Floor area: the declaration error that undermines a permit and the usability of the project

An investor who takes over an office building restructured in the 2010s discovers, three months after signing, that the mezzanine level used as a work floor was never included in the floor area declared in the building permit. The asset is let, its valuation rests on those square metres, and the planning file does not allow them to be regularised without revisiting the parking ratio imposed by the local urban plan (plan local d'urbanisme, PLU). The calculation error was a few dozen square metres; the economic exposure, for its part, lies in the capitalised rent of the area concerned and in the ability to sell the asset without a discount. This guide sets out the method for calculating floor area (surface de plancher) under Article L. 111-14 of the French Urban Planning Code, the most frequent declaration errors, the consequences of under-declaration (withdrawal, annulment in litigation, criminal penalty, tax reassessment) and the routes to regularisation. It is written from the standpoint of the person who buys, restructures or finances: the question is not only whether the permit was obtained, but whether the asset will remain usable over the long term.

What floor area measures: legal definition and scope (Arts. L. 111-14 and R. 111-22 of the French Urban Planning Code)

Floor area replaced net floor area (SHON) and gross floor area (SHOB) by Ordinance No. 2011-1539 of 16 November 2011, which came into force on 1 March 2012. Its definition now appears in Article L. 111-14 of the French Urban Planning Code.

The floor area of a building means the sum of the enclosed and covered floor areas, under a ceiling height greater than 1.80 m, calculated from the interior face of the building's façades.

Three cumulative criteria emerge from this text: the enclosed and covered character, a ceiling height greater than 1.80 metres, and measurement from the interior face of the façades. This last point is the major break with SHON, which was calculated on an external basis. An operator who reuses an old area survey without recalculating it automatically includes the thickness of the façade walls and overstates its floor area, or, conversely, applies SHON deductions that no longer exist.

Article R. 111-22 of the French Urban Planning Code then lists the deductions. They are exhaustive:

• the thickness of the walls surrounding the reveals of doors and windows opening onto the exterior;
• the voids and openings for staircases and lifts;
• areas under a ceiling height of 1.80 metres or less;
• areas fitted out for vehicle parking, including access ramps and manoeuvring areas;
• attics that cannot be converted for residential use or for professional, craft, industrial or commercial activity;
• technical rooms necessary for the operation of a group of buildings or of a building other than a detached house, including waste storage rooms;
• cellars and storerooms ancillary to dwellings, provided they are served only by a common area;
• a flat-rate share of 10% of the areas used for residential purposes, where the dwellings are served by internal common areas.

Not confusing the six areas of one and the same building

A Parisian building is described at the same time by several areas that never coincide. Confusion between them is the leading cause of errors in declaring floor area.

Floor area belongs to planning law and conditions the authorisation. Ground coverage (emprise au sol), defined in Article R. 420-1 of the French Urban Planning Code, is the vertical projection of the volume of the building: it governs other thresholds, notably as regards the coverage coefficient and environmental assessment. Taxable area, the basis for the development tax (taxe d'aménagement), now governed by Articles 1635 quater A et seq. of the French General Tax Code since the transfer of its administration to the DGFiP (the French public finance directorate) by Ordinance No. 2022-883 of 14 June 2022, follows the interior-face logic but does not allow the same deductions: enclosed and covered parking areas remain taxable, as do cellars, and the flat-rate allowance for residential use does not apply. Habitable area (surface habitable), defined in Article R. 156-1 of the French Construction and Housing Code, relates to residential leases. The private area known as Carrez area, which stems from Law No. 96-1107 of 18 December 1996, concerns the sale of co-ownership (copropriété) lots. Finally, lettable usable area, often calculated according to professional standards, serves for marketing but has no administrative significance.

Practical consequence: a compliant Carrez certificate says nothing about planning regularity. A lease signed on a usable area greater than the authorised floor area is a warning sign, not proof.

Calculation method: the five steps to carry out in order

The calculation of floor area is not a single measurement but a sequence. Any inversion of steps produces a discrepancy.

First step: delimit the enclosed and covered volumes. An uncovered terrace, a balcony, an open loggia, a canopy or a covered yard does not generate floor area. By contrast, the subsequent enclosure of a loggia or the covering of a courtyard creates floor area, even without any extension of ground coverage. This is one of the recurring sources of non-compliance in older buildings restructured in successive lots.

Second step: measure from the interior face of the façades, level by level. Internal load-bearing walls, partitions and posts are not deducted. Only the thickness of the walls surrounding the reveals of openings onto the exterior is deducted. Mezzanines, intermediate floors and technical platforms are levels in their own right provided they are enclosed, covered and have sufficient headroom.

Third step: exclude areas under 1.80 metres. In attics and under sloping roofs, this requires a survey of heights and not a flat-rate estimate. The plans must show the 1.80 metre line. A file that relies on a percentage allowance for attic space is vulnerable.

Fourth step: apply the deductions of Article R. 111-22, and only those. Each deduction is subject to a strict condition. Cellars are deducted only if they are served exclusively by a common area: a cellar accessible from a dwelling remains floor area. Technical rooms are deducted only if they serve a group of buildings or a multi-occupancy building, not a detached house. Attics are deducted only if they are genuinely not convertible, which is assessed by reference to the structure and the access, not the declared use. The 10% allowance requires service by internal common areas and applies only to the portion used for residential purposes.

Fifth step: break down the areas between those created, demolished and existing areas retained, by use category and sub-category. The Cerfa permit application forms require this breakdown, which must tie in with the use categories and sub-categories of Articles R. 151-27 and R. 151-28 of the French Urban Planning Code, as clarified by the Order of 10 November 2016 as amended. In a major restructuring, it is this breakdown, and not the total, that determines the application of the PLU rules: ceilings by use category, parking obligations, and the social mix requirements of Article L. 151-15 of the French Urban Planning Code.

The most frequent declaration errors and how they work

A good-faith error and a deliberate understatement produce the same legal effects, with one decisive nuance: fraud deprives the applicant of the benefit of the time limits.

The first family of errors stems from the reuse of an old area survey. Operations on buildings authorised before March 2012 involve files expressed in SHON. Mechanical carry-over, without recalculation from the interior face, distorts the base and, above all, distorts the calculation of the area created in an extension or an additional storey.

The second family stems from deductions applied outside their conditions. Deducting a technical room in a detached house, deducting attics that are in fact served by a fixed staircase, applying the 10% allowance to dwellings served by external walkways, deducting a car park part of which is in fact fitted out as a storage room: each of these approximations understates the declared area.

The third family, the most costly in a restructuring, stems from the change of use of an area previously deducted. Converting a basement car park into a gym, an archive room or a catering space brings back into floor area square metres that had been excluded as parking. The operation therefore creates floor area without touching the built volume. The same reasoning applies to the conversion of attics or the transformation of cellars. The applicable formalities and the obstacles specific to this type of operation are set out in our article on the change of use of a property asset.

The fourth family stems from unanticipated threshold crossings. Floor area governs the authorisation regime: above the thresholds of Articles R. 421-14 and R. 421-17 of the French Urban Planning Code, an extension moves from a prior declaration to a building permit. For an individual building for their own use, recourse to an architect becomes compulsory above 150 m² of floor area, a threshold lowered by Law No. 2016-925 of 7 July 2016 and Decree No. 2016-1738 of 14 December 2016. An under-declaration that artificially keeps the project below a threshold undermines the authorisation in its very nature: it is no longer a calculation defect, it is an authorisation issued under an inapplicable regime.

Consequences of under-declaration: withdrawal, litigation, criminal law, tax

Administrative withdrawal and the exceptional regime for fraud

Article L. 424-5 of the French Urban Planning Code strictly limits withdrawal: a permit, whether tacit or express, may be withdrawn only if it is unlawful and within three months of its issue. After that period, it may be withdrawn only at the request of the beneficiary. This safeguard protects the good-faith operator.

It falls away in the event of fraud. The administrative case law has long accepted that a decision obtained by fraud may be withdrawn at any time, with no time limit. A deliberate understatement of floor area intended to escape a PLU rule, an authorisation threshold or a parking obligation falls within this scope. The evidential issue then shifts to intent: an isolated, explicable discrepancy on one side, a systematic discrepancy relating precisely to the parameter that triggers a constraint on the other.

Third-party litigation and the display of the permit

The time limit for third-party appeals is two months from the first day of continuous display of the permit on the site, under Article R. 600-2 of the French Urban Planning Code. The mandatory particulars on the sign, set by Articles A. 424-15 et seq., include the authorised floor area. The administrative case law holds that the particulars on the sign must enable third parties to assess the scale and nature of the project. An erroneous or missing floor area may thus deprive the display of its triggering effect and leave the appeal period open well beyond the two months expected. On the role of display in triggering the bar on appeals and the third party's decision timetable, see our analysis of consulting a building permit application that has been filed.

For an investor, the consequence is direct: a permit displayed for more than two months is cleared of challenge only if the display is regular and accurate. The bailiff's report (constat d'huissier) produced in the data room must be read together with the plans, not merely filed. Article R. 600-3 of the French Urban Planning Code nevertheless provides a long-stop: no action for annulment is admissible once six months have elapsed from completion of the building.

Criminal penalties based on the square metre

Article L. 480-4 of the French Urban Planning Code penalises carrying out works without authorisation or not in conformity with the authorisation issued. The fine is between €1,200 and an amount that may not exceed, in the case of the construction of floor area, a sum equal to €6,000 per square metre of area built, demolished or rendered unusable, and €300,000 in other cases. In the event of a repeat offence, a six-month prison sentence may be added. The basis is therefore the irregular square metre itself: the under-declaration determines both the offence and the amount.

To this are added the restitution measures of Article L. 480-5 (bringing into conformity or demolition) and, on the civil side, the demolition action of Article L. 480-13, open to a third party who suffers harm, in the zones exhaustively listed, provided that the permit has first been annulled for abuse of power and that the action is brought within two years of that annulment becoming final.

The tax aspect

The area declared in the permit feeds into the assessment of the development tax and, in the Île-de-France region, of the tax on the creation of offices, commercial premises and storage premises under Articles L. 520-1 et seq. of the French Urban Planning Code. An understatement exposes the taxpayer to a reassessment with interest and, where applicable, surcharges. In a Parisian office operation, this reassessment is not marginal: it is calculated on a per-square-metre basis and concerns an asset whose real area is, by hypothesis, greater than the area declared.

Regularising: which routes, in what order, on what timetable

The question is never "can one regularise" in the abstract, but "can one regularise the project as it is used, in light of the planning rules applicable on the date of regularisation".

Before completion, the amending permit. It presupposes that the building is not yet completed. The administrative case law has significantly widened its scope: substantial changes may be authorised by an amending permit provided the project is not overturned in its general design. An adjustment of floor area falls within this scope, provided that the new area remains compliant with the PLU rules, in particular as regards density, massing, parking and social mix. The conditions of admissibility of the amending permit and the boundary with the refiling of a new permit are dealt with separately in our article on the amending building permit during construction.

During proceedings, regularisation under the supervision of the judge. Article L. 600-5 of the French Urban Planning Code allows the judge to order a partial annulment limited to the defective part of the project. Article L. 600-5-1, in the wording resulting from the ELAN Law No. 2018-1021 of 23 November 2018, requires the judge, where a defect can be regularised, to stay the proceedings so that a regularisation permit may be produced. A defect relating solely to floor area is frequently held to be capable of regularisation. This mechanism favours the operator, but it freezes the operation for the whole duration of the stay.

After completion, the ordinary-law regularisation permit. It is examined under the rules in force on the date of the application, and not those applicable to the initial permit. This is the economic tipping point: a PLU revised since, a more restrictive safeguarding and enhancement plan, or a new easement may make an area impossible to regularise that could have been regularised ten years earlier.

The administrative limitation period of Article L. 421-9. Where a building has been completed for more than ten years, the refusal of an authorisation cannot in principle be based on the irregularity of the original building. The exceptions are decisive and must be checked one by one, in particular the one that removes the benefit of the limitation period where the building was constructed without any permit. In other words, works not in conformity with a permit that was obtained are covered after ten years; a building erected without authorisation is not. This distinction governs the whole audit strategy on an older asset. Moreover, the administrative limitation period does not extinguish the criminal offence on the same timetable, the public prosecution of the offence being time-barred six years from completion of the works.

The compliance inspection and the certificate of non-objection. The declaration certifying completion and conformity of the works (DAACT) under Article R. 462-1 gives the authority a three-month period to object, extended to five months in the cases of compulsory inspection referred to in Articles R. 462-6 and R. 462-7. The certificate attesting the absence of objection is the document that every purchaser must require. Its absence is not a missing formality: it is a sign that conformity has never been cleared.

The real exposure in a restructuring or asset takeover operation

For an investor, an error on the floor area of a building permit is not a planning matter. It is a matter of valuation, financing and leasing.

Valuation rests on let square metres. If a portion of those square metres is not authorised, it is not lasting. The corresponding rent is capitalised in the acquisition price although it is legally precarious. The discount does not appear on acquisition; it appears on resale, when the next purchaser carries out a more demanding audit, or on renewal, when the disputed area has to be removed from the base of the lease.

The lease is the second point of exposure. Article 1719 of the French Civil Code requires the landlord to deliver premises that allow the agreed use. A tenant faced with an administrative impossibility of using part of the premises has levers: the defence of non-performance (exception d'inexécution), a rent reduction, termination at the landlord's fault, and a claim for damages. In a commercial lease, the question is compounded by an issue of permitted use and of ERP (public-access building) compliance where the disputed area receives the public.

Financing is the third point. Institutional lenders make drawdown conditional on production of the permit, the DAACT and the certificate of non-objection. An area irregularity identified during the life of the loan may trigger a default clause or a remediation obligation, at the very moment when the asset faces an energy capex need.

What to require in due diligence

The planning audit is not limited to the existence of a permit. The verification covers the consistency of a chain:

• the initial permit, all amending permits and any prior declarations, with the plans stamped by the authority;
• the DAACT and the certificate of non-objection to conformity, or proof that the inspection period has expired;
• the display report and the clearing of appeals, including as regards the accuracy of the particulars on the sign;
• an adversarial survey of the existing floor area, recalculated under Article R. 111-22 and compared with the authorised area;
• the breakdown by use category and sub-category, compared with the uses actually carried on and the leases in force;
• the development tax notices and, in the Île-de-France region, the office-creation tax notices, whose basis reveals the areas declared;
• the feasibility of regularisation under the PLU in force, and not the one applicable to the original permit.

Where a discrepancy appears, the contractual instruments must be calibrated accordingly: a specific representation and warranty on planning compliance, an escrow indexed to the estimated cost of regularisation or reinstatement, a condition precedent of obtaining a regularisation permit, and a price adjustment based solely on the authorised square metres. A general asset and liability warranty, capped and of short duration, does not cover a risk whose time horizon for emerging often exceeds the warranty period.

Securing usability over time, not only the acquisition deed

Floor area does not stop producing effects once the permit has been cleared. It conditions the regulatory trajectory of the asset.

It first governs the capacity for change. A building whose real floor area exceeds the authorised area has, in effect, used up a density that it will not be able to draw on later. Any subsequent application, whether an additional storey, an extension or a change of use, will require the existing situation to be regularised as a prerequisite. The value-creation project then runs into a liability that must be cleared before it is even examined.

It next governs the application of sector-specific regimes. The tertiary energy-efficiency scheme (dispositif éco-énergie tertiaire), derived from Article L. 174-1 of the French Construction and Housing Code and Decree No. 2019-771 of 23 July 2019, applies to buildings housing tertiary activities over a floor area greater than or equal to 1,000 m², aggregated where applicable on a single site. A real area greater than the declared area may bring an asset within the scope of the consumption-reduction obligation, with the associated investment and reporting. The reverse is just as problematic: an erroneous reference declaration undermines the declared trajectory.

Finally, it governs document management. In an asset held in a portfolio, tenant works, fit-outs of floors, closures of patios and creations of technical mezzanines follow one another without the planning file being systematically updated. The drift is cumulative. The discipline to be put in place is simple: any work altering an enclosed and covered volume is subject to a prior floor area check, and the consolidated planning file is kept up to date like a title deed.

Conclusion: treating floor area as a valuation parameter

Floor area is the only figure in a permit file that appears at the same time in the planning rules, the tax base, the display sign, the amount of the criminal fine and the price of the asset. An error on this parameter is never confined to the administrative sphere. It reopens appeal periods that were thought to be cleared, it provides the basis for a penalty calculated per square metre, it burdens the building's capacity for change and it contaminates the valuation.

Our position is as follows: in a restructuring or takeover operation, the floor area survey must be recalculated on an adversarial basis, and not taken from the seller's documents. The audit must address whether regularisation is possible under the PLU in force on the date of acquisition, not merely the existence of an old permit. Before signing, have an adversarial survey of the existing floor area prepared by a surveyor or an architect, compare it with the permit and its amendments, and make payment of part of the price subject to the documentary clearing of conformity.

Frequently asked questions

How exactly is the floor area of a building calculated?

The calculation of floor area consists in adding up, level by level, the enclosed and covered areas under a ceiling height greater than 1.80 metres, measured from the interior face of the façades, in accordance with Article L. 111-14 of the French Urban Planning Code. Only the deductions exhaustively listed in Article R. 111-22 are then applied: reveals of exterior openings, voids and openings for staircases and lifts, areas under 1.80 metres, parking, non-convertible attics, technical rooms of multi-occupancy buildings, cellars served only by a common area, and the 10% allowance for residential use served by internal common areas. Internal partitions and posts are not deducted.

What is the difference between floor area, taxable area and Carrez area?

Floor area belongs to planning law and determines the authorisation regime. Taxable area serves as the basis for the development tax, governed since Ordinance No. 2022-883 of 14 June 2022 by Articles 1635 quater A et seq. of the French General Tax Code: it does not allow the same deductions, notably for covered parking and cellars. The private Carrez area, which stems from Law No. 96-1107 of 18 December 1996, concerns the sale of co-ownership lots and has no administrative significance. A compliant Carrez certificate therefore does not demonstrate in any way the planning regularity of a property.

Can a building permit be withdrawn if floor area is under-declared?

Yes. Article L. 424-5 of the French Urban Planning Code allows an unlawful permit to be withdrawn within three months of its issue. Beyond that, the permit can no longer be withdrawn of the authority's own motion, except in the case of fraud: the administrative case law accepts that a decision obtained by fraud may be withdrawn at any time. A deliberate understatement of area intended to circumvent a threshold of the local urban plan or a parking obligation falls within this exceptional regime.

Does an error in the area shown on the display sign extend the third-party appeal period?

It can. The two-month appeal period provided for in Article R. 600-2 of the French Urban Planning Code runs only from a regular display, including the particulars of Articles A. 424-15 et seq., among them the authorised floor area. The administrative case law requires that these particulars enable third parties to assess the nature of the project; an erroneous indication on this point may deprive the display of its triggering effect. There remains the long-stop of Article R. 600-3, which makes any action for annulment inadmissible six months after completion of the building.

What criminal penalties apply to works that do not conform to the authorised area?

Article L. 480-4 of the French Urban Planning Code provides for a fine of between €1,200 and an amount that may not exceed €6,000 per square metre of area built, demolished or rendered unusable, or €300,000 in other cases. A six-month prison sentence may be added in the event of a repeat offence. The judge may also order, on the basis of Article L. 480-5, bringing into conformity or demolition. Public prosecution is time-barred six years from completion of the works.

After how long is an irregular area time-barred?

Article L. 421-9 of the French Urban Planning Code provides that, where a building has been completed for more than ten years, the original irregularity can no longer justify a refusal of authorisation. This limitation period is subject to decisive exceptions, notably where the building was constructed without any permit, where it exposes people to a risk of death or injury, or where it is located in certain protected areas. In practice, works not in conformity with a permit that was obtained may benefit from this limitation period; a building erected without authorisation does not.

What should be checked in due diligence on floor area before acquiring an asset?

The verification covers the consistency between the initial permit and its amendments, the DAACT and the certificate of non-objection to conformity, the display report, and an adversarial survey of the existing building recalculated under Article R. 111-22. It is also necessary to compare the breakdown by use category and sub-category with the uses actually carried on and the leases in force, and then to assess whether regularisation is possible under the PLU in force on the date of acquisition, and not the one applicable to the original permit. Where a discrepancy is identified, a specific representation and warranty, an escrow or a condition precedent of regularisation are preferable to a general asset and liability warranty.