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C-DRONE GUIDE · 27 JULY 2026

Real estate due diligence by drone: technical audit before acquisition, price

In a commercial property acquisition — logistics warehouse, office building, retail park, hotel — hidden capex almost always sits in the same place: the roof. End-of-life waterproofing, cracked rooflights, ageing rooftop plant: hundreds of thousands of euros the classic visit never sees, for lack of access. Technical due diligence relies on the vendor's reports; the shrewd buyer checks them against an independent record. That is exactly what the drone delivers: in one day, the true, dated condition of an asset's — or a whole portfolio's — roofs, terraces and façades, thermography included. Here are the method, typical cases, and prices observed in 2026.

Published on 27 July 2026, reviewed on 28 July 2026 — regulations in force as of July 2026.

Due diligence's blind spot: the roofs

A data room holds leases, statutory diagnostics, sometimes a technical audit — rarely a recent, exhaustive record of the roofing. Yet on a 20,000 m² warehouse, waterproofing renewal runs to hundreds of thousands of euros: it is often the first price-negotiation item. The drone flight documents what nobody goes to see: membrane condition and upstands, cracked rooflights and smoke vents, corroding steel decks, gutters colonised by vegetation, plant fixings — following the detailed grid of our drone roof inspection guide.

Thermography adds the invisible: waterlogged insulation zones under the waterproofing — the method of our flat-roof leak detection guide — and envelope insulation defects. The protocols of drone building thermography are formalised by research: a study by Entrop and Vasenev published in 2017 in Energy Procedia worked precisely on designing a protocol for building thermography by drone — conditions, trajectories, interpretation (see the study on Google Scholar).

One audit day, one whole asset

The typical sequence on one asset: systematic photographic flight over the roofing (every slope, terrace and unit), façade passes — cracking, expansion joints, cladding, as in our façade inspection guide — thermography if conditions allow, and context shots: car parks, grounds, fences, visible easements. All georeferenced and timestamped. On a multi-site portfolio, the same team covers two to four assets a day depending on size and spread: the uniform protocol makes assets comparable with each other — something reports from different sources never allow.

The deliverable is calibrated for the data room: a report structured by element with defect grading (sound / watch / works to price), full-resolution photos, and affected areas measured on the orthophoto — the base the buyer's consultant turns into capex figures. The audit dovetails with the tertiary decree obligations the buyer will inherit: better to measure the envelope before signing.

Discretion, access, timing: the real constraints

Due diligence has its codes: confidentiality (the deal is not public; the provider signs the NDA and the mission presents on site as an ordinary technical inspection), access negotiated with the vendor or occupier — flights happen with the site operator's agreement, tenants informed — and short timelines: the exclusivity window counts in weeks, the drone audit fits within days, authorisations included for most zones. On dense urban sites or near airfields, the pilot handles the usual steps described in our flying in cities guide.

The same protocol works on the sell side: a vendor producing a recent, honest drone record of the roofing defuses the discount negotiation — a logic already described for homebuyers in our roof check before buying guide, transposed here to commercial assets.

Prices observed in 2026

Ranges observed in 2026 (excl. VAT):

Against the value of a commercial acquisition, the drone audit costs less than an hour of legal advice — on the item that concentrates the bad surprises. Request a quote stating the number of sites, their locations and the deal's timetable.

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Put it into practice

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