Originally published February 2013. Reviewed 7 October 2026. These six checks help you prepare for a garage-conversion assessment; they do not establish that an existing garage is suitable or approved for residential use.
Garage conversion into a granny flat: six checks before you commit
A garage may look like an economical starting point, but the conversion can require structural, fire-safety, moisture, services and energy-efficiency work. Compare the complete conversion scope with a purpose-built granny flat before deciding.
1. Boundaries, setbacks and fire separation
Measure the garage’s position relative to boundaries and other buildings. Ask the designer and certifier to assess the relevant setbacks, wall construction, openings and roof details for the proposed residential use. A wall’s distance from a boundary alone does not confirm that the whole conversion complies.
2. Usable room and ceiling heights
Measure the space available after new floor finishes, insulation and ceiling linings are allowed for. Sloping ceilings require an assessment of the applicable room-height provisions and the usable floor area; simply averaging the highest and lowest points is not an adequate compliance check.
The ABCB room-height provisions illustrate why room use and the area beneath a sloping ceiling matter. Your certifier must identify the code edition and provisions applicable to your proposal.
3. Bathroom, kitchen and service connections
Plan the location of plumbing and drainage before finalising the layout. A raised floor or work to the slab may affect available height and the construction scope. Have the proposed water, wastewater and electrical work assessed by the relevant qualified professionals rather than assuming existing garage services are sufficient.
4. Existing frame, slab and roof
Arrange an assessment of the existing structure, its condition and suitability for the proposed work. The engineer and certifier can identify the evidence, strengthening or replacement work needed. An existing garage approval does not establish that its structure is suitable for a dwelling.
5. BASIX and energy-efficiency commitments
Check the BASIX assessment pathway for the proposed conversion and the commitments specified for that project. Do not assume every conversion uses the same rainwater, hot-water, glazing or insulation package. The NSW Planning Portal provides BASIX guidance for secondary dwellings and conversions. Confirm that the design and quote cover the relevant commitments.
6. Moisture, termites and waterproofing
Check the existing building for moisture and termite issues, and plan the wet-area waterproofing and any required protection or repair work. Identify the inspections and documentation needed for the conversion before work begins.
Compare the complete proposal
Ask for a written scope covering the retained structure, required alterations, services, finishes and approval work. Compare it with a new-build option on the same property. Our garage conversion overview and approval checklist provide further starting points.
We coordinate your design, approvals and building processes. Talk to our team about your garage and intended layout before relying on a conversion budget or beginning work.