You don't say where the rising damp is, I presume it is in the enclosed area that was originally shown as a patio?
Setting that aside, there are two issues at the outset – is the area of the rising damp common property, and what is causing the rising damp. The common property issue may be affected by the original council approval but the more important thing is what is showing on the strata plan.
The opinion of the EC members is not really relevant if the owner takes the dispute further, because the EC members are not qualified to determine that. The EC should engage some experts to determine the cause of the rising damp (struggler is right) and then look at the common property issue. The question there is, are faults in the common property causing the rising damp?
It may be that the failure to obtain council approval would be a factor, but then you have to look at a number of things such as is the area being used as a habitable room, and would the council give approval for that now. You can ask a council to approve a structure, or part of a structure, that has not obtained approval. As long as it meets council requirements the council would likely give that approval.
This case has some similar facts, it's complicated but worth reading.
Symes v SP 31731 [2001] NSWSC 527