Drone building inspection: what does it show, and what doesn't it?

A drone can get close to a facade or roof without scaffolding, an aerial work platform (cherry picker) or anyone on the roof. That makes an inspection easier to organise, but it does not change what a camera can see. Here is what a drone building inspection shows, where its limits lie and when to combine it with someone on site.

What does a visual drone building inspection show?

Everything visible from outside, at close range and from angles you cannot reach from the ground. The basis is an ordinary (RGB) camera taking photos and video.

On a drone facade inspection, you look for cracks, spalling brick or render, damaged cladding and staining that can point to damp. A drone roof inspection covers the roof covering, upstands and edges, and gutters and outlets that are getting blocked. At joints and junctions, you see open or dried-out joints, sealant around windows and the junction between facade and roof. Cladding panels, trims or equipment that have worked loose and could fall also stand out.

On solar panels, a visual inspection shows broken glass, heavy soiling, loose cabling and nests under the array. How much soiling costs in yield, and how often cleaning makes sense, is covered in how often to clean solar panels.

What does thermal imaging from a drone add?

A thermal camera makes temperature differences visible that the naked eye cannot see. It helps to find heat loss, insulation problems and damp, but only when conditions are right.

Buildwise, the Belgian building research centre, describes how a thermal camera records infrared radiation and turns it into an image in which each pixel has a temperature value. Among its applications it lists heat loss, damp and infiltration problems, and inspections at height by drone of roofs, facades and solar panels (Buildwise).

The Carbon Trust sets out the conditions for a reliable survey of the building envelope: a temperature difference between inside and outside of at least 5 °C and more commonly 10 °C, no sun on the surface before and during the survey, no precipitation, and little wind. That is why such surveys often take place in the dark or early in the morning, and why winter is often advocated. The organisation also notes that outdoors, usually only qualitative thermography gives robust results, and that reading the images takes suitable knowledge and experience (Carbon Trust).

Why glass and metal distort the image

Brick and plaster emit their own heat well, glass and metal much less so. Such materials reflect the temperature of their surroundings, like a mirror (Carbon Trust). According to camera maker Teledyne FLIR, an accurate temperature measurement is unlikely when emissivity is below 0.5, and polished metal such as copper or aluminium usually sits below 0.10 (Teledyne FLIR). On a glazed facade or a metal roof, a thermal image therefore often shows the sky or a neighbouring building rather than the material itself.

For solar panels there is a dedicated technical specification, IEC TS 62446-3. It defines the thermographic inspection of PV modules and plants in operation, with requirements for the equipment, ambient conditions, procedure, report and the qualification of the person carrying it out (IEC).

What can a drone not see?

Anything behind the surface, anything that needs a calculation and anything that has to be touched. A drone is a remote camera and measures nothing in the structure.

A camera cannot see inside a cavity wall, under the roof covering or behind cladding panels. A thermal camera measures radiation from the surface, so a problem behind it only shows up if it changes the outside surface temperature. A drone gives no structural calculation either: it shows where a crack is and what it looks like, but whether it affects the stability of the building is for a structural engineer or architect to judge. And hands-on tests, such as pulling on a fixing, tapping render, opening up a joint or taking a sample, are beyond a drone.

How are the findings reported?

In a good report, every photo is tied to a spot on the facade or roof, with a short, factual description of what can be seen. A contractor or engineer then knows straight away where to look.

What matters is that every finding is located, that the description says what is visible without drawing conclusions the images cannot support, and that it is clear what needs attention first. If a building is inspected regularly, you also want to compare the same spot over the years. Soiling found during the inspection can be the basis for targeted cleaning; how that works by drone is explained in how drone cleaning works.

When should you combine a drone inspection with rope access or an aerial work platform?

When a finding has to be touched, measured or repaired. The drone shows where to look, and someone on site confirms it.

A typical sequence starts with a drone inspection of the whole building. A rope access technician or an aerial work platform then comes in only where a loose element, a crack or damp needs closer investigation, so access at height is limited to the zones that need it.

Which rules apply to a drone flying close to a building?

That depends on the category the flight falls into. The open category sets strict distances from people and built-up areas; outside those limits, the flight falls under the specific category.

According to EASA, a flight in the open category stays below 120 metres. In subcategory A2, with a class C2 drone, you keep a horizontal distance of 30 metres from uninvolved people (5 metres with the low-speed function), and in A3, 150 metres from uninvolved people and urban areas (EASA, open category). A flight outside those limits falls under the specific category (EASA, specific category). In Belgium, depending on the flight, that requires a declaration based on a standard scenario, an operational authorisation or a LUC certificate, through the FPS Mobility and Transport (FPS Mobility).

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