Architects designed a "curtain" structure that would cover all but one side of the building in glass. The Herald understands that the average cost to residents would be $150,000 each.
The apartment's body corporate held its AGM on Wednesday night, where the majority of residents voted in favour of the plan.
But real estate private equity firm Lamont & Co, which owns 53 carparks in the complex, opposed it. Lamont would have been required to pay $800,000 under the proposal.
Because Lamont has separate titles for each of its carparks, its had 53 votes out of a total of 175.
Lamont, which is owned by brothers Tim and Andrew Lamont, are due to later this year start work on 75 apartments, SKHY, situated next to Luna Apartments.
One Luna resident, who asked not to be identified because they are worried it could disadvantage him during repair negotiations, said it was unfair that Lamont had such influence over the vote.
"Of course none of us want to be paying this but all the experts tell us we have to do this, and the Council is dictating we've got to do this. We don't have a choice so we've just got to be pragmatic and get it done.
The man said the saga was causing huge levels of emotional and financial stress to apartments residents.
"I know people who have done fire sales - just basically sold their apartments at auction for $200,000 - $300,000 under market value because the stress has become too much.
"Personally, I've had to go to the doctor to get sleeping pills in the first time in my life. You just feel totally helpless."
He believed the cost of the project would actually exceed $20m, given the remedial work that had already gone into it.
Property manager Theunis Judeel, who at one stage managed 12 apartments at Luna but now manages six, said there was a great deal of consternation among residents at Wednesday's AGM.
He pointed out that there was another party who owned 47 carparks but only got one vote because they were all under the same title.
"What happens in a situation like this is people get very fired up and they let their emotions rule."
Tim Lamont referred the Herald's inquiries to his lawyer, Tim Rainey.
"Their position is that they have concerns about the ways in which the body corporate is proceeding with the work and the cost allocation, which they are being asked to meet for work that does not affect them or impact on their units in any way," Rainey said.
"They're hopeful that something can be done to resolve their concerns and that the matter can proceed. But they are simply at this point doing what they are entitled to do as unit owners to voice their concerns."
He hoped the body corporate would address their concerns and see if they can be met.
Rainey said the body corporate was proposing "quite a radical solution to address what are some fairly isolated areas of leaks around some decks".
"The costs have grown significantly because of choices the body corporate and its consultants are making about the works. What is mostly concerning for my clients is they have been given no real information about any work that is going to be affecting their car parks."
Body corporate chairman Campbell McGill said in a statement that its decisions regarding the project were based on information and recommendations from expert consultants retained for that purpose.
"The cost of the project has escalated significantly as a result of additional defects in the building which have come to light as a result of investigations carried out by the body corporate's expert consultants," he said.
"The Lamonts have been provided with the same information as every other owner in the complex and when they have requested more information it has been promptly provided to them. All parties hope to solve the current impasse soon."
