Imagine a Melbourne homeowner comparing two granny flat plans online. Both appear to be about the same size. Both have two bedrooms, one bathroom and an open living area. One carries a lower starting price, so it looks like the obvious choice.
Then the block is checked. The cheaper plan places the bathroom and kitchen on the far side from the existing services. Its wider footprint conflicts with usable backyard space, and the proposed windows need another look for privacy and siting. The second plan may be easier to adapt even though its headline price is higher.
This is why granny flat plans and prices should not be compared as two isolated numbers. The right comparison is the plan, the property and the complete scope needed to deliver it.
First, ask what the word “plan” means
Online results often place very different products side by side.
A plan may be:
- a marketing floor plan that shows a possible layout
- a set of drawings sold separately from construction
- a standard design that still needs site-specific changes
- a coordinated drawing and specification package developed for a building permit
These are not equivalent. A visually complete floor plan does not confirm that the dwelling suits the title, setbacks, easements, access, services, orientation or approval pathway of a Victorian property.
It also does not show whether engineering, energy documentation, service design or construction details are included. Before comparing prices, confirm exactly what the plan allows you to do next.
Check whether the plan fits the Victorian pathway
Planning Victoria defines a small second home as a self-contained dwelling of 60 square metres or less on the same lot as an existing home. A building permit is always required. A planning permit is not required in many cases, but lot size, zone, overlays and other controls can change the pathway.
A layout above 60 square metres does not meet that small second home definition. Even within 60 square metres, a plan still has to respond to siting, amenity, design and safety requirements.
The Granny Flat Rules Victoria guide explains the broader framework. The Council Approval Guide helps separate planning questions from the building-permit process.
Five plan choices that can change the project response
Two plans with similar floor area can create different work on the same block.
1. Footprint and external shape
A simple rectangular footprint may use the backyard differently from a wider, stepped or L-shaped design. Extra corners, roof junctions and wall length can also change the amount of structure, cladding, flashings and labour involved.
The point is not that one shape is always cheaper. It is that floor area alone does not describe construction complexity or land fit.
2. Kitchen, bathroom and laundry position
Wet areas affect internal plumbing and the route to external service connections. A compact arrangement may reduce internal complexity, but the actual result depends on where water, sewer and stormwater can connect on the property.
Do not assume “plumbing included” also means every external connection across the block is included.
3. Windows, doors and orientation
Glazing affects light, ventilation, privacy, energy performance and the relationship with the existing home and neighbours. Moving a window or entry may look like a small plan change, but it can affect documentation, materials and site response.
Choose a plan for the actual orientation and outlook, not just the front elevation shown online.
4. Foundation interface
A displayed design normally begins with a standard site assumption. The footing or support solution still needs to respond to the ground, slope, drainage and engineering information.
Consumer Affairs Victoria advises that soil information and foundation data are important for footing design and an adequate cost estimate. A standard plan does not remove that site-specific step.
5. Access and construction method
The plan has to become a building behind an existing home. Side access, fences, trees, overhead constraints and the route for materials or modules can affect site preparation, handling and sequencing.
If access changes the practical construction method, it can also change the usefulness of the original advertised price.
Before shortlisting a layout, use the Land Eligibility Check to review usable space, access, services and obvious planning constraints.
Separate the displayed price from the total project cost
The label attached to a plan matters less than the written scope behind it.
| Cost layer | What to confirm |
|---|---|
| Drawing or concept price | Is this only a floor plan, or does it include site-specific documentation? |
| Base build or package | What structure, internal work, fixtures and finishes are included? |
| Site preparation | Are clearing, excavation, levelling, drainage and reinstatement included? |
| Foundations | Is the allowance based on actual soil, slope and engineering information? |
| Service connections | Where do water, sewer, stormwater and electricity responsibilities start and finish? |
| Approvals and professional work | Which design, surveying, engineering, energy and permit tasks are included? |
| Completion items | Are steps, paths, decks, fencing, landscaping and other external works included? |
| Total project cost | What remains excluded, estimated or unresolved before the dwelling is ready for its intended use? |
For a fuller breakdown of these layers, see Granny Flat Cost Victoria.
Look closely at allowances, not just inclusions
An item can appear in a quote without its final cost being settled.
Consumer Affairs Victoria distinguishes prime cost items, such as fixtures or finishes not yet specifically selected, from provisional sums for work that cannot yet be priced exactly. Excavation is a common example of work that may remain provisional until better site information is available.
When comparing plans and prices, mark every line as:
- Defined: product, quantity and responsibility are clear
- Allowed: an estimate is included but may change
- Excluded: the owner must budget for it elsewhere
- Unknown: more property or design information is needed
This exposes uncertainty before a low headline figure becomes the working budget.
Compare plans using the same property brief
Use one brief for every option you review:
- intended use and number of occupants
- maximum practical floor area for the block
- usable backyard dimensions and setbacks
- access route and construction constraints
- service locations and connection responsibilities
- required finishes and completion standard
- confirmed inclusions, exclusions and allowances
- approvals and professional work
Then ask each supplier to price the same outcome. If one amount stops at a delivered shell and another includes site works and completion, they are not competing prices.
The How We Build page shows how land review, design, documentation and construction planning connect before the final scope is set.
Start with the block, then narrow the plans
Online plans are useful for identifying what you like. They are less reliable as a final budget tool until the property and scope are checked.
Send MPLUS the address, the preferred bedroom count and how you want to use the dwelling. A Free Land Check can identify obvious land, access, service and planning issues before you rely on a plan or displayed price.
