Does a dual occupancy require a separate Building Approval after Development Approval?

Yes. A new dual occupancy generally requires a separate Building Approval (BA) after Development Approval (DA).

The DA provides planning approval, while the BA assesses the detailed building work against the Building Act 2004, applicable building regulations and the National Construction Code (NCC). A licensed building surveyor is appointed as the certifier for the BA process.

Reference: ACT Complying with your development approval - https://www.planning.act.gov.au/applications-and-assessments/development-applications/complying-with-your-development-approval