Damp and moisture meters
A pinless meter read high on foil-backed board. Why should that reading not be written up as rising damp in the wall behind?
The pinless reading on foil-backed board should not be written up as rising damp in the wall behind. A pinless meter is an aid that reacts to whatever sits near the surface, and foil behind a board can lift that reading without the masonry being wet. The high figure belongs to the lining the meter was held on. It is not a diagnosis of the wall, and it is not proof that moisture is rising from the ground.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Foil is put there as a vapour layer or as the back of a board. A pinless meter cannot tell that metal skin from water in a wall. Writing the number up as rising damp invents a cause the instrument never identified. The survey should say where the meter was placed and what the lining in front of it actually was.
If the wall itself needs seeing, that means an edge, a lifted board or an agreed opening, not another pass of the same meter on the same foil. Salts, a bridged course or a tide mark would be separate observations, each only a reason to investigate further. Keep this reading out of any rising-damp sentence in the report.
What should you ask your surveyor?
- Was the high reading taken on foil-backed board, and where was that board fixed?
- Did you see the wall behind the foil at any point, or only the lining?
- Will you keep this reading out of any comment about rising damp?
What are the typical next steps?
- Do not write the pinless reading up as rising damp in the wall.
- Record that the meter was on foil-backed board and is only an aid.
- If the masonry must be checked, find a way of seeing it rather than re-reading the foil.
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Also asked about this
If the meter reads high, is the wall behind definitely wet?
No. On foil-backed board a pinless meter can read high because of the foil. That figure is not the wall and it is not rising damp.
Would pins in the same board diagnose the wall?
No. Pins in the board still meet the board. They do not, by themselves, prove that moisture is rising in the masonry behind it.