How Living Surface Is Calculated in France: The Carrez Law, Boutin Law and What Buyers Need to Know in 2026

When you view a French apartment listing, the advertised living surface number is probably one of the first pieces of information you notice — alongside the bedroom count and the asking price. What is less obvious is that French property law uses a specific and legally-defined method for calculating that living surface, and the method is materially different from what most UK and international buyers intuitively assume. The loi Carrez (Carrez Law) and the loi Boutin (Boutin Law) define exactly what counts as living surface in different legal contexts, and understanding the difference matters for everyone buying, selling or letting French property — particularly in the Alpine property market where ski-in ski-out apartments often have interesting geometry with sloped ceilings, mezzanine levels and basement storage areas.

The Carrez Law was introduced in 1996 with the specific purpose of protecting apartment buyers from misleading or exaggerated surface measurements. It applies to the sale of any apartment in a co-owned building (copropriété), which covers essentially all French apartments. The Boutin Law was introduced in 2009 and applies to residential rental contracts, using a slightly different surface definition. Both laws exist alongside the unofficial ‘surface habitable’ concept used in casual real estate marketing, and the three measurements can produce meaningfully different numbers for the same property.

This guide sets out the detailed rules for calculating living surface under French law, the practical differences between Carrez, Boutin and marketing-level ‘surface habitable’, why the differences matter for buyers, how the measurement is verified and legally protected, what to do if you think a measurement is wrong, and the specific issues that affect French Alpine property where architectural features like sloped ceilings and ski-storage spaces can produce unusual measurement outcomes. It is the technical guide every serious French property buyer should read before signing their first compromis de vente.

The Carrez Law applies to all apartment sales within a copropriété (co-owned building) and defines the ‘superficie privative Carrez’ that must be stated in the sale contract. The rule is straightforward in principle but has specific exclusions and edge cases that matter in practice. The Carrez surface is calculated as the total floor area inside the private portion of the apartment, measured from the inside of the walls, minus specific exclusions including walls and partitions, stairs and stair wells, openings for windows and doors, and any area with a ceiling height below 1.80m.

The 1.80m ceiling height rule is the most practically significant exclusion and has direct impact on Alpine properties where sloped ceilings under the roof are common. Any area where the ceiling height is below 1.80m does not count towards the Carrez surface, even if the floor is fully usable (for example, for sleeping or storage). This can produce significant differences between the total physical floor area of an apartment and the legally-defined Carrez surface — a top-floor apartment with a sloped ceiling might have 85m² of physical floor area but only 65m² of Carrez surface if substantial areas are below the 1.80m threshold.

Other Carrez exclusions include basement cellars (caves), garages, parking spaces, attics (combles) that are not converted to habitable use, terraces and balconies, verandas and conservatories, and any annex spaces that are physically separate from the main apartment. These spaces are all part of what the buyer is purchasing and they contribute to the overall value of the property, but they do not count towards the Carrez surface figure that appears in the sale contract. A Carrez surface of 75m² may represent a property with total usable area of 100m² once basement storage, balcony and covered terrace are included.

The legal significance of the Carrez measurement is substantial. If the actual Carrez surface of the apartment turns out to be more than 5% smaller than the surface stated in the sale contract, the buyer has the right to a proportional reduction in the purchase price. This remedy is specifically created by the Carrez Law and gives buyers genuine legal protection against misrepresentation of apartment size. The seller is required to engage a qualified surveyor (géomètre-expert or similar) to measure the Carrez surface before sale, and the measurement certificate must be attached to the sale documentation.

The Boutin Law applies to residential rental contracts in France and uses a slightly different living surface definition from the Carrez Law. The ‘surface habitable Boutin’ is calculated similarly to Carrez but with some additional exclusions — notably, the Boutin measurement also excludes any enclosed technical spaces such as boiler rooms, as well as certain areas that are outside the core living function of the apartment. The Boutin measurement is typically 2-5% smaller than the Carrez measurement for the same apartment.

The practical significance of the Boutin Law is primarily for residential rental contracts and for rental property marketing. Landlords must state the Boutin surface in residential rental contracts, and rental pricing calculations (rent per square metre) typically use the Boutin surface rather than the Carrez surface. For buyers who plan to let their property on long-term residential rental contracts, understanding the Boutin surface is important for setting rental rates and for ensuring contract compliance with French rental law.

For Alpine property buyers, the Boutin measurement matters primarily for apartments that will be used for long-term residential rental (for example, commuter-belt apartments in Saint-Gervais or Samoëns that are let to year-round residents under long-term contracts). For apartments used primarily for short-term holiday rental (tourist rental under tax-classified meublé de tourisme frameworks), the Boutin measurement is less directly significant because the rental contracts are under a different legal framework. However, it is still useful to understand both measurements to avoid confusion between different surface numbers on the same property.

When a property is marketed for sale with both Carrez and Boutin measurements, buyers should look carefully at both numbers and understand why they differ. A meaningful difference (more than 2-3%) typically indicates specific technical spaces or layout features that reduce the Boutin figure below the Carrez figure. The surveyor’s measurement certificate will typically explain the exclusions applied to each calculation, and reviewing this certificate is worthwhile for buyers wanting full clarity on what they are actually purchasing.

Alongside the legally-defined Carrez and Boutin measurements, French property marketing often references a more general ‘surface habitable’ figure that may or may not match the technical definitions. This informal measurement sometimes includes areas that are excluded from Carrez and Boutin (for example, storage rooms or mezzanine levels with ceiling heights below 1.80m), and buyers looking at marketing materials should not assume that the advertised surface habitable matches the legally binding Carrez number. The difference can be material and affects the perceived value of the property.

A common pattern in Alpine property marketing is to advertise a generous ‘surface habitable’ number that includes useful storage or mezzanine spaces, and then have a smaller Carrez measurement when the legal survey is performed. This is not necessarily dishonest — the usable areas are genuinely part of the property and contribute to the value — but it means buyers should ask specifically for the Carrez measurement before committing to a price. The marketing number tells you about total useful space; the Carrez number tells you about the legally-defined living surface. Both matter, but they tell you different things.

Best practice for buyers is to explicitly request the Carrez measurement certificate (attestation Carrez or mesurage Carrez) as part of the pre-purchase due diligence, alongside the other standard French property sale documentation. The certificate will state the precise Carrez surface, describe the exclusions applied, and will be dated and signed by the qualified surveyor who performed the measurement. This is a legally-required document and should be available to any serious buyer before the compromis de vente is signed.

If the marketing figure and the Carrez figure differ significantly, buyers should understand why. A 10-15% difference is not uncommon for apartments with substantial mezzanine or sloped-ceiling areas, and is usually legitimate. A larger gap may indicate concerns about how the property has been marketed, and in some cases may warrant a direct conversation with the selling agent or the seller’s notaire to clarify the measurement basis. Experienced French property specialists can help buyers interpret the measurements and identify any genuine concerns.

French Alpine apartments often have architectural features that create interesting measurement challenges. The most common is the sloped ceiling under a traditional chalet-style roof, which may create substantial usable floor area that falls below the 1.80m Carrez threshold. Top-floor apartments in particular often have significant areas excluded from the Carrez measurement due to the roof slope, and buyers should expect these apartments to have Carrez surfaces that are materially lower than the physical floor area.

Mezzanine levels are another common feature that affects measurement. Many Alpine apartments have upper mezzanines used as sleeping or study spaces, and whether these count towards the Carrez surface depends on the specific ceiling height in the mezzanine area. Full-height mezzanines (1.80m or more throughout) typically count fully; partial-height mezzanines count only for the portion above the 1.80m threshold. Buyers should ask for a clear explanation of how mezzanine areas have been treated in the Carrez certificate.

Ski storage and boot rooms are another Alpine-specific consideration. These are functionally important spaces for the intended use of the property, but they are typically excluded from the Carrez measurement because they are classified as annex storage rather than living surface. A buyer who is heavily weighting a property’s appeal on the size and quality of the ski storage area should recognise that this space contributes to the value and usability of the property but does not show up in the Carrez number.

Balconies and terraces, which are among the most desirable features of Alpine apartments, are entirely excluded from the Carrez measurement. A large south-facing balcony with mountain views might be one of the key reasons a buyer is choosing a specific apartment, but it does not appear in the Carrez surface number. This is not a problem but buyers should understand that the Carrez number is not a complete measure of the overall appeal and usability of the property — it specifically measures the enclosed interior living area above the 1.80m ceiling threshold.

The Carrez measurement is legally required to be performed by a qualified professional — typically a géomètre-expert (land surveyor) or a similar qualified technical professional with recognised French credentials for property measurement. The professional must follow the specific measurement methodology defined in the Carrez Law and must provide a dated and signed certificate stating the measurement result and the exclusions applied. This certificate is a core document in the French property sale process and should be available to any serious buyer during the pre-purchase due diligence phase.

If a buyer has concerns about the accuracy of a Carrez measurement, they have the right to commission their own independent measurement through a separate qualified surveyor. This is relatively rare in practice but is a legitimate option for buyers who have specific reasons to doubt the seller’s measurement. The cost of an independent measurement is typically €300-€800 depending on the size and complexity of the apartment, and the timeframe from commissioning to certificate is usually 1-2 weeks.

The legal remedy for a Carrez measurement that proves to be more than 5% smaller than the stated figure in the sale contract is a proportional reduction in the purchase price. This means that a buyer who discovers after completion that their apartment is significantly smaller than stated can demand a refund calculated as the proportional overstatement applied to the purchase price. The remedy must be claimed within one year of the signing of the acte de vente, and the process typically involves the buyer commissioning an independent measurement to document the discrepancy.

In practice, successful Carrez refund claims are rare because the sale-side measurement is usually accurate and any discrepancies are typically within the 5% tolerance. However, the existence of the legal remedy creates strong incentives for sellers and their agents to provide accurate measurements, and the Carrez framework has materially improved the reliability of French apartment surface information since its introduction in 1996. For most buyers, the framework works well and delivers the intended buyer protection without requiring active use of the remedy.

Price per square metre is one of the most commonly used comparison metrics in French property, and the specific surface measurement used in the calculation affects the comparison. Professional valuations typically use Carrez surface as the denominator for price-per-m² calculations on apartment sales, producing a consistent and comparable figure across the market. This means that when you see price-per-m² figures in market reports, they are usually based on Carrez measurements rather than informal marketing figures.

For apartments with unusual geometry (sloped ceilings, multiple mezzanine levels, large annex spaces), the Carrez-based price-per-m² figure may look higher than expected because significant usable space is excluded from the denominator. A €750,000 apartment with 75m² Carrez but 95m² total usable area has a Carrez price-per-m² of €10,000 but a total-usable price-per-m² of €7,900. Both numbers are meaningful — the Carrez figure is the standard market comparison, and the total usable figure is the practical cost per square metre of what you actually get to use.

Buyers comparing apartments across different geometry profiles should look at both measurements to understand the true comparative value. A central Les Gets apartment with 80m² Carrez and 100m² total usable area might offer better value than a central Morzine apartment with 85m² Carrez and 88m² total usable area, even if the Les Gets Carrez price-per-m² looks higher on first comparison. The full picture requires understanding both the Carrez measurement and the total usable area.

For rental yield calculations, the effective denominator is typically the total usable area rather than the Carrez measurement, because rental guests use the full usable space (including mezzanines with lower ceilings, sloped ceiling areas etc) without distinguishing based on the legal measurement definition. This means that rental yield calculations based on Carrez surface only may understate the true yield on apartments with significant non-Carrez usable space, and buyers should ensure that yield analyses use meaningful denominators for their specific property profile.

The most important practical step for buyers is to explicitly request and review the Carrez measurement certificate before signing the compromis de vente. This certificate should be provided by the seller as part of the standard French property sale documentation pack (dossier de diagnostic technique), alongside the energy performance certificate (diagnostic de performance énergétique or DPE), the lead paint survey (for older buildings) and several other required documents. A sale without a valid Carrez certificate should not proceed.

Buyers should compare the Carrez measurement against any marketing figures for the property and understand the source of any differences. A modest difference (less than 5%) is normal and reflects the technical exclusions of the Carrez framework. A larger difference warrants a conversation with the selling agent or the seller’s notaire to understand the basis of the marketing figure and confirm there are no concerns about how the property has been presented.

For apartments with unusual architectural features — sloped ceilings, mezzanines, multi-level layouts — buyers should specifically ask how these features have been treated in the Carrez measurement and whether the exclusions are documented in the measurement certificate. This information is important for understanding the practical usability of the apartment and for comparing across different candidate properties during the shortlisting phase.

Finally, buyers should understand that the Carrez measurement is a technical legal definition and does not fully capture the practical usability or appeal of a property. A smaller Carrez surface with excellent layout, great views and premium specification may be a better buy than a larger Carrez surface with poor layout or compromising features. Experienced French property specialists help buyers understand the measurements in context rather than as isolated numbers, and the Domosno team walks every buyer through the surface measurement interpretation as part of the pre-purchase due diligence process.