A dual key apartment or property is one which (most commonly) has a self contained studio accessed by a door, inside the main apartment. There is a shared common hallway, but separate lockable doors to each home. So in reality the title belongs to just one owner, but they can rent each portion separately, or live in one and rent the other.

Aussie does consider lending for dual key apartments provided that the applicant can provide a minimum of a 20% deposit.