Damp and moisture meters
Mould rings the bathroom ceiling around an extractor that did not spin. Why is that a fan and moisture note rather than a roof leak?
It is a fan and moisture note because the mould rings an extractor that did not spin, which is the pattern of moist air left in the room, not a leak tracking from the roof. The stain or growth sits around the fan that failed to turn. A roof leak would be argued from a path in the covering above, not from a ring around a dead extract. The survey has seen the mould and the fan that did not spin. It has not opened the roof, has not measured the fan, and has not decided that rain is the source.
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?
Bathrooms put a lot of moisture into a small volume of air. An extractor is there to take it out. If the fan does not spin, that moisture stays and often marks the ceiling immediately around the grille, which is the cold or still spot beside the failed fan. That geography matters. It is a poor match for a roof defect arriving at random. The survey did not clock the fan's flow and did not lift the covering above.
Ask an electrician or a fan installer to see why it did not spin, and keep the roof out of the first explanation unless the survey actually found a roof path. Tell the solicitor this is a ventilation and moisture note. Do not start with a roofing quote for a ring around a dead fan. If the fan is repaired and the mould returns with a different pattern, that is a later observation. It is not what this inspection has recorded.
What should you ask your surveyor?
- Where does the mould sit relative to the extractor?
- Did the fan spin at all when you tested the switch?
- Did you see any roof defect you are linking to this ceiling?
What are the typical next steps?
- Read the mould as a fan and moisture note.
- Do not start by blaming the roof.
- Get the extractor that did not spin checked as a fan.
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 ceiling is under a flat roof, must the mould be a leak?
No. A flat roof overhead is a location. The mould rings a fan that did not spin, which is why the note is moisture and extract, not a roof leak. The survey has not opened that roof and has not named it as the source.
Does dead mould mean the fan has since been cured?
No. Mould that looks dormant still rings a fan that did not spin on the day. The survey has not said the fan now works, and it has not measured it. Old growth does not convert the note into a roof leak either.