C-DRONE GUIDE · 21 JULY 2026
Drone crack diagnosis after drought (subsidence): method and price for insurance
After a dry summer, new cracks appear on façades: a consequence of clay-shrinkage subsidence, a phenomenon affecting a growing share of French houses as droughts recur. Precisely documenting the extent and progress of these cracks is a key step in the file sent to the insurer once a natural-disaster status is declared. A drone can photograph every façade without scaffolding and track how the damage evolves from one season to the next. Here is how this mission works, and what it costs in 2026.
Published on 21 July 2026, reviewed on 21 July 2026 — regulations in force as of July 2026.
Clay-shrinkage subsidence, a phenomenon hard to document from the ground
Clay-shrinkage subsidence happens when clay soil loses some of its water during a prolonged drought: it shrinks, deprives the foundations of even support, and the building's structure settles unevenly. The resulting cracks typically appear diagonally, at the corners of openings and where two parts of a building of different heights meet — areas sometimes hard to observe fully from the ground, particularly on a tall gable end or a hard-to-reach rear façade.
The phenomenon is also gradual: a crack can open, stabilise in winter as the soil swells back with rain, then reopen the following summer. Documenting this progression requires repeated surveys, with the same framing and scale, to demonstrate worsening damage to the insurer — an exercise that hand-held ground photos, taken year after year, rarely reproduce with the same rigour.
The scale of the phenomenon at national level has been quantified by scientific research: a study published by Corti, Muccione, Köllner-Heck, Bresch and Seneviratne in 2009 in the journal Hydrology and Earth System Sciences modelled past droughts in France and their link to building damage compensated under the natural-disaster insurance scheme, confirming the direct sensitivity of houses to successive drought episodes.
How a crack-assessment mission works
The drone photographs each façade with a systematic framing, at a constant distance, which allows precise comparison between two shooting campaigns carried out several months apart. Every crack spotted is photographed close up, with a reference scale in frame to measure its width, supplemented where needed by an overview locating the defect on the façade.
On a single-family house, the mission covers every façade, including the high parts of a gable or party wall rarely visible from the garden, as well as the junction with extensions or outbuildings — frequent weak points in cases of differential settlement. The delivered report links each crack to its location, its measurement and, where monitored over time, a visual comparison between successive campaigns.
Precisely quantifying cracks from drone imagery has been the subject of recent research: a study published by Bhowmick, Nagarajaiah and Veeraraghavan in 2020 in the journal Sensors developed computer-vision and deep-learning algorithms able to automatically detect and measure crack width on surfaces from drone-captured video — an approach directly transferable to tracking façade cracks.
Regulatory framework and place in the natural-disaster claim
The flight falls under the open category, sub-category A1 or A2 depending on proximity to the neighbouring house and people present: 120 m maximum height, a remote pilot registered as an operator on AlphaTango. In a dense residential area, the main point of care is third parties present in neighbouring gardens, who must be respected and informed if the flight comes close.
The drone survey documents the file sent to the insurer once the official natural-disaster order is published — an administrative procedure separate from the flight itself, following a timetable specific to each municipality. As with a post-flood assessment, this aerial survey complements but never replaces a visit from an insurance loss adjuster or, where structural damage is confirmed, a foundation-engineering firm.
The price of a drone crack assessment in 2026
The price mostly depends on the number of façades to cover and whether monitoring over time is needed. Orders of magnitude observed in France in 2026:
| Service | Observed price (excl. VAT) |
|---|---|
| One-off photo/video record of a house's façades | €200 to €450 |
| Orthophoto mapping of a housing estate | €1,000 to €2,500 |
| Multi-season monitoring for a claims file (per campaign) | €150 to €300 |
| Annual monitoring package (2 campaigns, summer/winter) | €600 to €1,200 |
A survey carried out soon after the first cracks appear, before any underpinning work begins, greatly eases the processing of the file with the insurer.
Frequently asked questions about drone crack diagnosis
Can the drone measure a crack's exact width? Yes, with a reference scale in frame: the measurement remains indicative, though, and a ground-mounted crack gauge gives finer tracking over time.
Is the drone survey enough on its own for the natural-disaster claim? No: it documents and substantiates the extent of the damage, alongside the insurance loss adjuster's visit, who remains the sole decision-maker.
Should you wait for the official disaster declaration before calling in a drone? No, it is better to document early: a survey done as soon as cracks appear gives a useful baseline even before the order is published.
Can the drone also document a party wall or a rear façade? Yes, that is precisely one of its strengths: it covers areas hard to reach from the ground, subject to the neighbour's consent if the flight goes over their property.