Damp and moisture meters
Mould sits on a lintel above a trickle vent that is shut. Has humidity been measured?
No. Humidity has not been measured. Mould sits on a lintel above a trickle vent that is shut, and the visit recorded those two things: the growth and the closed vent. It did not measure humidity, air temperature or moisture in the air, and it did not run a test that would explain the mould. A shut vent is a clue that background air may not be entering there. The survey has not decided whether the mould is condensation, a leak, or something else.
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?
Mould needs a surface that stays damp enough for growth. A cold lintel over a closed trickle vent is a place where still air can leave moisture on the masonry, but that mechanism is a hypothesis until the air and the fabric are checked. The surveyor can see staining or spots and a vent that is shut. Seeing them does not give a humidity figure and does not open the lintel. Wiping the growth off would not be a measurement.
Ask the solicitor what the seller knows about the mould and whether anyone has checked the vent and the lintel. If you want humidity known, that is a separate damp investigation, not a reread of this note. A lender may ask for that investigation where mould is left unexplained. The home survey has not measured humidity and has not prescribed a cure. Do not treat the shut vent as a completed diagnosis.
What should you ask your surveyor?
- Where is the mould on the lintel described?
- What state was the trickle vent recorded in?
- Which tests of the air does the report say were not done?
What are the typical next steps?
- Read the mould and the shut vent as a visual note.
- Commission a damp investigation if humidity must be known.
- Do not wipe the growth and call that a diagnosis.
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
Does opening the vent on the day of the visit count as a test?
No. Even if the vent were opened for a moment, humidity would still not have been measured, and the report records the vent as shut. A position of a slot is not a moisture reading in the air. The survey saw mould on the lintel. It has not explained it with a humidity result.
Was the lintel opened to see if water is tracking through?
No. The lintel was not opened. Mould on its face and a trickle vent that is shut were recorded from the room. Tracking through the wall, a cold bridge, or air that is simply too still are all still possible. Humidity was not measured, so none of those causes has been selected.