Guided damp and leak checker

Why is my wall
or ceiling damp?

Follow the timing, location and visible clues to narrow down the likely source of mould, bubbling paint, water stains or an active roof leak.

Check the symptoms ↓

?Clues before conclusions

01Problem-led
questions

02Six common
causes compared

03Urgency and
safety guidance

04No destructive
testing required

Follow the evidence

What is the damp telling you?

This is a symptom checker, not a remote diagnosis. Damp can travel along slabs, walls and roof timbers, so the visible mark is not always the entry point.

Describe what you can see

Where is the main mark?When is it worst?Is plumbing nearby or above?Roof above the area

Select every sign that applies

White salts, a tide mark or damage mainly below 1 metreBlack mould, especially in corners or behind furnitureBubbling paint, soft plaster or a spreading stainAn active drip or wet ceilingA musty smell or recurring dampnessSagging ceiling, water near electrics or rapid water flow

Do not climb onto a wet or unprotected roof. Never touch wet electrical fittings or a sagging ceiling.

Pattern recognition

Six causes, different clues

Painting over damp rarely works because the visible finish is usually the symptom, not the source.

After rain

Points toward roof details, parapets, exterior cracks, windows or drainage.

Low tide mark

Salts and damage near floor level can indicate rising or laterally penetrating moisture.

After water use

Raises suspicion around supply pipes, waste pipes, showers and concealed waterproofing.

Cold-room mould

Black mould in corners or behind furniture often tracks humidity and condensation.

Do not hide the evidence

Find the source before repainting.

Fresh paint, sealer or silicone can temporarily hide a moisture problem while damage continues underneath.

Plan paint after repairs →

Common questions

Damp diagnosis FAQs

How can I tell rising damp from a leaking pipe?+

Rising damp often forms a broad, relatively consistent low-level band with salts and damaged plaster. Pipe leaks may be more localised and can change with water use. Testing is needed because the patterns can overlap.

Why does a roof leak appear far from the hole?+

Water follows gravity but can travel along membranes, battens, rafters and slab cracks before dropping at a joint or light fitting. Trace upward and outward rather than inspecting only above the stain.

Is black mould always caused by a leak?+

No. Mould needs moisture, but that moisture may come from condensation and poor ventilation rather than rain or plumbing. External leaks must still be ruled out.

When is a damp problem urgent?+

Act immediately when water is near electricity, a ceiling is sagging, water is flowing rapidly, sewage is involved or structural movement is visible. Keep people away from the affected area.