A couple buys a gently sloping plot of land, signs with the notary, and then discovers that the rectangular house plan drawn from the catalog won’t work: the clay soil requires special foundations and the local PLU limits the ridge height. The project is delayed by three months even before the first shovel hits the ground.
This kind of situation remains common. It can be avoided by approaching each stage of a house project with an operational method rather than just a wish list.
Carbon threshold RE2020: what changes concretely for new construction
Since January 1, 2025, the construction Ic threshold (carbon indicator) for new individual houses has dropped from 640 to 530 kg CO₂e/m² of floor area, representing a decrease of about 17%. In practice, certain classic combinations like concrete plus polystyrene are no longer compliant without resorting to low-carbon materials.
This includes structural wood, bio-sourced insulation (wood fiber, cellulose wadding), or low-carbon concrete. For a construction project submitted from 2025, it is necessary to rethink the composition of walls, floors, and the insulating envelope right from the design phase, not at the final costing stage.
The choice of builder or architect also hinges on this: request the FDES (environmental and health declaration sheets) for the proposed materials. A professional who cannot calculate the construction Ic of their own wall catalog is not up to date with the regulations. To explore the various facets of a real estate project, the presentation of the Expertise Maison site gathers useful resources on construction as well as renovation.
Mandatory energy audit: a constraint that weighs on resale
Classic guides often talk about DPE, but rarely about the mandatory energy audit, which is a distinct and much more detailed document. Since April 1, 2023, selling a house rated F or G requires this audit, which includes at least two costed work scenarios.
Properties rated E have been affected since January 1, 2025. The schedule is already set: D ratings will follow on January 1, 2034, and then C ratings in 2044. In other words, a house purchased today with a D rating will need to undergo this audit in less than ten years to be resold.
The concrete impact on a renovation project: if you buy an old house to renovate, incorporate from the start a bundle of work that improves the DPE rating by at least two letters. Moving from F to D, for example, avoids being stuck at resale and opens access to aid such as MaPrimeRénov’.
What the audit includes and what it costs
The mandatory energy audit includes an analysis of the building, heating and ventilation systems, and then proposes two work pathways with budget estimates. Feedback on the price varies depending on the size of the property and the region, but it is an item to budget for as soon as the compromise is signed if you are the buyer.
Land and contract: checks that no one catches after signing
It is often said that you need to “choose your land well,” but the real issue lies in the documents consulted before signing. Three checks can change the trajectory of a house project:
- The G2 AVP soil study: it identifies risks (expansive clay, high water table, unstable fill) and conditions the type of foundations. Without it, the builder works blindly, and cost overruns arise during construction.
- The operational urban planning certificate: it confirms that your project is feasible on the plot (height, footprint, setbacks). The information certificate alone is not sufficient.
- The CCMI construction contract: if you go through a builder, check that the delivery guarantee at the agreed price and deadlines is backed by a guarantor (insurer or bank). This is the only real protection against bankruptcy during construction.
These three points cannot be caught after signing. A plot bought without a soil study can generate foundation costs that absorb the entire project margin.
Energy renovation: prioritizing work by return on investment
When renovating an old house, the temptation is to redo the kitchen or bathroom first. Visually, it is gratifying. Financially and technically, it is a mistake if the thermal envelope is not addressed.
Insulating the attic and walls remains the item with the best return on investment before any boiler or window replacements. An efficient boiler in a house that leaks through the roof will not solve the energy consumption problem.
Logical order of renovation work
On site, a precise sequence is followed to avoid breaking what has just been installed:
- Demolition and major works (structural repairs, openings in load-bearing walls)
- Technical networks: electricity, plumbing, ventilation
- Thermal insulation of walls, floors, and attics
- Partitions, plastering, interior woodwork
- Floor and wall coverings, then finishes (painting, tiling)
Reversing this sequence, for example, installing flooring before redoing plumbing, guarantees damage and costly repairs. A detailed construction schedule by lot is the best tool for budget control.
Professional support: architect, project manager, or builder
The choice of professional depends on the type of project. For new construction under CCMI, the builder manages everything with a delivery guarantee. For heavy renovation or an extension, an architect or project manager coordinates the trades without a commercial link to the companies, ensuring an independent view on the quality of execution.
Beyond a certain floor area threshold, hiring an architect is mandatory. In any case, check the ten-year insurance and the perfect completion guarantee of each participant before the start of the work. The perfect completion guarantee allows one year to correct defects noted upon receipt of the work.
A successful house project relies less on decorative inspiration than on the rigor of the upstream steps: regulatory compliance, soil study, choice of RE2020 compatible materials, and selection of properly insured professionals. These decisions made in the first weeks determine the final budget and the quality of the housing for the next twenty years.