Three causes, three patterns
- Condensation: black spot mould in cold corners, around windows and behind furniture; worst in winter; often with a musty smell.
- Penetrating damp: a localised stain that worsens after rain; often on a chimney breast, below a roof detail or behind a blocked gutter.
- Rising damp: a horizontal tide mark up to about 1 m with white salts and crumbling plaster; present all year.
The over-diagnosis problem
Rising damp is diagnosed far more often than it occurs, usually with a prong meter that cannot distinguish salts from moisture. Before any chemical damp-proof course, insist on a moisture profile and a check for bridged DPC, raised paths and render below the line.
What Damp Check adds
A scored diagnosis from your photos and answers, with confidence; an on-site tier with moisture profiling and thermal imaging when the picture is unclear; and a fix matched to the cause.
General information for England, not advice on your property. Rules change; we check the current position in every report.