Penetrating dampness occurs when rainwater is allowed to ingress through the external walls of a property. The causes of penetrating dampness vary but can normally be attributed to leaking rainwater goods such as gutters and downpipes or poorly maintained external masonry such as missing pointing. Other problems associated with penetrating dampness can include heat loss and frost damage where moisture freezes and expands in the capillaries of bricks causing cracking.

This dampness is not exclusive to solid walls and can affect cavity walls due to badly installed wall ties, insulation and or blockages within the cavity. This can allow bridging to occur between the external and internal skins.

It is typically recognised internally as localised damp patches with discoloured, flaking or blistered paint. In extreme cases, blown plasters are common. Externally, discolouration and/or deterioration of masonry with moss growth in areas of ingress are common symptoms.