French tax authorities expand AI checks for undeclared property expansions

French tax authorities are widening their use of AI tools to catch undeclared property expansions, and are now targeting constructions such as pagodas, verandas, and garden sheds.

Authorities have been using satellite images and AI for several years to check for undeclared swimming pools, and similar technology is now being expanded to search for other extensions. 

While the AI tools could previously pick up undeclared work such as sheds and verandas, the Direction générale des Finances (DGFiP; tax authorities) is now specifically targeting them in its searches, reports French public service broadcaster FranceInfo.

It estimates it will find hundreds of thousands of undeclared works and is aiming to recover around €100 million in unpaid taxes. 

The DGFiP has warned property owners across France to ensure all property extensions have been correctly declared, or they risk fines alongside additional tax payments.

The AI tools compare satellite images with records held by the tax offices, however any action can only be taken after a manual check is made by an official.

Property expansions must be declared

Similarly to undeclared swimming pools, the searches typically relate to works that should have been reported on completion for payment of the taxe d'aménagement, often called the garden shed or swimming pool tax. 

This is a one-off tax that is required on all property extensions of 5m² or more (new rooms, extensions, outhouses, sheds, etc) as well as certain structures such as carports, swimming pools and even sheds. 

You can read more about the tax in our article here. Some good news is that in 2026; rates have lowered for the first time in several years.

Extensions must be declared within 90 days of completion to comply with the rules.

Declarations are now usually made through the Biens immobiliers section of a property owner’s personal space on the French tax site, however may still be possible through physical forms – if in doubt, ask your local centre des impôts foncier (section of the tax office dealing with property taxes). 

These declarations also allow the tax office to check if a property's value and comfort has increased, thus potentially adding to the base value used for it in calculations of the taxe foncière property owner's tax. 

You should note, however, that the tax authorities ask that any new construction or extension be reported to them for this reason, thus it is advisable to do so, even if you believe the work to be exempt from taxe d'aménagement (eg. because it is under 5m2). 

Why the new campaign? 

The widespread success of AI and satellite technology to find undeclared swimming pools has encouraged the DGFiP to expand its searches. 

In place for several years, the use of the tools has likely been honed so that even these smaller changes can be identified with more confidence.

AI tools are used to check satellite images of properties, checking for the presence of new features. In some cases, the tools check for shadows where structures are not immediately obvious.

In addition, the use of technology makes the checks much cheaper than previously, allowing swathes of territory to be assessed in a short amount of time. 

“There's definitely been a tightening of information, with inspection methods that ultimately cost very little compared to what they used to, " said tax lawyer Frédéric Naïm to FranceInfo. 

"Before, tax officials would come on-site, which was very expensive, and now, it's not nearly as costly to conduct inspections,” 

It will also allow tax authorities to update information held about properties – something it is also aiming for with the controversial update on ‘comfort features’ included in homes. 

Capturing an undeclared property expansion can lead to a windfall for the authorities. 

Alongside allowing for a recalculation of the taxe foncière for the property, and the backdated taxe d'aménagement (calculated either on a m² basis or a fixed rate for certain extensions), fines can also be levied against owners who do not declare extensions. 

These can range from €1,200 to €6,000 per m² of undeclared extensions, alongside a 10% additional penalty on the unpaid taxe d'aménagement. 

Authorities can also demand up to four years of increased taxe foncière payments based on the new calculations.