HomesAndHedge guides

Damp, mould and structural problems: identify it, judge it, act

Most home damp is condensation, not rising damp, and many wall cracks are cosmetic rather than structural. This hub helps you tell the difference, judge how worried to be, fix what you safely can, and decide when an independent surveyor or specialist is the right call.

Damp, mould and cracks are unsettling because they can mean anything from a poorly ventilated bathroom to a serious structural fault. The single most useful thing you can do is identify which problem you actually have, because the fixes are completely different and an expensive treatment for the wrong diagnosis solves nothing.

Each guide follows the same shape: how to identify it, how serious it is, what you can do yourself, and who to call when you cannot. A standing caution from the Property Care Association is worth keeping in mind: some firms that offer a "free damp survey" also sell the remedial work, so for anything costly it is worth getting an independent opinion before agreeing to treatment.

Rising damp Moderate: real but often misdiagnosed, so confirm the cause first Black mould Moderate: a health concern, especially for the vulnerable, and a damp signal Condensation Low to moderate: usually fixable without building work, but feeds mould Subsidence High: concerns the building structure, so always get it assessed Cracks in walls Varies: most are cosmetic, but wide growing diagonal cracks are serious Dry rot High: spreads through masonry and weakens structural timber Damp proofing Moderate: needed only when rising damp is confirmed, so diagnose first Efflorescence Low: harmless in itself, but recurring salts can flag a damp source

Frequently asked questions

Is my damp problem rising damp or condensation?

Condensation is far more common. It shows as water on cold surfaces and black mould in corners, behind furniture and around windows, and is worst in winter. True rising damp affects ground-floor walls only, leaves a tide mark up to about a metre, and is comparatively rare. If in doubt, get an independent diagnosis before paying for treatment.

Do I need an independent damp survey?

For anything beyond simple condensation it is worth it, because the treatment is expensive and easy to misdiagnose. The Property Care Association notes that many damp surveys are carried out by firms that also sell the treatment. An independent surveyor, or a Royal Institution of Chartered Surveyors (RICS) member, has no incentive to over-diagnose.

Which damp problems can I fix myself?

Condensation and the mould it causes are usually within your control: improve ventilation, heat the home more evenly and reduce moisture from drying washing or cooking. Penetrating damp from a blocked gutter or cracked render is often a simple repair. Rising damp, dry rot, subsidence and structural cracks need a professional assessment.

Oliver Mackman

Editor, HomesAndHedge

Oliver leads HomesAndHedge's editorial coverage of home and garden problems. He researches and writes the plain-English explainers on pests, invasive plants, damp and mould, drainage and wildlife, drawing on guidance from bodies such as the Property Care Association, the RHS and the NHS, and is clear about when a job needs a qualified professional.

Last reviewed: 8 June 2026