G’day kiwipaul – it’s often necessary to read between the lines of some posts, and with regard to chilliblue’s post I assumed that as the carports are shown on the Strata Plan and are presumably within the stratum, then there’s a better than average chance that they form part of the Lots concerned, and that as such their external areas including vertical supports and the roofs are Common Property.
So in that circumstance, S65A of the NSW Strata Schemes Management Act (the Act) applies, where the Owners Corporation (O/C) can authorise individual Proprietors to make additions / changes to that Common Property by way of a Special By-Law (SBL) with standard conditions, or by way of a Consent (under that SBL) with specific conditions.
The Act states that unless the O/C’s consent includes a condition that on-going maintenance of the addition/ alteration to the Common Property is the responsibility of the Proprietor, and that Proprietor agrees, then all maintenance and repairs becomes the responsibility of the O/C [S65A(3)].
In chilliblue’s case, I again assumed that as the additions/changes to the carports had been done “over time and without any documented approval” (read no authorisation, no consent, no conditions), that those additions /changes would now be deemed Common Property and be the responsibility of the O/C.
So back to your point about what’s stopping “every man and his dog making alterations and additions to their property without permission on the understanding that it becomes common property and O/C responsibility to maintain”?
Well, the answer at my Plan is a really diligent Executive Committee, (hopefully) honest Proprietors who own-up if they’re the ones who made the alterations/ changes, and a Special By-Law supported by a Register of Common Property Additions /Changes stating that any additions / changes that are not shown on the Register are unauthorised under S65A, and that maintenance and repairs of those are the responsibility of the present and subsequent Proprietor/s of the Lot/s concerned.
PS — I just hope that after all this chilliblue‘s in NSW and not in some other country (like Queensland Aye) where different rules may well apply 
. Wouldn’t consistency be great!