The cheapest sensible granny flat in Frankston is $135,000, and here is exactly what you give up
In 2026, a legal, connected, occupancy-permitted 45 to 50 m² one bedroom granny flat on a flat Frankston block with good access lands at $135,000 to $165,000 all in. Mid tier is $175,000 to $215,000. Premium is $230,000 to $300,000. Below about $120,000 you are not buying a dwelling, you are buying a shell, a studio, or a quote with the site costs removed.
The three tiers below are delivered prices, not build-only prices. Each one assumes a Frankston, Carrum Downs or Seaford block with a Class A, S or M site classification, services within about 15 m, and side access wide enough for a bobcat. Add $8,000 to $35,000 for a sloping site, reactive clay needing piers, a Special Building Overlay, or a rear yard you can only reach through a 900 mm gate.
Three tiers, priced for 2026
| Tier | Delivered price 2026 | What you get | What you give up | Who should pick it |
|---|---|---|---|---|
| Budget 45 to 50 m², 1 bedroom | $135,000 - $165,000 | Standard plan from a fixed range, waffle raft slab, fibre cement weatherboard, 2.4 m ceilings, single glazed aluminium windows, vinyl plank floors, laminate benchtops, one split system, electric heat pump hot water, 7 star NatHERS achieved with insulation rather than glazing, shared meters with the house, concrete path. | No deck, no landscaping, no separate meters, no second bedroom, no design changes, longer lead time because you take a slot in the standard schedule. Resale and rental appeal is average. | A family member moving in, or a landlord chasing yield rather than a showpiece. |
| Mid 55 to 60 m², 1 or 2 bedroom | $175,000 - $215,000 | Custom plan drawn to your block and orientation, 2.55 m ceilings, double glazed windows, 10 to 14 m² covered deck, stone look benchtops, better bathroom fittings, separate electricity meter, dedicated stormwater, upgraded insulation, basic landscaping and a clothesline that is actually in the sun. | Not architectural. Standard roof form, standard joinery carcasses, no solar or battery, no second bathroom. | Most people. This is the tier that rents well, ages well and does not annoy you in year three. |
| Premium 60 to 75 m², 2 bedroom | $230,000 - $300,000 | Architectural plan, mixed cladding, 2.7 m ceilings, double glazing throughout, engineered timber floors, stone benchtops, second toilet or ensuite, solar and battery, full landscaping and fencing, separate water and power services sized for a future subdivision, coastal specification where the block needs it. | Roughly $70,000 more than mid tier for perhaps $60 a week more rent. The premium is lifestyle and resale, not yield. | Owners building for themselves, downsizers, dual-occupancy plans, or blocks in Frankston South and Mt Eliza where the main house sets a high bar. |
Delivered means permit, soil test, engineering, slab, build, connections, stormwater and handover cleaning. Indicative 2026 figures for Frankston City and the Mornington Peninsula. Call (03) 9022 1391 for a fixed price against your block.
Our recommendation: mid tier, at around $185,000 for a 55 m² one bedroom or $205,000 for a modest two bedroom. The step from budget to mid buys double glazing, a deck, separate metering and a plan drawn for your orientation, and those four things are what separate a granny flat that people want to live in from one that is merely legal.
Where money can safely be saved
Every one of these is a real saving that costs you nothing in durability or compliance.
- Keep it a rectangle. Every external corner costs money in framing, flashing, cladding waste and labour. A simple 6 m by 9 m box beats an L-shaped plan of the same area by $8,000 to $15,000.
- Put the wet areas back to back. Kitchen and bathroom sharing one plumbing wall saves $2,000 to $4,000 in pipework and one day of trade time.
- Build it close to the house. Combined water, sewer, power and data trenching runs roughly $120 to $220 per lineal metre. Moving the flat 20 m further down the yard adds $2,400 to $4,400 before you touch the building.
- Use standard openings. A stock sliding door and standard window sizes save $600 to $1,500 against custom sizes, and they arrive faster.
- Take the work that comes after handover. Landscaping, fencing, the letterbox, blinds and the shed are all things you can do yourself or shop separately for. That is $6,000 to $14,000 out of the contract, and none of it affects the occupancy permit.
- Stay at or under 60 m². A small second dwelling of 60 m² or less can avoid a planning permit in many Victorian situations. Going to 62 m² can trigger a planning assessment worth $4,000 to $9,000 and three to four months. That is the single most expensive two square metres in the whole project. See Victorian granny flat permit rules.
- Book off peak. Quoting is quietest for builders in June and July, and a February to April slab and frame avoids both the winter mud and the pre-Christmas crush. Booking early in the calendar year is worth a genuine 2 to 4 per cent on some contracts, and it is worth more in schedule certainty. More on that on the best time to build on the Peninsula.
Want to know which tier your block can actually take?
A 60 minute site visit tells you the site classification, the service runs and the real number. Free, no obligation.
Where saving money is a false economy
These are the line items we watch people delete, and then pay for twice.
- The soil test and engineering, $1,400 to $2,800. Skipping it does not remove reactive clay from Carrum Downs or Skye, it just moves the discovery to the day the excavator arrives. A slab redesign after the fact costs $6,000 to $20,000 and a month.
- Stormwater to the legal point of discharge, $2,500 to $9,000. Water has to get from your new roof to a lawful discharge point. Dumping it into the yard floods the neighbour, breaches the permit, and around the low lying parts of Seaford and Carrum Downs it can put water under your own slab. See backyard drainage for a Frankston granny flat.
- Waterproofing to the standard, $1,800 to $3,500. A failed shower membrane is a $12,000 to $25,000 repair because it takes the floor, the wall sheet and the cabinetry with it.
- Glazing and insulation. Meeting 7 star NatHERS on the cheapest possible path leaves you with a flat that is expensive to heat. Double glazing on the west and south elevations is $3,500 to $7,000 and it changes the comfort of the building every day it exists.
- A written fixed price contract. A quote full of provisional sums and prime cost items is not a price, it is a starting bid. Every provisional sum is a place the number can move after you have signed.
- Domestic building insurance. It is compulsory for domestic building work over the Victorian threshold of $16,000, and the premium on a build this size is typically $900 to $2,200. If a builder offers to leave it off to save you money, that is the end of the conversation. Details on granny flat warranties in Victoria.
What a suspiciously low quote is leaving out
When a headline price is $40,000 below everyone else, it is almost never because the builder is cleverer. It is because the scope is smaller. Take the cheap quote and check it line by line against this list, because these are the items that get quietly excluded.
- Soil test, geotechnical report and structural engineering: $1,400 to $2,800.
- Building permit and the building surveyor’s inspections: $2,500 to $4,500.
- Planning application where one is triggered: $4,000 to $9,000 including drawings and fees.
- Water and sewer connection or a build over asset consent through the water authority: $3,000 to $12,000.
- Electrical supply, switchboard and a separate meter: $1,800 to $9,000 depending on whether you extend from the house or bring in a new supply.
- Stormwater to the legal point of discharge: $2,500 to $9,000.
- Piers or screw piles on reactive clay or fill: $350 to $650 each, and a small flat can need 12 to 20.
- Floor coverings, window furnishings and the letterbox: $6,000 to $14,000.
- Path, crossover works, temporary fencing, site toilet and waste bins: $3,000 to $9,000.
- GST, if the price was quoted excluding it.
Add those back and the $99,000 special is a $150,000 build with a marketing number on the front. Our quote comparison guide has the line by line checklist, and Frankston site costs covers the ground works in detail.
Victorian rules and programs that change the maths
The biggest lever in Victoria is not a rebate, it is the planning pathway. A small second dwelling of 60 m² or less can avoid a planning permit in many situations, which takes three to four months and $4,000 to $9,000 out of the project. It does not remove the building permit, and it does not apply if the lot is small, the title is restricted or an overlay is in play, so the address has to be checked before you design to that number.
On energy, Victoria has required 7 star NatHERS thermal performance and a Whole of Home rating for new dwellings since 1 May 2024. New dwellings that need a planning permit cannot connect to gas, so almost every granny flat we build now is all electric with a heat pump hot water unit. That removes a gas connection worth $1,500 to $3,000 from the budget and removes a second supply charge from the running costs forever.
Solar Victoria runs rebates and interest free loans on solar panels and hot water systems for eligible households, and the federal home battery discount that began in July 2025 reduces the cost of adding storage. Both programs change their amounts and eligibility from year to year, so confirm the current figures before you count them in your budget rather than trusting a number on a brochure. On the other side of the ledger, a second dwelling on the same title does not create a new title, so there is no stamp duty, but renting it out can affect your land tax position and the capital gains treatment of your main residence. Twenty minutes with your accountant before you sign is the cheapest professional advice in the whole project, and our financing page covers how people usually fund it.
When we tell people not to build
If your total budget is under about $120,000, do not build a dwelling. You will either end up with a badly compromised one or with a half finished job and a variation letter. There are two better answers. A garden studio at $28,000 to $75,000 gives you a room, power and data without the kitchen, bathroom, permit load and connection cost. A garage conversion, where the garage is already lined and dry, can produce a usable extra room for $35,000 to $90,000, although turning it into a lawful self-contained dwelling brings back most of the same requirements.
We also do not chase the bottom of the market. We do not build 25 m² kit shells, we do not quote without a soil test, and we will not leave stormwater or insurance out of a contract to make a number look better. If the cheapest possible figure is the only thing that matters, we are the wrong builder and we would rather say so on this page than at the deposit stage. If you want to see where the money goes at each tier, start with the 2026 pricing guide, then choose the cladding, then size the building properly. If you are weighing factory built against site built, that comparison is here.
Budget questions we get asked in Frankston
What is the cheapest granny flat you can legally build in Frankston?
Is a modular granny flat cheaper than one built on site in Frankston?
Where can I safely save money on a granny flat build?
What does a suspiciously cheap granny flat quote leave out?
Are there Victorian rebates or programs that reduce the cost?
When is a granny flat the wrong answer?
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