A granny flat, or secondary dwelling to use the planning term, is one of the most popular projects we work on. It's easy to see why: it adds rentable, usable space to an existing block, the approval pathway is often fast and predictable, and the return on investment can be strong.
But there's a lot of misinformation floating around about what's allowed, especially on the Northern Beaches. Here's a clear-eyed look at the rules and what they mean for your property.
The NSW state-wide rules
Secondary dwellings in NSW are governed by the State Environmental Planning Policy (Housing), commonly called the Housing SEPP. This policy applies across the state and overrides local council rules in most circumstances.
Under the Housing SEPP, a secondary dwelling is a self-contained dwelling on the same lot as a principal dwelling. Key rules:
- Maximum size: 60 square metres (gross floor area, including any covered outdoor area that forms part of the dwelling)
- Minimum lot size: 450 square metres (this is a hard floor: no granny flat is permitted on lots smaller than this under the SEPP)
- Maximum 1 secondary dwelling per lot
These rules apply across NSW, including the Northern Beaches.
Setbacks and height
The setback rules under the Housing SEPP depend on the zone and the position of the structure:
- Rear setback: 3 metres from the rear boundary is the general minimum, but this can vary
- Side setbacks: 900mm from the side boundary for lots up to 900sqm; 1.5m for wider lots
- Height: Maximum 8.5 metres (to ridge), though most detached granny flats are single storey
Importantly, where the secondary dwelling is attached to or part of the principal dwelling, the setback rules of the principal dwelling apply, not the SEPP setbacks. This matters if you're converting an existing garage or adding a rear addition that incorporates the secondary dwelling.
Northern Beaches specifics
On the Northern Beaches, the Housing SEPP generally applies, which means CDC is usually available for secondary dwellings on compliant lots. This is good news. It means council approval is not required, and a private certifier can assess and approve the project.
A few things to watch for on the Northern Beaches:
Heritage conservation areas: Significant parts of Manly, Balgowlah, Seaforth, and parts of Curl Curl and Freshwater are within heritage conservation areas. Within these areas, secondary dwellings are still permitted under the SEPP, but CDC is not available, so you need a DA.
Flood-affected land: Parts of Narrabeen, Collaroy, and lower-lying areas near Dee Why lagoon have flooding overlays. Additional flood report requirements apply, and CDC may not be available depending on the flood category.
Battle-axe lots and unusual configurations: The SEPP setback rules can get complicated on irregular lots. A building designer familiar with Northern Beaches sites will know how to interpret these.
What can you actually fit in 60sqm?
Sixty square metres sounds small. In practice, a well-designed 60sqm granny flat works as a genuinely comfortable one-bedroom dwelling, or a compact two-bedroom if you're strategic about layout.
A typical layout might include:
- Open plan kitchen, living and dining (~25sqm)
- One bedroom (~12sqm)
- Bathroom with laundry (~7sqm)
- Entry, storage and circulation (~6sqm)
- Covered outdoor area (not counted toward GFA if unenclosed)
The covered outdoor area is worth understanding carefully. A pergola or covered patio attached to the granny flat does not count toward the 60sqm gross floor area if it's unenclosed on at least two sides. This can meaningfully extend the liveable footprint.
CDC vs DA for granny flats
For most Northern Beaches properties over 450sqm that aren't in heritage areas or flood zones, CDC is the right pathway. Typical approval time is 2 to 4 weeks from lodgement with a certifier.
DA is required when:
- The property is in a heritage conservation area
- The lot is flood-affected and CDC is excluded
- The design requires any variation from the SEPP standards
What does a granny flat cost on the Northern Beaches?
Construction costs in Sydney for a granny flat typically run $180,000–$280,000 for a well-finished detached structure, depending on size, materials, and site access. Costs on the Northern Beaches tend to be at the higher end due to transport access in some areas.
Approval and consultant costs to budget:
- Private certifier (CDC): $2,000–$3,500
- Structural engineer (if needed): $1,500–$3,000
- BASIX: $500–$800
The rental return on a one-bedroom granny flat on the Northern Beaches is typically $450–$600 per week at current market rates, which can make the investment very compelling.
Next steps
If you're wondering whether a granny flat is feasible on your property, the first step is a site assessment. We can check your lot size, zone, heritage status, and flood overlay, and give you an honest picture of what's achievable.
Get in touch and we'll take a look.