Whether its the lot owner, the owners corporation or the builder, doing nothing is not an option. Non action just causes more damage.
I’m glad someone has made this point. I’m trying to find the line in the Act or Regs that says fixing a problem while you are waiting for a resolution of who is at fault is okay.
But as Kaindub says, make sure you have established from the beginning where the fault or defect lies so that the builder can’t turn round and say the common property was damaged during the repairs.
All that aside, get it fixed as soon as possible.