How do surveyors check for damp?

Damp is one of the most common things a survey uncovers, and one of the most worried-about. The good news is that "damp" is not a single problem but several, each with a different cause and a different fix. Here is how a chartered surveyor approaches it.

The three kinds of damp

Most damp falls into one of three categories. Penetrating damp enters horizontally through a defect such as a failed roof, cracked render, blocked guttering or a leaking pipe. Rising damp draws moisture up from the ground through walls where a damp-proof course is absent, bridged or failed. Condensation forms when warm, moist air meets cold surfaces in poorly ventilated rooms, and is by far the most common cause of the black mould seen around windows and in bathrooms.

How a surveyor assesses it

A surveyor combines several methods rather than relying on any one. A visual inspection looks for tide marks, staining, blown plaster, peeling paint, salt deposits and mould. A moisture meter gives readings that indicate elevated moisture, though readings must be interpreted with care, since meters can respond to salts and other materials, not just water. Just as important is professional judgement: the pattern, location and likely source of the damp, read in the context of the building's age and construction.

A note on moisture meters

Moisture meters are a useful tool but not an infallible one. A high reading does not by itself prove rising damp; it indicates moisture that needs explaining. This is why a careful surveyor treats a meter as one input among several, and is cautious about the "rising damp" diagnoses that sometimes lead to unnecessary and expensive chemical treatments.

Why the cause matters more than the symptom

Treating the symptom without fixing the cause wastes money. Condensation is often resolved by improving ventilation and heating, at modest cost. Penetrating damp is fixed by repairing the defect letting water in. Rising damp, where genuinely present, may need a new damp-proof course. Identifying which you are dealing with is the whole point of a proper assessment.

What to do if damp is found

Read what the report says about the likely cause and recommended action. Where the surveyor recommends a specialist damp and timber investigation, it is usually worth obtaining, both to confirm the cause and to price the remedy, which may also give you grounds to renegotiate. Be wary of free "damp surveys" offered by firms that also sell the treatment, as their incentives are not aligned with yours.