What defines property boundries within a strata plan?

The registered strata plan, specifically the floor plan, is the only document that legally defines the boundaries of the lots in the scheme. Every thing that is not part of a lot is common property. Each strata plan can be different. However, in a typical strata plan the following principles generally apply:

• Boundaries of lots that are defined by a structural feature such as a wall are shown on the floor plan by thick linework. The wall itself is common property.
• Boundaries of lots defined by measured lines only are shown by thin linework.Typically the only walls that are shown on the plan are the perimeter walls of the unit. These walls are common property. All internal walls (ie walls between rooms in the unit) are part of the lot. 
• The structure of the floors and ceilings are common property.
• Any tiles that were originally affixed to a common property surface (ie wall, floor or ceiling) at the time of registration of the plan are also common property, unless the plan specifically states otherwise.
• Any tiles affixed to non-common property walls belong to the lot.

In view of the above principles, tiles on a bathroom wall that is shown by thick linework on the floor plan or tiles on a bathroom floor, are common property provided that they were in place at the date of registration of the plan. It is possible for some bathroom walls (including the tiles) to be common property and others to be part of the lot.