A renovation project is largely decided before the first sledgehammer blow. The choice of materials, construction schedule and regulatory compliance have a far greater impact on the final result than the headline budget. Tackling home renovations without understanding these technical factors can lead to cost overruns, poor workmanship or administrative roadblocks that even a qualified contractor may not always be able to resolve.
Electricity conversion factor and EPC rating changes before renovation
The electricity conversion factor used to calculate the EPC rating has fallen from 2.3 to 1.9. This change makes a difference for homeowners with electrically heated properties: some have moved from an F rating to an E without touching a single wall.
Before starting an energy renovation, check whether your rating has changed under the new factor. A property reclassified as E no longer has the same renovation priorities as one that remains rated F or G. Insulating an unconverted loft, for example, is still worthwhile, but the return on investment changes if the starting EPC rating has shifted.
We recommend having your EPC recalculated before approving a renovation plan. An up-to-date assessment prevents you from basing the work on outdated information, which could lead to the wrong choice of insulation materials or an incorrectly sized heating system.
Planning a renovation project becomes more precise when you consult the renovation work guides on Mulot Bricole, which break down the work by trade.
Mandatory energy audits: two different documents for property sales and subsidised renovations
Since 1 January 2025, the mandatory energy audit for property sales applies to homes rated E, in addition to those rated F and G, which were already covered. This requirement applies to detached houses and buildings held in single ownership, but not to individual units sold as part of a condominium. The timetable provides for the requirement to be extended to homes rated D in the coming years.
A common source of confusion: the audit carried out for a property sale is not the same one used as the basis for a major renovation funded by MaPrimeRénov’. The first informs the buyer, who is not required to carry out the recommended work. The second is part of a supported renovation pathway and serves as the project’s technical reference.
A sales audit does not replace the steps required to obtain renovation funding. If you buy an E-rated property with an audit already carried out by the seller, you will probably need to commission a second one, tailored to your renovation plan, to qualify for funding schemes.
MaPrimeRénov’ and major renovations: pathway requirements
MaPrimeRénov’ rules have been tightened to steer households towards whole-home projects rather than isolated upgrades. In practice, a major renovation now requires support from Mon Accompagnateur Rénov’, an approved adviser who oversees the project from design through to completion.
This requirement changes how a renovation project needs to be planned. Previously, a homeowner could insulate the walls, then replace the windows, then change the boiler, applying for funding at each stage. This piecemeal approach is becoming less and less compatible with the scheme.
A major renovation project must address several areas at the same time:
- Thermal insulation (walls, roof and ground floors) combined with ventilation upgrades, since insulating without improving ventilation reduces indoor air quality and encourages mould growth
- Replacement of the heating system, sized according to actual heat loss after insulation, not the property’s original heat loss
- External windows and doors selected to match the target insulation level (standard double glazing is rarely sufficient if the walls are being externally insulated to an R-value above 4)
The overall budget increases, but so does the available funding. We find that households following this supported pathway achieve significantly better energy performance than those making improvements one at a time.
Technical order of renovation work: scheduling that avoids rework
The order of work determines the final quality of the project. Reversing the sequence of two tasks can mean redoing completed work, adding direct costs and extending the schedule.
The technical sequence follows a logic that moves from the building envelope inwards:
- Start with structural and shell work (foundation repairs, openings in load-bearing walls, roof framing): these tasks create vibrations and dust that are incompatible with finishes already in place
- Next, make the building weather-tight and secure (roofing, windows, waterproofing): until the building is enclosed, interior insulation materials and plasterboard risk getting damp
- Install technical systems (electrical wiring, plumbing and mechanical ventilation) before partitioning: running cables through closed walls means cutting channels and repairing the plaster
- Leave insulation, partitioning and finishes until last: painting, flooring and wall tiles should be done once no heavy trades are moving through the rooms
A common pitfall is ordering the kitchen or bathroom before the services have been installed. The location of water supplies, drains and sockets determines where the units can go. Approve the technical plans before signing with the kitchen supplier to avoid last-minute adjustments.
Quotes and contractors: what to check before signing
A renovation quote should specify materials by manufacturer and product reference, quantities and installation requirements. A vague description such as “loft insulation, supply and installation” makes it impossible to compare two quotes or check compliance when the work is complete.
Check that the contractor holds RGE certification (Recognized Environmental Guarantor) if you are applying for financial assistance. Without RGE certification, the contractor’s work is not eligible for MaPrimeRénov’. Check the certification in the official directory rather than relying solely on a business card.
The lowest price says nothing about quality. Compare quotes item by item: insulation thickness and thermal resistance, type of airtightness membrane, and the brand and AEV rating of the windows and doors. These technical specifications make the difference between work that lasts and a renovation that needs repairs after a few winters.
A successful renovation project depends on a reliable initial assessment, careful scheduling and well-documented material choices. Recent regulatory changes, particularly those affecting energy audits and MaPrimeRénov’ eligibility, make preparation even more critical than the work itself.
