Selling or buying a property means understanding the different methods used to calculate area: pricing, taxation, planning permissions and listings rely on accurate square meters. Living area, carrez law area, private area and floor footprint each follow distinct legal definitions. This guide explains the step by step calculation methods to help you enhance your property value, avoid disputes and secure your transactions. Keep reading to master these essential concepts.
Why do different area measurements exist in real estate?
Depending on whether you are selling, renting, building or declaring your property to the tax authorities, the calculation method changes. That is why the construction and housing code defines several measurement standards, governed by different legislative texts, including the 2009 law on housing mobilisation and the fight against exclusion.
Living area is used for rentals and for calculating certain tenant benefits. Carrez area (or private area) is mandatory for condominium sales. Usable area and corrected area are used in social housing and taxation. Finally, floor area and floor footprint frame planning permissions such as building permits.
Understanding these distinctions helps you avoid disputes, ensures your listings are compliant and helps you value your property at the right price.
The 6 main area measurements and when to use them
Living area (boutin law): unfurnished rental, energy performance certificate
Carrez area (private): sale of condominium units
Usable area / corrected area: social housing, housing benefits
Net internal floor area (shon): former planning reference (until 2012)
Floor area: building permit, prior works declaration
Floor footprint (emprise): footprint calculation for planning
Living area: definition, included rooms and boutin calculation
Legal definition: article r111-2 and the boutin law
A dwelling’s living area is defined by article r111-2 of the construction and housing code. It corresponds to the built floor area after deducting the areas occupied by walls, partitions, steps and stairwells, ducts, and door and window reveals.
This definition is the legal basis for the boutin law, which has required this area to be stated in any unfurnished main residence lease contract since 2009. The purpose of this regulation is to protect tenants by ensuring transparent information about the space actually available for everyday living.
Which rooms count and what is the minimum ceiling height?
To calculate living area correctly, you must include only living spaces where the ceiling height reaches at least 1.80 m. Built in closets count if they meet this height requirement and if their floor is level with the room floor. Heated laundry rooms that are accessible from inside the home are also included.
Rooms included
Bedrooms, living room, lounge: all main living spaces
Kitchen: whether open plan or separate
Dining room: if separate from the main living room
Bathroom and toilet: sanitary areas within the dwelling
Hallways and internal circulation areas
Converted attic space: if height is at least 1.80 m
Rooms excluded
Cellars, basements and garages: storage or parking areas
Conservatories and unheated glazed volumes: non permanent extensions
Balconies, terraces and loggias: outdoor areas
Unconverted attics and loft spaces: storage areas
Unheated storage rooms and unheated utility rooms: external annexes
This distinction is essential to avoid confusion with other regulated area measurements.
Steps to calculate the living area of a house
Start by measuring the length and width of each eligible room, then multiply these dimensions to obtain the area of each space. Add up all these areas to obtain the total living area.
Deduct the areas occupied by walls, partitions, stair steps, technical ducts, and door and window reveals. Also exclude any zones where the ceiling height is below 1.80 m, especially under sloping roofs.
The formula can be summarized as follows:
Living area = sum of room areas (height at least 1.80 m) minus deductions (walls, stairs, reveals).
Mandatory mention and accepted margin of error
For a rental, stating the living area in the lease is mandatory. You can do the measurement yourself or use a certified surveyor to ensure a reliable measurement.
The law allows a 5% margin of error. If the actual area is more than 5% smaller than the area stated in the lease, the tenant can demand a proportional reduction in rent. In condominium sales, a similar error on the carrez area can lead to a reduction in the sale price.
To avoid these issues, consider contacting an Optimhome advisor or real estate agent who can guide you through the steps and direct you to the right professionals.
Carrez law private area: rules, exclusions and penalties
Units concerned in condominium properties
The carrez law applies to all condominium units offered for sale, whether apartments, commercial premises or professional units. This obligation applies only to properties under vertical or horizontal condominium status.
Individual houses not subject to condominium regulations are not covered. You must state the carrez area in the preliminary sales agreement and in the final deed, otherwise the deed may be void.
Carrez measurement: attics, mezzanines and stairs
Carrez area is calculated by measuring the floors of enclosed and covered spaces. You must measure the area of each element (rooms, attics, mezzanines), then deduct the areas occupied by walls, partitions, steps and stairwells, ducts, and door and window reveals.
Only parts with a ceiling height of at least 1.80 m are counted. Convertible attics and mezzanines are included if they meet this minimum height. However, the following are excluded from carrez area: storage spaces such as cellars, garages, parking spaces, terraces, balconies, loggias and unenclosed conservatories.
Consequences of an error on the sale price
In the event of a measurement error, the law provides a 5% tolerance. If the actual area is more than 5% smaller than the area stated in the deed, the buyer can bring an action to reduce the sale price proportionally to the difference found.
This action must be brought within one year from the signing of the final deed. To secure the transaction and avoid disputes, it is strongly recommended to use a chartered surveyor or a certified professional to carry out the carrez measurement.
Usable area and corrected area: benchmarks for renting and social housing
Difference between living area and usable area
Usable area complements living area by adding 50% of the area of the dwelling’s outbuildings reserved for the occupant’s exclusive use.
These annexes include cellars, storage rooms, balconies, accessible upper floor terraces, drying rooms, sheds and parts of annex rooms with a ceiling height greater than 1.80 m, within a limit of 9 m² per dwelling. This concept, defined by article r.353-16 of the construction code, makes it possible to assess more precisely the practical value of a property, notably in social housing where it is used to calculate capped rents.
Usable area therefore makes it possible to value certain annex spaces which, although excluded from living area, improve occupants’ comfort.
Corrected area: calculation method
Corrected area corresponds to living area to which correction coefficients are applied, taking into account maintenance condition, equipment and the dwelling’s situation. Historically used for social housing rents before 1996, it has since been replaced by usable area in most social housing schemes.
Note that renovation works can change a property’s usable area by transforming annexes or converting attics, which directly affects rent calculations or the valuation of the dwelling.
Floor area: key differences compared with living area
Floor area and living area serve different purposes. Living area measures the space actually usable every day inside a home, while floor area is mainly used for planning permissions and local taxation.
Defined by the planning code, it includes all enclosed and covered areas, calculated from the internal face of the façades, including attics, cellars and parking areas. Unlike living area, it is not limited to rooms used for day to day living.
How to calculate floor area
To calculate floor area, add up the areas of all enclosed and covered levels of your construction, measured from the internal face of the façade walls. You must then deduct the thickness of external walls and partitions, voids and stair openings, as well as covered parking areas.
Since 2012, the calculation also takes into account the thickness of insulation materials, which you must deduct to encourage energy performance. This deduction supports construction or renovation projects using enhanced insulation, without reducing the permitted area.
Impact on planning permissions
Floor area directly determines the type of permission required for your works. A prior works declaration is sufficient for projects creating up to 40 m² of floor area in an urban zone covered by a local planning plan.
Above this threshold, or from 20 m² if the total floor area of the building exceeds 150 m², a building permit becomes mandatory. These thresholds strictly frame extensions, upward additions and new builds, making accurate floor area calculation essential before any project.
Criterion
Living area
Floor area
Purpose
Rental, energy diagnosis
Planning permissions, taxation
Included spaces
Rooms used for living with height at least 1.80 m
All enclosed and covered levels
Deductions
Walls, stairs, reveals
Walls, insulation, voids, parking
Regulatory threshold
Mandatory in rental lease
40 m² prior declaration / 150 m² building permit
Annexes conservatory basements garages do they count in living area?
Elements always excluded
Regulations systematically exclude several categories of annexes from the calculation of living area under the boutin law. Cellars, unconverted basements, garages and parking spaces are never included, even if their height exceeds 1.80 m, because they are not everyday living spaces.
Terraces, balconies, loggias and conservatories are also excluded, as these glazed or outdoor volumes are not considered permanently enclosed and heated. The shon, a former planning concept replaced in 2012 by floor area, also included these annexes.
Annexes excluded from the calculation
Cellars, basements and garages: storage and parking spaces
Terraces, balconies, loggias: open outdoor areas
Conservatories and unheated glazed volumes: seasonal extensions
Unconverted attics and loft spaces: raw storage areas
Special cases closet laundry room balcony
Some internal spaces require a more nuanced interpretation. A built in closet or storage space inside the dwelling is included in living area if its ceiling height is at least 1.80 m and it is accessible without going outside.
Likewise, an internal laundry room used daily and meeting the height requirement is included in the calculation. However, a balcony or loggia, even if enclosed, remains excluded because it does not meet the requirements of being permanently enclosed and covered living space.
To avoid confusion when renting or selling, always check these criteria or use a certified professional.
Living area error and property tax what are the consequences?
Financial risks linked to an incorrect area
An incorrect living area declared to the tax authorities leads to an incorrect property tax assessment, which is based on the cadastral rental value that takes into account the dwelling’s surface area.
If the tax authorities identify an underestimated area (undeclared extension, omitted converted attic), you may face a tax reassessment going back up to four years, with penalties from 10% to 40% depending on how the error is classified. Conversely, an overestimated area makes you pay more tax every year than you actually owe.
How to correct an area error
To correct an inaccurate area, you must file an amended declaration with the property tax office responsible for your property, ideally by registered letter with acknowledgement of receipt.
Attach the necessary supporting documents: measurement carried out by a chartered surveyor, plans, and the notarial deed stating the legal area. You have one year from receiving the property tax notice to challenge it. If the actual area is smaller than the area used, the tax authorities will refund the overpayment for the current year.
FAQ about living area
Is a balcony included in living area?
No, a balcony is not part of living area. Like terraces, loggias and unenclosed conservatories, it is excluded because it is not an enclosed and heated space. Living area only includes interior rooms where the ceiling height is at least 1.80 m. However, these annexes may be valued in usable area for certain calculations related to social housing.
Does a garage count in living area?
No, a garage is systematically excluded from living area, whatever the type of property. The same applies to cellars, basements, storage rooms and parking spaces, which are considered annexes. These spaces do not meet the criteria for habitable living rooms defined by the construction code. They can, however, be listed separately in property listings and contribute to the overall value of the property.
Are toilets included in living area?
Yes, toilets are included in the calculation of living area, just like the kitchen, bathroom, bedrooms and hallways. As long as the ceiling height is above 1.80 m and it is an enclosed and heated space that is an integral part of the dwelling, toilets are included. This rule applies to rentals as well as property diagnostics.
Where can I find the living area declared to the tax authorities?
You can view your property’s area in your public finances online account on impots.gouv.fr, under manage my properties. The area declared to the tax authorities is measured on the floor between walls or partitions, rounded down to the nearest square meter, and is used to calculate the cadastral rental value for property tax. If works change the surface area, you must update your declaration via the secure messaging system in your personal account.
What living area is required depending on the number of people?
Article r111-2 of the construction and housing code sets a minimum area of 14 m² and a habitable volume of 33 m³ per person for the first four occupants when establishing a construction program. Beyond the fourth occupant, you should plan an additional 10 m² and 23 m³ per person. For renting, a dwelling must offer at least 9 m² with a ceiling height of 2.20 m, or 20 m³ of habitable volume.
