Dual Occupancy vs Granny Flat: Which Is Right for You?

If you've got a decent-sized block and want to add value or income, two options come up again and again: build a granny flat, or develop a dual occupancy. They sound similar, but they're very different beasts — in cost, in what you can do with them, and in how councils treat them. Choosing the wrong one can leave money on the table or land you in an approval process you didn't need.

Here's how the two compare, and how to work out which fits your block and your goals.

What Each One Actually Is

A granny flat (formally a "secondary dwelling") is a smaller, self-contained home that is subordinate to the main house on the same lot. It shares the title with the main dwelling and is capped in size — in NSW, for example, secondary dwellings are limited to 60 sqm of internal floor area under the Housing SEPP, while other states set their own limits through council schemes.

A dual occupancy is two principal dwellings on one lot — either attached (like a duplex) or detached (two separate houses). Neither is subordinate; they're treated as two full homes, which is why dual occupancies open up options a granny flat can't.

Cost to Build

Granny flats are cheaper because they're smaller and simpler. Build costs commonly land in the $180,000–$250,000 range depending on size, finishes and site works. A dual occupancy is a much bigger project — you're building two full dwellings, so costs run into the several-hundred-thousand-dollar range and up, plus demolition if you're knocking down an existing home.

Rental Income

A granny flat adds one modest rental to a property you already own — often the fastest, lowest-cost way to create extra cashflow. In many states, including Queensland, secondary dwellings can now be rented on the open market, which has transformed their appeal. Our guide to Queensland granny flat rules covers that change in detail.

A dual occupancy can generate two full rents — materially more income — but at a much higher build cost and with a longer, more involved approval and construction timeline.

Can You Subdivide and Sell Separately?

This is where dual occupancy pulls ahead as a wealth-creation strategy. Because both dwellings are principal dwellings, a dual occupancy can frequently be subdivided or strata titled into two saleable properties — subject to your zone allowing it and meeting minimum lot size and other controls. Two titles are usually worth more combined than one dual-occupancy block, which is the core of the "build and split" play.

A granny flat generally cannot be sold separately from the main house, because it's a secondary dwelling on a shared title. If separate sale is your goal, dual occupancy is almost always the path. If you want to explore splitting a dual occupancy, see our guide to subdividing a residential block.

Approval and Complexity

Granny flats are typically the simpler approval. In some states and situations, a compliant secondary dwelling can be approved through a fast-track complying-development pathway rather than a full assessment. Dual occupancies are more likely to require a full development application, especially if you also want to subdivide — that's effectively two approvals to manage.

Which Should You Choose?

A granny flat is usually the better fit if you:

• Want extra income or family accommodation at the lowest cost.
• Are keeping the property long term and don't need to sell the second dwelling.
• Have a block that suits a modest secondary dwelling but not two full homes.

A dual occupancy is usually the better fit if you:

• Want the option to subdivide and sell one or both dwellings.
• Have a larger block in a zone that permits two principal dwellings.
• Are prepared for a bigger budget and a longer approval and build timeline in exchange for higher upside.

Run the Numbers Either Way

Whichever path you lean toward, the decision should be driven by feasibility, not just preference. A granny flat with strong rental yield can outperform a marginal dual occupancy that barely breaks even after subdivision costs. Work through both scenarios with our development feasibility guide before you commit.