The approvals are the same
A lot of transportable and "DIY" granny flats are sold as if they skip the paperwork. They don't. In July 2026 Building and Energy and Consumer Protection warned that "DIY" and "permit-free" claims for prefabricated buildings may be misleading. There are no special exemptions for prefabricated buildings.
| Transportable (built in a factory) | Built on site | |
|---|---|---|
| Planning approval | Not needed if it meets the deemed-to-comply rules, including 70 m² or less | Same |
| Building permit | Needed | Needed |
| Registered builder | Needed if the permit is required and it's worth over $20,000 (unless you're an approved owner-builder) | Same |
| Power and plumbing | Licensed electrician and plumber | Same |
| Where the work happens | Mostly in a factory, then delivered and installed | On your block |
| Site access | Usually needs room for a truck and often a crane | Normal builder access |
Where they really differ
Payments
Consumer Protection's advice for modular homes: pay only a small deposit, then make progress payments tied to real stages, such as delivery of materials, manufacturing stages and installation. Ask for proof that each stage is done before you pay, for example a visit to the factory.
Who's responsible
The builder named on the building permit is responsible for making sure the finished building meets the standards. With a transportable, make sure you know who that is: the factory, the installer, or both.
Getting it onto the block
A transportable has to be trucked in and placed. Check the route, driveway width, overhead power lines and trees before you sign. A built-on-site flat avoids this, but takes longer on your property.
Questions to ask either type of builder
- Will you put in writing that the building and work meet all legal requirements?
- Who applies for the building permit, and who is named as the builder?
- What exactly is included: footings, connection to services, stormwater, steps, delivery and crane?
- What does the home indemnity insurance cover?
For more on picking a builder, read choosing a granny flat builder. To check the size limit, use the 70 m² calculator.