A Melbourne homeowner finds three three-bedroom granny flat designs online. Each looks similar in the pictures, but the advertised prices are far apart.
One is a supply price. Another includes installation but not service connections. The third appears more complete, although the site allowance is still provisional.
The homeowner does not really have three comparable prices. They have three different scopes.
That distinction matters in Victoria, where the floor area, property conditions, building requirements and included work can affect whether a three-bedroom design is practical and what the completed project may cost.
Why three-bedroom price lists are difficult to compare
Bedroom count is only one part of the cost.
Two plans can both have three bedrooms but differ in:
- gross floor area
- kitchen and bathroom specification
- number and size of windows
- storage and circulation
- structural system
- energy-efficiency solution
- delivery and installation method
- foundations
- site works and service connections
- external completion work
An advertised price can still be accurate for the product described. The problem begins when the buyer assumes it covers a different scope.
The Granny Flat Cost Victoria guide is a useful starting point for organising the costs before comparing the headline numbers.
Start with Victoria's 60 square metre definition
Planning Victoria defines a small second dwelling as a self-contained home with a gross floor area of 60 square metres or less, located on the same lot as an existing dwelling.
A building permit is always required. A planning permit may not be required in many ordinary circumstances, but the property still needs to be checked for its zone, overlays, lot size, siting requirements and other controls.
The official applicant guidance explains that the 60 square metres is measured using the total floor area, including roofed areas, from the outside of external walls or the centre of party walls.
This does not prohibit the words “three bedroom” on a floor plan. It does mean the complete layout must work within the applicable floor-area and building requirements if it is intended to use the small second dwelling pathway.
Bedroom labels do not confirm:
- compliant room dimensions
- comfortable circulation
- storage
- natural light and ventilation
- access
- buildability on the selected block
Review the Granny Flat Rules Victoria guide before treating a national three-bedroom price list as a Victorian project option.
The seven layers of a complete project cost
A useful quote separates the total into seven layers.
1. Base build
This is the dwelling itself at the specification stated by the supplier or builder.
Check the floor area, wall and roof system, windows, internal lining, kitchen, bathroom, laundry, flooring, painting, heating and cooling, electrical fixtures and selected finishes.
Do not assume “standard” means the same thing across two companies.
2. Site preparation
The backyard may need clearing, excavation, levelling, temporary protection, fence removal or reinstatement, spoil removal and construction access.
A clean digital floor plan does not show those conditions.
3. Foundations and engineering
The structural and foundation solution needs to suit the dwelling and the site.
Soil conditions, slope, drainage and the selected construction system can influence engineering and foundation scope. A generic foundation allowance should not be treated as final until the supporting site information is available.
4. Delivery and installation
For modular or prefabricated construction, ask how the dwelling reaches the property and how it is placed.
Transport, crane access, traffic management, overhead obstructions, fence removal and restricted working space may sit outside the displayed building price.
5. Service connections
Power, water, sewer and stormwater routes vary between properties.
Connection length, capacity, excavation, upgrades and authority requirements can affect the scope. A three-bedroom plan does not automatically have the same service cost on two neighbouring blocks.
6. Approvals and professional work
A building permit is part of the Victorian pathway. Depending on the property and proposal, the project may also require drawings, engineering, soil information, drainage work, reports or planning input.
The Council Approval Guide explains why the approval pathway needs to be checked rather than assumed.
7. Completion and external works
Clarify what is needed before the dwelling is genuinely ready for its intended use.
Possible items include steps, paths, decks, fencing, landscaping, blinds, appliances, clothesline, bins, external lighting and restoration of disturbed areas. Their inclusion depends on the agreed scope.
A three-bedroom layout can change the specification
Within a compact floor area, adding a third bedroom is not just a matter of drawing another internal wall.
The designer still needs to balance living space, kitchen function, bathroom access, storage, circulation, doors, windows and furniture zones.
Cost can change when the layout requires:
- additional doors and windows
- more internal walls and electrical points
- custom cabinetry or compact storage
- altered plumbing routes
- a second toilet or upgraded bathroom arrangement
- different heating and cooling
- non-standard structural openings
More bedrooms do not always create the largest increase. A second bathroom, complex shape or premium finish selection may have a greater effect than the bedroom label itself.
This is why a simpler two-bedroom layout can sometimes offer better value if it is more comfortable, easier to place and better suited to the intended occupants.
From price, estimate, quote and contract are different
Cost certainty usually develops in stages.
| Cost document | What it can tell you | What still needs checking |
|---|---|---|
| Advertised from price | Entry price for a stated model or package | Property, inclusions, exclusions and completion scope |
| Preliminary estimate | Early direction using known assumptions | Reports, selections, site conditions and unresolved allowances |
| Scoped written quote | Price for described plans, specifications and work | Provisional sums, prime cost items, exclusions and contract terms |
| Signed contract | Agreed work, documentation and price basis | Variations and the treatment of allowed price adjustments |
Consumer Affairs Victoria recommends comparing written quotes for the same plans and specifications. It also warns that the cheapest quote may omit items or use a base allowance that does not cover the required materials and finishes.
Its current guidance distinguishes prime cost items, provisional sums and variations. These should be identified rather than hidden inside one headline price.
Use a like-for-like comparison sheet
Place each quote beside the same questions:
| Cost layer | Quote A | Quote B | Quote C |
|---|---|---|---|
| Gross floor area | |||
| Base build specification | |||
| Site preparation | |||
| Foundations and engineering | |||
| Delivery and installation | |||
| Services | |||
| Permits and reports | |||
| External completion works | |||
| Prime cost items | |||
| Provisional sums | |||
| Explicit exclusions | |||
| Total known scope |
Blank cells are not savings. They are questions.
A Land Eligibility Check can help identify which site questions need answers before the comparison is reliable.
When a smaller design may be better value
A three-bedroom plan may suit a household that genuinely needs three separate sleeping rooms and can accept a compact shared living area.
A two-bedroom design may be the better decision when it provides:
- more usable living space
- better storage
- easier furniture placement
- simpler site fit
- fewer custom changes
- a lower complete project scope
The right choice depends on the occupants, property and budget, not the largest bedroom count that can be drawn into a brochure.
Understanding how MPLUS builds can help you compare the practical delivery and completion steps behind a plan.
Check the block before relying on the price
A three-bedroom price list cannot confirm whether the plan suits your backyard.
Access, easements, slope, soil, drainage, services, existing trees and siting controls can affect both feasibility and total project cost.
MPLUS can review the basic property factors before you rely on an advertised number. Start with a Free Land Check, then compare plans and prices using a scope that reflects your actual block.
