Converting a garage into a granny flat, studio or extra bedroom in NSW is a change from a non-habitable Class 10a building to habitable space under the National Construction Code. It needs approval: a complying development certificate if the result meets the secondary dwelling standards in State Environmental Planning Policy (Housing) 2021 or the relevant Codes SEPP standards, otherwise a development application. The building usually needs real upgrades to become habitable, often to the slab, damp-proofing, ceiling height, insulation, natural light and ventilation, and fire separation near boundaries. A secondary dwelling also needs a BASIX certificate. Councils also look at the parking the garage used to provide. For investors, an approved conversion can add rental income. An unapproved one is a liability that can surface at sale, in a lease dispute or after a complaint.
Key takeaways
- A garage is a Class 10a non-habitable building under the National Construction Code; a granny flat is habitable accommodation, so the conversion is a change of building classification that must be approved.
- A secondary dwelling can be complying development if it meets the standards in State Environmental Planning Policy (Housing) 2021; if not, a DA is required.
- Existing garages often need upgrades to meet habitable standards: moisture protection, ceiling height, insulation, light and ventilation, and fire separation where close to a boundary or the main house.
- A secondary dwelling needs a BASIX certificate, and its thermal performance and other commitments must be built in.
- Development consent cannot be granted retrospectively for a conversion already built; a building information certificate is the usual way to regularise it, and it does not authorise the use.
Who this is for: investors and home owners in Sydney and regional NSW thinking of converting a detached or attached garage into a granny flat for rental, a home office or extra living space, and buyers looking at a property where this has already been done.
Why does a garage conversion need approval?
Because it changes what the building is. The Australian Building Codes Board’s NCC classification guidance describes Class 10a buildings as non-habitable buildings including sheds, carports and private garages, and Class 1a as a single dwelling, being a detached house, or one of a group of attached dwellings. A garage fitted out for people to live or sleep in is no longer Class 10a. Whether the result is part of the main house or a separate secondary dwelling, the building must meet the standards for habitable accommodation, and the planning use must be approved.
The NSW Department of Planning’s fact sheet on garden sheds makes the same point about outbuildings generally: non-habitable structures cannot be used as extra living space without approval, potentially as complying development.
Which approval pathway applies?
| Proposal | Usual pathway |
|---|---|
| Garage converted to a secondary dwelling meeting the Housing SEPP secondary dwelling standards (lot, size, setbacks, height) | Complying development certificate from a certifier or council |
| Attached garage converted to a habitable room within the house, meeting the Housing Code standards | Complying development certificate |
| Conversion that does not meet complying standards, for example a garage on the boundary with no setback | Development application |
| Heritage item or heritage conservation area, or other excluded land | Development application |
| Conversion already built without approval | Building information certificate for the building work; separate approval for the use |
The secondary dwelling rules sit in Chapter 3 of State Environmental Planning Policy (Housing) 2021, including the floor area cap, which is the greater of 60 square metres or the percentage the LEP allows. Note that some NSW Planning Portal pages still refer to the former Affordable Rental Housing SEPP 2009; the Housing SEPP replaced it.
What building upgrades are usually needed?
A building consultant’s report on the existing structure is the starting point, because garages are built to a lower standard than habitable rooms. Typical issues:
- Slab and moisture. Garage slabs often lack a vapour barrier and sit low; damp-proofing and floor level changes may be needed, and the floor level must also suit stormwater and flood requirements.
- Ceiling height. Habitable rooms need a minimum ceiling height under the NCC; low garage roofs may not achieve it.
- Light and ventilation. A roller door is not a window. New openings may be needed, which raises privacy and setback questions.
- Fire separation. A garage close to a boundary or to the main house may need fire-rated walls or other measures once it becomes habitable.
- Termite management, insulation and services. New wet areas need waterproofing; plumbing and electrical work must be certified.
- Energy performance. A secondary dwelling needs a BASIX certificate under State Environmental Planning Policy (Sustainable Buildings) 2022, and the commitments must be built.
Planning issues councils raise
The most common is parking. If the original consent relied on the garage for the house’s required parking, converting it removes that space, and the council will look for replacement parking that meets the DCP. The second is setbacks and privacy: a garage built on or near a boundary, then given windows and a living use, changes the relationship with the neighbour. The third is the overall site: landscaped area, private open space for both dwellings, and access to the secondary dwelling. For a detached garage at the rear with lane access, these can work well. For an attached front garage, the result is often better as an extra room in the main house than as a separate dwelling.
Buying a property with a converted garage
Ask for the approval. If there is none, the NSW Department of Planning’s practice note on building information certificates explains that development consent cannot approve building work after the event, so a building information certificate is the usual way to regularise the structure. A BIC does not approve the use. Renting out an unapproved conversion as a separate dwelling leaves the owner exposed to compliance action, and it can complicate leasing, insurance and finance. Price that risk before exchange.
The steps for an investor
- Check the planning certificate, the original consent and any parking conditions.
- Commission a building report on whether the structure can reasonably be upgraded to habitable standards.
- Test the secondary dwelling standards in the Housing SEPP (or the Housing Code for an extra room) to choose CDC or DA.
- Design the conversion with new openings, parking, open space and access resolved.
- Obtain the BASIX certificate and Sydney Water building plan approval where pipes are nearby.
- Obtain the CDC or DA, then the construction certificate where a DA is used.
- Build with all critical stage inspections, and obtain the occupation certificate before anyone moves in.
Definitions
- Class 10a building
- A non-habitable building such as a shed, carport or private garage under the National Construction Code.
- Class 1a building
- A single dwelling, being a detached house, or one of a group of attached dwellings such as a townhouse.
- Secondary dwelling
- A self-contained dwelling on the same lot as a principal dwelling, commonly called a granny flat, regulated by Chapter 3 of the Housing SEPP.
- BASIX certificate
- The certificate setting the energy, water and thermal performance commitments for new residential development in NSW.
- Building information certificate
- A council certificate that prevents certain orders against an existing building, used to regularise unauthorised building work.
Frequently asked questions
Can I turn my garage into a granny flat without approval?
No. Changing a garage into habitable accommodation is a change of building classification and use that needs a complying development certificate or a DA.
Can a garage conversion be approved as complying development?
Yes, if the resulting secondary dwelling meets the Housing SEPP standards and the building can meet the National Construction Code for habitable space. Otherwise a DA is needed.
Do I need BASIX for a garage conversion?
A new secondary dwelling needs a BASIX certificate, and the commitments on it must be built in.
What if the previous owner converted the garage without approval?
A building information certificate can regularise the building work if it meets the council’s tests, but it does not approve its use as a separate dwelling.
We assess garage conversions as part of our granny flat planning service, confirming whether a CDC is achievable or a DA is needed and resolving parking and setbacks early. For BASIX and thermal assessments, our sister company NathersPro can help. To get started, request a fee proposal.
Sources and references
- Australian Building Codes Board, NCC Navigator: Building classifications, accessed October 2026
- State Environmental Planning Policy (Housing) 2021, Chapter 3 Part 1 Secondary dwellings, accessed October 2026
- NSW Department of Planning and Environment, Garden sheds and similar structures: rules for exempt development, accessed October 2026
- NSW Department of Planning and Environment, Practice Note: Building Information Certificates, accessed October 2026
- State Environmental Planning Policy (Sustainable Buildings) 2022 (BASIX), accessed October 2026
Information disclaimer. This article is general planning information prepared by the URBA Planning Team and is current at the date of publication. It is not planning, legal or financial advice for any specific property. Planning instruments, development control plans, state policies and the National Construction Code are amended regularly and councils interpret them differently; the controls quoted here should be confirmed against the versions in force at the date of lodgement and against the consent authority’s current requirements. Reliance on this article is at the reader’s own risk. URBA Planning, a division of Contrive Consultants Pty Ltd, accepts no liability for loss arising from its use. For advice on a specific site, contact URBA for a fee proposal.