Refereeing has never been so clear. Since April 1, 2025, almost all departments have increased their transfer rights, wearing the notary fees in the old one at 7 to 8.5% of the purchase price, an increase authorized by the 2025 finance law and applicable until April 30, 2028. Added to agency fees and the cost of a move, these friction costs make the change of residence more and more expensive, at a time when the extension of an existing property varies between 2,000 and 3,000 €/m², depending on the technique.
For many ownersthe real question is no longer “should we move?” but “When is it in our interest to stay?”. “The real trade-off is not based on the price per square meter alone, but on the difference between the cost of the extension and the “all-inclusive” cost of a moving to bigger”asks Alexandre Gioffredy, founder of Greenkub, specialist in wooden frame extensions. “As long as the local purchase price per square meter clearly exceeds the construction cost, it is in your interest to densify your own property.”
A tipping threshold which varies from single to double depending on the zone
The tipping point therefore depends less on the absolute price than on the difference between what a square meter costs to purchase and what it costs to build. Three major landmarks are emerging. In the Paris region and inner suburbs, the extension almost systematically becomes a winner from 5,500 to 6,000 euros per square meter upon purchase. “We add the square meter to 2,500 euros where we would buy it for more than 6,000, without transfer costs”summarizes the manager.
In the large regional metropolises – Lyon, Bordeaux, Nantes, Aix – the threshold is around 4,000 to 4,500 euros per square meter. On the other hand, in medium-sized towns, below 2,800 to 3,000 euros per square meter, the calculation tightens and the moving can become competitive again, unless there is an attachment to the place: children’s school, family proximity, garden, etc. A nuance that calls for caution when price local per square meter is getting closer to the construction cost, and that the financial difference is no longer enough to justify the construction site.
Wood frame, masonry, elevation: three techniques, three budgets
THE cost of the extension depends closely on the process. The wooden frame costs between 2,000 and 2,800 euros per square meter: dry site, short deadlines, good thermal performance, it is suitable for single-storey extensions or on constrained land. Traditional masonry, between 2,200 and 3,200 euros per square meter, remains relevant to remain consistent with an existing building or in an area to be strong heritage requirement.
Raising the height, finally, is the most expensive – 2,800 to 5,000 euros per square meter -, due to the reconstruction of the structure, the scaffolding and the water protection, but it is the only option when the ground no longer allows the footprint to be extended.”Wooden frame as soon as there is land available on the ground, elevation only in dense areas where the ground is lacking, masonry for heritage connections.recommends the founder of Greenkub.
The hidden costs of moving that tip the scales
This is often where the decision comes down to. On the moving side, “owners forget the cost of friction”alert Alexandre Gioffredy: notary fees (7 to 8%), agency fees (4 to 5%), moving physical, sometimes double transitory charge, and, depending on the nature of the property sold, possible taxation on the capital gain upon resale. “SFor a property worth 500,000 euros, these cumulative costs often exceed 50,000 to 60,000 euros, or already 20 to 25 square meters of extension financed.
In other words, the equivalent of an additional room goes to waste as soon as the move is made. On the extension side, certain positions should not be underestimated either: development tax, soil and structural study, connections to the existing part (roof, electricity, heating), refinishing at the junction and, sometimes, partial rehousing during construction. Real amounts, but which remain incommensurate with the friction cost of a sale followed by a repurchase.
Urban planning and added value: secure before launching
There remains the administrative stage, where most of the delays occur. Up to 20 square meters — or 40 square meters in an urban area covered by a PLU —, a prior declaration is sufficient, with an instruction lasting approximately one month. Beyond this, or if the total floor area exceeds 150 square meters, the building permit becomes compulsory (instruction of two to three months, recourse to an architect imposed above this threshold). The classic pitfalls to be aware of are a poorly anticipated PLU (land footprint, heights, distances to separating boundaries), a perimeter ABF which extends the deadlines, and especially the third-party appeal deadline of two months after posting, during which a neighbor can contest.
“The right reflex is to secure urban planning feasibility before committing to anything.”insists Alexandre Gioffredy. Finally, a well-conducted extension is largely reflected in the price of resale : the recovery is generally between 70 and 90% of the cost, and more in tight markets where additional square meter is rare. The operation is therefore profitable in immediate use value as in heritage valueon two conditions, warns the founder of Greenkub: that the extension remains coherent with the property and that it provides a differentiating use — master suite, open living room, office.
To note
The surface thresholds and processing times are covered by the Town Planning Code and may vary depending on the PLU of your municipality; the applicable DMTO rate depends on your department. Construction costs and recovery rates on resale are indicative orders of magnitude which depend on the local market, the condition of the property and the quality of the workmanship. For any significant operation, a feasibility study and consultation with a professional (architect, notary) are recommended before any commitment.
