Tool · moisture register · symptom to cause
Damp checker. Name the damp before you treat it.
Most damp treatments fail because they treat the wrong kind of damp. Answer four questions about what you’re seeing and we’ll rank the likely causes — condensation, water getting in, rising damp or a leak — with what to check and what genuinely fixes it.
Check your damp
Side by side
The four kinds of damp, and what actually fixes each.
| Type | Where it shows | Tell-tale signs | Worse when | The real fix |
|---|---|---|---|---|
| Condensation | Cold corners, window reveals, behind furniture, external walls | Black mould spots, streaming windows | Winter, mornings, after cooking and bathing | Ventilate, reduce moisture, heat evenly |
| Penetrating | Any height, usually on one wall | Patches that grow after rain | Wind-driven rain | Repair the defect outside, let it dry |
| Rising | Low on walls, below about 1 m | Tide mark, white salts, crumbling plaster | Fairly constant | Remove bridging and fix drainage first |
| Leak | Near baths, showers, pipes, appliances | Localised staining, ceilings below bathrooms | After use | Trace and repair, dry out, check timbers |
Black mould
Why black mould keeps coming back.
Black mould on walls is almost always a symptom of moisture — usually condensation — rather than a problem in its own right. Cleaning it off without dealing with the moisture means it returns within weeks. The lasting fix is to reduce the moisture that reaches cold surfaces:
- Clean it properly with a fungicidal wash, wearing gloves; don’t dry-brush it.
- Ventilate at source — use extractor fans in kitchens and bathrooms, and keep trickle vents open.
- Dry clothes outside or in a vented dryer where possible.
- Heat more evenly — cold rooms and cold walls attract condensation.
- Leave a gap behind furniture on external walls so air can move.
- Look for a cause if one wall keeps growing mould: a cold bridge, missing insulation or water getting in.
If you rent, damp and mould is your landlord’s responsibility to investigate and fix. Government guidance for landlords, published after the death of two-year-old Awaab Ishak, is clear that damp and mould should not be blamed on tenants’ “lifestyle”.
Older homes
Solid walls work differently.
Traditional stone and brick buildings — much of the housing across Yorkshire and the Pennines — were built from permeable materials that absorb moisture and let it evaporate. Historic England’s guidance on damp in historic buildings warns that modern moisture barriers are often inappropriate for these buildings and can trap moisture, speeding up decay. That’s why cement pointing, cement render, gypsum plaster and vinyl paints are so often behind the damp in older houses, and why the fix is frequently to restore breathability rather than to inject or seal.
More in our guides to getting rid of black mould,dry rot vs wet rot,woodworm,rising damp,treating damp walls,damp proof courses andcavity wall insulation and damp. Local help: damp surveys in Leeds,Manchester and Sheffield.
Common questions · damp and mould
Asked about damp.
How do I know if it’s condensation or damp?
Condensation is linked to moist indoor air and cold surfaces: black mould in corners and around windows, streaming glass, and worse in winter. Penetrating damp follows rain and can appear at any height. Rising damp stays low on the wall with a tide mark and salts. A leak concentrates near a pipe or fitting. Many homes have more than one, which is why an independent investigation looks at the whole building.
How do I get rid of black mould on walls?
Clean it with a suitable fungicidal wash rather than dry brushing, which spreads spores, then deal with the moisture that let it grow: ventilate kitchens and bathrooms, keep trickle vents open, avoid drying washing indoors, and heat more evenly. Anti-mould paint helps only once the humidity is under control. If mould keeps returning to one wall, look for a cold bridge or water getting in.
Is black mould dangerous?
Damp and mould can harm health, particularly for children, older people and anyone with respiratory conditions, according to UK Health Security Agency guidance. Removing the cause of the damp is the lasting fix. If you rent, it is your landlord’s responsibility to investigate and put right, and government guidance is clear that it should not be blamed on “lifestyle”.
What does rising damp look like?
A tide mark on the lower part of internal walls, usually below about a metre, with white fluffy salts, crumbling plaster and decaying skirting boards, and fairly steady whatever the weather. It is far rarer than it is diagnosed: most low-level damp turns out to be bridging, raised ground, leaking drains or rainwater goods.
Why does damp come back after treatment?
Because the treatment matched a symptom, not the cause. Damp-seal paint, injected damp proof courses and tanking all work in the right situation and fail in the wrong one. In older solid-walled homes, modern impermeable finishes can make things worse by trapping moisture.
Do I need a damp survey?
If the damp keeps returning, you have been quoted for damp-proofing or tanking, or you are buying a house with a damp flag on its survey, an independent damp survey is worth it. It finds the actual cause, and it is independent because there is no treatment to sell you.
Sources and further reading
Where this comes from.
- Damp in historic buildings — Historic England’s technical advice on diagnosing and treating damp in traditional buildings.
- Damp and mould: understanding and addressing the health risks — government guidance for rented housing providers (GOV.UK).
- Approved Document C — the Building Regulations guidance on resisting moisture (Planning Portal).
- Homeowner advice — the Property Care Association’s guidance on damp, timber decay and mould.
Still not sure?
Diagnose it before you treat it.
An independent damp survey finds the actual cause — and we sell no damp-proofing or treatment, so the advice is only about what the building needs.
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