Penetrating damp is also damp within the masonry, and is often confused with rising damp, however it occurs by water being drawn in laterally, typically on to the face of the wall. Water is driven (via wind etc.) and drawn (via capillary action) into the network of capillaries and ultimately showing as damp on the internal surface, much the same as rising damp.
It occurs normally due to any source of water whatever the cause, it might be rain continually driven onto the surface, but is equally likely to be the result of a historically badly designed extensions with roof surfaces meeting overwhelming gutters etc and overflowing, constantly striking the surface of the wall. If the brick or wall surface is of a porous nature or has surface damage opening the capillary network, the water can be driven or drawn in. Equally it can occur in the lower zone of the property due to splash in the zone near the ground.
Penetrating damp shows externally with damaged masonry, growth of moss, lichen and algae and darkened patch that persist and feel damp and cold to touch. Internally it will look very similar to rising damp but normally at a higher level.
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