Casa Daily Glossary

Dual Occupancy vs Secondary Dwelling — what's the difference?

Also known as: dual occupancy · duplex · secondary dwelling · DOA

Dual occupancy and secondary dwelling sound similar but trigger completely different planning rules. Picking the wrong one will cost you 3-6 months of timeline and tens of thousands of dollars in unnecessary fees. The distinction is simple once you know it.

Definitions

A secondary dwelling is a smaller, subordinate dwelling on the same lot as a main dwelling. It's typically Accepted Development if it fits the size limits. A dual occupancy is two dwellings of equal status on a single lot — duplex pair, attached pair, or two detached homes. Dual occupancy is usually Code Assessable (occasionally Impact Assessable) and triggers a full DA.

When each makes sense

Secondary dwelling: lowest friction, fastest path to extra yield, best for holding investments where you want a rental-yield boost. Dual occupancy: higher upside, both dwellings sell or rent at full residential pricing, best for sites where the lot dimensions actually accommodate two equal dwellings without compromise.

Yield comparison

Secondary dwelling: $200K-$280K build cost, $450-$650/wk rent, gross yield 8-15% on the marginal investment. Dual occupancy: $700K-$950K build cost (both dwellings), $700-$1,100/wk per dwelling, gross yield 7-9% on total project cost — but with a saleable end product and a clear path to community-title subdivision down the track.

FAQ

Common questions.

Can a secondary dwelling become a dual occupancy later?
Effectively yes, via an MCU re-classifying the use, plus often a building works DA to bring the secondary dwelling up to the equal-status threshold. Most owners don't bother — the original status determines what's saleable.

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