Granny Flats

The minimums

Under the Housing SEPP a secondary dwelling is permitted in every residential zone where a house is permitted. The CDC fast-track needs 450 m² and 12 m; smaller lots can still get one by DA.

How it works

The secondary dwelling stays on the same title as the house — it cannot be subdivided off or strata-titled. That is what separates it from a duplex: it adds a rental or a home for family, not a saleable second lot.

It can be detached in the backyard, attached to the house, or converted from part of an existing house or garage. Height is limited to a single storey under the fast-track code on most lots.

The build cost is modest and the approval is quick, so on a block that cannot reach the duplex minimums a granny flat is usually the best return available.

Common pitfalls

• Access — the certifier wants a path at least 1 m wide from the street to the flat door, unobstructed by the house.
• Trees — a large tree in the backyard can stop the fast-track. Check the council's tree controls before you draw the footprint.
• Bushfire — on bushfire prone land the flat needs a BAL assessment and construction to match; it can still be approved but costs more.
• Sewer — the sewer main often runs across the back of the lot. Building over or near it needs Sydney Water approval and a concrete-encased pipe.
• Floor area — 60 m² is the internal floor limit; a verandah does not count, but a carport can under some councils' reading. Confirm before you design to the limit.