The four common causes of damp are condensation, penetrating damp, rising damp and plumbing leaks.
Clues to each cause
Condensation forms when humid indoor air meets a cold surface. It commonly appears on windows, external walls and ceilings, and may vary with indoor humidity.
Penetrating damp occurs when rainwater enters through the roof or an external wall. It may appear or worsen during rain, especially near roof leaks, damaged exterior finishes, gutters or downpipes. Blocked or overflowing gutters and downpipes can cause penetrating damp; they are not a separate type of damp.
Rising damp occurs when ground moisture moves upwards through porous masonry by capillary action. It generally affects the lower part of walls connected to the ground and may occur where a damp-proof course is absent, defective or bridged. Low-level damp is not proof of rising damp because leaks, condensation and external drainage conditions can produce similar signs.
Plumbing leaks can come from water-supply or waste pipes, fixtures, appliances, overflows and failed seals. Damp may appear near bathrooms, kitchens, laundries or pipe routes and persist regardless of rainfall. Water can travel along framing or pipework, so the visible stain may not identify the leak’s location.
These moisture mechanisms are addressed in Australian Building Codes Board guidance on condensation and in National Construction Code provisions covering weatherproofing and damp-proofing.
Location, timing and weather provide clues but do not confirm the cause. Do not open walls, climb onto roofs or disturb electrical fittings to investigate damp.
If moisture is near electrical equipment, keep clear and contact a licensed electrician. Call emergency services if there is sparking, fire or immediate danger. For suspected concealed leaks, contact our Sydney plumbing team or another suitably qualified professional.