Fugt (damp / moisture)

Moisture is the root cause behind most mould and rot damage, so it is the moisture you should chase, not the stain. Typical sources are rising ground damp in masonry basement walls without a damp course and poorly ventilated crawl spaces. Signs are salt efflorescence, flaking plaster, dark patches and a musty smell.

Rising ground damp mainly affects older masonry basement walls without a damp course between foundation and masonry. Water is drawn up into the wall and leaves salt and flaking plaster.

Crawl-space damp is often caused by closed or too-small ventilation openings and condensation when warm summer air meets cold surfaces. Over time it can cause mould and wood-decaying fungus.

Always trace a damp patch back to its source, the roof, plinth, pipes or ventilation, before you price a repair. The symptom is easy to see, the cause is what costs.

Damp is something to have assessed, not automatically serious damage. A building surveyor can decide whether it is surface damp or a structural fault.