A site identified, a budget estimated on the back of an envelope, and the desire to start work as soon as possible: this is often the stage where construction projects go off the rails. The gap between what one imagines financing and what the construction site actually requires creates tensions that only advice from construction experts can help anticipate.
Even before discussing plans or materials, the solidity of a real estate project hinges on three decisions that are almost always underestimated.
Individual house construction contract: what the guarantees really cover
We sign an individual house construction contract (CCMI) thinking that everything is locked in. In practice, the scope covered by the builder’s guarantees stops where the work carried out directly by the buyer begins.
Doing the tiling, painting, or fencing oneself to reduce costs is common. But these reserved works fall outside the scope of the builder’s legal guarantees. If a defect appears on a service that you have carried out or had carried out by a contractor outside the contract, neither the ten-year guarantee nor the guarantee of perfect completion applies.
The concrete issue: before signing, list precisely what remains your responsibility and have these items priced by an independent professional. A building expert can check if the reserved works are realistic for your skill level and your actual budget. You can explore Concept Maison for your real estate project to structure this reflection from the planning phase.
Another point confirmed by site feedback: the signing of the contract does not guarantee the start of work. It is still necessary to obtain final financing, the building permit cleared of any appeals, and to verify that all administrative documents are compliant. This “last administrative mile” regularly blocks projects that are otherwise well advanced on paper.
PTZ and financing: deciding between new construction and buying old
Since April 1, 2025, the zero-interest loan is available for the construction of new individual houses across the entire territory. This extension is planned until December 31, 2027, providing a clear window for ongoing projects.
The PTZ only covers part of the operation. It must be supplemented by another form of financing (traditional bank loan, personal contribution, social access loan). A common mistake is to calibrate one’s budget by counting on the PTZ as the main contribution, whereas it functions as a supplement.
Check your borrowing capacity before choosing the land
We visit plots, get excited about a location, and then discover that the cost of development or the nature of the soil blows the budget. A bank advisor or loan broker calculates the borrowing capacity by including not only the price of the land and construction but also notary fees, connections, and development tax.
Feedback varies on this point, but several brokers recommend finalizing the financing simulation even before the first land visit. This avoids wasting several months on an oversized project.
- Have the total cost of the project (land, construction, development, taxes) estimated before making an offer on a plot.
- Request a financing eligibility certificate from your bank or broker to strengthen your case with the land seller.
- Check your eligibility for the PTZ with an accredited organization by providing your reference tax income from two years prior.
RE2020 and real performance: comparing promises to site data
The environmental regulation RE2020, applicable to new constructions, imposes thresholds on energy consumption and the carbon footprint of buildings. Since September 2026, performance data for buildings subject to RE2020 is accessible in open data via the Observatory of energy and environmental performance of new buildings.
In practical terms, this means that one can compare the actual observed performances on delivered constructions, not just the values announced in a commercial description or a builder’s brochure. For a house project, consulting this data allows you to verify if the intended builder keeps their promises on comparable sites.
Insulation, low-carbon materials: ask the right questions to the builder
A construction expert does not just validate a plan. They challenge the builder’s technical choices in light of the RE2020 requirements and your actual budget. The items that significantly affect costs include:
- The construction method (wood frame, low-carbon concrete, brick) directly influences the carbon balance and the price per square meter.
- External thermal insulation is more expensive to install but reduces thermal bridges, improving performance measured at delivery.
- The heating system (heat pump, pellet stove, connection to a heat network) must be consistent with the building’s envelope to meet regulatory thresholds.
Ask the builder for their RE2020 references with actual consumption data, not just theoretical simulations. The open data from the Observatory now allows for cross-referencing this information.
Site visit and acceptance of work: two stages where the expert changes the game
The acceptance of work is the legal act that triggers the guarantees (perfect completion, biennial, ten-year). Signing the acceptance report without reservations means accepting the property as is. Any defect not mentioned at that time becomes much more difficult to address.
A building expert accompanying you during the acceptance visit identifies defects that a non-professional would not see: structural cracks hidden by the coating, air tightness defects, non-compliance of joinery with the contract description. The cost of this expertise remains modest compared to the corrections avoided.
Before acceptance, also plan for one or two intermediate site visits. These allow for detecting discrepancies between the plan and execution before the main work is completed, when corrections are still possible without major additional costs.
A real estate project under construction is managed like a sequence of irreversible decisions. Each poorly calibrated step (vague contract, underestimated financing, rushed acceptance) will cost more later, often well beyond the initially planned budget. Structuring your project with independent professionals from the start remains the only reliable way to maintain control over costs and the quality of the delivered housing.
