Unit owner,
I am a big believer in getting it right. Just because your fellow owners haven’t done the right thing previously doesn’t mean that you sholdn’t.
From my understanding of the situation, you should seek OC approval (via an ec meeting) to lodge a DA and also you should seek a special resolution at a general meeting for the addition to common property and also an exclusive use by-law.
This will best protect you should an issue arise in the future.
I have had a client that had created an additional room inside their unit, without the correct consents, council was made aware and issued them with orders to remove the additional walls. I understand that the owner may have been fined by Council also.
mr s