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C-DRONE GUIDE · 15 SEPTEMBER 2026
Timber roof framing and drones: what an aerial survey documents, decay and hidden wood-boring insects, price
A barn awaiting conversion, a farmhouse on the market, a communal hall or a listed church spire: as soon as an old timber frame enters a renovation project or a property deal, the same question comes up — what state is the wood in, under the covering? A drone photographs what sticks out: broken tiles, exposed rafters through a gap, a sagging ridge line. It sees neither the decay progressing under a covering that is still watertight, nor the galleries that the house longhorn beetle or the furniture beetle bore inside the wood for years before an exit hole ever betrays their presence. Here is what an aerial survey concretely brings to a renovation or acquisition file, where its reach stops, and why it replaces neither a timber-frame diagnostician nor, in the areas concerned, the statutory termite diagnosis.
Published on 15 September 2026, updated on 22 September 2026 — regulations in force as of September 2026.
What an aerial survey actually documents: covering, roof overhangs, ridge-line deformation
Seen from a drone, a timber frame is never revealed directly: what the camera captures is the covering that protects it — tile, slate, lead or zinc depending on the building — and the few spots where that covering has already failed. A high-resolution orthophoto and a photogrammetric 3D model usefully document several indirect clues: broken, shifted or missing tiles exposing sarking boards or a rafter, an underlay visible through a gap, moss and vegetation concentrated where damp lingers, and above all the geometry of the ridge line — a sag, a twist or a warp in the roof plane, often the first visible sign of an ongoing structural deformation.
On this last point, survey precision matters: a study published in 2025 in the proceedings of the 42nd International Symposium on Automation and Robotics in Construction (ISARC), by Nick Chodura, Melissa Greeff and Joshua Woods, evaluates the optimal flight parameters for 3D reconstruction of complex rooftops: a ground sampling distance (GSD) of 0.75 to 1.26 cm combined with 85% image overlap gives the best model accuracy for minimal flight time (see the study). At this level of detail, two surveys taken months or years apart make it possible to objectively measure the progress of a suspected sag — a quantified benchmark that neither a one-off ground observation nor a plain set of photos provides.
An intact covering can hide a rotten frame: what photogrammetry does not see
Decay in a timber frame almost never starts where the eye looks. It settles first at bearing points — the end of a purlin built into a wall, a tie-beam housing on a wall plate, the foot of a rafter against a blocked gutter — exactly where damp lingers and where the covering, seen from above, can stay perfectly intact for years. A drone documents a surface: as long as a tile or slate has not failed, no camera — RGB, multispectral or thermal — sees through a sound covering to reveal the condition of the wood beneath it.
This is the structural limit of any aerial survey applied to a timber frame: it objectifies a geometry and an envelope, never a mechanical strength. Only a timber-frame diagnostician can establish a reliable sanitary assessment, by probing suspect members with an awl, backed up if needed by a resistograph — an instrument that measures resistance to a fine needle driven along the grain and reveals weakened wood without dismantling anything. The drone survey keeps its use upstream: it points that diagnostician to the areas where the covering already shows signs of weakness, rather than having them probe an entire frame at random.
The central honesty point: wood-boring insects, an attack invisible from the air
Two insects dominate old timber frames in France: the house longhorn beetle (Hylotrupes bajulus), whose oval exit holes of 6 to 10 mm signal an attack already underway, and furniture beetles (family Anobiidae), recognisable by their round holes of 1 to 3 mm and the fine bore dust they leave on the ground. In both cases, the larva develops inside the wood, sometimes for several years, boring galleries invisible from the surface; the exit hole only appears when the adult insect emerges, often once the frame is already weakened. According to an INRS report on wood biodeterioration (2021), more than 10% of old dwellings show signs of attack by wood-boring insects or wood-decaying fungi during inspections carried out before renovation work.
The honesty point. No drone detects a wood-boring larva: the attack plays out under the surface of the wood, beyond the reach of any aerial camera. Active detection of this kind of infestation relies on a radically different technique — in contact with the wood, not from the air. A study published in 2026 in Sensors by Lisa Anna Limmer, Burkhard Plinke, Constanze Messal and Stephan Biebl details the principle and experimental validation of acoustic emission detection: a sensor placed directly on the timber records the structure-borne sound produced by a feeding larva, making it possible to localise larval activity without dismantling anything (see the study). This is the exact opposite of a drone survey: a sensor in contact with the wood, member by member, rather than a remote camera over the whole roof.
This limit connects to another point of vigilance, distinct but often confused with it: the termite diagnosis. Article L. 133-6 of the French construction and housing code requires, in areas delimited by a préfecture order — around fifty mainland départements, wholly or in part —, a termite-presence report dated less than six months before any authentic sale deed. Termites operate largely underground or within the thickness of masonry: this statutory diagnosis, too, relies on a ground-based inspection, never on an aerial image. A drone survey never substitutes for it; it documents geometry and covering, not the sanitary condition of the wood or the presence of a pest.
Who commissions this survey, the combined method, and 2026 prices
Demand mainly comes from heritage architects (ACMH) preparing a file on a listed or registered building, from notaries and buyers commissioning a survey before purchasing a barn or farmhouse to convert, from carpenter-joiners pricing frame repairs without climbing up on every visit, from co-ownership managers handling an old building with a flat roof or a mansard attic, and from local authorities owning old communal buildings — town halls, market halls, communal barns. In every case, the most effective method combines two separate services rather than expecting everything from the drone: an aerial survey for geometry and covering, then, on the areas it flags, a ground-based timber-frame diagnostician.
Ranges observed in France in 2026, excluding VAT:
| Service | Observed price (excl. VAT) |
|---|---|
| Photogrammetric survey and orthophoto of a standard roof (house, barn) | €350 to €650 |
| Full 3D model with ridge-line geometry measurement | €600 to €1,000 |
| Tracking a suspected sag over time (two compared passes) | €900 to €1,600 |
| Listed or registered building, large hall or spire (complex access) | €1,200 to €2,500 |
These missions build on our drone roof inspection and surveying and photogrammetry services, and on the technique detailed in our guide to nadir or oblique photogrammetry. For a listed building, our guide to historic-monument roof inspection details the specific framework for heritage architects and regional heritage authorities; before an acquisition, see also our guide to real estate due diligence by drone and, for a façade, our guide to facade diagnosis before renovation. The regulatory information on this page reflects the rules in force in September 2026. For a renovation project or an acquisition, request a quote stating the type of building, its heritage status if any, and the priority objective — understanding a visible deformation or preparing a conversion file.