Damp Misdiagnosis: How It Happens, and How to Protect Yourself

Rising damp is diagnosed far more often than it actually occurs. This isn't a fringe opinion — it's been raised publicly by a former chair of RICS's own Building Surveyors' Faculty. Here's the real mechanism behind it, what it can cost you, and how to tell whether a diagnosis is actually evidence-based.

This is a mainstream concern, not a conspiracy theory

Three separate, credible voices within UK surveying and building conservation have raised the same concern, independently, over a number of years:

Jeff Howell, the former Sunday Telegraph "Homefront" columnist, made the same case at length in his book The Rising Damp Myth, arguing that a significant share of the damp-proofing industry is built on the misuse of a single tool: the handheld moisture meter. Elaine Blackett-Ord, a conservation-accredited surveyor, has raised the identical concern specifically for period and traditional buildings, where what looks like rising damp is usually a ventilation or breathability problem instead.

This concern reached a formal, institutional conclusion in September 2022, when RICS, Historic England and the Property Care Association jointly published Investigation of Moisture and its Effects on Traditional Buildings — a position statement, also backed by Cadw, Historic Environment Scotland, Northern Ireland's Historic Environment Division, the SPAB and the IHBC, setting out an evidence-first diagnostic standard specifically because misdiagnosis had become a widely recognised problem.

The mechanism: what a moisture meter actually measures

A standard handheld moisture meter doesn't measure water. It measures electrical resistance, and was originally calibrated for timber. When it's pressed against masonry, anything conductive in the wall — dissolved salts, a metal corner bead, foil-backed plasterboard — will push the reading up, regardless of whether liquid water is actually present. Used on its own, it's a screening tool, not a verdict. That's not our opinion; it's what BS 6576, the British Standard covering rising damp diagnosis, itself says: a meter reading is qualitative, not conclusive.

A proper diagnosis sits above the meter, using tools that can actually confirm what's happening: a calcium carbide ("Speedy") test to measure total moisture content directly, and — where it matters — gravimetric laboratory analysis, the only method that separates genuine free water from moisture being held by salts. That's the standard we work to on every survey.

Hygroscopic salts: the single biggest trap

This is the mechanism behind most repeat "failed damp-proof course" cases we're asked to look at. Historic ground moisture — or old rising damp that was never fully treated — leaves nitrate and chloride salts embedded permanently in the plaster and masonry. Those salts don't go away on their own. They sit in the wall and keep pulling moisture out of humid air indefinitely, completely independent of whether there's any active water ingress at all.

There's a simple way to tell the two apart. Efflorescence — a white, powdery surface deposit — is usually a one-off leftover from a past wetting event, and it washes or brushes away once the source is fixed and doesn't come back. Where that wetting event was a flood or a significant escape of water, the drying process itself has to be done correctly or the salts and moisture stay in the fabric — covered in our guide to drying out a property safely after flooding. Genuine hygroscopic salt contamination behaves differently: the patch keeps re-wetting with humidity, on a cycle, regardless of the weather or whether any leak has been fixed.

Two more things worth knowing

• The "penny-sized dots" pattern. A visible line of small circular marks in the mortar or brick, low down on an external wall, is physical evidence of a past chemical injection — useful if you're assessing a property's treatment history, including your own.
• Older electro-osmotic systems. Some properties treated between 1962 and 1974 have an older electrical damp-proofing system installed. If it's switched on during a moisture-meter survey, it produces artificially high readings that look exactly like active rising damp. It needs to be switched off before any meaningful reading can be taken.

What misdiagnosis actually costs

Getting the diagnosis wrong isn't a small mistake. The costs stack in layers, and most of them are avoidable.

Survey issues — damp among them — are the second-biggest cause of UK house sale collapses, behind only mortgage and lending problems, so a diagnosis that surfaces late doesn't just cost the treatment; it risks the sale itself.

It isn't always an honest mistake

In 2019, Weatherproof UK Ltd cold-called two elderly residents in Rugby and Lillington, Warwickshire, telling them their homes had rising and penetrating damp. Both signed contracts on the spot — £1,995 and £1,750 — and were unlawfully made to waive their statutory 14-day cooling-off period in the process. Warwickshire County Council's Trading Standards team brought in an independent chartered building surveyor, who found that neither property showed damp requiring a damp-proof course, and both already had existing, functioning ones. The company was ordered to pay over £21,000 in compensation and costs.

It's the same pattern that shows up in cavity wall insulation compensation claims: CIGA, the industry's own guarantee body, explicitly warns homeowners to be wary of cold-callers and claims-management companies exploiting genuine problems. Whether the mistake is honest or not, the protection is the same — a diagnosis you can see the evidence for, and the right to a second opinion.

What an evidence-based diagnosis actually looks like

External inspection before internal. Visual evidence weighed alongside — not instead of — moisture readings. Ventilation and humidity assessed separately, since condensation is the type most often mistaken for rising damp. A diagnosis reached before any treatment is recommended, not the other way round. This is the process we follow on every survey — see our full breakdown of how we carry out a thorough damp survey.