It is quite possible that what could be mistaken for rising damp could, in fact, be penetrating damp.
Penetrating damp is damp than comes in from outside the home, usually as a result of rainfall.
There are specific causes of penetrating damp in each case, so you will have to investigate your particular situation (with the help of a trusted damp specialist or surveyor, if appropriate) to see what has caused your problem, and decide on the best damp treatment.
Some common possibilities:
Overflowing or leaking guttering or downpipes
Cracks or damage in the mortar or render
Cracked, damaged or porous bricks
Something which is bridging the cavity wall
Plants near walls outside
Raised ground level against wall outside
moss or algae on an outside wall could indicate penetrating damp
Moss or algae growing on the outside of your wall can often show you where walls get too wet on the outside. This may lead to penetrating damp on the inside.
So make sure the inside can 'breathe' in order to let moisture evaporate naturally - as the original building design intended.
There are also certain breathability aspects - such as avoiding modern paints which 'seal' the wall, or non-breathable cement render.
On more modern homes, they are often built with, for example, a cement render intended to protect against rain and the elements... Which is fine...
But where it cracks or is damaged, it starts letting water in, and because the walls can't breathe, the water does not evaporate naturally, and starts causing your damp problems in its efforts to 'escape'.
Older properties were always designed to 'breathe' inside and out. So you should take care not to 'seal' your breathable walls (inside or out) with cement render/mortar or acrylic paints etc.