
This had been a well-known phrase in the United Kingdom in the mid-1970s. It wasn’t exactly a popular phrase, but its meaning was understood well enough in those days and is certainly still understood by those who spent their formative years in the Swinging Seventies UK.
Basically, rising damp refers to a symptom or appearance of neglect, old age, decrepitude, etc. In short, the phrase emphasises personal failure or failing qualities.