NSW planning law calls a granny flat a "secondary dwelling". Its maximum size, the lots that qualify and its position on the block are mostly decided by the State Environmental Planning Policy (Housing) 2021, with your council's local environmental plan (LEP) filling some gaps. These are the basics worth checking before you pay for drawings.
What the rules treat as a granny flat
A secondary dwelling is a self-contained home that shares a lot with the main house, which the planning documents call the principal dwelling. It can stand on its own, be attached to the house, or be created inside it. The controls were shifted from the former Affordable Rental Housing SEPP into the Housing SEPP in late 2021, so older brochures you find online may quote an instrument that no longer applies.
- Each lot is limited to a single principal dwelling plus a single secondary dwelling.
- A lot carrying a granny flat approved under these provisions can't be subdivided, so the flat can't later be sold off on its own title.
- Granny flats are allowed in every residential zone from R1 through to R5. Other zones depend on what your LEP permits.
How big a granny flat can be
The Housing SEPP limits a secondary dwelling to 60 m² of floor area, unless another planning instrument covering your land allows more. A few LEPs do, so read yours. There is also a second cap that people often overlook. Combined, the house and its granny flat must stay within the maximum floor area allowed for a dwelling house on that lot. Under complying development, that combined figure also counts attached structures including a garage, carport, deck, verandah, pergola or terrace.
In some rural zones, councils use an optional LEP clause (clause 5.5) that sets their own size limit and a maximum distance between the two homes. Those figures can't be relaxed through the usual clause 4.6 variation request.
Lot size: why 450 m² matters
To use the complying development pathway, your lot needs an area of at least 450 m². One exception applies: a granny flat created wholly inside an existing house.
A smaller lot doesn't rule a granny flat out. You can still lodge a development application (DA), which council assesses on its merits. For a DA, the SEPP lists "non-discretionary" standards: a site area of 450 m² for a detached granny flat, and no reduction in the number of parking spaces on site. If a proposal meets those two benchmarks, council can't insist on more for those particular matters, although it still weighs everything else.
Setbacks, height and the other complying standards
A granny flat approved as complying development also has to satisfy the Housing SEPP's Schedule 1. The schedule controls minimum lot width, maximum building height, side and rear setbacks (which increase on bigger lots), landscaped area, open space for residents, earthworks and drainage. It has been amended over time, so work from the current text rather than an old fact sheet. Under a DA, the setbacks usually come from your council's development control plan (DCP) instead.
Some land can't use complying development at all. Examples include bush fire prone land at the two highest ratings, BAL-FZ (flame zone) and BAL-40, and the higher hazard parts of flood affected lots. Your section 10.7 planning certificate is the place to start, and our guide to Reading your planning certificate before you design explains what to look for.
Building code points that shape the design
Planning approval is just one part of the picture. Under the National Construction Code (NCC), a granny flat is a separate Class 1a dwelling. It needs its own smoke alarms, waterproofed wet areas, structural design, and a BASIX certificate for energy and water. Any external wall sitting less than 900 mm from a side boundary or the rear boundary must be built as a fire-resisting wall, which affects cladding choices and windows on that side. The Housing SEPP doesn't ask for an extra car space, but don't remove existing spaces without checking any earlier consent for the property.
A plan assessment before lodging can pick up setback, height and fire separation problems while they are still easy to fix. CertifiBuild can then issue the CDC, act as principal certifier and handle the inspections up to the occupation certificate. See our granny flats page, or request a quote with your address and plans.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Hornsby Shire Council, Northern Beaches Council, Wollondilly Shire Council, Canterbury-Bankstown Council, Woollahra Municipal Council, Georges River Council.
Suburb pages with local planning notes: Balgowlah, Bargo, Bass Hill, Bellevue Hill, Beverly Hills, Blakehurst, Bringelly, Brookvale, Burraneer, West Pennant Hills. You can also browse every service area.
Sources
- Secondary dwellings guidance, NSW Department of Planning
- State Environmental Planning Policy (Housing) 2021, NSW Legislation
- Fire separation of external walls (Housing Provisions 9.2), ABCB