EXPERTISE — OFF-PLAN SALES (VEFA) FRENCH RIVIERA
You have just moved into your new apartment in Sophia Antipolis. Everything is perfect… except you can hear your neighbors coughing, walking, and even their television. You have checked the seals and windows, but the noise persists. The developer tells you it is normal. But an acoustic test conducted in Antibes last year revealed that 40% of new homes delivered under off-plan sales (VEFA) have soundproofing defects. So, what does the standard really say?
What You See — and What It Really Hides
You hear airborne noises (voices, TV) and impact noises (footsteps, falling objects). The developer installed a double plaster partition and a floating screed. But the sound passes through. Why?
What I often see in such cases is a failure of the mass-spring-mass principle. On a case in Antibes last year, I measured a lack of decoupling of the floating screed: it touched the perimeter wall in several places. Result: impact noise transmitted directly to the structure. The VEFA plan indicated a 5 mm resilient strip, but in reality it was crushed or missing in some places.
The Calculations That Change Everything: Sound Reduction Index
The French standard NF S 31-057 (part 1) defines the sound reduction index R (in dB) for airborne noise. For a separating wall between dwellings, the French Technical Document DTU 20.1 (paragraph 6.2) requires R ≥ 53 dB. In practice, we measure the emitted and received sound levels. Formula: R = L1 – L2 + 10 log(S/A), where S is the wall area (m²) and A is the equivalent absorption area of the receiving room (m²).
Take a real case in Antibes: wall area S = 12 m², absorption area A = 8 m² (furnished room). L1 = 85 dB (loud voice), measured L2 = 38 dB. Calculation: R = 85 – 38 + 10 log(12/8) = 47 + 10*0.176 = 48.8 dB. Result: 48.8 dB < 53 dB. Non-compliant. The defect often comes from sound bridges (screed not decoupled, poorly installed seals).
What Happens If You Do Nothing
At 6 months, the defect worsens: resilient strips compress, cracks appear. At 2 years, impact noises become unbearable. At 5 years, secondary pathologies occur: cracks in partitions, tile detachment. The cost of remedial work (removing screed, installing new insulation) can reach €150/m², i.e., €3,000 for a 20 m² room.
Frankly, waiting only increases the bill. On a case in Antibes, a homeowner waited 18 months before acting: the developer invoked the expired one-year warranty for perfect completion. He had to pay €8,000 for repairs.
Recourse and Guarantees: What You Can Demand
The one-year warranty for perfect completion (garantie de parfait achèvement) covers defects of conformity, including soundproofing. The standard NF S 31-057 (paragraph 5.2) and DTU 20.1 (paragraph 6.2) are enforceable. Send a registered letter with acknowledgment of receipt (LRAR) to the developer with your measurements. If they refuse, file a claim with the Grasse judicial court. An acoustic expert (like me) can carry out a joint inspection. In Antibes, I obtained €12,000 in damages for a similar defect. Do not delay.
📅 Mis à jour le 20/08/2026 — Par Cassini Expertise, expert bâtiment indépendant 06 & 83. Devis gratuit : 04 22 46 06 04.
Questions fréquentes
What are the legal guarantees for soundproofing in off-plan sales in France?
In France, off-plan sales (vente en l'état futur d'achèvement) are covered by the 'garantie de parfait achèvement' for one year after delivery, which requires the developer to fix any non-conformities, including soundproofing defects. After that, the 'garantie biennale' covers equipment for two years, and the 'garantie décennale' covers structural issues for ten years. If soundproofing fails to meet the acoustic regulations (NRA), you can claim under these guarantees.
How can I measure soundproofing in an apartment myself?
You can use a sound level meter (decibel meter) to measure the noise level in your apartment when a neighbor makes noise, but for accurate results, it's best to hire a professional acoustic engineer who will conduct standardized measurements (e.g., tapping machine or airborne noise) according to ISO standards. They can compare the results with the French acoustic requirements (NRA) to determine if the insulation is faulty.
Can I sue the developer for faulty soundproofing in a new apartment?
Yes, you can sue the developer for non-conformity or hidden defects (vices cachés) if the soundproofing is defective. You must act within the legal time limits: for the 'garantie de parfait achèvement', you have one year after delivery; for hidden defects, you have two years after discovery, but no later than five years after delivery. It's advisable to send a formal notice (mise en demeure) and gather evidence before taking legal action.