first. The heat pump is then oversized, and any subsequent envelope investment loses some of its return. This is typically the scenario you try to avoid by planning ahead.
Solar: the crowning step
Photovoltaics logically come last in the sequence. Why?
First, because a well-insulated home heated by a heat pump consumes an amount of electricity compatible with a 10–15 kWp solar installation. Sizing coherence happens at that point.
Next, because solar is quick to install (2–4 days) and has no structural interaction with the other works. It can be scheduled in the final phase without constraint.
Finally, because PV grants (lump sum from Pronovo + cantonal) are stable and do not depend on the rest of the project. Nothing is lost by doing it last.
Typical gross cost for 8–12 kWp in 2026: CHF 17,000–26,000. Net after grants: CHF 11,000–17,000.
MVHR: useful when the envelope is very airtight
Controlled ventilation (single-flow or double-flow MVHR) becomes relevant once the home has been made very airtight. A properly insulated and airtight home carries an increased risk of condensation and dampness if air is not adequately renewed.
MVHR is generally dealt with last, because it requires ductwork runs that can be intrusive, and you do not want to open walls after a completed EWI.
Indicative costs:
- Single-flow hygro-adjustable ventilation: CHF 4,500–8,500.
- Double-flow ventilation with heat recovery: CHF 12,000–22,000.
Double-flow MVHR recovers 75–90 % of the heat from extracted air, closing the energy optimisation loop. In a CECB class A home, it is almost always present.
The whole-building renovation bonus
This is the least-known grant lever and one of the most rewarding. Several cantons in Suisse romande (notably Vaud, Fribourg, Neuchâtel) award a bonus when a project combines several energy measures within a limited period (typically 18–24 months).
The bonus generally represents 15–30 % additional aid compared with the sum of individual grants. On a CHF 200,000 gross project, that can mean CHF 25,000–50,000 in bonus, provided the works are coordinated.
Conditions vary by canton, but the general principle:
- Several combined measures (for example: envelope + heating, or envelope + heating + PV).
- Completion within a short period (18–24 months depending on the canton).
- Prior CECB+ mandatory to validate the coherence of the programme.
- Single consolidated application submitted in advance.
Many homeowners lose this bonus by carrying out works in several waves, sometimes for simple scheduling reasons. Factoring in the bonus during planning can justify bringing forward or delaying an operation by a few months.
The typical sequence of a whole-building renovation project
Here is a realistic timeline for a 1980s detached house aiming for CECB class B–A.
Months 1–2. CECB+ and planning file. Selection of contractors for each package.
Months 3–4. Submission of consolidated grant application (canton + municipality). Application for the whole-building renovation bonus.
Months 5–6. Phase 1: loft insulation, airtightness, windows if planned.
Months 7–9. Phase 2: facade (EWI + render), if included in the renovation. Scaffolding for 6–10 weeks.
Months 10–11. Phase 3: heating replacement (heat pump), MVHR.
Months 12–13. Phase 4: photovoltaic installation.
Months 14–16. Full commissioning, adjustments, grant payment requests.
Over 14–16 months, the project remains well within the whole-building bonus deadline (18–24 months), with a coherent and coordinated operation.
When the budget does not cover everything at once
This is the most common situation. A whole-building renovation is rarely affordable in a single go. A few principles for optimising a phased approach.
Commission a CECB+ before starting. Indispensable for obtaining the prioritised figures.
Phase 1: loft + heating if end of life. This is the most profitable and most impactful combination. It focuses on the most important quarter of the total budget.
Phase 2 (3–5 years later): EWI if the facade needs rendering. Combine with the mandatory render.
Phase 3 (6–10 years later): PV + MVHR where relevant.
A phased approach loses the whole-building renovation bonus, but remains more profitable than no renovation. The calculation depends on the available budget and the intended sale horizon.
Our advice for 2026
Every energy renovation in Suisse romande should begin with a CECB+. It is the tool that turns an intuition into a structured plan. The cost (CHF 700–1,500) is negligible compared with the mistakes it prevents.
Then, two principles:
- Envelope before systems. A heat pump in a thermal sieve remains a thermally leaky home heated by a heat pump. The reverse is rarely true.
- Whole-building wherever possible. The whole-building renovation bonus more than pays for the coordination.
A well-ordered renovation increases a property's value by 15–25 % on resale, saves 60–80 % on running costs, and turns a house classed F into class B–A. It is the most structurally important investment a homeowner can make on their property over the decade.