Questions about your Balgowlah project.
Is a rear extension always cheaper than adding upstairs?
Not necessarily. Excavation, access, existing structure, services and the amount of retained-home work can change the comparison. Develop enough detail to compare the full scope of both options.
Can an older addition be included in a new renovation?
It can be investigated, but its structure, condition and approval history need checking. Existing drawings and past consent documents are useful starting material.
Can we keep a separate living room?
Yes, that can be part of the brief. Consider where quiet activities happen and how the new family space connects to the kitchen and garden.