What is the maximum size for a granny flat?

Maximum sizes vary by state. In NSW, secondary dwellings under the complying development provisions can be up to 60 square metres. Other states have different limits. Your certifier can advise on the specific thresholds that apply in your jurisdiction.

Can I build a granny flat on any property?

Not necessarily. Most states require minimum lot sizes and the property must be zoned to allow secondary dwellings. Flood-prone land, heritage conservation areas, and bushfire zones may have additional restrictions. Your building certifier can advise on eligibility.

Is a granny flat the same building class as a house?

Yes. Granny flats are classified as Class 1a under the NCC, the same as a standalone house. They must meet the same construction standards for structure, fire safety, energy efficiency, and weatherproofing.

What is the maximum size for a granny flat?

Maximum sizes vary by state. In NSW, secondary dwellings under the complying development provisions can be up to 60 square metres. Other states have different limits. Your certifier can advise on the specific thresholds that apply in your jurisdiction.

Can I build a granny flat on any property?

Not necessarily. Most states require minimum lot sizes and the property must be zoned to allow secondary dwellings. Flood-prone land, heritage conservation areas, and bushfire zones may have additional restrictions. Your building certifier can advise on eligibility.

Is a granny flat the same building class as a house?

Yes. Granny flats are classified as Class 1a under the NCC, the same as a standalone house. They must meet the same construction standards for structure, fire safety, energy efficiency, and weatherproofing.

Do I Need a Building Certifier for a Granny Flat?

Yes, you need a building certifier

Granny flats (secondary dwellings) are classified as Class 1a buildings under the NCC and require full building certification, the same as a new house. A building certifier must assess the plans, issue the construction certificate or building permit, inspect the work at mandatory stages, and provide the occupation certificate before the granny flat can be occupied.

Skipping certification is not an option. An uncertified granny flat can be ordered to be demolished, will not be covered by insurance, and will create complications when selling the property.

Fast-track approval in NSW

NSW offers a particularly streamlined pathway for granny flats through the complying development process. If your secondary dwelling meets the State Environmental Planning Policy (Exempt and Complying Development Codes) criteria, a private certifier can issue a Complying Development Certificate (CDC) combining planning and building approval in as little as 10 business days.

The NSW complying development pathway typically allows secondary dwellings up to 60 square metres on properties that meet minimum lot size requirements. Your certifier can quickly assess whether your property qualifies.

State-by-state differences

Each state has different rules for secondary dwellings. NSW has the most permissive framework with the CDC pathway. Queensland allows secondary dwellings in many zones. Victoria requires a building permit and the secondary dwelling must comply with local planning scheme provisions. Other states vary in their approach.

Maximum sizes, minimum lot sizes, setback requirements, and planning pathway options differ significantly between states. Your building certifier can advise on the specific requirements in your jurisdiction.

What affects the certification cost

Granny flat certification typically costs $1,500 to $3,500 depending on the state, certifier, and complexity of the design. A standard design on a straightforward site sits at the lower end. Sites with bushfire, flood, or reactive soil considerations increase the assessment work required.

If using the CDC pathway in NSW, the combined planning and building approval fee is often less than pursuing a separate DA and CC through council.

Official Sources

Verify the information in this guide against these official government resources.

Australian Building Codes Board
The body responsible for the National Construction Code.