Different moisture sources can coexist. This guide helps organise an investigation; it is not a remote diagnosis or a substitute for a survey.
Observe the pattern
- Ask whether damp follows rainfall, a plumbing use, cold weather or a particular room's activity.
- Note location around roofs, windows, walls, ceilings and plumbing, and whether adjacent rooms are affected.
- Record condensation on cold surfaces without assuming it explains every patch.
Check the building and services
- Inspect relevant gutters, roofs, seals, pipework, external levels and ventilation paths.
- Confirm extract fans actually move air to the intended outlet.
- Assess heating, insulation and thermal bridges with appropriate expertise.
Test the diagnosis
- Ask the investigator to explain the evidence, uncertainties and proposed remedy.
- Compare the result after repair and an appropriate drying period.
- Escalate persistent or conflicting findings rather than commissioning repeated cosmetic treatments.
Example: two causes overlap
A fictional bathroom has a leaking pipe and inadequate extraction. Repairing the pipe may remove one source while moisture problems continue. Record and address both findings, then check whether the room remains dry in ordinary use.
What to do
- Record the location, timing and pattern of moisture.
- Check building defects, heating and ventilation.
- Obtain a competent diagnosis and verify the chosen repair.
Evidence to keep
- Dated photographs, weather or use pattern and inspection notes.
- Readings with context, diagnosis and repair results.
Sources and guidance
- Damp and mould: health risks and landlord actionUK Government · checked 20 October 2026
- Fitness of homes for human habitation: landlord guidanceWelsh Government · checked 20 October 2026
- Awaab’s Law: scope and requirementsScottish Government · checked 20 October 2026