Convert a Garage to a Granny Flat: Feasibility and Costs
To convert a garage to a granny flat, first establish whether the existing building can become a lawful dwelling. The slab, ceiling height, structure, moisture protection, access and services need assessment before you budget for a kitchen. Reusing a roof and walls does not guarantee a cheaper project.
Get a feasibility assessment that identifies what can stay, what must change and what remains unknown. Then compare the conversion with a new dwelling on the same site. Don’t compare a fit-out quote with a complete new-build contract.
Check classification and planning feasibility
A private garage is generally a non-habitable Class 10a building. A dwelling has different requirements. The ABCB building-classification guidance explains the distinction, but the practitioner assessing your conversion must establish the classification and applicable requirements for the proposal.
Collect the existing approval records, title, survey and available construction drawings. Ask whether the proposed use is permitted and whether the existing position can satisfy the relevant controls. A garage lawfully built near a boundary is not automatically suitable for occupation as a dwelling in that same position.
Approval names vary across Australia. NSW’s CDC and DA routes are examples, not national document names. Use the approval guide to prepare questions for your local authority.
Inspect the slab, roof and usable height
Have the structure assessed before assuming it can carry altered loads or new openings. Investigate the slab’s condition, moisture protection and suitability for the proposed floor finish. Don’t specify a topping slab as a universal remedy: extra floor thickness can reduce headroom and affect doors, thresholds and drainage.
Measure finished ceiling heights with proposed insulation, linings and floor build-up allowed for. The relevant requirements depend on room use and the design. Ask the practitioner to identify any non-compliant area and a priced remedy. Raising a roof or changing a slab may make a new build worth comparing.
Record uncertainties in the scope. If concealed construction needs investigation, agree how that inspection will happen and how findings will affect the quote. An attractive render cannot establish the condition of an existing building.
Design a dwelling around services and safety
| Area | Question to resolve before fit-out |
|---|---|
| Water and wastewater | Where can lawful connections run, and does the proposed bathroom layout suit the available levels? |
| Electricity | What supply, switchboard and wiring work is needed for the intended appliances? |
| Fire safety | What separation, opening protection and alarm arrangements apply to this building and its neighbours? |
| Energy and ventilation | Which assessment and construction details apply to the conversion? |
| Access and parking | Does losing the garage affect an existing approval condition or a required parking space? |
Use the actual site and classification for fire-safety advice. A single boundary-distance rule cannot resolve every relationship between an attached garage, the main house and another dwelling. Have the required details shown on the plans.
For electricity billing options, read the meter guide. Separate billing is a different question from whether the existing installation can serve the new dwelling.
Compare a conversion quote with a new build
Ask for separate costs for investigation, design, approvals, structural alterations, service connections, weather protection, insulation, internal linings and fit-out. Include demolition, waste removal and reinstatement of affected outdoor areas. Identify provisional items and who carries the risk if the existing structure differs from the assumptions.
Then obtain a comparable new-build scope. The conversion may preserve useful structure, but it may also constrain the layout or require substantial remedial work. This guide does not support a fixed conversion price or a promised percentage saving.
Our quote comparison guide helps align inclusions. Ask the same questions about GST, exclusions, programme and completion documents for both options.
Plan inspections before closing up the work
Agree the inspection and documentation sequence with the responsible practitioner before starting. Confirm which work must remain visible and who books each inspection. Keep approved drawings available to trades and have proposed changes checked before installation.
Before occupation, obtain the completion or occupancy documentation required in your jurisdiction. Do not assume that a final invoice or a working kitchen establishes permission to live there. If the intended use is rental, check the tenancy obligations and approval conditions separately.
Frequently Asked Questions
Can I carry out the conversion myself?
Check owner-builder eligibility and trade licensing for the actual work. Owner-builder permission does not authorise restricted work or replace project approvals.
Does a low ceiling rule out conversion?
It requires assessment. Have the finished height and any proposed remedy checked and priced before deciding whether conversion is worthwhile.
Must I replace the lost parking space?
Check the existing consent and current planning requirements. Losing approved parking and providing parking for a new dwelling are separate questions.
By The Granny Flat Guide Team. Last updated October 2026. About our research · Project budget calculator
How much does council approval add to your build budget?
Council and certifier fees sit outside the builder quote. In NSW, a CDC pathway through a private certifier often lands between roughly $3,000 and $8,000 once survey, BASIX and Sydney Water checks are included, while a full DA can cost more because of longer consultant time and holding costs. Victoria and Queensland use different fee schedules, so treat any single number as a starting point. Model your own project in our cost calculator, then browse the supplier hub or send us an enquiry when your footprint is settled.
What design choices affect approval speed?
Setbacks, height, floor area and tree protection overlays decide whether you stay on a fast CDC track or drop to a slower DA. Staying under common 60 sqm internal caps, keeping adequate side and rear setbacks and connecting services without major easement conflicts usually keeps the pathway simpler. If your block is sloped, flood-affected or heritage-listed, expect extra reports before council or your certifier can sign off. Use the setback checker and approval wizard against your address before you pay for custom drawings.
Primary sources
These cards are an editorial summary of official pages. The Granny Flat Guide is not a certifier, council or licensed builder. Check the live official URL before you lodge or sign.
- Your Home (Australian Government)Your Home: Australia's guide to environmentally sustainable homes
- Australian Building Codes BoardNational Construction Code
- NSW Planning PortalState Environmental Planning Policy (Housing) 2021
- Victorian Building AuthorityBuilding Act 1993 / small second dwelling settings
- Queensland PlanningPlanning Act 2016
- WA Planning (DPLH)Planning and Development Act 2005
- PlanSA (South Australia)Planning, Development and Infrastructure Act 2016
- QBCC (Queensland)Queensland Building and Construction Commission licensing
See our editorial standards for how we research and update guides.
