Granny Flat Costs in Australia: Prices and Project Budgets

Compare granny flat costs by the work included, not the lowest advertised price. A materials kit, a completed module at the factory and an occupied dwelling on your property are different purchases. This guide shows a dated supplier example and how to build a complete project budget.

Updated 2 October 2026. We have removed unsupported national and city price ranges from this guide. The supplier prices below are advertised examples, not an Australian average. Get written quotes for your address before committing to a budget.

Start with the supply stages below. Then read the five cost drivers and use our line-item breakdown to check what each quote leaves for you to arrange.

Published prices show why scope matters

On 2 October 2026, Outhaus advertised its Standard 8.4 one-bedroom model, 28.6 m², at three supply stages. Each amount included GST and was quoted ex yard.

These are one supplier’s advertised product prices, not independently audited completed-project costs or a recommendation. Confirm current specifications and delivery area directly. The large difference between the kit and complete-module price illustrates how much work can sit outside an appealing starting figure.

Don’t compare that small module with a 60 m² two-bedroom build without accounting for the different area, facilities and installation scope. Nor should you double a small-model price and assume the result is a reliable larger-model budget.

Get local quotes instead of applying a city average

We don’t have a verified dataset of comparable completed granny flats in each capital city. A table of precise city ranges would hide differences in building size, fit-out, foundations, delivery and approval costs.

Send the same brief to suppliers serving your area. Include the address, survey if available, desired rooms, proposed location and intended use. Ask each supplier to identify what it has inspected and which amounts remain estimates. Regional work can involve freight or trade travel, while a metropolitan site may have difficult access; neither location is automatically cheaper.

For NSW-specific charges to investigate, use our NSW budget guide. For every state, obtain the actual authority and utility charges relevant to your proposal.

Compare responsibilities across build paths

A materials kit leaves assembly and the remaining construction with you or your contractors. A factory-built module can include more completed work, but delivery, lifting and site installation still need a defined scope. A builder-managed contract can combine more tasks, with exclusions that still need checking.

None of those labels establishes which finished project is cheapest. Give each supplier the same address, plan and specification. Ask who handles engineering, approval documents, site work and handover, then price everything left outside the contract. Use the owner-builder checklist if you are considering taking on the coordination yourself.

Find the work outside the advertised price

Break exclusions into tasks that someone can quote. For design and approvals, identify the required reports, application fees and practitioner scope. For site work, obtain the foundation design and check access, excavation, retaining and disposal. Ask the relevant utility or contractor to assess connection work for the address.

Fit-out needs the same treatment. Specify the kitchen, appliances, bathroom fixtures, waterproofing, flooring and internal finishes. Check delivery and installation as well as supply prices. Include external work needed to use the dwelling, such as paths and drainage, rather than leaving it until the last invoice.

Keep provisional amounts separate from fixed quotes, record expiry dates and avoid counting an item twice. The line-item breakdown provides a structure for that comparison. These categories are a checklist, not unsupported national price bands.

Worked example: how separate costs add up

Hypothetical arithmetic example, not a quote or cost benchmark. The amounts below are invented to demonstrate a budget structure. They are not prices from a completed build. Replace every amount with evidence for your own project and remove overlaps between contractor scopes.

4 smart ways to save on the build

1. Be your own project manager: Compare the cost of managing trades yourself with a builder-managed contract. Include your time, insurance, rework risk and responsibilities; a saving is not guaranteed.
2. Choose a simple design: Extra corners, complex roofs and custom windows add cost. A simple rectangle is usually cheapest.
3. Do the unlicensed work yourself: Keep licensed trades for plumbing and electrical. Painting, landscaping and final clean are common DIY saves.
4. Source your own finishes: Compare kitchens, bathrooms and flooring across suppliers before you lock a builder’s allowance.

Next step: lock a build path, then price the lot

Keep three figures visible: the supplier contract, separately quoted work and unresolved allowances. Then:

1. Read the five cost drivers so you know what will push your quote up or down.
2. Map quotes to the line-item breakdown.
3. Run the cost calculator, then get three like-for-like quotes for your address.

A secondary dwelling can add rental income, house family or support resale. It only works if the budget includes slab, services and approvals, not just the shell.

State rules hub

Approval requirements and site conditions affect what must be priced. Check the rules for your address before ordering a design, and give all suppliers the same confirmed planning brief.

• NSW rules
• Victoria rules
• Queensland / Brisbane
• Western Australia
• South Australia
• Tasmania

Frequently Asked Questions