You are claiming a sum in court, or contesting the sum claimed from you: you need to justify it. An expert report or a quote strengthens the argument, and it then falls to the other party to demonstrate a different amount. Yet valuation reports often propose percentage deductions to allow for the condition of a property, works to be carried out or contamination. A decision of the PARIS Court of Appeal of 8 September 2022 (case no. RG 21/130177), given in a pre-emption matter, shows what is gained by costing and what is risked by settling for a percentage.
The framework: the court sets the price in a pre-emption case
When a French municipality exercises its right of pre-emption at a price below the one stated in the seller’s declaration of intent to sell (déclaration d’intention d’aliéner) and the seller refuses, the price is set by the expropriation judge (French Planning Code, article L. 213-4). The judge relies on the parties’ submissions, on the opinion of the Government Commissioner (commissaire du Gouvernement, the State’s valuation officer in these proceedings) and, if ordered, on an expert appraisal.
Each party must prove the facts necessary for the success of its claim (French Code of Civil Procedure, article 9). Whoever asks for a deduction for works must therefore establish that the works are necessary and what they cost.
The case
An SCI (société civile immobilière, a French property-holding company) sells a plot of 23,844 m² and files a declaration of intent to sell at €1,400,000. The city pre-empts at €476,880. The SCI refuses and the expropriation judge is seised. After an expert appraisal, the first judge sets the price at €1,144,512.
The city appeals. It asks in particular for a 22 % deduction for clearing and decontaminating the site.
A deduction for works that could have been costed
The Government Commissioner notes that “no sufficiently precise data to date makes it possible to determine any decontamination cost”. The city explains the absence of costing by its lack of access to the site. A pollution audit had nevertheless been carried out, and that audit specifically recommended costing the decontamination. It was therefore probably possible to obtain a quote or a technical estimate, if necessary by asking the judge for an investigative measure to gain access.
This is the point that holds my attention. A percentage deduction expresses an opinion; a quote expresses a cost. Before a judge, the second carries more weight than the first, because it can be discussed item by item.
The solution adopted by the court
The court reasons in three steps.
A unit value and a deduction for occupation. It adopts €60 per m², so 23,844 m² × €60 = €1,430,640, then applies a 20 % deduction for occupation, because the land is subject to long leases: €1,144,512. This is the first judge’s figure.
Costed demolition costs. It deducts €50,400 of demolition costs (€80 × 630 m²), an amount that no party seemed to contest. The deduction is logical: the cost is identified, measured, and no one disputes it. This gives €1,094,112.
A flat-rate deduction for contamination. For decontamination, on the other hand, the court settles for a 10 % deduction, set “in the light of the audit’s findings”. On the gross value of the land, that represents €143,064, and the price adopted comes to €951,048.
The approach is understandable: the court seeks to close the case with a credible amount. But it treats two items of the same nature differently. Demolition costs are deducted at their real cost; decontamination costs at a percentage, when the audit itself called for a costing. A percentage remains debatable by construction: 10 % rather than 5 % or 22 %, no one can prove it.
What each party could have done
To protect its interests, the SCI could have had the decontamination costs assessed precisely. With a quote or a feasibility study, it could have argued that the real cost was below €143,064, or at least anchored the debate on figures. Without a costing, it was left with a flat rate that it could only contest with an opinion.
The city, for its part, could have obtained more than 10 % had it demonstrated a higher decontamination cost. It asked for 22 %; without justification, it was not followed.
The absence of a precise assessment always ends up penalising one of the parties, without anyone knowing in advance which one.
What the valuation expert does
The Charte de l’expertise en évaluation immobilière (the French property valuation charter, 6th edition, November 2025) states that soil pollution surveys and environmental risk assessments fall outside property valuation and require qualified and insured specialists (Title II, chapter 10). The expert must, on the other hand, flag any potential contamination on or near the property, a requirement also found in the European Valuation Standards 2025 (EVS 5, §4.2.5).
In practice, when works or decontamination weigh on the value, the approach I follow is this:
- identify the item and its cause (wear, upgrading to standards, asbestos removal, demolition, decontamination);
- obtain a costing from a professional in the field concerned: a contractor’s quote, a study by a specialist firm, or failing that a documented ratio;
- deduct this cost from the value before works, stating the source and date of the costing;
- keep the percentage deduction for cases where no costing is possible, explaining why and framing the rate with references.
A flat-rate deduction is not illegitimate in itself. It becomes fragile as soon as a costing was within reach. The report that explains what it has costed, what it could not cost and why, gives the judge what he needs to decide on facts rather than on opinions.
Further reading
The valuation of works and of losses affecting a property is presented on the Property loss of value page. On the same theme: how to estimate the average property price in your town and what a valuation report contains.
What next
Has your property lost value because of a third party?
Neighbouring construction, hidden defect, wrong floor area, overpayment at purchase: the loss of value and the loss of enjoyment quantified with the method accepted by French courts.
Free quote, by email or by phone. No commitment before the quote is accepted. Fees are never linked to the value of the property (Charte de l’expertise, Title I, §2.1).
