C-DRONE GUIDE · 3 SEPTEMBER 2026

Buildings near a Seveso site (PPRT): what a drone survey adds to the diagnostic, price

Around every French site classified Seveso upper-tier — a refinery, a fuel depot, a chemical plant, a storage platform — a technological risk prevention plan (PPRT) delimits zones where existing homes and buildings must sometimes be reinforced to protect their occupants: glazing resistant to a blast overpressure wave, roof and structure reassessed against a thermal or toxic risk. Before any works quote, a preliminary diagnostic establishes what needs doing, building by building. For a local authority coordinating support for dozens of residents, a social landlord owning an entire housing stock inside the prescription zone, or a managing agent who must produce a dated condition report for each affected condominium, the hardest part to document is usually the same: the real state of roofs, surfaces nobody ever sees without scaffolding or a platform lift. That is exactly where an aerial drone survey helps the diagnostician, without replacing them. Here is how this mission fits with the PPRT process, what stays funded and until when, and the prices charged in 2026.

Published on 3 September 2026, reviewed on 11 September 2026 — regulations in force as of September 2026.

The PPRT: why an industrial site can require works next door

Technological risk prevention plans have existed since the law of 30 July 2003, known as the Bachelot law, adopted after the AZF disaster in Toulouse (21 September 2001): 31 dead, thousands injured, and damage several kilometres from the plant. Codified in articles L.515-15 and following of the Environmental Code, these plans apply around every site classified Seveso upper-tier: based on the worst plausible accident scenarios (explosion, fire, toxic cloud), they delimit concentric zones where future development is constrained and where existing buildings can be made subject to prescriptions.

The response differs by zone. Closest to the site, in the most exposed sectors, a PPRT can go as far as expropriation or a right of abandonment — the owner can force the local authority to buy the property. Further out, in the so-called "blue" zones, the logic changes: residents are no longer relocated, the existing building is reinforced instead, so it protects its occupants in the event of an accident. Depending on the hazard retained for the zone — overpressure, thermal effect, toxic — the prescribed works typically target glazing (blast-wave resistance), the roof and its ability to limit smoke ingress or fire spread, and sometimes the structure itself. France counts several hundred approved PPRTs, concentrated around its historic industrial basins — the Seine valley, the Étang de Berre, the Rhône valley, the North and Grand Est regions in particular.

The preliminary diagnostic: what it assesses, what the drone adds

Before any works quote, a preliminary diagnostic must be carried out on each affected home or building, by a diagnostician specifically trained in technological risks — a distinct profession from standard property diagnostics (energy performance, asbestos, lead). It is this professional who determines, by cross-referencing the hazard retained for the zone with the building's actual condition, which works to prescribe: the type of glazing to replace, weak points in the roof, any structural reinforcement needed. A personalised support scheme, funded by the State and run by an operator partnered with the Anah housing agency, helps blue-zone residents build this file, right through to the post-works inspection visit.

The drone is not meant to replace this diagnostician — the regulatory qualification is theirs, not a drone pilot's. What it adds is a dated, usable record of the roof, the part of the building hardest to examine closely without access equipment: the type and condition of the covering, existing openings (roof lanterns, smoke vents, chimney stacks) that affect performance in a smoke scenario, visible defects (cracks, displaced tiles) that point the diagnostic toward closer examination. Across a stock of several dozen homes in a blue zone, documenting every roof from the ground or by ladder takes days; an aerial pass covers the whole perimeter in half a day, with geolocated, time-stamped images the diagnostician can use directly in the file. It is the same logic — checking a roof's condition without climbing onto it — that we detail in our comparison of drone versus cherry picker for roof inspection.

2026 funding: the tax credit extension, and the local authority's and operator's share

The historic obstacle to PPRT-prescribed works was never technical: it was funding. A tax credit (article 200 quater A of the French tax code), capped at €20,000 per home, covers the diagnostic and the prescribed works for owners occupying their main residence; this scheme, regularly renewed from one finance law to the next, has been extended to 31 December 2026. It combines, without replacing, a contribution from the local authority and from the operator at the origin of the risk (article L.515-19 of the Environmental Code): added together, these three sources can cover up to 90% of the total cost of the diagnostic and works for an owner-occupier.

This three-way funding explains why the local authority — often the town or the inter-municipal body coordinating support for residents — has a direct interest in a reliable, dated condition survey before committing funds: it must justify how its contribution was used, and the co-financing industrial operator expects the same rigour. An aerial survey report, with geolocated images and a flight date, fits naturally into this shared funding file — on the same principle we describe for the collective EPC and multi-year works plan in condominiums, where a dated building record likewise conditions access to funding.

A mission at the scale of the perimeter, not the home

A blue-zone perimeter almost never covers a single home: it is typically an entire residential neighbourhood, a cluster of condominiums, or a social landlord's whole housing stock caught in one block. For the operator coordinating support — often commissioned by the local authority — handling residents one by one, with a different firm inspecting each roof, multiplies both cost and delay. A pooled aerial campaign across the whole perimeter, flown over one or two days, produces a dated, comparable record of every roof in the area, later passed on home by home to the appointed diagnosticians — the same pooling logic we detail for a social landlord's housing-stock audit, where the saving comes precisely from the number of roofs covered in a single mobilisation.

The same survey serves a second time, later: the post-works inspection visit, which checks that the prescriptions were actually implemented, can likewise rely on a before/after comparison from aerial imagery — useful for the operator to justify closing the file with the funder, and for the local authority to keep a usable record of its prevention policy.

Flying near a Seveso site: constraints and 2026 prices

A PPRT perimeter is, by definition, adjacent to an industrial site classified Seveso upper-tier: mission preparation starts with checking the airspace zoning (map of regulated zones, operator to contact if the flight approaches the site's boundary) before even looking at the neighbouring buildings. This caution is not specific to drones: the technical literature documents precisely why aerial inspection is favoured near a hazardous installation. A systematic review by Sairul Izwan Safie and Raudhah Khairil, published in 2025 in Transportation Research Interdisciplinary Perspectives, surveys current practice for drone-based inspection in chemical plants: it notes that aerial imagery reduces human exposure to hazardous areas while requiring a specific regulatory framework and mission preparation for this type of site (see the study on Google Scholar). For a mission documenting neighbouring buildings, that translates into a flight kept clear of the industrial site's boundary, with prior coordination with the operator where the perimeter requires it.

Ranges observed in 2026, excl. VAT:

These amounts cover the flight, image processing and delivery of a set of geolocated, time-stamped images the diagnostician can use — they do not include the regulatory diagnostic itself or the works. The regulatory information on this page reflects the rules in force in September 2026; the tax credit's timeline and the zone perimeters should be re-checked with the prefecture or the support operator before any commitment. For a local authority, a social landlord or a managing agent affected by a PPRT, request a quote stating the exact perimeter, the number of homes and the funding file's contact (Anah operator, local authority, appointed diagnostician).

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Put it into practice

• Drone roof inspection: rates and cities covered from €200
• Roof inspection in Rennes Bretagne
• Roof inspection in Villeurbanne Auvergne-Rhône-Alpes
• Roof inspection in Tours Centre-Val de Loire

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