Duplex vs. Granny Flat: Which One Actually Makes More Money?

If you own a block in Sydney and you're thinking about how to make it work harder, the duplex vs. granny flat question comes up fast. Both add income. Both add value. But they're very different propositions — and the right answer depends almost entirely on your block, your council, and your long-term plan.

Here's how to think through it properly.

What's the Actual Difference?

A granny flat (secondary dwelling) sits on the same lot as your existing home. One title, one owner, two dwellings. Usually up to 60sqm, approved via a simple CDC process in most Sydney councils.

A duplex is a dual-occupancy development — two self-contained homes on one lot. You can strata subdivide and sell one, own both and rent both, or live in one and rent the other. Significantly more floor area, significantly more value.

The Numbers: Rental Yield

• Granny flat: Rental income $400–$650/week in most Sydney suburbs. Build cost $150,000–$220,000. Yield solid, payback period typically 5–8 years.
• Duplex: Each dwelling rents for $600–$1,100/week depending on size and suburb. Combined yield often exceeds $90,000/year. Build cost $650,000–$950,000 all-in. But — you can sell one side and recover most of your build cost entirely.

Approval: What Takes Longer?

Granny flats are usually CDC-approved in 10–15 business days if the design meets SEPP requirements. Fast, predictable, low-risk.

Duplexes typically require a DA (Development Application) with council, which runs 3–6 months in most Sydney LGAs. Some councils have made dual-occupancy CDC-eligible on R2 zoned land — but check your specific area before assuming.

The Block Size Question

Most Sydney councils require a minimum lot of 600–700sqm for a duplex. Granny flats can go on lots as small as 450sqm. If your block is under 550sqm, the duplex conversation usually ends there.

Which One Should You Build?

Come to a consultation with your title dimensions, your zoning, and a rough sense of what you want to do with the property in 5 years. That's all we need to give you a straight answer.