Can you assess a building's condition from a photograph or satellite image?

The temptation is understandable: if there is a Street View image of the façade and an aerial view of the roof, why not 'diagnose' the building from a computer? Some services already produce entire paragraphs about cracks, corrosion and waterproofing based on these images. Before placing any confidence in such a diagnosis, it is important to understand what a photograph can actually show - and what it is physically impossible for it to reveal.

The first problem: the photograph is not from today

Street-level images are captured in survey campaigns: in a large city they may be updated every year or two, while in smaller towns the last survey may have taken place five, eight or ten years ago. Aerial imagery has the same problem. The direct consequence is that the 'crack' you see may have been repaired years ago, while the pristine façade in the photograph may since have deteriorated - or be covered in scaffolding right now. A diagnosis based on an image with no verified date is a diagnosis of the past.

The second problem: are you sure it is the right entrance?

Anyone who has looked up their own home on a map knows that building-entrance geolocation is less reliable than it seems. Map pins may place a street number on the neighbouring building; streets may have been renamed; two façades on a corner may compete for the same coordinates; and buildings may have several entrances. An automated assessment that downloads 'the façade photograph' from an address could confidently be describing the building next door. With an aerial view, determining exactly which roof belongs to which unit in a condominium building is even more difficult.

The third problem: the resolution is not sufficient for professional conclusions

At the resolution of a street-level image, an expansion joint, a rainwater-pipe shadow, a rain streak and a structural crack may be indistinguishable. In an aerial view, 'vegetation in the corners of the roof' could be harmless moss, accumulated pollen or a genuine waterproofing problem - there is no way to tell from 200 metres above. Building inspectors do use their eyes, but they also use their hands, a sounding hammer, a moisture meter, exploratory openings and physical access to the roof. There is a reason for that.

The fourth problem: the important issues are not visible

Even if the photograph were current, showed the correct entrance and had high resolution, it still could not reveal what matters most: the type and condition of the structure (no public register records whether a building uses concrete, steel or load-bearing walls - only the technical plans or an inspection can establish this), concealed services, internal soil and waste pipes, damp behind tiling, or the condition of the floor slab beneath the flooring. By definition, most costly building defects are invisible from the street. If they were visible, the seller would already have repaired them before listing the property.

Does this mean automated visual assessment is useless?

Not exactly. As a general guide that is honest about its limitations, it can provide context: the surroundings, the apparent building type and the street's overall appearance. The problem is not the tool but how it is presented. When general guidance is couched in the language of an expert report - 'deterioration of waterproofing along the northern perimeter' or 'corrosion of fixings' - despite no one having visited the building or verified the image date, the service is selling a level of precision that does not exist. One simple question strips away that pretence: when was the analysed image taken, and how was it verified as showing this property? If the service cannot answer, you have your answer.

What does work: a professional inspection (and it costs less than you think)

There is only one reliable way to establish the true physical condition of a property: have an arquitecto técnico (technical architect), aparejador (building surveyor) or professional inspector visit it. A typical pre-purchase inspection costs between €200 and €400 and examines services, damp, windows and doors, the apparent condition of communal elements and the weaknesses commonly associated with the building's period. Compared with a purchase worth hundreds of thousands of euros, it is the cheapest insurance you will ever buy - and the report also gives you technically grounded evidence for negotiations.

The sensible order for due diligence is therefore: first, the instant official information (risks, Cadastre, market and surroundings - a few minutes and a few euros); next, the private documents you should request from the seller and building manager; and finally, once the purchase is serious, an in-person inspection. Each layer acts as a filter: do not pay to inspect a home in a preferential flood-flow zone, and do not reject a home because of an old photograph when a professional inspector might have approved it.