C‑DRONE
Night aerial view of an illuminated urban area

C-DRONE GUIDE · 29 JULY 2026

Drone-assisted works acceptance: roof and façade quality control, decennial warranty

Practical completion (réception des travaux) is the act by which the developer declares acceptance of the building, with or without reservations: it is also the point at which the legal warranties that protect the building for one, two or ten years start to run, depending on the type of defect. On that day, the architect or project manager walks the site and records everything found in the official report — but even a thorough ground-level visit sees neither the real condition of a flat roof, nor the upper façades, nor the edge flashings, precisely the areas where the defects that turn into long, costly disputes hide, for want of being reserved in time. A drone flight carried out before or during acceptance documents these blind spots in high resolution and gives the developer what is needed to draft precise, photographed and geolocated reservations. Here is how this quality control is organised, and prices observed in 2026.

Published on 29 July 2026, reviewed on 30 July 2026 — regulations in force as of July 2026.

Practical completion: where the legal warranties start running

Practical completion is defined by article 1792-6 of the French civil code as the act by which the developer declares acceptance of the building, with or without reservations; it is recorded adversarially, either amicably or, failing that, by the court. This moment freezes a state of affairs: from that date run the one-year warranty of perfect completion (garantie de parfait achèvement, owed by the contractor for any defect reserved in the official report or notified in writing within the year), the two-year functional warranty for detachable fittings, and the ten-year decennial warranty for defects affecting the building's soundness or making it unfit for its purpose.

The practical stake fits in one sentence: whatever is not seen, or not noted, on acceptance day risks never being repaired under the warranty of perfect completion. For a developer — social landlord, promoter, local authority, joint ownership — mobilising a thorough inspection before signing is therefore not a formality but a financial safeguard; it is the same stake documented in our guide on pre-construction condition surveys, applied here to the building itself rather than to its neighbours.

What a drone documents that a ground-level visit misses

A works acceptance visit often happens at a fast pace: several trades, a tight schedule, a ground-level walk-through covering the rooms, the surroundings, sometimes the roof structure visible through a hatch — rarely the whole of a flat roof, the edge flashings, the ventilation stacks or the top of a four-storey façade. A drone covers these surfaces in one to two hours: waterproofing membrane, upstands and flashings, rainwater outlets, roof guardrails, façade expansion joints, render and cladding at height — all points the report compares against the execution drawings and the as-built file (dossier des ouvrages exécutés) handed over by the contractor.

The reliability of this kind of survey depends on parameters a professional mission controls: a study by Guido Morgenthal and Norman Hallermann, published in 2014 in Advances in Structural Engineering, shows that a drone flight's ability to reveal a defect depends directly on distance to the structure, lighting and shot stability (see the study on Google Scholar): which is why an acceptance mission is prepared like an ordinary roof inspection — flight path, image overlap, flight plan — rather than a courtesy flyover.

Precise reservations, photographed and geolocated

The difference lies in how the official report is worded. "Possible roof leaks" is a fragile reservation, easily disputed by the contractor; "membrane lifted over 1.5 m at the north-west corner, level with the gutter marked on the plan" is another matter entirely: dated, geolocated, backed by a high-resolution image appended to the report, it is no longer up for debate — it gets fixed. Each defect spotted by the drone is tied to a point on the roof or façade plan, letting the architect draft reservations that hold up and the contractor know exactly where to intervene.

This traceability also serves later on: if a dispute arises over the origin of a defect discovered afterwards, the dated photographic record from acceptance stands as reference, following the same evidentiary logic detailed in our construction disputes and expert evidence guide. For a complex structure — a technical roof, a multi-material façade — this location plan is sometimes complemented by a georeferenced orthophoto, overlaid on the execution drawings.

Clearing reservations: checking corrections before the perfect-completion warranty expires

A reservation is only as good as the check that follows its correction. Once the contractor has redone the work, a second flight repeats exactly the same viewpoints as the initial survey: comparing before and after, image against image, establishes unambiguously whether the defect has been fixed, partly addressed, or left unchanged. This photographic clearing of reservations is scheduled within the deadline set in the official report, and preferably well before the one-year warranty of perfect completion expires: past that point, asserting an uncorrected defect becomes markedly harder.

For a multi-building scheme — joint ownership, housing estate, commercial development — this verification pass is organised as a single tour, in the same spirit as the upstream drone construction monitoring: same flight paths, same operator, one consolidated comparative report for the whole developer.

Prices observed in 2026

Ranges observed in 2026 (excl. VAT):

Scheduled a few days before the acceptance date, this check gives the contractor time to fix issues before the official report is signed. Our drone roof inspection page presents the service; request a quote stating the planned acceptance date, the type of structure and the number of buildings involved.

Request a free quote

Put it into practice

Also worth reading