Check feasibility before choosing a package
A granny flat adds a self-contained home to a property with a main dwelling. Start by confirming what your land can accommodate and how you intend to use it. Then compare designs and complete project quotes for that site.
Land
Identify the zone, overlays, easements and usable building area.
Purpose
Explain whether the home is for family, tenants or another intended use.
Budget
Include work outside the building package, such as access and connections.
Sequence
Confirm approvals and responsibilities before committing to construction.
Compare building approaches
Choose an approach that works with your block, access and proposed layout. The advertised package name is only a starting point: ask where the supplier’s responsibility begins and ends.
- Built on site
- Ask about site supervision, access for trades, deliveries and disruption to the main home. Establish which design changes are included before construction.
- Modular or prefabricated
- Confirm transport dimensions, delivery access, crane requirements, foundations and work completed after placement. Factory production does not remove site or approval requirements.
- Kit or shell package
- List the work still needed to reach a finished, occupiable home, and who supplies it. Compare that complete scope with other proposals.
What should the building quote include?
Give each builder the same site information and specification. A lower headline price is difficult to assess when a different party must arrange major parts of the project.
- Design and approvals
- Survey, site reports, drawings, engineering, application fees, certification and required inspections. Name who arranges and pays for each.
- Site preparation
- Demolition, clearing, excavation, rock removal, retaining work and foundations. Identify allowances that depend on a site inspection or soil report.
- Building and fit-out
- Floor plan, structure, cladding, insulation, windows, kitchen, bathroom, laundry, appliances and finishes. Compare the same specifications.
- Services and drainage
- Connection routes, trenching, capacity upgrades, metering, wastewater and stormwater design. Ask what happens if existing infrastructure cannot be used.
- Delivery and access
- Transport, crane placement, temporary fencing, traffic management and protection of the main house or neighbouring property.
- External work and handover
- Paths, steps, decks, landscaping, fencing, waste removal, final documentation and rectification of defects. Record anything left for you to organise.
- Allowances and exclusions
- Separate fixed work from provisional sums, optional upgrades and excluded work. Ask how variations are approved and priced before work starts.
For a builder’s explanation of site conditions, connections and allowances, see Backyard Grannys’ quote-scope guide. Its examples describe that company’s approach, rather than a national price schedule.
Start with your state or territory
Planning permission, building approval and permission for the intended use are distinct checks. Size alone does not establish eligibility. Give the authority your address, site plan and proposed use so it can assess the rules that apply.
New South Wales
Complying development is conditional. The state guidance specifies a lot of at least 450m² for that pathway, with an exception for a secondary dwelling wholly within an existing house. A council development application may still be possible when the complying pathway is unavailable. NSW secondary dwelling guidance.
Victoria
Amendment VC306 changed the planning definition to a maximum of 80m² from 15 October 2026. Planning permits are normally unnecessary in eligible zones, subject to exceptions and other controls; a building permit is normally required. The state page says corresponding building-system changes are still to follow. Confirm the current building and siting requirements with your council and building surveyor before relying on the new planning limit. Victoria’s small second home provisions.
Queensland
New secondary dwellings require building approval. Ask the local council whether development approval is also needed. Changes allowing unrelated occupants to rent a secondary dwelling do not remove planning, building or fire-safety obligations. Queensland secondary dwelling guidance.
Western Australia
The state’s ancillary dwelling guidance describes compliant dwellings up to 70m². Confirm whether your proposal meets the planning exemption conditions and check the building permit process separately. WA ancillary dwelling information; Joondalup’s local building permit guidance.
South Australia
PlanSA says ancillary accommodation still needs planning and building approval. Confirm how the current Planning and Design Code applies to your site and proposed accommodation. PlanSA ancillary accommodation guidance.
Tasmania
Check the State Planning Provisions and relevant Local Provisions Schedule with your council, along with building and plumbing requirements. The Commission’s secondary-residence amendment page describes a draft proposal, so do not treat the proposed larger area as an established entitlement. Tasmanian Planning Commission amendment status.
Australian Capital Territory
Confirm the Territory Plan, lease conditions and development and building approval requirements for the block. ACT guidance says a block with a primary and secondary residence cannot be subdivided. ACT approval and secondary residence guidance.
Northern Territory
An independent unit needs building approval through an NT registered building certifier. Planning exemptions depend on the zone, overlays and compliance with relevant requirements. Demountable structures also need to meet applicable planning and building rules. NT independent unit guidance.
Sources reviewed 16 October 2026. Rules can change during a project; confirm the requirements again when preparing an application. For a broader overview, see our renovation approvals guide.
Resolve services and access early
Ask the designer and relevant providers to identify connection points, existing capacity and any upgrade work. Include the proposed routes for water, wastewater, electricity, communications and stormwater in the site assessment.
Establish how residents, emergency services, trades and deliveries will reach the dwelling. Consider bins, laundry, outdoor space and access past the main home. If you plan to rent, confirm metering and lawful billing arrangements rather than assuming shared services will be suitable.
Plan for rental use without assuming a return
Confirm that the proposed rental or short-stay use is lawful before modelling income. Ask a local property manager for comparable properties with similar access, privacy, parking, condition and inclusions.
Separate expected rent from cash flow after expenses. Allow for vacancy, management, insurance, maintenance and any borrowing costs. Test what happens if rent is lower, the property is empty or costs rise. ASIC’s Moneysmart property investment guide explains these risks and costs.
Building a second dwelling does not guarantee a particular increase in property value or a fixed payback period. Get advice about your circumstances before making an investment decision.
Choose a layout for the people using it
Set priorities before adding bedrooms. A studio keeps sleeping and living space together; a separate bedroom offers more privacy; an additional bedroom competes with living space, storage and circulation within the permitted footprint.
- Privacy: consider entry paths, outdoor areas, window placement and noise between the two homes.
- Daily use: draw furniture, storage, laundry and kitchen work areas into the plan.
- Comfort: discuss daylight, shading, ventilation and insulation with the designer.
- Changing needs: discuss steps, doorway access and bathroom usability for the intended occupants.
These are design questions, rather than a substitute for the applicable building and accessibility requirements. Ask the designer to show how the proposed home meets those requirements.
Agree the project stages and timing
Ask for a written programme from feasibility to handover. Identify who owns each stage: design and reports, applications, site preparation, construction or factory production, connections, inspections and completion documents.
Clarify when the quoted construction period begins and what must happen first. Record lead times, decisions you must make, payment milestones and how weather, variations or approval delays affect the schedule. Confirm the required final sign-off before anyone moves in.
