Damp meter readings, defined: the figures a handheld moisture meter shows on a wall, floor or timber, which indicate relative moisture rather than measure water, and which count as evidence only when logged with location, date and a photo.
Damp meter readings are the numbers a handheld moisture meter shows when held or pinned against a surface. In UK surveying they are the first-pass tool in a damp survey, used to map where moisture is present and how far it spreads.
The definition matters because the number on the screen is routinely read as a percentage of water in the wall. It is not. On anything other than timber the meter measures conductivity or capacitance and converts it to a scale, so the reading is an indication to be interpreted, not a fact to quote on its own. A reading with no context is weak evidence in a damp dispute; a pattern of readings with context is often the strongest.
What damp meter percentages mean
Most meters were designed for timber and their percentage scale is calibrated for wood. Used on plaster, brick or concrete, the reading is a wood moisture equivalent (WME): the level timber in contact with that surface would reach. The bands surveyors work with are approximately:
- Timber: indoor joinery normally sits in the low to mid teens. Readings in the high teens warrant attention; timber in the twenties and above is at risk of decay.
- Walls and plaster (WME): readings under roughly 20 are generally treated as dry, readings in the twenties as moderate and worth investigating, and readings well above that as high. The exact bands depend on the meter, so the manufacturer's scale is the reference.
Two things distort readings on masonry. Salts left by old damp conduct electricity and push the number up on a wall that has since dried; foil-backed plasterboard, cables and pipes do the same. This is why a surveyor reads a pattern rather than a single number.
Pin versus pinless meters
- Pin meters push two metal pins into the surface and measure electrical resistance between them. They read at the depth of the pins, leave small holes, and are the more reliable of the two on timber. On hard masonry they read the surface only.
- Pinless (capacitance) meters are pressed flat against the surface and send a signal into the material, typically to a depth of a couple of centimetres. No holes, fast to scan a whole wall, but readily fooled by anything conductive behind the surface.
Neither type measures water content in masonry. The definitive method is a calcium carbide test or laboratory analysis of a drilled sample, which RICS guidance treats as the way to confirm rising damp.
Why a reading needs a photo, a location and a date
A reading is a value at a point in space and time; strip either and it stops being evidence. What makes a reading usable in a housing disrepair complaint, a deposit dispute or an insurance claim for water damage:
- The meter display in the photo, in contact with the surface, so the number and the place are in one frame.
- The location: room, wall, height above floor, distance from the corner, ideally on a sketch so the same points can be read again.
- The date and time, from a source other than memory, plus heating and weather conditions if condensation is possible.
- The material, the meter model and its scale.
- Repeat readings at the same points weeks apart.
Awaab's Law, with its timescales for social landlords to investigate damp and mould, makes this practical rather than academic: the landlord has to show what was found, when, and what was done.
Damp meter readings example: a ground-floor flat with a black patch behind the sofa
A tenant in a housing association flat reports mould on the living room wall. The surveyor takes pinless readings on a grid across the wall: high in a band from skirting to about a metre, dry above, and dry on the same wall next door. Each reading is photographed with the meter on the wall and the point marked on a sketch.
Six weeks later, after the heating has been on and an extractor fitted, the same points are read again. The band has not moved. That rules out condensation as the whole story, and the external inspection finds a raised patio bridging the damp-proof course. Without the first grid, the second visit would be a fresh opinion; with it, the two sets of readings are a comparison anyone can check.
What damp meter readings do not do, and the mistakes people make
They do not diagnose the cause. Rising damp, penetrating damp, condensation and a leaking pipe can all produce the same number.
They do not measure water in a wall. Quoting a WME figure as a percentage of moisture content is a common error in reports and a recurring point of challenge.
The recurring mistakes: one reading offered as proof of damp; no note of where on the wall it was taken; the meter photographed away from the surface; no repeat visit.
Where damp meter readings go
The readings, photos and sketch form part of the property inspection or damp survey report, kept on the property file and disclosed in a dispute. Readings taken by a tenant or contractor between visits are useful too, if recorded the same way. See tenant repair reporting with photos for how to ask for them.
Venta Capture, a product of VentaVid, lets the person in the property record readings that stand up. The tenant, contractor or housing officer is sent a secure, personal capture link and follows guided steps in the mobile browser, with no app: a photo of the meter on the wall at each marked point, the reading typed in, the room and wall chosen from a list. The submission arrives timestamped and sealed, so the next visit compares against a fixed record. See the Venta Capture pages.
In practice: see how field service teams use Venta Capture.