Surveys & Condition
Damp Meters, Thermal Imaging And What Instruments Prove
Survey instruments detect indications rather than diagnose causes, and the readings they produce are frequently reported as findings when they are only starting points.
Instruments used during a survey carry an air of precision. Each measures something narrow, and the gap between what is measured and what is concluded is where mistakes occur.
A damp meter measures conductivity
The common handheld instrument passes a small current between two pins and reports the electrical resistance of whatever lies between them.
Moisture reduces resistance, which is why the reading correlates with dampness. So do salts in plaster, foil-backed materials, and certain adhesives and paints.
The device is calibrated for timber, so a reading taken on plaster is being used outside its design purpose, and the number displayed is an indication rather than a moisture content.
High readings do not identify a cause
Water reaching a wall from the ground, from a leaking gutter, from a failed seal and from condensation all produce elevated readings at the same point.
Distinguishing between them requires the pattern of readings, the height and distribution of staining, the external condition of the building and often instruments of a different kind.
A report that lists readings and recommends a chemical treatment without establishing a cause has skipped the diagnostic step entirely.
Thermal imaging shows surface temperature
An infrared camera produces an image of surface temperature differences. It does not see through walls and does not detect water directly.
Damp surfaces appear cooler because evaporation removes heat, and missing insulation appears as a temperature difference, so both show up as patterns worth investigating.
Conditions have to be right for the image to mean anything: a meaningful temperature difference between inside and outside, and surfaces not recently warmed by sunlight or heating.
Other tools have similar limits
Moisture can be measured more reliably by taking a physical sample and analysing it, which is invasive and therefore rarely done during a pre-purchase inspection.
Drainage cameras, borescopes and monitoring gauges each answer one question well, and each requires access that a non-invasive survey does not have.
This is why reports recommend specialist investigation. The general surveyor has established that something merits attention using the tools available within their remit.
Who is holding the instrument
A contractor offering a free damp inspection is quoting for work, and the reading supports a recommendation the contractor benefits from.
An independent professional paid a fee for an opinion has no interest in the remedy chosen, which is the structural reason the two reports often differ.
The useful question to ask of any reading is what else could produce it, because an instrument that cannot rule out alternatives has not proved the one being asserted.
Questions readers ask
Does asbestos in a house have to be removed?
Often not. Undamaged, bonded material that will not be disturbed is commonly managed in place. Removal is a decision driven by condition and planned works.
Will a normal survey tell me if there is asbestos?
No. A standard survey may flag material that could contain it, but confirmation requires sampling and laboratory analysis by a competent specialist.
