It is very tricky – we had an owner who did extensive renovations a number of years ago with approval, we have now discovered that they did a number of other things including installing an electric meter in their lot with related rewiring etc. and installation of gas piping through the common property into their unit. We are looking at putting in a by-law to cover those things to make it clear that they are responsible for those works. We have been advised that some of the electrical wiring is dangerous and we have to fix that asap.
Another owner went ahead with other extensive renovations including removal of a load-bearing wall with no approval from either the OC or the Council. We had to stop the work going any further until everything was sorted.
In my lot I found when I was having some work done that a load-bearing wall had been partly removed in the past and was being propped up with newspaper. I had to get a bricklayer to put in a supporting beam.
So there are two issues, work can have a serious effect on the integrity of the building, and an owner can later require the OC to repair/maintain work or structure that strictly speaking is not their responsibility.
I like Jimmy’s suggestion, it covers off most bases other than the ongoing issue of work being undertaken that compromises the integrity of the building.