Quick Answer
A granny flat in Melbourne typically costs $100,000–$250,000 for a prefab or modular unit, or $180,000–$350,000+ for a custom-built flat. The total depends on size, site conditions, and whether you build a detached dwelling or convert an existing garage or shed. Most SE Melbourne homeowners on a standard 600–800 m² block pay around $150,000–$220,000 all up for a quality 50–60 m² standalone granny flat with full council approval.
Complete Cost Breakdown
Prefab and Modular Granny Flats
Prefab or modular granny flats are manufactured off-site and craned onto your property. They are faster to build (4–8 weeks on-site) and generally cheaper than custom builds.
| Size | Prefab Cost (supply only) | Installed (incl. site works) |
|---|---|---|
| Studio (25–30 m²) | $55,000–$85,000 | $90,000–$130,000 |
| 1-bedroom (40–45 m²) | $80,000–$120,000 | $120,000–$170,000 |
| 2-bedroom (55–65 m²) | $110,000–$160,000 | $160,000–$230,000 |
| 2-bedroom premium (65–80 m²) | $150,000–$200,000 | $200,000–$280,000 |
Custom-Built Granny Flats
Custom builds are constructed on-site by a builder and offer more flexibility in design, finishes, and layout. They take longer (3–6 months) but can better integrate with your existing home’s style.
| Size | Basic Finish | Mid-Range Finish | High-End Finish |
|---|---|---|---|
| 40 m² | $130,000–$160,000 | $160,000–$200,000 | $200,000–$250,000 |
| 55 m² | $165,000–$200,000 | $200,000–$260,000 | $260,000–$330,000 |
| 70 m² | $200,000–$240,000 | $240,000–$310,000 | $310,000–$400,000+ |
Garage and Shed Conversions
Converting an existing double garage into a self-contained studio or one-bedroom flat is the most cost-effective option, typically costing $60,000–$120,000 depending on the extent of works required.
| Conversion Type | Cost Range | Notes |
|---|---|---|
| Single garage to studio | $45,000–$80,000 | Adds kitchenette, bathroom, insulation, windows |
| Double garage to 1-bed flat | $70,000–$120,000 | Full kitchen, laundry, bathroom, new façade |
| Large shed conversion | $80,000–$140,000 | Depends heavily on existing structure quality |
On-Costs and Site Works
The building cost is only part of the total. Always budget for these additional items:
| Item | Typical Cost | Notes |
|---|---|---|
| Council planning permit | $1,500–$5,000 | Required in most Melbourne councils |
| Building permit | $2,000–$4,000 | Mandatory for all new dwellings |
| Surveyor and plans | $3,000–$8,000 | Drafting plans, title surveys, overlays check |
| Utility connections (water, sewer) | $5,000–$20,000 | South East Water or Yarra Valley Water connection fees |
| Electrical connection/sub-board | $3,000–$8,000 | Separate meter is optional but simplifies billing |
| Site preparation (earthworks) | $5,000–$25,000 | Slope, tree removal, fill required |
| Landscaping and fencing | $5,000–$20,000 | Privacy screen, new fence sections |
What Affects Granny Flat Costs in Melbourne?
1. Block Size and Zoning
Victoria’s planning rules require a minimum lot size of 300 m² for a second dwelling under the Residential Growth Zone, with most standard residential zones (GRZ, NRZ) requiring 500–600 m² or more depending on your council. Councils like Casey, Cardinia, and Greater Dandenong have different overlay requirements — always check the Planning Property Report at planning.vic.gov.au before buying a modular unit.
2. Detached vs Attached
A fully detached granny flat requires a separate structure with its own footings, utilities connections, and weatherproofing on all sides. An attached flat (e.g., building a second storey or adding to the side of the main house) can share a party wall, reducing some construction costs but adding structural engineering requirements.
3. Slope and Access
Melbourne’s SE suburbs include both flat land (Cranbourne, Pakenham, Officer) and hilly terrain (Narre Warren North, Lysterfield, parts of Berwick). A steep block requires retaining walls, additional footings, and sometimes a more complex modular crane lift — potentially adding $15,000–$40,000 to the project.
4. Finishes and Fixtures
The difference between a $120,000 and a $200,000 granny flat is often in the finishes: engineered stone vs laminate benchtops, ducted vs split system heating/cooling, full-height tiling vs painted bathroom walls, and double-glazed windows vs standard aluminium frames.
5. Rental Income Potential
In SE Melbourne, a well-finished 2-bedroom granny flat in Narre Warren, Cranbourne, or Berwick typically rents for $380–$450 per week. At $400/week, the gross annual income is $20,800 — representing a 9–14% gross yield on a $150,000–$220,000 build cost.
Council Planning Rules in SE Melbourne
Each Melbourne council has different rules for granny flats (officially called “dependent person’s unit” or “second dwelling” in Victorian planning). Key requirements across SE Melbourne councils include:
- Casey Council: Minimum lot size typically 500 m² in GRZ; planning permit usually required for detached second dwellings
- Cardinia Council: Check for Neighbourhood Character overlays in Pakenham; 600 m² minimum common in NRZ areas
- Greater Dandenong: Incremental development guidelines apply; setbacks from rear boundary critical
- Frankston Council: Some areas have Vegetation Protection overlays — check for trees before excavation
- Mornington Peninsula: Strict environmental overlays on many properties; septic tank requirements common outside town supply areas
A planning permit application typically takes 6–12 weeks and costs $1,500–$5,000 in council fees. Engaging a town planner ($1,500–$3,000) to prepare the application can significantly improve approval chances and speed.
Tips and Gotchas
- Get the planning permit before buying a kit. Many homeowners buy a modular flat then discover their block doesn’t meet the council’s minimum lot size or setback requirements. The permit comes first.
- Check underground services before excavation. Call 1100 (Dial Before You Dig) — underground gas, water, and drainage pipes in older SE Melbourne suburbs often run through backyards in unexpected locations.
- Separate the utility meters. A separate electricity meter for the flat (around $500–$1,500 extra) avoids disputes with tenants and lets you bill them directly.
- Budget for bushfire overlay checks. Many properties in Narre Warren North, Berwick, and Lysterfield have BAL (Bushfire Attack Level) ratings that require additional construction specifications and can add $10,000–$30,000 to the build.
- Don’t skip the soil test. Reactive clay soils in the SE Melbourne growth corridor (Cranbourne, Officer, Pakenham) require engineered footings. Skipping the soil test and getting it wrong costs far more to fix.
- Understand stamp duty implications. Adding a second dwelling can affect your property’s land tax classification. Speak to your accountant before starting the build.
- Consider future rental compliance. If you plan to rent the flat, ensure it meets Victoria’s Residential Tenancies Act minimum standards — including adequate heating, ventilation, and waterproofing.
- Don’t forget private open space. Council planning rules typically require a minimum private open space area for both the main dwelling and the granny flat. This limits how much of the backyard the flat can occupy.
Local Melbourne Resources
- Planning.vic.gov.au Property Reports — check zoning, overlays, and secondary dwelling eligibility for any Melbourne property
- Victorian Building Authority (VBA) — verify builder registration and find licensed building surveyors
- Bunnings Warehouse — hardware, fixings, and landscaping supplies for site preparation works
- Reece Plumbing — fixtures, pipes, and fittings for bathroom and kitchen fit-out
- Housing Industry Association (HIA) — find registered builders for granny flat construction across Melbourne
- Consumer Affairs Victoria — Building and Renovating — understanding your rights, contracts, and dispute resolution
Frequently Asked Questions
Do I need council approval for a granny flat in Melbourne?
Yes, in most cases. Victoria requires a planning permit for a second dwelling on most residential lots. Some exemptions exist for “dependent person’s units” in certain zones, but you still need a building permit from a registered building surveyor. Always check with your council before starting.
How long does it take to build a granny flat in Melbourne?
A prefab or modular granny flat typically takes 4–8 weeks on-site once permits are approved, but the full process — planning permit, building permit, site works, and connection of services — usually takes 6–12 months from start to move-in. Custom builds take 3–6 months of construction time on top of the permit phase.
Can I rent out my granny flat in Melbourne?
Yes, you can rent a granny flat to a third party (not just a family member) in most Melbourne zones. The flat must meet the Residential Tenancies Act minimum standards including adequate heating, ventilation, and waterproofing. A separate entrance is also recommended for rental purposes.
What is the maximum size for a granny flat in Melbourne?
Victoria doesn’t have a single universal maximum size, but councils typically limit secondary dwellings to 60–70% of the main dwelling’s floor area, and most standard planning permits cap them at 60–80 m². Check your specific council’s planning scheme for the applicable size limit on your block.
Does adding a granny flat increase property value?
Generally yes — a legal, well-built granny flat with separate access and services typically adds $100,000–$200,000 to a Melbourne property’s market value, depending on location and quality. Properties with approved rental income are particularly attractive to investors.
What’s the difference between a “granny flat” and a “secondary dwelling” in Melbourne?
In Victorian planning law, a “dependent person’s unit” (DPU) is designed for a family member with a dependency relationship to the main occupants. A “second dwelling” or “dwelling (second)” can be rented independently. Different planning rules apply to each — a second dwelling generally requires a higher-standard planning permit and must meet stricter habitability requirements.
Final Thoughts
A granny flat is one of Melbourne’s most popular property additions for good reason: it adds liveable space, generates rental income, and increases property value. Costs range from $90,000 for a small prefab studio to $350,000+ for a large custom-built two-bedroom flat on a complex site.
The key to staying on budget is doing the planning legwork first. Get the property report, speak to your council’s planning department, commission a soil test, and get three builder quotes before signing anything. In SE Melbourne’s growth corridors — from Officer and Pakenham to Narre Warren and Cranbourne — demand for granny flat builders is high, so booking early and having your permits ready will keep your project moving.