The Paris bioclimatic PLU: what it locks down before a restructuring or a vertical extension

A Paris asset showing a discount of 20 points against the market in its arrondissement is rarely worth what it appears to be worth. In most cases, the gap is explained not by the technical condition of the building but by what the planning document allows, or no longer allows, to be done with its square metres. Since the Council of Paris approved the bioclimatic PLU (plan local d'urbanisme, the local urban plan) in November 2024, the question of the feasibility of a major restructuring, a change of use class or a vertical extension arises before the offer, not after the preliminary agreement is signed. This guide sets out the locks that the document places in the way of an investor or fund arbitrating on a residential or office asset in Paris, and the sequence of checks to be carried out before committing to a price.

What the bioclimatic PLU changes in the economic reading of an asset

The Paris local urban plan remains a document governed by Articles L. 151-1 et seq. of the French Town Planning Code: report of presentation, sustainable planning and development project, planning and programming guidelines, written and graphic regulations, and annexes containing the public utility easements. Its legal value has not changed. Its logic has.

The 2006 PLU was read as a document on buildability: it defined a maximum volume and rules on siting. The bioclimatic PLU is read as a document of constraints on use and environmental constraints. It does not merely say how much may be built, it says what must be kept (deep soil (pleine terre), housing, shops), what must be produced (social or affordable housing) and what may no longer be transformed.

The consequence for the business plan is direct. An investor who models the creation of floor area by vertical extension, the conversion of offices into housing or the reverse, or the densification of an inner-block area, is now working on assumptions most of which are legal assumptions, not technical ones. A restructuring plan validated by an architect says nothing about whether the permit will be obtained. Analysis of the zone regulations, the graphic atlas and the site-specific protections must come before the financial modelling, not validate it after the event.

Two points of method. First, the PLU is not the only filter: the Marais safeguarding and enhancement plan, the perimeters of remarkable heritage sites, and the surroundings of historic monuments (Article L. 621-30 of the French Heritage Code, with the binding opinion of the Architect of the Buildings of France) are superimposed on the municipal regulations. Second, the document, like any PLU, may be challenged directly or by way of exception, which creates a specific uncertainty discussed below.

Deep soil and inner-block areas: the constraint that neutralises any extension of the footprint

Article L. 151-22 of the French Town Planning Code allows the regulations to impose a minimum share of unsealed or eco-developable surfaces, possibly weighted according to their nature, in order to contribute to maintaining biodiversity and nature in the city. The Paris bioclimatic PLU makes this a structuring axis, combining deep soil requirements, planting requirements and site-specific protections of open spaces entered on the plan.

For the investor, the effect is mechanical. The cadastral area of the plot is no longer an indicator of usable footprint. An inner courtyard, an inner-block garden, a planted strip at the rear may be subject to protection under Articles L. 151-19 or L. 151-23 of the French Town Planning Code, depending on whether the ground is heritage or ecological. This identification has heavy consequences: works affecting the protected element require authorisation, and the demolition of a building identified under Article L. 151-19 requires a demolition permit under Article R. 421-28 of the same Code.

Three scenarios recur regularly in Paris transactions and run up against this lock:

• covering a courtyard to create a continuous office floorplate or a through-hall;
• constructing a rear building at the back of the plot, intended to absorb the floor area removed at the front;
• extending a basement under an open space, the creation of car parks or underground technical rooms often being incompatible with a deep soil requirement in the strict sense, which presupposes continuity of the natural ground.

The check to be carried out before the offer is a check on the ground, not a paper exercise. A surveyor's plan, the actual state of the ground (surfaces, existing basements, underground footprints) and the protection plans must be superimposed. The gap between the theoretical built footprint and the usable footprint determines the number of square metres that can actually be created, and therefore the price.

Heights, building envelope profile and vertical extension: where the volume ends

A vertical extension in Paris remains one of the few sources of floor area creation in a dense urban fabric. It is also the item on which feasibility assumptions are the most fragile.

The regulatory filter

The buildable volume results from the combination of three sets of rules: the height ceiling applicable to the sector, as shown on the heights plan, the building envelope profile (gabarit-enveloppe) that determines the permissible shape of the top of the building, and the rules on setbacks and views between buildings. The general Paris ceiling, historically set at 37 metres, comes with local reductions and height lines that are read plot by plot. A building that does not reach the ceiling cannot necessarily be extended upwards: the envelope profile and the setback from the building opposite or at the back of the plot may neutralise all or part of the difference.

Derogations are not rights

Two levers are regularly invoked. Article L. 152-5 of the French Town Planning Code allows the competent authority to depart from the rules on footprint, height, siting and external appearance in order to authorise, in particular, external insulation or a roof extension that improves energy performance. Article L. 152-6 opens, in municipalities located in high-demand areas (zones tendues), specific derogations, in particular for the vertical extension of a building completed more than two years earlier where the extension tends towards alignment with the highest adjoining building, and for the conversion of offices into housing.

These derogations are options, not acquired rights. The issuing authority assesses, gives reasons and may refuse. A business plan that includes a derogatory vertical extension in its base case in fact includes a decision-making risk. Prudence calls for valuing the derogatory extension as an option, not as a given, and for treating its grant, where appropriate, as a separate condition precedent.

The private-law filter, too often overlooked

The vertical extension of a building in co-ownership (copropriété) requires a collective decision. Article 35 of Law No. 65-557 of 10 July 1965, in its wording resulting from the ELAN Act No. 2018-1021 of 23 November 2018, subjects the decision to extend upwards in order to create private premises to the majority of Article 26. Article 36 gives a right to compensation to co-owners who suffer loss as a result of the operation. In addition there are private-law easements: easements of view, contractual easements against raising the building entered in an old deed, and common-courtyard easements created on the basis of Articles L. 471-1 et seq. of the French Town Planning Code. An audit of the title deeds over thirty years is here as decisive as reading the regulations. The question of who owns the right to build upwards is dealt with in our article on vertical extension in co-ownership.

Protection of housing and use classes: the lock on use

The French Town Planning Code organises use classes and sub-classes in Articles R. 151-27 and R. 151-28. The regulations may prohibit certain use classes, or make them subject to conditions, by sector. In Paris, this power is used to protect housing, to limit the development of offices in certain districts and to preserve commercial diversity at ground level, Article L. 151-16 allowing the identification of frontages where commercial diversity must be maintained.

For the holder of a tertiary asset, the question is no longer only one of rental value. It is one of reversibility. Converting obsolete offices into housing is encouraged. The reverse operation, removing housing to create offices or activity space, is locked, including where the housing is vacant or dilapidated. A purchaser who buys a mixed-use building expecting to upgrade the upper floors to tertiary use must check whether the regulations impose protection of existing housing, and where applicable an obligation to replace the residential floor area removed.

Two distinct regimes must also be dovetailed, and confusing them is a classic source of disputes. Change of use class (changement de destination) is governed by the French Town Planning Code: it requires a prior declaration, or a building permit where it is accompanied by works altering the load-bearing structure or the facade. Change of use (changement d'usage) is governed by Articles L. 631-7 et seq. of the French Construction and Housing Code, with in Paris a regime of authorisation and compensation. The two authorisations are independent. Obtaining one does not dispense with the other. On the authorisation for a change of use class and how it fits with change of use, see our analysis of the formalities applicable depending on the change envisaged.

Furnished tourist lettings come under the same logic of workability. Law No. 2024-1039 of 19 November 2024 strengthened the levers available to municipalities in high-demand areas, both as regards the regime of authorisation for change of use and as regards the possibility for the planning document of reserving new buildings for housing used as a main residence. A Paris residential business plan based on a short-term yield must be tested against both sets of rules before the offer.

Social mix easement: the levy on the operation's balance sheet

Article L. 151-15 of the French Town Planning Code allows the regulations to define, in urban or to-be-urbanised zones, sectors in which, where a housing programme is carried out, a percentage of that programme is allocated to categories of rental housing that it defines in compliance with the objectives of social mix.

Article L. 151-41, 4° of the French Town Planning Code: the regulations may delimit land on which are established reserved sites for the carrying out, in compliance with the objectives of social mix, of housing programmes that it defines.

The social mix easement (servitude de mixité sociale) and the reserved site (emplacement réservé) for housing produce different economic effects, which must be distinguished. The easement applies when the operation exceeds a floor area threshold set by the regulations and imposes a percentage of social, affordable or intermediate housing. The reserved site allocates the plot itself to a specified programme, by nature poorly compatible with an alternative project.

Three parameters must be recorded plot by plot, because they drive the price: the floor area threshold that triggers the requirement, the percentage imposed, and the category of housing concerned. An operation that crosses the threshold by a few tens of square metres bears the easement in full, which may justify resizing the programme. Conversely, Article L. 151-28 of the French Town Planning Code allows increases in buildable volume in return, in particular, for the delivery of social rental housing or enhanced energy performance. The bonus does not always offset the levy, but it must be modelled.

Two points of law to bear in mind. Article L. 105-1 of the French Town Planning Code lays down the principle that planning easements are not compensated, except in the limited cases that it lists: the loss of value resulting from a social mix easement gives no right to compensation. By contrast, the owner of land burdened by a reserved site has the right of surrender (droit de délaissement) provided for in Articles L. 152-2 and L. 230-1 et seq., which allows the owner to give formal notice to the beneficiary authority to acquire. This right is a real negotiating lever, provided that its timing is mastered.

In addition, in certain sectors, there is the power under Article L. 151-14 to impose a proportion of dwellings of a minimum size. The constraint appears secondary. It is not: it depresses the average price per square metre of a residential programme calibrated on small units.

The litigation risk attached to the building permit

A building permit in Paris for a major restructuring or a vertical extension in an established urban fabric has a not insignificant probability of being challenged. The timetable of the operation must take this into account.

The key time limits

Proper display on the site starts the two-month time limit for third-party challenges provided for in Article R. 600-2 of the French Town Planning Code. The person bringing the challenge must, on pain of inadmissibility, notify it to the author of the decision and to the holder of the authorisation within fifteen days, in accordance with Article R. 600-1. The third party's standing to bring proceedings is regulated by Article L. 600-1-2, which requires that the construction directly affect the conditions of occupation, use or enjoyment of their property. In parallel, the competent authority has three months in which to withdraw an unlawful permit, under Article L. 424-5. The time limits and the absence of suspensory effect of a third-party challenge to a building permit are dealt with separately in our article on this area of litigation.

In practice, complete clearance therefore requires combining the third-party challenge period, the administrative withdrawal period and, where applicable, the time limit for a challenge by the prefect in the exercise of legality review. A preliminary agreement whose term is set on the two-month period alone is badly calibrated.

Suspension and regularisation

The interim suspension application (référé-suspension) under Article L. 521-1 of the French Code of Administrative Justice is the main weapon of the objecting third party. The administrative courts widely accept that the execution of a building permit causes a sufficiently marked prejudice to the applicant's interests to satisfy the condition of urgency, which shifts the whole debate onto serious doubt as to lawfulness. On the applicant's side, Articles L. 600-5 and L. 600-5-1 of the French Town Planning Code allow partial annulment or a stay of proceedings with a view to regularisation by an amending permit. Article L. 600-7 opens, under strict conditions, an action for damages against an abusive challenge.

The specific risk of a recent planning document

A recently approved PLU is an exposed PLU. Article L. 600-1 of the French Town Planning Code confines to a period of six months from the date the document takes effect the raising by way of exception of its unlawfulness for defects of form or procedure. After that period, only grounds of substantive lawfulness remain available, but they remain so without limit of time. Article L. 600-12 provides that the annulment or declaration of unlawfulness of a PLU brings back into force the document immediately preceding it. Article L. 600-12-1 nevertheless limits the effects of that annulment on authorisations already issued where the defect found is unrelated to the rules applicable to the project.

For the investor, the reading is twofold. A project that is not feasible under the bioclimatic PLU but would be feasible under the previous document must not be valued on the assumption of an annulment: the risk is too heavy and too long. Conversely, a project authorised under the new document retains a residual exposure that must be dealt with by contract, through a condition precedent of a cleared permit and a clear allocation of the risk between seller and purchaser.

The sequence of planning due diligence to be followed before the offer

The order of the checks matters as much as their content. A feasibility study carried out after the preliminary agreement is signed costs an immobilisation indemnity or a renegotiation from a position of weakness.

• Plot-by-plot regulatory extract. Zone, applicable written regulations, heights plan, heritage and ecological protections, commercial frontages, social mix sectors, reserved sites, annexed public utility easements. Consulting the Géoportail de l'urbanisme does not dispense with reading the written regulations, which alone are enforceable in their detail.
• Operational planning certificate (certificat d'urbanisme opérationnel). Article L. 410-1 of the French Town Planning Code makes it possible to freeze for eighteen months the planning provisions, the tax regime and the administrative limitations on property rights. In the context of a recent document, the freeze is a negotiable asset.
• Compliance audit of the existing building. Authorisations obtained, declarations certifying completion and conformity of the works, differences between the actual state and the authorised plans. Article L. 421-9 of the French Town Planning Code prevents, after ten years from completion and subject to the exceptions it provides for, a refusal from being based on the irregularity of the original construction. This limitation period does not erase every risk, in particular in a protected zone.
• Use class and use test. Current use class within the meaning of R. 151-27 and R. 151-28, target use class, planning authorisation required, authorisation for change of use under L. 631-7 of the French Construction and Housing Code, any compensation.
• Long-term workability test. Obligations to reduce energy consumption in the tertiary stock arising from Article L. 174-1 of the French Construction and Housing Code, the timetable for the progressive ban on letting the least efficient dwellings arising from Law No. 2021-1104 of 22 August 2021, and co-ownership constraints on facade and roof works.
• Contractual translation. Term of the preliminary agreement aligned with the real clearance timetable, separate conditions precedent for the permit and for derogatory authorisations, escrow, and seller's representations and warranties on the absence of planning disputes and on the conformity of earlier works.

Each of these checks produces a figure in the model: a creatable floor area, a percentage of social housing, a delay before first rental income, a probability of litigation. It is this conversion of the regulatory into the financial that distinguishes a tenable offer from one to be renegotiated.

Conclusion

The bioclimatic PLU must not be read as an environmental document with a programmatic purpose but as an instrument for controlling the use of Paris buildings. It shifts the creation of value from densification to requalification, and it makes a change of use class away from housing much harder than it was. In this framework, the discounts shown on obsolete tertiary assets or on dilapidated buildings reflect less and less a technical risk and more and more a risk of authorisation.

The position is as follows: in Paris, legal feasibility must now be examined before architectural feasibility, and not the reverse. An attractive site plan drawn up without prior reading of the zone regulations and of the site-specific protections produces a false valuation.

Before any firm offer on a Paris asset involving a restructuring, a conversion or a vertical extension, have a plot-by-plot regulatory feasibility note drawn up, apply for an operational planning certificate to freeze the rules while your file is being processed, and set the term of your preliminary agreement on the real clearance timetable for the permit, including the third-party challenge period and the administrative withdrawal period. The additional cost of these checks is marginal compared with the difference in price that they make it possible to argue for.

Frequently asked questions

Since when has the Paris bioclimatic PLU applied to permit applications? The document was approved by a deliberation of the Council of Paris in November 2024 and became enforceable once the publicity formalities provided for in Articles R. 153-20 and R. 153-21 of the French Town Planning Code were completed. Applications filed after that date of enforceability are examined under the new regulations, subject to the freezing effects attached to a planning certificate issued earlier under Article L. 410-1. For a file in progress, the date of the complete application is the reference point to check first.

Is a vertical extension still possible in Paris under the bioclimatic PLU? Yes, but feasibility is checked in three stages. First the height ceiling of the sector and the applicable building envelope profile, then the rules on setbacks and views in relation to neighbouring buildings, and finally the possible use of the derogations in Articles L. 152-5 and L. 152-6 of the French Town Planning Code, which remain discretionary powers of the competent authority. In co-ownership, there is in addition the vote provided for in Article 35 of the Law of 10 July 1965 and any compensation provided for in Article 36.

Does the social mix easement give the owner a right to compensation? No. Article L. 105-1 of the French Town Planning Code lays down the principle that planning easements are not compensated, apart from the cases exhaustively listed. A reserved site for housing follows a different logic: the owner may exercise the right of surrender under Articles L. 152-2 and L. 230-1 et seq. and give formal notice to the beneficiary authority to acquire the land, which is a negotiating lever in its own right.

What time limit should be allowed for a Paris building permit to be cleared of any challenge? The third-party challenge period is two months from the first day of proper and continuous display on the site, under Article R. 600-2 of the French Town Planning Code. To it must be added the three-month withdrawal period open to the administration under Article L. 424-5 and, where applicable, the period for the prefect's legality review. An administrative appeal to the issuing authority extends the period for legal proceedings. A preliminary agreement set on two months only exposes the purchaser to acquiring a permit that is not final.

Can Paris housing still be converted into offices? This is the most locked operation. It requires passing two distinct filters: the change of use class under the French Town Planning Code, subject to the zone regulations that protect existing housing, and the change of use under Article L. 631-7 of the French Construction and Housing Code, subject in Paris to a regime of authorisation and compensation. Obtaining one is not the same as obtaining the other, and the compensation is a cost to be modelled before the offer.

Can a challenge to the bioclimatic PLU undermine a permit already obtained? A plea of unlawfulness based on a defect of form or procedure is no longer admissible beyond six months from the date the document takes effect, under Article L. 600-1 of the French Town Planning Code. Grounds of substantive lawfulness remain available. Article L. 600-12-1 nevertheless limits the consequences of annulment of the document on authorisations issued where the defect found is unrelated to the rules applicable to the project, and Article L. 600-12 brings the previous document back into force. The risk exists but should not be overstated in a business plan.

How does the deep soil coefficient affect the valuation of a plot? It reduces the footprint that can actually be used, above and below ground, and frequently prohibits courtyard infill or construction at the back of the plot. Valuation must therefore start from the net buildable footprint, obtained after superimposing a surveyor's plan, the protections entered under Articles L. 151-19 and L. 151-23 and the requirements for unsealed surfaces based on Article L. 151-22. The gap with the cadastral area is often the first argument for renegotiating the price.