Granny flat certification in NSW

How many homes can my lot have?

In planning terms a granny flat is a secondary dwelling: a self-contained home that can sit within, attached to or detached from the main house. The lot may hold only the main house and a single granny flat, and subdividing it is prohibited.

If you go through council with a development application (DA), the limit is 60 square metres unless council's own plan permits a larger floor area. Together, the two homes must also stay under council's maximum floor area for a house. State rules do not ask for an additional parking space, although taking away existing parking can create problems under an earlier approval.

Can I use the fast-track route?

A CDC (approved by a private certifier under set state standards) can be used in every residential zone except R5 Large Lot Residential. For a detached or attached granny flat, the lot needs an area of 450 square metres or more. The design also has to comply with the state's fixed standards. That minimum lot size is not required for a granny flat built wholly within an existing house.

One CDC can approve a new house together with a granny flat. The maximum floor area test now includes the main house, the granny flat and any attached garage, carport, deck, balcony, patio, pergola, terrace or verandah.

The low and mid rise housing reforms of 2024 and 2025 were aimed at duplexes, terraces, townhouses and apartments. Granny flats still have separate rules, so duplex lot requirements are not applied to them.

How close can it be to the house?

A detached granny flat is a separate Class 1 building. Some outside walls must be fire-resisting. That applies to any wall less than 1.8 metres from the main house, or less than 900 mm from a boundary that is not next to a road or public space. These walls need a fire rating of 60/60/60 tested from outside, or masonry or masonry veneer at least 90 mm thick. Windows in that wall need fixed fire windows rated -/60/- or similar. Doors must be self-closing solid core doors at least 35 mm thick.

Where a granny flat is attached, the wall it shares with the house is a separating wall. It must meet the rules for a wall between two townhouses, including extending right up to the roof covering's underside.

Can the flat go above or below the house?

No. Under the building code, a Class 1 home cannot be located over or under another home. Putting a flat beneath the main house, or on an upper storey above it, turns the building into Class 2 (the apartment category), which falls outside our Class 1 and 10 scope. A flat over a private garage is handled differently and can remain Class 1.

Turning a garage or shed into a flat

It can work, but the law sees it as changing what the building is used for, not a simple fit-out. Garages and sheds are Class 10a buildings. Once someone lives in it, it becomes a Class 1a dwelling, and it must then meet the NCC (National Construction Code) for a home. An occupation certificate (OC) is required before a building whose use has changed is occupied.

Ceiling height tends to be the first problem. A habitable room other than a kitchen needs at least 2.4 metres. Kitchens, bathrooms, laundries and corridors need 2.1 metres. Under a sloping ceiling, a habitable room needs 2.4 metres across at least two thirds of its floor, and any part lower than 1.5 metres is left out of that calculation.

Measure the existing ceiling before paying for drawings. Raising a roof or lowering a floor to find the height is major work. The fire separation distances to the house and side boundaries covered above also apply to a converted structure.

What Sydney Water checks on a granny flat

Sydney Water's guidance says a Section 73 compliance certificate is generally not needed for a secondary dwelling no larger than 60 square metres that is approved by council or as complying development, including one built alongside minor works or a knock down rebuild of the main house.

The exception is a lot inside a Priority Sewerage Scheme or Pressure Sewer Scheme area. There, Sydney Water states a Section 73 certificate is required.

Whichever applies, Sydney Water still assesses the plans for any building or excavation work and for any new connection to its system. That application is made online through its Tap in service, and it is worth lodging as soon as the site plan is settled.

Sewer pipes under the backyard

Backyards are where granny flats usually go, and they are also where Sydney Water pipes may run. Before building over or next to any Sydney Water asset, you need its written approval.

Some assets cannot be built over at all, including pressure mains and gravity sewers 750 mm or more in diameter. Maintenance structures, such as maintenance holes, must stay accessible and cannot end up inside a building unless the change was approved through a Section 73 process.

Where building close to a pipe is allowed, the certified plans must show the flat outside any easement and supported independently, so the pipe is protected and the flat stays standing if the pipe fails. The owner pays for investigation, design, protection and repairing any damage. If unapproved work affects a pipe, Sydney Water can direct its removal or change, and recover its costs if it does the work itself.

Renting out the granny flat

A rented granny flat must meet the minimum standards in the Residential Tenancies Act 2010. It has to be structurally sound, with adequate light in each room, adequate ventilation, and electricity or gas with enough outlets for lighting, heating and appliances.

It also needs adequate plumbing and drainage, a water connection supplying hot and cold water for drinking, washing and cleaning, and toilet and bathroom facilities that give privacy. These standards apply for the whole tenancy, not just on move-in day.

Smoke alarms add separate landlord duties. Alarms must be checked every year, removable batteries replaced yearly, and alarms replaced within 10 years of manufacture. A faulty alarm must be repaired or replaced within two business days, and a licensed electrician must work on any hard-wired alarm.