Why there's no fixed quote
Duplex approval cost and time depend on the approval pathway, the complexity of your site, the consultants required and how the council responds. A clean CDC on a regular lot is a very different exercise to a DA on a flood-affected, heritage-adjacent block. We give a tailored scope after a feasibility check, never a made-up flat rate.
Timeline: the honest ranges
- CDC: as fast as ~20 days for determination once documentation is complete, but design and documentation take time before that clock starts.
- DA: typically several months, varying widely by council, submission quality and whether an RFI is issued.
- Design and documentation before lodgement: allow additional weeks for feasibility, concept, consultant coordination and finalising drawings.
What moves the cost
- Pathway: CDC vs DA (a DA generally needs more reports and coordination).
- Consultants your site triggers: surveyor, BASIX/NatHERS, stormwater, arborist, bushfire, heritage, geotechnical.
- Site difficulty: slope, flood, bushfire, heritage and battle-axe access all add scope.
- Council fees and any required variations (e.g. a Clause 4.6 request).
How to keep it efficient
The cheapest project is the one designed for the right pathway the first time. A proper feasibility up front avoids the expensive mistake of drawing plans that can't be approved, the single biggest cost blowout we see.
Frequently asked questions
It varies by council, but a DA typically runs several months, and longer if an RFI is issued. A CDC on an eligible site can be determined in as little as around 20 days once documents are complete.
Authoritative sources: NSW Planning Portal.