Damp and moisture meters
The bathroom extractor duct stops in the loft instead of leaving the building. What moisture has that arrangement not removed from the house?
The bathroom extractor duct that stops in the loft has not taken that moisture out of the house. The fan may clear the room, but the damp air is released into the roof space instead of to the outside. What leaves the bathroom then stays in the building, where it can wet timbers and insulation. The survey can record where the duct ends. It has not proved the loft dry, and this is not rising damp.
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?
An extractor only helps the building if the duct discharges outside. A duct that finishes among the joists dumps bathroom moisture where it is hard to see and easy to forget. The visit notes the open end. It does not measure how much water arrived over a heating season, and it does not service or test the fan.
A grille on the bathroom ceiling is not the same as a run that leaves the building. Have the outlet traced and taken outside. Do not read damp in the loft from this duct as a failed damp-proof course in the walls below. The moisture in question is the moisture the fan never removed from the house at all.
What should you ask your surveyor?
- Did the duct end openly in the loft, or did you lose it before an outside grille?
- Was there staining or damp insulation near that open end?
- Are you separating this fan run from damp at the base of the walls?
What are the typical next steps?
- Extend the duct so that it discharges outside the building.
- Do not treat a running bathroom fan as proof the moisture has left the house.
- Keep any loft staining with this duct, rather than with a rising-damp label.
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 fan is noisy, is the duct doing its job?
Noise does not settle it. The point is where the duct ends. Stopping in the loft means the moisture is still inside the house.
Does this finding include an electrical test of the fan?
No. The survey records the duct route it could see. It does not electrically test the fan or certify the way it was wired.