Water penetration through walls is relatively common and is another form of water ingress.

Brick, stone and even rendered walls can be prone to water penetration. This can occur, even if they have cavity walls. 

Solid stone walls and brick can experience water penetration.

The main causes of water penetration in stone and brick walls are damaged or deteriorating mortar which can lead to water ingress through the render. Any cracks in the mortar, brick or stone will allow water to get in. This can occur for a number of reasons including more serious structural issues. 

Any remedial work to the walls such as the addition of cladding, insulation or re-rendering can all cause issues that may lead to water ingress.

Driving rain can lead to water being absorbed by stone, brick and render and eventual water ingress.

Water ingress can occur in cavity walls where wall ties have been incorrectly installed. If the ties are angled down towards the inner leaf or if insufficient or too much mortar was used in installation (attaching to the wall ties and bridging the gap in the cavity) this can encourage water ingress. If metal wall ties were used then these can corrode over time and cause cracks. Water ingress from wall tie issues is usually more visible as you can see damp around the location of the tie positions.