Intrusive Investigation

An intrusive investigation is a site investigation technique that goes beyond visual inspection to physically access concealed elements of a building or structure. Where visual inspection — including 360° photography and thermal imaging — is limited to what can be seen from accessible surfaces, an intrusive investigation involves removing finishes, cutting openings, drilling cores, or excavating to expose and assess materials or conditions that are hidden.

Intrusive investigations are typically commissioned when a visual inspection raises concerns that cannot be resolved without access to concealed elements. Common triggers include: suspected structural defects where the visual evidence is inconclusive, the need to assess the condition of a concealed structural element (the root of a column in its foundation, the condition of a flat roof deck beneath insulation, the type and condition of a wall tie in a cavity wall), or the requirement to take material samples for laboratory analysis (chloride content, carbonation depth, asbestos identification, soil bearing capacity).

The decision to commission intrusive investigation involves a trade-off between the value of the information obtained and the cost and disruption of the investigation — which includes not just the investigation itself but also the reinstatement of any openings made. In occupied buildings, intrusive investigation requires careful programming to minimise disruption to occupants.

Pre-investigation photographic surveys are valuable precisely because they provide the spatial baseline against which post-investigation findings can be located. If a core is drilled at a specific location to assess carbonation depth, that location should be documented photographically before drilling — both to record the pre-existing surface condition and to anchor the sample location to the floor plan so that results can be interpreted in their structural context.

360° panoramic documentation before and after intrusive investigation has become standard practice in condition-monitoring programmes for critical infrastructure, where the need to track investigation locations across survey campaigns over years or decades makes spatial accuracy essential.