Damp and moisture meters
A gap at the skirting shows dot-and-dab plasterboard on an outside wall, and mould is in that gap. Why can that void be a cold spot without being rising damp?
That void can be a cold spot, with mould fed by condensation, without the moisture being rising damp. A gap at the skirting shows dot-and-dab plasterboard on an outside wall, and mould is in that gap. Dot-and-dab leaves a cavity of still air between the board and a cold external leaf. The gap at the skirting is a view into it. Cold surfaces in an unventilated void grow mould without any water rising through the masonry. The survey can record the lining and the mould. It has not diagnosed rising damp, and it has not proved damp 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?
Rising damp is a claim about moisture moving up a wall from the soil. A mouldy void behind plasterboard is often a claim about air and a cold face. The two can be confused because both leave marks low down. Here the low mark is inside the gap the dabs created, on an outside wall. That location fits a cold spot. It does not fit a cavity-free diagnosis copied from a solid wall, and it does not, by itself, fit an injected damp course.
Ask the surveyor whether any reading was taken on the masonry itself or only in the gap, and keep a damp-proofing quote away until that is clear. Ventilation and the lining are the first conversation, not a chemical treatment the report did not specify. Tell the solicitor the mould is in a dot-and-dab void. The survey has not called it rising damp.
What should you ask your surveyor?
- What of the dot-and-dab void was visible at the skirting gap?
- Where exactly was the mould, in the void or on the masonry?
- Did you diagnose rising damp, or only record a cold gap?
What are the typical next steps?
- Treat mould in the gap as a cold void, not as proved rising damp.
- Ask whether any reading was on the masonry rather than in the void.
- Do not buy an injection off a lining the survey did not call rising damp.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the room smells musty, is the whole wall damp from the ground?
A smell records air in the room. It does not prove rising damp, and the survey located mould in the gap behind dot-and-dab on an outside wall. That void can be cold and mouldy on its own. The inspection has not shown moisture rising through the wall. The smell is not that missing proof.
Does foil-backed board stop the cold spot?
The survey did not identify the board as foil-backed, and a backing would not turn the gap into rising damp either way. Mould in the void is explained, on what was seen, as a cold spot behind the lining. The report has not specified a new board and has not diagnosed moisture from the ground.